Wastes oxygen-demanding

Oxygen-demanding wastes Plant and animal material... 

Sewage and other oxygen-demanding wastes are termed as water pollutants because ... 

The rate of bacterial oxidation at any instant is proportional to the amount of the oxygen-demanding wastes left at that instant, i.e., the reaction follows First Order Kinetics and theoretically should be completed in infinite time. It has however been found that nearly 70 to 80% of the total BOD is exerted in the first five days. The sample is therefore incubated for 5 days at 20 C (roughly a mean value of temperatures of natural bodies of water) and the BOD values are reported as BOD5. A polluted sample may consume more oxygen in 5 days than present in water (nearly 9 mg/1 at 20°C) and so, before analysis, is diluted with a specially prepared Dilution Water . The diluted sample is taken in two bottles. The dissolved oxygen (D.O.) in one bottle is delennined immediately and in the other after 5 days of incubation. The BOD of the sample is then given by... 

Another test is the total oxygen demand (TOD) test, which oxidizes the waste in the presence of a catalyst at 900°C in a stream of air. Under these harsh conditions, all the carbon is oxidized to CO2. The oxygen demand is calculated from the difference in oxygen content of the air before and after oxidation. The resulting value of TOD... 

If the composition of the waste stream is known, then the theoretical oxygen demand can be calculated from the appropriate stoichiometric equations. As a first level of approximation, we can assume that this theoretical oxygen demand would be equal to the COD. Then, experience with domestic sewage indicates that the average ratio of COD to BOD will be on the order 1.5 to 2. The following example will help to clarify these relationships. 

Several methods have been developed to estimate the oxygen demand in waste water treatment systems. Commonly used laboratory methods are biochemical oxygen demand (BOD), chemical oxygen demand (COD), total oxygen demand (TOD), total organic carbon (TOC), and theoretical oxygen demand (ThOD). 

The radicals are then involved in oxidations such as formation of ketones (qv) from alcohols. Similar reactions are finding value in treatment of waste streams to reduce total oxidizable carbon and thus its chemical oxygen demand. These reactions normally are conducted in aqueous acid medium at pH 1—4 to minimize the catalytic decomposition of the hydrogen peroxide. More information on metal and metal oxide-catalyzed oxidation reactions (Milas oxidations) is available (4-7) (see also Photochemical technology, photocatalysis). 

Sewer Disposal. Photoprocessing and printing wastes tend to be aqueous solutions that ate combined with other plant effluents and sent to the local sewer plant for treatment. The parameters of concern include silver, pH, and biological oxygen demand (BOD). BOD is a measure of how well a waste material degrades in the environment. Lower values ate preferred. Silver-bearing waste streams ate typically treated on-site, and the treated effluent is released to the drain. The printer usually receives a small cash credit for silver recovered. 

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