Effect of external electric current on denitrification efficiency and sludge flocculation of anoxic zone using AO process

doi:10.16085/j.issn.1000-6613.2020-2269

Abstract

Abstract:

Biological nitrogen removal could be achieved using nitration liquid internal circulation in AO process, which was difficult to ensure the anoxic condition of anoxic zone and thus led to unsatisfactory nitrogen removal and poor sludge flocculation. In order to enhance biological nitrogen removal, external electric current was used to enhance the sludge activity and bioflocculation in the anoxic zone. The changes of sludge contact angle, zeta potential and particle size were explored and the composition of extracellular polymeric substances (EPS) was analyzed using three-dimensional excitation emission matrix fluorescence spectroscopy (3D-EEM) and Fourier transform infrared spectroscopy (FTIR) under different current intensities. The effects of external electric current on the pollutants removal and sludge properties were investigated. The results showed that removal efficiencies of TN and COD and enzyme activity increased with the increase of the current intensity when the current intensity was lower than 30mA. When current intensity was 30mA, ORP was -135mV, and nitrate reductase activity and removal efficiency of TN were the highest [0.37μg/(mg·min) and 79.43%]. When current intensity was 40mA, dehydrogenase activity and removal efficiency of COD were the highest [50.86mg/(L·h) and 80.65%]. When current intensity was lower than 40mA, the ratio of protein (PN)/polysaccharide (PS), contact angle and average particle size of sludge increased and zeta potential of sludge decreased with the increase of current intensity, which was beneficial to sludge flocculation. Fluorescence intensity of tryptophan and tyrosine was improved and there were no obvious changes in functional groups of EPS based on the analysis of 3D-EEM and FTIR. When the current intensity was 40mA, the bioflocculation of sludge was the optimum and flocculation ability (FA) was 40.33%. Effluent suspend solid (ESS) was 13.95mg/L and sludge volume index (SVI) was 66.5mL/g. When current intensity was higher than 40mA, sludge flocculation gradually deteriorated with the increase of current intensity. Therefore, the efficiency of biological denitrification and the sludge flocculability could be improved when the current intensity was controlled at 40mA.

Key words: electric current, wastewater, bioreactors, denitrification, enzyme, extracellular polymeric substances, flocculation

摘要：

AO工艺利用硝化液内循环实现生物脱氮，很难保证缺氧区的缺氧条件，导致脱氮效果不理想，污泥絮凝性差。为了达到强化生物脱氮的目的，本研究采用外加电流提高缺氧区的污泥活性和生物絮凝性，探索不同电流强度下污泥接触角、zeta电位和污泥粒径的变化，结合三维荧光光谱（3D-EEM）与傅里叶变换红外光谱（FTIR）分析胞外聚合物（EPS）的组成，考察外加电流对污染物去除和污泥性质的影响。结果表明：当电流强度低于30mA时，随着电流强度的增加，TN和COD去除率提高，酶活性增强。当电流强度为30mA时，ORP为-135mV，硝酸盐还原酶活性达到最强[0.37μg/（mg·min）]，TN去除率达到最高79.43%；当电流强度为40mA时，脱氢酶活性达到最强[50.86mg/（L·h）]，COD去除率达到最高80.65%。当电流强度低于40mA时，随着电流强度的提高，蛋白质（PN）与多糖（PS）的比值增加，污泥接触角增大，zeta电位减小，平均粒径升高，污泥絮凝性增强；由3D-EEM和FTIR分析可知，色氨酸和酪氨酸类的荧光强度增强，EPS的官能团无明显变化。当电流强度为40mA时，污泥重絮凝能力（FA）为40.33%，出水悬浮物（ESS）为13.95mg/L，污泥容积指数（SVI）为66.5mL/g，污泥絮凝性最好。随着电流强度的继续提高，污泥絮凝性逐渐变差。因此，将电流强度控制在40mA，可以同时实现提高生物脱氮效率和污泥絮凝性的目的。

关键词: 电流, 废水, 生物反应器, 反硝化脱氮, 酶, 胞外聚合物, 絮凝性

CLC Number:

X703

ZHANG Lanhe, YUAN Zhentao, ZHAO Haojie, ZHAO Juntian, ZHU Yining, CHEN Zicheng, JIA Yanping, TIAN Shulei. Effect of external electric current on denitrification efficiency and sludge flocculation of anoxic zone using AO process[J]. Chemical Industry and Engineering Progress, 2021, 40(11): 6369-6377.

张兰河, 袁镇涛, 赵浩杰, 赵君田, 祝艺宁, 陈子成, 贾艳萍, 田书磊. 外加电流对AO工艺缺氧区脱氮效率与污泥絮凝的影响[J]. 化工进展, 2021, 40(11): 6369-6377.

Figures/Tables 8

COD /mg·L^-1	TN /mg·L^-1	TP /mg·L^-1	c(NH $4 +$ -N) /mg·L^-1	c(PO $4 3 -$ -P) /mg·L^-1	T/℃
480±20	71±3	7±1	60±5	6.5±1	20±5

COD /mg·L^-1	TN /mg·L^-1	TP /mg·L^-1	c(NH $4 +$ -N) /mg·L^-1	c(PO $4 3 -$ -P) /mg·L^-1	T/℃
480±20	71±3	7±1	60±5	6.5±1	20±5

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