Study On S-TE Pretreated Sludge For Hydrogen Production

A large quantity of waste sludge is produced from the biological processes. Ifuntreated sludge is disposed to the environment, it can lead to serious environmentalproblem. The main composition of sewage sludge is microorganism, which containsmany organic matters, such as proteins, carbohydrates and lipids in the sludge floc,the organic matters in sludge are a feasible resource for utilization. Hydrogen which isa clean energy has a high energy yield, it can be produced from economical andfriendly biological method. Most studies on the anaerobic hydrogen productionexploited various organic wastewater and biomass, reducing organic pollutant andobtaining energy simultaneously. Hydrogen is an important intermediary produced inthe anaerobic fermentation, generally consumed by methanogenic bacteria and otherbacterium. Additionally, most organics in sludge are microbial cytoplasm, whichcannot be used by hydrogen producing-bacteria due to the block of microbial cell wall.Thus the inoculum sludge used in hydrogen fermentation needs to be pretreated to killthe methanogenic bacteria and disrupt cell walls, releasing more organics. Comparedwith other traditional physical of chemical pretreatments, Solubilization byThermophilic Enzyme（S-TE） based on microbial cryptic growth is more cost-effectiveand safer as well as lower energy cost and easier operation. Combined with thefollowing process, the plant can not only discharge little sludge, but simultaneouslyenhance biogas production. Based on the latest sludge fermentative hydrogenproduction researches, the S-TE pretreatment is investigated systematically.The objective of using mariculture organic waste for anaerobic hydrogenfermentation is reducing organic pollutant and obtaining clean energy hydrogensimultaneously. In this study, mariculture organic waste is used for hydrogenproduction, and the effect of different pretreated methods of sludge, solubilization bythermophilic enzyme （S TE）, acid, alkaline, sterilized, and microwave areinvestigated on hydrogen production. The results show that the maximum hydrogenyield was22.0mL/g VSS, which is obtained from sterilization pretreatment, whereas the minimum hydrogen yield of7.6mL/g VSS is obtained from acid pretreatment. Bymonitoring profiles of soluble COD, protein carbohydrate, pH value, VFAs andethanol during the fermentation, the conclusion from is drawn from this paper that thesoluble carbohydrate was the main nutrient resource for hydrogen production, thefermentation stops after the carbohydrate was largely consumed. The maincomposition of VFAs is acetic acid, and ethanol is produced at the end of fermentation,which suggests the presence of solvation during fermentation. More nutrients can bereleased from mariculture organic waste after S TE pretreatment than otherpretreatments, and the pH value is remained stable during the fermentation.Three influential factors of fermentative hydrogen production from S-TE treatedsewage sludge are investigated, including S-TE treatment time, sludge concentration,initial pH. The results show that the performance of S-TE treated sludge is affected bythe treatment time, and8h is optimal for high hydrogen yield, the hydrogen yieldreaches30.3mL/g VSS then, but longer treatment time than that is negative. Thehighest hydrogen yield of S-TE treated sludge occurs in the initial pH at6.0, reaching32.9mL/g VSS. The hydrogen yield decreases when the pH is higher or lower. Theoptimal sludge concentration for hydrogen production is11.23g/L, with a highhydrogen yield of50.2mL/L.To better exert the predominance of S-TE treated sludge in anaerobicfermentative hydrogen production, the uniformity design experiments for4-factor and10-level are done for aiming at initial pH, C/N, C/P and Fe²⁺concentration, usingS-TE treated sludge as substrate. A quadratic response function is used to correlate theobjective functions with the independent variables and the response functioncoefficients are determined by regression analysis. An initial pH of6.4, C/N ratio of200, C/P ratio of1000and Fe²⁺concentration of85mg/L yields the highest hydrogenyield of68.4mL/g VSS. Initial pH is found to have a profound effect on metabolismof soluble carbohydrate and protein. The appearance of propionic acid makes negativecorrelative correlation with the hydrogen yield in S-TE treated sludge fermentation.