Readily biodegradable COD as an indicative parameter in estimating the efficacy of sewage for biological excess phosphorus removal

The objectives of this research were to develop a reliable measurement technique to quantify the readily biodegradable substrates present in a sewage and to investigate their role in biological excess phosphorus removal, under acclimated conditions for each substrate added, leading to the characterization of a given sewage with respect to its natural efficacy in the biological excess phosphorus removal process. The experimental work during this study involved two laboratory scale systems in which one was used to quantify the readily biodegradable substrates in the feed while the other was used as a biological excess phosphorus removal system. The readily biodegradable content of the feed was changed using different dosages of sodium acetate, sodium propionate, sodium butyrate and glucose. The effects of these compounds (both as specific substrates and as general readily biodegradable substrates) on the various elements of the biological excess phosphorus removal mechanism (such as anaerobic phosphorus release, aerobic phosphorus uptake, overall phosphorus removal, anaerobic carbon storage and aerobic carbon consumption) were investigated. Results of this study showed that almost all the different elements of the biological excess phosphorus removal process compared very well among the different substrates used when the readily biodegradable substrates (quantified as readily biodegradable COD) was used as the unit of measurement. Also, the overall phosphorus removal efficiency improved with increasing amounts of readily biodegradable substrates entering the system. A direct relationship existed between the phosphorus release in the anaerobic zone and the phosphorus uptake in the aerobic zone, according to P uptake (mg/L) = 1.21 + 1.701 x P release (mg/L) with the constant of correlation being 0.985. The results of this study also showed the importance of carbon storage. A definite link existed between the carbon storage (as PHB or PHV) and phosphorus release under the anaerobic conditions, and between the carbon consumption and phosphorus uptake under aerobic conditions. However, during the glucose addition trial, a second carbon storage compound (glycogen) was found to be stored under aerobic conditions and consumed under anaerobic conditions. An excellent linear relationship existed between the PHB synthesis and glycogen consumption, with the estimated mean value for the increase in the amount of PHB per unit of glycogen consumed being approximately 0.41, on a weight basis. In terms of specific substrates, for the same dosage as COD, their effectiveness in biological excess phosphorus removal had the following decreasing order: acetate > propionate > butyrate > glucose It was noticed during the study that whenever there was a reduction in the dosage of the added simple carbon substrates, the steady-state biological excess phosphorus removal continued for a period of upto 5 days at the same higher level before decreasing to the new lower level, reflecting the reduced substrate dosage. But, as a corollary, when the substrate dosage was increased, the excess phosphorus removal increased immediately without the presence of any significant lag period.Applied Science, Faculty ofCivil Engineering, Department ofGraduat