The Anaerobic Gas Production Of Sludge Treated By Alkali And Ozone

Waste activated sludge is the inevitable by-products of conventional activated sludge process, and the anaerobic digestion is the sustainable sludge treatment and disposal. However, sludge hydrolysis is known as the limiting step of anaerobic digestion due to the cell walls are difficult to break. Therefore, large volume of digester, long retention time and high disposal cost are needed. Various pretreatments methods are used to improve sludge hydrolysis, in which alkaline and ozone pretreatments are investigated widely. However, the few investigations about combination of alkaline and ozone are studies. In this study, the changes of organic matters, biogas production and sludge characteristics after performances of alkaline,ozone, and their combination were compared are investigated. Simultaneously, the optimal conditions for sludge anaerobic digestion were determined. Finally, the feasibility of practical application is analyzed.The research results indicated that the dewatering and settling of sludge decreased after alkaline pretreatment, while the decrease of sludge dewatering, and increase of sludge settling were observed after ozone pretreatment. The disintegration performances of different pretreatments followed the order: alkaline followed by ozone pretreatment > ozone followed by alkaline pretreatment >alkaline pretreatment > ozone treatment> untreated sludge. The optimum conditions of alkaline pretreatment is p H = 12, and the optimal dosage of ozone pretreatment is0.3 g O3 / g SS. The optimal condition of combined pretreatment of alkaline and ozone occulted at p H = 12 and ozone dosage of 0.3 g O3 / g SS.The anaerobic digestion performances of disintegrated sludge suggested that the volatile fatty acids and biogas of combined pretreatment are better than alkaline or ozone pretreatment, the change order are as follows: ozone followed by alkaline pretreatment > alkaline followed by ozone pretreatment > alkaline pretreatment >ozone treatment> untreated sludge. Particularly, the optimum of biogas was observed at ozone dosage of 0.12 g O3/g SS with p H=12, which was almost 1.94 times of untreated sludge. The methane percentage reached 48.8% after combined pretreatment, while only 21.2% methane was produced in untreated sludge.UV spectral analysis showed macromolecules such as humic-like substances and the aromatic compounds containing C = C and C = O bonds were enhanced in the sludge supernatant. In the fluorescence spectroscopy analysis, sludge was mainly composed of aromatase protein and byproducts of soluble cells. There is no changes were observed in the species, but the concentration are increased after alkaline pretreatment. It is also found that aromatase protein, soluble cell byproducts, andhumic are the primary components in alkaline pretreated sludge supernatant. The aromatic protein, fulvic acids, soluble cell byproducts and humic substances were the mainly products after the combined pretreated sluge.The investigation about combined pretreatment of alkaline and ozone have guiding significant for sludge anaerobic digestion, which enhanced the sludge biochemical degradation and biogas production. However, the further analysis of technical economics are needed for its practical application.