Table 7111 Oxygen Demand And Organic Carbon Parameters

Parameter Description

BOD5 Biochemical or biological oxygen demand exerted in 5 days; the oxygen consumed by a waste through bacterial action; generally about 45-55% of THOD.

COD Chemical oxygen demand. The amount of strong chemical oxidant (chromic acid) reduced by a waste; results are expressed in terms of an equivalent amount of oxygen; generally about 80% of THOD.

THOD Theoretical oxygen demand. The amount of oxygen theoretically required to completely oxidize a compound to CO2, H2O, PO4 3, SO4 2, and NO3.

TOC Total organic carbon; generally about 30% of THOD.

BODl The ultimate BOD exerted by a waste in an infinite time.

IOD Immediate oxygen demand. The amount of oxygen consumed by a waste within 15 min (chemical oxidizers and bacteria not used).

Source: R.A. Corbitt, 1990, Wastewater disposal, Chap. 6 in Standard handbook of environmental engineering, edited by R.A. Corbitt (New York: McGraw-Hill Publishing Company).

lutants are subject to discharge standards. Examples of priority pollutants and their health-related concerns are listed in Table 7.1.12.

Pathogenic organisms in wastewater can be categorized as bacteria, viruses, protozoa, and helminths; Table 7.1.13 lists examples of such organisms present in raw domestic wastewater. Because of the many types of pathogenic organisms and the associated measurement difficulties, col-iform organisms are frequently used as indicators of human pollution. On a daily basis, each person discharges from 100 to 400 billion coliform organisms, in addition to other kinds of bacteria (Metcalf and Eddy, Inc. 1991). In terms of the indicator concept, the presence of coliform organisms indicates that pathogenic organisms may also be present, and their absence indicates that the water is free from disease-producing organisms (Metcalf and Eddy, Inc. 1991). Total coliform and fecal coliform are often used as indicators of wastewater effluent disinfection.

The quantities of fecal coliform (FC) and fecal streptococci (FS) discharged by humans are significantly different from the quantities discharged by animals. As a result, the ratio of the FC count to the FS count can show whether the suspected contamination derives from human or animal waste. Table 7.1.14 gives example data on the ratio of FC to FS counts for humans and various animals. The FC/FS ratio for domestic animals is less than 1.0; whereas the ratio for humans is more than 4.0.

Some differences can be delineated between municipal and industrial wastewater discharges. For example, fluctuations in industrial wastewater flow rates typically exceed those for municipal wastewater. Industrial plants may not operate continuously; there may be daily, weekly, or seasonal variations in operations, reflected by flow rate variations. In addition, the number and types of contaminants in industrial wastewater can vary widely, and the concentrations can range from near zero to 100,000 mg/l

O_ Nitrosomonas

HNO2 + O2 Nitrobacter HNO3 + biomass rrrrr

â– Carbonaceous oxygen demand

O_ Nitrosomonas

HNO2 + O2 Nitrobacter HNO3 + biomass rrrrr

â– Carbonaceous oxygen demand

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