Feasibility Of Microalgal-bacterial Granular Sludge For Aquaculture Wastewater Treatment

Nowadays,microalgal-bacterial granular sludge（MBGS）process is expected to be widely used in environmental sustainable municipal wastewater treatment due to its low energy consumption and high efficiency.As the fastest-growing agricultural industry in the world,the aquaculture industry brings aquaculture wastewater.This paper systematically investigated the feasibility of treating aquaculture wastewater by MBGS process through the analysis of pollutants removal,sludge characteristics,microorganisms community and functional genes,so as to provide theoretical basis and technology for the further engineering application of MBGS process.The main conclusions of this paper are as follows:（1）MBGS process was competent to remove respective 64.8%,84.9%,70.8%,50.0%and 84.2%of chemical oxygen demand（COD）,ammonia–nitrogen（NH₄⁺-N）,nitrate–nitrogen（NO₃^--N）,nitrite–nitrogen（NO₂^--N）and phosphate–phosphorus(PO₄^3--P)under non-aerated conditions within 8 h.Further metagenomics analysis implied that microbial assimilation was the main contributor in organics,nitrogen and phosphorus removals while considerable nitrate and nitrite removals were also obtained with the synergy between microalgae and bacteria.These above results show that the MBGS process has a prospect of becoming an effcient and environmentally friendly alternative in aquaculture wastewater treatment.（2）The removals of nitrogen compounds in MBGS system with different concentrations of sulfamethoxazole（SMX）were all close to 100%after adaptation;10mg/L SMX inhibited the removal of organics in the light condition,but did not significantly affect the removal of PO₄^3--P;the removals of SMX at 5.0 mg/L and 10 mg/L were significantly higher than that at 1 mg/L（p<0.05）,which might be attributed to the microbial adaptability of MBGS under antibiotic pressure.10 mg/L SMX significantly reduced the sludge concentration and glycogen content,but increased the chlorophyll content and extracellular polymeric substances secretion of MBGS,which might be due to the microbial protection of MBGS against antibiotic.These above results show that MBGS has adaptability to antibiotics and can be used for the treatment of aquaculture wastewater containing antibiotics.（3）Tubular photo-reactor was used to investigate the performance of MBGS system in aquaculture wastewater treatment under day-night conditions with natural light.Results showed that daytime was favorable for NH₄⁺-N removal while nighttime for NO₃^--N removal.Over 99%of NO₂^--N could be removed most likely due to the high abundance of genes related to nitrite reduction during the whole experiment.However,the PO₄^3--P removal was found to be sensitive to the weather condition,ranging from 35.3%to 96.6%.It was also observed that dissolved oxygen produced by microalgae in daytime was sufficient for creating a 6-h aerobic condition for the system in nighttime for sustaining heterotrophic metabolism,which suggested that a balance between carbon dioxide and oxygen in MBGS process could be preserved under day-night conditions with natural light.These above results show that continuous flow MBGS process can realize the efficient removal of aquaculture wastewater under the condition of natural day-night cycles.