Immobilized Bacterial-microalgal Consortium For The Cattle Manure Anaerobic Digestion Effluent Treatment

Anaerobic digestion effluent(ADE)was produced as the rapid development of the intensive livestock industry or biogas production process.The ADE contained high concentrations of carbon(C),nitrogen(N),phosphorus(P)and residual antibiotic with an unbalanced ratio of C/N.The inappropriate disposal of ADE caused irreversible environmental issue s.The photobioreactor(PBR)could be use to develop the bacterial-microalgal consortium,which accerelated the pollutant degradation.To enhance the ADE treatment efficiency,the following questions needed to be solved: the high concentration of nutrients and organics showed inhibition to the growth of bacteria and microalgae,microalgae cell harvest and u ndesirable degradation of veterinary antibiotics.Accordingly,this study aimed at investigating the ADE treatment as well as microalgae bioenergy accumulation based on the immobilized microalgal-bacterial consortium system.The bacterial-microalgal consortium systems were developed to investigate different concentrations of nutrients and organics to the effects of ADE treatment and microalgae bioenergy accumulation.The results showed that the high concentrations of nutrient s and organic matters in the PBR(625 mg/L SCOD)inhibited microalgae's internal enzyme synthesis process,resulting in the inhibition of microalgae bioenergy accumulation.Interestingly,the suitable environment in the PBR(272 mg/L SCOD)was conductive to format a stable bacterial-microalgal consortium system,which enhanced the microalgae photosynthesis with the highest microalgae biomass(1466.0±34.6 mg/L)and lipid productivity(59.1±3.1 mg/L).Moreover,PBR(167 mg/L SCOD)obtained the highest ADE treatment performaence under the six bacterial-microalgal consortiums,and the maximum removal rates of TN,TP and COD were as high as ?100%,?100% and 97.4±0.5%.In addition,the enrichment of functional bacteria,such as Acinetobacter,Citrobacter and Brevundimonas,played an important role in enhancing ADE tre atment efficiency and microalgae bioenergy accumulation during the treatment of actual ADE wastewater.In conclusion,the ADE treatment and microalgae bioenergy accumulation can be realized in the bacterial-microalgal consortium systems.To obtain the optimum ADE treatment efficiency,the concentration of carbon source,nitrogen source and phosphorus source in the actual ADE wastewater should be properly controlled in the practical engineering applications.To further enhance the ADE treatment efficiency as well as suspended microalgae cells harvest,this study developed the immobilized microalgal-bacterial consortium system aiming at enhance the ADE treatment and microalgae bioenergy accumulation.The three bacterial-microalgal consortium systems including suspended microalgae of PBR(SCV),immobilized microalgae of PBR(ICV)and immobilized microalgae-powered activated carbon of PBR(ICV+PAC)were developed.During the process,the ADE treatment efficiency,microalgae cell harvest and the shifts of community structure were compared among the three bacterial-microalgal consortium systems.The results showed that compared with the lower nutrient removal rate in PBR(SCV),the removal rate of TN and TP in the PBR(ICV)and the PBR(ICV+PAC)up to ?100%.The results of three-dimensional fluorescence spectroscopy-parallel factor analysis(EEM-PARAFAC)showed that PBR(ICV+PAC)exhibited the highest removals of macromolecular proteins,such as C2(tyrosine)and C3(tryptophan).The removal rates were as high as 92.1±3.2% and 74.9±2.6% in C2 and C3,respectively.In addition,PBR(ICV+PAC)obtained the maximum microalgae bioenergy accumulation,and its chlorophyll a content and lipid yield were 25.2±1.2 mg/L and 65.7±2.6 mg/L?d,respectively.In terms of the community structure constitution,the group of immobilized microalgae of PBR(ICV)and PBR(ICV+PAC)exhibited similar bacterial microbial community structure,which was significantly different from the suspended microalgae of PBR(SCV).The enrichment of functional bacteria genus among the three bacterial-microalgal symbiotic systems,such as Opitutus,Acinetobacter and Brevundimonas,played an important role in the removal of pollutants and the accumulation of microalgae bioenergy.Hence,the immobilized microalgal-bacterial consortium system of PBR(ICV+PAC)obtained a desirable ADE treatment efficiency,which also realized the separation of microalgae cells and bacteria as well as high microalgae bioenergy production.The immobilized microalga-bacterial consortium enhanced the ADE treatment efficiency,the veterinary antibiotics degradations needed to be further investigated.This study selected a common veterinary antibiotic existed in the actual ADE of sulfamethoxazole(SMX),and explored SMX degradation efficiency,degradation mechanism and possible degradation pathways in the PBR(ICV+PAC).Moreover,the effects of SMX on the ADE treatment efficiency,microalgae growth and microbial community structure of the three microalga-bacterial consortiums were discussed.The results showed that PBR(ICV+PAC)obtained the highest SMX removal efficiency of 99.0±0.2%,followed by PBR(ICV)(94.8±2.6%)and PBR(SCV)(80.4±1.4%).PBR(ICV+PAC)obtained the highest proportion of live microalgae cells(86.2%),chlorophyll a(6.6±0.4 mg/g)and MLSS accumulation(4.6±0.6 g/L).This result indicated that PBR(SCV)was significantly inhibited by SMX in the suspended microalgae group,and inhibition effect by SMX was effectively alleviated in the immobilized microalgae group of PBR(ICV)and PBR(ICV+PAC).SMX inhibited reactor operation,with the removal rates of TN,TP and COD of 66.5±1.3%,65.6±1.4% and 58.6±1.7%,respectively in the PBR(SCV).Fortunately,the microalgae immobilization coupled with PAC adsorption accelerated the formation of a stable bacterial-microalgal consortium system,which allowed a significant improvement for the ADE treatment in the PBR(ICV+PAC).In the PBR(ICV+PAC),the TN,TP and COD removal rates were as high as 98.5± 0.7%,98.5±0.6% and 72.1±1.3%,respectively.This study found that SMX significantly shifted the microbial community structure among different bacterial-microalgal consortium systems.At the level of 16 S r RNA,the enrichment of some functional bacteria,such as Pseudomonas,Brevundimonas and Hydrogenophaga,played an important role in the degradation of SMX.At the level of 18 S r RNA,Chlorella vulgaris(C.vulgaris)was the dominant microalgae species among the three bacterial-microalgal consortium systems.Therefore,immobilized microalgae with PAC accelerated the formation of a stable bacterial-microalgal consortium system,and the functional microbial community enrichment enhanced the degradation of SMX in the PBR(ICV+PAC).