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Chapter 27 : Assessing the Efficiency of Wastewater Treatment
The purpose of wastewater (WW) treatment is to prevent water pollution and thereby protect public health and preserve the value of the receiving water (RW) as a resource. This chapter talks about evaluation of the overall performance of the entire wastewater treatment plant (WWTP) and not with the performance of individual unit processes. The emphasis of the chapter is on an overall evaluation of WWTP treatment efficiency. The objectives of WW treatment, the concepts of efficiency and effectiveness of WW treatment, and the difference between WW treatment processes and sludge treatment processes are reviewed to establish a context for the discussion. Limits for the parameters discussed in the chapter are often conditions of National Pollutant Discharge Elimination System (NPDES) permits. The study was designed to find how new ways of measuring water pollution at bathing beaches can be effectively used to protect swimmer's health. A method for predicting the rate of consumption of dissolved oxygen (DO) by microorganisms in the RW body is essential for assessment of the potential of a final effluent (FE) to cause pollution. Mathematical models are used to extrapolate biochemical oxygen demand (BOD)5 results both to deoxygenation of the receiving water (RW) and to substrate concentration in WW. The chemical oxygen demand (COD) test was developed because the BOD5 test requires 5 days for completion and therefore is not suitable either for operational control of treatment processes or for real-time evaluation of the efficiency of WWTP performance.
The BOD5 test for evaluating the effectiveness of wastewater treatment is carried out by incubating diluted samples of wastewater and effluent in sealed bottles for 5 days at 20°C and measuring the oxygen depletion.
Curve representing oxygen consumption versus time during the exertion of first-stage BOD.
Bioassays for toxicity of wastewater and effluents using fish require large amounts of laboratory space and technician time. Shown are the steps and equipment needed for a P. promelas larval survival and growth test.
Diagram of a basic test procedure for a toxicity bioassay using an alga.
Parameters of water pollution
Summary of test preparations, test conditions, and test acceptability criteria for the green alga [S. capricornutum (P. subcapitiata)] Printz algal assay bottle test
Comparison of various types of WET tests