碳氮比对水芹浮床系统去除低污染水氮磷效果的影响

随着我国经济的快速发展,农业面源污染问题日益严重,加剧了淡水水质恶化的趋势。本研究以浮床水芹(Oenanthe javanica)系统和无植物对照(Control)为对象,研究了其对不同碳氮比农村低污染水定义为农业生产或农民生活过程中产生的,富含植物生长所需的氮、磷等养分与多种微量元素且满足城镇污水处理厂污染物排放标准一级B要求(GB 18918—2002一级B:TN≤20 mg·L~(-1),TP≤1 mg·L~(-1))的那部分污水]中氮(N)、磷(P)、化学需氧量(COD)的净化效果。试验所用低污染水为生活污水(TWW)和外加碳源生活污水(高碳氮比,TWW-HC)两种。整个试验历时82 d,中间换水一次。试验结果表明水芹浮床系统接纳高碳氮比低污染水对氮磷的去除效果较好。外加碳源能在短时间内快速降低低污染水中N、P的浓度,试验3 d时TWW-HC中总氮(TN)、氨氮(NH4+-N)、总磷(TP)的去除率分别达40.8%、38.4%、62.8%。整个试验周期TWW-HC组对TN的去除率为73.9%~96.0%,高于TWW组(60.6%~85.9%);该组对TP的去除率为68.0%~81.1%,高于TWW组和Control组(TP去除率分别为21.3%~54.9%和19.2%~58.1%)。收获时TWW-HC处理水芹生物量、平均株高和相对生长速率均显著高于TWW处理(P0.05)。TWW-HC处理通过植物吸收带走的N、P分别占系统对N、P去除量的58.2%和37.6%,明显高于TWW处理(相应比例分别为8.7%和11.0%)。这说明通过外加碳源调节进水C∶N比促进了水芹的生长和对污水中养分的吸收利用,有利于水芹浮床系统对N、P的去除。

Effect of carbon/nitrogen ratio in low pollution wastewater on nitrogen and phosphorus removal in a floating-bed Oenanthe javanica system

As the rapid development of the economy and agriculture, the water quality of many rivers and lakes is degrading due to agricultural non-point source pollution. The low polluted wastewater (LPW) is an eutrophic water body containing N, P and many microelements, meeting the Pollutant Discharge Standard of Municipal Wastewater Treatment Plant (Class one, B level). LPW can be reused before draining into downstream water system. Rural LPW mainly comes from agricultural production and farmer’s livelihood, including sewage tail water, farmland runoff and polluted river water. In this paper, the effect of C︰N ratio of LPW on the removal of nitrogen (N), phosphorus (P) and chemical oxygen demand (COD) of LPW was studied with floating-bed Oenanthe javanica system as the research subject to provide reference for increasing purification efficiency of floating-bed plant system. In the experiment, domestic sewage with or without glucose addition of floating-bed Oenanthe javanica system were two treatments (TWW-HC and TWW treatments), and no plant floating-bed system was used as the control treatment. The experiment lasted for 82 days with once water exchange in median time of the process. The results showed that N and P removal performance were better in TWW-HC treatment than that in TWW. External carbon addition rapidly reduced N and P contents, and the removal rates of total nitrogen (TN), ammonia nitrogen (NH4+-N) and total phosphorus (TP) were 40.8%, 38.4%, and 62.8%, respectively, under TWW-HC treatment after 3 days of treatment. The removal rate of TN of TWW-HC was 73.9%-96.0% during the whole experiment, which was higher than that of TWW (with the removal rate of 60.6%-85.9%). The removal rate of total phosphorus (TP) was 68.0%-81.1% in TWW-HC, which was higher than that in TWW and control treatments (with the removal rates of 21.3%-54.9% for TWW and 19.2%-58.1% for control, respectively). The biomass, average plant height, and relative growth rate of O. javanica were significantly higher in TWW-HC than in TWW. Plant uptake of TWW-HC accounted for 58.2% of the removed N amounts and 37.6% of the removed P amounts, greatly higher than those of TWW (8.7% of the removal N amounts and 11.0% of the removal P amounts). More than 80% of the removed N amounts were eliminated by other pathways in TWW treatment, but the percentage was only 37.3% in TWW-HC. Sedimentation contributed for 16.0% of the removed N amounts in control treatment, but only 8.5% in TWW and 4.6% in TWW-HC, respectively. Similar tendency was found in TP removal pathways. These results showed that the floating-bed O. javanica system evidently reduced N and P amounts in sediments compared to control. Results also indicated that increasing C︰N ratio to an appropriate range of LPW was beneficial for growth and nutrient uptake of O. javanica, which also contributed to N and P removal efficiently.