Research On Urban Sewage Sludge Treatment With Themophilic Aerobic-mesophilic Anaerobic Digestion

As the sewage sludge processing standards of state and industry turned higher and higher, the traditional sludge treatment and disposal process got more and more incompatible with the new standards, it has become a major problem in the environment area. Anaerobic digestion has become widely used in domestic processing of sludge stabilization because of its small power consumption, handling, low cost, recyclable energy, etc, but there were problems with long sludge retention time, and low digestive efficiency. themophilic aerobic-mesophilic anaerobic digestion (AerTAnM technology) combined the advantages of themophilic aerobic digestion and mesophilic anaerobic digestion, while maintaining a high rate of VSS removal and pathogenic bacteria kill, through hydrolysis of themophilic aerobic stage, many complex organic was acetylated, thereby, the biodegradability of degradable organic matter was improved, these matters will be removed better In the follow-up anaerobic digestion process.The urban sewage sludge was treated with themophilic aerobic-mesophilic anaerobic digestion, and the factors which effected the digestion rate has been researched, including the feed sludge concentration, sludge dosage rate, stirring speed and solid retention time (SRT) of themophilic aerobic sludge. The results showed that when the total solid and VSS of feed sludge were 4% and 26g/L, stirring speed was 100r/min, the temperature of themophilic system was 55±1℃, SRTwas 2d, aeration was 0.2-0.3m3/h, the mesophilic temperature was 35±1℃, sludge dosage rate was 8%, SRT was 12.5d, then SRT of the two-phase system was 14.5d, sludge digestion efficiency was the best, the VSS removal rate reached above 45%, the biogas yield was 1.06L per VSS removal, the fecal coliform and ascaris eggs killing rate beyond 95%, the digested sludge met the class of urban sewage treatment plants discharge standards for sewage sludge(CJ 3025-93).The running stability and digestion effects of urban sewage sludge treatment by themophilic aerobic - mesophilic anaerobic digestion techenology, single-phase themophilic aerobic digestion techenology and single-phase mesophilic anaerobic digestion techenology was comparatively studied. By examining changes of pH, volatile organic acids, total alkalinity during the operation, the results of operation stabilitity of the three sludge digestion process were as follows:pH, volatile organic acids and total alkalinity changes little during AerTAnM digestion and single-phase mesophilic anaerobic digestion techenology stable operation, they were kept in the appropriate range category of anaerobic digestion, the system operated stably, while the stability of single-phase themophilic aerobic digestion techenology was bad. By examining VSS,COD and pathogenic bacteria removal rate,gas production, ect, the results of digestion effect of the three sludge digestion process were as follows:The organic matter and pathogens removal effect of single-phase themophilic aerobic digestion and AerTAnM digestion was better, each technology could Stable meet the standards stably, In comparison, single-phase mesophilic anaerobic digestion techenology was difficult to achieve standards. In short, AerTAnM digestion technology has reduced the total retention time (SRT), Improving the efficiency of organic removal and gas production,Improving pathogen inactivation rate,operation load and the system stability, reducing investment and operating costs,ect.