电动脱除孔隙水削减底泥内源磷的效果研究

Performance of sediment phosphorus reduction via electrokinetic drainage of pore water

选择污染严重的底泥为研究对象,采用基于孔隙水脱除的电动修复装置,进行了底泥脱水排磷实验,探究了电动脱除孔隙水的底泥减磷效果,分析了底泥各形态磷在电动脱除孔隙水中的迁移转化过程.结果表明:电动脱水过程中阴极总脱水量为5740mL,远大于阳极(2121mL),但脱水中总磷浓度为阳极大于阴极,80%以上的磷从阳极排出,电迁移在电动脱水排磷中起主要作用,通电使排磷总量增加了70%以上,其中在0.25V/cm的电压梯度下修复18d的条件下,排磷量最大;电动脱水排磷效率在通电48h内达到最高[0.73mg/(kW·h)],随后急剧减小;经过电动脱水排磷后,底泥含水率下降了14.07%,底泥总磷降幅最高可达231.92mg/kg,底泥中交换态磷(Ex-P)、铁结合态磷(Fe-P)、闭蓄态磷(Oc-P)、钙结合态磷(Ca-P)平均脱除率分别为80.01%、14.75%、40.65%和19.22%,其中阳极酸化导致氧化铁的溶解和Ca-P的释放,故阳极附近Oc-P、Ca-P降幅较大,而阴极碱化使Fe-P释放,故阴极附近Fe-P降幅较大.经计算可知,通过电动脱除孔隙水,底泥中生物可利用性磷(Ex-P+Fe/Al-P)平均下降了14.12%,底泥内源磷释放的风险得以降低.

In this study, heavily polluted sediment and electrokinetic treatment apparatus functioned with pore water drainage were used to conduct experiments, which aimed to assess the impacts of pore water drainage on sediment phosphorus reduction, and analyze the migration and transformation of sediment phosphorus fractions due to electrokinetic drainage of pore water. The experimental results showed that the total effluent volume drained from cathode was 5740 mL, which was greatly higher than 2121 mL drained from the anode. However, effluent total phosphorus concentration of anode was higher than that of cathode, and more than 80% of the phosphorus was discharged from the anode effluent. Electromigration played a major role in the phosphorus separation, and applying of voltage gradient caused more than 70% increase in phosphors discharge when compared to none powered control. Moreover, the maximum amount of phosphorus discharge achieved when the treatment lasted 18 days under a voltage gradient of 0.25 V/cm. During powered 48 h, the efficiency of phosphorus discharge dropped sharply after reached its peak of 0.73 mg/(kW·h). In contrast to original sediment samples, pore water drainage caused 14.07% and 231.92 mg/kg reduction in sediment moisture content and total phosphorus storage. Moreover, the average decrease in sediment phosphorus fractions of Ex-P, Fe-P, Fe-P, Oc-P and Ca-P were 80.01%, 14.75%, 40.65% and 19.22%, respectively. Anode acidification promoted the dissolution of iron oxide and the liberation of Ca-P, and led to greater decrease of Oc-P and Ca-P near the anode zone. For cathode, alkalinization caused the release of Fe-P, and much more reduction of Fe-P occurred near the cathode zone. Finally, calculated average reduction in sediment bioavailable phosphorus(Ex-P+Fe/Al-P) content was 14.12% when electrokinetic drainage pore water applied, and the risk of sediment phosphorus release thus could be potentially restrained.