| Recirculating aquaculture is a new mode of aquaculture technology which has lots of advantages,such as the intensive degree and breeding effect.At present,the core of water treatment is biological purification to remove the nitrogen and phosphorus by bacteria and algae.However,the problem of unstable biological purification effect and excessive pollutants in the seawater often occur in our application.Electrochemical treatment technology make use of a series of physical and chemical reactions to promote the pollutants decomposition and transformation under the electric field,with fast reaction speed and high treatment efficiency.what's more,which has obvious advantages in the treatment of seawater.Previous studies mainly focused on the treatment of ammonia by electrochemical technology.Based on this,in this paper we explored the comprehensive removal of inorganic nitrogen,organic matter and bacteria in recirculating mariculture system and carried out the study of energy consumption during the electrochemical operation.In view of the high concentration accumulation of nitrate,the experiment verified the technical feasibility of simultaneous removal of ammonia and nitrate.Then,the response surface analysis method was used to optimize the simultaneous removal of nitrate,the efficiency of nitrogen removal rate was improved remarkably.On the basis of the above test,the electrolysis technology was applied to the recirculating aquaculture system to compare the aquaculture effect under the modes of biological purification and electrochemical treatment.The main conclusions of the experiment were as follows:(1)The removal efficiency of various pollutants by electrochemical was positively correlated with the current density.As the current density increased from 2mA/cm~2 to 12 mA/cm~2,the removal rate of ammonia increased from 46.9%to 97.8%,the removal rate of nitrite increased from 32%to 95.5%,and the removal rate of COD risen from 25.7%to 73.1%.(2)The hypochloric acid generated by electrolysis and the increased Redox potential played a good role in sterilization.After 40 min of reaction,the sterilization rate in different current density groups reached 100%.It took 72 hours for the free chlorine produced after electrolysis to decrease from 20.2 mg/L to 1.7 mg/L.Free chlorine had potential influence on cultured organisms,which was the main reason affecting its large-scale promotion.(3)The response surface model was used to optimize the removal conditions of nitrate,and the results showed that the nitrate removal rate was the highest when the current density was 25.6 mA/cm~2,the area ratio of anode and cathode plates was 1.6:1,the plate spacing was 2.5 cm,and the initial pH value was 6.6.The highest removal rate was 81.5%,the removal rate of ammonia also reached 87.3%.There was no accumulation of nitrite under this condition.The experiment showed that the response surface optimization method could significantly improve the removal efficiency of inorganic nitrogen.(4)The recirculating system with electrochemical treatment could effectively reduce the content of ammonia,nitrate and bacteria.However,the content of transaminase and antioxidant enzyme in Verasper variegatus increased due to the free chlorine,which were 20.81-86.07%higher than that in the biological group.In addition,there was a certain gap on specific growth rate,feed coefficient and other growth indexes. |
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