Studies On Comprehensive Bioremediation Technologies For Eutrophication Pollution Of Coastal Water

Eutrophication of coastal water can cause a series of world‐wide problems, such as the frequently occurring of harmful algal bloom, the oxygen deficit of bottom water, the ebb of fishery resources and the decline of biodiversity. In allusion to the eutrophication features of coastal water body, it is necessary for various environmental scientists to develop a high‐efficient, low cost and strong operabilitive technology for eliminating eutrophication pollution in coastal water body.In this research, several kinds of marine creatures, which have different niche and reciprocal behaviours, such as large algae, filter‐feeding bivalve and marine bacteria were seleceted and applied alone or in combination for bioremediation of eutrophication water in laboratory and in‐situ mesocosm enclosure experiments. Based on these results, the comprehensive bioremediation technologies for eutrophication water were developed in order to high‐efficiently removing of eutrophication pollutants and improving of coastal water quality. These results could provide the theoretical foundation and be helpful for large‐scale application of bioremediation to control eutrophication of coastal water. The main results of this paper are as follows:(1) According to the nitrosation activity, nitrification activity, and COD (chemical oxygen demand) degradation efficiency, several bacterial strains, including nitrite bacteria, nitrate bacteria and organic matter degradading bacteria, were screened. The optimum conditions for bacterail growth were also established. For nitrite bacteria, the optimum pH value was7.0~9.0and the optimum tempurature value was25~35℃, and the bacterial nitrosation activity was suppressed with the presence of the high concentration of organic matters. For nitrate bacteria, the optimum pH value was7.0~9.0and the optimum tempurature value was25~35℃. For the organic matter degradading bacteria, the optimum initial COD value was5.0~200mg/L, the optimum pH value was6.0~9.0, the optimum tempurature value was25~35℃.(2) According to the removal efficiency of TSS (total suspended solid), a kind of bivalve of chlamys farreri larvae, which had high filter‐feeding efficiency of TSP, was screencd. And the optimum conditions for chlamys farreri growth were also established as follows: dosing density as400~600individual chlamys farreri per cubic meter of seawater, and saliny as22.00~35.00.(3) According to nutrient uptake efficiency, a kind of large algae of asparagus, which had high uptake efficiency of nitrogen and phosphorus nutrient and had a high economic value. And the the optimum conditions for asparagus uptake nutrient were also investigated. The uptake rate of NO3‐N and NH4‐N increased with the increase of the concentration of NO3‐N and NH4‐N in the concentration range of0.056~2.240mg/L and asparagus adsorbed NH4‐N preferentially the other optimum conditions for asparagus uptake nutrient as follows: N:P ratio as16:1, temperature as18~25℃, saliniy as28.00~32.50and initial pH as7.0~8.5(4) The in‐situ mesocosm enclosure experiments were set up and the comprehensive bioremediation technologies for eutrophication coastal water were developed on the base of combination application of bacteria, filter‐feeding bivalve and large algae. The results showed that the eutrophication pollutants in coastal seawater were removed high‐efficiently with the combination of bacteria, chlamys farreri and asparagus. During the90‐d bioremediation period, the removel rates of DIN and PO4‐P of the comprehensive remediation system were94.2%and99.2%, and increased51.2%and8.0%than that of control system, respectively. The removel rates of COD and TSS of the comprehensive remediation system were40.6%and85.1%, respectively. After bioremediation, the water dissolved oxygen value increased73.0%and pH value also increased remarkalbly than before bioremediation. Meanwhile, the total number of heterotrophic bacteria of the comprehensive remediation system was decreased than that of control system. The above results demonstrated that the water qualities improved by comprehensive bioremediation.