Search

The potential of two types of sludge obtained from the anaerobic–anoxic–oxic (A 2 /O) and membrane bioreactor (MBR) processes as lipid feedstock for biodiesel production via in situ transesterification was investigated. Experiments were conducted to determine the optimum conditions for biodiesel yield using three-factor and four-level orthogonal and single-factor tests. Several factors, namely, methanol-to-sludge mass ratio, acid concentration, and temperature, were examined. The optimum yield of biodiesel (16.6% with a fatty acid methyl ester purity of 96.7%) from A 2 /O sludge was obtained at a methanol-to-sludge mass ratio of 10:1, a temperature of 60 °C, and a H 2 SO 4 concentration of 5% (v/v). Meanwhile, the optimum yield of biodiesel (4.2% with a fatty acid methyl ester purity of 92.7%) from MBR sludge was obtained at a methanol-to-sludge mass ratio of 8:1, a temperature of 50 °C, and a H 2 SO 4 concentration of 5% (v/v). In this research, A 2 /O technology with a primary sedimentation tank is more favorable for obtaining energy from wastewater than MBR technology. [ABSTRACT FROM AUTHOR]

Sewage treatment produces sewage sludge, which is in large amount and continue to increase. The sludge contains considerable lipid and they can react with methanol to produce biodiesel. Normally acid catalyst was used in the transesterification reaction with sludge as a raw material, because sewage sludge contains a lot of free fatty acid which is an inhibition factor for transesterification reaction by alkali catalyst. However, alkali catalyst has other advantages such as easy to separate and fast reaction speed. As a result, in this research in-situ transesterification by alkali catalyst with sewage sludge as raw material was discussed. KOH/activated carbon as solid base catalysts were prepared by using wet impregnation method, which were used as catalysts in sewage sludge in-situ transesterification reaction. The influence of the catalyst mass fraction (15%,20%,25%,35%,45%), and dosage of catalyst (0.1g,0.2g,0.3g,0.35g,0.4g,0.5g,0.6g,0.7g), on the in situ-transesterification has been examined. The results show that: 25% (mass fraction, the same below) KOH/activated carbon was used as catalyst in the reaction process. When the mass ratio of alcohol and sludge was 10:1, reaction temperature was 60°C, catalytic amount (3wt%)and reaction time was 8h,the yield of FAME was 6.8%. Those were the optimum conditions. The surface features of catalyst were analysed by BET. [ABSTRACT FROM AUTHOR]

High value-added reutilization of sewage sludge from wastewater treatment plants (WWTPs) is essential in sustainable development in WWTPs. However, despite the advantage of high value reutilization, this process must be based on a detailed study of organics in sludge. We used the methods employed in life sciences to determine the profile of lipids (cellular lipids, free fatty acids (FFAs), and wax/gum) in five sludge samples obtained from three typical WWTPs in Beijing; these samples include one sludge sample from a primary sedimentation tank, two activated sludge samples from two Anaerobic-Anoxic-Oxic (A2/O) tanks, and two activated sludge samples from two membrane bioreactor tanks. The percentage of total raw lipids varied from 2.90% to 12.3%. Sludge from the primary sedimentation tank showed the highest concentrations of lipid, FFA, and wax/gum and the second highest concentration of cellular lipids. All activated sludge contained an abundance of cellular lipids (>54%). Cells in sludge can from plants, animals, microbes and so on in wastewater. Approximately 14 species of cellular lipids were identified, including considerable high value-potential ceramide (9567–38774 mg/kg), coenzyme (937–3897 mg/kg), and some phosphatidylcholine (75–548 mg/kg). The presence of those lipid constituents would thus require a wider range of recovery methods for sludge. Both cellular lipids and FFAs contain an abundance of C16–C18 lipids at high saturation level, and they serve as good resources for biodiesel production. [ABSTRACT FROM AUTHOR]

Treatments for and methods of disposing of municipal sewage sludge have a limited ability to produce high-value products. The number of studies on using sludge for energy recovery—including those that use sludge lipids to produce biodiesel—has increased considerably. This study reviews and compares methods for all steps in the process of producing biodiesel from municipal wastewater sludge, including sludge pretreatment and lipid extraction methods, catalyst selection, and byproduct generation, and its economics analysis. Sludge drying by heat maybe the most efficient method but cost a lot, and drying by vacuum and chemicals are expected for future advancement. In the lipid extraction, organic solvents are costly and unfavorable to the environment. Therefore, alternative extractant that are more efficient, and environmentally friendly are of potential use but still need price reduction. In terms of catalysts, H 2 SO 4 is an efficient and cheap catalyst in practical use but consumes a lot in operation. Solid acid catalysts are promising alternatives because of cost saving and environmental benign. Some new catalysts such as ionic liquid and enzymes are just promising in the much further future. The byproducts of different biodiesel production processes have been classified and been made downstream and environmental risk analysis. The optimization and greenness of catalysts and byproducts promote the commercialization of sewage sludge for biodiesel production. In addition, biodiesel refining by membrane technique is promising. Image 1 • Sludge biodiesel production processes are reviewed and compared. • Solid acid catalysts are promising alternatives for H 2 SO 4. • Byproducts classified, downstream oriented and environmental risk analyzed. [ABSTRACT FROM AUTHOR]