Research On Ultrasonic Carbon-enriched Sludge Promoting Anaerobic Digestion Of Gas Production

Domestic sewage,as a carrier of resources and energy,has great potential for recovery.However,current sewage treatment processes often have high energy consumption,large carbon emissions,and low resource and energy recovery rates,which are difficult to meet the social sustainable development strategy.Recycling sewage resources and energy while reducing energy consumption is an important development direction for future sewage treatment technologies.Therefore,this paper proposes a new technology for the recovery of sewage resources and energy based on pollutant enrichment and anaerobic digestion.The purpose of this study is to realize the enrichment of sewage organic matter and nitrogen and ph osphorus resources by microsieve assisted with chemical coagulation and activated sludge enhanced coagulation,and to promote anaerobic digestion efficiency by ultrasonic treatment,thus,the resources and energy in sewage get effectively recovered.The enrichment regularity of microsieve assisted with chemical coagulation and activated sludge enhanced coagulation were studied.Through the removal efficiency of organic matter and nitrogen and phosphorus pollutants,the chemical types and dosages,the sludge dosages and the dosing position,the microsieve mesh size and revolutions were optimized,and the characteristics of the organic matter in the effluent and the resulting carbon-rich sludge were analyzed.The results showed that the COD enrichment efficiencies of the four coagulants were significantly different,followed by PFC>PAC>PAFC>Al2(SO4)3.When PFC dosage was 150 mg/L and PAM dosage was 5 mg/L,the enrichment efficiencies were better and the VSS/TSS of carbon-rich sludge was higher;The activated sludge was added before chemical coagulation and when the dosage was 1500 mg/L,the enrichment efficiency of pollutants significantly improved.In particular,the SCOD and NH4+-N enrichment efficiencies of sewage were greatly increased,and the enrichment efficiencies were respectively 56.01% and 45.05%,which was 7.4 times and 6.0 times higher than the results of no sludge added.but the introduce of activated sludge caused a decrease in the VSS/TSS of the carbon-enriched sludge;The microsieve could greatly trap the aggregated floccules and dissolved substances adsorbed on flocs when the microsieve mesh size was less than 100 ?m and the revolutions was 30 rpm.The carbon-enriched sludge produced by sludge enhanced coagulation combined with microsieve process was subjected to ultrasonic cracking.When the acoustic energy density was 2.1 W/m L for 20 min,the SCOD concentration increased from the initial 95.88 mg/L to 1362.51 mg/L,at a rate of 14.2 times,the protein and polysaccharide were also well dissolved.Treated by the low acoustic energy density for a short-time,NH4+-N enriched from sewage could rapidly released,and NH4+-N increased slowly continuously increasing the sound energy density and time,the increased NH4+-N mainly comes from the hydrolysis of proteinaceous substances.The TP was nearly proportional to the ultrasound time,and acoustic energy density greater than 1.5 W/m L was more conducive to TP release.According to the the relationship between the specific energy consumption and the elution amount of organic components and nitrogen and phosphorus,the ultrasonic specific energy consumption of carbon-rich sludge was better controlled within 6000-8000 k J/kg.According to the FITR analysis,the sludge contained multiple functional groups,mainly from proteins and polysaccharides.The protein and polysaccharide contained in the "coagulation + microsieve" carbon-enriched sludge and the "sludge-enhanced coagulation + microsieve" carbon-enriched sludge were higher than the activated sludge.After ultrasonic treatment,the protein and polysaccharide dissolved out and the absorption peaks weakened,favoring the later anaerobic digestion.A static anaerobic digestion experiment was carried out.The results showed that the gas production rate of carbon-rich sludge were significantly higher and they had higher CH4/CO2 values.The gas production rates of three types of carbon-enriched sludge,including "coagulation+microsieve"(R1),"sludge-enhanced coagulation+microsieve"(R2),and "sludge-enhanced coagulation+microsieve" with ultrasonic treatment(R3),were 531 m L/g VS,326 m L/g VS and 610 m L/g VS,respectively.they were 2.5,1.5,and 2.8 times that of the control sludge(R0),respectively.Throughout the digestion process,both VFAs and NH 4+-N remained low level with no acid inhibition or ammonia inhibition.The potential for phosphorus recovery of R2 and R3 was great.R3 had the highest removal rate of substrate,and the removal rates of TS,VS,and TCOD were 51.7%,58.4%,and 49.9%,respectively.As a whole,the heavy metal content of sludge was in the lower category and had no inhibition to the anaerobic digestion process.