Increasing biogas production by thermal (70°C) sludge pre-treatment prior to thermophilic anaerobic digestion

Abstract

The objective of this work was to investigate the effect of a low temperature pre-treatment (70 ºC) on the efficiency of thermophilic anaerobic digestion of primary and secondary waste sludge. Firstly, effect of sludge pre-treatment time (9, 24, 48 and 72 h) was evaluated by the increase in volatile dissolved solids (VDS), volatile fatty acids (VFA) and biogas production in thermophilic batch tests. Secondly, semicontinuous process performance was studied in a lab-scale reactor (5 L) working at 55 ºC and 10 days solid retention time. The 70 ºC pre-treatment showed an initial solubilization effect (increasing VDS by almost 10 times after 9 h), followed by a progressive generation of VFA (from 0 to nearly 5 g•L-1 after 72 h). Biogas production increased up to 30 % both in batch tests and in semi-continuous experiments. Our results suggest that a short period (9 h) low temperature pre-treatment should be enough to enhance methane production through thermophilic anaerobic digestion of sludge.

Effects of heavy metals as stress factors on anaerobic digestion processes and biogas production from biomass

“…In this step both solubilization of particulate matter and biological decomposition of organic polymers to monomers or dimers take place. Thermal, chemical, biological and mechanical processes, as well as combinations of these, have been studied as possible pretreatments to accelerate sludge or biomass hydrolysis (Ferrer et al 2008) since these pre-treatments cause the lysis or disintegration of sludge cells permitting the release of intracellular matter that becomes more accessible to anaerobic microorganisms. On the other hand, in anaerobic digestion, acidogenic and methanogenic microorganisms have different optimal growth conditions with different physiologies, growth kinetics, nutrient requirements, and sensitivity levels to environmental changes (Jeong et al 2010).…”

“…Mass reduction, biomethane production and improved dewatering properties of the treated sludge or biomass waste are the main features of the process (Ferrer et al 2008). The anaerobic digestion process is characterized by a series of biochemical transformations brought about by microbial consortia which convert complex macromolecules into low molecular weight compounds (biomethane, carbon dioxide, water and ammonia).…”

Oxygen Effects in Anaerobic Digestion – A Review

“…This heat generation can be used to elevate the reactor temperature into the thermophilic range (~ 55 o C). Thermophilic anaerobic digestion generally delivers superior process efficiencies compared to mesophilic (~ 35 o C) digestion [114,137], mainly due to the faster kinetics at elevated temperatures [22,138]. Another aspect of great importance is that thermophilic anaerobic digestion can extensively reduce the pathogens content in the digestate [61,129,137].…”

“…Various types of pre-treatment for AD has been suggested for enhanced waste treatment and stabilisation, such as thermal, ultrasonic, chemical (ozone, H 2 O 2 , etc.) and enzymatic pre-treatment [34,97,[112][113][114][115]. The feasibility of many such treatment options are, however, not well proven either economically or technically.…”

Enhancing biogas quality of indigofera plant waste through co-digestion with cow dung

“…The subtrates with high content of cellulose and lignin that interlink each other [10], becomes difficult to hydrolyze, so that the yield of biogas is low. To overcome this, some researchers have proposed some pretreatment processes before processing in AD, such as thermo-chemical [12], thermal [2,1], mechanical-chemical-enzymatic [3], alkaline [7], and biological [9] pretreatments. The methods are successful for enhancing the yield of biogas, but the pretreatment processes are less practical, as they require additional equipment and also sometimes use additional chemicals that may add an operational cost.…”