石化废水稳定塘系统下渗对地下水的影响

The Impact of the Petrochemical Wastewater Stabilization Pond System on Groundwater

稳定塘是一种古老而又不断发展的污水生物处理系统,目前在污水资源化方面有着广泛的应用,但是如果稳定塘系统防渗处理不当,会导致地下水污染。在中石化西北某市石化公司稳定塘中试工程一年多运行过程中,研究了3种稳定塘工程不同防渗层的防渗效果,连续对取样井中下渗后污水的水质变化情况进行监测,进而判断稳定塘系统对地下水的影响。结果表明,防渗效果优劣顺序是:红粘土机械压实>灰混土压实。污水下渗后水中TDS明显增大,平均浓度由1.2g·L-1增大到4.3g·L-1;包气带对COD、氨氮、石油烃、挥发酚、硫化物均有一定的净化效果,各污染物浓度分别减少了7.8%、24.1%、19.9%、35.3%、37.5%;氰化物浓度几乎不变。由于污水是经过二级生化处理的石化废水出水,其中的有机物大部分是难生物降解的有机物,进入含水层中将更难以去除,所以下渗对地下水污染风险最大的是污水中的有机物。此外,下渗使地下水水位上升从而造成土壤次生盐渍化。

The wastewater stabilization pond is an ecotypic wastewater treatment system, which is widely used in wastewater reclamation. However, wastewater stabilization pond system（ WSPS ） may bring groundwater pollution if the waterproof layer is not operated properly. A pilot test on WSPS in the northwest branch of SINOPEC CORP lasted more than one year, in which the anti-seepage capacities of three different waterproof layers of WSPS were measured and the impact of WSPS on the underlying aquifer was evaluated. The results indicated that the anti-seepage capacities of the different waterproof layers follow the order ： red clay mechanical compaction 〉ash-soil compaction 〉 red clay compaction. The TDS in the percolate increased from 1.2 g·L^-1 to 4.3 g·L^-1. COD, ammonia nitrogen, petroleum hydrocarbon, volatile phenol and sulfide were partly removed by unsaturated zone, with their concentrations decreased by 7.8%, 24.1%, 19.9%, 35.3 %, 37.5 %, respectively. The concentration of cyanide was almost unchanged. Most residual organic contaminants which survived the secondary biochemical treatment in the petrochemical wastewater were immune to the biodegradation, especially in the aquifer. So the organic contaminants from seepage flows brought the greatest risk for groundwater pollution. In addition, the groundwater level rise caused by seepage would result in the secondary salinization of soil.