Application - Wastewater Chemistries - Secondary Treatment

Most Frequently Asked Questions  


Parameter Purpose of Test Method
BOD5 Provides a relative measure of "food" available, the degree of stabilization of the wastewater and to estimate the effect of the effluent on the receiving water body. Used for plant loading/design, discharge rate for industrial facilities, and EPA NPDES reporting. 5 day test is too long for process control — many plants use COD or TOC as early estimate. Used to calculate % removal. 8043
8215
8229
Turbidity
Surrogate measurement for solids concentration. Often used to indicate solids carry-over from secondary clarifiers. Turbidimeter (2100xx) See instrument manual
pH
Maintain proper (narrow) pH range for optimal biological processes — especially nitrification. Can indicate plant upsets by industrial discharges or development of anaerobic conditions within the plant. Important condition for methane formation and avoiding ammonia toxicity in sludge digesters. pH meter & electrode - see instrument manual
 
Solids Most commonly measured and regulated parameter on NPDES permits. Used to measure mixed liquor suspended solids concentration, return activated sludge/waste activated sludge concentration, influent suspended solids concentration, effluent suspended solids concentration, and % removal. 8006
COD
Chemical Oxygen Demand
Used as a correlative/ early indicator of BOD levels. Some NPDES permits include COD as a surrogate for BOD; however, BOD is the standard reportable parameter for oxygen demand in municipal wastewater. COD provides a measure of organic "food" available to biological treatment steps and to estimate the effect of the effluent on the receiving water. (Note: Can be correlated to BOD on a plant-by-plant basis, if influent characteristics are constant.) 8000
10067
Nitrite, LR Indicative of the stage of conversion of ammonia and organic nitrogen forms to nitrate by the aerobic biological treatment steps (nitrification). Nitrite is the intermediate nitrogen form between ammonia and nitrate. Nitrite is highly toxic, and small amounts can upset the delicate biology of a wastewater plant. 8507
10019
10207
Ammonia Monitor conversion of ammonia and organic nitrogen forms to nitrite and nitrate during the WW treatment process. Provices information on process conditions in biological treatment stages. At high concentrations an pH, ammonia can be toxic to sludge digestion microbes. 8038
10031
10205
Nitrate, HR Indicative of the stage of conversion of ammonia and organic nitrogen forms to nitrate by the aerobic biological treatment steps (nitrification). 8039
10020
10206
Phosphate, Reactive LR Phosphorus effluent concentrations are often controlled by discharge permits, to limit addition of nutrients to the receiving body. Phosphate is removed via biological nutrient removal prcesses and/or chemical precipitation. Reactive (ortho) phosphate is the phosphorus form that is most available to biological species. Total Phosphate includes ortho-, poly-, and organic forms. 8048
8178
10209
Alkalinity Maintain buffering to mediate effects of acidic industrial discharges. Control nitrification conditions in secondary treatment processes. Maintain proper bacterial conditions in sludge digester. 8203
8221
Oxygen, Dissolved Measured to control aeration and save money. Also measures the amount of available oxygen for aquatic life in the effluent. DO is also commonly measured reportable parameter on NPDES permits. 8166
8215
8229
8316
8332
8333
Phosphate, Total LR Phosphorus effluent concentrations are often controlled by discharge permits, to limit addition of nutrients to the receiving body. Phosphate is removed via biological nutrient removal prcesses and/or chemical precipitation. Reactive (ortho) phosphate is the phosphorus form that is most available to biological species. Total Phosphate includes ortho-, poly-, and organic forms. 8190
10209
10210

Also Consider  

Parameter Purpose of Test Method
Metals Nickel, Molybdenum, Lead, Mercury, Zinc, Chromium, Copper, Arsenic — Measure heavy metal concentrations in effluent waters and ensure compliance with NPDES permit. Of concern in effluents and land-applied biosolids due to potential toxicity.  
Nitrogen, Total Total of ammonia, nitrate, nitrite, and organic nitrogen forms. 10071
10072
10208
Nitrite, HR Indicative of the stage of conversion of ammonia and organic nitrogen forms to nitrate by the aerobic biological treatment steps (nitrification). Nitrite is the intermediate nitrogen form between ammonia and nitrate. Nitrite is highly toxic, and small amounts can upset the delicate biology of a wastewater plant. 8153
10237
TKN
Total Kjeldahl Nitrogen
Total of organic and ammonia forms of nitrogen. 8075
Flow Measure standard in-pipe flow rate for NPDES permit requirements and to establish concentrations/total presence of key analytes.  
Nitrate, LR Indicative of the stage of conversion of ammonia and organic nitrogen forms to nitrate by the aerobic biological treatment steps (nitrification). 8192