Comparison of two‐stage thermophilic (68°C/55°C) anaerobic digestion with one‐stage thermophilic (55°C) digestion of cattle manure

Abstract

A two-stage 68 degrees C/55 degrees C anaerobic degradation process for treatment of cattle manure was studied. In batch experiments, an increase of the specific methane yield, ranging from 24% to 56%, was obtained when cattle manure and its fractions (fibers and liquid) were pretreated at 68 degrees C for periods of 36, 108, and 168 h, and subsequently digested at 55 degrees C. In a lab-scale experiment, the performance of a two-stage reactor system, consisting of a digester operating at 68 degrees C with a hydraulic retention time (HRT) of 3 days, connected to a 55 degrees C reactor with 12-day HRT, was compared with a conventional single-stage reactor running at 55 degrees C with 15-days HRT. When an organic loading of 3 g volatile solids (VS) per liter per day was applied, the two-stage setup had a 6% to 8% higher specific methane yield and a 9% more effective VS-removal than the conventional single-stage reactor. The 68 degrees C reactor generated 7% to 9% of the total amount of methane of the two-stage system and maintained a volatile fatty acids (VFA) concentration of 4.0 to 4.4 g acetate per liter. Population size and activity of aceticlastic methanogens, syntrophic bacteria, and hydrolytic/fermentative bacteria were significantly lower in the 68 degrees C reactor than in the 55 degrees C reactors. The density levels of methanogens utilizing H2/CO2 or formate were, however, in the same range for all reactors, although the degradation of these substrates was significantly lower in the 68 degrees C reactor than in the 55 degrees C reactors. Temporal temperature gradient electrophoresis profiles (TTGE) of the 68 degrees C reactor demonstrated a stable bacterial community along with a less divergent community of archaeal species.

Research advances in dry anaerobic digestion process of solid organic wastes

“…A multi-stage system can improve both stability of the process and performance, but is more expensive and complicated in construction and operation. It was found that the two-stage digester had a 6 to 8% higher specific methane yield and a 9% more effective volatile solids removal than the single-stage digester when thermophilically treating cattle manure (Nielsen et al, 2004). A 21% increase in methane yield was observed when a two-stage digester was used to ferment municipal solid waste instead of singlestage reactor (Liu et al, 2006).…”

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

“…As stated in the introduction, low temperature thermal treatment has been pointed as a predigestion step, enhancing the biological activity of some hydrolytic bacteria [15].…”

“…We hypothesize that thermophilic conditions itself may accelerate the hydrolytic step of sludge digestion concealing the possible effect of the majority of the pretreatments 19 applied. As suggested by other researchers, low temperature thermal treatment may be assimilated to a biological treatment enhancing the activity of thermophilic bacteria with the optimal activity around 70ºC, thus within the thermophilic range of operation [15]. On the other hand, the possible effect of anaerobic sludge acclimation to a sludge input of different characteristics as is pretreated sludge should be considered.…”

“…Some authors have concluded that thermal treatment applied at temperatures around 70ºC enhance biological activity of some thermophilic bacteria population with optimum activity temperatures in the high values of the thermophilic range [15]. Thus, low temperature thermal treatment may be considered as a predigestion step.…”

The Co-fermentation of Organic Substrates: A Review Performance of Biogas Production under Different Salt Content

“…So, bio-energy of organic waste avails both the targets: i. organic waste dropping ii waste recovery, iii and biofuel production as substitutional and renewable source. The leftovers of waste after AD procedure performances as superior muck that can be facilely applied in agricultural soils as a replace for fertilizer [11]. AD system is conditional on specific microbial assembly for devolution of biowaste out of main steps namely hydrolysis, acetogenesis and methanogenesis as shown in Fig 1. Investigators have indicated that methanogenesis is the rate-limiting stage for easily degradable materials whereas hydrolysis is the average shackling step for complex organic wastes due to formation of toxic byproducts like complex heterocyclic synthesises and un-likeable volatile fatty acids(VFAs).…”