Simultaneous Nitrogen and Phosphorus Recovery from Sludge-Fermentation Liquid Mixture and Application of the Fermentation Liquid To Enhance Municipal Wastewater Biological Nutrient Removal

Abstract

Recently, waste activated sludge (WAS) fermentation for short-chain fatty acids (SCFAs) production has drawn much attention because the waste biosolids produced in wastewater treatment plants (WWTP) can be reused, and the produced SCFAs can be applied to promote biological nutrient removal (BNR). Usually, after WAS fermentation, the fermentation liquid is separated and then the recovery of ammonium and phosphorus, which are released during WAS fermentation, is conducted to prevent the increase of nitrogen and phosphorus loadings to WWTP. As an alternative to the traditional process, this paper investigated the recovery of ammonium and phosphorus in the formation of struvite before sludge-liquid separation, and its positive effecton the following sludge-liquid filtration separation. First, the conditions for ammonium and phosphorus recovery from the WAS fermentation mixture were optimized by response surface methodology (RSM). Then, the effect of ammonium and phosphorus recovery on sludge filtration dewatering was investigated. With ammonium and phosphorus recovery, it was observed that the specific resistance to filtration (SRF), the capillary suction time (CST), and the sludge volume after filtration reduced by 96.9, 99.6, and 88.7%, respectively, compared with no ammonium and phosphorus recovered sludge. Third, the mechanisms for ammonium and phosphorus recovery significantly enhancing sludge dewatering capacity were investigated. The formation of struvite, the neutralization of 5 potential, the increase of magnesium ion, which was added during ammonium and phosphorus recovery, and the decrease of sludge polymeric substance caused the improvement of sludge dewatering. Finally, the fermentation liquid was used as the additional carbon source of BNR, and the nutrient removal efficiency was obviously enhanced.