Key factors affecting on bio-hydrogen production from co-digestion of organic fraction of municipal solid waste and kitchen wastewater

Sustainable management of food waste; pre-treatment strategies, techno-economic assessment, bibliometric analysis, and potential utilizations: A systematic review

Food waste (FW) contains many nutritional components such as proteins, lipids, fats, polysaccharides, carbohydrates, and metal ions, which can be reused in some processes to produce value-added products. Furthermore, FW can be converted into biogas, biohydrogen, and biodiesel, and this type of green energy can be used as an alternative to nonrenewable fuel and reduce reliance on fossil fuel sources. It has been demonstrated in many reports that at the laboratory scale production of biochemicals using FW is as good as pure carbon sources. The goal of this paper is to review approaches used globally to promote turning FW into useable products and green energy. In this context, the present review article highlights deeply in a transdisciplinary manner the sources, types, impacts, characteristics, pre-treatment strategies, and potential management of FW into value-added products. We find that FW could be upcycled into different valuable products such as eco-friendly green fuels, organic acids, bioplastics, enzymes, fertilizers, char, and single-cell protein, after the suitable pre-treatment method. The results confirmed the technical feasibility of all the reviewed transformation processes of FW. Furthermore, life cycle and techno-economic assessment studies regarding the socio-economic, environmental, and engineering aspects of FW management are discussed. The reviewed articles showed that energy recovery from FW in various forms is economically feasible.

Electron donor addition for stimulating the microbial degradation of 1,4 dioxane by sequential batch membrane bioreactor: A techno-economic approach

The presence of 1,4 dioxane in wastewater is associated with severe health and environmental issues. The removal of this toxic contaminant from the industrial effluents prior to final disposal is necessary. The study comprehensively evaluates the performance of sequential batch membrane bioreactor (MBR) for treating wastewater laden with 1,4 dioxane. Acetate was supplemented to the wastewater feed as an electron donor for enhancing and stimulating the microbial growing activities towards the degradation of 1,4 dioxane. The removal efficiency of 1,4 dioxane was maximized to 87.5 ± 6.8% using an acetate to dioxane (A/D) ratio of 4.0, which was substantially dropped to 31.06 ± 3.7% without acetate addition. Ethylene glycol, glyoxylic acid, glycolic acid, and oxalic acid were the main metabolites of 1,4 dioxane biodegradation using mixed culture bacteria. The 1,4 dioxane degrading bacteria, particularly the genus of Acinetobacter, were promoted to 92% at the A/D ratio of 4.0. This condition encouraged as well the increase of the main 1,4 dioxane degraders, i.e., Xanthomonadales (12.5%) and Pseudomonadales (9.1%). However, 50% of the Sphingobacteriales and 82.5% of Planctomycetes were reduced due to the inhibition effect of the 1,4 dioxane contaminate. Similarly, the relative abundance of Firmicutes, Verrucomicrobia, Chlamydiae, Actinobacteria, Chloroflexi, and Nitrospirae was reduced in the MBR at the A/D ratio of 4.0. The results derived from the microbial analysis and metabolites detection at different A/D ratios indicated that acetate supplementation (as an electron donor) maintained an essential role in encouraging the microorganisms to produce the monooxygenase enzymes responsible for the biodegradation process. Economic feasibility of such a MBR system showed that for a designed flow rate of 30 m³∙d^-1, the payback period from reusing the treated wastewater would reach 6.6 yr. The results strongly recommend the utilization of mixed culture bacteria growing on acetate for removing 1,4 dioxane from the wastewater industry, achieving dual environmental and economic benefits.

A comprehensive review on current status and future perspectives of microbial volatile fatty acids production as platform chemicals

Volatile fatty acids (VFA), the secondary metabolite of microbial fermentation, are used in a wide range of industries for production of commercially valuable chemicals. In this review, the fermentative production of VFAs by both pure as well mixed microbial cultures is highlighted along with the strategies for enhancing the VFA production through innovations in existing approaches. Role of conventionally applied tools for the optimization of operational parameters such as pH, temperature, retention time, organic loading rate, and headspace pressure has been discussed. Furthermore, a comparative assessment of above strategies on VFA production has been done with alternate developments such as co-fermentation, substrate pre-treatment, and in situ removal from fermented broth. The review also highlights the applications of different bioreactor geometries in the optimum production of VFAs and how metagenomic tools could provide a detailed insight into the microbial communities and their functional attributes that could be subjected to metabolic engineering for the efficient production of VFAs.

Anaerobic co-digestion of agricultural wastes toward circular bioeconomy

A huge amount of agricultural wastes and waste activated-sludge are being generated every year around the world. Anaerobic co-digestion (AcD) has been considered as an alternative for the utilization of organic matters from such organic wastes by producing bioenergy and biochemicals to realize a circular bioeconomy. Despite recent advancement in AcD processes, the effect of feedstock compositions and operating conditions on the biomethane production processe has not been critically explored. In this paper, we have reviewed the effects of feedstock (organic wastes) characteristics, including particle size, carbon-to-nitrogen ratio, and pretreatment options, on the performance of an anaerobic digestion process. In addition, we provided an overview of the effect of key control parameters, including retention time, temperature, pH of digestate, volatile fatty acids content, total solids content, and organic loading rate. Lastly, based on the findings from the literature, we have presented several perspectives and prospects on priority research to promote AcD to a steppingstone for a circular bioeconomy.

Valorisation and emerging perspective of biomass based waste-to-energy technologies and their socio-environmental impact: A review

The economic developments around the globe resulted in the increased demand of energy, which overburdened the supply chain sources of energy. Fossil fuel reserves are exploited to meet the high demand of energy and their combustion is becoming the main source of environmental pollution. So there is dire need to find safe, renewable and sustainable energy resources. Waste to energy (WtE) may be viewed as a possible alternate source of energy, which is economically and environmentally sustainable. Municipal solid waste (MSW) is a major contributor to the development of renewable energy and sustainable environment. At present the scarcity of renewable energy resources and disposal of MSW is a challenging problem for the developing countries, which has generated a wide ranging socioeconomic and environmental problems. This situation stimulates the researchers to develop alternatives for converting WtE under a variety of scenarios. Herein, the present scenario in developing the WtE technologies such as, thermal conversion methods (Incineration, Gasification, Pyrolysis, Torrefaction), Plasma technology, Biochemical methods, Chemical and Mechanical methods, Bio-electrochemical process, Mechanical biological treatment (MBT), Photo-biological processes for efficacious energy recovery and the challenges confronted by developing and developed countries. In this review, a framework for the evaluation of WtE technologies has been presented for the ease of researchers working in the field. Furthermore, this review concluded that WtE is a potential renewable energy source that will partially satisfy the demand for energy and ensure an efficient MSW management to overcome the environmental pollution.

Effect of starvation period on microbial community producing hydrogen from paperboard mill wastewater using anaerobic baffled reactor

The aim of this study is to highlight the robustness and potentials of the anaerobic baffled reactor (ABR) configuration on keeping the microbial richness and diversity after starvation period of 7 days. The module at steady state operating conditions provided an average volumetric hydrogen production (VHP) of 0.2 ± 0.08 and 0.423 ± 0.5 l/d in the 1st and last compartment (C4). The VHP was gradually decreased from 0.2 to 0.003 l/d and from 0.423 to 0.1 l/d in compartments (C1 and C4) respectively during feed less period. However, the VHP was substantially increased up to 0.035 and 0.152 l/d in 1st (C1) and fourth compartment (C4) within 24 h, after reoperation of the ABR. Moreover, the H₂ producers of Clostridiaceae, Ruminococcaceae, and Enterobacteriaceae families were dominant in the reactor after reoperation process. Quantitative polymerase chain reaction and next-generation sequencing methods results revealed that the microbial community structure was mainly composed of Proteobacteria, Firmicutes, Chloroflexi, Bacteroidetes, Planctomycetes, and Actinobacteria. The results showed the unique properties of the ABR configuration for keeping the microbial richness and diversity during feed less period.

Fermentative H2 production from food waste: Parametric analysis of factor effects

Factorial fermentation experiments on food waste (FW) inoculated with activated sludge (AS) were conducted to investigate the effects of pH and the inoculum-to-substrate ratio (ISR [g VS_AS/g TOC_FW]) on biohydrogen production. The two parameters affected the H₂ yield, the fermentation rate and the biochemical pathways. The minimum and maximum yields were 41 L H₂/kg TOC_FW (pH = 7.5, ISR = 1.74) and 156-160 L H₂/kg TOC_FW (pH = 5.5, ISR = 0.58 and 1.74). The range of carbohydrates conversion into H₂ was 0.37-1.45 mol H₂/mol hexose, corresponding to 9.4-36.2% of the theoretical threshold. A second-order predictive model for H₂ production identified an optimum region at low pHs and high ISRs, with a theoretical maximum of 168 L H₂/kg TOC_FW at pH = 5.5 and ISR = 1.74. The Spearman's correlation method revealed several relationships between the variables, suggesting the potentially governing metabolic pathways, which turned out to involve both hydrogenogenic pathways and competing reactions.

Magnetite/graphene oxide nano-composite for enhancement of hydrogen production from gelatinaceous wastewater

The effect of substrate to inoculum (So/Xo) ratio and supplementation of magnetite/graphene oxide (MGO) nano-composite material on hydrogen production from gelatinaceous wastewater via dark fermentation process was investigated. Results demonstrated that optimum So/Xo ratio of 1.0gCOD/gVSS achieved maximal hydrogen yield (HY) of 79.2±11.9mL H2/gCOD removed. Supplementation of anaerobes with 100mg/L MGO promoted HY up to 112.4±10.5mL H2/gCOD removed. Moreover, the degradation efficiency of carbohydrates, proteins and lipids was improved to 80.8±7.6, 34.4±2.3 and 31.4±2.2%, respectively. Acetate (HAc) and butyrate (HBu) concentrations increased from 102±6.8 to 125.3±6.3 and from 31.1±1.5 to 48.8±3.5mg/gVSS, respectively. However, propionate (HPr) concentration dropped from 35.9±2.7 to 15±1.3mg/gVSS. Hydrogenase enzyme activity increased 9-folds and the anaerobes elongated from ca. 1.8-2.9 to ca. 2.5-5.1μm with MGO addition. Moreover, Proteobacteria, Firmicutes, Clostridia and Bacilli were detected with the batches supplemented with MGO.

Biomethanation of vegetable market waste in an anaerobic baffled reactor: Effect of effluent recirculation and carbon mass balance analysis

In the present study, feasibility of biomethanation of vegetable market waste in a 4-chambered anaerobic baffled reactor (ABR) was investigated at 30d hydraulic retention time and organic loading rate of 0.5gVS/L/d for one year. Indicators of process stability viz., butyrate/acetate and propionate/acetate ratios were consistent with phase separation in the different chambers, which remained unaltered even during recirculation of effluent. Chemical oxygen demand (COD) and volatile solids (VS) removal efficiencies were observed to be consistently high (above 90%). Corresponding biogas and methane yields of 0.7-0.8L/g VS added/d and 0.42-52L/g VS added/d respectively were among the highest reported in case of AD of vegetable waste in an ABR. Process efficiency of the ABR for vegetable waste methanation, which is indicated by carbon recovery factor showed that, nearly 96.7% of the input carbon considered for mass balance was accounted for in the product.

Impact of pH Management Interval on Biohydrogen Production from Organic Fraction of Municipal Solid Wastes by Mesophilic Thermophilic Anaerobic Codigestion

The biohydrogen productions from the organic fraction of municipal solid wastes (OFMSW) were studied under pH management intervals of 12 h (PM12) and 24 h (PM24) for temperature of 37 ± 0.1°C and 55 ± 0.1°C. The OFMSW or food waste (FW) along with its two components, noodle waste (NW) and rice waste (RW), was codigested with sludge to estimate the potential of biohydrogen production. The biohydrogen production was higher in all reactors under PM12 as compared to PM24. The drop in pH from 7 to 5.3 was observed to be appropriate for biohydrogen production via mesophilic codigestion of noodle waste with the highest biohydrogen yield of 145.93 mL/g COD_removed under PM12. When the temperature was increased from 37°C to 55°C and pH management interval was reduced from 24 h to 12 h, the biohydrogen yields were also changed from 39.21 mL/g COD_removed to 89.67 mL/g COD_removed, 91.77 mL/g COD_removed to 145.93 mL/g COD_removed, and 15.36 mL/g COD_removed to 117.62 mL/g COD_removed for FW, NW, and RW, respectively. The drop in pH and VFA production was better controlled under PM12 as compared to PM24. Overall, PM12 was found to be an effective mean for biohydrogen production through anaerobic digestion of food waste.

Dry anaerobic co-digestion of organic fraction of municipal waste with paperboard mill sludge and gelatin solid waste for enhancement of hydrogen production

The aim of this study is to investigate the bio-H2 production via dry anaerobic co-fermentation of organic fraction of municipal solid waste (OFMSW) with protein and calcium-rich substrates such as gelatin solid waste (GSW) and paperboard mill sludge (PMS). Co-fermentation of OFMSW/GSW/PMS significantly enhanced the H2 production (HP) and H2 yield (HY). The maximum HP of 1082.5±91.4 mL and HY of 144.9±9.8 mL/gVSremoved were achieved at a volumetric ratio of 70% OFMSW:20% GSW:10% PMS. COD, carbohydrate, protein and lipids conversion efficiencies were 60.9±4.4%, 71.4±3.5%, 22.6±2.3% and 20.5±1.8% respectively. Co-fermentation process reduced the particle size distribution which is favorably utilized by hydrogen producing bacteria. The mean particle size diameters for feedstock and the digestate were 939.3 and 115.2μm, respectively with reduction value of 8.15-fold in the mixtures. The volumetric H2 production increased from 4.5±0.3 to 7.2±0.6 L(H2)/L(substrate) at increasing Ca(+2) concentrations from 1.8±0.1 to 6.3±0.5 g/L respectively.