Effect And Mechanism Of Acidification And Formation Of Secondary Minerals On Dewaterability Of Sewage Sludge In Bioleaching

With high-speed economic and social development,the capacity and efficiency of sewage treatment is increasing.Hereby,a huge amount of excess sludge has been produced.As we know,sewage sludge is the potential fertilizer source and soil amendment because of the abundant Nitrogen,Phosphorus,Kalium and organic matters.At the same time,the existence of high content water,heavy metals,and pathogenic bacteria in sewage sludge has severely restricted the popularization and application of the technology of municipal sludge agricultural resources use.Even worse,treated improperly,the sludge will pollute our environment greatly.Bioleaching is a new technology that removes heavy metals from sludge by acidophilic thiobacillus which can oxidize the Fe2+ and S0 in sludge.It was reported that bioleaching can also kill the pathogenic bacteria and enhance the dewaterability of sewage sludge.By now,the mechanism of removal of heavy metals in bioleaching has already been studied widely,but the effecting mechanism on dewaterability of sludge has rarely been reported.This paper mainly studied the effect of acidification and secondary minerals on dewaterability of sewage sludge.The sewage sludge from Taihuxincheng,Wu Xi sewage treatment plant was taken and studied.Batch experiments were performed to exploit the effect and the mechanism of bioleaching on sludge dewaterability by the inoculation of Acidithiobacillus ferrooxidans LX5 in this study.Besides,chemical leaching experiments using sulphuric acid were also performed as control to study the effect of acidification on sludge dewaterability.During the processes of both biological and chemical leaching,Zeta potential,cell lyses,morphology,and structure of sludge flocs were monitored.Results showed that acidification in bioleaching could improve the dewaterability and settleability of sludge by improvement of Zeta potential and formation of sencondary minerals.At strong acid condition,sludge cells could be decomposed,resulting in the increase of total dissolved phosphorus in centrifugal liquor of chemical leached sludge.Batch experiments in certain conditions were performed to synthesis secondary minerals formed in sludge bioleaching.XRD pattern showed that Schwertmanniet was formed in sludge bioleaching.Then,Schwertmanniet was added in sewage sludge,and it came out that Schwertmanniet could enhance the dewaterability and get rid of suspended solid in sludge,due to charge neutralization and adsorption bridging and providing the water transmitting passages by skeleton builder.However,there are only about 1.5g sencondary minerals formed in 1L bioleaching sludge,so sencondary minerals formed in bioleaching have little influence on dewaterability of sludge.In the sludge bioleaching process,decrease of pH and formation of secondary minerals happens at the same time,therefore experiments with different pH and addition of Schwertmanniet were carried out,and two factors variance analyses with duplication was applied.It showed that acidification,addition of schwertmanniet,and interaction effect of them could obviously affect the dewaterability of sludge.Moreover,coupling effect of bio-acidification and seconderary minerials formed in bioleaching with 2 g·L-1 Fe2+ and inoculation of A.ferrooxidans LX5 was estimated to reduce specific resistance of sludge by 83.41%.