Anaerobic Digestion of Sewage Sludge with High Solid Content and Its Use as Fertilizer

Abstract

In local cities with decentralized small wastewater treatment plants (WWTPs), centralized anaerobic digestion at a WWTP that accepts more sludge from others can serve as the energy hub of the region. In this system, transportation of sewage sludge with a high solid content by vehicles and the use of digested sludge as fertilizer are promising. The present study evaluated the effect of high solid content on anaerobic digestion and on the quality of the digested sludge as a fertilizer in a 1,100-day continuous laboratory experiment. Mixed sewage sludge with 10% total solids was subjected to mesophilic anaerobic digestion with a volatile solids (VS) removal ratio of approximately 0.6. The acceptable organic loading rate was lower than 3.2 kgVS/(m 3 ·d). The viscosity increased to 8.5 dPa·s, but computational fluid dynamics analysis confirmed that mixing need not be upgraded under conditions of high solid content. Component and eluted material analyses of the digested sludge as a fertilizer confirmed that the high solid content in the sewage sludge does not limit the use of digested sludge as a fertilizer according to the Japanese Fertilizer Control Act. The results showed that this centralized anaerobic digestion system is useful for sludge management in small facilities.Keywords: anaerobic digestion of high solid sewage sludge, computational fluid dynamics (CFD), fertilizer

Anaerobic Codigestion of Grass and Sewage Sludge: Laboratory Experiments and Feasibility Analysis

“…Viscosity. Viscosity of the digested sludge is a concern because it can affect the mixing performance and subsequent dewatering treatments (Hidaka et al, 2015). Previous research demonstrated that minimum CST, maximum solids recovery and minimum total solids in the liquid stream were correlated with minimum liquid stream viscosity (Abu-Orf et al, 2003).…”

Anaerobic Digestion of Oxidation Ditch Sludge at Low Temperatures with Hyperthermophilic Pretreatment

“…Operational conditions in the continuous experiment is summarized in Table 3. An organic loading rate (OLR) was gradually increased from 0.38 to 0.94 kgVS/ (m 3 •d) for start-up in Term 0. The diluted raw dewatered sludge was fed into A and AH reactors in Term 0.…”

“…The diluted raw dewatered sludge was fed into A reactors and the pretreated diluted dewatered sludge was fed into AH reactors in both Terms 1 and 2. OLRs were adjusted to 0.94 kgVS/ (m 3 •d) and 0.47 kgVS/(m 3 •d) in Terms 1 and 2, respectively, which were within or lower than typical values of 0.6-1.6 kgVS/(m 3 •d) in case of no mixing [12]. The corresponding hydraulic retention times (HRTs) in Terms 1 and 2 were 46.7 d and 93.4 d, respectively.…”

“…In Japan, there are approximately 2,200 wastewater treatment plants (WWTPs), among which only 300 large or middle scale WWTPs have anaerobic digesters [1]. In local cities with decentralized small WWTPs, centralized anaerobic digestion at a WWTP that accepts more sludge and other waste biomass can serve as an energy hub of the region [2][3][4]. Around 1,000 small scale WWTPs whose treatment capacity is less than 1,000 m 3 /d use oxidation ditch processes (ODs), and have no anaerobic digestion.…”

“…Contrary to WWTPs with pipeline networks for sludge in large cities [5], dewatering sewage sludge for less sludge volume is helpful for transporting sludge to a centralized WWTP. This means that high solids anaerobic digestion is promising [3,4].…”