Effect On The Methane Production From The Enhancing Anaerobic Digestion System After Pre-treatment And The Additives

With the rapid growth of sewage sludge in China and the energy crisis in the world, anaerobic digestion has been one of the most attractive methods for the sludge stabilization and treatment processes. However, the stability of the sludge cell walls is the big barrier for the the acceleration of anaerobic digestion systems, and methane production is also very low due to the lowest activities of Me theanogensin the traditional systems In this work, some pre-treatment process, i.e. alkali treatment, pH adjustment and thermal treatment were introduced to disintegrate the sludge cells, and some bio-additives of reduced coenzymeⅡ(NADPH), Acetyl Coenzyme A, Para-aminobenzonic Acid (p-aminobenzoic acid), SDS and hexadecyl trim ethyl ammonium chloride were also added to accelerated the activity of methanogens in the system. and the main conclusion in details were as follows:(1) Single factor experiments and orthogonal experiments were applied in the part I, to investigate the optimal operation condtions operaion conditions for sludge disintegration processes. It was found that the disintegration process of sludge was influenced significantly by the reaction time, pH value and temperature, and the optimum conditions were as follows: pH of 11, thermal temperature of 120℃, and the reaction time of 15min. The SCOD, SCOD/TCOD and TOC in supernatant of the treated sludge were14810 mg/L, 49.29% and 4560mg/L, respectively, TN increased by 27%, and the removal rates of TSS and VSS were about 22.85% and 40.93%, respectively. Meanwhile, the molecular weight distribution (MWD) in sludge supernatant was analyzed by GPC (Gel Permeation Chromatography) after alkaline thermal hydrolysis treatment. It was found that the percentage of the fraction > 1000KDa MW in supernatant increased from 20.94% to 31.70% as pH value changed from the origin to 11, and from 20.94% to 49.83% as temperature increased to 120℃, respectively. The sludge cells could be disintegrated greatly under the thermal conditions and an right pH range of.above 11. Then the sludge after pre-treated under the optimal conditions were introduced into the anaerobic digestion systems. Results showed that per Accumulated Methane Production (AMP) was 166.23 mL/g-VSS, with the increase ratio of 27.86%, compared to the the raw sludge AGP per VSS without pretreatment, and the corresponding maximum methane production was obtained 6 days early, with the value of 68.14%,while the consult group was only 64.18%.(2)Effect of the additives on the methane production in the anaerobic digestion system were tested here, and the reduced coenzymeⅡ(NADPH), Acetyl Coenzyme A, Para-aminobenzonic Acid (p-aminobenzoic acid), SDS and hexadecyl trim ethyl ammonium chloride were applied. The results indicated that the introduction of reduced coenzymeⅡ(NADPH) could accelerate the methane production greatly, with 15.9 higher than that in the control group. The AMP could reach to 127.13mL/g-VSS under the optimal conditions of solid content of 3%, temperature of 35℃, and the dosage of NADPH of 50mg/L, and it increased by 11.12% than that in the control group.Effect of the other factors, such as AMP per VSS, the rate of gas production, methane content, SCOD, pH variation, VSS reduction, were also studied in the sludge anaerobic digestion system, and it was found that the maxum AMP per VSS was obtained under the conditions of initial pH of 8.5, temperature 55℃and solid content 3%.(3)Finally, a model of biogas production by sludge anaerobic digestion was developed, supposed that hydration reaction was the rate-limiting step in anaerobic digestion system. Organic gas production rate onstant kh were chosen as the key dynamic parameters for the model. The degree of hydration reaction was determined by the volume of gas production, it was feasible to use first-order hydration dynamic model for the reaction process of anaerobic dynamic. It was found out that and kh were in the max value of 223.978mL/g-VSS and 0.14218d-1,respectively, as the dosage of NADPH was 50mg/L, compared to other experimental groups. Based on hydrolysis degree of various organic components (carbohydrate, fat and protein), the calculation results of methane production was203.40 mL/g-VSS, gas output 403.64 mL/g-VSS.