不同规格生态沟渠对排水污染物处理能力的研究

Comparative Research on Effects of Ecological Ditches Different in Specification Treating Pollutants in Drainage

利用三种不同深度规格的生态沟渠(E0.80、E1.05和E1.30),通过控制相同的表面水力负荷,比较研究了动态进水(TN 0.86~6.13 mg·L^-1、TP 0.11~0.28 mg·L^-1)条件下生态沟渠对农业面源主要污染物的去除效果,同时考察其耐冲击负荷能力和适宜建造长度。结果表明:整个试验期间,三种不同深度规格的生态沟渠对铵态氮(NH4+-N)、总氮(TN)、总磷(TP)和悬浮物(SS)的去除率均达到50%以上,其中E1.30对污染物的去除效率较高,NH4+-N、TN、TP和SS的总平均去除率分别为64.8%、63.1%、71.8%和60.8%。同时,E1.30的污染物出水浓度较为稳定,耐冲击负荷能力相对较强。进水浓度较高情况下,E1.30在TN、TP出水浓度为2 mg·L^-1和0.2 mg·L^-1时所需长度分别为27.4 m和4.9 m,为三种规格生态沟渠中最短。表明生态沟渠是有效去除农业面源污染物的技术,在实际应用中可因地制宜地建设E1.30规格的生态沟渠,并可辅以高效吸附氮磷材料等其他措施,进一步提高生态沟渠对农业面源污染物的去除能力。

【Objective】With rapid development of the socioeconomy and agriculture of China, the use of chemical fertilizers and pesticides is growing excessive in total amount and rate. As a result, non-point source (NPS) pollution emerges with pollutants flowing into water environments with surface runoff and drainage and via other channels. According to the “Bulletin of the First National Survey of Pollution Sources in China” published by Ministry of Environmental Protection of China in 2010, agricultural NPS pollution contributed up to 57.2 % and 67.4 % to the total discharge of N and P in the country, respectively. Ecological ditches, as a special kind of wetland systems, can be used to manage agricultural NPS pollution with balanced ecological and environmental benefits. In order to understand how ecological ditches, different in depth (E0.80, E1.05 and E1.30), can reduce main NPS pollutants under the same hydraulic surface loading (0.60 m^3·m^-2·d-1), it is essential to evaluate pollutant removal efficiency and anti-shock loading capacity of the ditches.【Method】For this study, an experiment was conducted at the Zhuanghang Experimental Station (121°23′15″E, 30°53′24″N) of the Shanghai Academy of Agricultural Science, China. The experiment had three eco-ditches, the same in length (90 m) but different in depth (0.80 m, 1.05 m and 1.30 m). Aquatic evergreen species, Vallisneria natans, was grown in all the three eco-ditches, the same in density. Simulated agricultural NPS pollution water was diverted from a river and spiked with a certain amount of urea and KH2PO4 till it was the same in N and P content as that in the effluent of local farmlands. And then it was introduced into the eco-ditch systems dynamically. Before the experiment, the eco-ditch systems were stabilized for a period of time before the experiment began, and the experiment period lasted 20 d. The inflow TN and TP concentrations were 0.86~6.13 mg·L^-1 and 0.11~0.28 mg·L^-1, respectively.【Result】Results showed that under the dynamic conditions of the experiment, all the three ecological ditches were all quite high in NPS pollutants removal efficiency, regardless of the difference in depth. The mean ammonia nitrogen (NH4+-N), total nitrogen (TN), total phosphorus (TP) and suspended substance (SS) removal rate of Ditch E0.80was 61.4%, 58.7%, 64.0% and 58.5%, respectively, of Ditch E1.05, 54.7%, 62.5%, 70.2% and 51.1%, respectively, and of Ditch E1.30, 64.8%, 63.1%, 71.8% and 60.8%, respectively, throughout the entire experiment time. Obviously Ditch E1.30 was the highest in pollutant removal efficiency. With the same inflows the same in pollutant concentration, the average TN and TP concentration in the effluent measured at the point of 22.5 m and 45 m down the ditch was the lowest in Ditch E1.30 and the average TN and TP concentration was reduced down to 2 mg·L^-1 and 0.2 mg·L^-1 at the point of 27.4 m and 4.9 m, respectively, down the ditch, in Ditch E1.30. The course was much shorter in Ditch E1.30, then in Ditch E0.80. For the latter it was 54.5 m and 9.8 m, respectively. Meanwhile, the concentrations of pollutants in the effluent from Ditch E1.30 were relatively stable, indicating that Ditch E1.30was the highest in anti-shock loading capacity.【Conclusion】Compared with Ditch E0.80 and Ditch E1.05, Ditch E1.30 is obviously higher in pollutant removal efficiency and anti-shock loading capacity, when they are used to manage agricultural NPS pollution. So it is recommended that in practice, ditches 1.30 m in depth should be built site-specifically. This research is expected to be of great practical guiding significance to control of agricultural non-point source NPS pollution. However, more researches should be done on further improvement of pollutant handling efficiency of the ecological ditches and on land-saving as well by altering the linear spatial structure, setting up drop dams at intervals, laying down beds of substrates (like zeolite, etc.) at intervals and optimizing plant configuration (keeping plants growing at the bottom and on the walls of the ditches).