Study On The Effectiveness Of Black Liquor Synergized With Alkaline Thermal Conditioning Of Sludge To Enhance Anaerobic Fermentation

With the development of light industry in recent years and the improvement of environmental standards,sewage treatment plants have been continuously built.As a by-product of sewage treatment,the output of papermaking waste sludge is also increasing.At present,anaerobic digestion is a more mainstream process used in sludge treatment,and the biogas produced can be used as a fuel to realize the resource utilization of sludge.However,due to the fact that part of the organic matter is in the cells and part of the extracellular polymer,it is difficult to use it directly,which leads to the low efficiency of anaerobic digestion.Therefore,a certain pretreatment is often used to improve the biodegradability of sludge before anaerobic digestion,thereby speeding up the anaerobic digestion process of sludge.Alkaline thermal pretreatment technology can significantly improve the effect of anaerobic digestion of sludge.However,due to the high cost of the alkaline pretreatment technology due to the investment of chemicals,and the chemical is not easy to recover,it is necessary to develop a more reasonable pretreatment alkali source,so that the alkaline thermal pretreatment technology of sludge can be easily promoted and applied.In this study,the waste sludge of paper making was treated with black liquor of bagasse pulping by caustic soda process,and the effect on the properties of sludge and the efficiency of anaerobic fermentation of sludge was discussed.The caustic soda black liquor is a typical alkaline waste liquid in the pulping and papermaking process,which contains a large amount of soluble organic matter.Black liquor as the alkali source of sludge alkali thermal pretreatment,on the one hand,the residual alkali in the black liquor can be used to promote the dissolution of sludge organic matter,on the other hand,the degradable organic matter in the black liquor can also bring additional methane production.In addition,the black liquor alkali thermal treatment sludge can also improve efficiency of acid production by anaerobic fermentation.The specific research results are as follows:(1)After alkali thermal treatment of the sludge,soluble organic matter such as protein polysaccharides increases,black liquor and sodium hydroxide are equivalent to the organic matter dissolution of the sludge during the alkali thermal treatment of the sludge,and sludge particle size can be reduced,which is conducive to the subsequent anaerobic fermentation of sludge.Compared with the p H of sludge after sodium hydroxide alkali thermal treatment,the p H of sludge after black liquor alkali thermal treatment decreased less because the black liquor itself contained more organic acid salts,and black liquor alkali thermal treatment further improves the rheological properties of sludge and worsens the dewatering performance of sludge.(2)After alkaline thermal pretreatment,the organic matter of the sludge is released,and the anaerobic methane production rate of the sludge is increased by 40%-45% compared with the untreated sludge.Under weak alkaline conditions,the hydrolysis rate of the black liquor alkaline thermal conditioning group is higher than that of the sodium hydroxide alkaline thermal treatment group,while under strong alkaline conditions because of the presence of humic acids in the black liquor,the hydrolysis rate of the black liquor group is reduced.The results of phase separation anaerobic test show that the methane production in the liquid phase is much better than that in the solid phase after simple centrifugal phase separation,and most of the methane production is in the liquid phase.Black liquor,as a low-cost alkali source for alkaline thermal pretreatment of sludge,is 17% and 39% lower in cost and 7% and 30% higher in revenue than sodium hydroxide under two p H conditions,respectively,compared with sodium hydroxide.(3)Alkaline thermal treatment of sludge can effectively increase the net yield of volatile fatty acids of sludge.Under weak alkaline conditions,The black liquor alkaline thermal conditioning group produces slower gas than the sodiμm hydroxide treatment group,and has a greater impact on methane production,but has a smaller impact on the sludge hydrolysis acidification process.Under strong alkaline conditions,the dosage of black liquor is large.The activity of hydrolyzing bacteria and methanogens is inhibited by the strong alkalinity of the black liquor and the large amount of humic acids contained in the black liquor,which leads to significant changes in the microbial community structure of the anaerobic fermentation system.