Promising carbon utilization for nitrogen recovery in low strength wastewater treatment: Ammonia nitrogen assimilation, protein production and microbial community structure

Acetic acid and sodium acetate are generally supplied to wastewater treatment plants (WWTPs) in China to improve total nitrogen (TN) and total phosphorus (TP) removal, and the addition of carbon source also facilitates to increase sludge growth rate and further provides material basis for the extraction of proteins and amino acids from activated sludge. To recycle ammonia nitrogen resources, a system that combined adsorption and anaerobic-anoxic-oxic (A/AAO) process for treating low strength wastewater was established. Experimental results showed that by the addition of carbon substrate from a mixture of anaerobically fermented adsorption sludge, the average removal efficiency of chemical oxygen demand (COD), ammonia nitrogen, TN, and TP were 88%, 96.9%, 93.9%, and 92.1%, respectively, and the ratio of nitrogen assimilation to nitrogen dissimilation significantly increased by a factor of 2.5. Through energy analysis (based on adenosine triphosphate, ATP), sludge flocculation capacity and settling property, it was found that the AAO process sludge presented the logarithmic growth characteristics. The respective sludge protein and amino acids contents increased by over 11.4% and 40.3%, and the synthetic products of glutamic acid, alanine and aspartate increased through the assimilation of ammonia nitrogen, thereby indicating that replenishing the carbon substrate could markedly enhance protein and amino acids contents in AAO process sludge. Moreover, the diversity of the microbial community in adsorption process was relatively rich, the diversity in the adsorption process sludge was the highest, while the diversity of the AAO process sludge evidently decreased. The microbial community in each process was similarly based on 16S rDNA gene sequence analysis, microflora was prominent in the AAO process, with Dechloromonas, Flavobacterium, Zoogloea, Unclassified_Rhodocyclaceae and Thauera as the dominant species. Promising carbon utilization facilitates contaminants removal in low strength wastewater treatment and is conducive to protein production through ammonia nitrogen assimilation.