土壤渗滤系统出水氨氮浓度不稳定的成因探究

Causes leading to the instability and the corresponding examination of the effluent ammonia concentrations in the soil's aqua-system

为解决土壤渗滤系统出水氨氮浓度不稳定的问题,设计了土壤与河泥按不同比例组合的混合填料土壤渗滤系统,并以模拟生活污水为考察对象,在水力负荷为0.15 m/d的条件下,研究了进水氨氮负荷、溶解氧质量浓度及容积利用率对系统出水氨氮质量浓度的影响。结果表明：当进水氨氮质量浓度由20 mg/L增加至35 mg/L时,出水氨氮质量浓度在短时间内也会大幅提升,9~15 d可恢复处理能力;系统出水氨氮质量浓度随进水溶解氧质量浓度降低而升高,当进水溶解氧质量浓度小于0.5 mg/L时,出水氨氮质量浓度甚至高于进水;容积利用率为38.72%的系统出水氨氮质量浓度低于容积利用率为25.82%的系统;增加土壤中有机质含量,可以改善土壤环境,缩短系统启动时间,提高系统容积利用率,增强土壤渗滤系统抗冲击负荷能力,从而使出水氨氮质量浓度保持在较低水平。

This paper is aimed to introduce its authors＇ study on the soil aquifer treatment system and its application to removing the am-monia nitrogen from the simulated domestic sewage. As is known, such soil aquifer treating system is advantageous in some aspects as compared with the conventional activated sludge process, such as the simplified operations to lower the production cost, energy saving and/ or higher efficiency. However, there remains a lot of problems to be dealt with in this way for eliminating the ammonia nitrogen, especial- ly, for the instable concentrations of ammonia nitrogen in the efflu- ent. To solve the aforementioned problems and improve the removal efficiency and ensure the stability of effluent ammonia nitrogen con- centration, we have worked out a method for combining the raw soil and the river mud as fillers in the intended soil aquifer system treat- ment. Taking the simulated domestic sewage as our research goal, we have studied the impact of the influent ammonia nitrogen and the dis- solved oxygen concentration on the removal rate of ammonia nitrogen under the hydraulic loading of 0.15 m/d. What we have found from the above experiments suggests that all the three factors, especially, the dissolved oxygen, tends to have a strong impact on the effluent ammonia nitrogen concentration. For example, when the dissolved oxygen is dropping, the removal efficiency of ammonia nitrogen tends to drop down significantly. But, when the influent dissolved oxygen stayed below 0.5 mg/L, the concentration of the effluent ammonia nitrogen would go up even higher than that of the influent. Neverthe- less, when the influent ammonia nitrogen concentration increased from 20 mg/L to 35 mg/L, the effluent ammonia nitrogen concentra- tion would increase about 10 mg/L, and, then, it may return to its original state of 7 mg/L in 9 - 15 d. However, when the capacity uti- lization increased from 25.82% to 38.72%, the effluent ammonia nitrogen concentration decreased significantly. In that situation, the organic matter in the mud soil would increase from 1.75% to 7.95%, and, then, if50% of the river mud was added to the raw soil, adding the soil organic matter could not only improve the growth environment of nitrifying bacteria, but also could help to shorten the start-up time and promote the capacity utilization of the system, therefore it is necessary to maintain the concentration of effluent am- monia nitrogen at a relative low level.