Synchronous Implementation Of Strengthening Partial Nitrification & Denitrification And In-situ Sludge Reduction During Landfill Leachate Treatment Based On Bioaugmentation

For wastewater treatment industries,it has been two burning questions of the enhancement of treatment efficiency and reduction of excess sludge in the background of the rising problem of environment nowadays.These problems have attracted to many researchers who have devoted themselves into the innovation and modification of treatment techniques and/or processes to improve the efficiency and sustainability of the systems.The enhanced biological method（i.e.,bioaugmentation）,as a direct way without any chemical additions,has been one of the most advantageous and eco-friendly method for synchronously achieving the enhancement of effluent water quality and reduction of excess sludge.In this study,landfill leachates as a kind of high-concentration ammonia-nitrogen wastewater with low ratio of C/N was treated using an anoxic-oxic-settling-anoxic（A-OSA）process coupled with the novel microbial agents（beneficial microorganisms;BM）.The enhancement of partial nitrification&denitrification process and in-situ sludge reduction process can be come true simultaneously.The contrast tests（i.e.,with（A-OSA-B）and without（A-OSA-C）BM）were adapted in this experiment in order to figure out the contribution of BM to the consequence.To identify the microbial community composition and gene function related to metabolism,16S r RNA sequencing was determined to detect the characteristic of microorganisms in two systems and working solution of BM.The relative abundance of gene functions related to metabolism was reached 51.26%.Furthermore,the best dosage of BM with the dominant genus of Acetobacter（32.8%）and Gluconacetobacter（33.1%）was 20%（v/v）d^-1（calculated as the volume of side-stream reactor）.During the 60-day operation,A-OSA-B maintained a lower concentration of mix liquor suspended solids(MLSS=3230 mg L^-1)and mix liquor volatile suspended solids(MLVSS=2480 mg L^-1),compared with A-OSA-C(MLSS=7191 mg L^-1;MLVSS=4785 mg L^-1),because of the result of in-situ sludge reduction.In this case,A-OSA-B still remained a higher biotreatment efficiency,which removal rate of ammonia,removal efficiency of dissolved organic matters and removal rate of total nitrogen were 0.7%,0.4%and 4.1%,higher than A-OSA-C,respectively.It was attributed to the higher utilizing rate of substrate and uptake rate of oxygen of ammonia oxidizing bacteria,the lower utilizing rate of substrate and uptake rate of oxygen of nitrite oxidizing bacteria,and higher denitrification rate of denitrification bacteria in A-OSA-B,compared to A-OSA-C.Moreover,according to the result of 16S r RNA,the abundant denitrification bacteria（e.g.,Thermomonas and Acinetobacter）were enriched in the anoxic zone of A-OSA-B,and the microbial diversity and species richness increased due to the inoculation of BM.These phenomena contributed to the results mentioned above.Besides,the rate of excess sludge production（calculated as total suspended solids）and observed sludge yield coefficient of A-OSA-B were 53.6%and 54.2%lower than that of A-OSA-C.It was suggested to the higher rate of endogenous metabolisms in both main stream reactor and side-stream reactor of A-OSA-B.The characteristics of sludge properties were changed through the inoculation of BM.In order to detect the characteristic of in-situ sludge reduction happened in A-OSA-B,the concentrations of protein and polysaccharides from extracellular polymeric substance（EPS）and dehydrogenase activity were further discussed.Both protein&polysaccharides concentrations and dehydrogenase activity in A-OSA-B kept relatively higher values,compared to that in A-OSA-C,which may facilitate the process of EPS release and degradation for in-situ sludge reduction.Furthermore,abundant hydrolytic and fermentative bacteria（e.g.,Xanthomonadaceae:5.2%,Porphyromonadaceae:5.7%）were enriched in side-stream reactor of A-OSA-B.It was conducive to the hydrolysis of EPS and sludge flocs.The gene functions related to in-situ sludge reduction were up-regulated in both main stream reactor and side-stream reactor of A-OSA-B,which was beneficial to the realization of in-situ sludge reduction.Hence,the enhancement of partial nitrification&denitrification process and reduction of excess sludge were achieved simultaneously through the A-OSA process coupled with BM.The results of this study provide a new idea and a theoretical basis for handling the problem of effluent quality and excess sludge.