Best available carbon sources to enhance the via-nitrite biological nutrients removal from supernatants of anaerobic co-digestion

The best available external carbon source to enhance the short-cut nitrification-denitrification (SCND) and denitrifying phosphorus removal via nitrite (DPRN) was investigated using a demonstration sequencing batch reactor (SBR) to treat anaerobic supernatant. The SBR was inoculated with conventional activated sludge and fed with liquid effluent from anaerobic co-digestion of waste activated sludge and organic fraction of municipal solid waste. After the 20 day-long start-up, a stable and reliable via-nitrite pathway was achieved. Then, five best available carbon sources (acetic acid, glycerol, organic fraction of the municipal solid waste (OFMSW) fresh drainage liquid, OFMSW fermentation liquid, cattle manure and maize silage (CM&MS) fermentation liquid) were investigated. Glycerol did not cause major enhancement on nutrients removal. On the other hand, we found specific denitritation rates in the range 0.51-1.16 kgNO2-N kgVSS-1 per day for OFMSW and CM&MS related carbon sources. Specific consumptions were 2.1-2.3 kgCOD kgNO2-N-1rem for acetic acid and glycerol respectively, while OFMSW and CM&MS involved higher ratios 2.7-3.1 kgCOD kgNO2-N-1rem. Thanks to the presence of Short Chain Fatty Acids (SCFA), namely butyric and propionic acids, the fermentation liquids contemporary enhanced the DPRN up to 0.81 kgPO4-Puptaken kgNO2-N-1removed. Thanks to the use of biowaste material, the cost of the external carbon source can be lower than 0.1 € kgCOD-1 when OFMSW is fermented. Therefore, the total specific cost for nitrogen removal may decrease of 22% when the OFMSW fermentation liquid is used instead of methanol.