| Biological drip filter tower is an effective method for the treatment of metabolic waste from circulating aquaculture,and the development of filler is one of the key factors to improve the efficiency of biological drip filter tower treatment.An ideal filler should have a stable adhesion site for microorganisms,sufficient water retention,large void rates,large specific surfaces,and mechanical strength.Therefore,the search for an efficient and low-cost biological filter material plays an extremely important role in the promotion and application of biological drip filter towers and the development of circulating aquaculture.EPP foam material has the advantages of seismic energy absorption,heat resistance,oil resistance,heat insulation,light weight,impact resistance and floating,and energy saving,which is expected to be applied in the biological drip filter tower.In this study,the differences of three membrane hanging methods were compared,and the factors of biofilm quantity,SEM and microbial community were examined,and through the optimization of process parameters and EPP filler modification,to achieve the purpose of improving the speed of film hanging,improving nitrification efficiency and improving economic benefits.This study provides a theoretical basis and data support for the practical application of EPP filler in the treatment of wastewater from circulating aquaculture systems in biological drip filter towers,and provides new ideas and new paths for the sustainable development of aquaculture.The specific research content is as follows:1.Compared with natural membrane hanging,inoculation membrane hanging and activated sludge method,it is found that activated sludge method has the shortest membrane hanging time,the mature time of membrane hanging is 10 days,and the treatment efficiency of high concentration aquaculture wastewater is higher,and the accumulation of nitrite is small.At the same time,the biofilm quantity was 1.24,and the biofilm species were more abundant and the biofilm was thicker under SEM.Through sequencing,it was found that the diversity index of biofilms under activated sludge method was higher,the species were richer,proteobacteria and nitrocellulose were richer,so the membrane hanging speed was faster,the nitrification process was faster,and the degradation efficiency was higher.On the other hand,chlorobacteria in activated sludge can attach to EPP filler,indicating that EPP filler has good biocompatibility.2.The two EPP fillers were modified with polyvinyl alcohol.The contact angles of the fillers were 94.49° and 90.49°,respectively.The contact angles of the fillers were 65.5° and 72°,respectively,reflecting that the hydrophilicity of the modified fillers was significantly improved.Before and after laminating,the filler was examined under SEM,and an obvious layer of film could be found,indicating that the laminating was successful.The membrane hanging speed of the packing before and after mulching was compared,and the mature time of the packing after mulching was12 days,4 days earlier than that of the packing with OTU mulching,indicating that polyvinyl alcohol mulching can improve the membrane hanging speed of EPP packing in the biofilter.When the membrane is mature,the wastewater with ammonia nitrogen concentration of 10mg/L is treated with the packing with higher efficiency,faster speed and less nitrite accumulation.The amount of biofilm after mulching was significantly higher than that with OTU mulching.Through SEM microscopy,it can be found that the biofilm of the packing is thicker and more complex,indicating that PVA can make the packing have good hydrophilicity and film formation,and improve the film hanging speed.3.When C/N of EPP filler is 5,the degradation efficiency is the highest and the removal effect is also good.The reactor has the best treatment effect when the initial ammonia nitrogen concentration is 10mg/L.Meanwhile,under this condition,the packing has the highest treatment load.The maximum ammonia nitrogen treatment load of the packing is 1721g/(m3·d),and the average ammonia nitrogen treatment load is 1665g/(m3·d).In this experiment,when the circulating water flow rate was0.5mg/L,the ammonia nitrogen removal rate was the highest,reaching 0.25mg/(L·h).4.It takes 8 days for medium-sized reactor to mature with acclimated activated sludge.It takes 8 days for the reactor to process the simulated aquaculture wastewater of 10mg/L after the maturity of membrane hanging,and the removal rates of ammonia nitrogen and nitrite are above 95%.The highest ammonia nitrogen treatment load of the packing is 1200g/(m3·d),and the average ammonia nitrogen treatment load is600g/(m3·d).It indicates that EPP filler can attach microorganisms well and has high degradation efficiency.The dry weight of the upper,middle and lower layers of the reactor was 0.061 g,0.062 g and 0.066 g,respectively.The dry weight of the lower layer was the heaviest and the biofilm quantity was relatively high.Under THE microscope of SEM,it was found that the lower biofilm was thicker and the species were richer.After high-pass sequencing,shannon value and OTU of the lower packing were the highest,which were 3.2063 and 519,respectively,reflecting that there were more microorganisms attached to the lower packing and more species. |
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