Research On The Optimization Mixing Time Of Sewage Sludge Hot Pretreatment/anaerobic Digestion Process

With the construction of urban sewage treatment works the rapid development of sludge treatment, the high energy consumption to some extent exacerbated by China's current energy crisis. Thus to develop energy saving technology of sludge disposal has become a top priority. Anaerobic digestion complete response takes a long time, sludge retention time high up to 20d-30d, the hydrolysis reaction is the rate-limiting steps in anaerobic digestion. In order to improve the efficiency of anaer- -obic digestion requires the use of effective pretreatment, therefore, pretreatment of anaerobic digestion is very necessary. Another anaerobic digester as a bioreactor, its energy consumption mainly from two aspects: the heating of sludge and sludge mix- -ing. Many sewage treatment plant use 24 hours continuou stirring, while ensuring the treatment effect, but the energy is wasted, so study on the mixing time to anaerob- -ic digestion has its practical significance.This paper studies the conditions of thermal treatment of sludge, characteristics of sludge treatment and thermal pretreatment on anaerobic digestion performance. The results show that the thermal treatment last 5min at 170℃can achieve the desir- -ed results, to extend the processing time has not changed much. Moisture content was 84%, 90%, 96% of the sludge by microwave after the thermal treatment, the SCOD,VSS,SS,alkalinity,ammonia concentration of sludge increases, pH value after the thermal treatment have different levels of reduction. Affected by the sludge concentration of hydrolysis efficiency. 84% moisture content of sludge VSS and SS dissolution rate all less than 90%, 96% of the sludge. Sludge by thermal pretreatment can improve its digestibility. Gas production and organic removal rate was higher than untreated sludge.In this paper, mixing conditions of thickened sludge anaerobic digestion was investigated. Experimental results show that at the 20d hydraulic retention time, pH in the digesters was between 6.9 and 7.5, with alkalinity in the range of 2060-2656 mg/L. The daily gas production per milliliter sludge and COD reductions were 5.37mL/mL and 48.4% for 2h/10h (mixing/idle), 5.16mL/mL and 43.3% for 4h /8h (mixing/idle), 4.68mL/mL and 39.1% for 12h/12h (mixing/idle), 4.34mL/mL and 33.9% for 24h mixing, respectively. Intermitent mixing in removal efficiency of organic matter and biogas production were better than continuous mixing. From the perspective of both energy consumption and treatment performance, the operation of anaerobic digestion at 2h mixing /10h halt was recommended.