The effect of temperature on the performance and stability of thermophilic anaerobic digestion

Abstract

Sustainable operation of an anaerobic sewage sludge digester requires the effective shuttling of carbon from complex organic material to methane gas. The accumulation of intermediates and metabolic products such as volatile fatty acids and hydrogen gas not only reveal inefficiency within the digestion process, but can be detrimental to reactor operation at sufficiently high levels. Eight anaerobic digesters (1 mesophilic and 7 thermophilic) were operated in order to determine the effect of steady-state digestion temperature on the operational stability and performance of the digestion process. Replicate reactors operated at 57.5°C, the highest temperature studied, were prone to accumulation of volatile fatty acids (4052 and 3411 mg/L as acetate) and gaseous hydrogen. Reactors operated at or below 55°C showed no such accumulation of intermediate metabolites. Overall methanogenesis was also greatly reduced at 57.5°C (0.09 L CH4/g VS fed) versus optimal methane formation at 53°C (0.40 L CH4/ g VS fed). Microbial community assessment and free energy calculations suggest that the accumulation of fatty acids and hydrogen, and relatively poor methanogenic performance at 57.5°C are likely due to temperature limitations of thermophilic aceticlastic methanogens.Keywords: Acetate; methane; hydrogen; propionate; temperature; thermophilic anaerobic digestion INTRODUCTION Stringent pathogen regulations required for the land application of domestic wastewater biosolids have revitalized interest in thermophilic anaerobic digestion. Since biological activity at these temperatures requires specialized organisms equipped with thermostable cell components and enzymes, thermophilic anaerobic digestion has recently been recognized as holistically unique biological process, rather than a close variation of mesophilic anaerobic digestion. As such, much of the fundamental discussion regarding anaerobic digestion technology, keeping mesophilic anaerobic digestion in mind, is inadequate for the development of a thorough understanding of the design parameters and operational variables that greatly affect thermophilic performance.

Effect of Silver Nanoparticles and Antibiotics on Antibiotic Resistance Genes in Anaerobic Digestion

“…Total and volatile solids (Method 2540-G), total alkalinity (Method 2320-G), pH (Method 4500), and gas volume (Method 2720) were analyzed as specified in Standard Methods (APHA et al, 1995). Headspace methane and carbon dioxide were analyzed using a Shimadzu Gas Chromatograph (Model GC-14A, Columbia, Maryland) with a thermal conductivity detector (TCD) as described in Wilson et al (2008). Volatile fatty acids were measured using a gas chromatograph with flame ionization detector per Wilson et al (2008).…”

Influence of high gas production during thermophilic anaerobic digestion in pilot-scale and lab-scale reactors on survival of the thermotolerant pathogens Clostridium perfringens and Campylobacter jejuni in piggery wastewater

“…Pathogen die-off in anaerobic treatment is influenced by many variables 80 including sensitivity of the specific types of pathogens, temperature, 81 retention time (reviewed by Bendixen, 1994), pH, free ammonia (Nielsen 82 and Ahring, 2007), volatile fatty acid (VFA) concentration (Kunte et al, 83 1988;Salsali et al, 2008;Wilson et al, 2008), moisture content, mixing, 84 pathogen density (Horan et al, 2004), availability of nutrients and the 85 presence of other microorganisms (Sidhu et al, 2001;Wrigley 2004). In 86 general, increasing digestion temperature reduces pathogen survival in an 87 exponential pattern with concomitant die-off at longer hydraulic residence 88 times.…”

Temperature affects microbial abundance, activity and interactions in anaerobic digestion

“…Temperature is one of important factors determining the performance and stability of the AD process (De Vrieze et al, 2015). Temperature affects AD performance through modulating microbial community composition and diversity, activities and their interactions, altering the biochemical conversion pathways and thermodynamic equilibrium of the biochemical reactions (Wilson et al, 2008). Due to different adaption potential of different microorganisms to temperature, microbial community composition and abundance will shift with the changes in temperature, which can result in a shift of both predominated methanogenic pathway and process stability (Pap et al, 2015).…”