Mesophilic anaerobic co-digestion of aloe peel waste with dairy manure in the batch digester: Focusing on mixing ratios and digestate stability

Enhanced degradation of enrofloxacin in mariculture wastewater based on marine bacteria and microbial carrier

This study aimed to isolate marine bacteria to investigate their stress response, inhibition mechanisms, and degradation processes under high-load conditions of salinity and enrofloxacin (ENR). The results demonstrated that marine bacteria exhibited efficient pollutant removal efficiency even under high ENR stress (up to 10 mg/L), with chemical oxygen demand (COD), total phosphorus (TP), total nitrogen (TN) and ENR removal efficiencies reaching approximately 88%, 83%, 61%, and 73%, respectively. The predominant families of marine bacteria were Bacillaceae (50.46%), Alcanivoracaceae (32.30%), and Rhodobacteraceae (13.36%). They responded to ENR removal by altering cell membrane properties, stimulating the activity of xenobiotic-metabolizing enzymes and antioxidant systems, and mitigating ENR stress through the secretion of extracellular polymeric substance (EPS). The marine bacteria exhibited robust adaptability to environmental factors and effective detoxification of ENR, simultaneously removing carbon, nitrogen, phosphorus, and antibiotics from the wastewater. The attapulgite carrier enhanced the bacteria's resistance to the environment. When treating actual mariculture wastewater, the removal efficiencies of COD and TN exceeded 80%, TP removal efficiency exceeded 90%, and ENR removal efficiency approached 100%, significantly higher than reported values in similar salinity reactors. Combining the constructed physical and mathematical models of tolerant bacterial, this study will promote the practical implementation of marine bacterial-based biotechnologies in high-loading saline wastewater treatment.

Anaerobic co-digestion of human excreta, food leftovers and kitchen residue: 1 ternary mixture design, synergistic effects and RSM approach

Anaerobic digestion of multiple substrates can generate more biogas while remaining stable, if positive synergistic effects are achieved. The type of co-digested substrates and the mixing ratio used, are the most important variables as each substrate has unique set of characteristics. Optimizing the volume ratios by testing various substrate mixing ratios is a popular method for determining the best-performing ratio of substrate mixture. The ternary mixture design has reportedly been found to quicken the process of testing different mixing ratios with high accuracy without running several experiments. Therefore, a ternary mixture design and a response surface approach are used in this work to ascertain the relationship between substrate mix and responses (biogas yield, methane yield, and synergy). The findings of the experiment revealed that R9 comprising 78.8 % human excreta, 11.8 % food leftovers and 9.4 % kitchen residue, had the highest methane production of 764.79 mLCH4/gVS and a synergistic index of 3.26. Additionally, the 3D response surface plots from the response surface model showed important and shared interactions between Human Excreta, (HE), Food Leftovers (FLO), and Kitchen Residue (KR). HE and KR had a similar positive synergistic effect on biogas yield, methane yield, and synergy, which was not the case for FLO. The response surface plots showed that the predicted responses (methane yield, biogas yield and synergy) increased with increasing HE and KR fractions and decreased with increasing FLO fractions in the substrate mixtures.

Bacterial community composition in a two-stage anaerobic membrane bioreactor for co-digestion of food waste and food court wastewater

This study investigated the microbial community of a two-stage anaerobic membrane bioreactor (2S-AnMBR) co-digesting food waste and food court wastewater. The hydrolysis reactor (HR) was dominated by Bacteroidetes and Firmicutes phylum, with genus Lactobacillus enriched due to food waste fermentation. The up-flow anaerobic sludge blanket (UASB) was dominated by genus such as Methanobacterium and Methanosaeta. The presence of Methanobacterium (91 %) and Methanosaeta (7.5 %) suggested that methane production pathways inevitably undergo both hydrogenotrophic and acetoclastic methanogenesis. Hydrogen generated during hydrolysis fermentation in the HR contributed to methane production in the UASB via hydrogenotrophic pathways. However, the low abundance of Methanosaeta in the UASB can be attributed to the limited inffluent of volatile fatty acids (VFA) and the competitive presence of acetate-consuming bacteria Acinetobacter. The UASB exhibited more excellent dispersion and diversity of metabolic pathways compared to the HR, indicating efficient methane production.

Sugarcane-bagasse-ash in enhanced mesophilic Co-digestion for biogas and nutrient recovery: A concept of developing rural circular bioeconomy

Conductive agro-industrial wastes as accelerants in the anaerobic digestion (AD) of organic waste is a good technique for developing a rural circular economy, such as producing bioenergy and biofertilizer. This study disclosed the a role of sugar cane bagasse ash (SCBA) in enhancing the bioenergy (biogas) yield and digestate fertility via anaerobic co-digestion (AcoD) of buffalo dung (BD) and vegetable residue (VR) under mesophilic conditions (37 ᴼC). Firstly, an optimal BD/VR ratio (1:3) was determined based on biogas yield by introducing five different BD/VR ratios (1:0, 3:1, 1:1, 1:3, and 0:1) into AcoD systems. Secondly, the biogas yield was increased further by adding SCBA at five different concentrations (0, 0.5, 1, 1.5, and 2 wt%). Experimental results disclosed that the 1.5 wt% of SCBA gave the highest cumulative biogas yield (153.67 mL/g VS), COD removal rate (31.18%), and fertility (5.08%). Moreover, a framework is suggested to understand the role of SCBA in the enhanced DIET mechanism. This work documents an environmentally friendly and economical technique for developing a rural circular bioeconomy via the AD of organic agro-waste.

Characterization of kitchen and municipal organic waste for biogas production: Effect of parameters

Globally, the production of municipal solid waste is rising annually because of consumerism and the urbanization process. In the past few years, different researchers have explored strategies for generating biogas from various organic wastes. In this study, kitchen waste and municipal solid waste were characterized by several physical-chemical parameters. Ten of these substrates were mono-digested for biogas production in batch reactors where cabbage showed a 96.36 ± 1.73% volatile solid and biogas yield of 800 ± 8.8 mL within 10 days, while cooked rice had an 83.00 ± 1.49% volatile solid, and a biogas yield of 2821 ± 31.03 mL within 28 days. The CN ratio for cabbage and cooked rice waste was 13.9 and 30.9 respectively, whereas their pH values were 6.2 and 7.2. Based on the characterization and biogas yields attained, cooked rice waste could be mono-digested for biogas production and no published work showed a high yield as the current study while the other substrates require co-digestion to improve the biogas yield.

Investigations into valorisation of trade wastewater for biomethane production

Biogas production from wastewater is one way that industrial sites can work towards the UN Sustainable Development Goals, while recovering a valuable resource. The objective of this study was to investigate the suitability of data collected by municipal wastewater service providers as a method of classifying and screening waste producers as potential sites for biogas resource recovery by anaerobic digestion. Industrial wastewater samples, including raw effluent and treated waste ready for discharge, were examined, and biomethane potential assays performed. Results of chemical analysis and lab-scale digestion were compared to historical service provider data, and patterns were observed. Biomethane yields of up to 357 mL/gVS and 287mL/gVS were achieved from raw and treated effluent respectively. Digestion at the top four prospects could produce over 4690 GJ of methane and save $47,000 in natural gas costs, offsetting 490 tonnes of CO2 equivalent annually. These streams, from logistics, waste management, food and animal product businesses, combined high levels of degradable substrates and low levels of inhibitory components. While it is unlikely that this type of screening program can be completely accurate, certain parameters, including high sodium concentration, are applicable for discounting the potential for biogas production. This knowledge can be a valuable tool in the process of selecting sites for future resource recovery, therefore increasing the uptake of these processes, resulting in economic, environmental, and climate change mitigation benefits.

Mineral residue accelerant-enhanced anaerobic digestion of cow manure: An evaluation system of comprehensive performance

Anaerobic digestion (AD) is an efficient technology for treating biowaste and generating biogas. A reasonable evaluation of AD performance is crucial to its development. Herein, a comprehensive evaluation system covering five dimensions (energy output, process stability, degradation efficiency, digestate fertility, and digestate safety) was established to assess AD performance. Each dimension in the evaluation system was assigned a specific indicator defined by a threshold or range. Additionally, the proposed evaluation system was applied to assess a case study of batch-mode mesophilic AD that employed three industrial waste residues as mineral accelerants (nickel‑iron slag, steel slag, and fly ash). The mineral accelerants enhanced the energy output (methane yield by 66.55 %-87.54 %) and the feedstock degradation (chemical oxygen demand removal ratio by 11.23 %-32.42 %). The digestates also retained promising safety (heavy metal contents of 190-1260 mg/kg) and fertility (total nutrient contents of 3.71 %-4.69 %). The evaluation system reasonably appraised the comprehensive performance of accelerant-enhanced AD systems with cow manure. This work provides a reliable methodology for evaluating and comparing the performance of different novel accelerants and can be applied to evaluate the comprehensive performance of large-scale biogas projects with cow manure.

Co-digestion of cow manure and food waste for biogas enhancement and nutrients revival in bio-circular economy

Anaerobic co-digestion (AcoD) with suitable substrate ratios may have the potential to improve biogas process and could play a better role in nutrient management for biocircular economy. The goal of this study was to enhance biogas yield from AcoD of cow manure (CM) and canteen food waste (CFW), and pertinent co-digestion of suitable substrate ratios for nutrient management i. e NPK from linear to biocircular economy, using ruminant intestinal fluid as a source of inoculum. A mesophilic (37 ± 1 °C) laboratory-scale AcoD with varying CFW/CM ratios of (0:1, 1:4, 2:3, 1:1, 3:2, 4:1, and 1:0) based on wet weight was performed. The AcoD systems of different CFW/CM ratios were evaluated with a loading rate of 400 g/L in the presence of 100 g cow intestinal fluid (CIF) inoculation. All experimental AcoD systems yielded greater biogas (147-300 cm3/g VS) than the mono-digestion in which only CM (135 cm3/g VS) and CFW (146 cm3/g VS) were digested anaerobically. The AcoD system of CFW/CM with 4:1 showed the highest biogas yield (300 cm3/g VS), and VS and COD reduction rate (39.51% and 65.15%, respectively), and nutrient contents (6.53%). Moreover, the experiment results were verified by modified Gompertz model. This work provided a window of opportunity to examine the anaerobic co-digestion technology beyond biogas production and to put the current low-cost technology to use for nutrient management and as a better component of the biocircular economy for agriculture in Pakistan in order to achieve sustainable development goals.

Experimentation of dyes extracted from the peels of red banana and aloe vera as sensitizers for TiO2-based dye-sensitized solar cells

As an attempt of utilizing the peels to extract dye sensitizers for dye-sensitized solar cell (DSSC), the peels of red banana (fruit) and aloe vera (leaf) were used in this study. As far as we know, for the first time the peels of red banana and aloe vera are being used as sensitizer for DSSC. Acetone and ethanol were used as solvent in extracting dyes from these peels. For the four extracted dyes, UV-visible and Fourier transform infra-red spectroscopic studies were carried out to know their absorption range and the functional groups present in it. DSSCs were made by using these extracted dyes as sensitizer and commercially available TiO₂ as semiconductor oxide. XRD and SEM were recorded for the prepared TiO₂ paste. To know about the performance of these solar cells, J-V characterization was taken and the efficiency of the DSSCs were determined. It was seen that among all the four DSSCs prepared, the DSSC made with the dye taken from aloe vera peel by using ethanol as solvent showed the higher efficiency of 0.679%.

Enhanced anaerobic co-digestion performance by using surface-annealed titanium spheres at different atmospheres

A series of surface-annealed titanium spheres (Ti-A, Ti-B, and Ti-C) in different atmospheres were used as accelerants in anaerobic co-digestion (AcoD) systems under magnetic field (MF). Surface-annealed titanium spheres and MF exhibit remarkable coupling and promoting effects on the AcoD performance. The cumulative biogas yield (435.84-552.60 mL/g VS) and total chemical oxygen demand (COD) degradation efficiency (59.76%-71.28%) of the AcoD systems with Ti_MF, Ti-A_MF, Ti-B_MF, and Ti-C_MF were significantly higher than control (357.66 mL/g VS and 51.5%). The digestates of the AcoD system with surface-annealed Ti spheres delivered excellent stability (49.83%-59.90%) and fertilizer (4.21%-4.56%). This work clarifies the possible role of surface-annealed Ti spheres in enhancing methanogenesis.

The Impact of Automation and Knowledge Workers on Employees’ Outcomes: Mediating Role of Knowledge Transfer

While there are existing empirical reviews regarding the relation between knowledge workers (KW) and knowledge transfer (KT), no study has examined the association of automation and knowledge transfer. The study describes knowledge workers as employees embedded with special abilities and having the main role of transfering their abilities to other workers in the organization. Additionally, automation (AUT) is described in the study as a technological process embedded with tacit knowledge. Therefore, using knowledge worker productivity theory and the technology acceptance model, this study aims to recommend and test a research model which examines the mediating role of knowledge transfer between automation, knowledge workers, and employee outcomes (employee creativity (EC) and innovative performance (IP)). The study evaluates the significant influence of knowledge transfer on innovative performance and creativity of other employees within the organization. This study applied a judgmental non-probability sampling research strategy to gather data from employees at an industrial firm in Japan by administering a questionnaire via Google Form. The data were analyzed with partial least squares based on structural equation modeling aimed at testing the predictive power and relationships of the model estimates. The results found support for the mediating role of knowledge transfer between automation and employee creativity as well as between automation and innovative performance. However, the study found partial support that knowledge transfer mediates the relationship between knowledge worker and employee creativity, as well as knowledge worker and innovative performance. In the same, automation and knowledge workers have significant impacts on knowledge transfer. Knowledge transfer has a significant impact on employee creativity and innovative performance.

Application of a Spiral Symmetric Stream Anaerobic Bioreactor for treating saline heparin sodium pharmaceutical wastewater: Reactor operating characteristics, organics degradation pathway and salt tolerance mechanism

In this study, a Spiral Symmetry Stream Anaerobic Bioreactor (SSSAB) was adopted for treating actual saline heparin sodium pharmaceutical wastewater (HSPW). After adaptation, under the influent COD of 8731 mg/L, OLR of 6.98 kg COD/(m³•d) and salinity of 3.57 wt%, the COD removal reached up to 82%. This value is much higher than the reported for the other reactors at similar salinity. Benzenes are the major organic compounds in HSPW. The main rate-limiting steps are the degradations of phenol and p-cresol. In addition, the degradation pathways of typical benzenes in HSPW were analyzed. After adaptation, the soluble salt content in the granular sludge increased, and the bacterial extracellular polymers (EPS), especially tightly-bound EPS also significantly increased. 16S rRNA analysis revealed that the microbial community in the anaerobic granular sludge (AGS) had become adapted to the HSPW treatment since Mesotoga (12.4%), Anaerophaga (9.0%), Oceanotoga (6.1%) and Aminobacterium (4.1%) increased from previously below 1.0% values. The relative abundance of Methanosarcina in the upper layer of the reactor (68.7%) is significantly higher than that at the bottom (3.8%). This proves the superiority of the SSSAB structure. Finally, a model for salt-tolerant microorganisms is given, which proposes a mechanism for this study and provides reference for other anaerobic biological treatments of high-salt containing wastewater.

Coconut-shell-derived bio-based carbon enhanced microbial electrolysis cells for upgrading anaerobic co-digestion of cow manure and aloe peel waste

Microbial electrolysis cells (MECs) and exogenous accelerants can augment anaerobic digestion performance. Herein, MECs and coconut-shell-derived bio-based carbon (CBC) accelerant are adopted to strengthen anaerobic co-digestion of cow manure and aloe peel waste. The MEC with the voltage of 0.6 V and CBC accelerant of 0.15 wt.% gained the highest cumulative biogas yield (444.20 NmL/g VS) and chemical oxygen demand removal rate (75.46%), which are 80.25% and 58.33% higher than those (246.44 NmL/g VS, 47.66%) of the blank group, respectively. The digestates embodied a utilization potential with thermogravimetric loss of 37.12%-50.67% and total nutrient content of 35.36-51.58 g/kg. These results benefited from excellent electrocatalytic activity of MECs and physicochemical properties of CBC accelerant. A general strategy for understanding improved methanogenesis was proposed based on integrated effects of MECs and CBC accelerant. This work will shed light on development of anaerobic co-digestion by combining MECs and bio-based carbon accelerants.

Anaerobic co-digestion of dairy manure and Japanese knotweed (Fallopia japonica) under thermophilic condition: Optimal ratio for biochemical methane production

Anaerobic co-digestion of animal manure and lignocellulosic biomass is a potent approach for sustainable biomethane production. Co-digestion of dairy manure (DM) and Japanese knotweed (JK), which was collected from a riverbank, was investigated at five different DM-to-JK mixing ratios (100:0, 90:10, 80:20, 60:40, and 0:100; wet weight basis) under thermophilic condition. The results showed that the methane yields obtain from the co-digestion of DM and JK were much higher than that obtained from JK alone (104 ml/gVS), which indicates the synergistic effect and the benefits of co-digesting JK with DM. The highest methane yield (232 ml/gVS) was obtained from the DM-to-JK ratio of 90:10, which was 14.9% and 123.1% higher than that from DM and JK alone, respectively. It also showed the highest synergistic effect (61 ml/gVS). However, further increase in JK ratios led to the decrease in methane yield and synergistic effect. Therefore, applying the co-digestion of DM and JK at a ratio of 90:10 is recommended for biomethane production.

Bio-Delignification of Green Waste (GW) in Co-Digestion with the Organic Fraction of Municipal Solid Waste (OFMSW) to Enhance Biogas Production

The organic fraction of municipal solid waste (OFMSW) is recognized as a suitable substrate for the anaerobic digestion (AD) process and is currently considered a mature technology. A promising strategy to enhance biogas yield and productivity is the co-digestion of OFMSW with other organic biomass, such as green waste (GW), a mixture of leaves, grass, and woody materials originated from private yards and public greenspace management. The main limitation to the use of GW for biogas production is the high percentage of the lignocellulosic fraction, which makes necessary a pretreatment of delignification to dissolve the recalcitrant structure. In this study, a new strategy of sustainable bio-delignification using the white-rot fungi Bjerkandera adusta (BA) in comparison with other chemical pretreatments were investigated. Untreated and treated GW were, respectively, submitted to anaerobic co-digestion with OFMSW. AD processes were carried out in a lab-scale plant for 30 days in thermophilic conditions (55 °C). Biogas cumulative production was increased by about 100% in the case of treated GW compared with that of just OFMSW, from 145 to 289 Nm3 CH4/ton SV, and productivity almost doubled from 145 to 283 Nm3/ton FM * day. The measured average methane content values in the cumulative biogas were 55% from OFMSW and 54% from GW. Moreover, over 95% of the biogas was produced in 20 days, showing the potential opportunity to reduce the AD time.

Static-magnetic-field coupled with fly-ash accelerant: A powerful strategy to significantly enhance the mesophilic anaerobic-co-digestion

The anaerobic-co-digestion (AcoD) of dairy-manure (DM) and aloe-peel-residue (ALR) waste is enhanced by combining static-magnetic-field (SMF) and fly-ash (FA). Varying SMF intensities (5-30 mT) were applied to the co-digestion digesters containing the optimum FA concentration (1.5 wt.%), which were selected from co-digestion systems with a varying FA (0-2 wt.%). All experimental groups exhibit the greater COD removal rates (51.56-64.19%) and cumulative biogas yields (604.14-671.64 mL/g VS) than reference group (37.77% and 433.19 mL/g VS). The digester with optimum FA concentration (1.5 wt.%) under 5 mT shows the highest biogas yield (671.64 mL/g VS), and exhibits superior digestate stability (45.4%) and fertility (7.01%) for fertilizer utilization. A powerful strategy for understanding the underlying mechanism of the SMF and FA accelerant in an enhanced AcoD system is proposed. This work documents an innovative technique for an enhanced AcoD system using the SMF coupled with FA accelerant.

Binary and ternary trace elements to enhance anaerobic digestion of cattle manure: Focusing on kinetic models for biogas production and digestate utilization

The effects of binary and ternary trace elements (TEs) (Fe/Co, Fe/Ni, and Fe/Co/Ni) on the anaerobic digestion (AD) of cattle manure were investigated using kinetic models (first-order, logistic, modified Gompertz, and Coats-Redfern) and experimental measurements. Binary and ternary TEs can significantly improve the biogas production rate and yield potential. The deviation between the predicted and measured data for biogas yield with logistic model (2.1%-5.3%) and modified Gompertz model (0.32%-2.9%) was smaller than that with first-order kinetic model (6.9%-9.9%). The Coats-Redfern model fitting indicated that the activation energy of digestates with trace elements during pyrolysis was reduced by 3.9%-26.2% compared with the control group. Meanwhile, digestates with TEs showed remarkable fertility (5.72%-5.95%). The combination of kinetic models and experimental measurements can effectively quantify the effect of TEs on AD performance and provide an informed choice for industrial production.

Strategies to boost anaerobic digestion performance of cow manure: Laboratory achievements and their full-scale application potential

Cow manure represents a surplus manure waste in agricultural food sectors, which requires proper disposal. Anaerobic digestion, in this regard, has raised global interest owing to its apparent environmental benefits, including simultaneous waste diminishment and renewable energy generation. However, dedicated intensifications are necessary to promote the degradation of recalcitrant lignocellulosic components of cow manure. Hence, this manuscript presents a review of how to exploit cow manure in anaerobic digestion through different incentives extensively at lab-scale and full-scale. These strategies comprise 1) co-digestion; 2) pretreatment; 3) introduction of additives (trace metals, carbon-based materials, low-cost composites, nanomaterials, and microbial cultures); 4) innovative systems (bio-electrochemical fields and laser irradiation). Results imply that co-digestion and pretreatment approaches gain the predominance on promoting the digestion performance of cow manure. Particularly, for the co-digestion scenario, the selection of lignin-poor co-substrate is highlighted to produce maximum synergy and pronounced removal of lignocellulosic compounds of cow manure. Mechanical, thermal, and biological (composting) pretreatments generate mild improvement at laboratory-scale and are proved applicable in full-scale facilities. It is noteworthy that the introduction of additives (Fe-based nanomaterials, carbon-based materials, and composites) is acquiring more attention and shows promising full-scale application potential. Finally, bio-electrochemical fields stand out in laboratory trials and may serve as future reactor modules in agricultural anaerobic digestion installations treating cow manure.

Blast-furnace slag cement and metakaolin based geopolymer as construction materials for liquid anaerobic digestion structures: Interactions and biodeterioration mechanisms

In order to promote the development of the biogas industry, solutions are needed to improve concrete structures durability in this environment. This multiphysics study aims to analyse the multiphases interactions between the liquid phase of an anaerobic digestion system and cementitious matrices, focusing on (i) the impacts of the binder nature on the anaerobic digestion process at local scale, and (ii) the deterioration mechanisms of the materials. Cementitious pastes made of slag cement (CEM III), innovative metakaolin-based alkali-activated material (MKAA), with compositions presumed to resist chemically aggressive media, and a reference binder, ordinary Portland cement (CEM I), were tested by immersion in inoculated cattle manure in bioreactors for a long period of five digestion cycles. For the first time it was shown that the digestion process was disturbed in the short term by the presence of the materials that increased the pH of the liquid phase and slowed the acids consumption, with much more impact of the MKAA. However, the final total production of biogas was similar in all bioreactors. Material analyses showed that, in this moderately aggressive medium, the biodeterioration of the CEM I and CEM III pastes mainly led to cement matrix leaching (decalcification) and carbonation. MKAA showed a good behaviour with very low degraded depths. In addition, the material was found to have interesting ammonium adsorption properties in the chemical conditions (notably the pH range) of anaerobic digestion.

Enhanced direct interspecies electron transfer with transition metal oxide accelerants in anaerobic digestion

Transition metal compounds have been widely used to enhance the anaerobic digestion (AD) performance, while the role of transition metal compounds in enhancing AD performance remains unclarified. In this work, the function of transition metal oxide accelerants (tantalum oxide, niobium oxide, hafnium oxide, and tungsten oxide) in enhanced AD systems was investigated from experimental and theoretical standpoints. Higher biogas production (565.01-617.85 mL/g VS), chemical oxygen demand degradation rate (67.17%-70.45%), total solids and volatile solids reduction rates (29.76%-34.71%, 51.83%-60.88%) were achieved in AD systems with transition metal oxide accelerants than the control (327.08 mL/g VS, 56.65%, 22.65%, and 41.18%). The first-principle density functional theory calculations, electron exchange capacity analysis, and the 16S rRNA gene pyrosequencing demonstrated superior electron transfer and exchange capacities as well as microbial consortia development in transition metal oxides-induced DIET mechanism. This work provides a promising strategy for understanding the function of high-performance accelerants in AD systems.

Waste-to-energy nexus: A sustainable development

An upsurge in global population due to speedy urbanization and industrialization is facing significant challenges such as rising energy-demand, enormous waste-generation and environmental deterioration. The waste-to-energy nexus based on the 5R principle (Reduce, Reuse, Recycle, Recovery, and Restore) is of paramount importance in solving these Gordian knots. This review essentially concentrates on latest advancements in the field of 'simultaneous waste reduction and energy production' technologies. The waste-to-energy approaches (thermal and biochemical) for energy production from the agricultural residues are comprehensively discussed in terms environmental, techno-economic, and policy analysis. The review will assess the loopholes in order to come up with more sophisticated technologies that are not only eco-friendly and cost-effective, but also socially viable. The waste-to-energy nexus as a paradigm for sustainable development of restoring waste is critically discussed considering future advancement plans and agendas of the policy-makers.

Critical evidence for direct interspecies electron transfer with tungsten-based accelerants: An experimental and theoretical investigation

Accelerants can significantly enhance the biodegradability in anaerobic digestion (AD), which can be attributed to the direct interspecies electron transfer (DIET) mechanism. However, critical evidence for DIET mechanism is absent. In this work, nano-scale tungsten (W)-based compounds (WC, W₂N, and W₁₈O₄₉) are employed to clarify the roles of W-based accelerants in AD systems. A DIET mechanism based on the W-based accelerants is proposed, and three critical pieces of evidence are provided: (i) First-principle density functional theory calculations provide theoretical evidence, illustrating that W-based accelerants are of zero band gap. (ii) Electrical conductivity evaluation further elucidates that W-based accelerants have superior electronic transport. (iii) Pyrosequencing of 16S rRNA gene confirms the existence of acetogens and methanogens in AD systems, which can act as electron-donor bacteria and electron-acceptor archaea, respectively. Combining theoretical with experimental results, the critical evidence provides a general strategy for understanding the DIET mechanism of accelerant in AD systems.

Enhanced anaerobic mono- and co-digestion under mesophilic condition: Focusing on the magnetic field and Ti-sphere core-shell structured additives

Enhancing anaerobic digestion performance is highly desired for its large-scale application. In the present work, magnetic fields (0-30 mT) and Ti-sphere core-shell structured additives (Ti-1 and Ti-2) are simultaneously introduced in anaerobic mono-digestion and co-digestions. Compared with the control group, the Ti-sphere core-shell structured additives increase the biogas yield by 27.12%-65.53% for mono-digestion and 8.47%-35.89% for co-digestion systems under the optimized magnetic field intensity (5 mT), respectively. Meanwhile, the degradation rate of total chemical oxygen demand is 54.68%-69.14% for anaerobic mono-digestion and 53.03%-78.25% for anaerobic co-digestion with Ti-sphere core-shell structured additives, respectively. The digestate with Ti-sphere core-shell structured additives exhibits the remarkable stability (45.24%-53.17%) and fertility (4.85%-4.97%). This work clarifies the effect of magnetic field in AD system, and proposes a possible mechanism for understanding the enhanced methanogenesis pathways induced by Ti-sphere core-shell structured additives.

Role of biomass-derived carbon-based composite accelerants in enhanced anaerobic digestion: Focusing on biogas yield, fertilizer utilization, and density functional theory calculations

The performance of anaerobic digestion (AD) can be improved by the addition of accelerants. Three types of biomass-derived carbon-based composites (Co/C, CoO/C, and Co₃O₄/C) were used as accelerants to investigate the effect on AD systems in this work. These accelerants significantly improved the cumulative biogas yield (576-585 mL/g VS), and the total chemical oxygen demand degradation rate (68.48-71.11%) compared to the reference group (435.8 mL/g VS, 50.74%). The digestates with accelerants exhibited exceptional stability (59.24-63.67%) and superior fertilizer utilization (3.50-4.55%). In addition, first-principle density functional theory (DFT) calculations were conducted to provide the theoretical basis for the direct interspecies electron transfer (DIET), and a general strategy was proposed to help understand the enhanced methanogenesis pathway induced by the biomass-derived carbon-based composites. These important findings provide a novel avenue for the development of composite accelerants for AD systems.

Development of sustainable approaches for converting the organic waste to bioenergy

Dependence on fossil fuels such as oil, coal and natural gas are on alarming increase, thereby causing such resources to be in a depletion mode and a novel sustainable approach for bioenergy production are in demand. Successful implementation of zero waste discharge policy is one such way to attain a sustainable development of bioenergy. Zero waste discharge can be induced only through the conversion of organic wastes into bioenergy. Waste management is pivotal and considering its importance of minimizing the issue and menace of wastes, conversion strategy of organic waste is effectively recommended. Present review is concentrated on providing a keen view on the potential organic waste sources and the way in which the bioenergy is produced through efficient conversion processes. Biogas, bioethanol, biocoal, biohydrogen and biodiesel are the principal renewable energy sources. Different types of organic wastes used for bioenergy generation and its sources, anaerobic digestion-biogas production and its related process affecting parameters including fermentation, photosynthetic process and novel nano-inspired techniques are discussed. Bioenergy production from organic waste is associated with mitigation of lump waste generation and its dumping into land, specifically reducing all hazards and negativities in all sectors during waste disposal. A sustainable bioenergy sector with upgraded security for fuels, tackles the challenging climatic change problem also. Thus, intensification of organic waste conversion strategies to bioenergy, specially, biogas and biohydrogen production is elaborated and analyzed in the present article. Predominantly, persistent drawbacks of the existing organic waste conversion methods have been noted, providing consideration to economic, environmental and social development.

Improving performance and phosphorus content of anaerobic co-digestion of dairy manure with aloe peel waste using vermiculite

Phosphorus content of the digestate is crucial for evaluating its fertilizer utilization in anaerobic digestion system. The vermiculite containing rich-phosphorus is firstly used as an accelerant in anaerobic batch co-digestion system of aloe peel waste and dairy manure. After introducing vermiculite, the cumulative biogas production (295.14-353.96 mL/g VS), chemical oxygen demand removal rate (45.53%-71.03%), and volatile solid removal rate (50.70%-52.76%) are remarkably higher than those of reference reactor (234.08 mL/g VS, 39.38%, 45.10%). The thermal and fertility analyses manifest the digestates with vermiculite possess superior stability, admirable fertilizer values (5.97%-6.81%), and excellent total phosphorus content (11.44-13.29 g/kg). The improved co-digestion performance can be attributed to the addition of vermiculite. This work introduces a novel approach for improving the performance of anaerobic co-digestion and the fertilizer utilization of digestate in the co-digestion systems.

Assessment of the biochemical methane potential of mono- and co-digested dairy farm wastes

This study aimed to evaluate the methane potential of mono- and co-digested dairy farm wastes. The tested substrates included manure from lactating, dry, and young cows, as well as waste milk and feed waste. The highest methane yield was achieved from the lactating cow manure, which produced an average of 412 L of CH₄ kg^-1 volatile solids, followed by young and dry cow manures (332 and 273 L of CH₄ kg^-1 volatile solids, respectively). Feed and milk yielded an average of 325 and 212 L of CH₄ kg^-1 volatile solids, respectively. Co-digesting the manures from lactating and young cows with feed improved methane production by 7%. However, co-digesting the dry cow manure with feed achieved only 85% of the calculated methane yield. Co-digesting manure and milk at a ratio of 70:30 enhanced the methane potential from lactating, dry, and young cow manures by 19, 30, and 37%, respectively. Moreover, co-digesting lactating, dry, and young cow manures with milk at a ratio of 30:70 enhanced the methane yield by 60, 30, and 88%, respectively. The cumulative methane production of all samples was accurately described using the Gompertz model with a maximum error of 10%. Carbohydrates contributed the most to methane potential, while proteins and lipids were limiting.

Evaluation of methane production and energy conversion from corn stalk using furfural wastewater pretreatment for whole slurry anaerobic co-digestion

In this study, corn stalk (CS) was pretreated with furfural wastewater (FWW) for whole slurry anaerobic digestion (AD), which increased the degradability of CS components, changed the parameters in pretreatment slurry and improved the biochemical methane potential (BMP). The ultimate goal was to optimize the time and temperature for FWW pretreatment and evaluate whether FWW pretreatment is feasible from BMP and energy conversion. The results of path analysis suggested that lignocellulosic degradability (LD) was the main factor affecting methane production with the comprehensive decision of 0.7006. The highest BMP (166.34 mL/g VS) was achieved by the pretreatment at 35 °C for 6 days, which was 70.36% higher than that of control check (CK) (97.64 mL/g VS) and the optimal pretreatment condition was predicted at 40.69 °C for 6.49 days by response surface methodology (RSM). The net residual value (NRV) for the pretreatment of 35 °C and 6 days was the highest (0.6201), which was the most appropriate condition for AD in real application.

A kinetic study of roadside grass pyrolysis and digestate from anaerobic mono-digestion

The aim of this research is to evaluate the thermogravimetric behaviour of roadside grass and its digestate obtained from mesophilic anaerobic mono-digestion by quantifying its impacts on biomass composition and properties. Thermogravimetric measurements were conducted in a laboratory furnace under nitrogen flowrate of 100 mL/min in the temperature range from 35 to 800 °C at five different heating rates of 2.5, 5, 10, 15 and 20 °C/min. Friedman and Kissinger-Akahira-Sunose differential and integral isoconversional models were applied to determine the distributions of activation energies and modified pre-exponential factors per reacted mass (degree of conversion). The investigation demonstrated that anaerobic digestion of roadside grass can be used to generate biochar-richer material (with significantly greater yield of final residues after pyrolysis) with less energy required for subsequent pyrolysis in comparison with raw roadside grass.

Semi-continuous anaerobic co-digestion of flotation sludge from broiler chicken slaughter and sweet potato: Nutrients and energy recovery

Energy production based on the proper allocation of environmental liabilities is in line with the concept of sustainability. Flotation sludge (S) is a type of waste derived from the physical treatment of the wastewater generated in significant quantities during chicken slaughter in Brazil. If not treated, this wastewater may contribute to pollution, but further treatment provides clean energy and nutrient recycling. The present study aimed at evaluating the reduction of (S) organic load by means of mono and co-digestion with sweet potatoes (P) while promoting its conversion into energy (methane) and nutrients (digestate). Semi-continuous reactors (60 L capacity) were used with a hydraulic retention time of 25 days. The reactors were fed daily with 2.4 L consisting of 60% digestate recirculation, 40% non-chlorinated water and 4.5% total solids (TS). Using nine reactors and six progressive periods, eleven conditions were evaluated with three replicates each. The percentages of (P) and (S) varied from 0 to 100. The best observed condition in terms of energy recovery and TS removal was 60% of P + 40% of S (p ≤ 0.05), as it presented values of at least an increase of 92% in total biogas volume, an increase of 123% in specific methane production, an increase of 98% in specific methane yield and an increase of 44% in TS removal efficiency compared to mono-digestions. The fertilizer potential of the digestate generated in the different conditions was calculated and evaluated according to the area of (P) production. The results varied from 3.6 to 10.8 ha of (P) using 100 m³ of digestate. A multivariate analysis showed that higher amounts of (P) in substrate composition favor energy recycling while higher concentrations of (S) enhance the production of a digestate with valuable agronomic characteristics.

High-rate anaerobic treatment of digestate using fixed film reactors

The effluent stream of the anaerobic digestion processes, the digestate, accommodates high residual organic content that needs to be further treated before discharge. Anaerobic treatment of digestate would not only reduce the residual organic compounds in digestate but also has a potential to capture the associated biogas. High-rate anaerobic reactor configurations can treat the waste streams using lower hydraulic retention times which requires less footprint opposed to the conventional completely stirred tank reactors. This study investigated the high-rate anaerobic treatment performance and the associated biogas capture from the digestate of a manure mixture composed of 90% laying hen and 10% cattle manures in fixed-film reactors. The results indicated that it was possible to reduce total chemical oxygen demand content of the digestate by 57-62% in 1.3-1.4 days of hydraulic retention time. The corresponding biogas yields obtained were in the range of 0.395-0.430 L_biogas/g VS_added which were found to be comparable to many raw feedstocks. Moreover, significant total phosphorus reduction (36-47%) and greenhouse gas capture (over 14.5-18.1 tCO₂e/d per m³ digestate) were also recorded in the anaerobic fixed-film reactors.

Mesophilic anaerobic co-digestion of acorn slag waste with dairy manure in a batch digester: Focusing on mixing ratios and bio-based carbon accelerants

Co-digestion of acorn slag waste (ASW) and dairy manure (DM) with two bio-based carbon (BC) accelerants are investigated via batch experiments under mesophilic condition. With the favorable synergistic effect of the mixed substrate and BC accelerant, the anaerobic digestion (AD) systems assembled with aloe peel-derived BC (2.16 g/L) show significantly improved methanogenesis on the basis of the optimum wet weight ratio of ASW to DM (1:3). The cumulative biogas yield is 580.9 mL/g VS, and the total chemical oxygen demand reduction is 79.37%. These results are higher than those of the AD systems without carbon-based accelerants. The feasibility of digestate utilization is evaluated by thermal and fertilizer analyses, which manifest outstanding stability and excellent fertility (6.93%-7.40%) of digestate in co-digestion systems. A general strategy for understanding the enhanced methanogenesis pathways, induced by BC in AD systems, is demonstrated. These important findings open an innovative opportunity for developing carbon-based accelerants in anaerobic co-digestion.

Treatment of feces from beef cattle fed the enteric methane inhibitor 3-nitrooxypropanol

The study evaluated the residual effect of the known enteric methane inhibitor 3-nitrooxypropanol (3NOP) on anaerobic digestion of cattle feces (feces) in a CH₄ potential batch test and two consecutive runs of an anaerobic leach bed reactor at a solids retention time of 40 days. The feces used in this study were collected from beef cattle fed forage- (backgrounding) or grain- (finishing) based diets supplemented with 3NOP in feedlot and metabolism studies. The results showed that CH₄ yields were not significantly different from treatments using control feces and feces collected from cattle fed a diet supplemented with 3NOP in both CH₄ potential and leach bed studies. Spiking feces with 200 mg 3NOP kg^-1 dry matter decreased CH₄ production rate by 8.0-18.1% estimated from the Gompertz equation, increased the lag phase time (0.4-3.4 d) in all the treatments, while there was no significant difference in the overall CH₄ yield. Results from this study showed that 3NOP can be used as an effective enteric CH₄ inhibitor with no residual effect on anaerobic digestion.

Steel slag as accelerant in anaerobic digestion for nonhazardous treatment and digestate fertilizer utilization

Accelerants can effectively enhance the performance of anaerobic digestion (AD) system. The effects of optimized steel slag as accelerant in the AD of cow manure and the fertility utilization of the digestate were investigated. Results show that all steel slags collected from different iron and steel companies (slag-1, slag-2, and slag-3) positively affect AD performance in terms of enhancing the biogas yield, methane yield, and chemical oxygen demand (COD) degradation rate. The cumulative biogas yield, methane yield, and COD degradation rate of slag-2 are 507.29 mL/g VS, 274.70 mL/g VS, and 58.62%, respectively. Thermal analysis reveals that the digestate with steel slag has excellent thermal stability and potential application as a component of nitrogen, phosphorus, and potassium organic compound fertilizers. The use of different steel slags as accelerants in the AD system provides a safe and economical avenue to realize the resource utilization and harmless treatment of waste resource.

A comprehensive review of anaerobic digestion of organic solid wastes in relation to microbial community and enhancement process

Organic solid wastes (OSWs) should be regarded as valuable resources rather than dead-end landfill waste that causes public health and odor concerns. Anaerobic digestion (AD) is an ideal approach for managing organic solid waste issues and involves using a group of anaerobic microorganisms to transform OSWs into useful products. In this review, over 100 publications related to AD of OSWs have been compiled, discussed, and analyzed. A comprehensive analysis of the environmental and safety impacts of AD, its key environmental factors, co-digestion, and pretreatment, as well as the AD of OSWs by various anaerobic microbes uncovered by high throughput sequencing-based approaches, is presented. The purpose of this review is to provide an outline of the current knowledge of AD processes from a multi-angle perspective. A comprehensive understanding of AD of OSWs and genome-enabled biology development could be helpful for providing up-to-date knowledge of AD, developing it, overcoming its drawbacks and, ultimately, improving global waste control for more efficient environmental management. © 2018 Society of Chemical Industry.

The survival of pathogenic bacteria and plant growth promoting bacteria during mesophilic anaerobic digestion in full-scale biogas plants

The introduction of biogas plants is a promising way to recycle organic wastes with renewable energy production and reducing greenhouse gas. Application of anaerobic digestate as a fertilizer reduces the consumption of chemical fertilizers. In this study, the survival of pathogenic bacteria and plant growth promoting bacteria (PGPB) in two full-scale biogas plants operated at mesophilic condition were investigated. Feedstock and anaerobic digestate samples were collected from biogas plants and bacteria load in samples were detected using standard dilution plate method. Pathogenic bacteria were reduced to not detected level through mesophilic digestion tank except for Campylobacter. However, it could be reduced by 98.7% through a sterilization tank. Bacillus was detected at 8.00 and 7.81 log₁₀  CFU/g dry matter in anaerobic digestates, and it was also resistant to sterilization tank. Bacillus spp. is considered to be the safe bacteria that hold remarkable abilities for promoting plant growth. The results showed that treatment at biogas plants is effective to reduce pathogenic bacteria in dairy manure, and sterilization could further reduce the sanitary risks of pathogenic bacteria relating to anaerobic digestate application. Anaerobic digestates could also be utilized as bio-fertilizer as the high load of plant growth promoting bacteria.

Thermophilic Co-Digestion of the Organic Fraction of Municipal Solid Wastes-The Influence of Food Industry Wastes Addition on Biogas Production in Full-Scale Operation

Anaerobic digestion (AD) has been used widely as a form of energy recovery by biogas production from the organic fraction of municipal solid wastes (OFMSW). The aim of this study was to evaluate the effect of the introduction of co-substrates (restaurant wastes, corn whole stillage, effluents from the cleaning of chocolate transportation tanks) on the thermophilic anaerobic digestion process of the mechanically separated organic fraction of municipal solid wastes in a full-scale mechanical-biological treatment (MBT) plant. Based on the results, it can be seen that co-digestion might bring benefits and process efficiency improvement, compared to mono-substrate digestion. The 15% addition of effluents from the cleaning of chocolate transportation tanks resulted in an increase in biogas yield by 31.6%, followed by a 68.5 kWh electricity production possibility. The introduction of 10% corn stillage as the feedstock resulted in a biogas yield increase by 27.0%. The 5% addition of restaurant wastes contributed to a biogas yield increase by 21.8%. The introduction of additional raw materials, in fixed proportions in relation to the basic substrate, increases biogas yield compared to substrates with a lower content of organic matter. In regard to substrates with high organic loads, such as restaurant waste, it allows them to be digested. Therefore, determining the proportion of different feedstocks to achieve the highest efficiency with stability is necessary.

Prognostic Assessment of the Viability of Hydrothermal Liquefaction as a Post-Resource Recovery Step after Enhanced Biomethane Generation Using Co-Digestion Technologies

In line with global efforts at encouraging paradigm transitions from waste disposal to resource recovery, the anaerobic co-digestion of substrates of wet hydrolyzed meat processing dissolved air flotation sludge and meat processing stock yard waste was investigated in the present study. It was demonstrated that the co-digestion of these substrates leads to the introduction of co-digestion synergizing effects. This study assessed biomethane potentials of the co-digestion of different substrate mixtures, with the preferred substrate mixture composed of stockyard waste and wet hydrolyzed meat processing dissolved air flotation sludge, present in a 4:1 ratio on a volatile solid mass basis. This co-digestion substrate mix ratio presented an experimentally determined cumulative biomethane potential of 264.13 mL/gVSadded (volatile solid). The experimentally determined cumulative biomethane potential was greater than the predicted maximum cumulative biomethane potential of 148.4 mL/gVSadded, anticipated from a similar substrate mixture if synergizing effects were non-existent. The viability of integrating a downstream hydrothermal liquefaction processing of the digestate residue from the co-digestion process, for enhanced resource recovery, was also initially assessed. Assessments were undertaken via the theoretical based estimation of the yields of useful products of biocrude and biochar obtainable from the hydrothermal liquefaction processing of the digestate residue. The environmental sustainability of the proposed integrated system of anaerobic digestion and hydrothermal liquefaction technologies was also initially assessed. The opportunity for secondary resource recovery from the digestate, via the employment of the hydrothermal liquefaction process and the dependence of the environmental sustainability of the integrated system on the moisture content of the digestate, were established. It is anticipated that the results of this study will constitute an invaluable basis for the future large-scale implementation of the proposed integrated system for enhanced value extraction from organic waste streams.

Low-cost composited accelerants for anaerobic digestion of dairy manure: Focusing on methane yield, digestate utilization and energy evaluation

To improve the methane yield and digestate utilization of anaerobic digestion (AD), low-cost composited accelerants consisting of urea (0.2-0.5%), bentonite (0.5-0.8%), active carbon (0.6-0.9%), and plant ash (0.01-0.3%) were designed and tested in batch experiments. Total biogas yield (485.7-681.9 mL/g VS) and methane content (63.0-66.6%) were remarkably enhanced in AD systems by adding accelerants compared to those of control group (361.9 mL/g VS, 59.4%). Composited accelerant addition led to the highest methane yield (454.1 mL/g VS), more than double that of control group. The TS, VS, and CODt removal rates (29.7-55.3%, 50.9-63.0%, and 46.8-69.1%) for AD with accelerants were much higher than control group (26.2%, 37.1%, and 39.6%). The improved digestate stability and enhanced fertilizer nutrient content (4.95-5.66%) confirmed that the digestate of AD systems with composited accelerants could safely serve as a potential component of bioorganic fertilizer. These findings open innovative avenues in composited accelerant development and application.

Pilot-Scale Anaerobic Co-Digestion of the OFMSW: Improving Biogas Production and Startup

This paper presents experimental results regarding anaerobic co-digestion of the organic fraction of municipal solid waste and fruit and vegetable waste in order to establish the efficiency of a 2 m3 volume pilot plant in terms of biogas and methane yield and stability of the process. The research study presents the feasibility of developing anaerobic digestion as an effective method for municipal solid waste management. The experiments were conducted in mesophilic conditions (35 °C). Domestic waste water was used as inoculum. The results showed that the inoculum presence, temperature, and pH control, were essential in order to improve biogas production and its composition. Using liquid inoculum, the CH4 percentage in the biogas oscillated between 44% and 51%, and the biogas production from 0.504 and 0.6 m3/day. Compared to domestic waste water, animal manure increased the CH4 concentration in biogas (up to 63%), while the daily biogas production increased by 26% and varied from 0.693 to 0.786 m3. The cumulative biogas production at the end of the experiments were 11.7 m3 and 15.89 m3, respectively. Using inoculum and co-digestion, the plant startup time was significantly reduced, the total solids content decreased from 22.7% to 19.8%, while the volatile solids decreased from 37.6% to 31.2%.

Experimental and feasibility assessment of biogas production by anaerobic digestion of fruit and vegetable waste from Joburg Market

Substrate-induced instability of anaerobic digestion from fruit and vegetable waste (FVW) results in low biogas yield. In this study, substrate management through fruit to vegetable mix ratio in a two-stage semi-continuous digester was investigated as a pathway for optimality of yield. The experiment conducted over 105 days with 62.52 kg of FVWs sourced from Joburg Market, South Africa showed that a stable process was achieved at a fruit to vegetable waste mix ratio of 2.2:2.8. At this ratio, optimal organic loading rate ranged between 2.68 and 2.97 kg VS/m³-d which resulted in a specific biogas yield of 0.87 Nm³/kg VS with 57.58% methane on average. The results of the experimental study were used as a feasibility assessment for a full-scale 45 tonnes/d plant for Joburg Market considering three energy pathways. The plant will produce 1,605,455 Nm³/y of biogas with the potential for offsetting 15.2% of the Joburg Market energy demand. Conversion of all biogas to biomethane was the most economically attractive energy pathway with a net present value of $2,428,021, an internal rate of return of 16.90% and a simple payback period of 6.17 years. This route avoided the greenhouse gas emission of 12,393 tonnes CO₂, eq. The study shows that the anaerobic digestion of FVWs as sole substrate is possible with financial and environmental attractiveness.

Dynamic Effects of Initial pH of Substrate on Biological Growth and Metamorphosis of Black Soldier Fly (Diptera: Stratiomyidae)

Edible insects have become a recognized alternative and sustainable source of high-quality proteins and fats for livestock or human consumption. In the production process of black soldier fly (BSF), (Hermetia illucens L. [Diptera: Stratiomyidae]), initial substrate pH is a critical parameter to ensure the best value of insect biomass, life history traits, and quality bio-fertilizer. This study examined the impact of initial pH values on BSF larvae production, development time, and adult longevity. The BSF were reared on artificial diet with initial pH of 2.0, 4.0, 6.0, 8.0, and 10.0; the control was set at 7.0. Final BSF larval weight was significantly greater in substrates having initial pH 6.0 (0.21 g), control 7.0 (0.20 g), and 10.0 (0.20 g) with no significant difference among them, whereas larval weight reared with initial pH 2.0 and 4.0 were lowest at 0.16 g (-23%). Prepupal weight was greatest when larvae were reared on substrates with initial pH 6.0 (0.18 g), control 7.0 (0.19 g), 8.0 (0.18 g), and 10.0 (0.18 g). In contrast, the prepupal weight of larvae reared on diets with initial pH 2.0 was lowest at 0.15 g (-22%). Larval development time was 21.19 d at pH 8.0, about 3 d (12.5%) shorter than that of those reared on diets with initial pH 6.0, 7.0 control, and 10.0. In all treatments, pH shifted to 5.7 after 3-4 d and 8.5 after 16-17 d except for two groups (2.0 and 4.0) where the pH remained slightly acidic 5.0 and 6.5, respectively.

Methane production and characteristics of the microbial community in the co-digestion of spent mushroom substrate with dairy manure

Spent mushroom substrate (SMS) is a potential biomass material generated during mushroom cultivation. In this study, the methane yield and microbial community resulting from co-digestion of SMS and dairy manure (DM) at different mixing ratios (0:4, 1:1, 3:1, and 1:3), were evaluated. Co-digestion analysis showed that the methane yield from the mixtures was 6%-61% higher than the yield from SMS or DM alone, indicating a synergistic effect of co-digestion of SMS with DM. For the SMS of F.velutipes (SFv) and P.erygii var. tuoliensis (SPt), co-digestion of DM/SMS at a ratio of 1:1 was optimal, but for the SMS of P. eryngi (SPe), co-digestion of DM/SMS at a ratio of 3:1 was ideal. The pH at all co-digestion ratios was in the range of 6.8-8.0, indicating that adding DM could increase the systemic buffering capacity. Methanosaetaceae was shown to be the predominant methanogens present during the co-digestion of DM/SMS.

Biomethanation macrodynamics of vegetable residues pretreated by low-frequency microwave irradiation

The effects of microwave irradiation on the digestibility and biogas production of cauliflower (Brassica oleracea var. botrytis) and cabbage (Brassica oleracea var. capitata) leaves were investigated using biochemical methane potential (BMP) assays. Cow dung was utilised as inoculum. Different microwave powers (87.5, 175 and 350W) were applied in a first set of runs for 15min. The second set consisted of 20, 25 and 30min irradiation at 350W. Based on ANOVA analysis (α=0.05), biogas production was significantly higher for the irradiated substrates compared to controls. The peak biogas production was 700ml for 36days HRT for 350W/25min. Peak COD, SCOD, volatile and total solids removals were 54.84%, 39.08%, 34.60% and 71.96%, respectively. Phosphate and total nitrogen increased significantly. Cumulative biogas production data fitted the modified Gompertz equation well. The highest biogas yield was 0.271L/g VS_removed at a 350W microwave irradiation for 30min.

Effect of low temperature of thermal pretreatment on anaerobic digestion of textile dyeing sludge

The minimization and methane production of textile dyeing sludge (TDS) can be simultaneously attained via anaerobic digestion (AD). However, the possible toxicity and complex recalcitrant organic matters involved in limited the hydrolysis of TDS. Therefore, the low-temperature of thermal pretreatment (LTTP) lasting for 1h at temperatures from 60 to 100°C was employed to accelerate the hydrolysis and subsequent methane generation of TDS. The results showed that LTTP with temperatures higher than 70°C obviously improve the AD performance of TDS. Highest accumulative methane production was achieved for 100°C pretreated TDS and from thermal analysis point of view it was due to the disintegration of some recalcitrant macromolecules in TDS. Nevertheless, 90°C pretreated TDS did not perform favorable methane yield as expected, attributing to the inhibited acetogenesis as well as the hindered methanogenesis which was simultaneously competed by dye reducer for electrons.

Biogas production from co-digestion of organic fraction of municipal solid waste and fruit and vegetable waste

The anaerobic co-digestion of organic fraction of municipal solid waste (OFMSW) and fruit and vegetable waste (FVW) was evaluated in terms of biogas and methane yield, volatile solids (VS) removal rate and stability of the process. The batch experiment was conducted in mesophilic conditions (35°C), with four different OFMSW/FVW ratios (VS basis) of 1/0, 1/1, 1/3, and 0/1. The methane yield from the co-digestion was higher than the mono-digestion for OFMSW and FVW. The optimal mixing ratio of OFMSW/FVW was found to be 1/3. The average cumulative biogas and methane yield in this condition was 493.8NmL/gVS and 396.6NmL/gVS, respectively, and the VS removal rate was 54.6%. Compared with the mono-digestion of OFMSW and FVW, the average increase in methane yield was 141% and 43.8%, respectively.

Performance evaluation of micro-aerobic hydrolysis of mixed sludge: Optimum aeration and effect on its biochemical methane potential

This study evaluated the performance of a micro-aerobic hydrolysis of mixed sludge and its influence as a pretreatment of this waste for its subsequent anaerobic digestion. Three experimental series were carried out to evaluate the optimum micro-aeration levels in the range from 0.1 to 0.5 air volume/min.reactor volume (vvm) and operation times within the range of 24-60 h. The maximum methane yield [35 mL CH₄/g volatile suspended solids (VSS) added] was obtained for an aeration level of 0.35 vvm. This methane yield value increased 114% with respect to that obtained with the non-aerated sludge. In the micro-aeration process carried out at an aeration level of 0.35 vvm, increases in soluble proteins and total sugars concentrations of 185% and 192% with respect to their initial values were found, respectively, after 48 h of aeration. At the above micro-aerobic conditions, soluble chemical oxygen demand (COD_S) augmented 150%, whereas VSS content decreased until 40% of their initial respective values. Higher COD increases and VSS decreases were found at 60 h of micro-aeration, but the above parameters did not vary significantly with respect to the values found at 48 h.