Enhancing biogas production from cattle manure: A circular economy approach with solar thermal pretreatment and soil conditioning.

Biogas production from cattle manure, pivotal for sustainable waste and energy management, encounters challenges from its low digestibility linked to lignocellulosic structures. This study investigates biogas efficiency enhancement through anaerobic digestion coupled with solar thermal (ST) pretreatment and digestate application in Napier grass cultivation (STAD-G). ST pretreatment at 40-60 °C for 20 h markedly increases methane yield, validated by pilot-scale trials that exhibited a 3.9-fold surge in methane production, attributed to improved acidification. Untreated manure's structure, however, impedes acidification, slowing methanogenesis as shown by lower volatile fatty acid concentration in effluents. In addition, utilizing digestate as soil conditioner notably improves grass yield (19.3 ± 0.8 ton dry/ha/year) and protein content, akin to urea fertilizer. Furthermore, the STAD-G system incurs higher upfront costs, it yields superior biogas efficiency and enhanced long-term financial returns. This integrated approach, by boosting economic and environmental sustainability, advocates for ST pretreatment as a key strategy in advancing sustainable agriculture and energy solutions.

Biodecolorization of biogas plant effluent derived from anaerobically digested distillery wastewater by naturally selected Pseudomonas putida.

Effluent from biogas plants can contribute to serious environmental issues due to its high organic compound content and its dark color. This study utilizes Pseudomonas putida strains isolated from activated sludge in a wastewater treatment plant to reduce the organic compound content and dark color of biogas plant effluent. The treatment of effluent from the anaerobic digestion of distillery wastewater with P. putida in the best evaluated conditions (sample concentration of 50% v/v, agitation and aeration rates of 250 rpm and 1.0 vvm for 6 days) produced significant decolorization and organic removal efficacies of 34.29 ± 0.87% and 38.94 ± 0.63%, respectively. Bioremediation efficiency was dependent on bacterial growth, and the organic content and dissolved oxygen in the sample during cultivation were key factors in bacterial growth. The naturally selected bacterium could tolerate relatively high levels of organic content and work synergistically with other indigenous microorganisms found in the biogas plant effluent. Therefore, the bioremediation of biogas plant effluent using naturally selected P. putida can feasibly be applied in biogas power plants where sterilization is not necessary.

Anaerobic digestion of hydrothermally-pretreated lignocellulosic biomass: Influence of pretreatment temperatures, inhibitors and soluble organics on methane yield.

Anaerobic digestion (AD) of lignocellulosic biomass has received significant attention for bioenergy production in recent years. However, hydrolysis is a rate-limiting in AD of such feedstock. In this study, effects of hydrothermal pretreatment of Napier grass, a model lignocellulosic biomass, on methane yield were examined through series of batch and semi-continuous studies. In batch studies, the highest methane yield of 248.2 ±â€¯5.5 NmL CH4/g volatile solids (VS)added was obtained from the biomass pretreated at 175 °C, which was 35% higher than that from the unpretreated biomass. The biomass pretreated at 200 °C resulted in formation of 5-hydroxymethylfurfural and furfural, which significantly inhibited methanogenesis. In semi-continuous studies, digester fed with the biomass pretreated at 200 °C at organic loading rate (OLR) of 4 g VS/L.d resulted in digester failure. Thus, OLRsoluble/OLRtotal ratio <200 is proposed as an operating criterion for effective operation of digester fed with pretreated biomass slurry.

Decentralized biorefinery for lignocellulosic biomass: Integrating anaerobic digestion with thermochemical conversion.

Anaerobic digestion (AD) of lignocellulosic biomass i.e. Napier grass (Pennisetum purpureum), was investigated via a series of batch and bench-scale experiments. Two semi-continuous bench-scale horizontal bioreactors were operated in parallel for nearly 300 days, and the reactors were able to handle the organic loading rate (OLR) up to 6 kg volatile solids (VS)/m3-d, which was among the highest OLR reported in the literature for lignocellulosic biomass. Hemicellulose was the main structural carbohydrate of lignocellulosic biomass per unit respective mass (dry weight) basis contributing to methane production. The cellulose- and lignin-rich digestate was further examined for its bioenergy potential via torrefaction and hydrothermal carbonization, and was found to have higher mass and energy yield compared with those of raw Napier grass. The produced solid char has energy content similar to bituminous coal with low ash content. Thus, this study provided a successful integration of anaerobic digestion with thermochemical conversion representing a biorefinery concept for lignocellulosic feedstocks.

Enhanced volatile fatty acids production during anaerobic digestion of lignocellulosic biomass via micro-oxygenation.

A series of batch experiments were conducted to investigate the effects of inoculum type, oxygen (O2) dosage, and incubation time on volatile fatty acids (VFAs) production during anaerobic digestion (AD) of Napier grass (Pennisetum purpureum), a high yielding energy crop. The results showed that anaerobically digested cattle manure (ADCM) as an inoculum generated significantly higher VFAs compared to that of anaerobically digested waste activated sludge (ADWAS) as an inoculum. Additionally, the incubation time of 3days and O2 dosage of 15mL/g volatile solidsadded showed the highest VFAs production when ADCM was used as an inoculum. Moreover, the VFAs production had a quadratic correlation with O2 dosage with R2 of 0.86. The Scanning Electron Microscopy (SEM) images of the digested fiber showed rough and crumbled surface structures as opposed to that of the undigested fiber, which was further confirmed by changes in structural composition of the digested fiber.

Anaerobic biorefinery: Current status, challenges, and opportunities.

Anaerobic digestion (AD) has been in use for many decades. To date, it has been primarily aimed at treating organic wastes, mainly manures and wastewater sludge, and industrial wastewaters. However, with the current advancements, a more open mind is required to look beyond these somewhat restricted original applications of AD. Biorefineries are such concepts, where multiple products including chemicals, fuels, polymers etc. are produced from organic feedstocks. The anaerobic biorefinery concept is now gaining increased attention, utilizing AD as the final disposal step. This review aims at evaluating the potential significance of anaerobic biorefineries, including types of feedstocks, uses for the produced energy, as well as sustainable applications of the generated residual digestate. A comprehensive analysis of various types of anaerobic biorefineries has been developed, including both large-scale and household level applications. Finally, future directives are highlighted showing how anaerobic biorefinery concept could impact the bioeconomy in the near future.

Anaerobic digestion of lignocellulosic biomass: challenges and opportunities.

Anaerobic digestion (AD) of lignocellulosic biomass provides an excellent opportunity to convert abundant bioresources into renewable energy. Rumen microorganisms, in contrast to conventional microorganisms, are an effective inoculum for digesting lignocellulosic biomass due to their intrinsic ability to degrade substrate rich in cellulosic fiber. However, there are still several challenges that must be overcome for the efficient digestion of lignocellulosic biomass. Anaerobic biorefinery is an emerging concept that not only generates bioenergy, but also high-value biochemical/products from the same feedstock. This review paper highlights the current status of lignocellulosic biomass digestion and discusses its challenges. The paper also discusses the future research needs of lignocellulosic biomass digestion.