Mixture Of Food Waste Research Articles

Strategic conversion of plastic containers with food waste into energy through thermochemical processes

Plastic valorization has received particular attention as an environmentally benign approach to achieve carbon neutrality and reduce greenhouse gas emissions. However, contaminated plastic and biomass waste mixtures suffer from single-stream recycling. Waste mixtures are currently discarded through landfilling and incineration. As a sustainable disposal and valorization method for converting plastic and biomass waste mixtures into energy-intensive products, especially syngas (H2 and CO), this study utilizes catalytic pyrolysis and a CO2 flow gas. A plastic container contaminated with a food waste mixture (PFW) was used as the model waste. The major products of the pyrolysis of PFW were liquid hydrocarbons (HC) (C7–30) and wax-like HCs with negligible formation of oxygen-containing HCs. However, the high production of wax-like HCs becomes a problem. Catalytic pyrolysis was employed to convert HCs into simpler product streams such as syngas. Although syngas formation tripled with the Ni catalyst, catalyst deactivation was observed. To suppress catalyst deactivation and promote CO formation, CO2 was introduced instead of N2. During the CO2-assisted catalytic pyrolysis, the syngas yield from PFW increased to 95.5 % because the chemical reactions between CO2 and liquid/wax-like HCs produced additional H2 and CO. The catalytic reaction with CO2 suppressed carbon deposition because long-chain HCs were converted to CO rather than coke.

Effect of larval instar and post‐harvest treatments on heavy metals in BSFL and frass reared on commercial food waste streams

SummaryThe use of black soldier fly larvae (BSFL) to valorise different organic waste streams and the subsequent use of resulting larvae as a feedstock ingredient is increasing rapidly in several regions across the globe. The lack of knowledge about several safety issues including chemical contaminants (e.g. heavy metals) seems to affect the upscaling and commercialisation of this product. This study evaluates the safety of the BSFL against chemical contaminants including heavy metals and mycotoxins in both BSFL and frass samples reared with different food waste streams (e.g. soy waste, customised bread‐vegetable diet, food waste mixture, supermarket and childcare centre) from two commercial production facilities. The effect of larval instars and post‐harvest treatments (e.g. blanching and drying) on the safety of the BSFL was also investigated. The concentration of heavy metals was primarily influenced by the concentration in the food waste streams. The concentration was also higher in 6th instar compared to 5th instar larvae. The effect of blanching and drying have a varied effect on the concentration of heavy metals. Mycotoxins were found to be below the limit of quantification for all samples. The outcomes of this study indicated that BSFL grown on food waste streams and the resulting frass is safe against different heavy metals analysed. The findings of this study will assist the commercial BSFL manufacturers with the identification of relevant control points to ensure the chemical safety of their products. Therefore, encourage the use of different food waste streams as feedstock for rearing BSFL.

Biochemical Conversion of Food Waste for Energy and Agricultural Applications: Towards Sustainable Restaurant Operation in Nigeria

One of the major problems faced by many restaurants in Nigeria is high operational cost resulting from high cost of energy, food ingredients and waste disposal. Indiscriminate disposal of food wastes contribute to environmental problems such as global warming and the spread of diseases. This paper presents the design and fabrication of a biogas plant for the conversion of biodegradable food wastes into biogas and agri-supplements which can be used for domestic and commercial purposes such as cooking/heating and agricultural applications respectively. This study is geared towards the domestication of an existing technology that has not been taken seriously in Nigeria. the anaerobic digester consists mainly of the slurry inlet, the digester, gas holder and effluent discharge pipe. The slurry, a mixture of food waste and water was fed in to the digester and allowed to digest anaerobically to generate biogas consisting mainly of methane. The digestate, a harmless solid/liquid mixturewas applied as organic manure to a small portion of land in an agricultural experiment.Results of combustion tests in a locally fabricated torch presented a long, blue and quite flame, similar to that of LPG. Digested fed crops grew faster and yielded better. This projecthas the potential to enhance the operational sustainability of restaurants by lowering the cost of cooking and heating, while also supplementing vegetable supply.

On the extraction of volatile fatty acids from food waste mixtures: Comparison between the use of liquid–liquid and magnetic nanoparticle technologies

The extraction of volatile fatty acids (VFAs) from an aqueous solution derived by fermentation of food waste is a key challenge in the context of the circular economy, thanks to their high economic and environmental impact due to their wide-ranging use in various industrial fields. In this work, we compared two different extraction methods: one novel and one classical. Firstly, iron oxide nanoparticles of around 10 nm were prepared and used as they are or functionalised using (3-Aminopropyl)triethoxysilane) (APTES) molecules, adipic acid and oleic acid. This was compared with a traditional industrial method (liquid–liquid extraction) that can guarantee high extraction of VFAs with high reproducibility. Indeed the use of dichloromethane, hexane, methyl tert-butyl ether and oleic acid presented extraction values of up to 30 % while iron oxide NPs showed results with low reproducibility. The comparison demonstrated the use of oleic acid as a promising solvent for liquid–liquid extraction of VFAs.

Bulking agent in dry anaerobic digestion as a key factor for the enhancement of biogas production

Dry anaerobic digestion (dry-AD) is an attractive process for solid wastes such as agri-food waste. However, some limitations mainly associated to lack of effective mixing, can hinder the methane production capacity of the systems. Bulking agent (BA) has been proposed as a solution to the compaction issues in systems without mechanical agitation, such as leaching bed reactors. However, effects of BA are still not clear, and, thus, the factors to consider for its dose has not been optimized yet. This work studies the effect of BA in dry-AD. Two substrates with different characteristics were proposed as models, bean peel as a lignocellulosic substrate and a mixture of food waste as a readily biodegradable substrate. Inert plastic rings were used as BA at different BA:S ratios. Assessed BA:S ratio did not affect the performance of methane production for the lignocellulosic waste, but it did significantly affect to the easily biodegradable substrate, showing up to a 28% of methane production increase. This result could be due to the presence of lignocellulosic compounds in the bean peel, behaving like a natural BA. In assays with an increased bed height, the compaction of the system was more severe, resulting in the rapid acidification of the processes. At these conditions, the positive effect of BA addition was more marked, allowing methane production and no acidification of the system. Thus, the addition of BA is a suitable strategy for improving methane production or stability in dry-AD systems without requiring the stirring of the systems.

Effect of Food Waste on The Growth Performance, Waste Reduction Efficiency and Nutritional Composition of Black Soldier Fly (Hermetia illucens (L.), Diptera: Stratiomyidae) Larvae

The rate of solid waste generation, especially in Malaysia, has become one of the major concerns for environmental and public health issues. Food waste accounts for the highest percentage of solid waste that ends up in landfills. Due to the living nature of humans and their involvement in agricultural, industrial, and municipal activities, the disposal of food waste happens on a regular basis. Due to the absence of an incineration plant, these wastes are commonly sent into landfills which are considered to be the most cost-effective method for disposal. Nevertheless, consideration for an alternative disposal method such as composting shall not be ruled out entirely. One of the established methods for composting food waste is the utilization of the larvae of the Black Soldier Fly. A study was conducted to assess the growth and nutritional composition, waste reduction capacity and nutritional composition of Black Soldier Fly Larvae (BSFL) reared on food waste. We found that the larvae reared with the food waste and effective microorganism (EM), LFWEM (BSFL reared with a mixture of food waste and effective microorganisms), have a slightly better relative growth rate (2.66 ± 0.35 day-1) compared to larvae reared with only food waste (2.44 ± 0.17 day-1). The waste reduction index was higher in the LFWEM group (5.36 ± 0.18 g/day) compared to the control group, LFC (BSFL reared with chicken feed) (4.85 ± 0.03 g/day) and the LFW (BSFL reared with food waste) group (5.13 ± 0.17 g/day). The nutritional composition of the BSFL reared using food waste shows some potential as it surpasses some of the amount of essential amino acids including Arginine, Histidine, Threonine and Valine, found in the commercially available animal feeds. This finding serves as a baseline to propose potential replacements for animal protein by using BSFL reared with food waste.

Comparison of Different Pretreatment Processes Envisaging the Potential Use of Food Waste as Microalgae Substrate.

A significant fraction of the food produced worldwide is currently lost or wasted throughout the supply chain, squandering natural and economic resources. Food waste valorization will be an important necessity in the coming years. This work investigates the ability of food waste to serve as a viable nutritional substrate for the heterotrophic growth of Chlorella vulgaris. The impact of different pretreatments on the elemental composition and microbial contamination of seven retail food waste mixtures was evaluated. Among the pretreatment methods applied to the food waste formulations, autoclaving was able to eliminate all microbial contamination and increase the availability of reducing sugars by 30%. Ohmic heating was also able to eliminate most of the contaminations in the food wastes in shorter time periods than autoclave. However, it has reduced the availability of reducing sugars, making it less preferable for microalgae heterotrophic cultivation. The direct utilization of food waste containing essential nutrients from fruits, vegetables, dairy and bakery products, and meat on the heterotrophic growth of microalgae allowed a biomass concentration of 2.2 × 108 cells·mL-1, being the culture able to consume more than 42% of the reducing sugars present in the substrate, thus demonstrating the economic and environmental potential of these wastes.

Application of solar drying as a pre-treatment method for storing wet feedstocks prior to use in anaerobic digesters: Effect on methane production and digestate composition

The objective of this study was to examine for the first time, the effect of solar-dried food waste (FW) and a mixture of FW with olive mill wastewater (OMW) on the anaerobic digestion of liquid pig manure (LPM) and cow manure (CM). A series of laboratory experiments were conducted using continuously operating reactors at mesophilic conditions. Solar-dried feedstocks were added to increase the initial volatile solids (VS) content in the feedstock (LPM and CM) by 20 % in both cases. The hydraulic retention time (HRT) was set at 20 days. The results show that the addition of solar dried feedstocks increased biogas production by 1.7 times. The reactor treating LPM and CM produced 403 – 427 ml/l/d biogas. After the addition of solar dried feedstocks, the biogas production reached the value of 711 ml/l/d and 676 ml/l/d for FW and the mixture of FW with OMW, respectively. In all cases, the estimated biodegradability of mixtures was over 50 %, while the VS removal was 23 % for maximum biogas production.

Potential Application of Black Soldier Fly Larva Bins in Treating Food Waste.

The increase in the global population has led to a rise in organic waste generation and landfill sites. Consequently, there has been a global shift in focus towards the utilization of BSFL to address these challenges. This study aims to design, develop, and test a user-friendly BSFL bin and identify the optimal MCCM for treating organic waste using BSFL. The four BSFL bins have a dimension of 330 mm (width) × 440 mm (length) × 285 mm (height). This study uses mixtures of food waste added with different MCCMs, including chicken feed, rice bran, and garden waste. We add the mediums to the BSFL bins every third day and measure the humidity, ambient temperature, pH, medium temperature, and BSFL weight and length. The measurements show that the fabricated BSFL bins can fulfill the BSF lifecycle requirements. Wild BSFs lay eggs in the medium of BSFL bins, and the hatched larvae decompose it. When they reach the prepupae stage, they climb the ramp into the harvesting container. The results show that the food waste without MCCM produced the heaviest (0.228 g) and longest (2.16 cm) larvae; the prepupae are 2.15 cm long and weigh 0.225 g; and the growth rate is 53.72%. However, the high moisture content of 75.3% makes the maintenance work challenging. The medium with MCCM has a markedly lower moisture content of 51-58%. A comparison of the three MCCMs shows that the chicken feed produces the larvae and prepupae with the highest growth rate (the larvae are 2.10 cm long and weigh 0.224 g, the prepupae are 2.11 cm long and weigh 0.221 g, and the growth rate is 72.36%) and the frass with the lowest moisture content (51.2%). An effective BSFL composting system is easy to manage and produces the biggest larvae. In summary, food waste mixed with chicken feed is the most suitable MCCM for treating organic waste using BSFL.

Optimum Conditions for Enhanced Biohydrogen Production from a Mixture of Food Waste and Sewage Sludge with Alkali Pretreatment

Given the increasing demand for hydrogen, owing to its environmentally friendly nature, it is important to explore efficient methods for hydrogen production. This study investigates dark-fermentative hydrogen production by the co-digestion of food waste and sewage sludge. Both wastes were subjected to alkali pretreatment (at pH 13) to enhance biodegradability. Batch tests were conducted to enhance hydrogen production from food waste and sewage sludge under various volatile solid (VS) concentrations of 1.5–5% and food waste to sewage sludge mixing ratios of 0:100–100:0. We found that alkali pretreatment was effective in increasing hydrogen yields. The maximum specific hydrogen production rate of 163.8 mL H2/g volatile suspended solid/h was obtained at a VS concentration of 5.0% and food waste composition of 62.5%. Additionally, VS concentration of 2.8% and food waste composition of 100% yielded a maximum hydrogen production potential of 152.1 mL H2/g VS. Our findings indicate that food waste and sewage sludge with alkali pretreatment are potential substrates to produce biohydrogen.

Boosting butyrate and hydrogen production in acidogenic fermentation of food waste and sewage sludge mixture: a pilot scale demonstration

Within the urban scenario, the application of a biorefinery technology value chain can foster the conversion of different organic substrates into marketable and added-value products. In this work, a pilot-scale dark fermentation (DF) process has been carried out as a key step for volatile fatty acids (VFA) and hydrogen production from the liquid fraction of sewage sludge and food waste mixture. Six operating conditions have been monitored in terms of yield and process stability, by changing the hydraulic retention time (HRT) from 4 to 6 days and applying a short-term hyper-thermophilic hydrolysis (70 °C, 8 h) on the same feedstock mixture. A tubular centrifugation was utilized to remove part of the biosolids (driven to biogas production) before the DF step, which was applied on the soluble and/or colloidal organic matter only. The hydrolysis step favored the following acidification process, in which a fermentation yield up to 0.42 g CODVFA/g VS0 was achieved at 5 days as HRT. Hydrogen production (up to 34.4% v/v and 0.046 m3 H2/kg VS0) was positively affected by the hydrolysis application and by the decrease of the HRT, highlighting the possibility to produce biohythane in the modeled two-phases anaerobic bioprocess. On the other hand, without the application of the hydrolysis, a selective production of butyric acid (up to 75% COD basin) was achieved, furnishing a different valorization route for the chosen urban organic feedstock. Changes in operating conditions and performances were also reflected by the adaptation of the microbial community, whose characterization highlighted the occurrence of several fermentative microorganisms (e.g., Clostridiaceae, Ruminococcaceae).

Seaweed (Gracilariopsis funicularis) biochar incorporation into a goat manure–food waste vermicompost for optimized vermidegradation and nutrient release

Vermicomposts are organic fertilizer sources that are being promoted; however, their concentrations of macronutrients such as NPK are very low. This study, therefore, evaluated the effects of amending goat manure–food waste mixture with biochar prepared from seaweed (Gracilariopsis funicularis) at 0% (control), 2, 4, 6, and 8% on vermicompost degradation and macronutrient release. After 10 weeks of vermicomposting, the highest pH of 9.06 was observed within the control, whilst the lowest was 8.7 in the 8% treatment. The electrical conductivity showed a positive relationship with the level of biochar incorporation with the highest of 16.5 mS/cm from the 8% treatment, whilst the lowest was within the control with 6 mS/cm. There were no significant differences between treatments on humification parameters; however, there were significant differences in the changes in a C/N ratio with the final C/N ratio of 14.4, 14.9, 16.7, 15.1, and 14.4 for the control, 2, 4, 6, and 8% treatments, respectively. A higher incorporation rate resulted in the higher concentration of potassium with a value of 32.3 g/kg at week 8. The final percentage change in Olsen P was 19, 14.2, 7.3, 4.1, and 3.0% for the 8%, 6%, control, 4%, and 2% treatments, respectively. An optimized level of 6% to 8% biochar incorporation ratio can be recommended. However, the incorporation of G. funicularis biochar does not seem to influence changes in the vermidegradation efficiency, though it can significantly improve the macronutrients such as P, K, and Mg concentrations as well as the macroelement concentrations.

Pre-composting of municipal solid wastes as enhancer of bio-hydrogen production through dark fermentation process

This study was focused on bio-hydrogen production from thermophilic dry anaerobic acidogenic co-digestion (55 °C and 20 % of total solids) of pre-composted mixtures of organic fraction of municipal solid waste (OFMSW) and food waste (FW). Three different mixture ratios of OFMSW:FW (80:20, 70:30 and 50:50) have been tested. The application of pre-composting improved the hydrolytic and acidogenic phases in the subsequent acidogenic co-digestion, reaching an increase in the bio-hydrogen production in the range of 45.4–46.7 %. In this sense, the best results were obtained for the pretreated mixture with the ratio 70:30, with 42.9 LH2/kg VSadded and 53.9 % of H2 in the biogas. Finally, the kinetic study has corroborated that pre-composting clearly enhances the kinetics of acidogenic fermentation of OFMSW and FW mixtures. In fact, the μmax and YP values for the pretreated mixtures have been increased by a 20 % and 33 % respectively.

Co-pyrolysis of plastics and food waste mixture under flue gas condition for bio-oil production

Growing global population increased the energy demand and generation of municipal solid wastes (MSW). MSW can be utilized to produce green renewable fuels via pyrolysis technology. This study investigated the co-pyrolysis of MSW represented by mixtures of food and plastic wastes, in a downdraft pyrolyzer using synthetic flue gas composition. The food wastes in this study included fish and chicken bones, and leftover rice, and plastics included polypropylene and polyethylene (high density and low density) plastics respectively. The effect of pyrolysis temperature and types of feedstocks on the bio-oil yield and quality were determined. Although the highest bio-oil yield was obtained at 400 °C for all feedstocks, GC–MS results indicated major compounds such as fatty acids, esters, amides, nitriles, sugars were more notable at 300 °C. The bio-oil exhibited high water contents due to combustion from the flue gas. Fish bone and plastic mixture has the lowest O/C ratio and the best calorific value of 33.9 MJ/kg compared to the other two feedstocks, however extensive treatments were required to be used as fuel. Overall, bio-oil from this study has the potential to be used as an alternative fuel from co-pyrolysis of food and plastic wastes with further treatments and processing.

Potential treatment of aged cow manure using spare capacity in anaerobic digesters treating a mixture of food waste and pig manure

With the increasing production of cow manure (CM) and the continuing decrease in the demand for manure compost, CM management has become an urgent and challenging task in Korea. In most cattle farms in Korea, CM mixed with bedding materials is left in pens exposed to the open air for several months before treatment, which makes CM an unsuitable feedstock for anaerobic digestion. This study examined the co-digestion of aged CM with a mixture of food waste and pig manure as the base substrate to assess the possibility of treating and valorizing CM using spare capacity in existing anaerobic digesters dealing with other wastes. The duplicate digesters initially fed with the base substrate were subjected to the addition of increasing amounts of CM (3–10% in the feed, w/v) over nine months. Co-feeding CM up to 5% in the feed (w/v) did not compromise the methanogenic degradation of the substrates, but adding more CM led to a significant performance deterioration likely related to the buildup of inhibitory free ammonia and H2S. Adding CM substantially influenced the digester microbial communities, especially methanogenic communities, and induced a dominance shift from aceticlastic Methanothrix to hydrogenotrophic methanogens as the CM fraction increased. The overall results suggest that the CM fraction should not exceed 5% in the feed (w/v) for its stable treatment with the base substrate in the experimental digesters. Although further studies are needed, anaerobic treatment using spare capacity in existing digesters can be a useful strategy for the management of aged CM.

Selective hydrogenation of vanillin to vanillyl alcohol over Pd, Pt, and Au catalysts supported on an advanced nitrogen-containing carbon material produced from food waste

Food waste worldwide has been threatening the environment and resulting in high carbon emissions. Although anaerobic fermentation is a potential solution transforming food waste into valuable chemicals, a large amount of the fermentation residue remains as solid waste. For closing the circular economy loop for food waste valorization, we proposed a thermo-chemical activation of a fermentation residue produced from a mixture of food waste and sludge to prepare a nitrogen-enriched, advanced carbon material. This could be used as a support to synthesize Pd/C, Pt/C and Au/C catalysts for the aqueous-phase hydrogenation of vanillin to vanillyl alcohol at mild reaction conditions. The produced alcohol increased sixfold the commercial value of the original aldehyde. The catalytic performance (based on the vanillin conversion and vanillyl alcohol yield) followed the order of Pd/C > Pt/C > Au/C. The Pd/C catalyst showed an excellent catalytic activity (>99% vanillin conversion and > 99% vanillyl alcohol selectivity) at optimized reaction conditions (i.e., 30 °C and 0.7 MPa H2 for 90 min, with 2 mmol vanillin/10 mg catalyst), along with high reusability and stability (up to four consecutive runs). These catalytic features outperformed those of a commercial Pd/C catalyst owing to: (i) high reduction degree and stabilization of the Pd particles on the carbon support, which accommodated a higher proportion of pyridinic than pyrrolic nitrogen, and (ii) rapid adsorption of the aldehyde group on the catalyst combined with rapid desorption of the newly formed hydroxymethyl group. This exceptional catalytic behavior was corroborated by efficient hydrogenation of other lignin-derived aromatic aldehydes, including p-hydroxybenzaldehyde and syringaldehyde, to their respective alcohols. Our results can bring a novel use for food waste in catalysis and represent a sustainable and efficient conversion of biomass into value-added chemicals and advanced materials.

Comparative Investigation of the Physicochemical Properties of Chars Produced by Hydrothermal Carbonization, Pyrolysis, and Microwave-Induced Pyrolysis of Food Waste.

This work presents a comparative study of the physicochemical properties of chars derived by three thermochemical pathways, namely: hydrothermal carbonization, HTC (at 180, 200 and 220 °C), pyrolysis, PY, (at 500, 600 and 700 °C) and microwave assisted pyrolysis, MW (at 300, 450 and 600 W). The mass yield of HTC samples showed a decrease (78.7 to 26.7%) as the HTC temperature increased from 180 to 220 °C. A similar decreasing trend in the mass yield was also observed after PY (28.45 to 26.67%) and MW (56.45 to 22.44%) of the food waste mixture from 500 to 700 °C and 300 to 600 W, respectively. The calorific value analysis shows that the best among the chars prepared by three different heating methods may be ranked according to the decreasing value of the heating value as: PY500, MW300, and HTC180. Similarly, a decreasing trend in H/C values was observed as: PY500 (0.887), MW300 (0.306), and HTC180 (0.013). The scanning electron microscope (SEM) analyses revealed that the structure of the three chars was distinct due to the different temperature gradients provided by the thermochemical processes. The results clearly show that the suitable temperature for the HTC and PY of food waste was 180 °C and 500 °C, respectively, while the suitable power for the MW of food waste was 300 W.

Plastic-containing food waste conversion to biomethane, syngas, and biochar via anaerobic digestion and gasification: Focusing on reactor performance, microbial community analysis, and energy balance assessment

To manage the mixture of food waste and plastic waste, a hybrid biological and thermal system was investigated for converting plastic-containing food waste (PCFW) into renewable energy, focusing on performance evaluation, microbial community analysis, and energy balance assessment. The results showed that anaerobic digestion (AD) of food waste, polyethylene (PE)-containing food waste, polystyrene (PS)-containing food waste, and polypropylene (PP)-containing food waste generated a methane yield of 520.8, 395.6, 504.2, and 479.8 mL CH4/gVS, respectively. CO2 gasification of all the plastic-containing digestate produced more syngas than pure digestate gasification. Syngas from PS-digestate reached the maximum yield of 20.78 mol/kg. During the digestate-derived-biochar-amended AD of PCFW, the methane yields in the biochars-amended digesters were 6–30% higher than those of the control digesters. Bioinformatic analysis of microbial communities confirmed the significant difference between control and biochar-amended digesters in terms of bacterial and methanogenic compositions. The enhanced methane yields in biochars-amended digesters could be partially ascribed to the selective enrichment of genus Methanosarcina, leading to an improved equilibrium between hydrogenotrophic and acetoclastic methanogenesis pathways. Moreover, energy balance assessment demonstrated that the hybrid biological and thermal conversion system can be a promising technical option for the treatment of PCFW and recovery of renewable biofuels (i.e., biogas and syngas) and bioresource (i.e., biochar) on an industrial scale.

Volatile Fatty Acids (VFA) Production from Wastewaters with High Salinity—Influence of pH, Salinity and Reactor Configuration

The hydrocarbon-based economy is moving at a large pace to a decarbonized sustainable bioeconomy based on biorefining all types of secondary carbohydrate-based raw materials. In this work, 50 g L−1 in COD of a mixture of food waste, brine and wastewater derived from a biodiesel production facility were used to produce organic acids, important building-blocks for a biobased industry. High salinity (12–18 g L−1), different reactors configuration operated in batch mode, and different initial pH were tested. In experiment I, a batch stirred reactor (BSR) at atmospheric pressure and a granular sludge bed column (GSBC) were tested with an initial pH of 5. In the end of the experiment, the acidification yield (ηa) was similar in both reactors (22–24%, w/w); nevertheless, lactic acid was in lower concentrations in BSR (6.3 g L−1 in COD), when compared to GSBC (8.0 g L−1 in COD), and valeric was the dominant acid, reaching 17.3% (w/w) in the BSR. In experiment II, the BSR and a pressurized batch stirred reactor (PBSR, operated at 6 bar) were tested with initial pH 7. The ηa and the VFA concentration were higher in the BSR (46%, 22.8 g L−1 in COD) than in the PBSR (41%, 20.3 g/L in COD), and longer chain acids were more predominant in BSR (24.4% butyric, 6.7% valeric, and 6.2% caproic acids) than in PBSR (23.2%, 6.2%, and 4.2%, respectively). The results show that initial pH of 7 allows achieving higher ηa, and the BSR presents the most suitable reactor among tested configurations to produce VFA from wastes/wastewaters with high salinity.

Acidogenic Fermentation of Urban Organic Waste: Effect of Operating Parameters on Process Performance and Safety

Biorefinery represents an innovative approach for waste management, where products at the end of their service life are seen as valuable resources for the production of high added value bio-products or bio-fuels. In this context, acidogenic fermentation is gaining scientific and commercial interest, since it allows to improve waste/wastewater treatability as well as additional recovery of volatile fatty acids (VFA), the building blocks for the chemical industry or precursors of reduced chemicals in conventional organic chemistry. This work illustrates the results of a study aimed at highlighting the effects of different inputs (feedstock composition and pre-treatment; temperature) on process performance and safety. The fermentation process was applied on a mixture of food waste and sewage sludge (FWs-SS) within the contest of Treviso municipality (northeast Italy). The VFA production and relative ratio respect to soluble chemical oxygen demand (CODSOL) were evaluated, as well as the variation of lower flammability limit (LFL) of flammable gaseous mixture, produced during the acidogenic fermentation. Thermal pre-treatment (72°C, 48 h) enhanced the solubilization of the organic matter, which was converted into VFA in batch mode under mesophilic conditions (37°C). The VFA level increased up to 30 ± 3 g COD/L, with high CODVFA/CODSOL ratio (0.86 ± 0.05). This condition was also characterized by the lowest level in volumetric percentage of flammable gases such as H2, CH4 and H2S. Variation of LFL of gaseous mixture as function of fermenter operating parameters has been investigated by Le Chatelier’s Law. The high concentration of CO2 (greater than 80% v/v) increased the LFL and therefore the flammable mixture was considered poorly hazardous. In practice, the variation of fermenter operating parameters to the final optimized protocol caused a continuous LFL growth, up to 29.3%, corresponding to a safer operation of fermentation reactor.