Research On Nitrous Oxide?N₂O?Release Characteristics From Intensive Aquaculture System And Its Reduction Strategies

With the growth of the population and the development of aquaculture technology,traditional aquaculture and fisheries cannot meet the demands of fish products.Intensive recirculating aquaculture system has developed rapidly at home and abroad in recent years due to its high-density fish production and management.However,the intensive recirculating aquaculture system can produce a large amount of nitrogen compounds,leading to the release of greenhouse gas(GHG):nitrous oxide(N2O),the increasing concentration and the strong greenhouse effect of which has attracted great attention from scientists.At present,few characters and the release mechanism of N2O was reported,as well as the limited study on the reduction of N2O emissions,which is caused by the denitrification process in waste water of intensive recirculating aquaculture systemThis study monitored the release of greenhouse gas N2O after building intensive recirculating aquaculture systems of laboratory-scale to clarify the impact of intensive aquaculture farming on global climate change.Addition of electron donor was used to examine the nitrogen transformation after mastered the mechanism of N2O production in the system,while optimizing of denitrification process for reducing N2O emissions during the cultivation procession the basis of mechanism of N2O production in the system,the influence of external carbon source as electron donor on nitrogen migration and transformation was explored,while the process of nitrite-dependent anaerobic methane oxidation(N-DAMO)was introduced,and the feasibility of N2O emission reduction in enhanced system that coupling methanogenesis with N-DAMO nitrogen removal process by electricity was discussed in intensive recirculating aquaculture system.The main conclusions are as follows:(1)The intensive recirculating aquaculture system is an important source of N2O emission.The N2O-N emission factor of the system is about 1.3%,and the global aquaculture system will cause 1.40×1011g N2O-N emission by 2030 according to this factor and FAO.The N2O emission rate was positively correlated with DO concentration,NO2-—N and NH4+—N concentration in the system,while the feeding rate and DO were determined as the key factors influencing the N2O emission.The results of stoichiometric analysis showed that the nitrification and denitrification processes can influence the emission of N2O significantly,contributing 50%to the release of N2O each.(2)The addition of carbon source could significantly reduce the emission of N2O by 83.4%in intensive recirculating aquaculture system.Adjust C/N ratio as 16:1 using soluble starch,and it turns out that external electron donor can strengthen the growth of heterotrophic microorganisms and enhance denitrification process effectively in the system.The concentration in the system was lower than that of the control group,which lead to better water quality.Furthermore,the addition of soluble starch also significantly improved the reproductive performance of fish and the accumulation of SMP in the system,which in turn increased the productivity of the aquaculture system.However,the addition of carbon sources reduced the emission of N2O while increased the amount of CO2 release by 91.1%,which increased the total GHGs emission of the system by 60.2%.The addition of carbon sources to make 76.2%of input-nitrogen released into the atmosphere in the form of gaseous nitrogen(i.e.,N2 and N2O)by promoting the denitrification process,which is much higher than 33.3%of the control group,and decreased the using efficient of nutrients.(3)The coupled system of electrochemically enhanced methanogenic biocathode methane production and partial nitrification with N-DAMO microorganisms can significantly reduce the N2O release of intensive aquaculture system.The N-DAMO microorganisms and methanogenic biocathode were successfully cultivated,and the emission of N2O during the N-DAMO process was as low as 0.045?mol·L-1·d-1based on the batch test while the CH4 production was up to 257.23±27.15 ?mol·L-1·d-1,and the N2O in MEC is under detection limit.Based on the results of this study,the coupled denitrifing system could reduce 54.17%of GWP while applying in intensive recirculating aquaculture system,which has significant environmental benefits and application prospects.