EPA-821-R-01-014
January 2001
METHOD 1683
Specific Oxygen Uptake Rate in Biosolids
Draft
January 2001
U.S. Environmental Protection Agency
Office of Water
Office of Science and Technology
Engineering and Analysis Division (4303)
1200 Pennsylvania Ave. NW
Washington, DC 20460
-------
Method 1683
Acknowledgments
This method was prepared under the direction of William A. Telliard of the Engineering and Analysis
Division (BAD) in conjunction within the U.S. Environmental Protection Agency's (EPA's) Office of
Science and Technology (OST). This method was prepared by DynCorp Information and Enterprise
Technology under EPA Contract 68-C-98-139.
Disclaimer
This draft method has been reviewed and approved for publication by the Analytical Methods Staff within
the Engineering and Analysis Division of the U.S. Environmental Protection Agency. Mention of trade
names or commercial products does not constitute endorsement or recommendation for use. EPA plans
further validation of this draft method. The method may be revised following validation to reflect results of
the study. This method version contains minor editorial changes to the February 1999 version.
EPA welcomes suggestions for improvement of this method. Suggestions and questions concerning this
method or its application should be addressed to:
Maria Gomez-Taylor
Engineering and Analysis Division (4303)
U.S. Environmental Protection Agency
1200 Pennsylvania Avenue, NW
Washington, DC 20460
(202)260-7134
Draft- January 2001
-------
Method 1683
Note: This method is intended to be performance based. The laboratory is permitted to modify or omit
any steps or procedure, provided that all performance requirements in this method are met. The
laboratory may not omit any quality control analyses. The terms "shall", "must", and "may not"
indicate steps and procedures required for producing reliable results. The terms "should" and "may"
indicate optional steps that may be modified or omitted if the laboratory can demonstrate that the
modified method produces results equivalent or superior to results produced by this method.
Draft- January 2001
-------
Method 1683
Method 1683
Specific Oxygen Uptake Rate in Biosolids
1.0 Scope and Application
1.1 This method is applicable to the determination of the specific oxygen uptake rate (SOUR) (Section
18.14) in biosolids (Section 18.2) treated in an aerobic process.
1.2 This method is for use in the Environmental Protection Agency's (EPA's) data gathering and
monitoring programs under the Clean Water Act, the Solid Waste Disposal Act, the Resource
Conservation and Recovery Act, the Comprehensive Environmental Response, Compensation, and
Liability Act, and the Safe Drinking Water Act. To confirm approval of this method for use in
compliance monitoring programs, consult the appropriate sections of the Code of Federal
Regulations (Reference 16.1).
1.3 This method was developed by integrating the analytical procedures contained in Standard Method
2710 B (Reference 16.2) with the recommendations described in the EPA Document
"Environmental Regulations and Technology: Control of Pathogens and Vector Attraction in
Sewage Sludge" (Reference 16.3) and the quality control (QC) procedures necessary to ensure the
validity of analytical results. This method is associated with EPA Method 1691: Municipal
Biosolids Sampling Guidance (Reference 16.4).
1.4
This method may not be applicable to sewage sludge (Section 18.11) with higher than two percent
solids or to sewage sludge digested at temperatures lower than 10°C or higher than 30°C.
1.5 Microorganisms in sewage sludge use oxygen as they consume organic matter. The level of
microbial activity in sludge is indicated by the microorganisms' oxygen uptake rate. High oxygen
uptake rates indicate high microbial activity and high organic matter content; low oxygen uptake
rates indicate low microbial activity and low organic matter content.
1.6 This method is performance-based. The laboratory is permitted to omit any step or modify any
procedure, provided that all performance requirements in this method are met. Requirements for
establishing method equivalency are given in Section 9.1.1.
1.7 Each laboratory that uses this method must demonstrate the ability to generate acceptable results
based on the performance criteria given in Section 17.
2.0 Summary of Method
2.1 The sample is maintained at the temperature of the digester from which it was drawn, from the time
of collection until the end of analysis. The sample is kept under aeration if the test cannot be run
expeditiously.
2.2 The total solids content (Section 18.15) of the sample is determined on an aliquot (Appendix A).
2.3 The sample is mixed, and the concentration of dissolved oxygen (DO) (Section 18.3) in the sample
is increased by aeration. An aliquot of the sample is placed in a biological oxygen demand (BOD)
bottle and kept well mixed. Using an oxygen-sensing probe, a manometer, or respirometer, DO is
recorded periodically over a 15-minute period, or until DO becomes rate-limiting (Section 18.10).
Draft- January 2001 1
-------
Method 1683
2.4 The oxygen consumption rate (Section 18.9) is calculated as the absolute value of the slope of the
linear portion of the DO versus time curve when an oxygen probe is used, or from calculations as
specified by the manufacturer of the manometer or respirometer. The SOUR is obtained by
dividing the oxygen consumption rate by total solids. The SOUR for the temperature at which the
aerobic digestion is occurring in the treatment works is corrected to 20 °C, as a standardization for
reporting purposes.
3.0 Definitions
Definitions for terms used in this method are given in the glossary (Section 18).
4.0 Interferences
4.1 SOUR determination is sensitive to the time lag between sample collection and analysis. To
minimize changes in the sample due to microbial activity over time, samples should be analyzed as
soon as possible after collection. The sample should be transported to the laboratory expeditiously
and kept under aeration if the SOUR test cannot be run immediately. The sample must be kept at
the temperature of the digester from which it was drawn.
4.2 This method may not be applicable to samples with total solids above two percent, samples that
remain heterogenous after mixing, and samples that contain solids that do not remain in suspension
and settle to the bottom of the container. In these cases, aeration and mixing are difficult, and the
method yields inconsistent results because samples can not be kept well mixed during analysis.
Although adequate mixing is essential, the samples must not be blended with a homogenizing
instrument. Homogenization is likely to change sample characteristics and the rate of oxygen
uptake significantly.
4.3 The results of the determination of SOUR are extremely sensitive to temperature variations. It is
essential that the SOUR test be performed at the temperature of the digester from which the sample
was drawn, because dissolved oxygen concentration and microbial activity are influenced by
temperature. Poor precision is obtained when duplicate determinations are not made at the same
temperature.
4.4 The SOUR for the sample reflects the temperature of the digester from which it was drawn. This
value is corrected to 20 °C by using Equation 3. The correction is valid only for digester
temperatures between 10°C and 30°C.
4.5 The fixed solids (dissolved inert mineral solids) (Section 18.4) in the wastewater in which the
sludge particles are suspended do not exert an oxygen demand and should not be part of the total
solids in the SOUR determination. Ordinarily, the fixed solids are such a small part of the total
solids that they can be ignored. If it is suspected that there is a high level of fixed solids in the
wastewater (a ratio of fixed to total solids greater than 0.15), the volatile solids content (Section
18.16) should be determined with Method 1684 (Reference 16.5) and be used instead of total solids
in the calculation of SOUR (Equation 2).
4.6 Aeration of the sample to at least 5 mg/L DO is critical. Low DO at the start of the test may limit
oxygen uptake and will be indicated by a decreasing rate of oxygen consumption as the test
progresses. Such data must be rejected as being unrepresentative of SOUR and the test must be
repeated with higher initial DO levels. The sample should be aerated again following procedures in
Section 11.4.
2 Draft-February 1999
-------
Method 1683
4.7 For samples suspected to contain high levels of oxidizable materials:
4.7.1 It is important not to oversupply samples with oxygen during initial sample aeration.
Prolonged aeration may lead to oxidation of significant portions of the organic matter in
the sample and may alter the characteristics of the sample. Procedures in Section 11.4
should be followed closely. After each attempt at sample aeration, DO should be checked.
Once the sample has reached a DO concentration of at least 5 mg/L, the sample should be
analyzed immediately.
4.7.2 High levels of oxidizable materials will result in high levels of microbial activity and rapid
rates of oxygen consumption. Measurements of DO concentration should be taken at
frequent intervals, especially in the first two minutes of the analysis (Section 11.5).
4.8 For calculation of the sample's oxygen uptake rate, only the linear portion of the DO versus time
curve should be used. The curved portion of the line signifies that DO may have become rate-
limiting, and the corresponding values must not be used to determine the oxygen uptake rate.
4.9 Air bubbles trapped among the solids in an aerated sample can cause falsely high DO readings.
Care should be taken to aerate the sample in a manner that does not cause air bubbles to become
entrained in the sample.
4.10 Oxygen probes may not be accurate below 1 mg DO/L. Any data that are recorded at or below 1
mg/L should not be used to calculate oxygen uptake rate.
5.0 Safety
5.1 This method does not address all safety issues associated with its use. Each chemical and
environmental sample should be regarded as a potential health hazard and exposure should be
minimized. The laboratory is responsible for maintaining a safe work environment and a current
awareness file of OSF£A regulations regarding the safe handling of the chemicals specified in this
method. A reference file of material safety data sheets (MSDSs) should be available to all
personnel involved in the chemical analysis. Additional information on laboratory safety can be
found in Reference 16.2 and Reference 16.6.
5.2 All personnel handling environmental samples known to contain or to have been in contact with
human waste should be immunized against known disease causative agents.
6.0 Equipment and Supplies
NOTE: Brand names, suppliers, and part numbers are for illustrative purposes only, and no
endorsement is implied. Equivalent performance may be achieved using apparatus and
materials other than those specified here. Meeting the performance requirements of this
method is the responsibility of the sampling team and laboratory.
6.1 Oxygen-consumption rate measurement device, either:
6.1.1 Probe with an oxygen-sensitive membrane electrode (polarographic or galvanic) OR
Draft- January 2001
-------
Method 1683
6.1.2 Manometer or respirometer with appropriate reporting capabilities and sample capacity of
at least 300 mL. The instrument should have an oxygen supply capacity greater than the
oxygen consumption rate of the sample, or at least 150 mg/L-h.
6.2 Stopwatch or other suitable timing device.
6.3 Thermometer ( ± 0.5°C).
6.4 Glass or plastic bottles of a suitable size (at least 800-mL) for sample collection.
6.5 Biological oxygen demand (BOD) bottles, 300-mL capacity.
6.6 Rubber gloves.
6.7 Magnetic stirring device such as a PTFE-coated stir bar and stirring plate capable of keeping the
sample well mixed during analysis.
7.0 Reagents and Standards
7.1 Reagent water —Deionized, distilled water. Autoclave at 121 °C for 20 minutes to sterilize.
7.2 Sand—Rinse sand. Bake at 400°C for eight hours to sterilize.
8.0 Sample Collection, Preservation, and Storage
8.1 Samples are collected in glass or plastic bottles, provided that the material in the sample does not
adhere to container walls. A volume of at least 700 mL should be collected. Sampling should be
done in accordance with Reference 16.3 and Reference 16.4.
8.2 Samples must be analyzed as soon as possible after sample collection. Samples must be
maintained at the temperature of the digester from which they were drawn from the time of
collection until the end of analysis.
9.0 Quality Control
9.1 Each laboratory using this method is required to operate a formal quality control (QC) program.
The minimum requirements of this program generally include an initial demonstration of
laboratory capability (Section 9.2). In the absence of an appropriate standard for SOUR, the
characterization of the method detection limit (MDL) and initial precision and recovery (IPR) is
not valid. The QC program for this method consists of the ongoing analysis of laboratory reagent
blanks and duplicates (Sections 9.3 and 9.4) as a continuing check on performance. The
laboratory is required to maintain performance records that define the quality of data generated.
Laboratory performance is compared to established performance criteria to determine if the results
of analyses meet the performance characteristics of the method.
9.1.1 In recognition of advances that are occurring in analytical technology, the analyst is
permitted certain options to improve accuracy or lower the costs of measurements,
provided that all performance specifications are met. If an analytical technique other than
the techniques described in this method is used, that technique must have a specificity
4 Draft- February 1999
-------
Method 1683
equal to or better than the specificity of the techniques in this method for standard oxygen
uptake rate in the sample of interest. Specificity is defined as producing results equivalent
to the results produced by this method for laboratory blank samples (Sections 9.3 and
18.5) and, where applicable, duplicate environmental samples (Section 9.4).
9.1.1.1 The laboratory is required to maintain records of modifications made to
this method. These records include the following, at a minimum:
9.1.1.1.1 The names, titles, addresses, and telephone numbers of
the analyst(s) who performed the analyses and
modification, and of the quality control officer who
witnessed and will verify the analyses and modification.
9.1.1.1.2 The analyte measured (SOUR).
9.1.1.1.3 A narrative stating reason(s) for the modification.
9.1.1.1.4 Results from all quality control (QC) tests comparing the
modified method to this method, including:
(a) Calibration (Section 10);
(b) Analysis of blanks (Section 9.3); and
(c) Analysis of duplicates (Section 9.4).
9.1.1.1.5 Data that will allow an independent reviewer to validate
each determination by tracing the instrument output
(weight, DO, or other data) to the final result. These data
are to include:
(a) Sample numbers and other identifiers;
(b) Sample preparation dates;
(c) Analysis dates and times;
(d) Analysis sequence/run chronology;
(e) Sample weight or volume;
(f) Sample temperature (°C);
(g) Copies of logbooks, printer tapes, and other
recordings of raw data; and
(h) Data system outputs and other data to link the
raw data to the results reported.
9.1.2 Analyses of laboratory blanks are required to demonstrate freedom from contamination.
The procedure and criteria for blank analyses are described in Section 9.3.
9.1.3 Analyses of duplicate samples are required to demonstrate method accuracy and precision.
The procedure and criteria for duplicate analyses are described in Section 9.4.
9.2 Initial demonstration of laboratory capability—The initial demonstration of laboratory capability is
generally used to characterize laboratory performance and method detection limits.
9.2.1 Method detection limit (MDL)—In the absence of an appropriate standard for SOUR, the
characterization of the MDL is not valid for this method.
Draft- January 2001
-------
Method 1683
9.2.2 Initial precision and recovery (IPR) — In the absence of an appropriate standard for SOUR,
the characterization of IPR is not valid for this method.
9.3 Laboratory blanks
9.3.1 Prepare and analyze a laboratory blank with each analytical batch (Section 18.1). The
blank must be subjected to the same procedural steps as a sample, and will consist of a 5 g
aliquot of sterile sand (Section 7.2) in 500 mL of sterile reagent water (Section 7.1).
9.3.2 Acceptance criteria for blank analyses will be determined during method validation studies.
9.4 Duplicate analyses
9.4.1 One sample per analytical batch must be analyzed in duplicate. The duplicate analyses
must be performed within the same analytical batch (Section 18.1).
9.4.2 The relative percent difference (RPD) between duplicate samples analyzed for SOUR must
be determined using Equation 1 .
Equation 1
RPD - 200
(Dl +D2)
Where:
Dl = SOUR in the environmental sample (mglg)lh
D2 = SOUR in the duplicate sample (mglg)lh
9.4.3 Acceptance criteria for duplicate analyses will be determined during method validation
studies.
9.5 The following QC analyses are not applicable to this method and are therefore not required:
method detection limit, initial precision and recovery, ongoing precision and recovery, matrix spike,
matrix spike duplicate, calibration verification, and quality control samples.
10.0 Calibration and Standardization
1 0.1 Oxygen probe — Follow manufacturer's calibration procedure exactly. Determine DO
concentration of a sample of reagent water using the membrane electrode method (Reference 16.2).
Calibrate the membrane electrodes with the sample of reagent water of known DO concentration.
When performing multiple analyses, calibration must be checked before each analysis against the
sample of reagent water of known DO concentration.
1 0.2 Manometer or respirometer — Calibrate the meter following manufacturer's calibration procedure
exactly.
Draft- February 1999
-------
Method 1683
11.0 Procedure
11.1 Filter the sample through a 1/4-inch screen to remove large objects.
11.2 Determine total solids (Appendix A).
NOTE: 777/5 method may not be applicable to samples with total solids high enough to
prevent adequate mixing during the analysis (Section 4.2).
11.3 Monitor the temperature of the sample during analysis to ensure that it remains constant. The
sample should have been kept at the temperature of the digester from which it was drawn from the
time of collection until analysis.
11.4 Increase dissolved oxygen (DO) concentration of the sample by shaking it vigorously in a partially
filled bottle or by bubbling air through it for five minutes. Check the DO concentration of the
sample.
11.4.1 If DO is 5 mg/L or greater, the sample is sufficiently aerated. Proceed immediately with
the analysis.
11.4.2 If DO is below 5 mg/L, repeat Section 11.4.
11.4.2.1 If the DO has not increased by more than 0.1 mg/L, the sample is
sufficiently aerated. Proceed immediately with the analysis.
11.4.2.2 If the DO has increased by more than 0.1 mg/L, continue repeating
Section 11.4 until the criterion in Section 11.4.1 or 11.4.2.1 is met.
NOTE: For samples suspected to contain high levels ofoxidizable materials, it is important
not to oversupply samples with oxygen during sample aeration. Procedures in Section 11.4
should be followed closely. After each attempt at sample aeration, DO should be checked.
Once the requirements in Sections 11.4.1 through 11.4.2.2 have been met, the sample should be
analyzed immediately to minimize oxidation of available materials. High levels ofoxidizable
materials will result in high levels ofmicrobial activity in a well-aerated sample.
11.5 Measurement of oxygen uptake rate
11.5.1 Oxygen probe
11.5.1.1 Fill one 300-mL biochemical oxygen demand (BOD) bottle containing a
magnetic stirring bar to overflowing with an appropriate volume of a
representative sample of the aerated sludge to be tested. Containers
should allow for complete mixing and oxygen availability.
11.5.1.2 Immediately insert the oxygen-sensing probe into the BOD bottle.
Displace enough sample with the probe to fill flared top of bottle and
isolate its contents from the atmosphere. Be sure that no large bubbles are
present. Activate the probe stirring mechanism or magnetic stirrer.
Draft- January 2001 7
-------
Method 1683
11.5.1.3 After the meter reading has stabilized, record initial DO reading and start
timing device. Record DO data at 15-second intervals for the first two
minutes of the analysis, then every 60 seconds. Record data over a 15-
minute period or until DO is no longer decreasing at a steady rate,
whichever occurs first. When DO is no longer decreasing at a steady rate,
this could indicate that DO has become rate-limiting.
11.5.1.4 The oxygen probe may not be accurate below 1 mg DO/L. Any data that
are recorded at or below 1 mg/L should not be used to calculate SOUR.
11.5.1.5 When multiple analyses are performed, calibration of the oxygen probe
must be checked before each analysis against a sample of reagent water of
known DO concentration.
11.5.2 Manometer or respirometer
11.5.2.1 Follow manufacturer's instructions for instrument startup, sample
volume, and sample container requirements.
11.5.2.2 After meter reading has stabilized, record initial reading, and start timing
device. Record data at 15-second intervals for the first two minutes of the
analysis, then every 60 seconds. Record data over a 15-minute period or
until DO is no longer decreasing at a steady rate, whichever occurs first.
When DO is no longer decreasing at a steady rate, this could indicate that
DO has become rate-limiting.
11.5.2.3 Refer to manufacturer's instructions for lower limiting DO value.
11.5.2.4 When multiple analyses are performed, instrument calibration must be
checked before each analysis or as recommended by the manufacturer.
For self-calibrating instruments, refer to the manufacturer's instructions.
12.0 Data Analysis and Calculations
12.1 Oxygen probe— Plot observed readings (DO, mg/L) versus time (minutes). Determine the slope
of the linear portion of the curve. The absolute value of the slope is the oxygen consumption rate
in milligrams per liter per minute (mg/L • min). A minimum of five data points in the linear portion
of the DO versus time curve is required to calculate the oxygen uptake rate.
12.2 Manometer or respirometer—Refer to manufacturer's instructions for calculating the oxygen
consumption rate.
12.3 Calculate the specific oxygen consumption rate (SOUR) for the sample, in milligrams per gram per
hour (Equation 2).
Draft- February 1999
-------
Method 1683
Equation 2
60 min
SOURT =
T TS h
Where:
SOURr = specific oxygen uptake rate in the sample, (mglg)lh
OUR = oxygen uptake rate in the sample, (mglmiri)
TS = total solids in the sample, (g)
T = temperature of the sample during digestion and analysis, °C
12.4 The SOUR for the sample will reflect the temperature in the digester from which the sample was
drawn. This value is corrected to 20°C (Equation 3), if the sample temperature is not 20°C. This
correction is applicable only if the sample temperature was between 10 °C and 30 °C and the
sample was maintained at that temperature from the time of collection until the end of analysis
(Section 4.4).
Equation 3
20 T
Where:
SOUR2Q = specific oxygen uptake rate at 20°C, (mglg)lh
SOURr = specific oxygen uptake rate in the sample, (mglg)lh
T = temperature of the sample during digestion and analysis, °C
0 = 1.05 above 20°C
13.0 Method Performance
13.1 Method performance (quality control acceptance criteria) for laboratory blanks and duplicate
samples will be determined during the laboratory validation of this method.
14.0 Pollution Prevention
14.1 Pollution prevention encompasses any technique that reduces or eliminates the quantity or toxicity
of waste at the point of generation. The Environmental Protection Agency has established a
preferred hierarchy of environmental management techniques that places pollution prevention as
the management option of first choice. Whenever feasible, laboratory personnel should use
pollution prevention techniques to address their waste generation. When wastes cannot feasibly be
reduced at the source, the Agency recommends recycling as the next best option.
14.2 For information about pollution prevention that may be applicable to laboratories and research
institutions, consult "Less is Better: Laboratory Chemical Management for Waste Reduction",
available from the American Chemical Society's Department of Government Relations and Science
Policy, 1155 16th Street N.W., Washington D.C. 20036, (202) 872-4477.
Draft- January 2001
-------
Method 1683
15.0 Waste Management
15.1 The laboratory is responsible for complying with all Federal, State, and local regulations governing
waste management, particularly hazardous waste identification rules and land disposal restrictions,
and for protecting the air, water, and land by minimizing and controlling all releases from fume
hoods and bench operations. Compliance with all sewage discharge permits and regulations is also
required. An overview of requirements can be found in Environmental Management Guide for
Small Laboratories (EPA 233-B-98-001).
16.0 References
16.1 Code of Federal Regulations 40, Ch. 1, Part 136, Table IB, Part 141 and 141.23.
16.2 "Standard Methods for the Examination of Water and Wastewater," 18th ed., American Public
Health Association, 1015 15th Street NW, Washington, DC 20005. 1-35: Section 1090 (Safety);
2-77: Section 2710 B (Oxygen Consumption Rate); 4-102: Section 4500 OG (Membrane Electrode
Method). 1992.
16.3 U.S. Environmental Protection Agency, 1992. Environmental Regulations and Technology:
Control of Pathogens and Vector Attraction in Sewage Sludge. Publ 625/R-92/013. Office of
Research and Development, Washington, DC.
16.4 U.S. Environmental Protection Agency, 1998. Method 1691: Municipal Biosolids Sampling
Guidance. Draft, September 1998. Office of Water, Washington, DC.
16.5 U.S. Environmental Protection Agency, 1998. Method 1684: Total, Fixed, and Volatile Solids in
Water, Solids and Biosolids. Draft, October 1998. Office of Water, Washington, DC.
16.6 "Safety in Academic Chemistry Laboratories," American Chemical Society Publication,
Committee on Chemical Safety, 3rd Edition, 1979.
17.0 Tables, Diagrams, Flowcharts, and Validation Data
Tables containing method requirements for QA/QC will be added after the validation study has
been performed.
18.0 Definitions
18.1 Analytical batch—A set of up to 10 samples analyzed during the same eight-hour shift. Each
analytical batch of 10 or fewer samples must be accompanied by a laboratory blank (Section 9.3),
and a duplicate sample (Section 9.4), resulting in a minimum of three analyses (1 sample, 1 blank,
and 1 duplicate sample) and a maximum of 12 analyses.
18.2 Biosolids—The treated residuals from wastewater treatment that can be used beneficially.
18.3 Dissolved oxygen (DO)—The quantity of oxygen present in solution.
18.4 Fixed solids—The residue left in the vessel after a sample is ignited (heated to dryness at 550°C).
10 Draft- February 1999
-------
Method 1683
18.5 Laboratory blank (method blank)—A reference matrix sample consisting of 5 g of sterile sand
(Section 7.2) in 500 mL of sterile reagent water (Section 7.1) that is treated exactly as an
environmental sample including exposure to all glassware, equipment and reagents that are used
with environmental samples. The laboratory blank is used to determine if interferences are present
in the laboratory environment, the reagents, or the apparatus.
18.6 May—This action, activity, or procedural step is neither required nor prohibited.
18.7 May not—This action, activity, or procedural step is prohibited.
18.8 Must—This action, activity, or procedural step is required.
18.9 Oxygen consumption rate (oxygen uptake rate, OUR)—The rate of oxygen usage by
microorganisms in a biological system.
18.10 Rate-limiting—The level of dissolved oxygen is rate-limiting when it is the factor that controls the
rate of oxygen uptake by the microorganisms in a sample.
18.11 Sewage sludge—solid, semi-solid, or liquid residue generated during the treatment process of
domestic sewage in a treatment works.
18.12 Shall—This action, activity or procedural step is required.
18.13 Should—This action, activity, or procedural step is suggested but not required.
18.14 Specific oxygen uptake rate (SOUR)—The mass of oxygen consumed per unit time per unit mass
of total solids in sewage sludge.
18.15 Total solids—The residue remaining after evaporation of liquid from and subsequent drying of a
sample of sewage sludge in an oven at 103°C to 105°C.
18.16 Volatile solids—The weight loss after a sample is ignited (heated to dryness at 550°C).
Determinations of fixed and volatile solids do not distinguish precisely between inorganic and
organic matter because the loss on ignition is not confined to organic matter. It includes losses due
to decomposition or volatilization of some mineral salts.
Draft- January 2001 11
-------
Appendix A - Method 1683
Appendix A: Total Solids in Solids and Biosolids
1.0 Scope and Application
1.1 This procedure is applicable to the determination of total solids in such solid and semisolid samples
as soils, sediments, sludges separated from water and wastewater treatment processes, and sludge
cakes from vacuum filtration, centrifugation, or other sludge dewatering processes.
1.2 This procedure is taken from EPA Method 1684: Total, Fixed, and Volatile Solids in Water,
Solids and Biosolids.
1.3 Method detection limits (MDLs) and minimum levels (MLs) have not been formally established for
this draft procedure. These values will be determined during the validation of Method 1684.
1.4 This procedure is performance based. The laboratory is permitted to omit any step or modify any
procedure (e.g., to overcome interferences, to lower the cost of measurement), provided that all
performance requirements in this procedure are met. Requirements for establishing equivalency
are given in Section 9.1.2 of Method 1683.
1.5 Each laboratory that uses this procedure must demonstrate the ability to generate acceptable results
using the procedure in Section 9.2 of this appendix.
2.0 Summary of Method
2.1 Sample aliquots of 25-50 g are dried at 103 °C to 105 °C to drive off water in the sample.
2.2 The mass of total solids in the sample is determined by comparing the mass of the sample before
and after each drying step.
3.0 Definitions
3.1 Total Solids—The residue left in the vessel after evaporation of liquid from a sample and
subsequent drying in an oven at 103 °C to 105 °C.
3.2 Initial precision and recovery (IPR)—Four aliquots of the diluted PAR analyzed to establish the
ability to generate acceptable precision and accuracy. An IPR is performed the first time this
method is used and any time the method or instrumentation is modified.
3.3 Method detection limit (MDL)—The lowest level at which an analyte can be detected with 99 %
confidence that the analyte concentration is greater than zero.
3.4 Ongoing precision and recovery standard (OPR, also called a laboratory control sample)—A
laboratory blank spiked with known quantities of analytes. The OPR is analyzed exactly like a
sample. Its purpose is to assure that the results produced by the laboratory remain within the
limits specified in this method for precision and accuracy.
3.5 Additional definitions are given in Section 18.0 of Method 1683.
-------
Appendix A - Method 1683
4.0 Interferences
4.1 Sampling, subsampling, and pipeting multi-phase samples may introduce serious errors (Reference
16.1). Make and keep such samples homogeneous during transfer. Use special handling to ensure
sample integrity when subsampling. Mix small samples with a magnetic stirrer. If visible
suspended solids are present, pipet with wide-bore pipets. If part of a sample adheres to the
sample container, intensive homogenization is required to ensure accurate results. When dried,
some samples form a crust that prevents evaporation; special handling such as extended drying
times are required to deal with this. Avoid using a magnetic stirrer with samples containing
magnetic particles.
4.2 The temperature and time of residue drying has an important bearing on results (Reference 16.1).
Problems such as weight losses due to volatilization of organic matter, and evolution of gases from
heat-induced chemical decomposition, weight gains due to oxidation, and confounding factors like
mechanical occlusion of water and water of crystallization depend on temperature and time of
heating. It is therefore essential that samples be dried at a uniform temperature, and for no longer
than specified. Each sample requires close attention to desiccation after drying. Minimize the time
the desiccator is open because moist air may enter and be absorbed by the samples. Some samples
may be stronger desiccants than those used in the desiccator and may take on water. If uptake of
water by a sample is suspected, the operator should weigh the sample to see if gains weight while
in the dessicator. If the sample is indeed taking up water, then a vacuum dessicator should be
used.
4.3 Residues dried at 103 °C to 105 °C may retain some bound water as water of crystallization or as
water occluded in the interstices of crystals. They lose CO2 in the conversion of bicarbonate to
carbonate. The residues usually lose only slight amounts of organic matter by volatilization at this
temperature. Because removal of occluded water is marginal at this temperature, attainment of
constant weight may be very slow.
4.4 Results for residues high in oil or grease may be questionable because of the difficulty of drying to
constant weight in a reasonable time.
4.5 The determination of total solids is subject to negative error due to loss of ammonium carbonate
and volatile organic matter during the drying step at 103 °C to 105 °C. Carefully observe specified
ignition time and temperature to control losses of volatile inorganic salts if these are a problem.
5.0 Safety
5.1 Refer to Section 5.0 of Method 1683 for safety precautions.
6.0 Equipment and Supplies
NOTE: Brand names, suppliers, and part numbers are cited for illustrative purposes only. No
endorsement is implied. Equivalent performance may be achieved using equipment and
materials other than those specified here, but demonstration of equivalent performance that
meets the requirements of this method is the responsibility of the laboratory.
6.1 Evaporating Dishes—Dishes of 100-mL capacity. The dishes may be made of porcelain (90-mm
diameter), platinum, or high-silica glass.
Draft- February 1999 A-3
-------
Appendix A - Method 1683
6.2 Watch glass—Capable of covering the evaporating dishes (Section 6.1).
6.3 Steam bath—For evaporation of liquid samples.
6.4 Desiccator—Moisture concentration in the desiccator should be monitored by an instrumental
indicator or with a color-indicator desiccant.
6.5 Drying oven—Thermostatically-controlled, capable of maintaining a uniform temperature of
103 °C to 105 °C throughout the drying chamber.
6.6 Analytical balance—Capable of weighing to 0.1 mg for samples having a mass up to 200 g.
6.7 Reference weights—2 mg, 1000 mg, and 50 mg class "S" weights.
6.8 Container handling apparatus—Gloves, tongs, or a suitable holder for moving and handling hot
containers after drying.
6.9 Bottles—Glass or plastic bottles of a suitable size for sample collection.
6.10 Rubber gloves.
6.11 No. 7 Cork borer (Optional).
6.12 Dessicant (Optional).
7.0 Reagents and Standards
7.1 Reagent water—Deionized, distilled, or otherwise purified water.
7.2 Quality Control Spiking Solution—If a commercially available standard that contains total solids
can be purchased, the laboratory may use that standard. The laboratory may also prepare a
spiking solution. One possible recipe is given below for a sodium chloride-potassium hydrogen
phthalate standard (NaCl-KHP).
7.2.1 Dissolve 0.10 g sodium chloride (NaCl) in 500 mL reagent water. Mix to dissolve.
7.2.2 Add 0.10 g potassium hydrogen phthalate (KHP) to the NaCl solution (Section 7.2.1) and
mix. If the KHP does not dissolve readily, warm the solution while mixing. Dilute to 1 L
with reagent water. Store at 4°C. Assuming 100% volatility of the acid phthalate ion, this
solution contains 200 mg/L total solids, 81.0 mg/L volatile solids, and 119 mg/L fixed
solids.
8.0 Sample Collection, Preservation, and Storage
8.1 Use resistant-glass or plastic bottles to collect sample for solids analysis, provided that the material
in suspension does not adhere to container walls. Sampling should be done in accordance with
Reference 16.2. Begin analysis as soon as possible after collection because of the impracticality of
preserving the sample. Refrigerate the sample at 4 °C up to the time of analysis to minimize
microbiological decomposition of solids. Preferably do not hold samples more than 24 hours.
A-4 Draft-February 1999
-------
Appendix A - Method 1683
Under no circumstances should the sample be held more than seven days. Bring samples to room
temperature before analysis.
9.0 Quality Control
9.1 Each laboratory using this method is required to operate a formal quality control (QC) program.
The minimum requirements of this program consist of an initial demonstration of laboratory
capability, and the ongoing analysis of laboratory reagent blanks, precision and recovery
standards, and matrix-spiked samples as a continuing check on performance. The laboratory is
required to maintain performance records that define the quality of data thus generated.
Laboratory performance is compared to established performance criteria to determine if the results
of analyses meet the performance characteristics of the method.
9.1.1 The analyst shall make an initial demonstration of the ability to generate acceptable
accuracy and precision with this method. This ability is established as described in
Section 9.2.
9.1.2 In recognition of advances that are occurring in analytical technology, the analyst is
permitted certain options to improve separations or lower the costs of measurements,
provided that all performance specifications are met. If an analytical technique other than
the techniques specified in this method is used, that technique must have a specificity equal
to or better than the specificity of the techniques in this method for total, fixed, and volatile
solids in the sample of interest. Specificity is defined as producing results equivalent to the
results produced by this method for laboratory-prepared solutions (Section 7.2) that meet
all of the QC criteria stated in this method.
9.1.2.1 Each time a modification is made to this method, the analyst is required to
repeat the Initial Precision and Recovery (IPR) test in Section 9.2.2 to
demonstrate that the modification produces results equivalent to or better
than results produced by this method. If the detection limit of the method
will be affected by the modification, the analyst must demonstrate that the
MDL is less than or equal to the MDL in this method or one-third the
regulatory compliance level, whichever is higher. The tests required for
this equivalency demonstration are given in Section 9.2.
9.1.2.2 The laboratory is required to maintain records of modifications made to
this method. These records include the following, at a minimum:
9.1.2.2.1 The names, titles, addresses, and telephone numbers of the
analyst(s) who performed the analyses and modification, and of
the quality control officer who witnessed and will verify the
analyses and modification.
9.1.2.2.2 A listing of pollutant(s) measured (total, fixed, and/or volatile
solids).
9.1.2.2.3 A narrative stating reason(s) for the modification.
9.1.2.2.4 Results from all quality control (QC) tests comparing the
modified method to this method, including:
Draft-February 1999 A-5
-------
Appendix A - Method 1683
(a) Initial precision and recovery (Section 9.2.2).
(b) Analysis of blanks (Section 9.3).
(c) Accuracy assessment (Section 9.5).
(d) Ongoing precision and recovery (Section 9.4).
9.1.2.2.5 Data that will allow an independent reviewer to validate each
determination by tracing the instrument output (weight,
absorbance, or other signal) to the final result. These data are to
include:
(a) Sample numbers and other identifiers.
(b) Sample preparation dates.
(c) Analysis dates and times.
(d) Analysis sequence/run chronology.
(e) Sample weights.
(f) Make and model of analytical balance and weights
traceable to NIST.
(g) Copies of logbooks, printer tapes, and other recordings of
raw data.
(h) Data system outputs, and other data to link the raw data
to the results reported.
9.1.3 Analyses of laboratory blanks are required to demonstrate freedom from contamination.
The procedure and criteria for blank analyses are described in Section 9.3.
9.1.4 Analyses of ongoing precision and recovery (OPR) samples are required to demonstrate
that the sample preparation and analysis are in control. The procedure and criteria for
OPR samples are described in Section 9.4.
9.2 Initial demonstration of laboratory capability - The initial demonstration of laboratory capability is
used to characterize laboratory performance and method detection limits.
9.2.1 Method detection limit (MDL) - The method detection limit should be established for total
solids using the QC spiking solution (Section 7.2). To determine MDL values, take seven
replicate aliquots of the diluted QC spiking solution and process each aliquot through each
step of the analytical method. Perform all calculations and report the concentration values
in the appropriate units. MDLs should be determined every year or whenever a
modification to the method or analytical system is made that will affect the method
detection limit.
9.2.2 Initial Precision and Recovery (IPR) - To establish the ability to generate acceptable
precision and accuracy, the analyst shall perform the following operations:
9.2.2.1 Prepare four samples by diluting the QC spiking solution (Section 7.2) to
1-5 times the MDL. Using the procedures in Section 11, analyze these
samples for total solids.
9.2.2.2 Using the results of the four analyses, compute the average percent
recovery (x) and the standard deviation (s, Equation 1) of the percent
recovery for total solids.
A-6 Draft-February 1999
-------
Appendix A - Method 1683
Equation 1
s=
»-l
Where:
n = number of samples
x = % recovery in each sample
s = standard deviation
9.2.2.3 Compare s and x with the corresponding limits for initial precision and
recovery in Table 2 (to be determined in validation study). If s and x meet
the acceptance criteria, system performance is acceptable and analysis of
samples may begin. If, however, s exceeds the precision limit or x falls
outside the range for recovery, system performance is unacceptable. In
this event, correct the problem, and repeat the test.
9.3 Laboratory blanks
9.3.1 Prepare and analyze a laboratory blank initially (i.e. with the tests in Section 9.2) and with
each analytical batch. The blank must be subjected to the same procedural steps as a
sample, and will consist of approximately 25 g of reagent water.
9.3.2 If material is detected in the blank at a concentration greater than the MDL (Section 1.3),
analysis of samples must be halted until the source of contamination is eliminated and a
new blank shows no evidence of contamination. All samples must be associated with an
uncontaminated laboratory blank before the results may be reported for regulatory
compliance purposes.
9.4 Ongoing Precision and Recovery
9.4.1 Prepare an ongoing precision and recovery (OPR) solution identical to the IPR solution
described in Section 9.2.2.1.
9.4.2 An aliquot of the OPR solution must be analyzed with each sample batch (samples started
through the sample preparation process (Section 11) on the same 12-hour shift, to a
maximum of 10 samples).
9.4.3 Compute the percent recovery of total solids in the OPR sample.
9.4.4 Compare the results to the limits for ongoing recovery in Table 2 (to be determined in
validation study). If the results meet the acceptance criteria, system performance is
acceptable and analysis of blanks and samples may proceed. If, however, the recovery of
total solids falls outside of the range given, the analytical processes are not being
performed properly. Correct the problem, reprepare the sample batch, and repeat the OPR
test. All samples must be associated with an OPR analysis that passes acceptance criteria
before the sample results can be reported for regulatory compliance purposes.
Draft- February 1999 A-7
-------
Appendix A - Method 1683
9.4.5 Add results that pass the specifications in Section 9.4.4 to IPR and previous OPR data.
Update QC charts to form a graphic representation of continued laboratory performance.
Develop a statement of laboratory accuracy for each analyte by calculating the average
percent recovery (R) and the standard deviation of percent recovery (SR). Express the
accuracy as a recovery interval from R-2SR to R+2SR. For example, if R=05% and
SR=5%, the accuracy is 85-115%.
9.5 Duplicate analyses
9.5.1 Ten percent of samples must be analyzed in duplicate. The duplicate analyses must be
performed within the same sample batch (samples whose analysis is started within the
same 12-hour period, to a maximum of 20 samples).
9.5.2 The total solids of the duplicate samples must be within 10%.
10.0 Calibration and Standardization
10.1 Calibrate the analytical balance at 2 mg and 1000 mg using class "S" weights.
10.2 Calibration shall be within ± 10% (i.e. ±0.2 mg) at 2 mg and ± 0.5% (i.e. ±5 mg) at 1000 mg. If
values are not within these limits, recalibrate the balance.
10.3 Place a 50 g weight and a 2 g weight on the balance. Verify that the balance reads 50.002 ±10%
(i.e., ±0.2 mg).
11.0 Procedure
11.1 Preparation of evaporating dishes-Heat dishes and watch glasses at 103 °C to 105 °C for 1 hour in
an oven. Cool and store the dried equipment in a desiccator. Weigh each dish and watch glass
prior to use (record combined weight as "Wdlsh").
11.2 Preparation of samples
11.2.1 Fluid samples-If the sample contains enough moisture to flow readily, stir to homogenize,
place a 25 to 50 g sample aliquot on the prepared evaporating dish. If the sample is to be
analyzed in duplicate, the mass of the two aliquots may not differ by more than 10%.
Spread each sample so that it is evenly distributed over the evaporating dish. Evaporate the
samples to dryness on a steam bath. Cover each sample with a watch glass, and weigh
(record weight as "Wsample").
NOTE: Weigh wet samples quickly because wet samples tend to lose weight by evaporation.
Samples should be weighed immediately after aliquots are prepared.
11.2.2 Solid samples-If the sample consists of discrete pieces of solid material (dewatered
sludges, for example), take cores from each piece with a No. 7 cork borer or pulverize the
entire sample coarsely on a clean surface by hand, using rubber gloves. Place a 25 to 50 g
sample aliquot of the pulverized sample on the prepared evaporating dish. If the sample is
to be analyzed in duplicate, the mass of the two aliquots may not differ by more than 10%.
A-8 Draft-February 1999
-------
Appendix A - Method 1683
Spread each sample so that it is evenly distributed over the evaporating dish. Cover each
sample with a watch glass, and weigh (record weight as "Wsample").
11.3 Dry the samples at 103 °C to 105 °C for a minimum of 12 hours, cool to balance temperature in an
individual desiccator containing fresh desiccant, and weigh. Heat the residue again for 1 hour, cool
it to balance temperature in a desiccator, and weigh. Repeat this heating, cooling, desiccating, and
weighing procedure until the weight change is less than 5% or 50 mg, whichever is less. Record
the final weight as "Wtotal."
NOTE: It is imperative that dried samples be weighed quickly since residues often are very
hygroscopic and rapidly absorb moisture from the air. Samples must remain in the dessicator
until the analyst is ready to weigh them.
12.0 Data Analysis and Calculations
12.1 Calculate the % solids or the mg solids/kg sludges for total solids (Equation 2).
Equation 2
W - W
% total solids = — ^ - £fL x 100
W , ~ ,.,
sample dish
or
mg tOtal SOlidS W total
^ QQQ QQQ
kg sludge Wsample - Wdish
Where:
W sam le = Weight of wet sample and dish (mg)
^ total = Weight of dried residue and dish (mg)
Wd,sh = Weight of dish (mg)
12.2 Sample results should be reported as % solids or mg/kg to three significant figures. Report results
below the ML as < the ML, or as required by the permitting authority or in the permit.
13.0 Method Performance
13.1 Method performance (MDL and quality control acceptance criteria) will be determined during the
multi-lab validation of this method.
13.2 Total solids duplicate determinations must agree within 10% to be reported for permitting
purposes. If duplicate samples do not meet this criteria, the problem must be discovered and the
sample must be run again.
14.0 Pollution Prevention
14.1 Pollution prevention details are given in Section 14 of Method 1683.
Draft- February 1999 A-9
-------
Appendix A - Method 1683
15.0 Waste Management
15.1 Waste management details are given in Section 15 of Method 1683.
16.0 References
16.1 "Standard Methods for the Examination of Water and Wastewater," 18th ed. and later revisions,
American Public Health Association, 1015 15th Street NW, Washington, DC 20005. 1-35:
Section 1090 (Safety), 1992.
16.2 U.S. Environmental Protection Agency, 1992. Control of Pathogens and Vector Attraction in
Sewage Sludges. Publ 625/R-92/013. Office of Research and Development, Washington, DC.
17.0 Tables, Diagrams, Flowcharts, and Validation Data
17.1 Tables containing method requirements for QA/QC will be added after the validation study has
been performed.
A-10 Draft- February 1999
------- |