Abstract
There are two biological systems available for removing phosphorus from waste water, conventional phosphorus removal (CPR) and denitrifying phosphorus removal (DPR) systems, and each is characterized by the type of sludge used in the process. In this study, we compared the characteristics associated with the efficiency of carbon utilization between CPR and DPR sludge using acetate as a carbon source. For DPR sludge, the heat emitted during the phosphorus release and phosphorus uptake processes were 45.79 kJ/mol e- and 84.09 kJ/mol e-, respectively. These values were about 2 fold higher than the corresponding values obtained for CPR sludge, suggesting that much of the energy obtained from the carbon source was emitted as heat. Further study revealed a smaller microbial mass within the DPR sludge compared to CPR sludge, as shown by a lower sludge yield coefficient (0.05 gVSS/g COD versus 0.36 gVSS/g COD), a result that was due to the lower energy capturing efficiency of DPR sludge according to bioenergetic analysis. Although the efficiency of anoxic phosphorus removal was only 39% the efficiency of aerobic phosphorus removal, the consumption of carbon by DPR sludge was reduced by 27.8% compared to CPR sludge through the coupling of denitrification with dephosphatation.
Highlights
Nitrogen (N) and phosphorus (P) are the key nutrients that cause eutrophication in waterways
The heat change for the conventional phosphorus removal (CPR) sludge associated with the release of phosphorous via anaerobic and aerobic processes was determined by microcalorimetry
The heat change of CPR sludge in anaerobic P release and excess aerobic P uptake was determined by microcalorimetry
Summary
Nitrogen (N) and phosphorus (P) are the key nutrients that cause eutrophication in waterways. The removal of nitrogen is accomplished by a two-stage treatment process, which consists of nitrification and denitrification. Both P removal and N removal require a carbon source. In denitrifying phosphorus removal (DPR), nitrate is used as an electron acceptor, which allows denitrification and P uptake to occur simultaneously using the same organic carbon source [1,2]. In this way, DPR offers an appropriate solution to the problems associated with the limitation of chemical oxygen demand (COD)
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