The Characteristics And The Sulfur Control Technology Of The High Solid Sludge Anaerobic Digestion In WWTP

With the increasing of the Municipal Wasterwater Treatment Plant（WWPT） and sewage treatment capacity, the production of sludge was also increased. In 2013 the sludge producted from WWPT was 30 million tons（the moisture content of sludge was calculated by 80%）, and the safe disposal rate of sludge was less than 20%. Anaerobic digestion which is a sludge stabilization process is commonly used in the removal of organic matter with the producing of biogas, however the limit of the hydrolysis process lead to a series of problems such as the lower efficiency, longer residence time and higher operating costs and so on. To solve this problem, a variety of researches on the pre-treatment of sludge were studied, and the thermal hydrolysis is an effic ient pretreatment technology, which can improve the efficiency of digestion and biogas production while improving the performance of sludge dewatering. High solids anaerobic digestion can reduce the volume of anaerobic digestion reactor and energy consumption while improving the yield per unit volume of methane, since the solids content of feed is increased to more than 10%. Meanwhile, the biogas, producing during the anaerobic digestion process, is a new type of energy which can be used as fuel, power, energy and chemical raw materials. H₂ S contained in the biogas must be removed before using because it is a highly toxic gas which has a detrimental influences to human and combustion equipment.（1） The component transformation test of high solids anaerobic digestion showed that: after thermal hydrolysis pretreatment, the cell wall of high solids sludge were damaged, and the organic material can effectively hydrolyze to liquid. The hydrolysis rate of VSS in the sludge can reached to 42.9%. the high solids thermal hydrolysis-mesophilic anaerobic digestion（TH-MAD） shows a best digestion performance and highest COD removal efficiency（43.1%） in all high solids anaerobic digestion system s; the stability of thermal hydrolysis-thermophilic anaerobic digestion（TH-TAD） system is poor due to the high concentration of ammonia and the COD removal rate of high solids anaerobic digestion process was less than 31.1% because of the limit of hydrolysis. hydrogen sulfide concentrations in biogas producing from high solids anaerobic digestion was below 210 ppm,which is far lower than the hydrogen sulfide concentration in biogas producing from conventional anaerobic, but still need to further treatment to meet the standard of biogas using;（2） The organic matter distribution of thermal hydrolysis sludge and the characteristics of high solids anaerobic digestion showed that: 74.0% of available organic matter in high solids sludge was transferred to the liquid phase after the hydrothermal pretreatment, which is the primary source of the biogas producing in anaerobic digestion and the methane production rate of the dewatering solution was greater than the thermal hydrolysis sludge; after centrifuging the solid-liquid two-phase volume ratio of thermal hydrolysis sludge was17:3. If the dehydration solution is treatmented by UASB process, the volume of reactor will be only 1.3% of AD anaerobic digestion reactor volume; At the same the high solids thermal hydrolysis-dewatering-dewatering solution anaerobic digestion process can meet own energy needs depend on the biogas combustion and without additional energy input, which can effectively reduce operating costs;（3） The sulfur inhibition in high solids anaerobic digestion tests show ed that: With the increasing Fe/S, the methane concentration is reduced in the anaerobic digestion process,and the feed was respectively high solids and thermal hydrolysis high solids with iron, and the maximum methane descent amount was respectively 10.7% and 10.0%; but the COD removal rate did not change significantly ranging from9% to 16.0%.the adding of the Fe（III） can effectively reduce the concentration of hydrogen sulfide, when the Fe/S increased from 0 to 7.75, the concentration of hydrogen sulfide in biogas,which producing from high solids and thermal hydrolysis high solids with iron, can respectively reduce to 21.4ppm and 14.1ppm.（4） Low concentrations of biological desulfurization of biogas test shows: With the increasing of the gas-liquid ratio, the outlet concentration of hydrogen sulfide showed an increasing trend, when the gas-liquid ratio reached on 16, the outlet concentration of hydrogen sulfide was 10.2±1.1ppm and the removal rate was 94.9%.The gas-liquid ratio can be appropriately reduced according to the actual operation in order to reducing the operating cost.The p H of nutrient solution is a major factor to affect the removal efficiency by influencing the solubility of hydrogen sulfide, with the decreasing of the p H,hydrogen sulfide outlet concentration tended to increase and the optimum p H is between7.5⁸.5.The temperature of circulating fluid is an environmental factor to influence the activity of desulfurization bacterial and the actual operating temperature can be controlled between 30³5 ℃,with the decreasing of temperature, the activity of bacteria will be weakened and the removal rate will decrease. A different concentration of dissolved oxygen will change the form of desulfurization product,but the removal of hydrogen sulfide can not be affected obviously;The biogas Biodesulfurization reactor shows a better desulfurization efficiency and high load by running a month continuously, and results appeared in the metagenome of the reactor shows the reactor has a better treatment effect and the bacteria in the reactor indeed exist a certain number of sulfur-oxidizing bacteria, autotrophic denitrification bacteria flower desulfurization and sulfur reducing bacteria,and the share of those bacterias was significantly higher than inoculated mud and sludge startup.