Research On Volatile Fatty Acids Production Performance From Waste Activated Sludge Fermentation Pretreated By High Salt Coupled Cation Exchange Resin

As the amount of sewage discharged by various industries increases year by year,the annual output of waste activated sludge,the by-product of sewage treatment,is huge.If it is not properly treated and disposed,it will cause serious problem to both the ecological environment and human health.The waste activated sludge is rich in a large number of organic carbon sources which can be utilized by microorganisms and has great potential for recycling.How to realize the disposal and recycling of waste activated sludge has become a hot issue in the field of sludge treatment.Because of slow rate of hydrolysis in the process of traditional waste activated sludge treatment and efficiency low of anaerobic fermentation,this study innovatively use sodium chloride,cation exchange resin(CER)and sodium chloride coupling cation exchange resin to pretreat waste activated sludge.Then analysis the effects on microbial cell lysis of different pretreatment methods,and evaluate their efficiency on enhancing volatile fatty acids(VFAs)production through the subsequent anaerobic fermentation process.CER pretreatment mainly uses ion exchange to replace calcium and magnesium which play a stabilizing role in the extracellular polymer(EPS)of sludge and destroy the floc structure of sludge,so as to release organic matter from EPS to the supernatant.Na Cl pretreatment mainly uses the osmotic pressure change to make the aging cells shrink,and release a large amount of organic matter inside the cells into the supernatant.Under the condition of single pretreatment,the particle size of sludge decreased obviously.SCOD of supernatant after CER pretreatment increased to 2956mg/L-4220mg/L on the fourth day,accounting for 20.5%-29.3% of TCOD.SCOD of supernatant after Na Cl pretreatment reached 2723mg/L-3988 mg/L on the second day,accounting for 18.8%-27.7% of TCOD.Under the condition of single pretreatment,a large number of proteins and polysaccharides were released into the supernatant,and the concentrations were significantly increased.The migration path of organic matter was intracellular ? tightly bound EPS ? loosely bound EPS ? supernatant.3DEEM showed that tryptophan proteins and aromatic proteins were the main proteins in the supernatant after the pretreatment of CER and Na Cl,which were biodegradable substances.After single pretreatment with CER or Na Cl,sludge was subjected to anaerobic fermentation to produce VFAs,and the production was significantly increased.The proportion of small organic acids was increased after pretreatment with CER,while this proportion was reduced due to the inhibition of the activity of acetogenic bacteria by Na Cl pretreatment.Combined with the effect of cell lysis and the enhancement of VFAs production in this study,the optimal amount of CER pretreatment was 3g/g SS,and the optimal amount of Na Cl pretreatment was 10g/L.NaCl can promote cells to secrete more organic matters to EPS,while CER has an obvious stripping effect on EPS.So,these two pretreatment methods are considered to be coupled.In addition,from the mechanism of these two pretreatment methods,CER pretreatment is relatively mild but the release rate of organic matter is slow,while Na Cl pretreatment releases organic matter at a faster rate but does great damage to cells.After coupling these two methods,sludge can be pretreated better.After coupling pretreatment,the particle size of sludge decreases with the increase of CER input in the coupling condition.On the contrary,the particle size increases with the increase of Na Cl input.After coupling pretreatment,the release amount and release rate of SCOD in supernatant were significantly increased,reaching 4620mg/L and 5107mg/L respectively on the second day after pretreatment,accounting for 32.0% and 35.4% of TCOD,respectively.The concentrations of protein and polysaccharide in the supernatant increased greatly,and the release amount and release rate were better than the single pretreatment.The main proteins in the supernatant are still tryptophan and aromatic proteins,which are easily biodegradable.The production of VFAs of coupled pretreatment was significantly more than that of the single pretreatment.Under the coupled conditions of 3g/g SSCER+10g/L Na Cl and 3g/g SSCER+15g/L Na Cl,the production of VFAs reached 5970 mg COD/L and 5431 mg COD/L respectively.The results showed that the coupled pretreatment is better than the single pretreatment,and it can be used as a mild but fast pretreatment method to produce VFAs rapidly in waste activated sludge anaerobic fermentation.What's more,the CER can be regenerated by washing,while Na Cl can be recycled by crystallization.So coupled pretreatment can be a green,economical and efficient pretreatment method.