Developing a food waste-based volatile fatty acids platform using an immersed membrane bioreactor

Approximately 1.3 billion tons of food waste is produced globally every year. In principle, all the resources in the supply chain are lost (e.g. land, energy, and water) when the food is not consumed as intended. Anaerobic digestion is an established biological technology to treat food waste, and is mainly employed for recovery of energy in the form of biogas. Volatile fatty acids (VFAs) are formed as intermediate products of the anaerobic digestion process, and can be applied as precursors for various essential biomaterials. The manipulation of the anaerobic digestion process to synthesize these intermediates instead of biogas is considered to recover more value from food waste. However, some bottlenecks that prevent large-scale production and application of VFAs still exist. Among the key issues to be addressed are the difficulty in recovering the VFAs from the fermentation medium and the overall low product yields. The goals of the present thesis were: 1) to investigate methods to boost the production of VFAs from food waste; 2) to continuously recover VFAs from food waste fermentation medium; 3) to determine the changes in the microbial structure during high organic loading of food waste in membrane bioreactors; and 4) to study a novel approach for applying food waste-derived VFAs for cultivating edible filamentous fungi. For continuous product recovery at high yields, an immersed membrane bioreactor was constructed with robust cleaning capabilities to withstand the complex anaerobic digestion medium. The membrane bioreactor was first operated without pH control and a yield of 0.54 g VFA/g VSadded was achieved when an organic loading rate of 2 gVS/L/d was applied. Moreover, only a 16.4% reduction in the permeate flux during a 40-day operation period was recorded. In the second experimental work, the immersed membrane bioreactor system was subjected to high organic loading rates of 4, 6, 8, and 10 g VS/L/d as a tool of manipulating the anaerobic digestion process towards high VFAs and hydrogen production. The highest yield of VFAs was attained at 6 g VS/L/d (0.52 g VFA/gVSadded), while at 8 g VS/L/d, a maximal hydrogen yield of 14.7 NmL/gVSadded was obtained. An analysis of the microbial structure revealed that the presence of Clostridium resulted in high production of acetate, butyrate and caproate. On the other hand, the relative abundance of Lactobacillus was found to influence lactate biosynthesis. Cultivation of edible filamentous fungi presents a novel possibility for application of food waste-derived VFAs. Due to the growing demand of single-cell protein, one of the potential uses for the fungal biomass is the production of animal feed. In this thesis, an edible filamentous fungus, Rhizopus oligosporus was grown solely on the VFAs recovered from the membrane bioreactors. It was revealed that high concentrations could inhibit fungal growth; thus, the dilution of the VFAs solution used as substrate was necessary. Furthermore, when a fed-batch cultivation technique was applied, a four-fold improvement in the biomass production relative to standard batch cultivation was realized. A maximum biomass yield of 0.21 ± 0.01g dry biomass/ g VFAs COD eq. consumed, containing 39.28 ± 1.54% crude protein, was obtained. With further improvements in the VFAs uptake and the biomass yield, this novel concept could be a fundamental step in converting anaerobic digestion facilities into biorefineries

Effect of heavy metals on syngas fermentation

The goal of this work was to establish the suitable and limiting concentrations of Zn, Cu and Mn compounds during syngas fermentation. The results showed that cells encased in polyvinylidene difluoride (PVDF) membranes had a faster accumulation of methane in reactors containing fermentation medium dosed with 5 mg/L of each heavy metal compared to free cells. It was also revealed that total inhibition of biohydrogen production occurred in medium containing 5 mg/L Cu, 30 mg/L Zn and 140 mg/L Mn while the most suitable metal concentration level was 0.1 mg/L Cu, 0.6 mg/L and 2.8 mg/L Mn. In addition, a comparison test showed that for the most suitable metal concentration in the medium, rate of performance at pH 6 and 7 was higher than at pH 5

Developing a food waste-based volatile fatty acids platform using an immersed membrane bioreactor

Approximately 1.3 billion tons of food waste is produced globally every year. In principle, all the resources in the supply chain are lost (e.g. land, energy, and water) when the food is not consumed as intended. Anaerobic digestion is an established biological technology to treat food waste, and is mainly employed for recovery of energy in the form of biogas. Volatile fatty acids (VFAs) are formed as intermediate products of the anaerobic digestion process, and can be applied as precursors for various essential biomaterials. The manipulation of the anaerobic digestion process to synthesize these intermediates instead of biogas is considered to recover more value from food waste. However, some bottlenecks that prevent large-scale production and application of VFAs still exist. Among the key issues to be addressed are the difficulty in recovering the VFAs from the fermentation medium and the overall low product yields. The goals of the present thesis were: 1) to investigate methods to boost the production of VFAs from food waste; 2) to continuously recover VFAs from food waste fermentation medium; 3) to determine the changes in the microbial structure during high organic loading of food waste in membrane bioreactors; and 4) to study a novel approach for applying food waste-derived VFAs for cultivating edible filamentous fungi. For continuous product recovery at high yields, an immersed membrane bioreactor was constructed with robust cleaning capabilities to withstand the complex anaerobic digestion medium. The membrane bioreactor was first operated without pH control and a yield of 0.54 g VFA/g VSadded was achieved when an organic loading rate of 2 gVS/L/d was applied. Moreover, only a 16.4% reduction in the permeate flux during a 40-day operation period was recorded. In the second experimental work, the immersed membrane bioreactor system was subjected to high organic loading rates of 4, 6, 8, and 10 g VS/L/d as a tool of manipulating the anaerobic digestion process towards high VFAs and hydrogen production. The highest yield of VFAs was attained at 6 g VS/L/d (0.52 g VFA/gVSadded), while at 8 g VS/L/d, a maximal hydrogen yield of 14.7 NmL/gVSadded was obtained. An analysis of the microbial structure revealed that the presence of Clostridium resulted in high production of acetate, butyrate and caproate. On the other hand, the relative abundance of Lactobacillus was found to influence lactate biosynthesis. Cultivation of edible filamentous fungi presents a novel possibility for application of food waste-derived VFAs. Due to the growing demand of single-cell protein, one of the potential uses for the fungal biomass is the production of animal feed. In this thesis, an edible filamentous fungus, Rhizopus oligosporus was grown solely on the VFAs recovered from the membrane bioreactors. It was revealed that high concentrations could inhibit fungal growth; thus, the dilution of the VFAs solution used as substrate was necessary. Furthermore, when a fed-batch cultivation technique was applied, a four-fold improvement in the biomass production relative to standard batch cultivation was realized. A maximum biomass yield of 0.21 ± 0.01g dry biomass/ g VFAs COD eq. consumed, containing 39.28 ± 1.54% crude protein, was obtained. With further improvements in the VFAs uptake and the biomass yield, this novel concept could be a fundamental step in converting anaerobic digestion facilities into biorefineries

Automation and artificial intelligence in filamentous fungi-based bioprocesses: A review

By utilizing their powerful metabolic versatility, filamentous fungi can be utilized in bioprocesses aimed at achieving circular economy. With the current digital transformation within the biomanufacturing sector, the interest of automating fungi-based systems has intensified. The purpose of this paper was therefore to review the potentials connected to the use of automation and artificial intelligence in fungi-based systems. Automation is characterized by the substitution of manual tasks with mechanized tools. Artificial intelligence is, on the other hand, a domain within computer science that aims at designing tools and machines with the capacity to execute functions that would usually require human aptitude. Process flexibility, enhanced data reliability and increased productivity are some of the benefits of integrating automation and artificial intelligence in fungi-based bio-processes. One of the existing gaps that requires further investigation is the use of such data-based technologies in the production of food from fungi

Effects of Heavy Metals and pH on the Conversion of Biomass to Hydrogen via Syngas Fermentation

The effects of three heavy metals on hydrogen production via syngas fermentation were investigated within a metal concentration range of 0-1.5 mg Cu/L, 0-9 mg Zn/L, 0-42 mg Mn/L, in media with initial pH of 5, 6 and 7, at 55 °C. The results showed that at lower metal concentration, pH 6 was optimum while at higher metal concentrations, pH 5 stimulated the process. More specifically, the highest hydrogen production activity recorded was 155.28% ± 12.02% at a metal concentration of 0.04 mg Cu/L, 0.25 mg Zn/L, and 1.06 mg Mn/L and an initial medium pH of 6. At higher metal concentration (0.625 mg Cu/L, 3.75 mg Zn/L, and 17.5 mg Mn/L), only pH 5 was stimulating for the cells. The results show that the addition of heavy metals, contained in gasification-derived ash, can improve the production rate and yield of fermentative hydrogen. This could lead in lower costs in gasification process and fermentative hydrogen production and less demand for syngas cleaning before syngas fermentation

Effects of Heavy Metals and pH on the Conversion of Biomass to Hydrogen via Syngas Fermentation

The effects of three heavy metals on hydrogen production via syngas fermentation were investigated within a metal concentration range of 0-1.5 mg Cu/L, 0-9 mg Zn/L, 0-42 mg Mn/L, in media with initial pH of 5, 6 and 7, at 55 °C. The results showed that at lower metal concentration, pH 6 was optimum while at higher metal concentrations, pH 5 stimulated the process. More specifically, the highest hydrogen production activity recorded was 155.28% ± 12.02% at a metal concentration of 0.04 mg Cu/L, 0.25 mg Zn/L, and 1.06 mg Mn/L and an initial medium pH of 6. At higher metal concentration (0.625 mg Cu/L, 3.75 mg Zn/L, and 17.5 mg Mn/L), only pH 5 was stimulating for the cells. The results show that the addition of heavy metals, contained in gasification-derived ash, can improve the production rate and yield of fermentative hydrogen. This could lead in lower costs in gasification process and fermentative hydrogen production and less demand for syngas cleaning before syngas fermentation

Bioengineering of anaerobic digestion for volatile fatty acids, hydrogen or methane production: A critical review

Anaerobic digestion (AD) is a well-established technology used for producing biogas or biomethane alongside the slurry used as biofertilizer. However, using a variety of wastes and residuals as substrate and mixed cultures in the bioreactor makes AD as one of the most complicated biochemical processes employing hydrolytic, acidogenic, hydrogen-producing, acetate-forming bacteria as well as acetoclastic and hydrogenoclastic methanogens. Hydrogen and volatile fatty acids (VFAs) including acetic, propionic, isobutyric, butyric, isovaleric, valeric and caproic acid and other carboxylic acids such as succinic and lactic acids are formed as intermediate products. As these acids are important precursors for various industries as mixed or purified chemicals, the AD process can be bioengineered to produce VFAs alongside hydrogen and therefore biogas plants can become biorefineries. The current critical review paper provides the theory and means to produce and accumulate VFAs and hydrogen, inhibit their conversion to methane and to extract them as the final products. The effects of pretreatment, pH, temperature, hydraulic retention time (HRT), organic loading rate (OLR), chemical methane inhibitions, and heat shocking of the inoculum on VFAs accumulation, hydrogen production, VFAs composition, and the microbial community were discussed. Furthermore, this paper highlights the possible techniques for recovery of VFAs from the fermentation media in order to minimize product inhibition as well as to supply the carboxylates for downstream procedures

MBR-Assisted VFAs production from excess sewage sludge and food waste slurry for sustainable wastewater treatment

The significant amount of excess sewage sludge (ESS) generated on a daily basis by wastewater treatment plants (WWTPs) is mainly subjected to biogas production, as for other organic waste streams such as food waste slurry (FWS). However, these organic wastes can be further valorized by production of volatile fatty acids (VFAs) that have various applications such as the application as an external carbon source for the denitrification stage at a WWTP. In this study, an immersed membrane bioreactor set-up was proposed for the stable production and in situ recovery of clarified VFAs from ESS and FWS. The VFAs yields from ESS and FWS reached 0.38 and 0.34 gVFA/gVSadded, respectively, during a three-month operation period without pH control. The average flux during the stable VFAs production phase with the ESS was 5.53 L/m2/h while 16.18 L/m2/h was attained with FWS. Moreover, minimal flux deterioration was observed even during operation at maximum suspended solids concentration of 32 g/L, implying that the membrane bioreactors could potentially guarantee the required volumetric productivities. In addition, the techno-economic assessment of retrofitting the membrane-assisted VFAs production process in an actual WWTP estimated savings of up to 140 â\u82¬/h for replacing 300 kg/h of methanol with VFAs. © 2020 by the authors

Food waste-derived volatile fatty acids platform using an immersed membrane bioreactor

Volatile fatty acids (VFAs) are the key intermediates from anaerobic digestion (AD) process that can be a platform to synthesize products of higher value than biogas. However, some obstacles still exist that prevent large-scale production and application of VFAs, key among them being the difficulty in recovering the acids from the fermentation medium and low product yields. In this study, a novel anaerobic immersed membrane bioreactor (iMBR) with robust cleaning capabilities, which incorporated frequent backwashing to withstand the complex AD medium, was designed and applied for production and in situ recovery of VFAs. The iMBR was fed with food waste and operated without pH control, achieving a high yield of 0.54 g VFA/g VSadded. The continuous VFA recovery process was investigated for 40 days at OLRs of 2 gVS/L/d and 4 gVS/L/d without significant change in the permeate flux at a maximum suspended solids concentration of 31 g/L

Bio‑hydrogen and VFA production from steel mill gases using pure and mixed bacterial cultures

A major source of CO2 emissions is the flaring of steel mill gas. This work demonstrated the enrichment of carboxydotrophic bacteria for converting steel mill gas into volatile fatty acids and H2, via gas fermentation. Several combinations of pure and mixed anaerobic cultures were used as inoculum in 0.5-L reactors, operated at 30 and 60 °C. The process was then scaled up in a 4-L membrane bioreactor, operated for 20 days, at 48 °C. The results showed that the enriched microbiomes can oxidize CO completely to produce H2/H+ which is subsequently used to fix the CO2. At 30 °C, a mixture of acetate, isobutyrate and propionate was obtained while H2 and acetate were the main products at 60 °C. The highest CO conversion and H2 production rate observed in the membrane bioreactor were 29 and 28 mL/LR/h, respectively. The taxonomic diversity of the bacterial community increased and the dominant species was Pseudomonas