Effect Evaluation And Microbial Community Analysis Of Aquaculture Wastewater Treatment System Of Grass Carp

With the increasing attention of the state to the protection of aquatic ecological environment and the quality and safety,the discharge or recycling of aquaculture wastewater has become the key to the green and high-quality development of aquaculture."Three ponds and two dams" is the most common mode used in aquaculture wastewater treatment at present.By combining physical and biological methods,a field scale treatment system of three ponds and two dams for aquaculture wastewater was constructed by engineering modifications of waste ponds and ditches.It involves multiple stages of purification,so as to effectively remove pollutants(total nitrogen,total phosphorus,COD,etc.)from aquaculture wastewater.Pollutant removal efficiency is a key metric for assessing the effectiveness of aquaculture wastewater treatment.Therefore,this study constructed a "three ponds and two dams" aquaculture wastewater treatment system and evaluated the pollutant removal effect of the system.At the same time,16 S r DNA sequencing was used to analyze the composition,diversity,assembly mechanism,and nitrogen cycle properties of the bacterial community in the aquaculture wastewater treatment system.The results will provide a theoretical basis for system improvement and optimization,standard discharge of aquaculture wastewater,operation management,and generalization and application of the system.The main results of this paper are as follows:(1)Construction and operation of aquaculture wastewater treatment system for three ponds and two damsGuangdong Shunde Junjian Modern Agricultural Technology Co.,Ltd.,has an aquaculture base of 41 hectares,of which the wastewater treatment facility covers 4.7hectares,accounting for about 10 percent of the aquaculture area.By designing the multistage ecological wastewater treatment process of "three ponds and two dams",the treatment process of the aquaculture pond-ecological ditch(1100 meters)-constructed wetland(0.42 hectares)-sedimentation pond(0.58 hectares)-filtration dam-aeration pond(0.65 hectares)-ecological purification pond(0.8 hectares)-filtration dam-clean pond(1.63 hectares)was constructed,and the wastewater treatment was carried out.The operational effectiveness of the system was initially assessed by monitoring the water quality index of the water outlets of the constructed wetland,sedimentation pond,aeration pond,ecological purification pond,clean pond,and other treatment links.During the sampling period,the average removal rates of total nitrogen,total phosphorus,COD,ammonia nitrogen,nitrate nitrogen,and nitrite nitrogen were 95.56±0.06%,97.36±0.27%,60.10±0.90%,67.14±4.91%,97.07±0.25%,and 97.67±0.10%,respectively.This indicates a stable operation of the system.(2)Microbial community composition and construction mechanism of aquaculture wastewater treatment system in three ponds and two damsThe sustainability of aquaculture wastewater treatment systems depends on the stability of microbial ecological processes.Due to the unique habitat characteristics of aquaculture wastewater treatment systems,in depth studies of ecological processes such as the distribution of microbial community structures and assembly patterns are lacking.The main microbial communities in sediments are Proteobacteria(24.52%),Chloroflexi(19.94%),and Actinobacteria(16.61%).The main phyla in the water samples were Actinobacteriota(45.59%),Cyanobacteria(25.36%),and Proteobacteria(12.03%).The composition of bacterial and microbial communities in sediment is affected to some extent by spatial location,but not by time.The composition of bacterial microbial communities in water is mainly affected by temporal variations but less by spatial variations.Bacterial collinear network analysis shows that coexistence is dominant among bacterial species in sediment,while competition is dominant among bacterial species in water.The null and neutral community models adopted in this study suggest that the assembly process of bacterial communities in water and sediment in wastewater treatment systems is mainly stochastic process.In this study,stochastic processes in wastewater treatment systems can be explained by strong migration effects and weak environmental filtration.Although microbial drift in water is usually passive and affected by velocity,this result also suggests that the flow field may induce a stochastic distribution of microbial communities.It has been pointed out that the stochasticity of different reaction ponds in a wastewater treatment system is larger than that of the whole system.Random processes are the dominant assembly processes of microbial communities,but some deterministic processes still affect community assembly.Aquaculture wastewater treatment systems may serve the function of regulating microbial community structure through physical,ecological,or physiological barriers that become isolated habitats.(3)Key bacterial communities and nitrogen metabolism characteristics of aquaculture wastewater treatment system in three ponds and two damsIn this study,the characteristics of microbial communities and the nitrogen cycling functional gene content in aquaculture systems are further explored.Proteobacteria and Chloroflexi are the dominant phyla in culture systems.From a functional point of view,the genera that differ significantly in our study are all related to nitrogen metabolism,a key function of microflora in wastewater treatment systems.Nitrosomonas and Nitrospira involved in nitrification were detected in this study.In all samples,the relative abundance of denitrifying genera is higher than that of nitrifying genera,suggesting that aquaculture wastewater treatment systems can remove nitrogen through denitrification under conditions of high exogenous nutrient input.Metabolism in microbial communities is most efficient for carbohydrates and amino acids,followed by polymers and carboxylic acids,and slowest for amines and phenols.A modular structure is a densely connected region in a microbial network.The sediment symbiosis network in the culture region in this study is more modular than in the treatment and water storage regions,suggesting that there are more ecological niches in the culture region and that the survival of bacterial communities is dominated by cooperative symbiosis models.This stronger cooperative relationship may increase overall metabolic efficiency,but not bacterial community stability.Comparison of the abundances of nitrogen cycle function genes in sediment samples.The nitrogen assimilation and nitrogen mineralization genes account for the majority of nitrogen cycle annotation reads in the culture system,which further provides more information on the nitrogen metabolism properties of the culture system.