Synergistic treatment of digested wastewater with high ammonia nitrogen concentration using straw and microalgae

Microalgae as a promising approach for wastewater treatment, has challenges in directly treating digested piggery wastewater (DPW) with high ammonia nitrogen (NH₄⁺-N) concentration. To improve the performance of microalgae in DPW treatment, straw was employed as a substrate to form a straw-microalgae biofilm. The results demonstrated that the straw-microalgae biofilm achieved the highest NH₄⁺-N removal rate of 193.2 mg L^-1 d^-1, which was 28.8 % higher than that of culture system without straw. The final NH₄⁺-N concentration in the effluent met the discharge standard of 5 mg L^-1. Furthermore, the total organic carbon (TOC) released from straw facilitated bacterial proliferation and the secretion of extracellular polymeric substances (EPS). The EPS and TOC increased the suspension viscosity and surface tension, thereby enhancing the residence time of CO₂ in the liquid phase and promoting CO₂ fixation. This study presented a novel method for the biological treatment of high-ammonia-nitrogen DPW.