Study On Sludge Pretreated By Thermophilic Enzyme And Thermophilic Hydrogen Production

An increasing amount of waste activated sludge (WAS) wasgenerated in wastewater treatment plants with the increasing sanitarysewage and the industrial wastewater. Compared to the research ofwastewater treatment, sludge decrease decrement and resource deservedthe same kind of respect. In this study, sludge was first hydrolysised byS-TE(solubilization by thermophilic enzyme) method. And thenlow-frequency ultrasound treatment has been used to enhance thistreatment process to shorten the pretreatment cycle and got a betterhydrolytic result. Then, a series of studies about the thermophilic andmesothermal hydrogen production were adopted to research theperformance of hydrog en production by pretreated sludge.In this study, a thermophilic strain was isolated and identified by16S rDNA gene sequence analysis, named Geobacillusstearothermophilus TP-12. This isolated strain was found to secreteextracellular hydrolytic protease to dissolve sludge effectively.Furthermore, low-frequency ultrasound promotion was applied toenhance sludge solubilization by the thermophilic enzyme. Theultrasound exposure time16.2s and the ultras ound density0.1219W/mLwere recommended by response surface methodology (RSM). With12htreatment under the optimal conditions, the soluble COD (SCOD),protein and carbohydrate were peaked at20.2%,16.8%and15.9%,respectively, higher than that without ultrasound, and about3.52,3.49and3.54times higher than raw sludge. Three-dimensional EEMspectroscopy was applied to evaluate the parameters of dissolved organicmatter (DOM) of dissolved sludge, to study the promotion effect ofultrasound. There are two similar peaks at Ex/Em of220/340and280/340nm, and higher fluorescence intensity scores than the controlgroup, which implies with low-frequency ultrasound assistance， thesludge solubilization by thermophilic enzyme is well accelerated withoutchanging the main path and product categories.Then the performance of thermophilic(55oC) and mesophilic(35oC)hydrogen production by p retreated sludge were studied. The resultsshowed that the maximal hydrogen yield was28.6%higher at55oC thanat35oC. As sludge concentration increased, the metabolic activity ofthermophilic hydrogen production bacteria was inhibited. The maximal hydrogen yield,19.9mL H2/g VSS was obtained at the lowestconcentration. The fermentation pattern was mixed-type based onbutyrate-type fermentation. When the TSS concentration of sludge was17612mg/L, the hydrogen yield of the sludge pretreated by thermophilicenzyme was48.6%higher than the control. And the adaptive phase ofhydrogen production flora was shortened, as well. Moreover, thebuffering capacity of pretreat ed sludge was much better than the rawsludge during the fermentation period.The buffering capacity of pretreated sludge was researched bythrough adding variant equivalent phosphate buffering agents. Thoughthe sludge that pretreated by thermophilic enzy me has the ability tostabilize pH value between6.4to6.5, a21.1%higher hydrogen yield wasobtained when0.05mol/L phosphate was adding. While high bufferingagent concentration cannot change fermentation type, it could conducethe accumulation of NADH, thus inhibiting hydrogen producing.Pretreatment method of thermophilic enzyme hydrolysis c ouldeffectively release soluble substances, and promote the performa nce ofhydrogen production. Compared to the fermentation at constanttemperatures, the hydrogen yields c ould be further increased underthermophilic condition.