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This study presents the effect of bioaugmentation of thermophilic anaerobic digestion of food waste with Methanosarcina thermophila grown on a wood-derived biochar. Two different supplementation regimes were tested, namely a single bioaugmentation (SBABC) in which 10% v/v of the microbes grown on biochar (1 g/L) is added at setup of the reactors, versus a routine bioaugmentation (RBABC) wherein the same amount of supplements were added over 10 feeding cycles. The optimally performing 'R' and 'S' reactors had increased methane yields by 37% and 32% over their respective controls while reactors SBABC 2 and 3 produced 21.89% and 56.09% higher average methane yield than RBABC 2 and 3, respectively. It appears that a single dose bioaugmentation is advantageous for improving AD as analysed in terms of average methane yield and VFA production. This study provides the basis for understanding how biochar and bioaugmentation can be used for engineering sustainable pilot-scale AD processes.

The concentric-tube internal loop airlift reactor is a typical reactor configuration which has been adopted for a myriad of chemical and biological processes. The reactor hydrodynamics (including mixing) and the mass transfer between the gas and liquid phases remarkably affect the operational conditions and thus are crucial to the overall reactor performance. Hence, this study aims at providing a thorough description of the basic concepts and a comprehensive review of the relevant reported studies on the hydrodynamics and mass transfer of the concentric-tube internal loop airlift reactors, taking microalgae cultivation as an exemplary application. In particular, the reactor characteristics, geometry, CFD modeling, experimental characterization, and scale up considerations are elucidated. The research gaps for future research and development are also identified.

Both biochar supplementation as well as bioaugmentation have been shown in literature to improve the methane yield of anaerobic digestion. In this study, the combination of both are evaluated by growing Methanosarcina thermophila on biochar support particles prior to augmentation of thermophilic food waste anaerobic digestion. Biochar stand alone, bioaugmentation solely, a combination of both added separately or grown together, and utilizing polypropylene (PP) microplastics as growth support instead were all tested when starting up a thermophilic process from mesophilic inoculum. Methanosarcina thermophila and biochar supplementation displayed synergy, with 5% M. thermophila on 1 g/L biochar presenting a 32% increase in specific methane yield over the control. Double the bioaugmentation dosage/concentration was also trialled with a thermophilic inoculum, and 10% M. thermophila grown on 2 g/L biochar displayed the best results with a 20% increase specific methane yield from its control standard.

Nano-biochar application was investigated for anaerobic digestion of orange peel waste. The application for methane production focused on the optimization of biochar feedstock, rescue of failed digesters, and microbial succession analysis. It showed that sewage sludge (SS) derived biochar had the highest performance enhancement among the different feedstocks, which could be ascribed to the improvement of electron transfer, interspecies hydrogen transfer, and supply of trace elements. Subsequently, nano SS biochar-amended digestate was evaluated for rescuing failed digesters, and the experimental results indicated its positive roles through gradual bioaugmentation operation. The dynamic analysis of microbial succession indicated the successful application was through the mechanism of restoring partially the functional microbial communities. The major reconstruction of functional microorganisms included bacteria phyla Hydrogenispora (24.5%) and Defluviitoga (18.8%) as well as methanogenic genera of Methanosarcina (41.5%) and Methanobacterium (27.3%). These findings would contribute to rescuing failed anaerobic digesters by bioaugmentation with biochar-amended digestate.

A wood waste-derived biochar was applied to food-waste anaerobic digestion to evaluate the feasibility of its utilisation to create a circular economy. This biochar was first purposed for the upgrading of the biogas from the said anaerobic digestion, before treating and recovering the nutrients in the solid fraction of the digestate, which was finally employed as a biofertilizer for the organic cultivation of three green leafy vegetables: kale, lettuce and rocket salad. Whilst the amount of CO2 the biochar could absorb from the biogas was low (11.17 mg g−1), it could potentially be increased by modifying through physical and chemical methods. Virgin as well as CO2-laden biochar were able to remove around 31% of chemical oxygen demand, 8% of the ammonia and almost 90% of the total suspended solids from the digestate wastewater, which was better than a dewatering process via centrifugation but worse than the industry standard of a polytetrafluoroethylene membrane bioreactor. Nutrients were recovered in the solid fraction of the digestate residue filtered by the biochar, and utilised as a biofertilizer that performed similarly to a commercial complete fertilizer in terms of aerial fresh weight growth for all three vegetables cultivated. Contingent on the optimal upgrading of biogas, the concept of a circular economy based on biochar and anaerobic digestion appears to be feasible.

This review is focused on the sustainable management of harvested water hyacinth (WH) via thermochemical conversion to carbonaceous materials (CMs), biofuels, and chemicals for energy and environmental applications. One of the major challenges in thermochemical conversion is to guarantee the phytoremediation performance of biochar and the energy conversion efficiency in biowaste-to-energy processes. Thus, a circular sustainable approach is proposed to improve the biochar and energy production. The co-conversion process can enhance the syngas, heat, and energy productions with high-quality products. The produced biochar should be economically feasible and comparable to available commercial carbon products. The removal and control of heavy and transition metals are essential for the safe implementation and management of WH biochar. CMs derived from biochar are of interest in wastewater treatment, air purification, and construction. It is important to control the size, shape, and chemical compositions of the CM particles for higher-value products like catalyst, adsorbent or conductor.

In this study, the looping materials of Fe

This review lays great emphasis on production and characteristics of biochar through gasification. Specifically, the physicochemical properties and yield of biochar through the diverse gasification conditions associated with various types of biomass were extensively evaluated. In addition, potential application scenarios of biochar through gasification were explored and their environmental implications were discussed. To qualitatively evaluate biochar sustainability through the gasification process, all gasification products (i.e., syngas and biochar) were evaluated via life cycle assessment (LCA). A concept of balancing syngas and biochar production for an economically and environmentally feasible gasification system was proposed and relevant challenges and solutions were suggested in this review.

The impact of algal biochar addition on mesophilic and thermophilic anaerobic co-digestion of algal biomass and food waste was investigated with a focus on semi-continuous operations and functional microbial communities. Under batch co-digestion, the highest co-digestion synergy was observed for a mixture of 25% food waste and 75% algal biomass. During semi-continuous co-digestion of 25% food waste-75% algal biomass mixture, biochar amended digesters exhibited a 12–54% increase in average methane yield (275.8–394.6 mL/gVS) compared to the controls. Elevated temperature induced narrow distributions of volatile fatty acids (VFAs) by inhibiting the production of branched VFAs. Genus Proteiniphilum was selectively enriched by 3.2 folds in mesophilic digesters with biochar amendment while genus Defluviitoga was selectively enriched in thermophilic digesters due to elevated temperature. Methanogenic communities were significantly different in mesophilic and thermophilic digesters. Biochar amendment contributed to shifts in the predominant methanogens leading to a more balanced state of two methanogenic pathways.

A food waste treating system was proposed in this study by combining biochar-assisted high-solid anaerobic digestion and subsequent steam gasification of the digestate. The effect of solid level, biochar dosage in anaerobic digestion on the properties of biogas, syngas, and final biochar products were investigated. Results showed that at a high total solid level and biochar dosage of 25 g/L and 50 g/L, the accumulative methane yield reached 110.3 mL CH4/g VS and 126.7 mL CH4/g VS, respectively. From steam gasification of different digestates under 850 °C for 15 min, a maximum of 34.92 mmol/g for the hydrogen yield and 11.44 MJ/m3 for the higher heating value could be obtained for the syngas. Furthermore, the by-product produced from steam gasification was a nutrient-enriched porous biochar, which was suitable to be used as compost. This study demonstrated a pathway for food waste treating to produce methane-enriched biogas, hydrogen-enriched syngas, and nutrient-enriched biochar.

In this study, the looping materials of Fe2O3, CaO, mechanically mixed CaO and Fe2O3, and chemically synthesized Ca2Fe2O5 were tested for comparison of the performance and gas evolution processes. The reaction mechanism was illustrated to have an insight into the Fe2O3/CaO-based chemical looping process. Results found that the reduction from Fe2O3 to Fe3O4 trended to form CO2 while the transition of Fe3O4 to Fe happened after 650 °C was most likely to release CO. CO2 adsorption by CaO during 400–600 °C and further desorbed at higher temperature for CO2 Boudouard reaction which enhanced the biomass conversion. Mechanically mixed CaO and Fe2O3 maintained the properties of CaO and Fe2O3 with CO2 transfer and oxygen releasing during chemical looping reaction process, while the synthesized Ca2Fe2O5 presented hard reducibility which prefer to generate CO with the highest concentration (34.96 vol%) during chemical looping process at 850 °C.

In this study, horticultural waste (HW) and sewage sludge (SS) with different mass ratios were co-gasified with steam at different temperatures to investigate the product distribution, gas synergistic interaction, and optimal design for gas products from co-gasification process. Results showed that with the increase of SS ratio in blends, the H2 content was increased and the syngas yield was decreased. The synergistic interaction was more significant at higher temperature which promoted the H2 production probably due to the reduction and steam oxidation of Fe species in SS during co-gasification process. The optimized highest effective gas content (82.92 vol%) was achieved with the highest HHV (11.40 MJ/m3) at the conditions of SS ratio = 0.80 and temperature of 900 °C. It indicates that steam co-gasification of HW and SS is a promising technology to produce desired syngas towards a clean and efficient waste management process.

In this work, activated carbon (AC) as an effective and low-cost adsorbent was successfully prepared from carbon residue (or char, one of the by-products from woody biomass gasification) via physical activation. The surface area of char was significantly increased from 172.24 to 776.46m(2)/g after steam activation at 900°C. The obtained activated carbons were then employed for the adsorption of dye (Rhodamine B) and it was found that activated carbon obtained from steam activation exhibited the highest adsorption capability, which is mainly attributed to the higher surface area and the abundance of hydroxyl (-OH) and carboxyl (-COOH) groups on the activated carbon surface. Moreover, it was also found that the adsorption capability significantly increased under the basic condition, which can be attributed to the increased electrostatic interaction between the deprotonated (negatively charged) activated carbon and dye molecules. Furthermore, the equilibrium data were fitted into different adsorption isotherms and found to fit well with Langmuir model (indicating that dye molecules form monolayer coverage on activated carbon) with a maximum monolayer adsorption capability of 189.83mg/g, whereas the adsorption kinetics followed the pseudo-second-order kinetics.

Lignocellulosic biomass waste, a heterogeneous complex of biodegradables and non-biodegradables, accounts for large proportion of municipal solid waste. Due to limitation of single-stage treatment, a two-stage hybrid AD-gasification system was proposed in this work, in which AD acted as pre-treatment to convert biodegradables into biogas followed by gasification converting solid residue into syngas. Energy performance of single and two-stage systems treating 3 typical lignocellulosic wastes was studied using both experimental and numerical methods. In comparison with conventional single-stage gasification treatment, this hybrid system could significantly improve the quality of produced gas for all selected biomass wastes and show its potential in enhancing total gas energy production by a maximum value of 27% for brewer's spent grain treatment at an organic loading rate (OLR) of 3gVS/L/day. The maximum overall efficiency of the hybrid system for horticultural waste treatment was 75.2% at OLR of 11.3gVS/L/day, 5.5% higher than conventional single-stage system.

The compositions of food wastes and their co-gasification producer gas were compared with the existing data of sewage sludge. Results showed that food wastes are more favorable than sewage sludge for co-gasification based on residue generation and energy output. Two decentralized gasification-based schemes were proposed to dispose of the sewage sludge and food wastes in Singapore. Monte Carlo simulation-based cost-benefit analysis was conducted to compare the proposed schemes with the existing incineration-based scheme. It was found that the gasification-based schemes are financially superior to the incineration-based scheme based on the data of net present value (NPV), benefit-cost ratio (BCR), and internal rate of return (IRR). Sensitivity analysis was conducted to suggest effective measures to improve the economics of the schemes.