Improvement Of Acidification Performance During Anaerobic Co-fermentation Of Waste Activated Sludge And Spent Mushroom Substrates Under Pretreatments

With the development of economy of China, the supply amount of water hasbecome larger and larger, hence the increasing amount of waste sludge coming from thesecond sediment tank of municipal sewage plant has become a difficult problem forpeople to solve. Consequently, producing shot chain fat acids (SCFAs) by waste sludgeanaerobic fermentation has become a potential way to treat waste sludge. However, cellwalls of sludge are so hard that it is difficult for breaking cells, besides, the ratio ofcarbon to nitrogen is too low for anaerobic system, which leads to the low efficiency ofsludge anaerobic digestion. Consequently, we can use exterior power to help breakingcell walls (sludge pretreatment technology) to accelerate the hydrolyzation. Addingof agaricus bisporus spent mushroom substrate(SMS) can raise the ratio of C/N andpromote sludge anaerobic fermentation.This study using waste sludge and SMS as raw material by anaerobicco-fermentation to produce SCFAs. Based on even design and analysis of responsesurface methods, using Design Expert software, on purpose of getting the biggestamount of SCFAs, the parameters of three pretreatment methods(alkaline、hot alkaline、double frequency ultrasonic) and the ratio of sludge to SMS were explored. Semicontinuous flow experiments were carried out according to the best parameters in orderto investigate the promotion of the ability to produce SCFAs of waste sludge and spentmushroom substrate co-fermentation system and the feasibility of practice.The optimum parameters for the three different sludge pretreatments are as follows:with the value of NaOH/TSS is0.075, the value of SMS/TSS is0.9, makes alkalinesludge pretreatment reaches estimated highest SCFAs yield which is7802mgCOD/L;with the value of NaOH/TSS is0.11, the value of SMS/TSS is0.82, treating at thetemperature of80.7℃for29.7minute makes alkaline sludge pretreatment reachesestimated highest SCFAs yield which is10235mgCOD/L; with the value of SMS/TSS is0.57, disposing sludge on ultrasonic machine for29.7minute under the energy densityof0.98kw/L makes ultrasonic sludge pretreatment reaches estimated higest SCFAs yieldwhich is8128mgCOD/L. All actual values are extraordinarily close to estimated valuesin validating experiments which can prove the reliability of the model.Semi-continuous flow sludge anaerobic fermentation experiments were carried out based on the previous research, the results showed that the co-fermentation system canremarkably improve the concentration of organic matter in the liquid phase and boostthe release of nitrogen and phosphate. Three sludge pretreatments all can accelerateprocess of sludge hydrolysis evidently, but the effects of pretreatments are different. Theimpact on subsequent acidification period under alkaline and hot alkaline pretreatmentwas stronger than ultrasonic pretreatment. The addition of SMS can not only raiseconcentration of carbohgydrate and protein but also elevate C/N ratio, which played avery important roll in promoting SCFAs yield. In terms of SCFAs yield and economicfactor, hot alkaline pretreatment was better than alkaline pretreatment, alkalinepretreatment was better than ultrasonic pretreatment, and each elevated SCFAs yield71.8%、66.7%、63.2%. Acetic acid and propionic acid were dominate among SCFAs inall three reactors, concentration of valeric acid was higher in alkaline reactor than others,concentration of butyric acid was higher in ultrasonic reactor than others. Proportion ofacetic acid is elevated in three reactors compared to solo sludge anaerobic fermentation.All in all, waste sludge and SMS co-fermentation can evidently improve the abilityof acidification and reach the goal of waste sludge disposal: reduce, reuse, recycle.