Partial nutrient removal under insufficient organic carbon from digested swine wastewater in sequencing batch biofilm reactor.

The objective of this study was to investigate the possibility of using a biofilm process for partial nutrient removal from digested swine wastewater containing low ratios of chemical oxygen demand (COD) to nitrogen and phosphorus; on average, 1.6 g COD g(-1) N and 7 g COD g(-1) P. We used a laboratory-scale sequencing batch biofilm reactor with alternating conditions of 4 hours anaerobic/ 12 hours aerobic, and a hydraulic retention time of 16 hours. Although the concentration of dissolved oxygen under aerobic conditions was > 2.5 mg L(-1), the efficiency of denitrification was up to 85% of the theoretical maximum at the available influent COD, with an ammonia removal rate of 0.73 g N m(-2) d(-1) and without the accumulation of nitrite or nitrate. Activity tests showed that the biomass from the reactor consisted of denitrifying polyphosphate accumulating organisms (DNPAO) that can use nitrite as an electron acceptor. The organic carbon in the digested swine wastewater was utilized very effectively through the denitrifying phosphorus uptake process, as implied by the low utilization ratios of COD to nitrogen, 4.2 g COD g(-1) N, and phosphorus, 14 g COD g(-1) P. A COD value as low as 50 mg L(-1) and an increased ratio of nitrogen to phosphorus from 4:1 to 6:1 in the effluent, which is more suitable for use as a liquid fertilizer, were achieved through the processes of nitrification and denitrifying phosphorus uptake in the sequencing batch biofilm reactor.