Study On The Characteristics Of Aquaculture Wastewater Purification In Fallow Fields

On the one hand,aquaculture wastewater is an important part of rural non-point source pollution.On the other hand,aquaculture wastewater is rich in nitrogen and phosphorus resources,which can be used as resources.This study combines the characteristics of aquaculture wastewater discharged in winter with the characteristics of paddy fields that need to divert water to adjust the soil during fallow in winter,and propose a technology for the reuse of aquaculture wastewater in fallow fields.This research focuses on the effect of this technology on the purification effect of aquaculture wastewater and soil fertility,and explores the removal methods of typical antibiotics in aquaculture wastewater.The main findings are as follows:Through the construction of an indoor test device,the influencing factors of water purification were studied,and the impact of wastewater reuse on soil nitrogen,phosphorus and organic matter content was explored.The results showed that when the water volume was 300 L·m^-2,the water purification effect was the best,and the removal efficiency of TN,TP,and CODcr were 87.6%,57.9%,and 60.4%,respectively.Planting plants could significantly improve the water purification effect.Cress（oenanthe javanica DC.）absorbed 28.7%and 16.2%of nitrogen and phosphorus,respectively,and calamus（acorus calamus L.）absorbed 32.6%and 14.9%.The concentration of DO in the upper water is relatively high,reaching 3.79mg·L^-1,and the removal rates of NH₄⁺-N,TP and CODcr can reach 95%,80%and 65%,respectively,while the hypoxic environment in the lower layer has a negative effect on NO₃^--N,the removal rate is the highest,reaching 98%.Through research and analysis of the purification effect of the typical antibiotic sulfamethoxazole（SMX）in the wastewater in the fallow field system.Analyze the contribution of soil adsorption and fixation,plant absorption and degradation to the removal of antibiotics.And study the impact of SMX on water purification,plant growth and microbial community structure.The results show that degradation is the main way to remove SMX in water,and the removal contribution rate is 62.6%-77.3%.The second is soil adsorption,with a removal contribution rate of 22.6%～37.3%.The contribution rate of cress absorption to SMX removal is only 0.035%～0.081%.The influence of SMX on the microbial community at the phylum level is not obvious.At the genus level,three types of dominant bacteria,Arthrobacter,Sphingomonas and Bacillus,that degrade SMX have been detected.And when the SMX concentration is 10 mg·L^-1,the relative abundance of the above three types of bacteria is the highest.SMX has a significant effect on water purification,and the removal effects of TN,NO₃^--N,TP and CODcr all decrease with the increase of SMX concentration.The growth of cress is under SMX stress,which is negatively correlated with SMX concentration.Within the higher concentration of SMX used in this experiment,the residual SMX in the cress has a certain risk to human health through the food chain.According to the research results of the small-scale test,carry out the engineering demonstration application test.Explore the water purification effect of fallow fields on aquaculture wastewater under natural conditions.Analyze the changes in soil fertility,and determine the feasibility of waste water harmlessness-resource reuse through risk assessment.The results show that about 18 days after irrigation,the overall water quality of the water can be restored to the background level.Receiving wastewater can improve soil fertility and increase the content of alkaline hydrolyzable nitrogen and available phosphorus in the soil.The biological diversity and structural stability of the soil itself have a good"buffering capacity"for environmental changes caused by irrigation wastewater,and there is no significant change in the structure of the microbial community.The actual production of antibiotics in fish ponds poses a moderate risk to the ecological environment of the water,and the concentration of heavy metals in wastewater is low,which meets the agricultural irrigation standards.The risk entropy of residual antibiotics in crops and soil is less than 0.01,and the risks to human health and soil ecology are negligible.