Study On Advanced Treatment For Tailrace Of Rural Domestic Wastewater With Economical Aquatic Plant Filter Bed

Rural domestic wastewater is the important pollution sources which lead to serious eutrophication of the Tai Lake.Therefore, choosing properly rural domestic wastewater treatment process can make the water reaching the discharging standard and reducing pollution risk. Though depth treatment of the tailrace of rural domestic wastewater can achieve recycling use of nitrogen and phosphorus nutrition elements in the tailrace wastewater and producing certain economic value. In this paper, two-stage aquatic plant filter bed(APFB) were used for processing the tailrace of rural domestic wastewater which processed by biological treatment process. By sifting through economical plants and different arrangement in collocation, plant species of APFB were enriched and the processing effect of economical APFB were improved. At last, reaching the aim of establishing "polluting-purification agriculture" and achieving the goal of recycling nitrogen and phosphorus resource. The main research results are as follows:(1) In summer and autumn, Amaranthus tricolor?Spinach Malabaricae and A. tuberosum Rottl. ex Spreng.'s average removal efficiency in each different arrangement in collocation, TP was 26.52%,29.12%?19.33%; NH4+-N was 20.88%.36.32%,34.32%; TN was 21.3%,30.5%,24.35%. In consequence, Spinach Malabaricae was the most suitable vegetable of the three planting in the APFB for pollutant removal. Amaranthus tricolor and A. tuberosum Rottl. ex Spreng. were suitable for high phosphorus and low phosphorus ammonia nitrogen and high ammonia nitrogen water purification respectively. Four different arrangements in collocation's pollutant removal performance in sequence were Ipomoea aquatica Forsk+Spinach Malabaricae> Ipomoea aquatica Forsk+A. tuberosum Rottl. ex Spreng.> Ipomoea aquatica Forsk+Amaranthus tricolor> A. tuberosum Rottl. ex Spreng.+A. tuberosum Rottl. ex Spreng.. When the Hydraulic loading of APFB increases from 0.14 m3/(m2d) to 0.30m3/(m2d), four different arrangements in collocation's removal rate's mean value of TP, NH4+-N?TN all have different varying decreases and the removal loads all increases. Among the four collocations,Ipomoea aquatica Forsk+A. tuberosum Rottl. ex Spreng. has the biggest increase, which is 0.14g/(m2d). Under a certain hydrotechnics condition, Amaranthus tricolor?Ipomoea aquatica Forsk and A. tuberosum Rottl. ex Spreng. were planted on three different densities(?i>?2,?3). The result showed that three kinds of vegetables'removal efficiency were on intimate terms with different densities. Under the certain hydrotechnics condition, with the increasing of depth of water in APFB, removal rates of TP?NH4+-N?TN were cut down, meanwhile, the removal loads increased. Ipomoea aquatica Forsk+Amaranthus tricolor and Ipomoea aquatica Forsk+A. tuberosum Rottl. ex Spreng.'removal rate first increased and then decreased with the water deepening which achieved maximum removal rate near 10 cm in APFB.(2) In winter and spring, with the insulation effect of plastic greenhouse, the experiment inspected the removal efficiency of Oenanthe javanica DC+ Chrysanthemum coronarium L. Chrysanthemum coronarium L.+ Medicago hispida Gaertn.?Lactuca sativa Linn.+ Nasturtium officinale R. Br. in one-stage APFB and two-stage APFB. Comparing from the vegetables' wastewater purification effect, the most suitable vegetable varieties in the order:Oenanthe javanica DC?Nasturtium officinale R. Br.?Lactuca sativa Linn.?Medicago hispida Gaertn., Chrysanthemum coronarium L.. Under a certain hydrotechnics condition, the effluent's mean concentration of two-stage APFB system in TP were 0.715mg/L?0.817mg/L?0.525mg/L respective; in NH4+-N were 5.045mg/L?7.704mg/L?5.297mg/L; in TN were 10.948 mg/L?19.108 mg/L?15.90mg/L.When the Hydraulic loading of APFB increases from 0.14m3(m2·d) to 0.30m3(m2d),hydraulic retention time decreases, then the removal rates of TP?NH4+-N?TN in each different arrangement in collocation reduce. Under a certain hydrotechnics condition, Oenanthe javanica DC? Chrysanthemum coronarium Land Lactuca sativa Linn.were planted on three different densities(?1? ?2??3). The result showed that three kinds of vegetables'removal efficiency were on intimate terms with different densities. Under the certain hydrotechnics condition, with the increasing of depth of water in APFB, removal loads of TP?NH4+-N?TN of Oenanthe javanica DC+ Chrysanthemum coronarium L.?Chrysanthemum coronarium L.+ Medicago hispida Gaertn.?Lactuca sativa Linn.+ Nasturtium officinale R. Br. were increased. Combined with the removal rates and the change trend of removal loads, choosing the best water depth in APFB is 1 Ocm.(3) According to the least squares method, setting test dates as function regression process and using the optimal principle could obtion the two-stage APFB's TP?NH4+-N?TN's optimal hydraulic loading(qbest)?optimal removal efficiency(?best) and the vegetables' optimal planting density(pbest)?optimal removal efficiency(?best) in APFB ecosystem. Through the values we can intuitively observe each vegetable arrangement in decontamination ability and provided the theoretical basis for plant's selection and collcation?choosing proper planting density and designing APFB in practical application.(4) Plants nutrient absorbing kinetic experimental results showed that the maximum uptake rate (Imax) and the Michaelis-Menten constant (Km) was significantly different between the six plants' root systems. Ipomoea aquatica Forsk'root system owned the maximum Imax and minimum Km, which was suitable for treatment of all levels of polluted water; Lactuca sativa Linn, was proper to purify polluted water with low level of nitrogen and phosphorus; Medicago hispida Gaertn. was applicable to repair polluted water with high H2PO4-,NH4+-N and low NO3-N concentration; A. tuberosum Rottl.ex Spreng should be selected as pioneer plant to purify polluted water with high level of nitrogen and phosphorus; Brassica juncea var. was more fit for low H2PO4-,NH4+-N and high NO3-N concentration wastewater purification; Coriandrum sativum had lower Imax and higher Km, which showed that Colocasia esculenta L. was not suitable for ecological rehabilitation. Analysising from the perspective of economic benefit, Lactuca sativa Linn.and Nasturtium officinale R. Br.'s economic benefit were the highest and theirs per mu yield economic benefits in high density(?1) were RMB 52700?RMB 37600 respective. The second were Ipomoea aquatica Forsk and Oenanthe javanica DC which were types of commonly used vegetable in mass production and theirs economic benefits were RMB 15600?RMB 14400.Taking the Ipomoea aquatica Forsk cultivated in summer and autumn and with the Nasturtium officinale R. Br. cultivated in winter and spring as an example, the APFB ecosystem yield was around RMB 26620 per 667m2.The results showed that the economical aquatic plant filter bed plants selected in the experiment almost had higher removal efficiency and could play good roles in advanced treatment for tailrace of rural domestic wastewater, at the same time, achieved considerable economic value.