| Eutrophication has been a serious problem of water environmental pollution. In addition, multiple contaminations composed of various pollutants have been a difficult problem in water environment remediation. Nitrogen, phosphorus and organic matters are relatively prominent pollutants among these pollutants while nitrogen and phosphorus are the main causes of eutrophication. Therefore, it is necessary to find out a remediation technology which can simultaneously and effectively remove various pollutants from water body. This study develops the research on removal of various pollutants by establishing algae-bacteria-submerged plant metabolic system and cooperative constructed wetlands in pond-bed intergrated constructed wetland. The prime work and achievements are as follows:(1) Research on the effect and mechanism of water purification in high rate algae pond. The research revolved around the group with high-algae-concentration influent in summer(HRAP-H), group with low-algae-concentration influent in summer(HRAP-L) and group with high-algae-concentration influent in autumn(HRAP-T). Each group had three influents with different algae concentrations. The aim of above arrangements was investigating the effect of influents with different algae concentration and temperature variation casued by season on the water purification of high rate algae pond(HRAP). Research showed that p H and DO presented diurnal variation in HRAP, which was propitious to ammonia volatilization and phosphate precipitation. Ammonia nitrogen in HRAP was mainly removed by ammonia volatilization and assimilation of algae, while HRAP-H had optimal removal efficiencies of NH4-N and TN. The effect of temperature variation on algae biomass was greater than the effect of algae concentration in influent on algae biomass. Phosphorus in HRAP was mainly removed by assimilation of algae and phosphate precipitation. HRAP-H had optimal removal efficiencies of PO3-P and TP among three groups. The organic matters in HRAP were mainly removed by aerobic degradation of microorganisms. HRAP-H had optimal removal efficiencies of DCOD among three groups. The effect of temperature variation on water purification in HRAP was greater than the effect of algae concentration in influent on water purification in HRAP. Therefore, HRAP-T had the worst removal efficiencies of various pollutants among three groups. In addition, hydraulic rention time(HRT) had a significant impact on water purification of HRAP while removal efficiencies of various pollutants in HRAP had been greatly improved with the extension of HRT.(2) Research on the effect and mechanism of water purification in submerged plant pond. The research revolved around the group with high-quality-concentration submerged plants in summer, group with low-quality-concentration submerged plants in summer and group with high-quality-concentration submerged plants in autumn. Each group had three kinds of submerged plant including Ceratophyllum demersum L., Myriophyllum verticillatum L. and Vallisneria spiralis L. The aim of above arrangements was investigating the effect of submerged plants and its biomass on the water purification of submerged plant pond. Simultanesouly, it was necessary to investigate the allelopathic effect and allelochemicals of submerged plants. The results indicated that p H and DO presented diurnal variation in submerged plant pond which was relevant with the algaes of influent. The NH4-N removal pathways in submerged plant pond included: the assimiliation of submerged plants, ammonia volatilization and nitrification. Submerged plant pond with Ceratophyllum demersum L. had the optimal removal efficiencies of NH4-N and TN among three kinds of submerged plant ponds.In addition, the nitrogen removal efficiencies of submerged plant pond in summer were greater than the nitrogen removal efficiencies of submerged plant pond in autumn. The phosphorus removal pathways in submerged plant pond included: 1. the assimiliation of submerged plants on soluble phosphates; 2. submerged plants provided attached surfacr for poly P bacterias and other microorganisms, which was propitious to the function of microorganisms on phosphorus removal. Additionally, p H variation was propitious to phosphorus precipitation. All groups in summer had obtained over 90.0% of PO3-P and TP removal while there were significant differences on PO3-P and TP removal among the groups in autumn. The main reason was: i) the low temperature in autumn had an impact on the growth of submerged plants, and ii) the low p H impeded phosphorus precipitation. In addition, organic matters were mainly removed by the degradation of microorganisms under aerobic conditions in submerged plant pond. Therefore, the oxygen contents in submerged plant pond had a significant impact on the removal of organic matters. The organics removal of submerged plant pond in summer was greater than that of submerged plant pond in autumn while the group with high-quality-concentration submerged plants in summer had optimal removal of organic matters among three groups. The removal efficiencies of various pollutants in submerged plant pond had been greatly improved with the extension of HRT. Effect of temperature variation on water purification of submerged plant pond was greater than the effect of submerged plan biomass on water purification of submerged plant pond. Comparing the allelopathic effect of three kinds of submerged plant, Vallisneria spiralis L. had the optimal allelopathic effect. Three submerged plants all had allelochemicals by the analysis of GC-MS.(3) Research on the effect and mechanism of water purification in horizontal subsurface flow constructed wetland. Organic matters were usually removed by the degradation of microorganisms under aerobic conditions in horizontal subsurface flow constructed wetland(HSSFCW). Therefore, the dissolved oxygen contents in HSSFCW had a significant impact on the removal of organics. In addition, three factors had significant effect on nitrogen removal in HSSFCW, including influent DCOD/TN, depth and plants. An increase in the DCOD/TN ratio led to increased reductions in NO3 and total nitrogen(TN) in planted and unplanted wetlands, but diminished removal of NH4. The planted HSSFCW exhibited a significant reduction in NH4 compared to the unplanted system. There was no significant difference in NO3 removal between the planted and unplanted wetlands. NH4 reductions were greater in planted wetland at the 20 cm and 40 cm depths while NO3 reductions were uniformly greater with depth in all cases, but no statistical difference was impacted by depth on TIN removal.(4) Research on the effect and mechanism of water purification in pond-bed integrated constructed wetland. The pond-bed integrated constructed wetland consisted of high rate algae pond, submerged plant pond and horizontal subsurface flow constructed wetland. High rate algae pond and submerged plant pond could improve the influents of horizontal subsurface flow constrcucted wetland by increasing the oxygen content and carbon source of wetland, which enabled the wetland to be a deep purification technology. The removal of NH4-N、TN and COD increased a lot in pond-bed integrated constructed wetland with the extension of HRT. Under the HRT of 3d and 5d, removal of PO3-P、TP and DCOD reached above 99.0% in pond-bed integrated constructed wetland.(5) The differences on removal efficiencies of various pollutants between single system and integrated system. In three single systems, high rate algae pond and horizontal subsurface flow constructed wetland echo like the head and tail. They had been the main disposal system in pond-bed integrated system while submerged plant pond acted as a bridge to promote the synergistic purification of three single systems. Under the HRT of 3d, removal of PO3-P、TP and DCOD reached above 99.0% in three single systems and pond-bed integrated constructed wetland. In addition, the removals of NH4-N and TN were 73.5% and 71.5% in integrated system, which were significantly higher than three single systems. Intergated system not only developed the advantages of single systems, but also offset the disadvantage of single systems. The integrated system makes advantage of the synergistic reaction among single systems to remove various pollutants simultaneously and effectively. |
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