How much oxygen is attually consumed depends on the extent to which the waste is biodegradable, that is. amenable to oxidation by microbes. Ammonia is totally biodegradable, and thus the theoretical nitrogenous oxygen demand (NOD) and the nitrogenous biochemical oxygen demand ultimately exerted (NBOD) are equal. Not so for carbonaceous com-pounds: the carbonaceous biochemical oxygen demand ultimately exerted (CBOD) may be significantly less than the ThOD if the compound is poorly degradable. To test this. oxygen consumption is measured in the laboratory, inhibiting the oxidation of ammonia so that only carbonaceous oxygen de-mand is exerted. The measurement is made over a period of five days, yielding the 5-day carbonaceous biochemical oxygen demand (COOD₅). The waste from Problem 5-8 was found to have a CBOD₅ of 90 mg/L and

Problem 5-8

Organic carbon (C) and ammonia nitrogen (NH₃) are oxidized to carbon dioxide (CO₂) and nitrate (NO₃-) respectively, by bacteria that are naturally present in wastewater and in natural systems such as lakes and rivers. Both of these reactions consume oxygen and may cause a negative impact on water quality. The amount of oxygen theoretically required to consume a carbonaceous (ThOD) or nitrogenous (NOD) waste may be calculated according to the stoichiometry of the reactions as outlined in this chapter. The production of coke, a fuel produced from coal for use in steel mills, generates a waste gram rich in ammonia, phenol, and naphthalene. Calculate the NOD and ThOD of a waste containing 25 mg/L of ammonia-nitrogen (NH₃-N), 50 ing/L of phenol (C₆H₅OH). and 150 mg/L of naphthalene (C₁₀H₈). What is the total theoretical oxygen demand of the waste?