EPA/600/R-15/080|May 2015 | www.epa.gov/research
United States
Environmental Protection
Agency
Thermo-Oxidation of Municipal Wastewater
Treatment Plant Sludge for Production of
Class A Biosolids
Office of Research and Development
National Risk Management Research Laboratory
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EPA/600/R-15/080
May 2015
Thermo-Oxidation of Municipal Wastewater
Treatment Plant Sludge for Production of
Class A Biosolids
by
Edith L. Holder
Robert J. Grosser
Ann Dougherty
Pegasus Technical Services, Inc.
Cincinnati, OH 45219
Contract No. EP-C-11-006
Richard C. Brenner
Work Assignment Manager
Land Remediation and Pollution Control Division
National Risk Management Research Laboratory
Cincinnati, OH 45268
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Notice
The U.S. Environmental Protection Agency (EPA), through its Office of Research and Development
(ORD), funded and managed the research described herein under Contract No. EP-C-11-006. It has
been subjected to the Agency's peer and administrative review and has been approved for publication as
an EPA document.
Any mention of trade names or commercial products does not constitute endorsement or
recommendation for use by EPA.
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Abstract
Bench-scale reactors were used to test a novel thermo-oxidation process on municipal wastewater
treatment plant (WWTP) waste activated sludge (WAS) using hydrogen peroxide (EbCh) to achieve a
Class A sludge product appropriate for land application. Reactor temperatures ranging from room
temperature to 90°C were tested with doses of 0.05, 0.1, and 0.2 g IHbCh/g volatile suspended solids
(VSS) applied. Measurements included total suspended solids (TSS), VSS, fecal coliform counts,
settling characteristics, and nutrient concentrations for chemical oxygen demand, total phosphorus,
ammonia nitrogen, and total Kjeldahl nitrogen. The best results, in terms of volatile solids destruction,
were obtained with an EbCh dose of 0.2 g/g VSS at 90°C, but a temperature > 65°C achieved fecal
coliform removal without re-growth potential, and 0.1 g IHbCh/g VSS yielded an acceptable product,
albeit with less solids mass reduction.
A market analysis was performed including development of conceptual treatment trains and cost
estimates. The preliminary conclusion of this analysis was that thermo-oxidation capital costs are much
less than those for implementing existing technologies, although the operating cost of the thermo-
oxidation process, per ton TSS, may be higher. Lower capital costs may place the process within the
budgetary limitations of small municipalities. Accordingly, the most attractive target market for this
process is believed to be smaller WWTPs with influent wastewater flows in the range of 1-6 million
gallons per day (mgd) that utilize extended aeration activated sludge systems, e.g., oxidation ditches,
producing 4,000-20,000 gallons per day (gpd) of WAS.
in
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Foreword
The U.S. Environmental Protection Agency (EPA) is charged by Congress with protecting the Nation's land, air,
and water resources. Under a mandate of national environmental laws, the Agency strives to formulate and
implement actions leading to a compatible balance between human activities and the ability of natural systems to
support and nurture life. To meet this mandate, EPA's research program is providing data and technical support
for solving environmental problems today and building a science knowledge base necessary to manage our
ecological resources wisely, understand how pollutants affect our health, and prevent or reduce environmental
risks in the future.
The National Risk Management Research Laboratory (NRMRL) is the Agency's center for investigation of
technological and management approaches for preventing and reducing risks from pollution that threaten human
health and the environment. The focus of the Laboratory's research program is on methods and their cost-
effectiveness for prevention and control of pollution to air, land, water, and subsurface resources; protection of
water quality in public water systems; remediation of contaminated sites, sediments and ground water; prevention
and control of indoor air pollution; and restoration of ecosystems. NRMRL collaborates with both public and
private sector partners to foster technologies that reduce the cost of compliance and to anticipate emerging
problems. NRMRL's research provides solutions to environmental problems by: developing and promoting
technologies that protect and improve the environment, advancing scientific and engineering information to
support regulatory and policy decisions, and providing the technical support and information transfer to ensure
implementation of environmental regulations and strategies at the national, state, and community levels.
Safe and cost-effective treatment and disposal of waste sludges generated by municipal wastewater treatment
plants (WWTPs) present numerous challenges and design options. Historically, most municipal WWTPs have
produced both raw primary sludge and excess treated secondary sludge for processing and disposal. Frequently,
these sludges have been processed together, resulting in the production of Class B biosolids for disposal in
landfills or application to agricultural land. A myriad of problems can be associated with land applying Class B
biosolids including unacceptable levels of vector attraction, nuisance and odor complaints, and claims of illness
from nearby residents. In recent years, many municipalities, particularly smaller communities, have opted to
construct WWTPs without primary clarifiers employing extended aeration activated sludge systems for
secondary treatment that produce only highly oxidized waste activated sludge (WAS). This project has evaluated
a novel WAS thermal-oxidation process employing a combination of heat and hydrogen peroxide for production
of Class A biosolids. Class A biosolids are a highly preferable alternative to Class B biosolids for beneficial use
of WWTP waste sludge products.
Cynthia Sonich-Mullin, Director
National Risk Management Research Laboratory
IV
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Contents
Notice ii
Abstract iii
Foreword iv
Figures vii
Tables vii i
Acronyms and Abbreviations ix
Acknowledgments x
1.0 Description and Objectives 1
1.1 Introduction and Background 1
1.2 Objectives 2
1.3 Technology Description 2
2.0 Feed Waste Activated Sludge Selection 4
2.1 Description of Wastewater Treatment Plants Considered 4
2.2 Rationale for Selection of Mason Wastewater Treatment Plant 5
3.0 Experimental Design 9
3.1 Description of Experimental Systems 9
3.2 Experimental Chronology and Conditions 11
3.3 Methods 11
3.4 Quality Assurance/Quality Control Considerations 12
4.0 Results and Discussion 13
4.1 Overview of Experiments 13
4.2 Initial Experiments 13
4.3 Experiments at 90°C, 75°C, and 65°C 16
4.4 Summer Experiments on Mason Waste Activated Sludge 20
4.5 Testing Waste Activated Sludge from Other Wastewater Treatment Plants 28
4.6 Summary of Results 29
4.7 Summary of Treatment and Discussion 31
5.0 Literature Review and Description of Competing Technologies 33
6.0 Market Analysis, Conceptual Treatment Trains, and Cost Estimates 37
6.1 Background 37
6.2 Market Analysis of Fertilizer 37
6.3 A Global View of Three Trends 38
6.4 Market Potential for Thermo-Oxidation Technology 39
6.5 Cost Estimates 39
6.5.1 Methodology for Conceptual Design and Costs for Thermo-Oxidation
Technology 40
6.5.2 Conceptual Treatment Trains 40
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Contents (continued)
6.6 Cost Comparison with Existing Systems 44
6.6.1 Landfilling 45
6.6.2 Mason Water Reclamation Plant, Mason, OH 46
6.6.3 Morris Forman Water Quality Treatment Center, Louisville, KY 46
6.6.4 Mill Creek Wastewater Treatment Plant, Cincinnati, OH 46
6.7 Summary of Market Analysis 46
7.0 Summary and Conclusions 48
7.1 Project Summary 48
7.2 Project Conclusions 49
8.0 References 54
Appendix A Variations on Conceptual Treatment Trains 59
Appendix B Quality Assurance Project Plan #L18881-QP-1-0 60
VI
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Figures
2.1 Flow Diagram of Mason Water Reclamation Plant 6
2.2 Aerial Photograph of Mason Water Reclamation Plant 7
3.1 Photograph of Aerobic Sludge Thermo-Oxidation Experimental System 9
3.2 Schematic of Aerobic Sludge Thermo-Oxidation Experimental System 10
4.1a TSS and VSS Reduction: Air vs. N2 in Headspace, H202 vs. No H202 15
4.1b % VSS Removed at 60°C for Triplicate Runs 15
4.2 Fecal Coliform (MPN) Results, 60°C, Air vs. N2, 0.2 g H202/g VSS vs. No H202 15
4.3 pH Results, 60°C, Air vs. N2, 0.2 g H202/g VSS vs. No H202 16
4.4 % VSS Removed at 90°C for Triplicate Runs 17
4.5 % VSS Removed at 75°C for Triplicate Runs 17
4.6 pH Results at 90°C and 75°C for Triplicate Runs 18
4.7 Fecal Coliform (MPN) Results at 75°C for Triplicate Runs 18
4.8 % VSS Removed at 65°C for Triplicate Runs 19
4.9 pH Results and NhU-N Concentrations at 65°C for Triplicate Runs 20
4.10 TSS and VSS Removals for Multi-Temperature Experiment 21
4.11 pH Results for Multi-Temperature Experiment 21
4.12 NhU-N Results for Multi-Temperature Experiment 22
4.13 Soluble COD Results as a Percent of Total COD for Multi-Temp. Experiment 23
4.14 TKN Results for Multi-Temperature Experiment 24
4.15 VSS Removal for Sequential Runs Using Mason WWTP Sludge 24
4.16 Composite Graph of % VSS Removal for Mason WWTP Showing Seasonal Effect 26
4.17 Sludge Settleability after 24 hours at 90°C 27
4.18 Settling Results of 1,000 ml of Reactor Contents 27
4.19 VSS Removal for Four Different WWTPs at 90°C, No H202 Control and 0.2 g H202/g
VSS Treated Triplicates 28
4.20 Regression Lines of % VSS Removal at 90°C for All 0.2g H202/g VSS Dosing
Experiments 31
6.1 Treatment Train 1 with Table of Construction Cost Estimates 41
6.2 Treatment Train 2 with Table of Construction Cost Estimates 42
VII
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Tables
2.1 Results of Preliminary Sampling of Five WWTPs in the Greater Cincinnati, OH Area 5
2.2 Wastewater Characteristics for October 2012 for Five WWTPs in the Greater Cincinnati
Area 5
2.3 2013 Influent Wastewater Characteristics for the Mason Water Reclamation Plant 7
2.4 2013 Plant Effluent Characteristics for the Mason Water Reclamation Plant 8
3.1 Instrumentation and Equipment Used in Experimental System 10
4.1 List of the Experiments with Operating Conditions and Analyses Performed 14
4.2 Comparison of Filterability of Suspended Solids at T = Initial and T = 8 hours* in Multi-
Temperature Experiment 22
4.3 Additional Measurements Performed on Four WWTPs 29
4.4 Averages of % VSS Removal and Increased Removal over Control by Treatment 30
6.1 Estimated Operating Costs for Treatment Trains 1 and 2 for 20,000 gpd WAS 43
6.2 Estimated Operating Costs for Treatment Trains 1 and 2 for 4,000 gpd WAS 44
6.3 Summary of Capital and Operating Costs for Existing Sludge Treatment and Disposal
Options 45
VIII
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Acronyms and Abbreviations
BOD5
CFR
CPU
COD
EPA
EQ
FSS
gpm
H202
Louisville Green™
MCRT
Milorganite™
mgd
mg/L
MPN
NRMRL
NH4-N
QA/QC
ppm
PFRP
PTSI
SRT
SVI
TKN
TP
TSS
TWAS
UC
VAR
vss
WAS
WTIC
WWTP
5-day biochemical oxygen demand
Code of Federal Regulations
colony forming units
chemical oxygen demand
U.S. Environmental Protection Agency
Exceptional Quality, refers to biosolids with low levels of specified metals
filterable suspended solids, solids passing through a filter
gallons per day
gallons per minute
hydrogen peroxide
pelleted dried WAS from the Morris Forman Water Quality Treatment
Center, Louisville, KY
mean cell residence time
pelleted dried WAS from the Milwaukee Metropolitan Sewerage District
million gallons per day
milligrams per liter
most probable number
National Risk Management Research Laboratory
ammonia nitrogen
Quality Assurance/Quality Control
parts per million
process to further reduce pathogens, from 40CFR Part 503
Pegasus Technical Services, Inc.
sludge retention time
sludge volume index
total Kjeldahl nitrogen
total phosphorus
total suspended solids
thickened waste activated sludge, 1.5%-2.5% solids
University of Cincinnati
vector attraction reduction, from 40CFR Part 503
volatile suspended solids
waste activated sludge
Water Technology Innovation Cluster
wastewater treatment plant
IX
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Acknowledgments
This research project and the preparation of this final report have been conducted by the National Risk
Management Research Laboratory (NRMRL) of the U.S. Environmental Protection Agency (EPA)
under Contract No. EP-C-11-006, Work Assignments 2-77 and 3-77 with Pegasus Technical Services,
Inc. (PTSI) from October 2012 through September 2014.
Funds for this project were provided by the Environmental Technology Innovative Clusters Program
(ETIC), a program operating within the EPA's Office of Research and Development (ORD).
Appreciation is extended to ETIC for selecting and underwriting the cost of this project.
The EPA/NRMRL Work Assignment Manager was Richard C. Brenner and Alternate Work Assignment
Manager was Paul T. McCauley.
The following PTSI staff designed and assembled the experimental apparatus, conducted the
experimental trials, performed the laboratory analyses, and prepared the final report with NRMRL input:
Makram T. Suidan, Raghuraman Venkatapathy, Edith L. Holder, Robert J. Grosser, Yonggui Shan,
Joshua P. Kickish, Elisha J. Bryan.
Dr. Suidan directed prior research at the University of Cincinnati to evaluate thermal oxidation
technology for the treatment of anaerobically digested wastewater treatment plant (WWTP) sludges, and
he was instrumental in the development of the concept for this project to apply the thermal-oxidation
process to the treatment of aerobic WWTP sludges. Dr. Venkatapathy provided valuable advice on
chemical engineering principles and experimental design. Ms. Holder performed nutrient analyses and
oversaw data recording, reduction, and interpretation. She also assumed primary responsibility for the
preparation of this report. Dr. Grosser conducted microbiological analyses, performed a literature
review, and contributed to the final report. Mr. Shan assembled and operated the experiment system,
collected experimental samples, adjusted system component performance as needed, and assisted with
data analysis. Mr. Kickish carried out the large majority of the solids analyses. Ms. Bryan assisted with
nutrient analyses.
Ms. Ann Dougherty, Sustainability Coordinator for Xavier University (Cincinnati, OH), under contract
to PTSI, visited several wastewater treatment plants, performed extensive market and cost analysis, and
developed several conceptual designs for the thermo-oxidation process. She authored Section 6.0
(Market Analysis, Conceptual Treatment Trains, and Cost Estimates) of this report and also contributed
to Section 7.0 (Conclusions). Her expertise in this specialized area of technology development and
market penetration/niche analysis was critical to completion of this report.
Finally, we wish to acknowledge the cooperation and assistance of the entire staff of the Mason, OH
Water Reclamation Plant, especially Mr. Keith B. Collins, Director of Public Utilities, and Mr. Robert
A. Beyer, Plant Operator III, in obtaining waste activated sludge (WAS) on a weekly basis as reactor
feedstock for our experimental runs.
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1.0
Description and Objectives
1.1 Introduction and Background
The biological treatment of wastewater, with biological growth primarily fueled by organic
carbon (human waste) in the incoming wastewater and oxygen added to the system, generates
activated sludge. The major portion of the activated sludge inventory after gravity settling is
continuously recycled to the head of the secondary treatment aeration tank as return sludge to act
as a 'starter' for new biological activity, and a smaller excess portion is wasted or removed from
the system to optimize process efficiency. This second portion is called waste activated sludge
(WAS).
Municipal wastewater treatment plant (WWTP) sludge is typically composed of a combination of
raw sludge from primary treatment and WAS that is digested, either anaerobically or aerobically,
to achieve solids mass reduction, vector attraction reduction (VAR), and a reduction in microbial
indicators of fecal contamination such as fecal coliforms. In most cases, the digested sludge is
subjected to mechanical dewatering to produce a drier material that can be incinerated, disposed
of in a sanitary landfill, or applied in bulk to agricultural land as biosolids. Some producers of
biosolids further dry the processed material to the point where it can be bagged and sold as a
commercial soil conditioner/fertilizer (e.g., Milorganite™ produced by the Milwaukee
Metropolitan Sewerage District).
WWTP sludge is generally processed to levels where it can meet Federal Class B sludge
regulations. The Class B regulations represent the minimum levels of pathogen reduction that are
acceptable for land application of biosolids (i.e., treated WWTP sludge). These regulations
specify that wastewater sludge must be treated by a process to further reduce pathogens (PFRP)
that will achieve a VAR goal of 38% reduction in volatile suspended solids (VSS) concentrations
or meet a fecal coliform level in the processed sludge < 2,000,000 MPN (Most Probable
Number)/g, or alternately < 2,000,000 CPU (Colony Forming Units)/g, based on the geometric
mean of seven samples. Some states require municipal WWTPs to meet both stipulations to
achieve a Class B rating. PFRPs include, among others, anaerobic sludge digestion at a mean cell
residence time (MCRT) of 15 days at a temperature of 35°C-55°C and aerobic sludge digestion at
a MCRT of 40 days at 20°C.
Land application of Class B biosolids, although widely practiced in the United States, has been
accompanied by numerous and ongoing public complaints over the years. These complaints
range from emanation of malodors from the applied fields to claims of illnesses caused by
volatilization of harmful compounds contained in the biosolids or direct contact with the
biosolids. These complaints can be circumvented and most likely dispelled by the land
application of biosolids treated to a higher level, namely Class A biosolids. The definition of
Class A biosolids mandates the reduction of fecal coliforms to < 1,000 MPN/g total dry solids or
reduction of Salmonella to < 3 MPN/4 g total dry solids in order to prevent regrowth of bacteria.
This requirement can be met at one of these times: 1) when used for bulk application to
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agricultural land or otherwise disposed, 2) when prepared for sale in bags or other containers for
domestic gardening use, or 3) when prepared to meet the requirements for Exceptional Quality
(EQ, refers to metal concentration limits).
1.2 Objectives
The objectives of this research project were to evaluate and optimize a new cost effective thermo-
oxidation sludge treatment process that meets Class A regulations and to generate a reliable
dataset that could substantiate these claims. Accomplishment of these objectives was expected to
result in the filing of a process patent application for production of Class A biosolids for bulk
spreading to agricultural land as a high-grade soil conditioner. A long-term goal of future studies
would be the optimization of process variables and equipment selections (possibly through a
licensing arrangement) and incorporation of additional sludge drying into the process for
production of a combination soil conditioner/fertilizer that can be sold for home use in bags.
Successful development of a dry, baggable soil conditioner/fertilizer would be anticipated to
support the subsequent filing of a product patent application.
In addition to presenting the data generated on this project and evaluating the performance of the
thermo-oxidation treatment process, this report includes a market niche evaluation of this process,
a conceptual design for two operating scenarios, construction and operating cost estimates for the
target market, and comparison with existing technologies. The rationale for including this
information in this report is to provide the reader with an understanding of the potential
applicability of this process in the real world.
1.3 Technology Description
The proposed thermo-oxidation process uses hydrogen peroxide (EfeCh) addition at elevated
temperatures to achieve increased levels of VSS destruction and VAR and disinfection of sludge
that has been previously treated with some level of biological treatment, either anaerobic or
aerobic. Previous research conducted at the University of Cincinnati (UC) has demonstrated
reduction in fecal coliforms to non-detection levels on a combination of primary sludge and WAS
treated in high-rate or short-term anaerobic digesters with a sludge retention time (SRT) of 5 days
followed by thermo-oxidation (Cacho Rivero, 2005). It was postulated that the thermo-oxidation
process would work equally well on aerobically digested sludge, highly oxidized aerobic sludge
(mixed liquor) taken directly from an extended aeration or oxidation ditch activated sludge
reactor, and possibly even mixed liquor taken from a lower-SRT conventional activated sludge
aeration tank. The theory behind this mating of first-stage biological treatment with follow-on
second stage thermo-oxidation (chemical) treatment is to use the microorganisms in the biological
treatment stage to cost-effectively oxidize (aerobic treatment) or reduce (anaerobic treatment)
most of the easy-to-degrade organics contained in the sludge matrix and to use the more
expensive chemical (fbCh) treatment to oxidize the more recalcitrant organic compounds that are
not easily degraded biologically. Using ffcCh to oxidize easy-to-degrade organics would
substantially increase chemical dose requirements and cost. Likewise, using microorganisms to
process the more difficult-to-degrade organics would result in long MCRTs and large reactors,
again at increased cost. The proposed two-stage scenario optimizes what each stage of the sludge
treatment train does best and most cost-effectively.
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Because the thermo-oxidation step acts as a rigorous final treatment stage that oxidizes residual
organics not removed in the preceding biological treatment phase, this stage does not have to be
as large as typically designed for and installed in conventional WWTPs. Thus, short-term
anaerobic or aerobic sludge digesters could be used instead of the conventional 15-day anaerobic
digester SRT and the conventional 40-day aerobic digester SRT. These smaller digestion
facilities represent significant potential capital and operating cost savings to the municipal
WWTP. Given the potential ability of the EbCh treatment reactor to cost-effectively handle a
fairly broad range of incoming sludge feed characteristics, it was postulated that possibly no prior
sludge digestion step may be required. Rather, the highly oxidized mixed liquor sludge produced
in an extended aeration activated sludge plant and possibly even less oxidized conventional
activated sludge mixed liquor (i.e., WAS) may be suitable for direct injection into the thermo-
oxidation reactor. Under this scenario, the thermo-oxidation process would be able to
accommodate undigested sludge feedstocks typically produced by municipal WWTPs, including
settled mixed liquor from an extended aeration secondary treatment system and possibly settled
mixed liquor produced by a conventional activated sludge system.
Another potential benefit of the thermo-oxidation process was that it was believed a fraction of
the nitrogen (particularly ammonia nitrogen [NH4-N]) inventory in the EfeChfeed sludge would be
solubilized during treatment in the thermo-oxidation reactor and recycled to the treatment plant
headwords in the reactor supernatant. If this did not happen, the entire nutrient load would be
transported to the application field in the biosolids. A significant fraction of this load, particularly
the easily released NH4 component, would be rapidly solubilized and discharged into the soil,
potentially exceeding the sorption capacity of the soil and contaminating ground and surface
waters. By removing the easily released nutrient components in the WWTP, the nutrients more
tightly bound to the biosolids would be released slowly as needed for soil conditioning and
fertilization.
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2.0
Feed Waste Activated Sludge Selection
2.1 Description of Wastewater Treatment Plants Considered
Five WWTPs in the Greater Cincinnati, OH area were visited, sampled, and considered as
candidates from which WAS would be collected on a routine basis as the feed sludge for the
thermo-oxidation project experimental runs. All five WWTPs use activated sludge for their
secondary biological treatment process. Only activated sludge systems with extended or long
SRTs were considered. None of the five utilize primary settling of raw influent sludge and,
therefore, do not produce primary sludge. In all five cases, the entire excess sludge mass is
generated as WAS withdrawn daily from their activated sludge aeration tanks and directed either
to aerobic digesters or gravity or mechanical thickeners prior to sludge dewatering. Following
dewatering, the WAS biosolids are either applied directly on agricultural land or, in one case,
further dried to a pelletized form before land application.
The five WWTPs were the Harrison Wastewater Treatment Plant, the Lebanon Wastewater
Treatment Plant, the Mason Water Reclamation Plant, the Sycamore Creek Wastewater Treatment
Plant, and the Lesourdsville Upper Mill Creek Water Reclamation Facility. Four of the five
WWTPs utilize oxidation ditch (continuously circulating in the mode of a race track) aeration
tanks; the fifth (Sycamore Creek) employs conventional plug flow extended aeration tankage.
The Mason WWTP utilizes the above-mentioned drying process to produce pelletized biosolids.
Raw wastewater samples were collected from four of the five WWTPs (all but Harrison).
Aeration tank mixed liquor samples were taken from all five WWTPs. The Harrison, Lebanon,
and Lesourdsville Upper Mill Creek WWTPs employ aerobic sludge digesters following
secondary treatment. Samples of aerobically digested sludge from these three WWTPs were
collected. The Mason WWTP routes its WAS in sequence through: 1) gravity thickeners, 2)
aerated sludge holding tanks (that serve as abbreviated aerobic sludge digesters), 3) centrifugation
dewatering, and 4) a Komline-Sanderson paddle dryer to produced dry (> 95%) biosolids.
Samples were taken from the aerated sludge holding tanks for the Mason WWTP. WAS from the
Sycamore WWTP is stored in holding tanks for a short period and then trucked to a large
metropolitan WWTP in Cincinnati for final disposal. Therefore, mixed liquor from the secondary
aeration tanks was the only type of sludge sample collected from the Sycamore WWTP.
All samples were collected on December 4, 2012. The samples were delivered to the National
Risk Management Research Laboratory (NRMRL) of the U.S. Environmental Protection Agency
(EPA) on the same day, refrigerated, and analyzed the next day for total suspended solids (TSS)
and volatile suspended solids (VSS). Results from this preliminary sampling/screening exercise
are summarized in Table 2.1. Additional information on raw wastewater characteristics is given
in Table 2.2 as taken from the October 2012 Ohio EPA Daily Discharge Monitoring Report for
each WWTP.
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Table 2.1. Results of Preliminary Sampling of Five WWTPs in the Greater Cincinnati, OH Area
WWTP
Harrison
Lebanon
Lesourdsville
Mason
Sycamore
Creek
InfluentWW, mg/L
TSS
*
117
468
227
166
vss
*
107
395
202
157
%VSS
*
91.5
84.4
89.2
95.4
Mixed Liquor, mg/L
TSS
1,681
2,863
2,558
2,069
3,713
VSS
1,432
2,443
2,193
1,650
3,060
%VSS
85.3
85.3
85.7
79.6
82.4
Aerobic Digester, mg/L
TSS
11,002
13,880
13,573
19,510f
*
VSS
9,142
11,400
11,463
14,220f
*
%vss
83.1
82.1
84.5
72.9f
*
* Not sampled
f Sampled from sludge holding tank
t No aerobic digester available
Table 2.2. Wastewater Characteristics for October 2012 for Five WWTPs
in the Greater Cincinnati Area
WWTP
Harrison
Lebanon
Lesourdsville
Mason
Sycamore Creek
Influent Flow, mgd
0.91
2.07
6.76
4.96
5.51
Raw WW Total BODS, mg/L
349
159
143
238
98
Raw WW TSS, mg/L
349
157
328
349
101
2.2 Rationale for Selection of Mason Wastewater Treatment Plant
The goal in screening several extended aeration WWTPs in the Greater Cincinnati area was to
enable selection of a WWTP that best fit the application for which the thermo-oxidation sludge
treatment process is envisioned, i.e., a WWTP with lower flows treating primarily domestic
wastewater. Accordingly, the ideal WWTP would have an average monthly influent flow rate in
the range of 2-10 million gallons per day (mgd) and similar raw wastewater five-day biochemical
oxygen demand (BODS) and TSS concentrations in the range of 150-350 mg/L. So that all
experiments could be run with the same solids content of 1.5%, it was also important to locate a
suitable sludge source with a concentration of at least 1.5% TSS. Feed sludge could then be
diluted with secondary effluent from the same WWTP, but it would not have to be thickened
using more cumbersome methodology such as porous pots to reach the feed goal.
The Mason WWTP best met the criteria. It is equipped with an Eimco Water Technologies
Carrousel™ oxidation ditch with an activated sludge mixed liquor SRT of approximately 25 days.
The nominal aeration detention time is 20-27 hours. With an average raw wastewater flow for
October 2012 of approximately 5 mgd consisting mostly of domestic sewage, it met the target
influent flow rate of 2-10 mgd. To eliminate the complicating factors of heavy metals or other
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industrial chemicals, a WWTP with minimal industrial contribution, such as Mason's was
preferred. It met the target influent BODS concentration range for all months in 2012 (data not
shown), and with two exceptions (358 mg/L in July and 386 mg/L in September), it also met the
target TSS concentration range. Another favorable parameter in choosing Mason was that it was
the only WWTP surveyed on December 4, 2012 that had a thickened WAS (TWAS) TSS
concentration > 1.5% or 15,000 mg/L (see first column under aerobic digester in Table 2.1).
Finally, we were afforded easy access to the plant, and the plant management was very
cooperative. It was, therefore, an easy choice as the feed sludge source. A flow diagram of the
Mason WWTP is shown in Figure 2.1. An aerial photograph of the plant is given in Figure 2.2.
OXIDATION DfTCH
DISTRIBUTION SCREENING
CHAMBER AND GPU
REMOVAL
BUILDING
Figure 2.1. Flow Diagram of Mason Water Reclamation Plant
Average monthly influent flow, influent total BODS, and influent TSS values are presented in
Table 2.3 for 2013, the period during which TWAS samples were being collected from the Mason
WWTP for experimental runs. These data provide additional validation in selecting the Mason
plant as the sludge source. Monthly maximum/average flow ratios, with two exceptions, ranged
from 1.5-1.8, indicating a tight (minimal leaks) sewer system. Average influent flow rates,
average influent total BODS, with one exception, and average influent TSS, with two exceptions,
were all within the target ranges.
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Figure 2.2. Aerial Photograph of Mason Water Reclamation Plant
Table 2.3. 2013 Influent Wastewater Characteristics for the Mason Water Reclamation Plant
(Beyer, 2014)
Month
January
February
March
April
May
June
July
August
September
October
November
December
2013 Average
Influent Flow
Average, mgd
6.14
5.77
7.15
6.29
6.08
5.53
6.55
5.41
5.67
5.64
5.68
6.67
6.05
Maximum, mgd
10.81
7.89
12.86
10.07
10.20
7.51
15.32
5.81
9.87
9.92
8.24
15.95
10.37
Maximum/
Average
Influent
Flow
1.76
1.37
1.80
1.60
1.68
1.36
2.34
1.07
1.74
1.76
1.45
2.39
1.71
Average Influent Total
BODS, mg/L
175
192
125
172
150
192
166
165
233
165
176
157
172
TSS, mg/L
236
296
179
298
244
320
234
346
320
266
247
283
272
-------
In Table 2.4, average monthly plant effluent values are summarized. As indicated, effluent
quality was excellent. Average monthly effluent total BODS, TSS, NH4-N, and total Kjeldahl
nitrogen (TKN) were all low. Some fraction of the oxidized nitrogen was denitrified in the
aeration tank anoxic zone, while the remainder appeared in the plant effluent as nitrite/nitrate
nitrogen (NO2-N + NO3-N).
Table 2.4. 2013 Final Effluent Characteristics for the Mason Water Reclamation Plant
(Beyer, 2014)
Month
January
February
March
April
May
June
July
August
September
October
November
December
2013
Average
Total
BODS,
mg/L
2.0
3.2
2.7
2.1
0.6
0.2
0.7
1.1
ND
0.6
0.4
0.4
1.2
TSS,
mg/L
3.0
4.1
3.9
4.6
2.7
2.4
5.3
3.0
3.0
3.6
3.3
4.2
3.6
Temperature,
°C
12.9
12.5
12.6
16.3
20.4
22.4
23.2
24.3
26.0
20.3
16.6
14.1
18.5
NH4-N,
mg/L
ND
ND
ND
ND
ND
ND
ND
0.8
ND
ND
ND
ND
NA
TKN,
mg/L
2.0
0.9
0.8
1.2
0.5
1.2
0.9
0.8
0.7
ND
1.1
1.3
1.0
NO2-N + NOs-N,
mg/L
5.0
5.9
4.7
5.0
9.8
4.4
4.5
4.4
4.6
6.1
5.4
6.5
5.5
Total P,
mg/L
2.0
1.8
2.1
1.7
2.0
0.5
0.4
0.4
0.4
0.6
1.2
2.3
1.3
ND = not detected; NA = not applicable
-------
3.0
Experimental Design
3.1 Description of Experimental System
Figure 3.1 is a photograph of the experimental system. Figure 3.2 is a schematic of the system
showing a single reactor set up. Table 3.1 lists the instrumentation and equipment used.
Figure 3.1 Photograph of Aerobic Sludge Thermo-Oxidation Experimental System
Thickened sludge collected from the Mason WWTP was diluted with effluent from the same plant
to make a sludge solution with -15,000 mg/L of TSS. In the initial runs, a carboy was used to
prepare a bulk solution, but there was less variability in TSS concentration when each reactor was
diluted individually in a 2-L graduated cylinder. As shown in Figure 3.2, 2 L of diluted sludge
solution were loaded into each of the four 4-L reactors (1) on stirring plates (2). Stir bars (3) were
used for mixing. The stirring plates were previously calibrated to yield a mixing speed of-150
revolutions per minute. The reactors were insulated with glass wool and heated to the desired
-------
1. 4-L Thermo-oxidation reactor; 2. Stirring plate; 3. 4-in. Stir bar; 4. Heating tape;
5. Temperature controller (thermocouple with rheostat); 6. Thermometer; 7. 10-mL Syringe;
8. Syringe pump; 9. Air humidifier; 10. Glass condenser; 11. 250-mL glass flask;
12. Refrigerated bath circulator, 13. Gas cylinder
Figure 3.2. Schematic of Aerobic Sludge Thermo-Oxidation Experimental System
No.
1
2
3
4
5
6
7
8
9
10
11
12
Table 3.1. Instrumentation and Equipment Used in Experimental System
Name
Thermo-oxidation Reactor
Stirring hot plate
Stir bars
Heating tape
Temperature controller
Thermometer
Syringe
Syringe pump
Air humidifier
Glass condenser
Erlenmeyer flask
Refrigerated bath circulator
Description
4 L, PYREX Corning aspirator bottle, #02-972F, Fisher
12" x 12", CinarecS, Thermolyne
4", Fisher
360 W, 1 15 V, #002-6x24-24-2.5-A, Delta Heat
CN91 1 1 A, 115V, Omega Engineering, Inc.
-50° to +250°C, #15-077-59, Fisher
10 ml, B-D
NE-300, New Era Pump Systems, Inc.
4 L, filling ceramic ring
Liebig, top and bottom joint 14/20, overall height 178 mm, Kimble
250 ml, Fisher
RTE-100, Neslab
temperature with heating tapes (4). The reaction temperatures were controlled by a temperature
controller rheostat (5) with a thermocouple. A thermometer (6) was inserted into each reactor as a
check for the temperature controller. A 50% ffcCh solution was injected into each reactor from a
10 mL syringe (7) using a syringe pump (8) over a 30-minute time period. Pressurized air and, in
10
-------
some early experiments nitrogen from a cylinder, was passed through an air humidifier (9) and
then distributed into the head space of each reactor through an inlet valve at ~ 200 mL/min.
Purged air exited out of the reactors through a condenser (10) to limit evaporation and allow the
condensate to flow back into each of the reactors. A small restrictor was installed in each
condenser outlet, and the gas exited through an Erlenmeyer flask (11) containing 200 mL water to
monitor direction of gas flow and to prevent back flow. Cooling water for the condensers was
pumped through a refrigerated bath (12).
An experimental run consisted of an initial period of approximately 1 hour for the reactors to
reach operating temperature. Time 0 was the initiation of FbO2 addition. Later sampling times
were designated in hours after Time 0. The usual time points were 1, 2, 4, 6 or 8, and 24 hours.
Since in an actual application, the sludge would be held probably no more than 4 hours, the later
time points were sometimes eliminated.
3.2 Experimental Chronology and Conditions
Experimental trials were conducted from early December 2012 through September 2013. After
initial measurements were conducted on samples collected from the five extended aeration
WWTPs and selection of the Mason WWTP as our plant of choice for reactor feed WAS, a series
of trials were performed from January 2013 through July 2013 at reactor temperatures ranging
from 60°C to 90°C. The initial runs utilized reactor purging with air vs. nitrogen gas. After no
observable difference, air was used as the purge gas for all subsequent trials. At the conclusion of
the trials, in August and early September 2013, test runs were conducted using sludge from four
other local WWTPs (two of the five WWTPs surveyed during our preliminary sludge selection
study plus two others in the local area) at the reactor temperature and FbO2 dosage determined to
be optimal in the Mason WWTP trials.
3.3 Methods
Measurements of TSS and VSS, fecal coliform MPN, COD, nutrients (NH4-N, TP, and for some
runs TKN) and sludge settleability were performed using the following methods:
Hach Company, Methods for measuring nutrients, http://www.hach.com/
Ammonia Nitrogen, Salicylate Method # 10031
Total Kjeldahl Nitrogen, Nessler Method # 8075
Chemical Oxygen Demand, Reactor Digestion Method # 8000
Total Phosphorus, Acid Persulfate Digestion Method # 10127
IDEXX Inc., Colilert 18 Fecal Coliform Protocol,
http://www.idexx.com/resourcelibrary/water/colilert-18-procedure-en.pdfand
http://www.idexx.com/resourcelibrary/water/water-reg-article5CV-v2.pdf
TSS and VSS: SOP: Determination of Total Suspended Solids (TSS) and Volatile Suspended
Solids (VSS) in Water, Wastewater, Activated Sludge, and Aqueous Extracts, Pegasus Technical
Services for U.S. Environmental Agency Contract EP-C-11-006, Revision 2. July 27, 2011.
Sludge Volume Index (SVI) and Settling: Standard Methods for the Examination of Water and
Wastewater. 20th Ed. American Public Health Association, American Water Works Association,
Water Environment Federation. Method #2710
11
-------
The guidance document for this project is U.S. EPA Quality Assurance Project Plan, Category III
Measurement Project, QAPP ID # L18881-QP-1-0, Thermo-Oxidation of Municipal Wastewater
Treatment Plant Sludge for Production of Class A Biosolids, approved on April 26, 2013 and is
attached as Appendix B.
The U. S. EPA Health and Safety Plan for this project is HASP ID # 2012-086, Rev. 1, approved
January 11,2013.
3.4 Quality Assurance/Quality Control Considerations
The transformations that must take place to produce a Class A biosolids from an untreated WAS
source stream involve the mass reduction of VSS, a reduction in vector attraction, an increase in
sludge stability, and destruction of pathogenic microorganisms. A chemical oxidant and heat
(i.e., elevated temperature less than boiling) were added to untreated WAS within a confined
reactor to effect these transformations. H2O2 due to its predictable properties, ease of handling,
and relatively low cost was selected as the oxidant of choice.
Although H2O2 and heat are known oxidants by themselves, they had not previously been applied
in combination to WAS to synergistically enhance sludge oxidation/destruction and stabilization.
Four H2O2 doses were selected for evaluation: no H2O2 (control) and 0.05, 0.1, and 0.2 g H2O2/g
applied VSS. Reactor temperatures evaluated ranged from 60°C to 90°C. It was decided to
operate at temperatures below the boiling point of water as this would simplify possible future
full-scale operation and maintenance requirements and lower construction costs.
While H2O2 dose and applied heat were the two independent variables selected for examination,
two dependent variables, time of reaction and WAS characteristics, required consideration in the
experimental design. It was not known a priori how much reaction time would be required to
reach an acceptable level of WAS treatment. A decision was made to use VSS destruction as the
measurement metric to define degree of treatment achieved as a function of time. It was expected
that VSS destruction would approach an asymptotic maximum with increasing reaction time
beyond which further treatment would have no additional oxidative potential. Consequently, the
experimental design included WAS sample collection from the reactors at detention times of 1, 2,
4, 8, and 24 hours to define the VSS die-off or destruction curve.
The use of sequential replicate experiments was the primary quality assurance/quality control
(QA/QC) mechanism built into our experimental design protocol to achieve consistent
performance and minimal deviation of results. Accuracy checks, precision calculations,
calibration of instrumentation, and determination of detection limits were used to ensure
acceptable QC and confidence levels for the obtained results. Precise, documented, and validated
data were needed to support the ultimate decisions made. To ensure the quality of the data, all
instruments were regularly calibrated and QA/QC checks were routinely performed. All TSS and
VSS measurements were performed in triplicate.
12
-------
4.0
Results and Discussion
4.1 Overview of Experiments
The complete list of experiments performed during this project is presented in Table 4.1. All
experiments were conducted between December 2012 and September 2013. During the course of
this project, temperature and IHbCh dosage were the principal parameters investigated. The
temperatures tested were room temperature, 35°C, 60°C, 65°C, 75°C, 80°C, and 90°C. Hydrogen
peroxide doses of none, 0.05, 0.1, and 0.2 g/g VSS were used. The Initial time point refers to
when the reactors were turned on and began heating. T = 0 was the actual start of treatment when
the reactors reached the experimental temperature and the addition of IHbCh began. There was
approximately 1 hour between T = Initial and T = 0. The other time points are hours after Time 0.
4.2 Initial Experiments
In the first complete experiment to test equipment and analytical protocols the reactors were run
at four temperatures: room temperature, 35°C, 60°C, and 90°C, and with either an air or nitrogen
headspace purge. The room temperature and 35°C test conditions showed no decrease in fecal
coliform MPNs. This result, as well as not meeting the EPA Part 503 Biosolids Rule, was
expected. So after the first complete experiment, these test conditions were no longer utilized.
During initial testing, reactors were operated with either an air or a nitrogen blanket to evaluate
the role of oxygen during the treatment. Figure 4. la shows the TSS (top group of lines) and VSS
(lower group of lines) results from a single trial run at 60°C comparing air vs. nitrogen in the
headspace and FkCh treatment of 0.2 g/g VSS vs. no treatment. In Figure 4. Ib, the data from the
60°C triplicate runs have been compiled and calculated as % VSS removed with error bars. Heat
alone destroys solids as the reduction begins prior to Time 0. The H2O2 treated reactors
demonstrated more solids destruction than the untreated control reactors. There was no
difference, however, between the reactors on the basis of the headspace blanket gas. So it was
concluded that atmospheric oxygen plays no role in H2O2 treatment. Having determined that the
headspace blanket gas has no relevance to treatment and because H2O2 treatment occurring in an
actual wastewater treatment plant would be in the open air, the use of a nitrogen blanket was
discontinued after these experiments.
The primary criterion for production of Class A biosolids is removal of pathogens. We chose to
use the Fecal Coliform Rule of less than 1,000 MPN/g dry solids from Subpart D of CFR Part 503
for this investigation. Figure 4.2 is a graph of fecal coliforms from the March 27th run. Samples
were taken throughout the course of the experiment, and then a diluted final sludge slurry sample
was held for 1 week at room temperature before being tested again to determine the potential for
coliform regrowth. The bold line at log 3 (1,000 MPN) delineates the maximum allowable fecal
coliform concentration. During the treatment phase at 60°C, while a reduction in numbers of
fecal coliforms was noted, regrowth occurred after 7 days.
13
-------
Table 4.1. List of Experiments with Operating Conditions and Analyses Performed
Dates
December 4 &
18,2012;
January 2 & 7,
2013
January 22 & 25,
2013
Februarys, 12, &
26,2013
March 19&27,
April 2, 2013
April 10, 16, &23,
2013
April 30, May 14 &
21,2013
May 29, June 4 &
11,2013
June 26, July 2,
2013
July 22, 25, & 26,
2013
July 23, 24, & 27,
2013
August 20, 2013
August 22, 2013
August 28, 2013
Septembers, 2013
Experimental Conditions
Preliminary experiments. Five Greater Cincinnati (OH)
plants: Harrison, Lebanon, Lesourdsville, Mason, and
Sycamore Creek testing equipment and addition of H2O2.
Mason plant. First complete experiment using sludge.
Either air or N2 purge. Four temps. Without H2O2. For 1st
run: A = Room temp. (RT) + air; B = 60°C + air; C = RT +
ISh; D = 60°C + N2. For 2nd run: E = 35°C + air; F = 90°C +
air; G = 35°C + N2; H = 90°C + N2.
Mason plant. Three trial runs. Fresh sludge each time.
Either air or ISh purge at 60°C. Reactor: A = air purge;
B = air purge with 0. 1 g H2O2/g VSS; C = ISh purge;
D = N2 purge with 0.1 g H2O2/g VSS.
Mason plant. Three trial runs. Fresh sludge each time.
Either air or ISh purge at 60°C. Reactor: A = air purge;
B = air purge with 0.2 g H2O2/g VSS; C = ISh purge;
D = N2 purge with 0.2 H2O2/g VSS.
Mason plant. Three trial runs. Fresh sludge each time
All air purge. 90°C, A = no H2O2,
B = 0.05, C = 0.1, D = 0.2 g H2O2/g VSS.
Mason plant. Three trial runs. Fresh sludge each time.
75°C, A = no H2O2,
B = 0.05, C = 0.1, D = 0.2 g H2O2/g VSS.
Mason plant. Three trial runs. Fresh sludge each time.
65°C, A = no H2O2,
B = 0.05, C = 0.1, D = 0.2 g H2O2/g VSS.
Mason plant. Two trial runs. Four temps., A = 65°C,
B = 75°C, C = 80°C, D = 90°C;
First trial with 0.2 g H2O2/g VSS, Second trial without H2O2.
Mason plant. Three trial runs. 90°C, A = no H2O2,
B = 0.1 g H2O2/g VSS, C = 0.2 g H2O2/g VSS.
Mason plant. Three trial runs using same sludge as July 22,
25, & 26. 65°C, A = no H2O2, B = 0.1 g H2O2/g VSS, C =
0.2 g H2O2/g VSS.
Sycamore plant; 90°C, A = no H2O2;
B, C, D = 0.2 g H2O2/g VSS.
Harrison plant; 90°C, A = no H2O2;
B, C, D = 0.2 g H2O2/g VSS.
Little Miami plant; 90°C, A = no H2O2;
B, C, D = 0.2 g H2O2/ g VSS.
Millcreek plant; 90°C, A = no H2O2;
B, C, D = 0.2 g H2O2/g VSS.
Analyses
TSS and VSS
TSS/VSS and MPN
TSS/VSS and MPN
TSS/VSS, MPN, pH, and
Nutrients
TSS/VSS, MPN, pH,
Nutrients, and TKN
TSS/TSS, MPN, pH,
Nutrients, TKN, SVI, and
Settling
TSS/VSS, MPN, pH,
Nutrients, TKN, SVI, and
Settling
TSS/VSS, pH, Nutrients,
TKN, SVI, and Settling
TSS/VSS, pH, Nutrients,
SVI, and Settling
TSS/VSS, pH, Nutrients,
SVI, and Settling
TSS/VSS, MPN, pH,
Nutrients, TKN, SVI, and
Settling
TSS/VSS, MPN, pH,
Nutrients, TKN, SVI, and
Settling
TSS/VSS, MPN, pH,
Nutrients, TKN, SVI, and
Settling
TSS/VSS, MPN, pH,
Nutrients, TKN, SVI, and
Settling
14
-------
-a
c
eg
16
15
14
13
12
11
0 8
A & air
C&D
a. March 19, 60°C
-1
1 2 4
Time, hours
24
b. VSS, 60°C, none & 0.2 g H2O2
March 19,27, &April 2
Figure 4.1 a. TSS and VSS Reduction: Air vs. Na in Headspace, HaOa vs. No HaOa
Figure 4.1 b. % VSS Removed at 60°C for Triplicate Runs
Fecal Coliforms, March 27
w
A, air, none
B, air, H202
C, N2, none
.D..N,,,.
Init.
168
2 4
Time, hours
The log 1 values are non-detects which actually means < 100 MPN/g TSS.
Re-growth at 7 days is > number graphed
Figure 4.2. Fecal Coliform (MPN) Results, 60°C, Air vs. Na, 0.2 g HaOa/g VSS
vs. No HaOa
15
-------
Another parameter tracked during this experiment was pH. It decreased with IHbCh treatment
while remaining essentially unchanged without added IHbCh. Figure 4.3 shows the trend in these
triplicate runs. This result correlated with an increase in NH4-N. On average, NH4-N changed
from 28 mg/L at the initial sample time to 108 mg/L in the control reactors to 400 mg/L in the
H2O2 treated reactors at 24 hours. Measurements for COD and TP indicated little change (data
not shown).
pH at 60°C, March 19, 27, & April 2
7.5
7.0
6.5
I
Q.
6.0
5.5
5.0
N2, H20
Init
24
Time, hours
Figure 4.3. pH Results, 60°C, Air vs N2, 0.2 g H2
-------
70
60 -
VSS, 90°C, Apr. 10, 16, & 23
50
•| 40
•a
0>
§
E 30
(D
w
w
> 20
10 -
0 5 10 15 20
Time, hours
Figure 4.4. % VSS Removed at 90°C for Triplicate Runs
VSS, 75°C, Apr. 30, May 14, & 21
50
0 5 10
Time, hours
Figure 4.5. % VSS Removed at 75°C for Triplicate Runs
25
17
-------
pH at 90°C
pH at 75°C
7.0
6.5
6.0
o. 5.5
5.0
4.5
4.0
I nit
7.5
7.0
6.5
6.0
5.5
5.0
4.5
0 1 2 4 8 24 Init 0124
Time, hours Time, hours
Figure 4.6. pH Results at 90°C and 75°C for Triplicate Runs
8 24
Figure 4.7 plots the fecal coliform counts (MPN) for triplicate runs at 75°C for the April 30 and
May 14 and 21 experiments. Only the no-FbCh-added control reactors had any bacterial growth
after the beginning of the experiment. However, none of the reactor conditions reached the
regulatory limit of 1,000 MPN/g, and there was no regrowth after 7 days. Fecal coliforms were
reduced to below the detection limit within 1 hour for all reactors at 90°C.
Fecal Coliforms, 75°C, 30 Apr, 14 & 21 May
I1 4
Init.
1
8
24
7 days
2 4
Time, hours
The log 1 values are non-detects which actually means < 100 MPN/g TSS.
Figure 4.7. Fecal Coliform (MPN) Results at 75°C for Triplicate Runs
18
-------
The next experiment tested an operating temperature of 65°C. Figure 4.8 is a graph of % VSS
removal vs. time. Similar results were found with higher VSS removals at increasing FfeCh
concentrations, but the totals were lower than at the higher temperatures, as well as lower than the
trials at 60°C in the spring (see Table 4.4 for specific values).
VSS, 65°C, May 29, June 4, & 11
0 5 10 15
Time, hours
Figure 4.8. % VSS Removed at 65°C for Triplicate Runs
This experimental set produced an anomaly. At 24 hours, the pH of the control and the two lower
concentrations of added FfeCh (0.05 and O.lg/g VSS) increased to higher values than the initial
pH. At the same time, the NH4-N concentrations increased dramatically in the same reactors
(Figure 4.9). The no dose reactors had the highest increase.
The results for fecal coliform MPNs at 65°C were similar to those obtained previously at 75°C.
Only in the no-added-FbCh control and the 0.05 g FbCh/g VSS reactors were coliforms detected
after the first 2 hours of the experiment, but the MPNs were lower than the regulatory limit of
1000 MPN/g. The control reactors produced regrowth after 7 days, but the FfeCh treated reactors
did not. With this result, it was decided that 65°C was the lowest temperature for FfeCh treatment
that produced consistent fecal coliform removal.
19
-------
pH at 65°C
Ammonia-N at 65°C
8.0
7.5
7.0
' 6.5
6.0
5.0
0.05 g H,O,
0.1 g H,0,
0-2gH,0,
400
300
E
200
100
Init
8 24
31 2 4 8 24 Init 0124
Time, hours Time, hours
Figure 4.9. pH Results and NhU-N Concentrations at 65°C for Triplicate Runs
4.4 Summer Experiments on Mason Waste Activated Sludge
The next experimental set compared solids decrease with time at four temperatures (65°C, 75°C,
80°C, and 90°C) with 0.2 g/g VSS vs. no-added H2O2 controls. Figure 4.10 depicts the results
for both TSS (top group of lines) and VSS (bottom group of lines) at these four temperatures.
After an initial drop, both TSS and VSS remained approximately the same in the no-added-FbCh
control reactors despite different temperatures inside the reactors. With FhCh treatment, a clear
delineation is evident between temperatures with the higher temperatures destroying more solids
than the lower ones. The pH was lower for treated reactors as well as being different between
temperatures; the higher the temperature the greater the pH decrease as illustrated in Figure 4.11.
In these experiments, measurements were made for both the total sample and a filtered sample
(Whatman Grade 3 with a 6-|im pore size) to determine the apportionment of the various
nutrients. Filterable suspended solids (FSS), those that pass through the filter, were increased
with treatment. The TSS of the initial sludge sample contained ~ 10% FSS. After heat
treatments, but without added FbCh, FSS as a percentage of TSS ranged from 25% to 35%,
increasing with temperature. FfeCh treatment increased FSS as a percentage of TSS to between
53% and 63%, also increasing with temperature to approximately twice that of the undosed
reactors (data in Table 4.2).
20
-------
TSS & VSS, June 26 & July 2
17
16
15
14
13
•o o
S£
10
9
8
7
6
5
With/Without 0.2 g H.O., A/E = 65°C, B/F = 75°C, C/G = 80°C, D/H = 90°C
without
with
without
with
I nit
1
8
Time, hours
Figure 4.10. TSS and VSS Removals for Multi-Temperature Experiment
7.5
7.0
pH Multitemp Experiment, June 26 & July 2
6.5
I
Q.
6.0
5.5
5.0
4.5
"*••-—.
0.2 g H202/g VSS and negative control
T-
-A-
65 °C Ctrl
75 "C Ctrl
80 °C Ctrl
90 °C Ctrl
65 °C
75 °C
80 °C
90°C
Init
8
0 24
Time, hours
Figure 4.11. pH Results for Multi-Temperature Experiment
21
-------
Table 4.2. Comparison of Filterability of Suspended Solids
at T = Initial and T = 8 hours* in Multi-Temperature Experiment
Treatment with 0.2 g/g H2O2
Filterable Suspended
Solids, mg/L
Initial
65°C*
75°C*
SOT*
90°C*
1,937
6,215
5,998
5,751
6,126
TSS, mg/L
15,773
11,567
11,275
10,842
9,808
% of TSS
12.3
53.7
53.2
53.1
62.5
No HzOz Treatment
Filterable Suspended
Solids, mg/L
Initial
65°C*
75°C*
SOT*
90°C*
1,283
3,283
4,102
4,468
4,553
TSS, mg/L
15,427
13,183
13,633
13,258
13,108
% of TSS
8.3
24.9
30.1
33.7
34.7
Result: Thermo-oxidative treatment increased filterable solids concentrations.
Next, comparisons were made to determine nutrient availability in the total and filtered samples.
NH4-N concentrations increased with treatment as the heat liberated it from organic compounds in
the sludge. Selected results are shown in Figure 4.12. Again, the 65°C reactor without FbO2
contained a higher concentration of NH4-N than did the FbO2 treated reactor. The inset graph
shows that the ratio of filtered to unfiltered concentrations is 70%-90% for all four temperatures,
treated and untreated. This ratio was true for all time points, indicating that most of the NH4-N
was in the soluble fraction. This would have implications for sludge stabilization.
NH -N, Selected Data
150
120
90
60
30
NH4-N at T - 2, % filtered / unfiltered
90°C, none
Init
0 2
Time, hours
Figure 4.12. NhU-N Results for Multi-Temperature Experiment
Measurements of total and soluble COD were also conducted. During the experiment, total COD
declined ~ 15% in both heat alone and heat plus H2O2 reactors. Data for soluble COD as a
percentage of total COD are shown in Figure 4.13. Soluble COD increased with time; the
reactors with added FbO2 increased faster, but these reactors plateaued such that control and
treated reactors yielded similar results by T= 8 hours.
22
-------
50
40
30
a?
a" 20
O
a
840
.
]§ 30
O
CO
20
10
65°C
80°C
75°C
90°C
Initial
T=0
no H202
T=2 T=8
0.2gH?02
Initial
T=0
T=2
T=8
Figure 4.13. Soluble COD Results as Percent of Total COD for Multi-Temp Experiment
TKN was analyzed on both filtered and total samples. For the T = Initial sludge, most of the
TKN was bound to the solids with a soluble fraction of- 5%. A small amount of TKN appears to
be destroyed by treatment (-10% with ffeCh treatment and - 5% by heat alone). After treatment,
no difference in total TKN was noted between the different reactor temperatures, but the soluble
fraction increased to 51% of the total for the FbCh-dosed reactors and 46% for the control
reactors. Statistical analysis using the Student t-test indicated no significant difference between
H2O2 treatment and control reactors for the unfiltered samples at each temperature, but a
significant difference (alpha = 0.05) between ffeCh treated and control reactors for the filtered
samples. Figure 4.14 summarizes these results.
As a final test of the thermo-oxidation process, our procedure changed. Instead of obtaining fresh
sludge for a trial run, it was decided to use the same sludge for multiple runs to eliminate any
variability induced by possible changes in the influent sludge to enable direct comparison of
results at 65°C and 90°C. During one week in July, the same Mason WAS was tested daily for a
total of six runs; three conducted at 65°C and three at 90°C, utilizing three test conditions:
control, 0.1 and 0.2 g H2O2/g VSS. Figure 4.15 illustrates VSS removals after 4 hours. At T = 0,
23
-------
TKN results, June 26 & July 2
1000
900
800
700
i
p 600
500
400
300
200
100
0.2 g HO
No H0
'I
40
O
10
.11
•Cr
X
I"
D"
d
01
fc
ff"
8
Figure 4.14. TKN Results for Multi-Temperature Experiment
VSS removed, July 22 - 27
30 -
2.
Q)
£ 20 -
5
T3
01234
Time, hours
Figure 4.15. VSS Removal for Sequential Runs Using Mason WWTP Sludge
24
-------
the 90°C reactors already had achieved a greater % VSS removal than did the 65°C reactors.
However, by T = 2 and T = 4 hours, the control reactors were similar for both temperatures. For
the same FkCh dose, a greater % VSS removal was achieved at 90°C than at 65°C, but this
difference was greater at 1 and 2 hours than at 4 hours when the 65°C reactors had achieved a
similar % VSS removal. The temperature difference affected the rate of the reaction more than it
impacted the total extent of VSS removal. Due to this change in protocol, the results obtained in
this experiment are perhaps only comparable to a single repetition of earlier experiments where a
fresh WAS influent was collected for each separate run. However, the VSS destruction results
described above do not corroborate test data produced on Mason WAS in April and May
experiments (see Figures 4.4 and 4.8). In the earlier trials, VSS destruction for the 0.1 and 0.2 g
H2O2/g VSS dosages was consistently 20% to 25% higher for the 90°C runs than the 65°C runs
from 2 to 24 hours, i.e., the extent of the lower temperature VSS destruction remained
consistently different along the run time.
Figure 4.16 is a composite graph by added H2O2 dose. It shows the average VSS removal with
error bars for each series of experiments from T = Initial through T = 4 hours for all tests
performed on this project. The first five triplicate experiments are depicted with a solid line. The
multi-temperature experiment in late June was not replicated and is shown in dashed lines. The
same sludge experiment at two temperatures in July are depicted with dotted lines. The lower
H2O2 doses, 0.1 and 0.05 g/g VSS, were not tested during the multi-temperature experiment. The
0.05 g H2O2/g VSS dose was only tested in three triplicate runs. This graph makes it easy to see
that some VSS removal was achieved based on temperature alone. Overall, an increase in VSS
removal was noted with increasing H2O2 dose at a particular temperature. However, as noted
previously, the tests run in the late winter or spring achieved greater removal percentages than
those conducted in summer. This reflects a difference in the sludge characteristics obtained from
the Mason WWTP during the two periods. The 90°C VSS removals from July are lower than
those obtained in June which are much lower than those obtained in April. The other temperature
tested several times was 65°C, but the tests performed in May, June, and July do not indicate the
same trend, presumably because by May the sludge at the plant was warmer. The error bars on
the 75°C runs in April and May are wider than most because of the differences between the April
30 and the May 14 and 21sludge quality. This seasonal variation makes it difficult to compare the
earlier and later experiments. Due to higher wastewater temperatures in the WWTP aeration tank
in the summer, more of the readily degradable organics were already biodegraded, leaving less
degradable material available to be oxidized by the H2O2 process.
TP was measured initially and at the end of most of the experiments. The concentration did not
change during the course of an experimental run, but the TP concentration in the WAS varied
between 600 and 1,000 mg/L, being lower in the cooler months (data not shown).
Beginning with the April 17th experiment, at the end of an experiment, reactor contents were
placed in a 1-L graduated cylinder and the volume that marked the boundary between the settled
solids and the overlying supernatant was recorded after 30 minutes and 24 hours. Figure 4.17 is a
photograph of an experimental run showing settleability after 24 hours. Figure 4.18 is a graph of
all 24-hour results. The 90°C results are shown in green, 80°C results in magenta, 75°C results in
red, and 65°C results in blue. The crosses represent each measurement that was made. Settling
was enhanced such that the volume containing solids was smaller with increasing H2O2 dose and
25
-------
0.05 g rtOJg, all runs
0.1 g H202/g, all runs
0.2 g H.OJg, all runs
60'C. Mar
65'C. May. Jun
75*C. Apr. May
WC. Apr
65'C. Jun
75'C. Jun
90'C. Jun
90'C. Jun
30 -*• BS'C. Jul
90'C. Jul
10
34 01234
Time, hours
Figure 4.16. Composite Graph of % VSS Removal for Mason WWTP Showing Seasonal Effect
26
-------
Figure 4.17. Sludge Settleability After 24 hours at 90°C: I - Raw Sludge, A - No H2O2,
B - 0.05 g H2O2/g VSS, C - 0.1 g H2O2/g VSS, and D - 0.2 g H2O2/g VSS
24-hour Settling Results
1000
800
I
600
400
200
4
H
•f
1
I
[
• 1
1
">
:
•
T2
^-_.
. •
— — -^
5?
•'
4
^t~JL~~~^'1-
0.25
95
Figure 4.18. Settling Results of 1,000 ml_ of Reactor Contents
27
-------
increasing temperature. Also, the settled solids occupied less volume for the experiments
performed in the spring as compared to the summer. This explains the variance along each line
for a particular experimental condition. The 30-minute results (data not graphed) exhibited a
similar difference, albeit smaller, between temperatures and treatments.
In some of the later experiments, solids concentrations were measured in the two fractions,
settled and supernatant. In summer, at 90°C and 0.2 g IHbCh/g VSS, after settling for 24 hours,
the bottom fraction contained > 2% TSS whereas the top fraction contained only 0.06% TSS.
4.5 Testing Waste Activated Sludge from Other Wastewater Treatment Plants
After the bulk of the year was spent using WAS from the Mason WWTP, it was decided to test
the optimized protocol with WAS from four different WWTPs. The Sycamore Creek and
Harrison WWTPs were two of the five plants surveyed in selecting the original WAS source for
the project. The Harrison WWTP, owned and operated by the City of Harrison, OH, employs an
oxidation secondary treatment process and does not utilize primary treatment. The other
WWTPs are three of the seven major facilities operated by the Metropolitan Sewer District of
Greater Cincinnati. The Little Miami and Mill Creek WWTPs are operated conventionally with
primary and secondary processes. As previously described, the Sycamore Creek WWTP is
equipped with a plug flow extended aeration system without primary sludge settling. Mill Creek
receives a substantial percentage of industrial wastewater, whereas the other three receive mostly
residential wastewater. The conditions tested were 90°C with H2O2 added at 0.2 g/g VSS in
triplicate reactors and no H2O2 added to a control reactor. Figure 4.19 plots the range of VSS
removals obtained. At 4 hours, the oxidation reactions were essentially complete.
VSS, August 20, 22, 28, & September 3
60
50
40
30 -
£
i
oo 20 -
10
Syc, Ctrl
Syc, 0.2 g
Harr, Ctrl
Harr, 0.2 g
L Mia, Ctrl
LMia, 0.2 g
Mill Cr, Ctrl
Mill Cr, 0.2 g
Figure 4.19. VSS Removal for Four Different WWTPs at 90°C, No H2O2 Control and 0.2
g H2O2/g VSS Treated Triplicates
28
-------
The four WWTPs produced similar results for the other parameters measured. Fecal coliforms
were reduced to non-detect levels, and no regrowth was observed after 7 days. Initially, pH was
near neutral (6.7 to 7.5); after 4 hours, the EbCh treatment pH values ranged from 4.6 to 5.8 and
the no-added-H2O2 control pH values varied between 6.3 and 7.5. Settling characteristics were
similarly improved. Other parameters are given in Table 4.3.
Table 4.3. Additional Measurements Performed on Four WWTPs
Initial &
after
4-hour
treatment
PH
NH4N,
mg/L
COD
soluble
fraction,
% of total
TKN
soluble
fraction,
% of total
Solids
settling
volume,
24 hr,
mL in 1 L
TSSin
bottom
fraction,
%
TSSin
top
fraction,
%
Sycamore Creek
Initial
Control
0.2 H2O2
avg.
6.7
6.3
4.6
0.5
40
87
2.0
26.0
32.2
1.7
49.3
66.7
1000
745
227
NA
1.5
4.0
NA
0.05
0.04
Harrison
Initial
Control
0.2 H202
avg.
7.3
7.3
5.3
29.2
41.5
93.8
1.0
26.7
45.7
2.4
41.7
67.8
975
910
343
NA
1.4
1.9
NA
0.15
0.06
Little Miami
Initial
Control
0.2 H202
avg.
7.5
7.5
5.8
44
25
79.3
1.0
28.2
47.5
4.0
44.2
68.6
900
770
400
NA
1.4
2.4
NA
0.08
0.09
Mill Creek
Initial
Control
0.2 H202
avg.
7.1
7.3
5.2
96
125.5
176.5
8.6
19.3
42.6
13.9
54
66.3
925
1000
325
NA
1.1
3.2
NA
No top
fraction
0.06
4.6 SUMMARY OF RESULTS
Table 4.4 summarizes data from all the experiments performed. The loading VSS/TSS ratio for
the Mason plant decreased as the season changed from winter to summer. The four different
WWTPs tested during a 2-week period in August and September exhibited intermediate
VSS/TSS ratios. The VSS removal in the control reactors for the experimental runs between
April 9 and June 11 at 90°C, 75°C, and 65°C, indicated a temperature effect with percent
removals of 32.6%, 28.9%, and 26.7%, respectively. In July where the same Mason WAS was
used on consecutive dates at 65°C and 90°C, only slightly better VSS removal was observed for
the higher temperature, presumably because of the lesser amount of degradable organics
available in the feed sludge during warmer weather. As indicated previously, the data generated
in this July experiment was different in that trial runs were performed using the same WAS
29
-------
instead of obtaining fresh material to be used as reactor feedstock for each individual run.
Percent VSS removals are listed both as the actual means and as percent increases over the
controls (subtracting out the control values).
Table 4.4. Averages of % Total VSS Removal and Increased Removal over Control by Treatment
Sludge
Source
Mason WWTP
Syca-
more
Creek
Harri-
son
Little
Miami
Mill
Creek
Experiment
Date (201 3)
Feb. 5, 12,
&26
Mar 1 9, 27 &
Apr 2
April 9, 16
and 23
Apr 30,
May 14 & 21
May 29, Jun
4&11
June26,
July2
June26,
July2
June26,
July2
June26,
July2
July 22, 25
and 26
July 23, 24
and 27
Aug. 20
Aug. 22
Aug. 28
Sept. 3
Loading
VSS/TSS
85.8
85.8
85.9
78.8
76.0
73.3
73.6
73.4
73.3
68.4
68.4
75.3
78.1
65.8
78.8
Temp,
°C
60
60
90
75
65
65
75
80
90
90
65
90
90
90
90
Hour
4
(24)
4
(24)
4
(24)
4
(24)
4
(24)
4
4
4
4
4
4
4
(24)
4
(24)
4
(24)
4
(24)
Total VSS Removed, %
0.05*
32.7
(39.1)
25.9
(32.5)
21.7
(27.9)
0.1*
28.0
(36.6)
42.9
(46.5)
31.3
(36.5)
22.0
(29.3)
25.1
23.2
0.2*
32.1
(48.3)
55.5
(61.5)
40.0
(44.4)
30.5
(35.8)
32.5
38.6
39.6
42.7
31.1
28.9
45.1
(51.6)
49.6
(54.5)
38.9
(44.6)
45.4
(52.5)
% Increased Removal
0.05*
6.5
(6.6)
1.8
(3.6)
2.6
(1.2)
0.1*
5.4
(2.5)
16.7
(14.0)
7.2
(7.7)
2.9
(2.6)
6.3
4.3
0.2*
7.8
(16.0)
29.3
(28.9)
15.9
(15.5)
11.4
(9.1)
18.4
21.9
22.5
25.7
12.3
9.9
23.0
(22.5)
25.7
(25.5)
13.1
(13.4)
24.0
(19.2)
Treatment received, Added g H2O2/g VSS
First value given is after 4 hours of treatment; Value in parenthesis is after 24 hours, when measured.
Figure 4.20 compares % VSS/TSS loading with % VSS removal for all experiments at 90°C and
0.2 g H2O2/g VSS for all WAS feedstocks tested. Regressions were performed using both the %
VSS removed values and the increase in removal after subtracting out the control % VSS
removal. Both regression lines have an R2 > 0.8 indicating reasonable correlation for a
biological system. These regressions imply that obtainable % VSS removal is directly correlated
with the initial loading ratio.
30
-------
co
o
cc
T3
O
§
00
00
70
60
50
40
30
20
10
Comparison: % VSS Removal at 0.2 g HO dosing
%Total
%lncrease
y=-33.4+1.03*x
R2=0.81
y = -43.52+0.87*x
R2=0.87
* other WWTP, not Mason
60
70
80
90
VSS/TSS, %
Figure 4.20. Regression Lines of % VSS Removal at 90°C for All 0.2 g hhCVg VSS Dosing
Experiments, Total % and % Increase (After Subtracting Out the Control % Removal Values)
4.7 SUMMARY OF TREATMENT AND DISCUSSION
The Part 503 Rule lists six alternatives for treating biosolids to Class A standards with respect to
pathogens. The alternative that most readily applies to this situation is Alternative 1 for
thermally treated biosolids. This alternative rule allows four temperature regimens. Regimen D
is the best fit requiring the % solids in the sludge to be < 7% and a temperature greater than 50°C
to be held for greater than 30 minutes. The calculation given in the regulations for Regimen D
where t is temperature in degrees Celsius is as follows:
Time in hours =
50,070,000 * 24
10°
.14t
Using this calculation, 60°C would require almost 5 hours of treatment time, but 65°C requires
less than 1 hour of treatment time using the experimental thermo-oxidation process. Anything >
70°C calculates to less than the mandated 30-minute holding time.
Since initial results using 60°C showed regrowth of fecal coliforms, experiments operated with
temperatures of 65°C or higher thereafter. Also, a shorter treatment time would be more cost
efficient, so 65°C or higher would be conducive to a 4-hour or less detention time. The highest
temperature of 90°C was chosen to stay below the boiling point of water as these reactors are not
operated under pressure.
There was concern with the increased production of NH4-N, especially since the concentration in
31
-------
the reactor was lower at 90°C than at the lower temperatures tested. A literature search revealed
that, "The reason for such high NH4+ formation in IHbCh added sludge is the extraction of the
amine groups from the protein molecules. These are formed by the degradation of the organic
nitrogen in digestion process by the OH' radicals formed as a result of IHbCh degradation" (Gen9
et al., 2002). Also, apparently at 90°C, NHs is outgassed more efficiently than at 65°C.
Another significant finding was that VSS removal varies with the season. The Mason
wastewater temperature was 3°C to 7°C higher in July than in April and May (see Table 2.4).
The higher July temperatures would be expected to promote more VSS biological degradation in
the oxidation ditch aeration tank than in April and May, thereby lowering the VSS fraction
available for destruction in the thermo-oxidation process in July compared to the colder months.
The VSS fraction for the aeration tank mixed liquor suspended solids decreased from 86% in
April to 76%-79% in May to 69% in July. This finding increased the difficulty of making
absolute comparisons between reactor operating temperatures as they were tested in different
months and, therefore, different seasons. The seasonal variation observed in VSS destruction in
the thermo-oxidation process was apparently due to the changing quality of the feed WAS, being
more oxidized in warmer weather. When WAS is more oxidized prior to sludge treatment, there
is less potential additional removal possible by thermo-oxidation treatment. It can be said that, in
general, higher operating temperatures and larger doses of JrbCh result in greater percent removal
ofVSS.
Sludge settling characteristics also improved with increasing operating temperature and added
JrbCh dose, with the best results obtained at the highest dose and temperature regime. The
thermo-oxidation process can improve sludge settling properties sufficiently such that it may
reduce the cost of sludge dewatering. The solubilization of COD and TKN serves to remove the
most readily available carbon and nitrogen so that these nutrients can be recycled back to the
head of the treatment plant hypothetically resulting in a more stable end product, i.e., a biosolids
soil amendment that because it will leach nutrients more slowly, will be less likely to cause
contamination via seepage to groundwater and runoff to rivers, streams, and lakes.
At the end of the study, other WWTP sludges were tested with similar results achieved at all
sites. This finding imparts confidence to the hypothesis that the thermo-oxidation process is a
potential treatment method applicable across the board to a wide variety of aerobic sludges.
32
-------
5.0
Literature Review and Description of
Competing Technologies
A literature review using the search terms thermo-oxidation and sludge was performed. Nothing
was found in the literature to prevent filing for a patent to further this technology. The following
discussion describes competing technologies from the literature search.
Municipal WWTPs generate sludge as a by-product of the physical, chemical and biological
processes used during treatment. Over 95% of sludge is water, and the solids portion is
composed of 59%-88% organic matter, which is decomposable and produces offensive odors
(Tyagi and Lo, 2011). Many processes can be used to handle sewage sludge produced at
WWTPs, the treatment of which can add up to 35% to 60% of a plant's treatment costs (Appels
et al., 2008). It has been estimated that about 10 million dry tons of sewage sludge are produced
every year in the United States (Bandosz and Block, 2006). The cost of sludge treatment is
highly dependent on the overall volume and water content of the produced sludge. Commonly
used disposal practices include incineration, landfilling, and land application. For
sludge/biosolids management, the current practice of anaerobic digestion followed by land
application is the most economical and environmentally sensible practice used (Murray et al.,
2008). Increasing sludge production can cause problems for both the WWTP operator and the
community, so more efficient treatments to reduce sludge production at the WWTP are needed
(Nah et al., 2000). Enhanced anaerobic digestion processes of particular interest are those that
have the potential to reduce the overall amount of biosolids to be disposed, while maximizing the
acceptability of the biosolids by increased pathogen inactivation and reduced biosolids odors.
By enhancing the rate limiting step of organic matter hydrolysis, reduction of solids and
methanization of sewage sludge can be improved (Li and Noike, 1992; Liu et al., 2009). Lysis
treatments can be considered mechanical, thermal, chemical, or biological, all of which
solubilize organic compounds making them more biodegradable. The literature contains
methods for sludge minimization such as acidic and basic thermal hydrolysis, ozonation,
ultrasound, microwave irradiation, Fenton's peroxidation, wet air oxidation, and advanced
thermal hydrolysis that utilizes heat and FbCh addition (described below).
In thermochemical hydrolysis methods, acid or base are added that solubilizes the sludge. These
processes are generally carried out at ambient or moderate temperatures because the addition of
the acid or base does most of the stabilization. The use of acidic or basic thermal hydrolysis is
limited because of the need for extremes in pH and the subsequent need for the sludge to be re-
neutralized. Other major drawbacks of this method are noxious odor generation, corrosion, and
fouling of the equipment.
Wet air oxidation is a destructive technology based on the oxidation of pollutants at high
temperature and high pressure in the liquid phase. Wet air oxidation promotes waste oxidation
under pressure (2-15 MPa) and temperature (180°C-315°C) with addition of oxidant such as pure
oxygen or air (Luck, 1999). The degree of oxidation is primarily a function of temperature,
33
-------
oxygen partial pressure, and residence time; actual operating conditions depend on the treatment
objectives. Products of the process are carbon dioxide, water, and low-molecular-weight organic
compounds with COD destruction efficiencies of 75%-90% (Khan et al., 1999). Sludge
treatment under relatively mild conditions (< 300°C) can reduce COD at a rate between 5% and
15% and significantly improve sterility, filterability, and dewatering properties (Kolaczkowski et
al., 1999). High capital and operating costs are associated with the elevated pressures and
temperatures used, long residence times, and use of construction materials that must be resistant
to high corrosion rates that occur under severe operating conditions (Mantzavinos et al., 1999).
Compared to conventional wet air oxidation, use of catalysts can enhance the reaction rate and
produce higher oxidation efficiencies or allow for reduced temperature resulting in a reduction of
capital costs. The catalytic process can be used for effluent pre-treatment prior to a biological
step or as a complete destruction process. Fenton's peroxidation is a wet air oxidation process
conducted at low temperature (20°C-55°C), atmospheric pressure, and a pH of 3, where H2O2 is
activated by iron salts (Erden and Flibeli, 2010). The process has been shown to significantly
reduce sludge volume, increase solubilization of organic matter, and improve sludge
dewaterability (Neyens and Baeyens, 2003), but it requires the addition of the catalyst and a
separation step such as precipitation to remove catalyst ions from the final effluent. This method
is also very corrosive due to the necessity of bringing sludge to a very low pH, and operation and
maintenance costs can be quite high.
Ozone (Os) is a powerful oxidant that has been used to aid in the destruction of cellular material
in WAS. During sludge ozonation, because of the complex composition of sludge, ozone
decomposes into radicals and reacts with the entire material: soluble and particulate fractions;
organic and mineral fractions. Using Os for sludge reduction has been widely studied. Optimal
consumed Os doses range from 0.05 to 0.5 g Os/g of total solids with optimum dosage dependent
on the type and concentration of sludge. It has been shown there is a phenomenon of
mineralization for higher Os doses, and the optimum dosage for any operation depends on the
type of sludge (Elliott and Mahmood, 2007). Moreover, ozonation modifies viscosity and
settlement of sludge (Bougrier et al., 2006) by stabilizing surface charges that disperses sludge
particles. Studies have shown a dependent relationship between Os dosage and released COD
where the oxidative treatment destroys floe structure and disrupts cell membranes of the
microorganisms (Weemaes et al., 2000). The limited solubility of Os in water makes it
applicable essentially to diluted solutions. Ozonation involves high capital and operational costs
because it requires high energy consumption for Os production, transfer to the sludge, and
production of liquid oxygen.
Ultrasonic treatment is influenced by three factors: supplied energy, ultrasonic frequency, and
nature of the influent (Bougrier et al., 2005; Aldin et al., 2010). The ultrasonic process leads to
the formation of cavitational bubbles in the liquid phase (Tiehm et al., 2001) where bubbles grow
and then collapse violently when they reach critical size. Generally, the most useful frequencies
are in the range of 20-200 kHz (Hua and Thompson, 2000). Extreme local heating and high
pressures at the liquid-gas interface are produced during the cavitational collapse of the bubbles.
Also, turbulence and high shearing phenomena occur in the liquid phase and highly reactive
radicals (H', HO2' and OH') and H2O2 can be formed that facilitate chemical reactions for
destroying organic compounds. Tiehm et al. (2001) showed that excess sludge can be degraded
more efficiently at low frequencies where mechanical effects facilitate solubilization of particles.
34
-------
The work of Bougrier et al. (2005) showed optimum ultrasonic energy was about 7000 kJ/kg TS
to obtain maximum biogas production and sludge solubilization. High capital and operating
costs of ultrasound units with high energy consumption by the equipment are major limitations
of this technique, and full-scale applications are rare.
Hydrogen peroxide addition has been shown to reduce sludge volume by the oxidation process.
The work of Kim et al. (2009) used H2O2 for excess sludge reduction and an alkaline pre-
treatment method to enhance the efficiency of H2O2 oxidation of the sludge. The solubility of
sludge was increased (Soluble COD/Total COD) and viscosity was decreased with improved
settleability of the sludge.
Thermal hydrolysis utilizes relatively low temperatures (100°C-175°C) and low pressure to
destroy cell walls allowing for cell contents to be available for degradation, but it also decreases
sludge viscosity and increases dewaterability. At near neutral pH, optimal conditions for thermal
hydrolysis have been shown to be 170°C and operation times between 30 and 60 minutes, where
hydrolysis temperature appears to be more important than contact time for sludge disintegration
to occur (Li and Noike, 1992). Thermal treatment results in the breakdown of the gel structure
of the sludge and the release of intracellular bound water (Weemaes and Verstraete, 1998).
Microwave irradiation is a thermal hydrolytic method receiving increased use because the
desired temperature can be reached more rapidly than conventional heating and energy
consumption is lower than conventional heating (Coelho et al., 2010). Bougrier et al. (2007)
found improved filterability and greater than 30% reduction in sludge production using thermal
hydrolysis treatment. Thermal hydrolysis has the potential to produce Class A biosolids because
it can be used on both primary sludge and WAS. As described in Abelleira et al. (2012), the
advanced thermal hydrolysis process depends on H2O2 addition and direct steam injection under
mild conditions with no catalyst added. At optimal conditions with oxygen at 30% of
stoichiometric balance, 115°C, and 24-minute reaction time, increased solubilization and
dewaterability levels of the solids were found. Camacho et al. (2002) found a synergistic effect
between temperature and H2O2 addition (at temperatures of 60°C and 95°C) for released TOC
and a linear relationship between the two parameters.
According to Bougrier et al. (2007) and Zhang et al. (2010), the energy required to perform the
process of heating the sludge for thermal treatment can be positively balanced by biogas
production. In order to form a complete calculation of cost, it is necessary to take into account
thermal losses, technological problems (pressure, materials, and exchanger fouling), investment
costs, maintenance costs, and integration in the whole wastewater treatment process.
To stabilize sludge, this study utilized thermal hydrolysis and H2O2 addition in a synergistic
effect operating under temperatures of 90°C and lower, without the addition of a catalyst, and at
ambient sludge pH. This work was based on the previous studies of Cacho Rivero et al. (2006a,
2006b) that investigated the use of combined oxidative and/or thermal treatments to enhance
anaerobic digestion of excess municipal sludge. Their results showed that this co-treatment
increased VSS destruction ranging between 27.2% and 29.0%. Class A biosolids were obtained
with all H2O2 dosages used in the study (0.5, 1.0, and 2.0 g H2O2/g VSS) (Cacho Rivero et al.,
2006a, 2006b). In continuing work, they tested lower doses of H2O2 (0.1, 0.25, and 0.5g/g
influent VSS) demonstrating increased solids destruction as well (Cacho Rivero et al., 2006c).
The lower dosage also produced Class A biosolids. For this study, dosages of H2O2 similar to
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and slightly lower than those used in this last study were investigated (0.05, 0.1, and 0.2 g
H2O2/g influent VSS) to determine if a more cost effective regimen would be effective for the
production of Class A biosolids from aerobic sludge.
Unlike conventional inorganic oxidizing agents such as chlorine and hypochlorite, ffcCh yields
no noxious or polluting byproducts. The only byproducts of the oxidant are water and dissolved
oxygen that can stimulate the activity of aerobic microorganisms. These conditions, which are
less harsh than other processes, would imply potential energy savings and the use of cost-
reducing technologies. ffcCh cost has been progressively decreasing over the last decade, and,
therefore, there are increasing incentives to expand its use in environment protection applications
(Perathoner and Centi, 2005).
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6.0
Market Analysis, Conceptual Treatment
Trains, and Cost Estimates
6.1 Background
More than 10,000 oxidation ditch WWTPs have been built in the United States since the 1970s.
This technology is used mainly in small to medium-sized communities, i.e., with populations of
5,000 to 50,000, and to treat wastewater flows of 1,900 to 19,000 cu m/day (0.5-5.0 mgd)
although there are also some oxidation ditch plants larger than 5 mgd. The advantages of the
technology are simple operation, reliable performance, and cost effectiveness (WEF, 2010).
Vendors selling package oxidation ditch plants today include Yokogawa (Japan); Veolia Water
Technologies (France); and Eimco, Parkson, WesTech, and Evoqua Water Technologies (United
States). Newer oxidation ditch designs incorporate multiple treatment zones to promote
biological phosphorus and nitrogen removal in addition to oxidizing particulate and soluble
organics.
6.2 Market Analysis of Fertilizer
Fertilizer production was a $56.2 billion business globally in 2008 and has grown by 10-15%
annually since then. This growth has been driven by global demand for food and higher
standards of living (Fertilizer Mixtures Market, 2009). More than 90% of fertilizer is inorganic,
manufactured from mined materials such as phosphorus, potassium, etc. Of the organic portion
of fertilizer, less than 3% is supplied by municipal waste sludge. In the European Union, the
land application and use of human waste as fertilizer is regulated through the Fertilizer's
Regulation, EC No. 2003/2003, promulgated in 2003. In the United States, these uses are
regulated by EPA through 40 CFR, Part 503, promulgated on February 19, 1993. Part 503
contains concentration limits for metals in biosolids, pathogen reduction standards, site
restrictions, crop harvesting restrictions and monitoring, record keeping, and reporting
requirements for land applied biosolids as well as similar requirements for biosolids that are land
applied or incinerated.
In the United States, popular lawn care products are made in part from reconstituted sewage
sludge or biosolids that are sold through brokers to fertilizer manufacturers. Some municipalities
have created their own products, including Milorganite™ from the Milwaukee, WI Metropolitan
Sewerage District and Louisville Green™ from the Morris Forman Water Quality Treatment
Center in Louisville, KY. One of the benefits of organic fertilizers is that the inorganic nutrients
(phosphorus, nitrogen, and potassium) are released slowly in bioavailable forms. Both leachate
runoff and plant burn are less likely when using organic products vs. chemical products. Organic
fertilizers made from WWTP sludge are provided to customers in bags or in bulk as dry pellets.
The pellets have little odor, are safe for animal exposure, and are easy to apply.
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Another segment of the organic fertilizer market demonstrating high growth, particularly in the
organic-market gardener segment, is fish fertilizer. Fish fertilizer products come in the form of
meals, emulsions, and enzymatically digested fish matter. Fish meal is ground, generally dried
at high heat, and used in soil applications. Fish emulsion, a popular product used in organic
agriculture, is applied as a soluble fertilizer. Enzymatic digestion offish allows minerals and
amino acids to become readily available to plants and makes those nutrients water soluble, but
requires the extra odorous digestion step at the processing plant (groworganic.com).
6.3 A Global View of Three Trends
Three trends currently are combining to create enhanced market opportunities for organic
fertilizers.
First, the 'energy-water nexus' is being studied worldwide. Large quantities of energy are
consumed by the water supply and wastewater treatment industries. Energy generation itself
requires large quantities of water. Waste is removed from homes on a water carrier. Globally,
many are asking if there is a way to eliminate some of the energy used in separating water from
waste and to re-use both, clean water and waste products, more effectively. And a third node can
be added to create an 'energy-waste-food production nexus'. Energy is required to produce
fertilizers for farmland, and water is needed for irrigating farmland. Products that close this loop
to create fertilizer and use water more efficiently for food production will be in demand.
Second, the supply of inorganic phosphorus is a limited resource. The scientific literature since
the 1950s (Asimov, 1974) has predicted that inorganic phosphorus deposits will be exhausted by
the end of the century, i.e., by 2100. In some countries, including the United States, supplies are
estimated for 15-35 years, or until 2030 to 2050. Additionally, the remaining inorganic
phosphate inventory contains cadmium and metals (Lougheed, 2011). When rock phosphate is
exhausted, organic phosphates that have not been rendered unsafe by mixing with hazardous or
nuclear wastes will remain. In the phosphorus cycle, this means that the trace amounts present
in human waste sludge constitute a valuable nutrient that will be needed to rebuild soils as soon
as they are generated. The future shortage of phosphorus is a strong incentive to not incinerate
or landfill waste sludge, but instead to treat it as a valuable product "to produce a health-friendly
fertilizer.. .for farmers who lack the means to purchase them" (Wanzala and Roy, 2006).
Third, more than one-third of the earth is now under water stress; either the quality or quantity
of water is not sufficient for society's needs, or the absence of water has already affected the
environment and human health. Approximately one-third of the United States currently is
experiencing water stress, primarily in the western regions (UNEP, 2008). The use of wet
organic fertilizer could provide a mechanism in some regions to return water directly to the land
in slow-releasing sludge complexes and relieve some of this stress.
The primary questions that must be addressed for the thermo-oxidation technology to be
considered a candidate for full-scale application are:
• Is there a way to use this treatment concept to supply liquid nutrients to farmers
legally, safely, and with minimal odor?
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• What regions and demographic areas would be the most likely markets for this
material?
• What would be acceptable capital equipment and operating costs?
6.4 Market Potential for Thermo-Oxidation Technology
The basic premise for assessing market penetration potential for the thermo-oxidation process is
that it can be used most beneficially in treating low concentration WAS streams. Concentrations
equivalent to l%-2% TSS were treated effectively in EPA bench-scale tests on this project,
meeting Part 503 requirements for Class A biosolids.
The analysis of most likely markets for this technology is based on the number of small WWTPs
(primarily plants equipped with oxidation ditches) that could benefit from this sludge treatment
method and would be likely customers based on demographics, environmental conditions, and
plant size. Approximately 10,000 oxidation ditch systems have been installed in the United
States since 1973 (WEF, 2010). For the purposes of this exercise, we assumed that 20% will
upgrade their sludge treatment system during the period 2015-2025, 75% are located in rural
areas, and 50% have capacities of 2 mgd or less. Further, we assumed that half are located in
western, plains, or southern states experiencing water stress:
• Possible customers = 10,000 oxidation ditches in United States x 20% to upgrade = 2,000
• Most likely customers = 2,000 possible customers x 75% rural x 50% in water stressed
regions x 50% small plants < 2 mgd = 375
The construction and operating cost estimates to follow for the thermo-oxidation process have
been developed to maximize the potential benefits for small capacity plants in small towns and
rural regions of the United States. This analysis assumes that municipalities in western,
southern, and plains states will be more receptive to the concept of re-using the water contained
in their waste sludge products. It further assumes that small towns and rural municipalities will
have greater incentive to upgrade to a simple system, and it follows from this assumption that
capital costs will be a limiting factor in choosing technologies.
6.5 Cost Estimates
The costs for the thermo-oxidation process have been estimated below in two ways. First, order-
of-magnitude estimates of heat requirements and chemical (FbCh) usage are estimated from the
results of the bench-scale tests reported herein. These values were used to estimate annual
operating costs for a system based on a defined wastewater profile. Second, estimates for
construction and annual operating costs for the conceptualized systems were compared with
construction and operating costs for two existing sludge treatment systems that produce a
marketable fertilizer product and also with costs for incineration and landfilling.
No attempt was made in these estimates to cost out post thermo-oxidation treatment dewatering
operations such as centrifugation or a belt filter press as the WWTP would have these costs
regardless of the sludge treatment process used. These dewatering processes would increase the
FbCh treated biosolids concentration from 1.5%-3% solids to 18%-22% solids, producing a
material with the consistency of loam. Another possibility that might be considered, especially
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in water stressed areas, is trucking the Class A treated material directly to fields without water
removal. Dewatered biosolids could be land applied with a spreader or slinger, while the un-
dewatered biosolids would be applied as a slurry.
6.5.1 Methodology lor Conceptual Design and Costs for Thermo-Oxidation
Technology
Two chemical treatment regimens have been considered in developing conceptual designs and
capital and operating cost estimates for the thermo-oxidation process. These two regimens are
the two higher dosage rates evaluated in the experimental trials, i.e., 0.1 and 0.2 g FbCh/g VSS or
alternately 10% and 20% treatment of VSS in the WAS. VSS concentrations are assumed to be
approximately 80% of TSS.
The lower FfeCh dose results in less chemical cost at the expense of achieving lower VSS
destruction. The higher dose will produce 10%-15% greater VSS destruction at twice the
chemical cost. Each potential user will be required to make an independent evaluation and
decision on dose vs. VSS destruction trade-off that best fits the needs of their facility.
In order to calculate energy requirements, a basic treatment train was conceptualized to
approximate a possible system with two variations for comparison. For clarification, it should be
noted that neither of these treatment trains is recommended for construction; rather, each
presents a combination of heating, mixing, and energy delivery alternatives that could be
considered when designing an actual system. Energy requirements were calculated for these
conceptual treatment trains. First approximation construction cost estimates were also prepared
for these trains consisting of a chemical feed system, a mixing tank, and, for one of the two
trains, a heat transfer mechanism. Engineering cost estimating construction curves (McGivney
and Kawamura, 2008), conceptual design level estimates from vendors, and information from
three interviewed wastewater treatment plants were used to approximate construction costs for
the two sludge treatment trains for two capacities:
• 6 mgd average influent wastewater flow with 20,000 gpd of WAS generation, as per the
Mason plant
• 1.2 mgd average influent wastewater flow with 4,000 gpd of WAS generation, i.e., one-
fifth the size of Mason's plant
6.5.2 Conceptual Treatment Trains
Two sludge treatment trains have been analyzed and costed, a simple large tank system with
steam heat and a more advanced system with smaller tanks and multiple heat exchangers with
steam heat. Each system includes an EbCh injection system and jacketed tanks heated by a steam
boiler. Treatment Train 1 and Treatment Train 2 schematics along with construction cost
estimates are shown in Figures 6.1 and 6.2, respectively. Additional treatment train variations
and layouts, including the re-use of heat from the system elsewhere in the WWTP and an in-line
heat exchanger treatment unit, are shown in Appendix A.
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A large open 20,000 gallon tank in batch use. Once per day, the tank is heated with steam to 90°C, H2O2
is injected, and temperature maintained for 4 hours. Treated sludge is discharged after it has cooled.
Belt filter press or
centrifuge
dewatering or
directly to field
Heat up to 90°C. Hold for 4
hours. Then allow to cool.
Construction Costs Estimates
Conceptual System Cost for WAS Volume of 20.000 qpd
H202 feed (1 unit) $50,000 (a)
$200,000
$290,000
Steam boiler (25 HP) $50,000
Subtotal, primary treatment equipment
Associated piping and pumps, 10% $20,000
Associated controls, 35% $70,000
Total
Conceptual System Cost for WAS Volume of 4.000 gpd
H202 feed (1 unit) $50,000
Treatment tank (1 each, 5,000 gal) $25,000
Steam boiler (5 HP) $25,000
Subtotal, primary treatment equipment $1 00,000
Associated piping and pumps, 10% $10,000
Associated controls, 35% $35,000
Total $145,000
(a) Estimated from sodium hydroxide feed curves (McGivney & Kamakura, 2008, page 45).
(b) Estimated from flocculation tank/paddle blade curves (Ibid., page 49).
Figure 6.1. Treatment Train 1 with Table of Construction Cost Estimates
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Three small closed tanks in continuous batch use with a continuous flow heat exchanger. As one tank is
being filled with sludge, the reaction is occurring in a second tank, and the third tank is emptying. H2O2 is
continuously injected into the pipe inlet. The tanks are maintained at 90°C with outgoing sludge heat
being transferred to incoming sludge in the heat exchanger.
Belt filter press or
centrifuge dewatering
or directly to field
• Construction Cost Estimates
Conceptual System Cost for WAS Volume of 20.000 qpd
H2O2 feed (1 unit) $50,000
Insulated tanks (3 each, 4,000 gal) $100,000
Steam boiler (25 HP) $50,000
Heat exchangers (2 each, 14 gpm) $150,000
(a)
$350,000
Subtotal, primary treatment equipment
Associated piping and pumps, 10% $35,000
Associated controls, 35% $123,000
Total $508,000
Conceptual System Cost for WAS Volume of 4.000 gpd
H2O2 feed (1 unit) $50,000
Insulated tanks (3 each, 1,000 gal) $50,000
Steam boiler (5 HP) $25,000
Heat exchangers (2 each, 3 gpm) $50,000 (b)
Subtotal, primary treatment equipment $175,000
Associated piping and pumps, 10% $17,500
Associated controls, 35% $61,300
Total ~ $254,000
(a) Estimate for custom heat exchanger (Thermal Transfer Systems; Self, 2014).
(b) Pilot equipment might be used for this low flow application of 3-5 gpm.
Figure 6.2. Treatment Train 2 with Table of Construction Cost Estimates
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Estimated operating costs for the two conceptual treatment trains are shown in Tables 6.1 and 6.2
for influent flows of 20,000 gpd and 4,000 gpd, respectively. The higher flow rate corresponds
roughly to the wastewater throughput at the Mason, OH WWTP and represents a large oxidation
ditch system. WAS production for Mason is approximately 550 dry tons VSS and 700 dry tons
TSS per year for the 20,000 gpd system and, by calculation, 110 dry tons VSS and 140 dry tons
for the smaller system. In Treatment Train 1, energy costs are based on no recovery of heat from
the treatment tank, i.e., 100% loss from the open tank. In Treatment Train 2, losses of 20% in
the heat exchangers and 5% in the tanks are assumed as reasonable estimates. Mixing energy is
not included in the estimates. Labor costs are not included in these estimates and are assumed to
be similar to the operation of other sludge treatment systems in a WWTPs of corresponding size.
Other units and assumptions include:
Ambient water temperature
Specific heat of sludge
Cost of electricity
H2O2 (50% purity) cost
20°C
4.19J/g°C
$0.10/kWh
$500/ton
To summarize Figures 6.1 and 6.2, estimated construction costs for the 20,000 gpd WAS flow
rate range from $290,000 for Treatment Train 1 to $508,000 for Treatment Train 2. Capital costs
for the 4000 gpd WAS flow rate system range from $145,000 to $254,000. The estimated capital
costs for the smaller system are approximately one-half of those for the larger system.
Table 6.1. Estimated Operating Costs for Treatment Trains 1 and 2 for 20,000 gpd WAS
Mass of influent sludge = 77,000 kg/day @ 2.25% TSS
Train 1 Train 2, Flow Velocity = 14 gpm
22.6 million 5.6 million
6,300 1,600
$630 $160
$164,000 $41,000
$16,400 $4,100
Total$ $180,000 $45,000
Energy needed (kJ/day)
kWh/day
Cost/day ($)
Annual calculated cost ($)
10% Energy distribution loss
Assumptions for each system:
Energy losses
Operation parameter
H2O2 Dosage: 10% of VSS
20% of VSS
Annual operating cost ($)
10% of VSS
20% of VSS
Operating cost/dry ton (TSS)
10% of VSS
20% of VSS
100% 5% thru insulation, 20% in Heat Exch.
1 shift/day Continuous
$55,000 $55,000
$110,000 $110,000
$235,000 $100,000
$290,000 $155,000
$336 $144
$415 $222
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Table 6.2. Estimated Operating Costs for Treatment Trains 1 and 2 for 4,000 gpd WAS
Mass of influent sludge = 15,400 kg/day @ 2.25% TSS
Same operating assumptions as given for the larger system (Table 6.1)
Train 1 Train 2, Flow Velocity = 3 gpm
Energy needed (kJ/day) 4.5 million 1.1 million
kWh/day 1,260 320
Cost/day ($) $126 $32
Annual calculated cost ($) $32,800 $8,200
10% Energy distribution loss $3,280 $820
Total $ $36,000 $9,000
H202 Dosage: 10% of VSS $11 -000 $11 -000
20% of VSS $22,000 $22,000
Annual operating cost ($)
10% of VSS $47,000 $20,000
20% of VSS $58,000 $31,000
Operating cost/dry ton (TSS)
10% of VSS $336 $144
20% of VSS $415 $222
Annual operating costs for the proposed system for the 20,000 gpd WAS flow range from
$235,000 (10% H2O2 dose) to $290,000 (20% H2O2 dose) for Treatment Train 1 and from
$100,000 to $155,000 (same two doses) for Treatment Train 2. A 100% loss of energy is
assumed in Treatment Train 1, and a 25% loss of energy is assumed in Treatment Train 2. The
estimated daily operating costs for Treatment Train 1 for the 20,000 gpd WAS flow are $630 for
heat energy and $150-$300 for H2O2 treatment, and for Treatment Train 2, $160 for heat energy
and $150-$300 for H2O2 treatment.
Operating costs for the 4000 gpd WAS flow rate are one-fifth of the costs of the 20,000 gpd
WAS flow. Annual operating costs range from $47,000-$58,000 for Treatment Train 1 and from
$20,000-$31,000 for Treatment Train 2. The estimated daily operating costs for Treatment Train
1 are $126 for heat energy and $30-$60 for H2O2 treatment. For Treatment Train 2, they are $32
for heat energy and $30-$60 for H2O2 treatment.
The operating costs per dry ton for either 20,000 gpd or 4000 gpd WAS using the 10% and 20%
H2O2 doses are the same: $340-$420/dry ton, respectively, for Treatment Train 1 and $145-
$220/dry ton, respectively, for Treatment Train 2.
6.6 Cost Comparison with Existing Systems
The two heat treatment systems used for comparing costs with the thermo-oxidation process are
the paddle sludge drying system utilized at the Mason, OH WWTP to make dry pellets, and the
rotary drum drying system installed at the Morris Forman WWTP in Louisville, KY to make the
Louisville Green™ product, also producing dry pellets. The costs for incineration are based on
costs provided by the Mill Creek WWTP in Cincinnati, OH that has operated this incinerator
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since 2010. The costs for landfill are based on information from Rob Schedel of Rumpke Waste
and Recycling (personal communication), also located in Cincinnati, OH.
Estimated costs for the above three existing systems plus landfilling are shown in Table 6.3.
Unit costs for the two heat treatment systems and incineration range from $100-130/dry ton;
landfill costs range from $40-100/wet ton. Generalized operating costs nationwide are assumed
to be -30%/+50% because we only have one example per system:
Paddle sludge drying system
Rotary drum drying system
Fluidized bed (incineration)
Landfilling (solidified)
$100/dryton
$115-$133/dryton
$50-$100/dryton(ash)
$100/wetton
The following are brief descriptions of the treatment systems and assumptions with a summary
in Table 6.3.
Table 6.3. Summary of Capital and Operating Costs for
Existing Sludge Treatment and Disposal Options
Summary of Options:
Rotary Drying
Morris Foreman, Louisville, KY [a,b]
Thermal treatment
Mason, OH [c]
Incineration
Mill Creek, Cincinnati, OH [d,e]
Landfilling [f]
Average
Flow
mgd
>100
6
>100
NA
Capital Costs
(Construction)
($)
68,000,000
4,000,000
50,000,000
NA
Annual
Production
Dry Tons
30,000
700
38,000
NA
Operating
Costs
$/Dry Ton
115-133
100
50-100
100
NA, not applicable
a. Tour with Robert Bates, Process Manager, Louisville Metropolitan Sewer District, May 30, 2014.
b. Robert Bates, Process Manager, Louisville Metropolitan Sewer District, report to Louisville
Board/City Council, 2014.
c. Tour with Robert Beyer, Industrial Pretreatment Coordinator, Mason Public Utilities, July 18, 2014.
System also includes two centrifuges at a cost of $0.5 million each. Total Komline-Sanderson paddle
drying system cost was $5 million.
d. Tour with Larry Scanlan, Operations Manager, and Edward Ewbanks, Regulatory Affairs, Mill
Creek Wastewater Treatment Plant, July 31 , 201 4.
e. Okazawa et al., Saving Money in Sewage Sludge Incineration with Indirect Heat Dryer, 1986.
f. Rob Schedel, Rumpke Waste and Recycling; nominal $40/wet ton; $100/dry ton.
6.6.1 Landfilling
General costs for landfilling biosolids vary across the United States based on a review of reports
from 2007-2013 (Juneau, AK, 2013; New Hampshire, 2007; and St. Petersburg, FL, 2011).
Current market prices for landfilling biosolids at the Cincinnati recycling center range between
$40 and $100/wet ton (Schedel, 2014). The lower cost applies to sludges with a higher solids
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content as determined using the Paint Filter Liquids Test (EPA Solid Waste Method 9095B).
The higher cost is for "wet" sludge that requires solidification prior to landfilling. These costs
were found to be representative throughout the country, but it is assumed that costs for landfill
disposal may vary from -30%/+50% nationally from the Cincinnati market prices.
6.6.2 Mason Water Reclamation Plant, Mason, OH
Our contacts were Robert Beyer, Industrial Pretreatment Coordinator, and Keith Collins,
Director. This plant has two oxidation ditches, a race track configuration with anoxic and
anaerobic areas for phosphorus and nitrate-nitrogen removal. The TWAS is fed to two
centrifuges for dewatering, followed by thermal drying in a Komline-Sanderson Paddle Dryer
that uses indirect, heated oil in the paddles and surrounding the treatment tank to dry the
biosolids to 95% dry pellets. The system includes solids handling equipment.
Mason distributes the dry product to local farmers at no cost who transport the material and
authorize that they have removed Exceptional Quality Class A Biosolids from the facility.
6.6.3 Morris Forman Water Quality Treatment Center, Louisville, KY
Our contact was Robert Bates, Operations Manager. This plant utilizes a conventional activated
sludge system. The TWAS, after dewatering, is fed through a Rotary Drum Dryer to produce
95% dry pellets. The system includes a Venturi scrubber and solids handling equipment.
Previously, Louisville Green™ was sold to turf industries and donated to local community parks.
Currently, the municipality contracts with a local marketing company for blending and sale to
bulk agricultural fertilizer manufacturers and for packaged distribution. The marketing company
pays Morris Forman $16.50/ton of biosolids.
6.6.4 Mill Creek Wastewater Treatment Plant, Cincinnati, OH
Our contacts were Larry Scanlan, Operations Manager, and Edward Ewbanks, Regulatory
Affairs. The TWAS is fed to a fluidized bed incinerator system. Mill Creek operates two of
three incinerators at a time under permit, with each incinerator requiring one operator. The
system includes tube sheet heat exchangers, Venturi scrubbers, and ash handling equipment.
The Mill Creek facility does not measure operating costs of this system. Material has been
accepted previously from local treatment plants at no charge. The capital cost of the system was
approximately $50 million. Annually, 38,000 dry tons are processed, and the system has an
estimated 30-year life. With an estimated 1.2 million total tonnage processed over the life of the
facility, prorated capital costs equate to $45/dry ton feed sludge.
Ash from the incineration process is stored for eventual disposal to landfill.
6.7 Summary of Market Analysis
The capital cost for WAS flow of 20,000 gpd at Mason, OH WWTP for the existing heat
treatment system was $4 million excluding the centrifuges. Capital cost, obviously, was much
higher to handle the greater flows for the larger systems at Morris Foreman, Louisville, KY and
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Mill Creek, Cincinnati, OH. Incineration systems cost estimates for lower WAS flow rates (i.e.,
4000 gpd) are both prohibitively high, and smaller systems are not commercially available. WAS
treatment operating costs for existing systems range from $50-133/dry ton at the larger
municipalities (see Table 6.3).
Capital costs for the proposed thermo-oxidation system for the 20,000 gpd WAS and 4000 gpd
WAS flows range from $290,000 to $508,000 and from $145,000 to $254,000, respectively,
depending on the treatment train selected. The estimated capital costs of the proposed system are
an order-of-magnitude lower than for the existing system at Mason. In contrast, WAS treatment
operating costs using the proposed thermo-oxidation system at $145 to $420/dry ton range from
1.5 to four times higher than for existing systems shown in Table 6.3 and three to four times
higher than for landfilling.
The bench-scale configuration most approximates Treatment Train 1. Treatment Train 2, while
adding capital cost with inclusion of a heat exchanger, will be more attractive in terms of
reducing operating costs. However, because it is a more complex system and would require
more operator time and expertise, it may be more suited to the 6 mgd than the 1.2 mgd plant size.
Therefore, while it appears that Treatment Train 2 would be the logical system to install due to
the operating cost savings, there may be a place for a version of Treatment Train 1. A small
WWTP could pour an in-ground concrete tank or use an above-ground steel tank for use as a
reaction vessel and operate it only during the day shift.
The market potential of the thermo-oxidation technology in the United States, based on an
estimated installed cost of $150,000 to $500,000 per system and 375 likely customers, is $56
million to $188 million. This is a niche market with customers who will need to be educated
about the future benefits of changing their current sludge disposal practices.
The enclosed estimates are based on laboratory/bench-scale studies. Next steps for development
of the technology would be pilot plant testing with interested technology vendors using their
products and equipment.
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7.0
Summary and Conclusions
7.1 Project Summary
Thermal oxidation of WAS was evaluated at bench scale as a cost-effective and novel method
for producing Class A biosolids. The thermo-oxidation process consists of two principal
treatment components, elevated temperature and ffcCh addition. ffcChis known to be a powerful
oxidant, and elevated temperature has been used historically to inactivate or destroy
microorganisms of fecal origin. The primary objectives of these experiments were to use the
simultaneous imposition of chemical oxidation and heat on WAS to:
1) Enhance sludge stability and reduce vector attraction via oxidation of a portion of the
VSS inventory, and
2) Reduce fecal coliform and/or Salmonella concentrations to levels required to meet
Class A biosolids standards.
Although the thermal oxidation process has been shown to be capable of producing Class A
biosolids when applied to anaerobically digested sludge (Cacho Rivero et al., 2005; 2006a;
2006b; and 2006c), it heretofore had not been evaluated on a feed sludge consisting of WAS.
WWTPs employing conventional activated sludge secondary treatment systems typically
produce both primary sludge and WAS. Anaerobic digestion is widely used to process a mixture
of these two excess sludge streams. Because the goal of this project was to evaluate this process
for the treatment of WAS only streams, WWTPs that either do not employ primary treatment (no
production of raw or primary sludge) or plants that do utilize primary treatment but process
WAS separately from their primary sludge were targeted. Those plants without primary settling
of influent wastewater are primarily limited to smaller WWTPs (1-6 mgd capacities) that do not
have land restrictions and frequently utilize extended aeration activated sludge systems with
nominal aeration detention times of 24 hours or greater and SRTs in excess of 15 days.
Recently, oxidation ditch technology has become the extended aeration system of choice for
many small communities. WWTPs with primary clarification generally are larger facilities, are
more likely to be land restricted, and are equipped with conventional activated sludge secondary
treatment systems. Conventional activated sludge units, by definition, have significantly shorter
nominal aeration detention times and SRTs, on the order of 4-8 hours and 4-6 days, respectively,
than do extended aeration systems. As such, WAS from conventional aeration systems usually
will be less oxidized than that from an extended aeration facility and, if not combined with
primary sludge for anaerobic digestion, may require follow-on aerobic digestion to achieve an
equivalent degree of oxidation as WAS taken directly from an extended aeration activated sludge
system.
In assessing potential markets for the thermo-oxidation process for treatment of WAS, it was
decided that the process would be best suited to handling feed streams that already are well
oxidized to minimize ffeCh dose requirements. Most larger plants with conventional activated
sludge systems (4-6 hours detention time) use anaerobic digestion or incineration of primary
48
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sludge and WAS. The use of extended aeration systems, particularly oxidation ditches, is on the
rise in smaller systems making this a good niche market for thermo-oxidation technology. This
market already boasts more than 10,000 oxidation ditches with high potential for continued
attractive growth.
Based on the above market priorities, a survey of extended aeration WWTPs in the Greater
Cincinnati area was conducted. Samples of WAS, mixed liquor, and influent wastewater were
collected and analyzed for five plants. The results of this preliminary survey indicated that WAS
from the Mason, OH oxidation ditch WWTP best met the requirements as a process feedstock.
The Mason WWTP operates a 6-mgd oxidation ditch facility in Warren County approximately
25 miles northeast of downtown Cincinnati. The Mason plant does not utilize primary settling of
raw sludge. WAS is taken directly from the oxidation ditch channels, settled in a gravity
thickener, and aerated in alternating fill-and-draw holding tanks. The TWAS is pumped from the
aerated holding tanks at 2-3% TSS through centrifuges that increase the TSS concentration to
18%-20%. The dewatered sludge is then fed to a Komline-Sanderson paddle dryer that produces
Class A biosolids pellets at 95%+ TSS in about 30 minutes of drying at 270°F-280°F.
A fresh batch of Mason TWAS was collected from the aerated holding tanks prior to centrifuge
dewatering and transported to the EPA laboratories in Cincinnati for each experiment. During
late August and early September, TWAS from four other WWTPs in the Greater Cincinnati area
was collected and used as reactor feedstock as a final test of the thermo-oxidation process.
Reliable and predictable VSS destruction and fecal coliform reduction are two essential
requirements for production of a high quality Class A biosolids product. VSS destruction is
necessary to decrease sludge mass, enhance sludge stability, and reduce vector attraction. Fecal
coliform reduction is an indicator of pathogen destruction and/or inactivation. The
experimental system was designed primarily to evaluate these two parameters, but other
attractive features of the thermo-oxidation process were uncovered and validated and are
discussed below.
Reactor temperatures ranging from 60°C to 90°C and FbCh dosages of 0, 0.05, 0.1, and 0.2 g/g
feed VSS were evaluated over 9 months from early December 2012 through mid-September
2013. Four bench-scale reactors were operated in parallel utilizing magnetic stir bars for
mixing (see Figure 3.2). Most trial runs were conducted over reaction periods of 24 hours.
After the reactors had reached the desired test temperature, FbCh was fed into the reactors
during the first 0.5 hour of treatment. Our test data over the first several months revealed that
VSS destruction was fairly well complete after 4 hours of reaction time with -15% incremental
destruction achieved over the next 20 hours of reactor detention time. Accordingly, in the latter
stages of the experimental program, reactor detention times and sample collection periods were
reduced to 4 hours. In subsequent process development and market penetration efforts, a
reactor detention time of 4 hours will be used.
7.2 Project Conclusions
• Based on observed VSS destruction rates, the major portion (>85%) of VSS destruction was
obtained in the first 4 hours of reaction time. Therefore, a design parameter of 4 hours
detention time has been established for this technology.
49
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• Compared to unheated WAS feedstock concentrations, substantial VSS destruction was
achieved by the application of elevated temperatures only, on the order of 10%-25%
depending on the applied temperature.
• Elevated temperature and EbCh together increased VSS destruction substantially over that
achievable with heat alone. At a given ffeCh dose, it is reactor temperature dependent. In
the spring of 2013, at 90°C a 30% increase in VSS destruction (55% dosed with 0.2 H2O2
g/g VSS vs. 25% undosed) was noted after 4 hours reaction time. This increase dropped to
17% (40% vs. 23%) at 75°C.
• VSS destruction in the thermo-oxidation process is also dependent on plant wastewater
temperature. As temperatures increased from spring (15°C-20°C) to July (23°C-24°C) in
2013, it was found that VSS destruction decreased. VSS destruction after 4 hours at a
reactor temperature of 90°C and an H2O2 dose of 0.2 g/g VSS dropped from 55% to 30%
and from 25% to 20% for the undosed reactor. This inverse relationship with wastewater
temperature vs. VSS destruction was attributed to higher rates of microbiological activity in
the oxidation ditch aeration system, resulting in less VSS available for destruction in the
thermo-oxidation process reactors. This conclusion is supported by the VSS/TSS ratios in
the activated sludge mixed liquor that decreased as a function of wastewater temperature
from 86% in April 2013 at 16°C to 69% in July 2013 at 23 °C.
• VSS destruction is directly related to FfeCh dose, i.e., the destruction increases with
increasing dose. As noted in Table 4.4, the 0.2 g FfeCh dose increased VSS destruction by
approximately 6% over 0.1 g dose in the summer and by roughly 12.5% in the spring. Of
the three doses evaluated, 0.05, 0.1, and 0.2 g FbCh/g VSS, the two higher doses are
recommended for practical application of the technology. Both of these doses will provide
acceptable levels of improved stability and reduced vector attraction. A decision regarding
dosage will be site specific, primarily determined by the degree of WAS minimization that
best fits the needs of the facility.
• Fecal coliform reduction is also directly related to reactor temperature. At a reactor
temperature of 90°C, fecal coliforms were reduced to below the detection limit of 100
MPN/g TSS after 1 hour of reaction time for all reactors. No regrowth was observed for
any of the reactors after 7 days at room temperature. At 75°C, fecal coliforms were also
reduced to below detection limits after 1 hour for the FbCh treated reactors. Fecal coliforms
were detected in the undosed reactors at levels below the Class A regulatory limit of 1000
MPN/g TSS, and no regrowth was seen after 7 days. A reactor temperature of 60°C
resulted in die-off of fecal coliforms, but regrowth above the regulatory limit occurred for
all reactors. At 65°C, fecal coliforms regrew in the undosed reactors, but not in the FbCh
treated reactors. Therefore, a thermo-oxidative treatment temperature of 65°C or greater is
recommended.
An unexpected attractive feature was the improved settleability achieved with
addition. Settling tests conducted over a 24-hour period in a 1-L graduated cylinder
exhibited high levels of improved settleability to thickened zones of down to 200 mL (see
Figure 4.17). Without FbCh addition, essentially no settling was observed even at elevated
temperatures. Therefore, it is concluded that the improved settleability of the post-treated
WAS was due primarily to the presence of FbCh. In the presence of FbCh, higher
temperatures do incrementally improve settleability (see Figure 4. 18). In an experiment
50
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conducted at 90°C with an H2O2 dose of 0.2 g/g VSS, the TSS in the bottom thickened zone
of settled WAS was 2.2% compared to 0.05% for the upper decant zone. This observation
suggests significant beneficial implications for any subsequent sludge dewatering
operations (i.e., centrifugation or a belt filter press) that may be considered by an individual
WWTP to increase biosolids concentrations.
• Another attractive feature of the thermo-oxidation process observed was the considerable
increase in soluble nitrogen achieved for four temperatures between 65°C and 90°C. The
soluble TKN fraction increased from 5% in the untreated sludge to 46% with heat alone and
51% for heat plus the 0.2 g FfeCh dose for all temperatures (see Figure 4.14). The
hypothesis is that the treatment caused the release of the less-tightly bonded nitrogen
species from the solids into the soluble fraction. This means that the more releasable
organic and ammonia forms of nitrogen will be recycled back to the headworks of the plant
in the dewatered supernatant rather than being released as a slug into the soil during land
application. Premature release of a slug of nitrogen species could contaminate ground
water via seepage or runoff to adjacent streams, rivers, and lakes. The more tightly bound
fraction is retained on the biosolids for slow, measured release to the soil, thereby
enhancing the soil conditioning and fertilization properties of the biosolids.
• After the Mason WWTP experiments concluded, trial runs were conducted on WAS from
four other WWTPs in the Greater Cincinnati area. VSS destruction of 45%-50% was
achieved after 4 hours of treatment (0.2 g FbCh/g VSS and 90°C) for three of the four plants
and approximately 38% for the fourth plant (the plant containing the highest percentage of
industrial wastes in its influent flow). These VSS destruction levels are contrasted to VSS
removals of 20%-25% for no-added-FbCh controls. The substantial increase in VSS
destruction noted for Mason's WAS was replicated for four other diverse plants (see Figure
4-19), indicating this technology is applicable to a wide range of WAS feedstocks.
• Conceptual order-of-magnitude cost estimates were prepared for two thermo-oxidation
trains, one in which energy consumed in heating process reactor contents is not conserved
and the other in which a large fraction of the heating energy is recovered by a heat
exchanger and reused. The estimates were based on two smaller WWTP sizes, the first
with a 6-mgd average influent flow and a WAS production rate of 20,000 gpd (Mason
WWTP parameters) and the second for one-fifth these rates with an average influent flow
of 1.2 mgd and a sludge production rate of 4000 gpd. These estimates assume the thermo-
oxidation process train is paired with a long-SRT oxidation ditch WWTP that does not
practice primary settling of raw sludge. Accordingly, the entire excess sludge production
from this type of WWTP is contained within the plant's WAS inventory. The capital cost
of the heat exchanger train was estimated at approximately 1.75 times larger than that of the
train that does not recover energy for both plant sizes. For the larger plant flow, the
estimates range roughly from $300,000-500,000 and for the smaller plant flow from
approximately $150,000-250,000.
• The penalty paid in capital cost for the heat exchanger train is offset by reduced operating
costs. Based on a reactor temperature of 90°C, estimated annual operating costs for the
heat exchanger train are about 40% of that for the energy non-recovered train at an assumed
FbCh dose of 0.1 g/g VSS for both size plants and approximately 55% at an assumed FfeCh
dose of 0.2 g/g VSS for both size plants. These estimated annual operating costs equate to
51
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unit operating costs of roughly $144-$336/dry ton for the smaller ffcCh dose for both size
plants and $222-$415/dry ton for the larger EbCh dose for both size plants. The larger unit
cost applies to the energy non-recovered train and the smaller unit cost to the heat
exchanger train.
• Estimated costs for the thermo-oxidation process were compared to estimated or published
costs for four sludge disposal options: paddle dryer system (used at Mason), rotary dryer
system (used at two large Midwest plants in Milwaukee, WI and Louisville, KY),
incineration, and landfilling (see Table 6.3). The thermo-oxidation process, obviously, is
most closely related to the dryer systems. Whereas the thermo-oxidation process treats
WAS as a slurry before any subsequent mechanical dewatering, the dryer systems utilize
dewatering prior to the treatment stage to create a sludge feedstock in the 20% range. As
such, the dryer systems produce pelletized biosolids with a TSS concentration of at least
95%. In contrast, the thermo-oxidation process has the option of supplying a slurry
biosolids product of 1.5%-3% solids or with second-stage mechanical dewatering a semi-
dry loamy biosolids of approximately 20% solids. Either thermo-oxidation option allows
transfer of water to the soil during land application, which becomes a distinct advantage in
water-short areas of the country.
• It is believed the optimum market niche for this technology is smaller community or rural
areas that increasingly are utilizing or switching to extended aeration systems,
predominately oxidation ditches. These types of WWTPs minimize and simplify plant
operations by eliminating the need to handle primary sludge and operate anaerobic
digesters. The entire excess sludge inventory is comprised of a highly oxidized WAS
stream that requires no further treatment prior to sludge processing. Long-SRT extended
aeration systems can be manipulated to remove nitrogen and phosphorus as well as organics
and solids and typically produce extremely high quality secondary effluents. With the
anticipated low-tech operating requirements for the thermo-oxidation process, the
technology would appear to be a perfect match for extended aeration WWTPs, particularly
those that utilize oxidation ditches.
• For the larger oxidation ditch facilities of 5-6 mgd, the thermo-oxidation process could
compete directly with the paddle dryer sludge drying system such as the one used at Mason.
The capital cost of the Komline-Sanderson paddle dryer at Mason, designed to handle an
average un-dewatered sludge flow of 20,000 gpd, was $4,000,000 excluding the cost of the
first-stage centrifuges. The two centrifuges added another $1,000,000. This cost is
contrasted to the capital cost of the thermo-oxidation train equipped with a heat exchanger
of approximately $500,000, or about 12% of that for the paddle dryer. Post- centrifugation
would add another $1,000,000. This cost difference could likely represent a strong
incentive for communities that otherwise might have to float a bond issue or raise capital in
some other manner. The final biosolids products for the two described technologies after
dewatering are different: one produces a final TSS concentration in the range of > 95%, the
other approximately 20%. Both products would be Class A biosolids transportable by the
customer and suitable for land application, although different in final water content, the
construction cost savings are valid.
• Annual operating costs for the thermo-oxidation process with a reactor temperature of 90°C
at the 5-6 mgd plant scale will be higher than those for the paddle dryer system, i.e., an
52
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estimated $144-$222/dry ton (0.1 g H2O2/g VSS for the former and 0.2 g H2O2 for the
latter) compared to a reported $100/dry ton. The lower dose achieves coliform reduction
equal to that for the higher dose at some sacrifice in VSS destruction. Operating at a
reactor temperature of 75°C to save $10,000-$15,000 in heating costs (thereby lowering
unit cost to roughly $130/dry ton for the lower H2O2 dose) would result in even less VSS
destruction but still meet Class A standards for fecal coliforms.
• The thermo-oxidation option that does not include a heat exchanger is believed to be better
suited to smaller plants in the 1-2 mgd flow range, even though operating costs would be
roughly twice that of a system with a heat exchanger. At an estimated annual operating
cost of approximately $50,000-$60,000, the unit cost is relatively high ($336-$415/dry ton),
but the estimated capital cost of only $250,000 and not having to operate a heat exchanger
could be very attractive to a small community with limited resources and personnel.
• The bottom line on thermo-oxidation process design is that options are available that will
meet Class A biosolids standards under a variety of conditions based on individual
community needs and preferences. VSS destruction percentages can be varied. Heating
energy can be conserved or not recovered. Capital costs can be reduced at the expense of
increased operating costs or increased to reduce operating costs. Capital cost is estimated
to be almost an order-of-magnitude lower than for a system designed to produce pelletized
biosolids in the target WWTP size range. Annual operating costs, while higher than that for
the pelletized systems, can be reduced by choosing lower reactor operating temperatures
and H2O2 doses.
• The potential domestic market for this technology is projected to be at least 375 facilities <
2 mgd and a lesser but still substantial number for plant sizes > 2 mgd. Considering just a
population of 375 facilities with an installed cost ranging from $150,000-500,000, the
estimated market potential is a conservative $56 million to $188 million.
• Although the operating cost of the thermo-oxidation process is higher per ton of VSS
treated, the capital cost is much less than for existing systems of comparable capacities. The
lower capital cost may place the system within the budget of small municipalities.
Although the life cycle cost of the system will be higher with higher treatment costs over
time, the benefits to the water balance in these municipalities or regions yields an even
higher life cycle benefit. There may also be a world market for the technology, depending
on the use of oxidation ditch or extended aeration technologies for wastewater treatment
globally. The applications would be different for developed and developing regions. In
developed regions where oxidation ditches are the primary method currently used for
wastewater treatment, thermo-oxidation systems could be added to increase the re-use of
local water. The developing world is also a potential market, with newly built systems able
to incorporate thermo-oxidation technology from the onset in cases where the simple
oxidation ditch will be the first system to be constructed (whether a commercial package
plant or locally built system) and high population growth is not predicted.
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8.0
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Appendix A
Variations on Conceptual Treatment Trains
Additional conceptual treatment trains could be considered for the pilot project.
Variations on the conceptual treatment trains include:
A large closed tank in batch use. Once per day, sludge treated with hhCb is heated to
90°C for 4 hours, then discharged in such a way as to take advantage of the heat elsewhere
in the plant.
"A
Plate heat exchanger
Belt filter press
or Centrifuge
Heat up to 90CC
A large heat exchanger in continuous use. hhCb is continuously injected into the heat
exchanger inlet. The heat exchanger has capacity for exchange and 4 hours of treatment
time. This is problematic with current technology. Two venders say that injecting steam into
piping with wastewater would have problems with particulate fouling.
20°C
303C
HA
80°C 90°C
Plug flow
heat
exchanger
90CC
1 V i
1
Zi Plug flow H2O2 reactor
Heat up to 90°C
^
Belt filter
press or
Centrifuge
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Appendix B
Quality Assurance Project Plan, L1881-QP-1-0
Category III Measurement Project
Thermo-Oxidation of Municipal Wastewater Treatment Plant Sludge
for Production of Class A Biosolids
U.S. Environmental Protection Agency
Contract No. EP-C-11-006
Work Assignment 2-77
Submitted to:
Richard C. Brenner
Work Assignment Manager
U.S. Environmental Protection Agency
Office of Research and Development
National Risk Management Research Laboratory
Land Remediation and Pollution Control Division
Soils and Sediment Management Branch
Cincinnati, OH 45268
Prepared by:
Robert Grosser, Ph.D.
Pegasus Technical Services, Inc.
Cincinnati, OH 45219
Revision 4
April 26, 2013
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TABLE OF CONTENTS
Section
1
2
O
4
5
6
7
8
9
Name
Project Description and Objectives
Organization and Responsibilities
Scientific Approach
Sampling Procedures
Measurement Procedures
Quality Metrics (QA/QC Checks)
Data Analysis, Interpretation, and Management
Reporting
References
Page
5
7
11
15
17
20
22
24
24
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LIST OF FIGURES
Figure No. Name Page
2.1 Organization Chart 9
2.2 Project Schedule 10
LIST OF TABLES
Table No.
2.1
4.1
5.1
6.1
7.1
Name
Project Contacts
Sample Preservation
Measurement Procedures
QA/QC Checks
Reporting Units
Page
10
16
19
21
23
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1. Project Description and Objectives
1.1 Project Description
Municipal wastewater treatment plant (WWTP) sludge is typically composed of a
combination of raw primary sludge and excess or waste activated sludge that is digested,
either anaerobically or aerobically, to achieve solids mass reduction, vector attraction
reduction, and a reduction in microbial indicators of fecal contamination such as fecal
coliforms. In most cases, the digested sludge is subjected to mechanical dewatering to
produce a drier material that can be incinerated, disposed of in a sanitary landfill, or applied
in bulk to agricultural land as biosolids. Some producers of biosolids further dry the
processed material to the point where it can be bagged and sold as a commercial soil
conditioner/fertilizer (e.g., Milorganite produced by the Milwaukee Metropolitan Sewerage
District).
WWTP sludge is generally processed to levels where it can meet Federal Class B sludge
regulations. The Class B regulations represent the minimum levels of pathogen reduction
that are acceptable for land application of biosolids (i.e., treated WWTP sludge). These
regulations specify that wastewater sludge must be treated by a process to significantly
reduce pathogens (PSRP) that will achieve a vector attraction reduction (VAR) goal of 38%
reduction in volatile suspended solids (VSS) or meet a fecal coliform level in the processed
sludge < 2,000,000 MPN (Most Probable Number)/g dried solids, or alternately < 2,000,000
CPU (Colony Forming Units)/g dried solids, based on the geometric mean of seven samples.
Some states require municipal WWTPs to meet both stipulations to achieve a Class B rating.
PSRPs include, among others, anaerobic sludge digestion at a mean cell residence time
(MCRT) of 15 days at a temperature of 35°C - 55°C and aerobic sludge digestion at a MCRT
of40daysat20°C.
Land application of Class B biosolids, although widely practiced in the United States, has
been accompanied by numerous and ongoing public complaints over the years. These
complaints range from emanation of malodors from the applied fields to claims of illnesses
and even deaths caused by volatilization of harmful compounds contained in the biosolids or
direct contact with the biosolids. These complaints can be circumvented and most likely
dispelled by the land application of biosolids treated to a higher level, namely Class A
biosolids. There are six treatment alternatives to create Class A biosolids as given in Title 40
Subpart 503 of the Federal Regulations. All treatment regimens mandate the reduction of
fecal coliforms to <1000 MPN/g dried solids or Salmonella to <3 MPN/4 g dried solids plus
additional treatment measures such as heat, high pH, listed Processes to Further Reduce
Pathogens (PFRP), or other undefined processes that also are demonstrated to reduce enteric
viruses to < 1 plaque forming unit/4 g dried solids and helminth ova to < 1/4 g dried solids.
1.2 Proj ect Obj ectives
The immediate objectives of this research project are to evaluate and optimize a new cost-
effective thermo-oxidation sludge treatment process that meets Class A regulations and to
generate a reliable dataset that can substantiate these claims.
The proposed thermo-oxidation process uses hydrogen peroxide (FfeCh) addition at elevated
temperatures to achieve increased levels of VSS destruction, VAR, and disinfection of sludge
that has been previously treated with some level of biological treatment, either anaerobic or
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aerobic. Previous research conducted at the University of Cincinnati (UC) has demonstrated
reduction in fecal coliforms to non-detection levels on a combination of primary and waste
activated sludges treated in high-rate or short-term anaerobic digesters with a MCRT of 5
days followed by thermo-oxidation (Rivero, 2005). It is postulated that the thermo-oxidation
process will work equally well on aerobically digested sludge, highly-oxidized aerobic
sludge (mixed liquor) taken directly from an extended aeration or oxidation ditch activated
sludge reactor, and possibly even mixed liquor taken from a lower-MCRT conventional
activated sludge aeration tank. The theory behind this mating of first-stage biological
treatment with follow-on second stage thermo-oxidation (chemical) treatment is to use the
microorganisms in the biological treatment stage to cost-effectively oxidize (aerobic
treatment) or reduce (anaerobic treatment) most of the easy-to-degrade organics contained in
the sludge matrix and to use the more expensive chemical (EfeCh) treatment to oxidize the
more recalcitrant organic compounds that are not easily degraded biologically. Using ffeCh
to oxidize easy-to-degrade organics would substantially increase chemical dose requirements
and cost. Likewise, using microorganisms to process the more difficult-to-degrade organics
would result in long MCRTs and large reactors, again at increased cost. The proposed two-
stage scenario optimizes what each stage of the sludge treatment train does best and most
cost-effectively.
Because the thermo-oxidation step acts as a rigorous final treatment stage that cleans up any
residual less-recalcitrant organics not removed in the preceding biological treatment stage,
the biological stage does not have to be as large as typically designed for and installed in
conventional WWTPs. Thus, short-term anaerobic or aerobic sludge digesters can be used
instead of the conventional 15-day anaerobic digester MCRT and the conventional 40-day
aerobic digester MCRT. These smaller digestion facilities represent significant potential
capital and operating cost savings to the municipal WWTP. Given the potential ability of the
H2O2 treatment reactor to cost-effectively handle a fairly broad range of incoming sludge
feed characteristics, it is possible that no prior sludge digestion step may be required. Rather,
the highly oxidized mixed liquor sludge produced in an extended aeration activated sludge
plant and possibly less oxidized conventional activated sludge mixed liquor may be suitable
for direct injection into the thermo-oxidation reactor. The bottom line on ffcCh reactor
biological feedstock characteristics is that the thermo-oxidation process should be able to
accommodate most sludge treatment options typically utilized by municipal WWTPs and
possibly even mixed liquor from a conventional activated sludge system.
Another benefit of the thermo-oxidation process is that some fraction of the nitrogen
(particularly ammonia) and phosphorus inventory in the EbCh feed sludge will be solubilized
during treatment in the thermo-oxidation reactor and recycled to the head of the treatment
plant works in the reactor supernatant. If this did not happen, the entire nutrient load would
be transported to the application field in the biosolids. A significant fraction of this load,
particularly the easily released ammonia component, would be rapidly solubilized and
discharged into the soil, potentially exceeding the sorption capacity of the soil and
contaminating ground water resources. By removing the easily released nutrient components
in the WWTP, the nutrients more tightly bound to the biosolids will be released slowly as
needed for soil conditioning and fertilization.
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2. Organization and Responsibilities
2.1 Project Personnel and Responsibilities
Mr. Stephen Wright is the U.S. Environmental Protection Agency (EPA) Project Officer for
EPA Contract No. EP-C-11-006. Mr. Jim Voit is the EPA Land Remediation and Pollution
Control Division (LRPCD) Quality Assurance (QA) Manager responsible for approving the
Quality Assurance Project Plan (QAPP). Mr. Richard Brenner is the EPA Work Assignment
(WA) Manager and Co-Principal Investigator for this WA responsible for project planning,
technical direction, and providing laboratory support during the studies. Dr. Paul McCauley
is Co-Principal Investigator for this WA responsible for project planning, technical direction
and providing laboratory support during the studies.
Dr. Karen Koran is the Pegasus Technical Services, Inc. (Pegasus) Project Manager. Dr.
Raghuraman Venkatapathy is the Pegasus On-Site Technical Manager responsible for
supervision of the Pegasus Team Staff. Mr. Steven Jones, ASQ CQA/CQE, with Shaw
Environmental & Infrastructure Inc., is the Pegasus Contract QA Manager and is responsible
for oversight of Pegasus Quality Program implementation, QA review of quality documents
and deliverables, and project assessments. Ms. Edith Holder, Pegasus On-Site WA Leader,
is responsible for providing support for laboratory studies and processing of all data
established. Mr. Yonggui Shan, Dr. Robert Grosser, and Mr. Joshua Kickish of Pegasus are
responsible for providing technical support throughout the project.
Project organization is shown in Figure 2.1, and project contacts are given in Table 2.1.
2.2 Project Schedule
The project schedule is shown in Table 2.2. All reactor set-ups will be done in batch, run for
a 24-hr time period followed by tear down. Sludge will not be stored for greater than 1 week,
so it will be collected as needed. It is assumed that a minimum of 16 study combinations will
initially be utilized: H2O2 at 0, 0.05, 0.1 and 0.2 g/g VSS and temperatures of 35, 60, 75 and
90° C with each run conducted in triplicate. Sludge will be used for one treatment in the
week that it is collected and stored. For example: FbO2 at 0.2 g/g VSS at the three test
temperatures could be run in 1 week using the same sludge. If this schedule is not possible,
additional arrangements will have to be made.
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EPA Project Officer
Stephen Wright
Pegasus Project Manager
Karen Koran, Ph.D.
EPA LRPCD QA Manager
Jim Voit
EPA WA Manager/
Co- Principal Investigator
Richard Brenner
Co-Principal Investigator
Paul McCauley, Ph.D.
Pegasus On-Site Manager
Raghuraman Venkatapathy, Ph.D.
Pegasus Contract QA Manager
Steven Jones, ASQ CQA/CQE
Pegasus On-Site WA Leader
Edith Holder
Pegasus On-Site Tech. Support
Yonggui Shan
Robert Grosser, Ph.D.
Joshua Kickish
Figure 2.1. Organization Chart
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Table 2.1. Project Contacts
Name
Stephen Wright
Jim Voit
Richard Brenner
Paul McCauley
Dr. Karen Koran
Dr. Raghuraman Venkatapathy
Steven Jones, ASQ CQA/CQE
Edith Holder
Yonggui Shan
Dr. Robert Grosser
Joshua Kickish
Phone/email
(513)569-7610
wright. stephen@epa. gov
(513)487-2867
voit.jim@epa.gov
(513)569-7657
brenner.richard@epa.gov
(513)569-7444
mccauley.paul@epa.gov
(513)569-7304
koran.karen@epa. gov
(513)569-7077
venkatapathy.raghuraman@epa.gov
(513)782-4655
steven.jones@cbi.com
(513)569-7178
holder.edith@epa.gov
(513)569-7606
shan.yonggui@epa.gov
(513)569-7529
grosser.robert@epa.gov
(513)569-7485
kickish.joshua@epa.gov
Responsibilities
EPA LRPCD Project Officer
EPA LRPCD QA Manager
EPA LRPCD WA Manager/
Co- Principal Investigator
EPA LRPCD Alternate WA
Manager/Co- Principal
Investigator
Pegasus Project Manager
Pegasus On-Site Technical
Manager
Pegasus Contract QA Manager
Pegasus On-Site WA Leader
Pegasus On-Site Technical
Support
Pegasus On-Site Technical
Support
Pegasus On-Site Technical
Support
Figure 2.2. Project Schedule
QAPP Preparation
HASP Preparation
Field Sampling
Laboratory Analyses
Data Analysis/Reports
Jan
2013
Feb
2013
Mar
2013
Apr
2013
May
2013
Jun
2013
Jul
2013
Aug
2013
Sep
2013
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3. Scientific Approach
3.1 Survey of Available Aerobic Sludge Sources
An aerobically digested sludge or highly oxidized sludge from an extended aeration plant in
the local Cincinnati area shall be selected as the initial feed sludge to the thermo-oxidation
reactors. If the trials with highly oxidized sludge produce promising results, additional trials
with conventional activated sludge mixed liquor may be evaluated.
A survey will be completed of available local plants from the Greater Cincinnati area that
either digest their sludge aerobically or operate a high-MCRT extended aeration type
municipal WWTP. Sludge samples from these WWTPs will be acquired and analyzed for
total suspended solids (TSS) and VSS content, organic and ammonium nitrogen, total
phosphorus, pH, and fecal coliforms. Following completion of the dataset for all sampled
WWTP sludges, the best sludge feedstock to be used for the experimental trials will be
selected. The optimum scenario would be to locate a municipal WWTP that uses aerobic
sludge digestion to treat its waste activated sludge. This would allow for both aerobically
digested sludge and aeration tank mixed liquor to be obtained from the same plant as reactor
feedstock for comparative purposes.
3.2 Design and Fabrication of Thermo-Oxidation Reactors
At least four thermo-oxidation reactor systems capable of being operated in the sludge
temperature range of 35°C - 90°C will be fabricated. All reactors will be used to conduct
experiments in triplicate. These reactors (Pyrex 1220-4L or equivalent) will have an
operating volume of 2 L and be equipped with a rubber stopper to close the opening and
allow for various holes for fittings, fiberglass insulation wrap, heat tape (Model #EFH-SH,
Electro-Flex Heat), and a temperature controller (Model #CN9000A, Omega) fitted with a
thermocouple to maintain operating temperatures in the desired 35°C - 90° C range. Each
reactor will also have a condenser (Model #282210-0000, Kimble) fitted through the stopper
to help maintain reactor volume during the higher temperature regimens. Adequate
headspace will be maintained above the operating sludge mixture to retain foaming possibly
generated by the addition of FbCh. FbCh will be metered into the reactors via a syringe pump
(Model #NE 300, New Era Pump Systems) and disposable 5- to 25-mL syringes depending
on the volume to be added. Samples will be removed from each of the reactors at each time
point with sterile pipettes by removing the rubber stopper allowing access to the stirring
sludge. Reactor temperatures will be monitored continuously with a digital readout
thermometer (Fisher Model #15-077-59) installed through the stopper of each reactor into the
mixing reactor sludge inventory. Reactor sludge contents will be mixed and maintained in a
homogeneous condition through the use of stir plates and 4-in. long magnetic stir bars.
3.3 Conduct of Preliminary Trials to Optimize Reactor Operating Conditions
Following establishment of thermo-oxidation reactor systems and selection of the initial
sludge feedstock for the study, a series of experiments will be conducted, as necessary, to
determine optimum reactor operating conditions. The facets of reactor operation that will be
evaluated include observation of foaming tendencies as a function of feed strategy,
minimization and control of foaming if necessary, and the time required to change reactor
operating temperature within the desired temperature range. The best TSS (or VSS)
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concentration at which to add the sludge feedstock to the reactor will also be determined. A
TSS of approximately 1.5% will be used as a starting point in defining the optimum sludge
solids concentration. Arriving at the desired concentration will most likely require either
thickening or dilution of the collected WTTP sludge. Porous pots will be used as a technique
for draining water from collected WTTP sludge if thickening is necessary to attain the
approximate desired TSS concentration. Dilution with sludge filtrate or plant final effluent
will be employed if the collected WTTP sludge has a TSS concentration higher than the
desired level.
3.4 Screening of Chemical Dose-Operating Temperature Combinations on Highly
Oxidized Aerobic Sludge
As many as 16 combinations of H^hdose and thermo-oxidation reactor operating
temperatures will be evaluated depending on interim results. These 16 combinations shall be
comprised from four H2O2 doses, 0 (or no H2O2), 0.05, 0.1, and 0.2 g/g reactor feedstock
VSS, and four operating temperatures, 35° C, 60° C, 75°C, and 90° C. The H2O2 will be
obtained from Fisher Scientific as a solution of 50% strength H2O2. Each combination of
dose and temperature conditions will be conducted in triplicate, yielding a total of 48
potential runs. The order in which these combinations are evaluated shall be based on a prior
randomized sequence. It is estimated that one batch of sludge collected from the selected
local WWTP can be used, if refrigerated, for up to 1 week before its characteristics change
sufficiently that another batch of sludge needs to be collected.
During this screening task, only pH measurements and TSS/VSS and fecal coliform
determinations on reactor feedstock, aerating sludge at different time intervals, and fully
treated sludge will be performed to define reactor performance as a function of operating
conditions. Chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), ammonium
nitrogen (NH/t-N), and total phosphorus (TP) analyses maybe performed on reactor
feedstock sludge and final treated sludge (e.g., on sludge samples collected after 24 hr of
treatment) during these screening tests to characterize the organic and nutrient content of the
before and after sludges for each new experiment.
3.5 Evaluation of Optimum Chemical Dose-Operating Temperature Combinations on
Highly Oxidized Aerobic Sludge
Using the results of the above screening tests and following consultation with the EPA WA
Manager, up to three sets of chemical dose and operating temperature test conditions shall be
selected as the best combination of performance and cost effectiveness for expanded testing.
These tests shall also be carried out in triplicate identically to or as optimized during the
screening tests in Section 3.4 above.
Because the purpose of these optimized tests will be to confirm compliance with Class A
biosolids regulations, analyses performed will include, as a minimum, TSS/VSS, fecal
coliforms, COD, TKN, NH/t-N, TP, and pH (the latter five are not regulated analytes).
Salmonella analyses may also be conducted if deemed necessary and useful. Other
pathogenic bacteria and/or virus analyses such as E. coli, Helminth ova, and enteric viruses
may be conducted to further define the germicidal impact of the imposed treatment regimes.
If other microbial analyses are added to the laboratory regimen, an Addendum to this QAPP
will be submitted.
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During these preliminary screening trials and subsequent tests, it is intended to sample
reactor contents at regular intervals throughout a test run to define VSS destruction and fecal
coliform disappearance rates. Each test run will be designed to operate for a period of at
least 24 hr. Sampling will be conducted more frequently in the early portion of test run
where reaction rates will be expected to be changing more rapidly. For example, a sampling
schedule similar, but not necessarily identical, to the following sequence will most likely
approximate the sampling schedule that will be used: 1) time (t) = initial time (i.e.,
immediately after the reactors have been charged with sludge feedstock at an approximate
TSS concentration of 1.5% but before the temperature controllers have been turned on to
increase reactor temperature to the target level; 2) t = 0 (i.e., immediately after the reactor
sludge contents have reached their target temperature, a temperature rise period anticipated to
range from 45 - 75 minutes, depending on temperature; 3) t = 1 hr; 4) t = 2 hr; 5) t = 4 hr; 6) t
= 8 hr; and 7) t = 24 hr.
During the above sampling sequence, those reactors scheduled to receive FbO2 doses will not
begin to receive them until immediately after the reactors have reached the target
temperature. FbO2 doses will be delivered to the reactors at constant rates with syringe
pumps (see Section 3.2) over a period of 15- 120 minutes. Initially, a dosing period of 30
minutes will be utilized. A review of screening test data may suggest that FbO2 effectiveness
could be enhanced by delivering the selected dose by splitting into two or more fractional
doses. In this event, sampling time points may be altered to accommodate the revised dosing
schedule.
Reactor temperatures will be maintained at target levels with the use thermocouples driven
by temperature controllers (see Section 3.2). All reactors will be wrapped with heat
insulation to maximize heat retention. Digital readout thermometers (Fisher Model No. 15-
077-59 or equivalent) calibrated from -50°C to 300°C will be permanently inserted through
the reactor stoppers into the mixing reactor contents to assist in tweaking the controllers to
maintain target temperatures within ±1°C rather than relying solely on controller settings.
Said digital readout thermometers will be calibrated against a NIST Traceable Calibrated
thermometer (Model No. 210-621 or equivalent).
To assist in separating the oxidative effect of dissolved oxygen transferred into the reactor
sludge from headspace atmospheric air, if any, from the oxidative impact derived from the
added FbCh , in some screening experiments two of the four reactors will be operated under a
headspace air blanket and the other two under a headspace nitrogen gas blanket. In these
experiments, all four reactors will be operated under a nitrogen blanket during the time it
takes the reactor contents to reach their target temperature. At that time (t = 0), two of the
reactors (one undosed control and one dosed with FbCh) will be switched to headspace air
blanket environments and the other two (one undosed and one dosed) will continue to operate
under a headspace nitrogen blanket environment.
3.6 Screening of Chemical Dose-Operating Temperature Combinations on Lesser
Oxidized Mixed Liquor Sludge
If the above test runs using highly oxidized aerobic sludge produce Class A biosolids under
cost-effective conditions and if time and budget constraints permit, the same or a smaller set
of screening tests will be repeated on a lesser oxidized mixed liquor sludge from a
conventionally operating activated sludge WWTP. Preferably, this mixed liquor reactor
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feedstock can be collected from the same plant from which the highly oxidized sludge will be
collected. If this situation is not available or feasible, mixed liquor sludge batches will be
collected from a completely different municipal WWTP as determined in Section 3.1 above.
The most rigorous combination of EbChdose (0.2 g/g VSS) and reactor operating
temperature (90° C) shall be evaluated first for compliance with Class A biosolids
regulations. If these regulations are not met, either even more rigorous conditions shall be
evaluated or this task may be terminated at this point (TBD by WA amendment). If
compliance with Class A biosolids regulations is demonstrated in the first rigorous test run,
the entire set of 16 test combinations shall be conducted and evaluated in triplicate as in
Section 3.4 as time and budget resources permit.
3.7 Evaluation of Optimum Chemical Dose-Operating Temperature Combinations on
Lesser Oxidized Mixed Liquor Sludge
Assuming the full complement of screening tests are carried to completion in Section 3.6
above, and further assuming that at least some of the chemical dose-operating temperature
combinations evaluated therein demonstrate compliance with Class A biosolids regulations,
more thorough evaluations will be conducted on up to three sets of optimized dose-
temperature conditions as in Section 3.5 above, again as time and available resources dictate.
3.8 Evaluation of Optimum Chemical Dose-Operating Temperature Combinations on
Biomass Concentrator Reactor (BCR) Sludge
A new activated sludge treatment process called the BCR has been developed by EPA
National Risk Management Research Laboratory (NRMRL) researchers. This technology
uses specially designed membranes to separate mixed liquor solids from treated effluent,
thereby permitting operation under higher mixed liquor suspended solids (MLSS)
concentrations and consequently higher MCRT levels than normally used in conventional
activated sludge systems. This technology has been selected for evaluation in FY 2013 under
the Water Technology Innovation Cluster (WTIC) Program. During the first portion of the
FY 2013 test period, the EPA NRMRL researchers via a WA to be carried out at UC on this
contract will be attempting to optimize performance on actual municipal wastewater in lieu
of the synthetic wastewater feed employed in previous trials. At some point in their
evaluation, said researchers will have optimized BCR operation and performance on actual
wastewater. At this point and following completion of the sections summarized above for
this WA, arrangements will be made with the staff conducting the BCR project to secure
highly oxidized mixed liquor sludge batches from the BCR reactor. The BCR sludge will be
subject to the same set of three optimized chemical dose-operating temperature combinations
used in Section 3.7 above for highly oxidized sludge obtained from a local municipal
WWTP, time and budget permitting.
3.9 Process Measurements
Process measurements for this study consist of critical measurements of TSS/VSS and fecal
coliforms, and non-critical measurements of pH, NfLt-N, TKN, COD, TP, and Salmonella.
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4 Sampling Procedures
4.1 Sampling Procedures
This study will utilize two primary sampling procedures. The first will be obtaining the
aerobic sludge from the selected municipal WWTP. The second will be removal of liquid
samples from the reactors followed by further sample processing in individual assays.
The aerobic sludge will be taken directly from either an aerobic sludge digestion system, an
extended aeration or oxidation ditch activated sludge reactor, and possibly even mixed liquor
from a lower-MCRT conventional activated sludge aeration tank. The sludge will be
collected in a large carboy (10-L volume), transferred back to the EPA AWBERC facility,
and kept at 5°C until used. The sludge will not be kept for more than 1 week under these
conditions.
Sludge slurry samples will be removed from reactors using large-bore, 25-mL or 50-mL
pipettes. The mixing/stirring action in the reactor prompted by the magnetic stir bars will be
maintained during the removal of the samples. While the reactor is under continuous stirring,
a 20-mL or 40-mL volume as required will be removed and placed in a 50-mL sample vial
(or equivalent) for further analysis. A sampling schedule per reactor of t = initial followed
by t = 0, 1, 2, 4, 8, and 24 hr or an approximation thereof will be followed. Only TSS, VSS,
fecal coliforms, and pH will be conducted at each of the hourly sampling events. The other
study parameters will be measured on the initial sludge feedstock and sludge samples
collected at the last sampling time point.
4.2 Sample Preservation
Most samples will be processed immediately upon removal from the reactors or within 24 hr
of removal where preservation will not be necessary. If not processed immediately but
within the 24-hr holding period, the sample will be kept refrigerated at 5°C. Any samples
needing preservation will be done as described in the individual assay method.
Table 4.1. Sample Preservation
Sample Type
TSS
VSS
Fecal Coliforms
Salmonella
pH
Ammonium Nitrogen
TKN
Total Phosphorus
COD
Container
Glass/Plastic
Glass/Plastic
Dilution bottle
Glass/Plastic
Glass/Plastic
Glass/Plastic
Glass/Plastic
Glass/Plastic
Glass/Plastic
Sample
Quantity
Entire filter
Entire filter
Full volume
Volume according
to method
lOmL
ImL
ImL
ImL
ImL
# collected per study
condition
23 (22 plus one blank control)
23 (22 plus one blank control)
8 (7 plus one blank control)
8 (7 plus one blank control)
4 (one sample from each reactor
16 (15 plus 1 blank control)
16 (15 plus 1 blank control)
16 (15 plus 1 blank control)
16 (15 plus 1 blank control)
4.3 Sample Labeling
Carboys used to bring the sludge back from the WWTP will be labeled with the source,
collection date, and collection time (samples will not be stored for greater than 1 week).
Within the laboratory, triplicate reactors will be labeled as A, B, or C and current working
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conditions (temperature and IHbCh concentration) noted on each. When samples are removed,
the reactor letter or designation, reactor working conditions, and date and time of sample
collection will be noted and recorded on a laboratory log sheet. For example:
A = reactor designation
90°C = working temperature
0.2 g/g VSS = reactor H2O2 dose
6.95 = sample pH
2 hr = sampling time point
5/1/13 = sample collection date
40 mL = sample volume collected
1,880 mL = remaining reactor slurry volume after sample withdrawal
300 mL/min = air or nitrogen flow through reactor headspace
5. Measurement Procedures
5.1 Sample Analysis
The aerobically digested sludge (and/or activated sludge mixed liquor) collected in the field
will be stored in a 5° C constant temperature room (CTR). The sludge will be concentrated to
a TSS concentration of approximately 1.5% either by dilution with WTTP final effluent or
thickening via the use of porous biopots. The collected sludge will be analyzed for TSS,
VSS, pH, fecal coliforms, COD NH4-N, TKN, and TP. Copies of all methods may be found
in the lab and on the L drive under L:\Public\NRMRL-PUB\Holder\Thermo-oxidative
process\SOPS and Methods. SOPs are attached here for ease of the reviewer.
The thermo-oxidative test reactors are 2-L heat-tape-jacketed (insulated) bottles with glass
ports at the bottom so that FkCh can be added to the bottom of the reactor. All work involved
with operating these reactors will be performed in a chemical fume hood. To run a test,
aerobically digested sludge (and/or activated sludge mixed liquor) will be loaded into the
reactor and brought to the desired temperature (35°C to 90° C). After the temperature is
stabilized, the desired dose of H2O2 (0.05-0.2 g/g VSS) will be added at the bottom of the
reactor using a syringe pump. Samples will be taken and measured for pH, TSS, VSS, and
fecal coliforms MPN routinely and for COD, nutrient species, and Salmonella MPN on
selected samples. After operating conditions have been optimized, additional analyses may
be added, and if so, an Addendum to this QAPP will be submitted.
5.1.1 pH Analysis
A pH probe will be calibrated with two pH standards to bracket the expected pH
readings. After calibration, the probe will be submerged into a 5 - 10 mL subsample and
the reading recorded after stabilization is achieved. pH will be measured at the
beginning, during, and the end of any experimental run.
5.1.2 Analysis for TSS and VSS
A well-mixed sample aliquot will be filtered through a pre-weighed standard 47-mm
glass-fiber filter. The residue retained on the filter is dried in an oven at 103°C - 105°C
until a constant mass is obtained. The mass of the residue on the filter represents the
TSS. The residue from TSS analysis is ignited in a muffle furnace to constant weight at
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550°C. The remaining solids represent the fixed suspended solids while the mass lost
during ignition is the VSS (see Pegasus SOP PTS-TSS-VSS). Analysis of TSS/VSS will
be done at every time point when sludge is removed from the reactors.
5.1.3 Analysis for Fecal Coliforms
Using the IDEXX Quanti-tray/2000® system, an MPN value for fecal coliforms is
measured in water. The dehydrated medium (Colilert®) will be dissolved in a 100-mL
aliquot of water or reactor contents or a dilution thereof, poured into the Quanti-Tray®,
heat sealed and incubated for 18 - 22 hr at 44.5°C + 0.2° C. A color reaction from
colorless to yellow occurs if the target bacteria are present. Using the heat sealer, the
media is divided between 49 large wells and 48 smaller wells. The number of positive
wells is tallied and multiplied by the dilution factor to determine the MPN. See SOP for
Analysis of Coliform Bacteria, Escherichia coli, and / or Enterococcus by IDEXX
Bacterial Media and Colilert-18 Fecal Coliform Protocol Addendum. Fecal coliforms
will be measured at the beginning, at all or selected sampling time points, and the end of
any experimental run. Fecal coliform distruction or disappearance is a key requirement
in establishing any treated sludge as a Class A product.
5.1.4 Analysis for Salmonella
The Rappaport-Vassiliadis agar medium-semisolid modification (MSRV) protocol in
EPA Method 1682 provides enumeration of Salmonella in biosolids and sludge based on
the MPN technique. The determination of Salmonella involves inoculating the
enrichment medium, tryptic soy broth (TSB), with a measured amount of sample and
incubating for 24 hr. After incubation, TSB is spotted onto the selective MSRV medium.
The MSRV medium uses novobiocin and malachite green to inhibit non-Salmonella
species, while allowing most Salmonella species to grow. Presumptively identified
colonies are isolated on xylose-lysine desoxycholate agar (XLD) and confirmed using
lysine-iron agar (LIA), triple sugar iron agar (TSI), and urease test medium, followed by
positive serological typing using polyvalent O antisera. A total solids determination is
performed on a representative biosolids and sludge sample and is used to calculate
MPN/g dry weight. Salmonella density is reported as MPN/4g dry weight.
5.1.5 Nutrient Analyses
Hach Test Kits and Hach methods will be followed for the analysis of ammonium
nitrogen (Method 10031), TKN (Method 8075), and total phosphorus (Method 8190).
Dilution of the sample may be necessary to obtain results in the linear range of the Hach
Test Kits.
In the ammonium nitrogen method, ammonia compounds combine with chlorine to form
monochloramine. Monochloramine reacts with salicylate to form 5-aminosalicylate.
5-aminosalicylate is oxidized in the presence of a sodium nitroprusside catalyst to form a
blue colored compound. The blue color is masked by the yellow color from the excess
reagent present to give a green-colored solution. Test results are measured by
spectrophotometer at 655 nm.
The TKN procedure involves digesting a sample with sulfuric acid and hydrogen
peroxide to convert organic nitrogen to ammonium sulfate. Using a modified Nessler
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method, ammonia complexes with the reagent to form a yellow coloration
[HgOHg(NH2)I]. Test results are measured by spectrophotometer at 460 nm.
Total phosphorus is determined by converting (hydrolyzing) condensed and organic
phosphorus, to reactive orthophosphate using sulfuric acid, persulfate, and heat.
Orthophosphate reacts with molybdate in the acid medium to produce a mixed
phosphate/molybdate complex. Ascorbic acid reduces the complex to produce an intense
molybdenum color. Test results are measured by spectrophotometer at 880 nm.
COD, defined as mg of oxygen consumed per liter of sample, is analyzed by acidifying
and heating sample with potassium dichromate. Oxidizable organic compounds react to
reduce dichromate (C^O?"2) to green chromic ion (Cr+3), which is then measured by
spectrophotometer at 620 nm. Silver is a catalyst, and mercury is used to complex
chloride interferences.
Table 5.1. Measurement Procedures
Parameter
Total Suspended Solids
Volatile Suspended Solids
Fecal Coliforms
Salmonella
pH
Ammonia Nitrogen
Total Kjeldahl Nitrogen
Phosphorus
Chemical Oxygen
Demand
Measurement
Critical
Critical
Critical
Non-critical
Non-critical
Non-critical
Non-critical
Non-critical
Non-critical
Method
SOP PTS-TSS-VSS
SOP PTS-TSS-VSS
IDEXX Quanti-tray
2000 method
EPA Method 1682
EPA Method 150.1
Hach Method 10031
Hach Method 8075
Hach Method 8 190
Hach Method 8000
Instrument
Drying oven, combustion
oven, analytical balance
(accuracy to 0.0001)
Drying oven, combustion
oven, analytical balance
(accuracy to 0.0001)
IDEXX tray, heat sealer and
black light
Various microbiological
growth media
pH probe and portable pH
meter
Spectrophotometer (655nm)
Spectrophotometer (460nm)
Spectrophotometer (880nm)
Spectrophotometer (620nm)
6. Quality Metrics (QA/QC Checks)
Calculation of relative percent difference (RPD) for replicates:
%RPD = 100*(Xi-X2)/((Xi+X2)/2), where Xi = value from replicate 1; X2 = value from
replicate 2.
Calculation of relative standard deviation (percent coefficient of variation, %-CV)
%CV = 100 * Standard Deviation/Mean
Calculation of analyte accuracy (control check standards)
% Recovery = 100 * (Known Value - Measured Value)/Known Value
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Table 6.1. QA/QC Checks
Analysis
TSS
vss
Fecal
Coliforms
Salmonella
pH
Ammonium
Nitrogen
TKN
Total
Phosphorus
Matrix
Slurry
Slurry
Slurry
Slurry
Slurry
Slurry
Std.
Solution
Slurry
Slurry
Std.
Solution
Slurry
Slurry
Std.
Solution
Slurry
QC Check
Blank
Precision
Blank
Precision
Negative
Control
Positive
Control
Negative
Control
Positive
Control
Instrument
Calibration
Accuracy
Blank
Accuracy
Precision
Blank
Accuracy
Precision
Blank
Accuracy
Precision
Method
Laboratory Blank
Triplicate
Laboratory Blank
Triplicate
Sterile buffer
Spiking of stock
solution in sterile
buffer
Escherichia coli
ATTC 25922
Salmonella
typhimurium
ATTC 14028
2 point calibration
Any of the pH
buffers used for
calibration (pH 4,
7, or 10)
Method
Blank
50mg/L
Duplicate
Method
Blank
l.Omg/L
Duplicate
Method
Blank
80mg/L
Duplicate
Frequency
Per batch
Per sample
Per batch
Per sample
Per batch
Per batch
Per batch
Per batch
Daily prior
to use
Prior to
sample
analysis
Per batch
Twice per
batch
one per
batch
Per batch
Twice per
batch
one per
batch
Per batch
Twice per
batch
one per
batch
Acceptance
Criteria
<2mg/L
85-115%
<2mg/L
85-115%
No wells turn
yellow and
fluorescence
Wells turn
yellow and
fluorescence
No growth in
nutrient
media
Growth in
nutrient
media
Per
manufacturer
Within ±0.5
pH units of
the expected
value
80-120%
75-125%
80-120%
75-125%
80-120%
75-125%
Corrective Action
Look for contamination
issues.
Source of problem
should be identified and
resolved before
continuing analysis.
Look for contamination
issues.
Source of problem
should be identified and
resolved before
continuing analysis.
Use new media vessel
and dilution buffer.
Use new media vessel
and dilution buffer.
If growth, rerun the test
and check growth
media sterility.
If no growth, rerun the
test. Confirm S.
typhimurium was used.
Troubleshoot
instrument.
Inspect/clean electrode.
Recalibrate.
Used to zero out the
instrument.
Investigate
contamination
problems, potential
recalibration.
Used to zero out the
instrument.
Investigate
contamination
problems, potential
recalibration.
Used to zero out the
instrument.
Investigate
contamination
problems, potential
recalibration.
76
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Analysis
COD
Matrix
Slurry
Std.
Solution
Slurry
QC Check
Blank
Accuracy
Precision
Method
Method
Blank
10,OOOmg/L COD
Triplicate
Frequency
Per batch
One per
batch
Per sample
Acceptance
Criteria
80-120%
50-150%
Corrective Action
Used to zero out the
instrument.
Investigate
contamination
problems, potential
recalibration.
7. Data Analysis, Interpretation, and Management
7.1 Data Reporting
Field data will be recorded in a notebook as needed. Analytical data, including replicates and
QA/QC data, will be manually entered into a spreadsheet and double-checked for accuracy of
input. All data will be combined into a single Microsoft Excel file for data reduction and
analysis.
All results will be reduced to the appropriate reporting units designated in the SOPs/ methods
by the analyst performing the test. The reporting units for each analysis are summarized in
Table 7.1. Results will be averaged and the mean, standard deviation, and/or the range will
be calculated.
Table 7.1. Reporting Units
Measurement
TSS
vss
PH
Fecal Coliforms
Salmonella
Ammonium Nitrogen
TKN
TotalPhosphorus
COD
Unit
mg/L
mg/L
pH units
MPN
MPN
mg/L
mg/L
mg/L
mg/L
7.2 Data Reduction and Validation
QC parameters determined from the above methods must be within the required ranges stated
in SOPs and this QAPP or analysis will need to be repeated. Instrumental and experimental
replication and blanks will assess whether the methodologies used were valid. These data
will be reviewed and assessed by the Pegasus On-Site WA Leader. Detected errors will be
corrected and other data in the same set investigated before it is released to the EPA WA
Manager.
7.3 Data Summary and Analysis
For the thermo-oxidative reactor treatments, comparisons will be made between treatments to
determine if there are any differences. The main interest in this research is the final product
of Class A biosolids, determined by the absence of fecal coliforms. If results of the
treatments are found to be 95% similar, no further analysis will be needed. If the treatments
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do not produce the final product of Class A biosolids, no further analysis will be needed. If it
is found that the results are different due to treatment (temperature and/or FbO2
concentration), additional research may be initiated in an attempt to further minimize costs
when the process is possibly utilized on a larger scale.
7.4 Data Storage
Field logs and laboratory records will be maintained in accordance with Section 13.2, Paper
Laboratory Records, of the Office of Research and Development (ORD) Policies and
Procedures Manual. Controlled access facilities that provide a suitable environment to
minimize deterioration, tampering, damage, and loss will be used for the storage of records.
Whenever possible, electronic records will be maintained on a secure network server that is
backed up on a routine basis, such as L:\Public\NRMRL-Pub\Holder\ Thermo-oxidative
process, which is currently in use. Electronic records that are not maintained on a secure
network server will be periodically backed up to a secure second source storage media,
transferred to an archive media (e.g., compact discs, optical discs, magnetic tape, or
equivalent), or printed. Electronic records that are to be transferred for retention will be
transferred to an archive media or printed, as directed by EPA.
8. Reporting
8.1 Monthly Reports
Monthly reports will be prepared by the Pegasus On-Site WA Leader, reviewed by the
Pegasus On-Site Technical Manager and the Pegasus Project Manager, and submitted to EPA
each month. Distribution of the monthly report to other agencies will be at the discretion of
the EPA WA Manager.
8.2 Final Report
The expected final product of this research will be at least a final report and tentatively one
journal article describing the results from the experimental conditions studied.
9. References
Cacho-Rivero, J.A. 2005. Anaerobic digestion of excess municipal sludge. Optimization
for increased solids destruction. Doctor of Philosophy Dissertation, University of Cincinnati,
Cincinnati, OH.
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&EPA
United States
Environmental Protection
Agency
PRESORTED STANDARD
POSTAGES FEES PAID
EPA
PERMIT NO. G-35
Office of Research and
Development (8101R)
Washington, DC 20460
Offal Business
Penalty for Private Use
$300
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