| The residual nitrogen discharged from sewage treatment plants is one of the main factors leading to severe eutrophication of surface water.Therefore,it is necessary to reduce nitrogen discharge from wastewater of sewage treatment plants.The lack of organic carbon in wastewater treatment plants limits denitrification efficiency;therefore,to meet stringent emission standards,external common organic carbon such as methanol and acetic acid is added to improve the nitrogen removal effect.Because food waste is rich in organic matter,the fermentation slurry containing volatile fatty acid produced by anaerobic fermentation can be used as additional carbon source to save the operation cost of sewage treatment plant.In this paper,the effects of different thermal hydrolysis pretreatment conditions on the dissolution of solid organic matter and anaerobic fermentation of food waste were studied.The formation process of main component of food waste as carbon source culturing denitrifying granular sludge production was studied;and the formation of nitrification and denitrification biofilm and the denitrification efficiency of the carbon source from food waste production was studied.(1)In this experiment,the hydrothermal pretreatment of food waste was conducted to explore the influence of different temperatures,processing times,substrate concentrations and different sulfuric acid addition amounts on the dissolution of organic matter,as well as the influence of subsequent anaerobic fermentation of solid part of food waste.The experimental results showed that soluble chemical oxygen demand(SCOD)increased with the increase of temperature between 110℃and185℃,and was higher than that of the normal temperature group.From the perspective of the availability of carbon source and economy,160℃thermal hydrolysis of food waste is the most suitable.After pretreatment,the concentration of SCOD in the fermentation process of food waste was in the order of normal temperature group,110℃,135℃and 160℃from high to low.It was found that the higher dissolved SCOD in the pretreatment stage,the lower SCOD in the fermentation slurry during fermentation.With the increase of heating time,the content of SCOD also increased.With the increase of total solid(TS),the SCOD of food waste after thermal hydrolysis pretreatment gradually increased,and the carbohydrate,protein and VFAs showed the same trend.The content of sulfuric acid added 0.5‰was compared with the control group without sulfuric acid,the SCOD obtained by thermal hydrolysis was 61.9%higher.The content of SCOD in the fermentation slurry of the control group without sulfuric acid was higher than that of the experimental group treated with sulfuric acid.(2)Secondly,the process of cultivating denitrifying granular sludge with different fermentation components of food waste was studied.In this study,Sodium acetate,VFAs,starch and lactic acid were added as carbon sources;four sequencing batch reactors were operated with nitrate loading rate of 0.24 kg N/m~3/d.The granulation process was explored by physical and biological characterization.DGS appeared cultured with soluble starch,acetate and lactate on days 43,59 and 64,respectively.After decreasing stirring rate from 200 rpm to 120 rpm,the average particle size of sludge cultured with sodium acetate,VFAs,starch and lactic acid increased from 110μm,140μm,199μm and 177μm on day 36 to 329μm,180μm,428μm and 306μm on day 67,respectively.The polysaccharide/protein in the extracellular polymeric substance of denitrifying sludge cultured with starch increased from 0.26 to 0.94 on day 67,and the hydrophobicity increased from the initial 40%to 80%on day 9,which was higher than that of sludge cultured from other carbon sources.The results showed that the better hydrophobicity and more polysaccharide of extracellular polymeric substances resulted in more rapid granulation of DGS added with soluble starch.Calcium ion can promote the formation of granules of denitrifying sludge by acetic acid culture,which makes its precipitation performance better.This study provided a feasible method for the rapid culture of DGS from the starch-dominated food waste fermentation liquid under low nitrate nitrogen load.(3)Last,the biofilm attaching effect of the composite carrier which was doped with activated carbon and zeolite and loaded on the surface of high density polyethylene bio-carrier and HDPE bio-carrier was studied.Using activated sludge from sewage treatment plants as inoculation sludge,the reactor was started under the condition of HRT=12 h,C/N=4,and the fermentation slurry of food waste as the carbon source.After 60 days of operation,nitrification and denitrification membrane was successfully attached to the filler.The surface of composite carrier and HDPE was covered by biofilm by SEM image,the biofilm presents a skeleton structure with holes,microbes gather on the skeleton.During 20-60 days,the increase rate was 0.02mg/d on composite carrier and 0.015 mg/d on polyethylene carrier,combined with the advantages of the hybrid system and the physical and chemical properties of activated carbon,the surface of the carrier has a larger specific surface area to promote attachment speed of microorganisms.The total nitrogen removal rate of biofilm on composite biocarrier and HDPE biocarrier was more than 85%. |
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