Effect of coordinated treatment of membrane bioreactor and powder activated carbon on marine aquaculture wastewater

With the rapid development of marine aquaculture industry, the amount of wastewater discharged is increasing and the water environment in the coastal areas is seriously deteriorated.Because of high concentration of total suspended matter; the content of soluble organic matter and inorganic matter in marine aquaculture wastewater is huge, whichresult indifficulties for treatment.In order to protect the marine environment and reduce the disease spread, the treatment of intensive aquaculture wastewater has become an inevitable trend.However, mariculture wastewater is more difficult to treat than that of freshwater, because of the effects of salinity, especially on membrane′s microbeeinhibition and contamination mitigation.In this paper, activated sludge within membrane bioreactor(MBR) disturbed by mariculture wastewater was investigated, during and after salt shock, meanwhile, effect of powdered activated carbon(PAC), was examined in parallel lab scale MBR, particularly on their contaminant removal performance and membrane fouling influence, within the salinity ranging from 0 g/L to 35 g/L.Concentration of chemical oxygen demand(COD), ammonia nitrogen(NH+4-N) and nitrite nitrogen(NO₂-N) were analyzed emphaticallyunder the long term effect of macriculture wastewater, besides,variation of microorganism properties, membrane flux, and floc particle size were studied.Particularly, salinity changes range from 0 g/L to 5 g/L were selected to analyze corresponding,composition and concentrationchanges of the dissolved organic matter in bulk solution soluble microbileproducts, SMP and sludge flocs extracellular polymers substances(extracellular polymeric substances, EPS), which could help to explain the relationship between the hydrophobicity of sludge and polysaccharide, protein.The results showed that PAC could improve the anti fouling ability of membrane, i.e.For MBR PAC,The COD removal efficiencyis 7.3% higher than that of MBR,combined with better removal stability of NH+4-N and NO₂-N.For MBR,the fluctuation of removal of NH+4-N and NO₂-N was more obvious.In the process of salinity changes, the membrane flux of two parallel lab scales presented a similar trend, in detail, the flux declined in the sensitive period andrecovered to a certain extent in stationary phase.However, the recovery period of MBR PAC system was shorter than that of MBR, the change of flux is moreobvious in MBR.In result, the membrane flux under MBR PAC system could be improved remarkable, which showed about 1.5 times than that of MBR, in the end, the flux of MBR was lower, and the membrane of MBR could be damaged.During the salinity changing process, PAC could increase the sludge relatively hydrophobic (RH) and average floc sludge particle size, at the same time, adsorption and flocculation ability of PAC would contribute the reduction of microbial metabolites, particularly for small molecular protein,obtaininga 34% reduction.At the end of operation, the sludge mean particle size of MBR PAC waslarger, and the value increased 52 μm than that of MBR.Conclusions could be made that introduction of PAC is a useful mitigation strategy for MBR.Slow down membrane fouling rate.MBR PAC is suitable for mariculture wastewater treatment, and the treatment effect is superior to MBR.