Effect Of Pretreatments Of Dewatered Sewage Sludge On Bio-methane Potential By Dry Anaerobic Digestion

Performance improvement of anaerobic digestion could increase yield of methane production and enhance renewable energy recover from the biodegradable waste.In this aspect design and optimization of different pre-treatment methods/conditions prior to anaerobic digestion could serve for the purpose.The present study was carried out with the aim to enhance hydrolysis of dewatered sewage sludge(with TS of 17-20%)to tackle the problem of low efficiency of dry anaerobic digestion(DAD).Different pre-treatment methods i.e.mechanical(ultrasonic),chemical(acid,ozone)and combined(ultrasonic-ozone)were investigated and evaluated in terms of biological methane potential(BMP)and organic matter degradation including TS,VS,and COD.Ultrasonic pre-treatment had the best result among the single technology,the BMP increased by 51.15% and TS,VS,and COD were reduced by 30.09%,36.92% and 33.88 respectively,over the control trail.Whereas ozonisation followed as the second best with BMP 46.94% higher than the control trail.Similarly,ozone pre-treatment reduced TS,VS and TCOD by 28.93%,30.63% and 35.85% respectively.However,as compared to the single pre-treatments methods,combined pre-treatment(ultrasonic + ozone)produced more significant results.Sludge which underwent combine pre-treatment resulted in 58.01% higher BMP than the control.Likewise,combined pre-treated sludge resulted in 53.70%,63.74% and 57.31% reduction in TS,VS,COD respectively when compared with the control.The study also showed that BMP increment of dewatered sludge positively correlated with specific energy,concentrations or dose of pre-treatments applied.Also in combined pre-treatment in which specific energy of ultrasonic was kept constant and only the ozone dose varied,highest BMP was obtained in the case with the highest dose of ozone.It is the first study on assessing effect of different pre-treatment on dry anaerobic digestion of sewage sludge.Referring to the results obtained,it could be concluded that the physical pre-treatment out-compete chemical ones.This is because the physical pretreatment such as ultrasonic not only lysis zoogloea cell in sludge but also keep the chemical characters of released compounds unchanged for subsequent AD process.In addition,energy consumption/agent cost need to be considered during full scale application as it in certain rang is in linear correlation with the BMP capacity.