Chapter 8 - Recovery of volatile fatty acids from sewage sludge through anaerobic fermentation

Abstract

Anaerobic fermentation for volatile fatty acids (VFAs) production is a promising technology for sewage sludge treatment and reutilization. The fundamental aspects and actual developments of VFA production from sewage sludge by anaerobic fermentation are critically reviewed. Based on fermentation mechanisms and microbiological analysis, controlling strategies for VFA production from sewage sludge were concluded into three aspects, namely methanogenesis inhibition, hydrolysis acceleration, and product optimization. At present, the preliminary process for VFA production has been determined, but research in this field is still full of challenges, as, for instance, the concentration and purity of VFAs are too low for further commercial applications. Though current attempts of pretreatment, cofermentation, high-solid fermentation, and liquid fermentation have shown great potentials in overcoming those bottlenecks, including low conversion rate of sludge organics, inappropriate compositions of substrates, low concentration of VFAs, and high cost of operation, there are still some possible difficulties for full-scale applications in both economic benefits and technical feasibility. Therefore, the application of VFAs from sewage sludge on externally added carbon for nitrogen and phosphorus removals in wastewater plants seems more practical recently. Finally, based on the difficult situations, most important perspectives need to be seriously considered before extensively preceding large-scale application of this technology.