The effect of upper mesophilic temperature and feed-to-seed ratio on batch anaerobic digestion systems

Abstract

This study investigated the effect of upper mesophilic temperature and feed-to-seed (F/S) ratio on anaerobic digestion using four 3.5 L batch-scale reactors. Initially, eight F/S ratios, ranging from 10/90 to 90/10, were explored at 37 degrees C, using a mixture of primary and secondary municipal sludge as feed. It was observed that the systems with low F/S ratios (40/60 and below) showed a stable performance while those with high ratios (50/50 and above) experienced the effect of organic overloading indicated by reduced removal of volatile solids (VS) in the feed, a drop in pH, volatile fatty acid (VFA) accumulation during the first 10 days of operation, and total gas production markedly lower than the corresponding theoretical values. Subsequently, the effect of temperature, in the 37 to 49 degrees C range, was studied at an F/S ratio of 20/80. Results revealed that an increase in temperature between 37 and 43 degrees C had a rather minimal effect on the process, with the exception of a moderate increase in total gas production. A further rise in the temperature in the 45 to 49 degrees C range however appeared to trigger an adverse effect evidenced by enhanced percent VSS reduction (possibly the result of cell lysis), VFA accumulation and an increase in the non-VFA total organic carbon (TOC) content. Therefore, it can be concluded that an operating temperature in the 37 to 43 degrees C range resulted in a stable and satisfactory reactor performance.

Studies on biogas production from vegetable market wastes in a two-phase anaerobic reactor

“…The specific stability indicators of AD process are pH and alkalinity, and process performance parameters are volatile solids reduction, VFA production, and methane generation. To enhance methane generation, many researchers have studied various operational parameters such as pH (Liu et al 2008), temperature (Rahman and Elefsiniotis 2010), OLR (Najafpour et al 2006), hydraulic retention time (HRT) (Fongsatitkul et al 2010), and inhibitory compounds (Chen et al 2008). In addition to these parameters, it has been shown that phase separation (White et al 1989) can also improve the overall efficiency of the process for various substrates and especially substrate with high organic loading value (Bouallagui et al 2004).…”

Microbial population dynamics in temperature‐phased anaerobic digestion of municipal wastewater sludge

“…16 Although extensive studies have been conducted to address the said issues, very few studies have considered for the thermophilic phase of the TPAD system in the intermediate zone between the mesophilic and thermophilic range i.e. 45 ∘ C; this was based on the assumptions that limited microbial activity occurred within the upper mesophilic or lower thermophilic range of 40-50 ∘ C. 17,18 However, several recent studies have reported that anaerobic digestion at 45 ∘ C can produce a remarkably identical (or even higher) liquid phase mass transfer rate and greater volumes of biogas, along with good quality effluent in terms of chemical oxygen demand (COD) reduction (80-90%) compared to mesophilic anaerobic digestion. [19][20][21][22] Despite the environmental and economic importance of the process, knowledge about the microbial consortia in general, and the bacterial community involved in anaerobic digestion in particular, is limited.…”

Investigation of the Performance and Kinetics of Anaerobic Digestion at 45°C

“…Ref. [12] exhibited a significant increase in VS removal with the rise in temperature and approaches a plateau at 45˚C. The degree of acidification (VFA/tCOD) was highest at 45˚C and was chosen as optimum temperature for acidogenic phase [13].…”