Study On Purifying The Aquacultural Wastewater With Immobilized Microorganism And Myriophyllum Aquaticum Integrated System

It is the premise of healthy, efficient and sustainable recirculating aquaculture water, tocontrol the water quality in a good situation.How to get one cost-effective purification way is theresearch focus recently. To achieve the high efficiency of purification, different input densities ofimmobilized microorganisms （I） and Myriophyllum aquaticum （M） were used to purifyeutrophic and mesotrophic aquaculture wastewater. Based on the above, Optimized input density ofimmobilized microorganisms and Myriophyllum aquaticum was used to purify aquaculturewastewater. The main results were summarized as follows:1. As the supporter, ceramics were utilized to immobilize the strains of Bacillus megateriumand Bacillus flexus., which are high-efficiency at denitrification. The eutrophic and mesotrophicartificial simulated aquaculture wastewater were purified by different input density of immobilizedBacillus megaterium and Bacillus flexus, and the variation of physicochemical parameters inwastewater were investigated. It showed that, until the7thday, the removal of CODMnperformanced by e-I_Mwas57.06%, significantly higher than that by e-I_M（35.46%） and e-I_L（17.79%）（P<0.05）. e-IHshowed higher removal rate of ammonium and nitrate removal rate,while there was no differences at the removal rate of nitrite between e-I_Mand e-IH（P>0.05）。Inthe preliminary period（0¹0days）, m-IHshowed good performance at removal of TN，but nodefferences at nitrite removal between e-I_Mand e-IH（p>0.05）during the last period（after10days）. m-IHshowed higher removal rate at TP than I_Land I_M。In addition, the Dehydrogenase（Deh）, Urease（Ure），Alkaline phosphatase （Akp） activity of microorganisms onceramics were also investigated. Result of redundancy analysis show that there was significantpositive correlation between the removal rate of TN, TP, CODMnand the Deh, Ure, Akp activity,which suggested that microorganisms on ceramics surface has played an important role in removalof nitrogen and phosphorus in wastewater.2. Before different input density of it was utilized to purify the eutrophic and mesotrophicaquaculture wastewater, Myriophyllum aquaticum was cultivated in the lab. The variation ofphysicochemical parameters in wastewater was investigated. Compared to MLand MM，MHshowed the higher removal rate of TN, while removal rate of nitrite performed by MHand MMwasno difference. At the last period, removal rate of ammonium by m-MMexceeded that by m-MH, until the35thd, removal rate reached84.23%, significantly higher than that by2-MH（69.03%）和2-ML（47.25%）（p<0.05）. Besdies, the Deh, Ure, Akp activity of microorganisms surroundingthe roots in wastewater were evaluated. RDA that there was significant positive correlationbetween the removal rate of TN, TP, CODMnand the Deh, Ure, Akp activity, which suggested thatmicroorganisms around the roots has played an important role in removal of nitrogen andphosphorus in wastewater.3. This experiment was conducted by employing immobilized microorganisms （I） onceramics and Myriophyllum aquaticum （M） and unloaded ceramsite （UC） to purifyaquaculture wastewater in the lab. Different nitrogen forms removed from aquaculture wastewaterand the dynamic distribution of four groups of bacteria involved in nitrogen cycling, ammonifiers（AB）, nitrosobacteria （NOB）, nitrifiers （NB） and denitrifiers （DB）, were evaluated.Our results revealed that the removal efficiency of nitrogen and chemical oxygen demand（CODMn） performed by the combined treatment （I+M） was significantly higher than whenused separately （P<0.05）. By the end of day15, the nitrite and ammonium removal rate by theI+M treatment reached50.83%and62.38%, respectively, significantly higher than I （39.55%and51.17%） or M （40.78%and53.31%） separately （P<0.05）. At the end of theexperiment（25thday）, CODMnremoval by the I+M treatment was significantly higher（67.23%） than that of treatment I （48.23%） or M （33.35%）（P<0.05）; the nitrateremoval rate （88.74%） was also significantly higher than I （67.85%）, but there was asignificant difference between I+M and M （P<0.05）. In addition, four groups of bacteria on theroots surface increased in certain extent compared with treatment M, and during the last period fourgroups of bacteria on the ceramic surfaces showed an overall downward trend, e.g. AB in treatmentI+M were1.8².6magnitudes lower than in treatment I. Principal response curve analysis（PRC） showed that Turbidity、NO₃^--N、TN contribute great to total difference, during theearly and middle stages of this experiment the combined treatment was more efficient at removingnitrogen than treatment I or M, but the overall differences between I and UC decreased greatly inthe later stage（after20thday） with differences between I+M and I becoming small.It showed that immobilized microorganisms and Myriophyllum aquaticum played animportant role in the nitrogen and phosphorus removal efficiency, the poisonous effect of NO₂^--Nand NH₄⁺-N on aquatic animals could be alleviated by their combination, making normalmetabolism of aquatic animals can be maintained. In practice, more factors should be taken intoaccount, eg. the level of eutrophication of wastewater, immobilized bacterial species compositionand their physiological and biochemical characteristics, to ensure that the aquacultural system isstableK,effcient and durable.