Introduction If nontoxic organic pollutants get discharged into a river, lake or stream, they should be pretty harmless, right?

Wrong! Organic pollutants, even if they have no toxicity, are one of the causes of water pollution because they will have an effect on the dissolved oxygen level in the water. This effect is called BOD or biochemical oxygen demand. Dissolved oxygen is essential to much of the aquatic life, so anything that affects the dissolved oxygen in water should be of concern.

ORGANICS (BOD, COD, TOC) The determination of wastewater quality set forth in environmental permits has been established since the 1970s in a series of laboratory tests focused on four major categories:

Analytical tests aimed at establishing the concentration (typically in mg/L or ppm) of organic (i.e., carbon-containing) matter have traditionally been used to determine the relative “strength” of a wastewater sample. Today there are THREE common laboratory tests used to determine the gross amount of organic matter (i.e., concentrations > 1.0 mg/L) in waste- water: BOD (biochemical oxygen demand) COD (chemical oxygen demand) TOC (total organic carbon) -

Is My WasteWater “HIgH-strengtH”? Wastewater generated by commercial, industrial and institutional facilities is typically referred to as “high-strength” com- pared to typical household wastewater. Table 1 shows the typical concentrations (mg/L) of organics found in untreated domestic wastewater. This table can be used to understand how non-sanitary process wastewater compares to typical domestic wastewater.

BOD amount of oxygen required by bacteria while stabilizing decomposable organic matter under aerobic conditions. Decomposable organic matter that can serve as food for bacteria, and energy is derived from its oxidation BOD measure pollution strength of wastewater or polluted water

BOD the most important analysis for in stream pollution-control activities BOD important in regulatory work BOD test bioassay procedure involving the measurement of oxygen consumed by living organisms (mainly bacteria) while utilizing organic matter present in a waste, under conditions as similar as possible to nature.

Concept for BOD test • Wet oxidation procedure in which living organisms serve as the medium for oxidation of the organic matter to CO2 and water. • Generalized equation:

Theoretically an infinite time is required for complete biological oxidation of organic matter, but for practical purposes, the reaction may be considered complete in 20 days. • But for practical reasons, 5 days was used since large percentage of the total BOD is exerted in 5 days. • 5 days BOD values only represent a portion of the total BOD values. • For most industrial and municipal wastewater, the 5-day BOD value is about 70 to 80 percent of the total BOD.

Environmental engineers are more interested on BOD exerted. Test – using dissolved-oxygen measurements Use 5-day result to total or ultimate BOD (yu) or BOD at some other time: y = BOD at any time t L = total or ultimate BOD k = determine by experiment

Temperature for BOD test • Temperature effects for microbial dynamics are constant at 20oC. • Predominant organisms responsible for the stabilization of organic matter in natural waters are forms native to the soil.

First order kinetics The rate of the reaction is proportional to the amount of oxidizable organic matter remaining at any time, as modified by the population of active organisms Once the population of organisms has reached a level at which only minor variations occur, the reaction rate is controlled by the amount of food available to the organisms:

Changes in organics during biological oxidization of polluted waters under aerobic conditions

Reaction constant Value of k (in some books, ∝) determines the speed of the BOD reaction without influencing the magnitude of the ultimate BOD. • k = 0.1 to 0.5 per day depending on the nature of the organic molecules • Simple sugars have high values of k rate, vice versa.

k is temperature-dependent, because microorganisms are more active at high temperature, where k values are higher.

The BOD curve: (a) Normal curve for oxidization of organics (b) The influence of nitrification

Chemical Characteristics Total Organic Carbon TOC test consists of acidification of the wastewater sample to convert inorganic carbon to CO2 which is then stripped. The sample is then injected into high temperature furnace where it is oxidized in presence of a catalyst. The CO2 that is produced is measured by means of infrared analyzer and converted instrumentally to original organic carbon content. The test is accurate and correlates to BOD well. Certain types of organic matter are oxidizing in TOC test so its valve is less than BOD test. For a typical domestic wastewater BOD5 / TOC ratio varies from 1.0 to 1.6. TOC is not widely used because of the cost of the instrument and the skill necessary in its operation.