Endogenous respiration processes of nitrifying/denitrifying bacteria under aerobic and anoxic conditions were investigated in a batch study using three identical bioreactors of size 5 L. The rate of digestion of microbial protoplasm was determined through the oxidation of cell tissue and the formation of new cellular materials using the Volatile Suspended Solids (VSS) method. Chemical Oxygen Demand (COD), ammonia, nitrate and VSS were monitored simultaneously at different sludge age. Three exponential phases of metabolism, starvation and death were observed during VSS reduction in both the aerobic and anoxic digestion. In the aerobic digestion, the average endogenous decay coefficient of volatile suspended solids was 0.055 L dayG 1 with a 95% confidence limit of 0.017 whereas 0.053 L dayG 1 was observed for anoxic digestion with a 95% confidence limit of 0.038 at 25±1°C. Results show that anoxic digestion has a slightly reduced decay rate than aerobic digestion. Therefore, the characterization of biomass and determination of stoichiometry coefficients is essential for understanding the activities of microbes in treatment processes.

Water body deterioration caused by natural and anthropogenic activities has been a source of concern for regulating agencies. Several problems such as eutrophication and blue baby syndrome are caused by the excessive presence of nutrients within the aquatic biota. This also presents danger to the benthic community. In this study, an integrated aerobic/anoxic attached growth bioreactor was evaluated for its performance in removing nutrients (ammonia and nitrate) from simulated synthetic low and medium strength domestic wastewater. The experiment was conducted in two stages. ) was low in both stages 1 and 2. In both stages 1 and 2, ammonia removal reached 98%. The HRT was found to exert slight influence in nutrient removal using the integrated bioreactor. At HRT of 7.2 and 12 days, effluent ammonia concentration of 1.1 and 0.6 mg LG 1 was obtained, whereas effluent nitrate was in the range of 0.55 and 0.22 mg LG 1 , respectively. Chemical Oxygen Demand (COD) was also monitored at steady states and was found below 20 mg LG 1 in both stages 1 and 2 at HRT of 12 days. This study, therefore demonstrates the capacity of an integrated bioreactor to mitigate the enormous challenge of water body deterioration and toxicity caused by indiscriminate discharge of polluted wastewater.

Produced water is the largest wastestream of oil and gas exploration. It consists of various organic and inorganic compounds that hinder its beneficial use. This study compared the treatment of produced water in a batch suspended and biofilm activated sludge process. The biofilm carrier material was made from Gardenia Carinata shell. COD, NH4 + -N and NO3-N removal was monitored in both the suspended (control) and floating carrier bioreactors. The results show a rapid reduction of produced water constituents in the floating carrier bioreactor. COD, NH4 + -N and NO3-N removal was in the range of 99%, 98% and 97% for the floating carrier bioreactor whereas it was 88%, 84% and 83% for the control bioreactor. The rapid reduction of COD, NH4 + -N and NO3-N clearly indicate that the floating carrier materials served as an attached growth medium for microorganisms, improved the breakdown of produced water constituents and reduced inhibition of microbial metabolic activities.