The Study On The Effect Of Biofloc On Water Quality And Plankton By Strain With Flocculation Activity

In this study,the strains with flocculating activity were extracted and selected from ponds in water as the tested strains,and glucose added as carbon sources in the water to cultivate biofloc,and the structure of biofloc,physical and chemical indexes of water quality and the changes of plankton studied.The main results were shown as follows:Experiment 1:Thirty-one species of strains were isolated and purified from cultured pond water,we firstly screen out the 7 species with flocculating activity by the flocculation effect of each strain on Kaolin suspension.The stability and further compares the flocculation rate and the flocculating activity of the strains on the screening of kaolin suspension,and 1 strains with stronger flocculation activity and more stable strain was finally selected,named strain BX-13.Bacterial colony morphology observation,physiological and biochemical analysis,identification and 16S rDNA sequence analysis of strain BX-13 were carried out,and the preliminary determination of the strain BX-13 was Bacillus subtilis.Experiment 2:In the experiment,the pond water as test water,and the strain BX-13 was used as the test flocculant,and glucose as the carbon source added to cultivate the biofloc.The strain BX-13 as the test strain,three treatments and one control group were designed,adding glucose as treatment I,the strain BX-13 and glucose were added as treatment II,only adding strain BX-13 as treatment III,the control group without nothing.The amount of heterotrophic microorganisms,total suspended solids and biofloc volum were detected,and the formation of the aggregates was analyzed by microscopic observation and analysis every 5 days.The results were shown as follows:only adding srain BX-13 failed to form clear biofloc,and the biofloc with mature structure were formed in the group adding glucose(treatment I)and the group simultaneous addition of glucose and flocculation activity of bacteria BX-13(treatment II),which indicated that organic carbon source is one of the key factors to biofloc formation,adding flocculating activity strain BX-13 without carbon source can not form biofloc,the mature biofloc in the treatment II was formed about fifteenth days,while that in the treatment I about twentieth days,the time of the biofloc cultivated by strain BX-13 about 5 days in advance,and the structure of biofloc in the treatment II was more stable than than in the treatment I.which showed that,the strain BX-13 can accelerate the formation of biofloc,and the biofloc cultivated by strain BX-13 was more stable than that cultivated by glucose.Compared with the biofloc cultivated by Staphylococcus aureus,the biofloc volume and the structure of that cultivated by the strain BX-13 were significantly better.Experiment 3:In the process of cultivating biofloc by strain BX-13,the water sample was tested,and the results showed that,the p H and dissolved oxygen content in the treatment I and treatment II were decreased significantly compared with that in the control,and the content of ammonia nitrogen and nitrite nitrogen decreased rapidly before the formation of mature biofloc(First to Fifteenth days),the change of the p H and the content of dissolved oxygen,ammonia nitrogen and nitrite nitrogen were not significant after fifteenth days.At fortieth days,the content of ammonia nitrogen and nitrite nitrogen in the treatment II decreased by 79.69% and 74.42% respectively,while that in the control were 23.08% and 29.55%,respectively.Which showed that,under the condition of this experiment,the ammonia nitrogen and nitrite nitrogen can be removed effectively by the biofloc cultivated by strain BX-13,and the content of the ammonia nitrogen and nitrite nitrogen concentration can be controled at low levels.Experiment 4:In the process of cultivating biological flocculation by using flocculant strain BX-13,the qualitative and quantitative analysis of plankton in each group were done.the results showed that,the species and abundance of Cyanobacteria and Chlorophyta decreased significantly(P<0.05)after the formation of biological flocculation,while the abundance of copepods and rotifers increased significantly(P<0.05),which indicated that the biofloc cultivated by the strain BX-13 can reduced the number of water in Cyanophyta and Chlorophyta,especially the more inhibitory obvious on Microcystis,Lyngbya,Platymonas,Gonium and Volvox,and effectively promote the growth of of feed plankton,such as rotifers,etc..The results above indicated that,the biofloc can be cultivated by using the strain BX-13 under the conditions of this study,the time of the formation of the biofloc was significantly shortened,and the structure of the biofloc cultivated by the strain BX-13 was relatively stable,and the ammonia nitrogen and nitrite nitrogen can be removed effectively,which can not only reduce the number of water in Cyanophyta and Chlorophyta,effective inhibition of the growth of Microcystis,Lynbya,Platymonas,Gonium and Volvox,but also promote the growth of feed plankton(rotifer and cladoceran).