分流制系统雨水管网混接旱天排放污染特征研究

A study on characteristics of dry-weather discharge pollution from separate storm drains with inappropriate flow entries

分流制排水系统中,雨水管网混接污水在旱天直排河道,造成河道水质恶化.本文以上海市某混接分流制排水系统(3.74 km^2)为研究对象,通过开展雨水管网旱天排放水质监测(SS、COD、BOD5、NH3-N、TN等),以及雨水管网旱天污染输移质量平衡分析,研究了混接雨水管网旱天排放污染特征.结果表明:①雨水管网旱天排放分为重力流排放和雨水泵开启排放两种情况,重力流排放水质与混接水量水质和河水倒灌相关,雨水泵开启排放水质与混接水量水质、管道淤泥冲刷和河水倒灌相关.②当旱天前期雨水泵不开泵时间小于2 d时,河水倒灌会对重力流排放和雨水泵站排放水质造成明显影响.③随着前期不开泵时间增加,管道淤积程度越发严重;雨水泵排放COD、BOD5、SS浓度与前期不开泵时间满足指数关系.④旱天重力流排放期间的管道底泥淤积量大于泵站排放期间的淤泥冲刷量,年度尺度上57%的淤积底泥通过旱天雨水泵开启排出,其余43%的淤积底泥在雨天随雨水泵排出,从而进一步加重了河道雨天污染.

Dry-weather discharge from the separate storm drains due to illicit sewage or other sources entries resulted in the water quality deterioration of receiving waters. In this study, a separate storm drains with inappropriate sewage entries(3.74 km^2) in Shanghai was investigated to determine the characteristics of dry-weather days discharge by performing water quality monitoring(SS, COD, BOD5, NH3-N, TN) and quantifying the mass balance of illicit discharge transport during dry-weather days. Our findings were listed as follows: ①For the separate storm drains, dry-weather discharge arose from two scenarios, that is, gravity flow discharge and pumping discharge as a result of storm pumps operation. Water quality of gravity flow was affected by flow discharges and water quality of illicit discharge types as well as river water intrusion. Water quality of pumping flow was determined by flow discharges and water quality of illicit discharge types, in-pipe sediments erosion and river water intrusion. ②When the antecedent non-pumping period was less than 2 d of dry-weather days, water quality of both gravity flow and pumping flow would be significantly affected by river intrusion;③The longer the antecedent non-pumping days, the more serious the sediments deposition would be. An exponential function was found between antecedent non-pumping days and pumping discharge concentration of SS, COD and BOD5. ④Over annual scale, the amount of deposited sediments under gravity flow was greater than that of scoured sediments under pumping discharge. It was estimated that throughout one year, 57% of the deposited sediments was flushed into the river due to storm pumps operation on dry-weather days, and the remaining 43% was flushed into the river on wet-weather days, further aggravating river pollution during rainfall.