Preliminary Study On Bio-purification Of Water In Intensive Fishpond

The experiments were designed to compare the purification efficiency of two different purification methods in reconstructed traditional fishpond through installation of brush biofilter purification unit and water spinach(Ipomoea aqutica) purification unit in intensive fishponds repectively.Improvement effects of the two purification ways to the eutrophication pond water wwew studied.Mechanism of the purification was discussee, which provides basis for establishing the intensive fishpond purification system.The indoor experiments were also carried out to study the proper planting densidy of Vallisineria spiralis and brush biofilter in fishpond water,which serve as a base for future research.1.In pond water purification experimentsTwo test ponds(No.1,No.2) and one control pond(each pond using plastic member to separate the culture unit and the purification unit) were used in the experiment to determine the water purification efficiency.A pump was used to pumping water from the purification unit to fish culture unit for water exchange.In the No.1 test pond's purification unit,brush biofilters was used for water purification,in the No.2 test pond's purification unit,used hydrophytes for water purification.In the fish culture area,No.1,No.2 and the control pond has same total stocking amount.the experiment was divided into three periods,change the density of brush biofilters,hydrophytes in the No.1,and No.2 test ponds' purification unit in each period.The results showed that:brush biofilters and hydrophytes have good function in removal of nutrients in pond water in every period.Purification results of the two biological purification methods are close on the whole.In pond No.1,DO was maintained at a higher level;brush biofilters had a better purification effect on TN,NO₃^-,NO₂ and TAN.In pond No.2,SD was maintained at higher level;hydrophytes had a better purification effect on P and TSS;the effect on DO need to be further studied.2.Indoor experiments on the nitrogen and phosphorus removal efficiency with diffrent density of Vallisineria spiralisResults of experiments under static condition indicate that the different density of Vallisineria spiralis has an obvious elimination effect on TAN,TN,PO₄^3-,TP and COD in pond water and can significantly improve the DO and pH value of the pond water. Compared with the removal ability to nitrogen,Vallisineria spiralis has better purification efficiency on phosphorus.Analysis of water quality condition in different experimental treatments according to Merrow index,the suggested proper density of Vallisineria spiralis plant in pond water is 3.6 g/L.3.Indoor experiments on the nitrogen and phosphorus removal efficiency by diffrent density of brush biofilterExperimental results indicate that under static condtition,brush biofilter of diffrent density has an obvious elimination effect on TN,NO₃^-,NO₂^- and TAN in pond water.To some degree,brush biofilter can improve the pond water DO and cause relatively low pH value. When the ratio of brush biofilter length to depth of water is about 1,the suggested proper density of brush biofilter in pond water is 8～9 ind/m².