Effects Of Improvement Of Nitrate Accumulation In Aquaculture Water By MBBR-Chaetomorpha Maxima Clonal Combined System

China as the largest aquaculture producer in the world,has developed kinds of ways to culture aquatic animals,such as pond culture,flow-though,recirculating aquacultural systems,etc..However,traditional ways,such as flow-thought way will produce a large number of pollutions and induce serious pollution to the surrounding aquatic environment.Due to the limited resources and demand on environmental protections,it is crucial to develop aquaculture in a sustainable way in China.Compared with the traditional aquacultural ways,the modern industrial recirculating aquacultural way could reuse the water by the integrated methods of engineering and chemistry.Moreover,high dissolved oxygen,further the optimal water quality is maintained in the systems.In the recirculating aquaculture systems,the autotrophic nitrification process converts ammonia nitrogen,which is most toxic to animals,into nitrite,and finally into nitrate which is relatively less toxic.In the recirculating aquaculture systems,if there is no denitrifying reactor,nitrate will be accumulated in a high concentration.Recent studies have shown that nitrate in a higher concentration would also affect the growth of cultured animals,even cause the death.Therefore,more attentions were focused on how to remove the nitrate in recirculating aquaculture system is attracting.Nitrate in seawater can be converted into nitrogen through denitrification by the microorganisms.However,this process takes a long time,required the additional carbon sources,and the strict control of the water conditions for the denitrification.Seawater plants,such as the algae,could absorb the ammonia nitrogen,nitrite,nitrate in seawater and convert them into their own cellular substances with relatively high efficiency,which could possibly solve or alleviate nitrate accumulation in aquaculture wastewater.In order to reduce the accumulation of nitrate in the circulating aquacultural system,this paper studied the ability of Chaetomorpha maxima to treat nitrogen in aquacultural wastewater,and the ability of MBBR-Chaetomorpha maxima clonal combined system to treat nitrogen salts,especially NO₃^--N,and P elements in aquacultural wastewater.The combined system could provide theoretical basis to develop the sustainable and optimal circulating water aquaculture system.The conclusions of current research are as follows:In a certain concentration range,the absorption rate of nitrogen is increased with the the rising of nitrogen concentration.When the input densit of Chaetomorpha maxima is 10±1 g/L,The removal rate of TAN is 40⁵0%,which is not affected by TAN concentration.the removal rate of NO₂^--N and NO₃^--N is decreases with the the rising of nitrogen concentration.Chaetomorpha maxima first choose to absorb TAN,when the concentration of TAN,NO₂^--N and NO₃^--N nitrate is the same.Then choose NO₂^--N and NO₃^--N when TAN is 1.5 mg/L.After 15 hours,the removal rates of TAN,NO₂^--N and NO₃^--N from aquaculture wastewater by Chaetomorpha maxima were 94.3%,100%and 82.2%.The removal rates of TAN,NO₂^--N,NO₃^--N,TN and TP in aquaculture wastewater(TAN:2.0±0.5 mg/L,NO₂^--N:0.1±0.05 mg/L,NO₃^--N:2.0±0.5 mg/L,PO₄^3--P:0.2±0.05 mg/L,TN:4.5±0.5 mg/L,TP:0.3±0.05 mg/L,temperature:20²5℃,salinity:31‰)by the MBBR-Chaetomorpha maxima complex system were about 90%,70%,50%,50%and 80%.The light intensity is 15000 lx.The removal rates of TAN and NO₂^--N by MBBR were 90%and 70%without algae,but the HRT was increased.After 2³ cycles of recovery,the HRT of MBBR can return to normal level.However,it was found that NO₃^--N accumulated in the water.The effluent NO₃^--N concentration reached 3.5⁴ mg/L,the TN and TP removal rate was basically zero.Chaetomorpha maxima had a certain effect on the microbial community structure in MBBR,especially nitrosobacteria and nitrifying bacteriareduced.And Chaetomorpha maxima had a negative effect on the formation of microbial membrane at the initial stage of membrane hanging.