Study On The Effect Of Different Pretreatments On The Anaerobic Digestion Performance Of Sludge

The anaerobic digestion of sludge stands out among various sludge treatment and disposal methods due to the recovery of methane and other energy gas.However,the conventional sludge anaerobic digestion has the disadvantages of low hydrolysis rate,long residence time and low organic matter removal rate which limit further promotion and application of anaerobic digestion.Changing the property of sludge and improving the biodegradability of sludge are important choices to solve the problems of sludge digestion and improve the anaerobic digestion performance of sludge.This study use thermal and thermal-alkali at low temperature to treat two different concentrations of sludge,investigate the changes of sludge characteristic and sludge anaerobic digestion performance at medium temperature after pretreatment;then elect out pretreatment parameter of thermal-alkali at low temperature which has considerable cell lysis effect with thermal treatment at high temperature(160 °C)through a series of experiments;finaly analyze the difference of anaerobic digestion performance under the same medium temperature.The conclusions are as follows:After pretreatments of sludge with different concentrations,organic matters are released and dissolved continuously,the contents of organic matters reduce,the contents of dissolved organic matters increase in the liquid phase and the most shifts toward the direction of molecular mass reduction.The changes of ammonia nitrogen and alkalinity also reflect the promotion effect of pretreatment on the degradation process of macromolecules.Pretreatment effect: thermal-alkali >thermal.The thermal not only enhances the contents of acetic acid,propionic acid and butyric acid contained in the raw sludge,but also produces isobutyric acid,isovaleric acid and valeric acid.The enhancement of small organic acids,acetic acid and propionic acidis,are particularly prominent due to the presence of alkali in thermal-alkali.The pretreatments also enhance the fluidity of the sludge.The results of continuous anaerobic digestion about raw and pretreated sludge with different pretreatments show that the pH value,alkalinity value,ammonia nitrogen content and volatile organic acid(VFA)content of three different sludge systems increase of some different degrees with the increase of sludge concentration.However,they all fluctuate within the controllable range of the system and do not inhibit the anaerobic digestion system.The application of pretreatment technology and the increase of sludge concentration can effectively improve the removal efficiency of organic matters in the sludge and can also snificantly increase the biogas production and methane production of the anaerobic digestion system,and hermal-alkali >thermal> raw sludge.The analysis of microbial community structure shows that large difference of the dominant communities occurs due to the difference of additional sludge treated after different pretreatments with the time going on,but the microbial contents correlated with anaerobic digestion are greatly improved.This paper also discusses the effects of different pretreatment methods on sludge organic matters and elects out pretreatment parameter of thermal-alkali at low temperature which has equivalent cell lysis effect with thermal at high temperature(160 °C): 60 °C,pH = 12.00.At 37 ± 1 °C,the study compares the anaerobic digestion performance of different sludge which treated with thermal-alkali at high temperature(160 °C,pH=12),thermal at high temperature(160 °C)and thermal-alkali at low temperature(60 °C,pH=12.00).The results show that thermal-alkali at high temperature> thermal at high temperature ?thermal-alkali at low temperature in terms of anaerobic digestion performance.The analysis of microbial community structure shows that there are large differences in different systems due to the big difference of supplemented sludge,but the contents of microbial related to methane production increase significantly.The energy consumption analysis of sludge pretreatment shows that,compare to thermal at high temperature,thermal-alkali at low temperature has higher economic benefits whose energy consumption of sludge pretreatment are 105.84 kJ/d and 39.54 kJ/d,respectively.The latter is much lower than required for thermal at high temperature.