Determination of inert Chemical Oxygen Demand (COD) fractions of Cumhuriyet University wastewater

Some amounts of inert products are given into environment due to biological degradation of
substrate in activated sludge system. The effluent of biological wastewater treatment consists
of inert substrate in influent flow, soluble microbial products and non degradable or slowly
degradable organic products.
Soluble inert COD (SI) must be determined for discharge standards since it did not give any
reaction in activated sludge system and was given with wastewater discharge. However
particular inert COD (XI) accumulated in system depending on sludge retention time due to it
is only wasted from system by wasted sludge.
This study focused on inert fractions of Cumhuriyet University campus wastewater which
consists of domestic, hospital and laboratory wastewaters. Experimental method was used
suggested by Orhon et al. and modified by Germirli et al. in order to determine directly influent
particulate and soluble inert fractions. According to the experimental procedure three aerobic
batch reactors, two with the wastewater and the third with glucose were run parallel. In the
reactors, the change in the soluble COD profiles is observed for a period during which all
degradable COD is entirely depleted, in other words, the COD profiles reach a plateau and
remain unchanged.
Wastewater samples were taken equalization tank in wastewater treatment plant. The
conventional parameters of campus wastewater characterization were as follows: Total COD
(CT0) = 372 mg l-1, total soluble COD (STO) = 124 mg l-1, total suspended solids (TSS) =177
mg l-1, ammonia (NH3) = 31.2 mg l-1, ortho-phosphate (PO4-P) = 11.3 mg l-1 and pH=7,4 .
In this study, in order to determine inert COD fractions in Cumhuriyet University campus
wastewater, three aerobic batch reactor systems were used. At the end of approximately 381
h operation, COD composition of campus wastewater were found to be CT0=372 mg l-1,
XS0=56 mg l-1, SS0=104 mg l-1, CS0=149 mg l-1, SI=12 mg l-1, XI=211 mg l-1, respectively.