Upgrading of the anaerobic digestion of waste activated sludge by combining temperature-phased anaerobic digestion and intermediate ozonation

Abstract

Upgrading of the anaerobic digestion of waste activated sludge (WAS) by the combination of temperature-phased two-stage digestion and intermediate ozonation was investigated by a continuous experiment with two processes, TM and TOM. The TM process is a temperature-phased two-stage system, which consists of a thermophilic digester and a mesophilic digester in series. The TOM process is a temperature-phased two-stage process with the intermediate ozonation. Two processes were operated at hydraulic retention times of 30 days for over 123 days. Waste activated sludge taken from wastewater treatment plant was fed as a substrate. Microbial community structure in each digester was analysed with molecular tools. Despite of less amount of ozone dose in TOM than ozone pre-treatment process, better effect of ozonation on performance improvement was obtained in TOM. TOM had the highest methane yield and COD(Cr) reduction among comparative processes. Furthermore, flocculation efficiency of TOM followed that of mesophilic digestion. Quality of dewatered supernatant is comparable to mesophilic digestion.

Enhanced Versus Conventional Sludge Anaerobic Processes: Performances and Techno‐Economic Assessment

“…iTPAD), affected significantly the soluble organics content of the supernatant, and sCOD and ammonia concentrations were noticeably higher compared with those of the reference MAD. In fact, as reported elsewhere (Kobayashi et al, 2009;Vindis et al, 2009), the thermophilic conditions resulted in an increase in the soluble nitrogen compounds, mainly ammonium ions, with the related potential risks of inhibition of the whole process. However, no inhibitory effects were observed because the ammonia level in all the digesters was always lower with respect to the methane inhibition level of 2000 mg/L (Han et al, 1997) and, at the same time, the pH measured during the digestion processes was not extremely alkaline (average pH value of 8.1 6 0.2).…”

Pre-treatments to enhance the biodegradability of waste activated sludge: Elucidating the rate limiting step

“…A niche application of AOPs could be the oxidation of refractory substances (e.g. mineralization of humic substances), or for the treatment of digested sludge, as it contains a higher fraction of refractory substances compared to WAS (Kobayashi et al, 2009).…”

Feasibility of thermophilic anaerobic processes for treating waste activated sludge under low HRT and intermittent mixing

“…This was due to solids degradation and solids sedimentation inside the digester (a discussion on this is provided in a subsequent section). Total ammonia nitrogen (TAN) concentration increased as the hydraulic retention time decreased, which could be due to the degradation of proteins and urea present in the sludge (Kobayashi et al, 2009). Other than the trial carried out at 5 days HRT, ammonia nitrogen concentrations reached 700 mg/L.…”