Study On Co-Digestion Of Sewage Sludge And Banana Straw In Two-Phase Anaerobic Fermentation Process

The construction and operation of sewage treatment plants in mounting number,the by-product of sewage treatment plants'technological end--the amount of sewage sludge will increasing,and the pollution on the environment will be more serious than before.Banana straw is the major agricultural and forestry wastes in subtropical and tropical regions,arbitrary treatment for it will cause pollution to the environment.For these problems,in this experiment,a single-phase anaerobic fermentation was carried out by mixing the sludge and banana straw in order to improve the anaerobic fermentation efficiency of the sludge,which can not only make resource use of the two solid wastes,but also reduce the volume of the two solid wastes.On the basis of single-stage anaerobic fermentation experiment,medium temperature and high temperature--medium temperature anaerobic fermentation experiment were carried out.To regulated the pH of acidogenic phase so as to increase VFA yield and further improved the yield of methane producing phase in subsequent stages.In addition,higher output VFA can also be used as a cheap and efficient carbon source for the upgrading of waste water plants.The main conclusions are as follows:In the experiment of single-phase anaerobic fermentation,the fermentation characteristics of five anaerobic fermentation systems were studied,including:sewage sludge,hot-alkali pretreated sludge,straw,alkali bath pretreated banana straw,hot-alkali pretreated sludge&alkali bath pretreated banana straw fermentation system.The anaerobic fermentation alone of the sludge and banana straw will lead to inhibition and revert to gas production after a period of time.But the sludge and banana straw after pretreated can remove the inhibition.Within 20 days of the fermentation,the methane yield of the hot-alkali pretreated sludge&alkali bath pretreated banana straw experimental group was 183 mg·L-1(VS).It is 2.1 times and 1.3 times of the hot-alkali pretreated sludge and alkali bath pretreated straw experimental group,and 3 times and 3.59 times of the sludge and banana straw experimental group.In addition to improve the methane yield,the stability of the fermentation system was also improved in the experimental group of hot-alkali pretreated sludge&alkali bath pretreated banana straw.In the experiment of medium-temperature two-phase anaerobic fermentation,the maximum VFA yield of each experimental group is 3905?7122 mg·L-1,in which the maximum concentration is pH=6.5,higher than that of the sludge alone fermentation.In methanogenic phase,fermentation process was almost completed within 20 days in each experimental group.The highest methane yield was 8.5 groups,280 mL/g(VS),and the methane yield was 1.24?1.53 times of the single-phase fermentation system of sewage sludge,the methane yield is significantly improved.The maximum VFA yield of each experimental group was 7080?10680 mg·L-1 in the high-temperature and medium-temperature two-phase anaerobic fermentation experiment,of which the maximum concentration was pH=8.5.In the group with the same pH value,the VFA concentration of the high-temperature acidogenic phase is significantly higher than the medium-temperature acid-producing phase,with the concentration increased by 16%?86%.The methane production rate of most experimental groups is over 98%account for whole methane production rate within 15 day in the high temperature and medium temperature two-phase system.The methane production speed is faster than the medium temperature two-phase system and the methane production rate is improved.The highest methane production rate was 405 mL·g-1(VS)in all experimental group with pH=10.5.It was 1.45 times higher than medium temperature two-phase system.Furthermore,the methane production rate of high-temperature and medium-temperature two-phase each experimental group within 15 day is 1.5-2.21 times than the single-phase medium-temperature system,which further improved the methane yield.