Enhanced energy recovery from cassava ethanol wastewater through sequential dark hydrogen, photo hydrogen and methane fermentation combined with ammonium removal

Effects of food wastes based on different components on digestibility and energy recovery in hydrogen and methane co-production

This study was conducted for four organic fractions (carbohydrates, proteins, cellulose, lipids) at an inoculum concentration of 30 % and a total solid (TS) of 8 % to investigate the effect of the main components of food waste on the performance of the two-stage anaerobic digestion. The results showed that the gas phase products were closely related to the composition of the substrate, with the carbohydrate and lipid groups showing the best hydrogen (154.91 ± 2.39mL/gVS) and methane (381.83 ± 12.691mL/gVS) production performance, respectively. However, the increased protein content predisposes the system to inhibition of gas production, which is mutually supported by changes in the activity of dehydrogenase and coenzyme F420. Butyric acid (53.19 %) dominated the liquid phase products in both stages, indicating that all four organic fractions were butyric acid-based fermentation and that the final soluble chemical oxygen demand degradation reached 72.97 %-82.86 %. The carbohydrate and cellulose groups achieved the best energy recovery performance, with conversion rates exceeding 65 %. The above results can provide a useful reference for the resource utilization of food waste.

Performance of an Innovative Low-Cost Recycled Filling (LCRF) in Anaerobic Treatment of Dairy Effluent-A Pilot-Scale Study

The rapid growth in dairy production leads to increasing outputs of high-load effluent, necessitating new methods of treating such waste. Anaerobic processes have been increasingly popular but are hamstrung by limited nutrient removal efficiency. The aim of the present study was to investigate whether low-cost recycled filling (LCRF) improves the anaerobic treatment of dairy effluent. The addition of LCRF was found to increase both COD removal (86.1 ± 2.6%-92.8 ± 1.6%) and P_tot. removal (22.1 ± 3.5% to 36.9 ± 4.6%) from the wastewater. The LCRF ensured near-neutral pH and stabilized the structure of the anaerobic microbe community (including Archaea) across all pollutant loads tested. This translated to efficient biogas production and high methane content in the LCRF reactors, peaking at 0.35 ± 0.01 m³/kg COD_removed and 68.2 ± 0.6% (respectively) in the best-performing variant.

Continuous dark and photo biohydrogen production in a baffled bioreactor and electrons distribution analysis

This work studied the sequential hydrogen production by dark and photo-fermentation (HPDPF) in continuous baffled bioreactors. Taken enzymatic hydrolysate of corn stover as initial carbon source, the influence of hydraulic retention time (HRT) of dark fermentation (DF) and the dilution ratio (DR) of dark fermentation effluents (DFEs) on the hydrogen production performance of the combined fermentation system and electron distribution were investigated. For DF unit, the highest hydrogen production rate (HPR) of 5.24 L/(L·d) was detected at HRT of 18 h, however, the maximum HPR of 4.60 L/(L·d) was obtained from DFEs with HRT of 12 h and DR of 1:0.5 during photo fermentation unit, meanwhile, the electrons in substrate partitioning to H₂ reached the maximum value of 35.69%. In terms of hydrogen yield, the optimum operating conditions of the combined system were HRT of 12 h (DF) and DR of 1:0.5(DFEs), in which the hydrogen yield reached 12.73 L/d.

Fermentative molecular biohydrogen production from cheese whey: present prospects and future strategy

Waste-dependent fermentative routes for biohydrogen production present a possible scenario to produce hydrogen gas on a large scale in a sustainable way. Cheese whey contains a high portion of organic carbohydrate and other organic acids, which makes it a feasible substrate for biohydrogen production. In the present review, recent research progress related to fermentative technologies, which explore the potentiality of cheese whey for biohydrogen production as an effective tool on a large scale, has been analyzed systematically. In addition, application of multiple response surface methodology tools such as full factorial design, Box-Behnken model, and central composite design during fermentative biohydrogen production to study the interactive effects of different bioprocess variables for higher biohydrogen yield in batch, fed-batch, and continuous mode is also discussed. The current paper also emphasizes computational fluid dynamics-based simulation designs, by which the substrate conversion efficiency of the cheese whey-based bioprocess and temperature distribution toward the turbulent flow of reaction liquid can be enhanced. The possible future developments toward higher process efficiency are outlined.

Development of novel strategies for higher fermentative biohydrogen recovery along with novel metabolites from organic wastes: The present state of the art

Depletion of fossil fuels and environmental concern has compelled us to search for alternative fuel. Hydrogen is considered as a dream fuel as it has high energy content (142 kJ g^-1 ) and is not chemically bound to carbon. At present, fossil fuel-based methods for producing hydrogen require high-energy input, which makes the processes expensive. The major processes for biohydrogen production are biophotolysis, microbial electrolysis, dark fermentation, and photofermentation. Fermentative hydrogen production has the additional advantages of potentially using various waste streams from different industries as feedstock. Novel strategies to enhance the productivity of fermentative hydrogen production include optimization in pretreatment methods, integrated fermentation systems (sequential and combined fermentation), use of nanoparticles as additives, metabolic engineering of microorganisms, improving the light utilization efficiency, developing more efficient photobioreactors, etc. More focus has been given to produce biohydrogen in a biorefinery approach in which, along with hydrogen gas, other metabolites (ethanol, butyric acid, 1,3-propanediol, etc.) are also produced, which have direct/indirect industrial applications. In present review, various emerging technologies that highlight biohydrogen production methods as effective and sustainable methods on a large scale have been critically reviewed. The possible future developments are also outlined.

Enhanced Biogas Production of Cassava Wastewater Using Zeolite and Biochar Additives and Manure Co-Digestion

Currently, there are challenges with proper disposal of cassava processing wastewater, and a need for sustainable energy in the cassava industry. This study investigated the impact of co-digestion of cassava wastewater (CW) with livestock manure (poultry litter (PL) and dairy manure (DM)), and porous adsorbents (biochar (B-Char) and zeolite (ZEO)) on energy production and treatment efficiency. Batch anaerobic digestion experiments were conducted, with 16 treatments of CW combined with manure and/or porous adsorbents using triplicate reactors for 48 days. The results showed that CW combined with ZEO (3 g/g total solids (TS)) produced the highest cumulative CH4 (653 mL CH4/g VS), while CW:PL (1:1) produced the most CH4 on a mass basis (17.9 mL CH4/g substrate). The largest reduction in lag phase was observed in the mixture containing CW (1:1), PL (1:1), and B-Char (3 g/g TS), yielding 400 mL CH4/g volatile solids (VS) after 15 days of digestion, which was 84.8% of the total cumulative CH4 from the 48-day trial. Co-digesting CW with ZEO, B-Char, or PL provided the necessary buffer needed for digestion of CW, which improved the process stability and resulted in a significant reduction in chemical oxygen demand (COD). Co-digestion could provide a sustainable strategy for treating and valorizing CW. Scale-up calculations showed that a CW input of 1000–2000 L/d co-digested with PL (1:1) could produce 9403 m3 CH4/yr using a 50 m3 digester, equivalent to 373,327 MJ/yr or 24.9 tons of firewood/year. This system would have a profit of $5642/yr and a $47,805 net present value.

Enhanced fermentative hydrogen production from industrial wastewater using mixed culture bacteria incorporated with iron, nickel, and zinc-based nanoparticles

The present study assessed the efficiency of utilizing mixed culture bacteria (MCB) incorporated with individual nanoparticles (NPs), i.e., hematite (α-Fe₂O₃), nickel oxide (NiO), and zinc oxide (ZnO), dual NPs (α-Fe₂O₃ + NiO, α-Fe₂O₃ + ZnO, and NiO + ZnO), and multi-NPs (α-Fe₂O₃ + NiO + ZnO) for hydrogen production (HP) from industrial wastewater containing mono-ethylene glycol (MEG). When MCB was individually supplemented with α-Fe₂O₃ (200 mg/L), NiO (20 mg/L), and ZnO NPs (10 mg/L), HP improved significantly by 41, 30, and 29%, respectively. Further, key enzymes associated with MEG metabolism, such as alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH), and hydrogenase (hyd), were rapidly and substantially enhanced in the medium. NiO and ZnO NPs notably promoted ADH and ALDH activities, respectively, while α-Fe₂O₃ exhibited superior impact on hyd activity. Maximum hydrogen production rate was concomitant with higher acetic acid production and lower residual acetaldehyde and ethanol. HP using MCB supplemented with individual NiO (20 mg/L) and ZnO NPs (10 mg/L) further improved by 8.0%-14% when dual and multi-NPs were used; the highest HP was recorded when multi-NPs were used. In addition, NPs incorporation resulted in substantial increase in the relative abundance of Clostridiales (belonging to family Clostridiaceae; > 83%). Overall, this study provides significant insights into the impact of NPs on hydrogen production from MEG-contaminated wastewater.

Microbiome involved in anaerobic hydrogen producing granules: A mini review

This mini review overviewed the latest updates on the anaerobic hydrogen fermentation using the granulation technology and the microbiome involved in the process. Additionally, the implication of various reactor design and their microbial changes were compared and provided the new insights on the role of microbiomes for rapid granules formation and long term stable operation in a continuous mode operation. The information provided in this communication would help to understand the key role of microbiomes and their importance in anaerobic hydrogen producing granular systems.

Wastewater: A Potential Bioenergy Resource

Wastewaters are a rich source of nutrients for microorganisms. However, if left unattended the biodegradation may lead to severe environmental hazards. The wastewaters can thus be utilized for the production of various value added products including bioenergy (H₂ and CH₄). A number of studies have reported utilization of various wastewaters for energy production. Depending on the nature of the wastewater, different reactor configurations, wastewater and inoculum pretreatments, co-substrate utilizations along with other process parameters have been studied for efficient product formation. Only a few studies have reported sequential utilization of wastewaters for H₂ and CH₄ production despite its huge potential for complete waste degradation.

Photosynthetic hydrogen production by alginate immobilized bacterial consortium

Photosynthetic hydrogen production from organic wastewaters using immobilized mixed culture with photosynthetic bacteria (PSB) was studied. A PSB consortium was immobilized by alginate matrix to form granules. The so-yielded granules exhibited minimal diffusional resistances to substrates and to illumination penetration but still produced more hydrogen from synthetic wastewater than the free cells at identical experimental conditions. Optimal granule size, cell loadings, and cell ages for granules and the minimum substrate concentration and maximum illumination intensity requited to maximize hydrogen production were studied. The applied alginate matrix can provide shield to embedded cells from external challenges, likely the produced proton gradients from the surroundings.

Ionic-liquid pretreatment of cassava residues for the cogeneration of fermentative hydrogen and methane

An ionic liquid of N-methylmorpholine-N-oxide (NMMO) was used to effectively pretreat cassava residues for the efficient enzymatical hydrolysis and cogeneration of fermentative hydrogen and methane. The reducing sugar yield of enzymolysed cassava residues with NMMO pretreatment improved from 36 to 42g/100g cassava residues. Scanning electron microscopy images revealed the formation of deep grooves (∼4μm wide) and numerous pores in the cassava residues pretreated with NMMO. X-ray diffraction patterns showed that the crystallinity coefficient of NMMO-pretreated cassava residues decreased from 40 to 34. Fourier transform infrared spectra indicated that crystal cellulose I was partially transformed to amorphous cellulose II in the NMMO-pretreated cassava residues. This transformation resulted in a reduced crystallinity index from 0.85 to 0.77. Hydrogen yield from the enzymolysed cassava residues pretreated with NMMO increased from 92.3 to 126mL/gTVS, and the sequential methane yield correspondingly increased from 79.4 to 101.6mL/g TVS.