Industrial-scale Study On The Transformation Characteristics Of Refractory Organic Matter In Urban Rivers By Upflow Anaerobic Biofilter

With the increasingly stringent requirements of the state and the public to improve the quality of water environment,how to further remove the refractory organic matter in polluted urban rivers has attracted extensive attention.Due to the natural characteristics and low pollution of urban rivers,the widely used activated sludge process is difficult to operate stably and efficiently.In this study,a Industrial scale upflow anaerobic biofilter(UAF)with more abundant biofacies and more suitable for low pollution water treatment was used in Xinhe River,where the tail water of sewage treatment plant is the main base flow,The effect of hydraulic retention time(HRT),an important operating parameter,on UAF transformation of refractory organic matter and the transformation characteristics of refractory organic matter in UAF were studied.The feasibility of UAF as a treatment and pretreatment unit for the removal of refractory organic matter in urban rivers was explored,so as to provide a pilot test reference for further improving the water quality of urban rivers.UAF size is 1.15 m×1.15 m×5 m,and the test duration is more than 200 days.Through analyzing the water quality and dissolved organic matter(DOM)properties of Xinhe River,the influence of HRT on UAF transformation of refractory organic matter,the transformation characteristics of refractory organic matter in UAF and the distribution characteristics of microbial population,the transformation characteristics of UAF to refractory organic matter in Xinhe River were explored.The results show that:(1)The source and composition of refractory organic matter in Xinhe River:COD and UV254 fluctuate between 49.77～309.55 mg/L and 0.096～0.217 cm-1,BOD5/COD is only 0.115～0.144,and most of the organic matter in Xinhe river is refractory organic matter,and mainly comes from the tail water and overflow of the sewage treatment plant,the combined sewage of rain and sewage,the sewage discharged from rural life and production,the river sediment and the soil on both banks;The main components of refractory organic matter in Xinhe are fulvic acid,humic acid,tryptophan and soluble microbial metabolites(SMP),accounting for about 90%;The results of equilibrium dialysis showed that about 84.14%of DOM had a molecular weight greater than 7 kDa.Gel permeation chromatography(GPC)showed that the peak area of humus DOM greater than 7kDa accounted for 84.57%.The ratio of DOM peak area of tryptophan and tyrosine larger than 7kDa was 95.11%,while the two type DOM had no peak in the range of less than 1kDa,so the main organic matter in New River was more than 7kDa.(2)The effect of HRT on improving the degradation characteristics of refractory organics:when HRT is 20h,UAF has the best degradation effect on refractory organic matter,and then the effect will become worse with the shortening or prolonging of HRT.UAF was run with four HRT,each HRT lasted for 40 days,the results showed that when HRT was 20h,the removal rate of UV254 was the highest,ranging from 18.40%to 33.64%;The results showed that the fluorescence intensity of the four characteristic peaks decreased most obviously,and the degradation effect of SMP was the best;The results of equilibrium dialysis showed that the average degradation amount and degradation rate of DOM with molecular weight of more than 10 kDa and 7-10 kDa were 7.71 mg/L(27.36%)and 7.50 mg/L(69.34%)respectively;The results of GPC showed that the DOM peak areas of humus,tryptophan and tyrosine over 7 kDa decreased by 25.35%and 25.22%,respectively;The most obvious improvement was in biodegradability.The ratio of BOD5/COD increased from 0.143 to 0.308.33.59%of the refractory organics were transformed into easily degradable organics,and the transformation amount was 24.58 mg/L.(3)Transformation characteristics of refractory organic matter along UAF:the removal of easily degradable COD,ammonia nitrogen and the consumption of dissolved oxygen are mainly carried out in the sludge layer at the bottom of UAF,while the transformation of refractory organics is mainly concentrated in the first half of UAF.In the front of UAF,the amount of DOM transformation more than 10 kDa and 7-10 kDa accounted for 64.99%and 69.21%of the total transformation amount,respectively;GPC results showed that the DOM peak areas of humus greater than 10 kDa and 7-10 kDa decreased by 25.43%and 25.22%,of which 17.91%and 22.42%occurred in the first half of UAF.The DOM peak areas of tryptophan and tyrosine proteins over 10 kDa,7-10 kDa decreased by 28.30%and 20.71%,of which 26.84%and 15.11%occurred in the first half of UAF.(4)Distribution characteristics of microorganisms along UAF:microbial diversity,microbial richness and microbial evenness in UAF decreased along the flow direction.In addition,the abundance of Chloroflexi,which can transform macromolecular organics and is related to biofilm formation,is higher in the front of UAF.Acidobacteria and Bacteroides,which mainly function in hydrolysis and fermentation,are abundant in the front of UAF.The abundance of Firmicutes,which can open aromatic rings,is higher in the front of UAF.Therefore,the growth of anaerobic biofilm in the front of UAF is better,and the transformation effect of refractory organic matter is more obvious.UAF can effectively transform refractory organics into easily degradable organics in rivers,improve the degradation characteristics of refractory organics,and finally further improve the quality of urban surface water.UAF can be used as a treatment and pretreatment unit to remove refractory organics in urban rivers.