Thermal pre-treatment of primary and secondary sludge at 70 °°C prior to anaerobic digestion

Abstract

In general, mesophilic anaerobic digestion of sewage sludge is more widely used compared to thermophilic digestion, mainly because of the lower energy requirements and higher stability of the process. However, the thermophilic anaerobic digestion process is usually characterised by accelerated biochemical reactions and higher growth rate of microorganisms resulting in an increased methanogenic potential at lower hydraulic retention times. Furthermore, thermal pre-treatment is suitable for the improvement of stabilization and could be realized at relatively low cost especially at low temperatures. The present study investigates the effect of the pre-treatment at 70 degrees C on thermophilic (55 degrees C) anaerobic digestion of primary and secondary sludge in continuously operated digesters. Thermal pre-treatment of primary and secondary sludge at 70 degrees C enhanced the removal of organic matter and the methane production during the subsequent anaerobic digestion step at 55 degrees C. It also greatly contributed to the destruction of pathogens present in primary sludge. Finally it results in enhanced microbial activities of the subsequent anaerobic step suggesting that the same efficiencies in organic matter removal and methane recovery could be obtained at lower HRTs.

A Review of Biochemical Process of Anaerobic Digestion

“…In other words, in a contex of a continuous culture, kinetic stress is defined as the imposition of a constantly reducing value of the solids retention time until it is lower than the limiting value; hence it will result in a washout of the microorganism [28]. Most researchers report that the rate-limiting for complex organic substrate is the hydrolysis step [29]- [35] due to the formation of toxic byproducts (complex heterocyclic compounds) or non-desirable volatile fatty acids (VFA) formed during hydrolysis step [36] [37]: whereas methanogenesis is the rate limiting step for easy biodegradable substrates [36] [38]- [40]. The anaerobic digestion process can be divided into two phase as illustrated in Figure 1.…”

Effects of thermal and mechanical pretreatments of secondary sludge on biogas production under thermophilic conditions

“…The temperature chosen to apply this treatment was 70ºC according to the work of Skiadas et al [14]. Treatment time has been established in 9, 24, 48 and 72 hours.…”

“…Low temperature thermal treatment has been pointed out as an effective treatment for increasing biogas production from both primary and secondary sludge [14].…”

Thermal-Alkaline Pretreatment on the Decomposition of the Streptomycin Bacterial Residue

“…Alkaline pretreatment is probably the best known and significant method for enhancing the biodegradation of complex materials (3,8,14,16,17 (6) suggested that alkaline pretreatment also removed acetyl and different kinds of uronic acid substitutions on hemicellulose, which lowered the extent of enzymatic hydrolysis of cellulose and hemicellulose. thermal-alkaline pretreatment could be applied to promote the dissolving and decomposition of microbial cells and organic material so as to improve the anaerobic digestibility (5,21). to our knowledge, there are no reports about anaerobic digestion of streptomycin bacterial residue.…”