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

Utilization of food waste for hydrogen-based power generation: Evidence from four cities in Ghana

Hydrogen gas will be an essential energy carrier for global energy systems in the future. However, non-renewable sources account for 96% of the production. Food wastes have high hydrogen generation potential, which can positively influence global production and reduce greenhouse gas (GHG) emissions. The study evaluates the potential of food waste hydrogen-based power generation through biogas steam reforming and its environmental and economic impact in major Ghanaian cities. The results highlight that the annual hydrogen generation in Kumasi had the highest share of 40.73 kt, followed by Accra with 31.62 kt, while the least potential was in Tamale (3.41 kt). About 2073.38 kt was generated in all the major cities. Hydrogen output is predicted to increase from 54.61 kt in 2007 to 119.80 kt by 2030. Kumasi produced 977.54 kt of hydrogen throughout the 24-year period, followed by Accra with 759.76 kt, Secondi-Takoradi with 255.23 kt, and Tamale with 81.85 kt. According to the current study, Kumasi had the largest percentage contribution of hydrogen (47.15%), followed by Accra (36.60%), Secondi-Takoradi (12.31%), and Tamale (3.95%). The annual power generation potential in Kumasi and Accra was 73.24 GWh and 56.85 GWh. Kumasi and Accra could offset 8.19% and 6.36% of Ghana's electricity consumption. The total electricity potential of 3728.35 GWh could displace 17.37% of Ghana's power consumption. This electricity generated had a fossil diesel displacement capacity of 1125.90 ML and could reduce GHG emissions by 3060.20 kt CO2 eq. Based on the findings, the total GHG savings could offset 8.13% of Ghana's carbon emissions. The cost of power generation from hydrogen is $ 0.074/kWh with an annual positive net present value of $ 658.80 million and a benefit-to-cost ratio of 3.43. The study lays the foundation and opens policy windows for sustainable hydrogen power generation in Ghana and other African countries.

Valorization of food waste by anaerobic digestion: A bibliometric and systematic review focusing on optimization

As food waste gets acknowledged as a global potential source of biomass, its valorization through anaerobic digestion becomes an attractive strategy. This work describes the state-of-the-art on the valorization of food waste by anaerobic digestion and the optimization of the process. The methodology used was a bibliometric and systematic review of the optimization of the process from 66 articles selected. Bibliometric mapping allowed us to identify that, until now, most studies have been focused on the: i) anaerobic co-digestion strategy in order to stabilize the process, ii) interest in the generation of biofuels to replace non-renewable fuels, iii) study of metabolic processes for a better understanding of the system iv) reactor design optimization and others facilities to increase process efficiency. The systematic analysis showed that the operational parameters has been extensively studied to optimize the process. Therefore, co-digestion has been the main strategy to improve the process. In this sense, knowledge of the substrate and co-substrate is extremely important to operate the reactors. For methane production, the ideal operating conditions indicated were: pH of 7, solids content between 4.0 and 15%, C/N ratio of 25, hydraulic retention time from 25 to 40 days and alkalinity from 2850 to 2970.5mgCaCO₃/L. In addition, the ideal OLR will vary mainly according to operating temperature, number of reactor stages, and raw material characteristics. This review indicates trends and knowledge gaps that are important to guide new research on the anaerobic digestion of food waste, pointing out the potential advantages, optimization strategies, by-products of interest and challenges of the process. The results were used for the development of references of ideal operating conditions for energy production, being able to guide the design and operation of reactors.

Sustainable microalgal biomass valorization to bioenergy: Key challenges and future perspectives

The global trend is shifting toward circular economy systems. It is a sustainable environmental approach that sustains economic growth from the use of resources while minimizing environmental impacts. The multiple industrial use of microalgal biomass has received great attention due to its high content of essential nutrients and elements. Nevertheless, low biomass productivity, unbalanced carbon to nitrogen (C/N) ratio, resistant cellular constituents, and the high cost of microalgal harvesting represent the major obstacles for valorization of algal biomass. In recent years, microalgae biomass has been a candidate as a potential feedstock for different bioenergy generation processes with simultaneous treating wastewater and CO₂ capture. An overview of the appealing features and needed advancements is urgently essential for microalgae-derived bioenergy generation. The present review provides a timely outlook and evaluation of biomethane production from microalgal biomass and related challenges. Moreover, the biogas recovery potential from microalgal biomass through different pretreatments and synergistic anaerobic co-digestion (AcoD) with other biowastes are evaluated. In addition, the removal of micropollutants and heavy metals by microalgal cells via adsorption and bioaccumulation in their biomass is discussed. Herein, a comprehensive review is presented about a successive high-throughput for anaerobic digestion (AD) of the microalgal biomass in order to achieve for sustainable energy source. Lastly, the valorization of the digestate from AD of microalgae for agricultural reuse is highlighted.

Strengthen "the sustainable farm" concept via efficacious conversion of farm wastes into methane

With escalating global demand for renewable energy, exploitation of farm wastes (i.e., agriculture straw wastes (ASWs), livestock wastewater (LW) and sewage sludge (SS)) has been considered to attain maximum methane yield (MY) via anaerobic digestion (AD). Results pointed that mixture of SS and LW as anaerobes' source with 20 g of ASWs/300 mL of working volume achieved maximum MY and volatile solid (VS) removal efficiency of 0.44 (±0.05) L/gVS and 51.4 (±4.1)%, respectively. This was mainly because of emerging heavy duty bacterial species (i.e., Syntrophorhabdaceae and Synergistaceae) and archaeal community (i.e, Methanosarcina and Methanoculleus) after 70 days of anaerobic incubation. This was acquired along with boosting enzymatic activity, especially xylanase, cellulase and protease up to 71.5(±7.9), 179.3(±14.3) and 207.2(±16.2) U/100 mL, respectively. Furthermore, the digestate contained high concentrations of NH₄⁺ (960.1±(76.8) mg/L), phosphorus (126.3±(10.1) mg/L) and trace metals, making it a good candidate as organic fertilizer.

Recent Approaches for the Production of High Value-Added Biofuels from Gelatinous Wastewater

Gelatin production is the most industry polluting process where huge amounts of raw organic materials and chemicals (HCl, NaOH, Ca2+) are utilized in the manufacturing accompanied by voluminous quantities of end-pipe effluent. The gelatinous wastewater (GWW) contains a large fraction of protein and lipids with biodegradability (BOD/COD ratio) exceeding 0.6. Thus, it represents a promising low-cost substrate for the generation of biofuels, i.e., H2 and CH4, by the anaerobic digestion process. This review comprehensively describes the anaerobic technologies employed for simultaneous treatment and energy recovery from GWW. The emphasis was afforded on factors affecting the biofuels productivity from anaerobic digestion of GWW, i.e., protein concentration, organic loading rate (OLR), hydraulic retention time (HRT), the substrate to inoculum (S0/X0) ratio, type of mixed culture anaerobes, carbohydrates concentration, volatile fatty acids (VFAs), ammonia and alkalinity/VFA ratio, and reactor configurations. Economic values and future perspectives that require more attention are also outlined to facilitate further advancement and achieve practicality in this domain.

Advances towards understanding long chain fatty acids-induced inhibition and overcoming strategies for efficient anaerobic digestion process

The inhibition of the anaerobic digestion (AD) process, caused by long chain fatty acids (LCFAs), has been considered as an important issue in the wastewater treatment sector. Proper understanding of mechanisms behind the inhibition is a must for further improvements of the AD process in the presence of LCFAs. Through analyzing recent literature, this review extensively describes the mechanism of LCFAs degradation, during AD. Further, a particular focus was directed to the key parameters which could affect such process. Besides, this review highlights the recent research efforts in mitigating LCFAs-caused inhibition, through the addition of commonly used additives such as cations and natural adsorbents. Specifically, additives such as bentonite, cation-based adsorbents, as well as zeolite and other natural adsorbents for alleviating the LCFAs-induced inhibition are discussed in detail. Further, panoramic evaluations for characteristics, various mechanisms of reaction, merits, limits, recommended doses, and preferred conditions for each of the different additives are provided. Moreover, the potential for increasing the methane production via pretreatment using those additives are discussed. Finally, we provide future horizons for the alternative materials that can be utilized, more efficiently, for both mitigating LCFAs-based inhibition and boosting methane potential in the subsequent digestion of LCFA-related wastes.

Application of magnetic multi-wall carbon nanotube composite into fermentative treatment process of ultrasonicated waste activated sludge

This study investigated the effect of supplementing nano-sized magnetite (Fe3O4 NPs), multi-wall carbon nanotubes (MWCNTs) and Fe3O4-MWCNTs composite on bioconversion of waste activated sludge to hydrogen, in batch systems. Substrate degradation efficiency (SDE) increased from 28 ± 3.8 (control) to 49 ± 5.9, 46 ± 4.8 and 52 ± 6.3% at optimal doses of 200 (Fe3O4 NPs), 300 (MWCNTs) and 200 mg/L (Fe3O4-MWCNTs), respectively. Based on dissolved iron and sludge conductivity measurements, superior SDE in Fe3O4 and MWCNTs batches have been assigned to enhanced dissimilatory iron reduction (DIR) and high sludge conductivity, respectively. Combined impacts for sludge conductivity and DIR were revealed in Fe3O4-MWCNTs system. In 200 mg/L (Fe3O4-MWCNTs) batch, catalytic activities of hydrogenase, protease and α-amylase peaked to 596, 146 and 131% (relative to control), respectively; as well as, highest volumetric H2 production of 607 ± 59 mL/L was acquired. Performance deteriorations at high concentrations of nanoparticles were caused by cellular oxidative stress induced by generated reactive oxygen species.

Paperboard mill wastewater treatment via combined dark and LED-mediated fermentation in the absence of external chemical addition

Paperboard mill wastewater (PMWW) was treated using two subsequent dark and photo up-flow intermitted stirring tank reactors (UISTRs) under different hydraulic retention times (HRTs) without external chemical use. HRT of 12 h revealed the maximum overall H₂ productivity of 1394.1(±70.6) mL/L/d with contents of 48.9(±2.5) and 47.4(±1.4)% for dark- and photo-processes, respectively. Overall substrate removal efficiency (SDE) of 58.9(±4.5)% was registered at HRT o 12 h. High H₂ productivity was ascribed to fermentation type occurred at dark reactor, since acetate and butyrate accounted for 70.9% of volatile fatty acids. Besides, pH and carbon to nitrogen ratio of dark reactor's effluent at HRT = 12 h were 5.5(±0.1) and 30.0(±2.5), respectively which are the optimum levels for photo fermentation process. Moreover, energetic and economic analyses emphasized on the superiority of 12 h-HRT, where net gain energy, daily saving and payback period accounted for 1319.5 kWh/d, 148.7 $/d and 9.8 years, respectively.

Nutrients balance for hydrogen potential upgrading from fruit and vegetable peels via fermentation process

The sole, dual and multi-fermentations of fruit and vegetable peels (FVPs) were investigated in order to balance nutrition hierarchy for maximizing hydrogen potential via Batch experiments. The highest volumetric hydrogen production of 2.55 ± 0.07 L/L and hydrogen content of 64.7 ± 3.7% were registered for multi-fermentation of M-PTBO (25% pea +25% tomato + 25% banana +25% orange). These values outperformed sole and dual fermentation. The multi-fermentation of FVPs provided sufficient nutrients and trace elements for anaerobes, where C/N and C/P ratios were at levels of 24.7 ± 0.2 and 113.2 ± 9.4, respectively. In specific, harmonizing of macro and micro-nutrients remarkably maximized activities of amylase, protease and lipase to 4.23 ± 0.42, 0.035 ± 0.002 and 0.31 ± 0.02 U/mL, respectively, as well as, substantially incremented counts of Clostridium and Enterobacter sp. up to 5.81 ± 0.23 × 10⁵ and 2.17 ± 0.09 × 10⁶ cfu/mL, respectively. Furthermore, multi-fermentation of M-PTBO achieved the maximum net energy gain and profit of 1.82 kJ/g_feedstock and 4.11 $/kg_feedstock, respectively. Nutrients balance significantly develops bacterial activity in terms of hydrogen productivity, anaerobes reproduction, enzyme activities and soluble metabolites. As a result, overall fermentation bioprocess performance was improved.

Investigation on hydrogen production from paper sludge without inoculation and its enhancement by Clostridium thermocellum

The feasibility and performance of hydrogen production from paper sludge without inoculation was investigated under thermophilic conditions. The maximum hydrogen production reached 64.32 mM with 7.4% PS. The dynamic changes in bacterial community structures during hydrogen production were investigated by analyzing 16S rDNA gene sequences using high throughput sequencing technology. The results showed that microbial community was dominated by order Clostridiales and Thermoanaerobacterales. Genus Thermoanaerobacterium and Ruminiclostridium played a leading role in the fermentation process, which was responsible for the hydrolysis of PS and hydrogen production. Effect of inoculation with Clostridium thermocellum on hydrogen production from PS was also studied. The results showed that C. thermocellum supplement significantly increased hydrogen yield and holocellulose degradation rate by 96.80% and 32.95%, respectively. In addition, inoculation of C. thermocellum enhanced VFA generation and shortened the lag phase of hydrogen production. The present study lays the foundation on the valorization of waste lignocellulose.

Co-fermentation of sewage sludge with ryegrass for enhancing hydrogen production: Performance evaluation and kinetic analysis

The low C/N ratio and low carbohydrate content of sewage sludge limit its application for fermentative hydrogen production. In this study, perennial ryegrass was added as the co-substrate into sludge hydrogen fermentation with different mixing ratios for enhancing hydrogen production. The results showed that the highest hydrogen yield of 60mL/g-volatile solids (VS)_added was achieved when sludge/perennial ryegrass ratio was 30:70, which was 5 times higher than that from sole sludge. The highest VS removal of 21.8% was also achieved when sludge/perennial ryegrass ratio was 30:70, whereas VS removal from sole sludge was only 0.7%. Meanwhile, the co-fermentation system simultaneously improved hydrogen production efficiency and organics utilization of ryegrass. Kinetic analysis showed that the Cone model fitted hydrogen evolution better than the modified Gompertz model. Furthermore, hydrogen yield and VS removal increased with the increase of dehydrogenase activity.

Biological H2 potential harvested from complex gelatinaceous wastewater via attached versus suspended growth culture anaerobes

The effect of cultural growth treating gelatinaceous wastewater on hydrogen fermentative was assessed using up-flow multi-stage anaerobic sponge reactor (UMASR) and anaerobic sequencing batch reactor (AnSBR). Both reactors were operated at five hydraulic retention times (HRTs). UMASR achieved the maximum COD removal efficiency of 60.2±4.4% at HRT of 48h. Moreover, UMASR exhibited superiority in the course of carbohydrates and proteins removal efficiencies' of 100 and 52.5±2.4% due to high amylase and protease activities' of 4.1±0.3 and 0.032±0.002U, respectively. Contrariwise, AnSBR assigned for the peak hydrogen production rate of 1.17±0.14L/L/day at HRT of 24-h. Lipase activity was quite high (0.307±0.023U) in AnSBR resulting in removal efficiency of 35.2±2.1% for lipids. Stover-Kincannon model emphasized that UMASR required lesser volume than AnSBR to sustain the same substrate degradation efficacy. Nevertheless, the net gain energy harvested from AnSBR surpassed UMASR by 4.0-folds at HRT of 24-h.

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.