Kinetics of methane production during anaerobic fermentation of chicken manure with sawdust and fungi pre-treated wheat straw

Fungal bioremediation approaches for the removal of toxic pollutants: Mechanistic understanding for biorefinery applications

Pollution is a global menace that poses harmful effects on all the living ecosystems and to the Earth. As years pass by, the available and the looming rate of pollutants increases at a faster rate. Although many treatments and processing strategies are waged for treating such pollutants, the by-products and the wastes or drain off generated by these treatments further engages in the emission of hazardous waste. Innovative and long-lasting solutions are required to address the urgent global issue of hazardous pollutant remediation from contaminated environments. Myco-remediation is a top-down green and eco-friendly tool for pollution management. It is a cost-effective and safer practice of converting pernicious substances into non-toxic forms by the use of fungi. But these pollutants can be transformed into useable products along with multiple benefits for the environment such as sequestration of carbon emissions and also to generate high valuable bioactive materials that fits as a sustainable economic model. The current study has examined the possible applications of fungi in biorefineries and their critical role in the transformation and detoxification of pollutants. The paper offers important insights into using fungal bioremediation for both economically and environmentally sound solutions in the domain of biorefinery applications by combining recent research findings.

Anaerobic fermentation of organic solid waste: Recent updates in substrates, products, and the process with multiple products co-production

The effective conversion and recycling of organic solid waste contribute to the resolution of widespread issues such as global environmental pollution, energy scarcity and resource depletion. The anaerobic fermentation technology provides for the effective treatment of organic solid waste and the generation of various products. The analysis, which is based on bibliometrics, concentrates on the valorisation of affordable and easily accessible raw materials with high organic matter content as well as the production of clean energy substances and high value-added platform products. The processing and application status of fermentation raw materials such as waste activated sludge, food waste, microalgae and crude glycerol are investigated. To analyse the status of the preparation and engineering applications of the products, the fermentation products biohydrogen, VFAs, biogas, ethanol, succinic acid, lactic acid, and butanol are employed as representatives. Simultaneously, the anaerobic biorefinery process with multiple product co-production is sorted out. Product co-production can reduce waste discharge, enhance resource recovery efficiency, and serve as a model for improving anaerobic fermentation economics.

Anaerobic co-digestion of grass and cow manure: kinetic and GHG calculations

Grass is a highly desirable substrate for anaerobic digestion because of its higher biodegradability and biogas/methane yield. In this study, anaerobic co-digestion of grass, cow manure and sludge was studied under mesophilic conditions for 65 days. Experiments were performed on a feed ratio of grass/manure from 5 to 25%, respectively. The maximum cumulative biogas and methane yield was obtained as 331.75 mLbiogas/gVS and 206.64 mLCH₄/gVS for 25% ratio. Also, the results of the experiments were tested on the three different kinetics model which are the first order kinetic model, modified Gompertz model and Logistics model. As a result of the study, it was found that by using grass nearly 480 × 10⁶ kWh/year electricity may be produced and 0.5 × 10⁶ tons/year CO₂ greenhouse gas emission mitigation may be reached.

Subcritical Water Pretreatment for Anaerobic Digestion Enhancement: A Review

This work reviews hydrothermal subcritical water pretreatment to enhance biogas production through anaerobic digestion. The complexity of the lignocellulosic structure has been the main limitation contributing to unsatisfactory biogas production throughout the anaerobic digestion. The high resistance of the structure to biological hydrolysis has increased the interest in applying pretreatment prior to anaerobic digestion to facilitate hydrolysis. Hydrothermal subcritical water technology, an environmentally friendly pretreatment that uses water as the main medium, is gaining prominence in biogas enhancement. However, the subcritical water pretreatment influence on structural properties, biogas production, and the production of anaerobic process inhibitors signifies a knowledge gap and needs an evaluation. This review presents the need for pretreatment reaction and properties in the subcritical water region, biogas production from subcritical water pre-treated waste, production of inhibitors, and its challenges are discussed. This pretreatment could be a promising option and further enhance biogas production throughout the anaerobic digestion process.

Production of oyster mushroom (Pleurotus ostreatus) on sawdust supplemented with anaerobic digestate

Anaerobic digestion of organic waste results in production of biogas and a nutrient-rich digestate that has an established use as fertilizer in plant production. This study evaluated use of anaerobic digestate based on a high concentration of organic household waste as a fertilizer in sawdust-based production of oyster mushrooms (Pleurotus ostreatus). Inclusion of 0.5 L of anaerobic digestate (AD) per kg sawdust gave similar productivity in terms of biological efficiency (79.5 ± 5.4 %), and protein concentration (24.7 ± 2.4 % of dry weight (dw)) as standard mushroom substrate (78.1 ± 5.3 %, and 21.9 ± 3.0 % of dw, respectively). However, mushroom growth was impaired at the highest concentration of anaerobic digestate tested, 1 L digestate per kg dw sawdust. Comparison of the AD-fertilized substrate with a mushroom substrate with standard components (sawdust, wheat bran, calcium sulfate) and with similar C/N-ratio revealed some differences in elemental composition of the fruiting bodies, with an major increase in sodium concentration for the AD-fertilized substrate compared with the standard substrate (413.3 ± 28.9 and 226.7 ± 30.6 mg kg^-1 dw, respectively). This difference can be explained by high sodium concentration in the anaerobic digestate, most likely due to inclusion of food scraps from households and restaurants in the biodigester feedstock. Screening of both substrates for a total of 133 micropollutants revealed that total sum of micropollutants was significantly higher in the AD-fertilized substrate (258 ± 12 ng/g dw substrate) than in the standard substrate (191 ± 35 ng/g dw substrate). Nitrogen losses during preparation of the AD-fertilized substrate were negligible.

Mechanism of dielectric barrier plasma technology to improve the quantity and quality of short chain fatty acids in anaerobic fermentation of cyanobacteria

The recycling of high value carbon resources from cyanobacteria has become a research hotspot. This work investigated the possibility of dielectric barrier discharge (DBD) plasma pretreatment to improve the anaerobic fermentation performance of cyanobacteria. The maximum accumulations of short-chain fatty acids (SCFAs) and acetic acid in DBD group were 3.30 and 1.49 times of that in control group. The physical effects of DBD plasma and the oxidative stress response of cyanobacteria cells could improve the solubilization of cyanobacteria polymer. The destruction of humus by DBD plasma can reduce the negative impact of humus on the early stage of anaerobic fermentation, thus facilitating the rapid start of anaerobic fermentation. The contents of Bacteroidetes, Firmicutes and Chloroflexi in DBD group were higher than those in control group, while the content of Proteobacteria was on the contrary, which was conducive to the hydrolysis and acidification process. The decrease of Methanosaeta sp. and Methanosarcina sp. abundance in DBD group might be another reason for the increase of acetic acid ratio. Under the joint action of plasma chemical oxidation and microbial degradation, the degradation effect of microcystin-LR in the anaerobic fermentation supernatant of DBD group was better than that of the control group, which was conducive to the recycling of cyanobacteria anaerobic fermentation supernatant. Therefore, DBD pretreatment was conductive to recycling valuable carbon source from cyanobacteria and can be further developed as a potential new pretreatment technology.

The advantages of co-digestion of vegetable oil industry by-products and sewage sludge: Biogas production potential, kinetic analysis and digestate valorisation

The production of edible vegetable oils generates considerable amounts of energy-rich waste, which is usually not utilised fully. Besides, inefficient management of such wastes can have a negative impact on the environment. On the other hand, this waste can also serve as a raw material for the production of high value-added products, such is biogas. The mono-digestion of seven different by-products and wastes from the vegetable oil industry was investigated in this study: Pumpkin seeds press cake (PSPC), grape seeds press cake (GSPC), olive mill pomace (OMP), coconut oil cake (CC), filtration additive (FA), spent bleaching earth (SBE) and sludge from a vegetable oil industry (SOI) wastewater treatment plant. In addition, co-digestion of these substrates was performed with municipal sewage sludge (SS). Besides inoculum, rumen fluid was added to the reactors to enhance biogas production. The biogas production potential of the tested substrates was monitored by measuring various parameters. A kinetic analysis was later carried out and a growth test was performed on the digestates to evaluate their potential for agricultural use. The highest biogas yields in the mono-digestion test were obtained with the substrates with the highest fat content: 1402, 1288, 830 and 750 mL of biogas/gVS for SOI, FA, PSPC and CC substrate, respectively. Co-digestion of SS with by-products of vegetable oil industry such as FA, SBE, CC, SOI and PSPC increased the biogas yields by 94.9%, 74.1%, 30.8%, 27.4% and 23.6% compared to SS mono-digestion. Furthermore, the data for mono-digestion of PSPC, GSPC, and FA, and co-digestion of SS with these substrates, CC and SBE, have not been found in the literature to date. The maximum methane content ranged from 61 to 74 vol%, while the chemical oxygen demand removal efficiency ranged from 42 to 78%. Relatively high fatty acids contents and ammonium concentrations were measured in the reactors. Kinetic analysis showed the best fit to the experimental data for the Cone kinetic model (R² > 0.98). The First order kinetic model, Monod, and the modified Gompertz model also exhibited high R² values. The digestates obtained from co-digestion proved to be excellent in the cress seeds growth test at digestate concentrations of 5-10 wt%, while higher concentrations had a toxic effect.

Semi-solid state promotes the methane production during anaerobic co-digestion of chicken manure with corn straw comparison to wet and high-solid state

Total solid content (TS) is an important factor for biogas production during anaerobic digestion. In this study, we explored the influence of different TS (5% wet, 15% semi-solid and 25% solid state) on the relative cumulative methane production (RCMP) during anaerobic co-digestion of chicken manure with corn straw. Results showed that total ammonium nitrogen and free ammonia nitrogen concentration increased with the increase of TS. Ammonium nitrogen in treatments at 15% TS was 2.25-2.76 times as high as that at 5% TS, which was below 3 times. The highest chemical oxygen demand removal and RCMP were obtained in the treatment of 15% TS with a ratio of 2:1 chicken manure: corn straw (based on TS). The RCMP in the treatments of 15% TS were 3.63-4.59 times higher than that of 5% TS based on the volume of substrates. The abundance of Caldicoprobacter improving the degradation of corn straw was significantly positively correlated with the RCMP, and the average abundance of Caldicoprobacter at 15% TS was 8.33 and 7.02 times higher than that at 5% and 25% TS, respectively. Structural equation models analysis suggested that TS significantly impacted the RCMP by indirectly impacting free ammonia nitrogen and microbial abundance. These findings indicated semi-solid state (15% TS) decreased ammonia nitrogen releasing and improved the abundance of Caldicoprobacter, and increased RCMP during anaerobic co-digestion of chicken manure with corn straw.

Optimization of subcritical water pre-treatment for biogas enhancement on co-digestion of pineapple waste and cow dung using the response surface methodology

The optimal pre-treatment method and conditions depend on the types of lignocellulose present due to the complexity and the variability of biomass chemical structures. This study optimized subcritical water pre-treatment to ensure maximum methane production from pineapple waste prior to anaerobic co-digestion with cow dung using the response surface methodology. A central composite design was achieved with three different factors and one response. A total of 20 pre-treatment runs were performed at different temperatures, reaction times and water to solid ratios suggesting optimum values for subcritical water pre-treatment at 128.52℃ for 5 min with 5.67 to 1 water to solid ratio. Under these conditions, methane yield increased from 59.09 to 85.05 mL CH₄/g VS with an increase of 23% biogas yield and 44% methane yield from the untreated. All pre-treatments above 200℃ showed reductions in biogas yield. Compositional analysis showed slight reduction of lignin and increase in α-cellulose content after the pre-treatment. Analysis using Fourier transform infrared spectroscopy and thermogravimetric analysis verified the presence of cellulosic material in pre-treated pineapple waste. Most of the hemicellulose was solubilized in the liquid samples after SCW pre-treatment. The crystallinity index of pineapple waste was reduced from 57.58% (untreated) to 54.29% (pre-treated). Scanning electron microscopy confirmed the structural modification of pre-treated pineapple waste for better microbial attack. Subcritical water pre-treatment is feasible as a promising method to enhance the anaerobic co-digestion process. Further study should be conducted to assess the scale-up of the process from pre-treatment to anaerobic digestion at the pilot plant level.

Trametes versicolor in lignocellulose-based bioeconomy: State of the art, challenges and opportunities

Although Trametes versicolor is one of the most investigated white-rot fungi, the industrial application of this fungus and its metabolites is still far from reaching its full potential. This review aims to highlight the opportunities and challenges for the industrial use of T. versicolor according to the principles of circular bioeconomy. The use of this fungus can contribute significantly to the success of efforts to valorize lignocellulosic waste biomass and industrial lignocellulosic byproducts. Various techniques of T. versicolor cultivation for enzyme production, food and feed production, wastewater treatment, and biofuel production are listed and critically evaluated, highlighting bottlenecks and future perspectives. Applications of T. versicolor crude laccase extracts in wastewater treatment, removal of lignin from lignocellulose, and in various biotransformations are analyzed separately.

Methane production from wheat straw pretreated with CaO2/cellulase

There are various lignocellulosic biomass pretreatments that act as attractive strategies to improve anaerobic digestion for methane (CH₄) generation. This study proposes an effective technique to obtain more CH₄via the hydrothermal coupled calcium peroxide (CaO₂) co-cellulase pretreatment of lignocellulosic biomass. The total organic carbon in the hydrolysate of samples treated with 6% CaO₂ and 15 mg enzyme per g-cellulose was 7330 mg L⁻¹, which represented an increase of 92.39% over the total organic carbon value of samples hydrolyzed with the enzyme alone. The promotion of the anaerobic digestion of wheat straw followed this order: hydrothermal coupled CaO₂ co-cellulase pretreatment > hydrothermal coupled CaO₂ pretreatment > enzymatic pretreatment alone > control group. The sample treated with 6% CaO₂ and 15 mg enzyme per g-cellulose gave the highest CH₄ production with a CH₄ yield of 214 mL g⁻¹ total solids, which represented an increase of 64.81% compared to the control group. The CH₄ yield decreased slightly when the amount of added cellulase exceeded 15 mg enzyme per g-cellulose.

This work reports methane production from wheat straw pretreated with CaO₂/cellulase.

Dual resource utilization for tannery sludge: Effects of sludge biochars (BCs) on volatile fatty acids (VFAs) production from sludge anaerobic digestion

Resource utilization of organic matters in tannery sludge has drawn great attention. In this paper, the influences of sludge biochars (BCs) on volatile fatty acids (VFAs) production from the anaerobic digestion of sludge supernatant (SST) were investigated. Experimental results demonstrated that the VFAs yields improved in the presence of BCs with rich functional groups. The maximum yield of VFAs was 1037.5 mg/g SCOD with the addition of BC-1 biochar (zeta potential -50.42 mV). BCs decreased ammonia nitrogen concentration, thus reducing inhibition for bacteria during the anaerobic digestion. Microbial community analysis indicated that the BCs affected microbial community structures and contributed to a favorable environment for bacteria. Especially, the BC-1 biochar with rich functional groups enhanced the relative abundance of acid-forming bacteria (Clostridiales). A dual strategy was proposed to improve the resource utilization efficiency for tannery sludge.

Agricultural Biogas—An Important Element in the Circular and Low-Carbon Development in Poland

The agricultural sector can play an important role in the transformation of the energy economy in Poland. Special attention in this paper has been paid to the development of the agricultural biogas market in Poland. The considerations mainly concern organizational and economic aspects. Agricultural biogas plant represents the circular cycle of matter and energy. It enables the establishment of low-carbon, resource-efficient links between the agriculture and energy sectors. This is an important element of the circular economy, where waste from agricultural production and the agri-food industry, coming from renewable resources, is transformed into goods with a higher added value. The social and economic needs of the present generation and future generations are considered. The paper presented the characteristics of the Polish market, i.e., the number of entities, the number and location of plants, as well as the production volumes. Analyses were performed in the area of raw materials used to produce agricultural biogas. The analyses were carried out between 2011 and 2018. According to analyses, the potential of the agricultural biogas market in Poland is currently being used to a small extent. It is necessary not only to provide institutional support but also to increase the awareness of farmers and managers in agri-food companies of the possibility of using production waste for energy purposes.