Abstract
The frequency of water exchange and reducing the risk of eutrophication to surrounding water bodies have always been water-quality control issues in recirculating aquaculture systems. In this study, maize straw biochar prepared through pyrolysis showed great potential for both bacterial immobilization and pollutant adsorption. Heterotrophic bacterial strains of Sphingomonas sp. PDD-57b-25 and Acinetobacter towneri were isolated in situ from wastewater for pollutant remediation through a 16S rDNA-based method, which has been rarely reported to date. The selected strains had higher ammonia nitrogen (NH4+-N, 63%), nitrite nitrogen (NO2--N, 38%), nitrate nitrogen (NO3--N, 25%) and total phosphorus (TP, 35%) assimilation capacities than those of other widely applied bacteria under similar medium conditions. In addition, more NH4+-N (+16%), NO2--N (+14%), NO3--N (+17%) and TP (+19%) was removed by biochar-immobilized isolated strains than dissociated strains, suggesting their use may provide a means of improving water-quality control in recirculating aquaculture. With specific additions (4 g l-1) of biochar-immobilized Sphingomonas sp. PDD-57b-25 and A. towneri, the dissolved inorganic nitrogen (approximately 0.45 mg l-1) and TP (approximately 0.09 mg l-1) levels were maintained below the clean water threshold for recirculating aquaculture of crab Eriocheir sinensis. Furthermore, the added strains exhibited high bio-safety and were capable of improving the yield and quality of crabs. Results indicate the potential applicability of biochar-immobilized Sphingomonas sp. PDD-57b-25 and A. towneri in agricultural sewage treatments. Further, the experimental methodology developed here may be used for the exploration of new strains for practical aquaculture.
Highlights
Crab Eriocheir sinensis aquaculture is one of the most important agricultural industries in Jiangsu Province, China, and plays a vital role in the promotion of local economies and human living standards
By further increasing the dose (6 g l−1) of biochar-immobilized ANRS5 and PRS4 (BIAP), more substantial water purification effects were obtained, with dissolved inorganic nitrogen (DIN) and total phosphorus (TP) levels fluctuating around approximately 0.45 and 0.09 mg l−1, respectively. These results suggest that, in practical applications, immobilized ANRS5 and PRS4 are capable of transforming different forms of nitrogen and phosphorus into their respective components in several biochemical steps (Cai et al 2007, Guedes et al 2019, Qin et al 2019)
Considering the very large cell quantity that was added to the aquatic environment, the results indicate that BIAP presents no bio-safety concerns for E. sinensis and might represent a potential economic value for aquaculture operations
Summary
Crab Eriocheir sinensis aquaculture is one of the most important agricultural industries in Jiangsu Province, China, and plays a vital role in the promotion of local economies and human living standards. The abovementioned nutrients are derived from the metabolic waste of aquatic animals and microbial decomposition of the remaining fish bait. Lowering their concentrations to within environmentally friendly ranges is a key issue in the successful implementation of crab aquaculture. Water replacement is the most widely applied approach to maintain DIN and TP at desirable levels in conventional crab cultivation (Qin et al 2019). With this strategy, discharged nutrients can result in eutrophication of surrounding water bodies. Any included pathogens may be dispersed, which could be hazardous to plants and animals
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