S-EPA
United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-084 July 1981
Project Summary
Facultative Lagoon Effluent
Polishing Using Phase
Isolation Ponds
E. Corbin McGriff, Jr.
The performance of "phase isola-
tion" lagoons was investigated at
Clinton, Mississippi, from May 1978
to May 1979. The study system con-
sisted of two facultative lagoons ar-
ranged in series followed by two
isolation ponds used alternately for
final polishing. The isolation ponds
were operated on a fill and draw basis
with isolation periods varying from 20
to 44 days.
The study indicated that phase
isolation would not consistently meet
the National Permit Discharge Effluent
System (NPDES) limitations of 15
mg/L-BODs, 30 mg/L-TSS, and 5
mg/L-TKN-N established for Clinton.
The isolation process did, however,
demonstrate its ability to produce the
following average effluent: pond 1,11
mg/L-BODs, 39 mg/L-TSS, and 3.7
mg/L-TKN-N; and pond 2, 13 mg/L-
BODs, 36 mg/L-TSS, and 3.9 mg/L-
TKN-N.
The Project Summary was devel-
oped by EPA's Municipal Environmen-
tal Research Laboratory, Cincinnati,
OH, to announce key findings of the
research project that is fully docu-
mented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
General History
Since the passage of the Federal
Water Pollution Control Act (PL 92-500}
in 1972, most cities and communities
have been required to upgrade their
existing treatment systems. A number
of communities have opted to use
facultative lagoon systems to meet the
secondary standards; for the most part,
however, it has been the small com-
munity whose economics dictate this
type of treatment.
A number of existing municipal lagoon
systems will not be able to comply with
EPA's secondary treatment standards
for municipal installations. The regula-
tions state that the effluent BOD5 and
suspended solids should not exceed an
arithmetic mean value of 30 mg/L on
samples collected in 30 consecutive
days. A final amendment to the second-
ary treatment regulation allows a case-
by-case adjustment in suspended solids
limitations for publicly owned stabiliza-
tion ponds if the following applies: the
pond has a design capacity of 2 mgd or
less, ponds are the sole process for
secondary treatment; and the pond
meets BOD limitations.
To assist the small community in
complying with the PL 92-500 standard
for secondary treatment, researchers
have investigated various concepts for
upgrading the basic lagoon system. One
such concept, termed "phase isolation"
by its originators in Woodland, California,
was reported to enhance existing lagoons
by isolating the effluent before discharge.
The system consisted of conventional
facultative ponds in series with a final
isolation pond operated on a fill and
dram basis. The isolation pond was
capable of producing a relatively solids-
-------
free upper water strata, that, when
discharged, would meet secondary
standards.
Because of the simplicity of phase
isolation demonstrated in California,
Clinton, Mississippi, was selected for a
demonstration project to evaluate the
isolation concept in a different geo-
graphical location. Clinton had been
issued the following NPDES limitations
based on a monthly average: BODs, 15
mg/L; SS (or TSS), 30 mg/L; TKN, 5
mg/L; and fecal coliform, 200/100 ml.
Project Scope and Objectives
The study was designed to evaluate
the phase isolation process on a seasonal
basis and to determine its applicability
in meeting local as well as national
standards Two existing facultative
ponds arranged in series were connected
to two isolation cells. Effluent from the
series facultative ponds was discharged
to either of the isolation ponds on an
alternate basis for final treatment.
Because of budget and pond configura-
tion constraints, a single isolation pond
depth was maintained throughout each
isolation pond. The effluent was isolated
from 20 to 44 days before being dis-
charged depending on the in situ water
quality. At the end of each isolation
cycle, the pond upper strata was dis-
charged and evaluated for effluent
quality
To evaluate the phase isolation
process, the following specific objec-
tives were outlines
1 To monitor biological, chemical, and
physical parameters during each
isolation cycle and during final
drawdown.
2. To determine whether the isolation
process will produce an effluent that
consistently meets Clinton's NPDES
limitations and the national EPA
secondary standards
Description of Study System
Clinton is a community of 15,500
people located about 10 miles west of
Jackson, Mississippi, and about 35
miles east of the Mississippi River.
Clinton's climate is significantly humid
during most of the year, with a relatively
short, cold season and a long, warm
season The proximity of the Gulf of
Mexico, about 150 miles south, and the
prevalence of southerly winds amounts
to a maritime characteristic during the
warm season.
Clinton currently uses four separate
facultative lagoons and one mechanical
treatment plant to treat approximately
18,248 mVday of domestic wastewater.
The existing treatment units are located
at various natural collection points
throughout the city. Clinton's one in-
dustrial park treats its own wastewater
and is totally separate from the munici-
pal system Except for a number of
typical commercial users, the municipal
system handles domestic wastewater.
The southwest facultative lagoon sys-
tem was selected as the study site
because of its convenient configuration,
with ponds 3 and 4 in series handling
city wastewater (Figure 1). Ponds 1 and
2, constructed for future expansion and
unused before this study, received the
Wastewater
Influent
effluent from pond 4 on an alternate,
basis where it was held from 20 to 44'
days.
The isolation ponds were separated
from the facultative ponds by typical
earthen dikes. A positive control valving
system was installed to divert effluent to
either isolation pond as required by the
study The facultative effluent was
introduced to the isolation ponds near
the center of each pond. Each isolation
pond was equipped with a typical control
structure that was adjusted according to
the drawdown requirements. Once the
drawdown level was reached, the dis-
charge valve was shut off and the fill
cycle was initiated.
Facultative Pond #3
1.85 ha
1S1* 752
• •
Isolation Pond # 1
2.03 ha
7 S3
B>
Facultative Pond #4
1.88 ha
2S7 2S2 2 S3
• • •
Isolation Pond #2
7.95 ha
/ V
*Sampling Locations
North
Figure 1. Facultative and isolation pond arrangement at Clinton, Mississippi.
-------
Discussion of Results
Isolation Pond Performance
Initially both isolation ponds were
filled with facultative pond effluent to an
operating study depth of approximately
1.83 meters, a depth selected because
of physical and economic constraints.
Pond 1 was filled first and began the
isolation period on May 24, 1978; pond
2 was started on June 21, 1978. Sub-
sequent isolation cycles were operated
by fill and drawdown control. At the
beginning of each isolation cycle, the
ponds were filled with a quantity of
facultative pond effluent equal to the
previous drawdown to maintain a study
depth of 1 83 meters. The isolation
period began when the study pond
reached the operating depth and was
terminated on the day of drawdown. On
an average concentration basis, isolation
pond 1 received 42 mg/L BOD5, 61
mg/L TSS, 17.6 mg/L TKN, and pond 2
received 54 mg/L BOD5, 57 mg/L TSS,
and 17.6 mg/L TKN.
In an effort to evaluate the perform-
ance of the study system, a broad list of
parameters, both total and soluble
forms, was used. The key parameters
used to evaluate the period of isolation
were BOD5, TSS, and TKN. The faculta-
tive pond effluent was held in isolation
until one or more of the following
decision points occurred: (1) the water
column concentration of TSS and BODs
decreased to a level below 30 mg/L and
15 mg/L, respectively; (2) the minimal
level of TSS and BODs was attained, and
these parameters appeared to be on the
increase; or (3) the facultative ponds
attained the maximum operational
capacity. Except for the initial isolation
period for each pond, this protocol was
followed In most cases, once it appeared
that a minimal level had been attained,
the effluent was held for a few more
days to establish the stability of the
water column quality. Using these
criteria as decision points during the
study, the isolation cycles, which varied
from 20 to 44 days, were measured
from the end of one fill to the beginning
of the drawdown. Each isolation cycle or
holding pond varied in duration depend-
ing upon evaluation of in situ quality.
During the study period, eight cycles
were evaluated for pond 1 and seven
cycles for pond 2.
Performance Summary
It appears that the phase isolation
process can, at times, produce an
effluent that will meet the NPDES
limitations for Clinton, Mississippi. As
demonstrated during this study, how-
ever, the process is not consistent in its
performance and should not be con-
sidered as a final process unit. Pond 1
produced an effluent that complied with
the NPDES limitations four out of eight
discharge cycles for TSS and seven out
of eight discharge cycles for BODs and
TKN. Pond 2 was in compliance two out
of eight discharge cycles for TSS, four
out of eight for BODs, and eight out of
eight for TKN. Both ponds complied with
the NPDES limits for dissolved oxygen,
fecal coliforrn, and pH. A significant
correlation between the area rainfall
and effluent BODs and TSS indicates
sensitivity of the process to climatic and
seasonal conditions.
A multiple regression equation with a
correlation coefficient of 0.935 provides
a predictive tool for effluent suspended
solids as a function of secchi depth,
TSS, BODs, COD, TOC, organic nitrogen,
ammonia nitrogen, nitrite and nitrate
nitrogen, and total phosphorus. A cor-
relation matrix showed a relationship
between the effluent suspended solids
and in situ secchi depth, suspended
solids, nitrate nitrogen, and total phos-
phorus.
Microscopic examinations revealed
the algal form of Chlorella to appear
most often in both isolation ponds, with
Oscillatoria, Ankistrodesmus, Pediastrum,
and Ulothrix dominating to a lesser
degree.
The full report was submitted in ful-
fillment of Grant No. R-805296 by
Environmental Protection Systems,
Inc., subcontractor to the City of Clinton,
MS, under the sponsorship of the U.S.
Environmental Protection Agency.
E, Corbin McGnff, Jr. is with Environmental Protection Systems, Inc., Jackson,
MS 39209.
Ronald F. Lewis is the EPA Project Officer (see below).
The complete report, entitled "Facultative Lagoon Effluent Polishing Using
Phase Isolation Ponds," (Order No. PB 81-205 965; Cost: $14.00, subject to
change) will be available only from:
National Technical Information Service
5285 Port Floy at Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
> US GOVERNMENT PRINTING OFFICE 1961 -757-012/7193
-------
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use S300
RETURN POSTAGE GUARANTEED
Third-Class
Bulk Rate
^
'
M
------- |