Start-up Of Thermophilic Anaerobic Digestion Research Articles

Effect of seed sludge source and start-up strategy on the performance and microbial communities of thermophilic anaerobic digestion of food waste

The objective of this study was to determine the effect of seed sludge on the start-up of thermophilic anaerobic digestion (AD) and to compare two methods of converting mesophilic to thermophilic consortium. Seed sludge source played an important role in the start-up while one-step temperature increase was the preferred start-up strategy. Biogas yields, pH and VFA levels of step-wise temperature increase reactors were initially comparable to that of the mesophilic control. However, they showed signs of instability and failure after temperature exceeded 50 °C. A great increase in absolute abundance of bacteria but reduced archaea for step-wise temperature increase reactors likely resulted in the over-supply of AD intermediates which were not consumed in time by methanogens, causing reactor souring. An initial drop in biogas and significant VFA accumulation were observed by one-step temperature increase reactors. However, owing to the successful acclimatization of thermophilic bacteria – Thermotogae, Thermoanaerobacterales, and Thermoanaerobacterium, as well as Methanosarcina, the one-step temperature increase reactor recovered from VFA accumulation and poor biogas yield within 10 days. By adopting the one-step temperature increase strategy and a suitable seed sludge, microbial consortia for thermophilic AD was established effectively, which aided the start-up of thermophilic AD of food waste.

Determining the composition of bacterial community and relative abundance of specific antibiotics resistance genes via thermophilic anaerobic digestion of sewage sludge

In this study, the effects of different temperature transitions on the dynamics of antibiotic resistance genes (ARGs) and bacterial community were investigated during start-up of thermophilic anaerobic digestion (AD) of sewage sludge. Although two thermophilic reactors showed dissimilar removal efficiencies of ARGs in batch mode, both the removal efficiency and reduction patterns of ARGs were similar in continuous stirred tank reactor (CSTR) mode, resulting in significant reduction of the total sum of the relative abundance of ARGs. Using network analysis to explore the correlation between bacterial community and some specific ARGs revealed that composition of the bacterial community played a vital role in the fluctuations in the relative abundance of the antibiotic resistome, demonstrating that shaping the development of ARGs was facilitated by vertical gene transfer. To facilitate eliminating ARGs, minimizing their hosts which persist even under long-term operations is vital in thermophilic AD.

Mixing strategies – Activated carbon nexus: Rapid start-up of thermophilic anaerobic digestion with the mesophilic anaerobic sludge as inoculum

This study evaluated the mixing – activate carbon nexus in anaerobic digestion with the aim of accelerating start-up of thermophilic anaerobic co-digestion of food waste and chicken manure using mesophilic anaerobic sludge as inoculum. Results showed that the methane yield in the continuous stirred reactor is 71.3% higher than that of intermittent agitated reactor, and the addition of activated carbon can further improve the yield of methane by 18.2%. Continuous mixing mode followed by intermittent mixing was proved to be an alternative strategy to accelerate start-up of thermophilic anaerobic digestion. The optimum mixing time of 120 s/hour were obtained using computational fluid dynamics modeling. Analysis of genomic annotation metabolism indicated that the addition of activated carbon enhanced the dominant metabolism pathways of amino acid, methane and energy. Results of enzymes gene expression suggested that carbohydrates esterases, glycoside hydrolases and glycosyl transferases were dominant, respectively.

The Start-up of Thermophilic Anaerobic Digestion of Municipal Solid Waste

The Start-up of Thermophilic Anaerobic Digestion of Municipal Solid Waste

Rapid establishment of thermophilic anaerobic microbial community during the one-step startup of thermophilic anaerobic digestion from a mesophilic digester

The purpose of this study was to explore how fast the thermophilic anaerobic microbial community could be established during the one-step startup of thermophilic anaerobic digestion from a mesophilic digester. Stable thermophilic anaerobic digestion was achieved within 20 days from a mesophilic digester treating sewage sludge by adopting the one-step startup strategy. The succession of archaeal and bacterial populations over a period of 60 days after the temperature increment was followed by using 454-pyrosequencing and quantitative PCR. After the increase of temperature, thermophilic methanogenic community was established within 11 days, which was characterized by the fast colonization of Methanosarcina thermophila and two hydrogenotrophic methanogens (Methanothermobacter spp. and Methanoculleus spp.). At the same time, the bacterial community was dominated by Fervidobacterium, whose relative abundance rapidly increased from 0 to 28.52 % in 18 days, followed by other potential thermophilic genera, such as Clostridium, Coprothermobacter, Anaerobaculum and EM3. The above result demonstrated that the one-step startup strategy could allow the rapid establishment of the thermophilic anaerobic microbial community.

Distribution of methanogenic potential in fractions of turf grass used as inoculum for the start-up of thermophilic anaerobic digestion

This study aims to investigate thermophilic methanogens in turf used as an inoculum. Results showed that Methanoculleus sp. regarded as hydrogenotrophic and Methanosarcina sp. regarded as acetoclastic methanogens were present in turf tested. However, active acetoclastic methanogens were present in turf soil only. The current study showed that thermophilic methanogens were present in various turf grass species: Stenotaphrum secundatum, Cynodon dactylon, and Zoysia japonica. Severe treatments of grass leaves under oxic conditions, including blending, drying and pulverizing did not affect the thermophilic hydrogenotrophic methanogenic activity of the grass. A dried and pulverized grass extract could be generated that can serve as a readily storable methanogenic inoculum for thermophilic anaerobic digestion. The methanogens could also be physically extracted into an aqueous suspension, suitable as an inoculum. The possible contribution of the presence of methanogens on grass plants to global greenhouse emissions is briefly discussed.

Rapid start-up of thermophilic anaerobic digestion with the turf fraction of MSW as inoculum

This study aims to determine suitable start-up conditions and inoculum sources for thermophilic anaerobic digestion. Within days of incubation MSW at 55°C, methane was produced at a high rate. In an attempt to narrow down which components of typical MSW contained the thermophilic methanogens, vacuum cleaner dust, banana peel, kitchen waste, and garden waste were tested as inoculum for thermophilic methanogenesis with acetate as the substrate. Results singled out grass turf as the key source of thermophilic acetate degrading methanogenic consortia. Within 4days of anaerobic incubation (55°C), anaerobically incubated grass turf samples produced methane accompanied by acetate degradation enabling successful start-up of thermophilic anaerobic digestion. Other essential start-up conditions are specified. Stirring of the culture was not conducive for successful start-up as it resulted specifically in propionate accumulation.

Effect of pre-aeration and inoculum on the start-up of batch thermophilic anaerobic digestion of municipal solid waste

In this study, a short pre-aeration step was investigated as pre-treatment for thermophilic anaerobic digestion of the organic fraction of municipal solid waste (OFMSW). It was found that pre-aeration of 48 h generated enough biological heat to increase the temperature of bulk OFMSW to 60 °C. This was sufficient self-heating of the bulk OFMSW for the start-up of thermophilic anaerobic digestion without the need for an external heat source. Pre-aeration also reduced excess easily degradable organic compounds in OFMSW, which were the common cause of acidification during the start-up of the batch system. Careful consideration however must be taken to avoid over aeration as this consumes substrate, which would otherwise be available to methanogens to produce biogas. To accelerate methane production and volatile solids destruction, the anaerobic digestion in this study was operated as a wet process with the anaerobic liquid recycled through the OFMSW. Appropriate anaerobic liquid inoculum was found to be particularly beneficial. It provided high buffer capacity as well as suitable microbial inoculum. As a result, acidification during start-up was kept to a minimum. With volatile fatty acids (VFAs-acetate in particular) and H 2 accumulation typical of hydrolysis and fermentation of the easily degradable substrates during start-up, inoculum with high numbers of hydrogenotrophic methanogens was critical to not only maximise CH 4 production but also reduce H 2 partial pressure in the system to allow VFAs degradation. In a lab-scale bioreactor, the combined pre-aeration and wet thermophilic anaerobic digestion was able to stabilise the OFMSW within a period of only 12 days. The stabilised inert residual material can be used as a soil amendment product.