Untreated Food Waste Research Articles

Enhancing volatile fatty acid production from food waste by H2O2-moderate temperature thermal pretreatment: Treating waste with waste in coal mining areas

Supplementing carbon sources in sewage treatment plants with organic matter from food waste is crucial for resource recycling in coal mining areas. In this study, a moderate-temperature H2O2 method was used to pretreat food waste from a coal mining area. The changes in the properties of the pretreated food waste and their influence on volatile fatty acids (VFAs) production during anaerobic fermentation were investigated. Additionally, the nitrogen and phosphorus removal rates obtained when glucose and fermentation slurry of food waste (FSFW) were used as carbon sources in the sewage treatment system were compared. Compared with untreated food waste, the soluble chemical oxygen demand (SCOD) increased by 58 % after pretreatment with 0.25 % H2O2 at 60 ℃, and the viscosity and oil content decreased significantly, which caused VFAs production to increase from 15,267 mg COD/L to 50,774 mg COD/L. When the H2O2 concentration increased to 2.0 %, the SCOD increased to 153 %, and the viscosity and oil content further decreased, but the VFAs production decreased to 7477 mg COD/L. This occurred because large quantities of ammonia nitrogen was formed at higher H2O2 doses, which inhibited VFAs formation. Moreover, the nitrogen removal rate was higher when FSFW was used as a carbon source than when glucose was used as a carbon source.

ACIDIC-ENZYMATIC CO-TREATMENT OF FOOD WASTE FOR HIGH SUGAR RECOVERY AND BIOGAS PRODUCTION

Food-waste (FW) has a high content of fermentable sugar which can be exploited to generate an alternative source of fuel that could replace fossil fuels. Anaerobic digestion (AD) is an approach to convert organic-waste into high-value products like biomethane and hydrogen. However, hydrolysis is deemed to be a rate-limiting process in the AD process, limiting biogas production. This study seeks to improve the hydrolysis process through pre-treating FW with chemical and biological treatments. We show that the enzymatic treatment substantially improved the hydrolyzation and solubilization of food waste, resulting in a three folds increase in biogas production compared to untreated food waste. A co-treatment of biological and enzymatic treatments significantly improved the hydrolysis process, solids reduction, and solubilization of the substrate. The soluble chemical oxygen demand (SCOD) and reducing sugar were increased by 50% and 25% respectively, compared to enzymatically treated only. However, the inhibitory effect of accumulated salts from the treatment has limited the application of anaerobic digestion. Our results reveal that using enzymatic and acidic pre-treatment can significantly enhance hydrolysis of FW to increase biogas production, highlighting the potential of AD.

Hydrothermal pre-treatment of hospital food waste for efficient bio-methane generation

Municipal solid waste management (MWM) in Malaysia has become a challenging task in recent years due to the growth of population, industrialization and an increase in quantity and variation in the types of waste generated. Major solid waste generated in Malaysia is organic waste which includes mainly food waste from households, food processing facilities, markets, food and beverages industry and hospitals. Therefore, it is crucial to identify ways to manage food waste (FW) properly and improve the energy recovery efficiency. This paper is aimed to study the impact of pre-treatment on food waste from Hospital Pakar Sultanah Fatimah (HPSF) as a method to decompose FW faster and to determine the potential of bio-methane generation. A compositional study showed that total solid waste generated was 2,301 kg with 67% waste from lunch followed by 31% from breakfast sessions daily. Hydrothermal pre-treatment was done using a Multipurpose Recycling Machine (MRM) at 1.6MPa for 15 minutes followed by anaerobic digestion with and without the inoculum addition. Un-treated FW with inoculum was used as control in this experiment. It was found out that at a controlled pH of 7, hydrothermal pre-treatment and addition of inoculum i.e. cow manure played an important role in anaerobic digestion process for enhancement of bio-methane production. It significantly reduced the lag phase by 4 days and produced biogas faster compared to nontreated FW and hence, increased the biogas volume up to 638.53 mL compared to 504.08 mL in non-treated FW at the same experimental conditions. Therefore, this study signified that hydrothermal pretreatment is an effective and a beneficial technique added to the waste through the generation of biogas energy.

Porous biochars with nitrogen defects prepared from hydrogel template-modified food waste for high-performance supercapacitors

The complex composition and heterogeneous nature of food waste limit the application of biochar materials derived from it in supercapacitors. In this study, biochar was prepared from simulated food waste using a hydrogel template and employed to fabricate supercapacitor electrodes. Food waste was first transformed into a soluble state through an advanced oxidation process (potassium persulfate/heat). Small-molecule polymerization was then performed to generate a structurally uniform food waste hydrogel (FWH). Urea was added during the synthesis of FWH to achieve the uniform incorporation of nitrogen into its structure. FWH biochar (FWHB) was obtained from FWH via pyrolysis at different temperatures (500, 700, and 900 °C). Then, we evaluated the physicochemical properties and electrochemical performances of the obtained FWHB samples. The FWHB pyrolyzed at 700 °C (FWHB700) exhibited a unique sponge-like microstructure with a high specific surface area of 693 m2∙g−1, which was 20 times that of untreated food waste biochar. FWHB700 also showed excellent energy storage performance, with a specific capacitance of up to 461 F∙g−1 at a current density of 1 A∙g−1. Based on physicochemical analysis and density functional theory calculations, the energy storage capacity of FWHB700 was found to be related to its high specific surface area, developed pore structure, as well as abundant nitrogen defects and heteroatom active sites. The symmetric FWHB700//FWHB700 supercapacitor delivered a high energy density of 9.99 Wh∙kg−1 at a power density of 125 W∙kg−1, with 88.2 % capacitance retention after 10,000 charge–discharge cycles. In summary, this study introduces a promising electrode material for energy storage and provides a new approach for the efficient utilization of food waste resources.

Recovery of biogas from food waste using treated and untreated anaerobic digestion

Biogas is an environmentally friendly, clean, and low-cost renewable energy source. This alternate sustainable source can be used for heat, power, or fuel and making it a good alternative for renewable energy. Biogas can be produced through anaerobic digestion of biodegradable organic materials without oxygen and can be improved by performing thermal treatment. In this study, biogas was recovered using treated and untreated food waste. The characterisation of food waste for its suitability for an anaerobic digestion process was studied by its total solids, volatile solids, pH value, and C/N ratio, following the APHA standard. The anaerobic digestion was treated in a water bath at a temperature of 70 °C for 45 minutes. The Biochemical Methane Potential method was conducted to determine the biogas production from treated and untreated anaerobic digestion. The treated and untreated anaerobic digestion were anaerobically digested at a mesophilic temperature of 37 °C and at a speed of 100 rpm for 15 days. The biogas produced was measured daily by using water displacement method. The total production of biogas for treated anaerobic digestion was 198.70 mL, meanwhile for untreated anaerobic digestion was 185.50 mL. Treated anaerobic digestion showed a slightly higher production of biogas in 15 days by 13.2 mL. The biogas yield obtained for treated and untreated anaerobic digestion was 51.21 mL/g and 47.80 mL/g for every 1 g of total wet sample. This study found that thermal treatment of anaerobic digestion helps in the degradation of organic content in food waste for anaerobic digestion, which leads to higher biogas recovery.

Fungal solid-state fermentation of food waste for biohydrogen production by dark fermentation

The dark fermentation process was evaluated for biohydrogen production from food waste through fungal solid-state fermentation (SSF). Three fungal cultures (one strain of Aspergillus tubingensis and two strains of Meyerozyma caribbica) were compared, being A. tubingensis the best hydrolyser culture for releasing soluble carbohydrates. The biochemical hydrogen potential of food waste hydrolysate (FWH) at different substrate-inoculum ratios obtained a lower hydrogen yield than untreated food waste (RFW). The highest hydrogen yield value corresponded to treatments RFW-20 and RFW-30 with 77.0 ± 2.6 and 76.9 ± 1.4 mL H2 normalized by per gram volatile solid added (NmL H2/gVSadded), respectively. The microbial community of food waste was analysed, being detected lactic-acid bacteria genera as Latilactobacillus and Leuconostoc. The presence of actively growing bacteria during the SSF could explain the lowest hydrogen yield (20.1–36.0 NmL H2/gVSadded) in the FWH treatment due to the substrate competition between lactic-acid bacteria and hydrogen-producing bacteria, where the lactic-acid bacteria were favoured by their faster growth rate.

Food waste solution at home: conventional and rapid composting techniques

Food waste is a significant concern in waste management in recent years due to the inevitable outcome of human consumption in modern society. It has happened in almost every home daily. In Malaysia, 44.5% of organic waste (OW) consists of food waste (FW), this figure would increase with population growth. Therefore, without effective FW management, untreated FW dumping will cause environmental pollution, thus affecting human health as well as ecosystems. Conventional methods such as landfill and incineration have long been the most popular practice to address the FW issues, offering simple and cost-effective approach. Most of the time, these methods are not sustainable since they pose other environmental pollution such as greenhouse gas (GHG) emissions and leachate contamination leading to groundwater pollutions. Other issues with landfills are that self-composting at landfill site takes a long time and most landfills in Malaysia are almost at full capacity. The composting technique has recently gained more attraction as a cost-effective and sustainable method for the FW issue. This paper reviews techniques of composting food waste at home by using a conventional natural and rapid process. The performance of each technique in terms of cost, sustainability, user-friendly and time are measured in this review. Finally, the future direction of food waste solution by sustainable composting technique is briefly discussed in this paper.

Significance of Pretreatment in Enhancing the Performance of Dry Anaerobic Digestion of Food Waste: An Insight on Full Scale Implementation Strategy with Theoretical Analogy

The aim of this study was to treat food waste containing 25% total solids (TS) through dry anaerobic digestion (dry AD) process at various pressures (0.5 to 2.5 kg/cm2) and different time duration (20 to 100 min) to understand the impact of pretreatment in enhancing the methane generation potential along with insights on scale up. The findings revealed that vs. reduction and methane yield of 60% and 0.25 L CH4/(g VSadded) can be achieved with pretreated food waste at two kilograms per square centimeter, while pretreatment of food waste at 2 kg/cm2 for 100 min enhanced the vs. reduction from 60% to 85% and methane yield from 0.25 to 0.368 L CH4/(g VSadded). However, the net energy indicated that 40 min of pre -treatment at two kilograms per square centimeter can be a suitable option as methane yield and vs. reduction of 0.272 L CH4/(g VSadded) and 70%, respectively was achieved. The vs. reduction and the methane yield of 45% and 0.14 L CH4/(g VSadded), respectively was obtained from untreated food waste which illustrated that pretreatment had significantly impacted on the enhancement of methane generation and organic matter removal which can make the dry AD process more attractive and feasible at commercial scale.

Enhanced lactic acid production from food waste in dark fermentation with indigenous microbiota

This study investigated the effects of pH, total solids (TS) content, and enzymatic pretreatment on lactic acid (LA) production from food waste with indigenous microbiota. A multilevel factorial design was applied to all the essential factors for making LA production the most efficient and productive. The experimental data revealed that all the tested factors had a significant effect on the LA produced. The production of LA was progressively increased with the increase of TS content from 50 to 150 g-TS/L. With enzymatic pretreatment, the maximum production of volatile fatty acids (VFAs) and LA was, respectively, 26.17 g/L and 12.87 g/L at a pH of 6 and 150 g-TS/L. A LA yield of 0.09 g/g-TS with a productivity of 1.29 g/L day was achieved at mesophilic temperature of 37 °C and optimal operating conditions. Interestingly, the production of VFAs was 2.6-fold, and LA was 3-fold higher compared to those obtained with untreated food waste under same conditions. These results showed that enzymatically pretreated food waste at TS 15% can provide high production of VFAs and LA. The high selectivity of LA in the fermentative product, along with others, could make downstream processing economical. The multilevel factorial design predicted optimum conditions and presented a good agreement with a mean error of less than 5%.

Enhancing degradation and biogas production during anaerobic digestion of food waste using alkali pretreatment

Alkali pretreatment of anaerobic digestion (AD) was investigated as a strategy to degrade complex organic matter such as fats. AD of food waste (FW) with alkali pretreatment was conducted using batch assays and long-term experiments for 70 days in two reactors. The aim of this study was to compare the impact of alkali pretreatment on solubilization and biogas production and to evaluate the performance in reactors with that of the untreated FW. The alkali pretreatment enhanced the solubilization of organic matter. The best biogas yield (829 mL/g VS) and methane content (65.48%) were obtained by the pretreatment with 1% CaO with the highest Pi, n (66.06%) of biodegradable soluble materials. The long-term reactors with pretreatment performed more steadily with higher biogas production under organic loading rates (OLR) over 5 g VS/(L⋅d). The bacterial community structure was different under various conditions. Methanosaeta and Methanospirillum were the dominant archaea in this study, while Methanosaeta increased in R1 at OLR of 6 g VS/(L⋅d). The study concluded that alkali pretreatment with 1% CaO appeared as a potential strategy for AD of FW.

Mesophilic anaerobic digestion of food waste: Effect of thermal pretreatment on improvement of anaerobic digestion process

The treatment of food waste (FW) is an important challenge in developed and undeveloped countries due to the rapid disintegration of this waste. Hence biogas technology is used to produce energy and to reduce the volume of waste. This technology has disadvantages in terms of sensitivity to nutritional imbalance and low biodegradability. In this case, several pretreatments have been applied to improve biogas production such as thermal pretreatment (TP). This study investigated the effects of TP on physico-chemical properties and methane yield (MY) improvement. With the effect of temperature and time treatment, soluble COD was increased and reaching 68.54 ± 2,4 mg/L recorded at (100 °C, 30 min), which was 43. 41% higher than control. In contrast, TP decreased the percentage of VS compared to the raw FW. Furthermore, anaerobic digestion (AD) of FW pretreated at 100 °C during 30min was tested, the MY was (382.82 mLSTP CH4/ g VS) which 23.68 % higher than untreated food waste. Biodegradability was increased from 83.2 ± 3 % to 91.4 ± 4.1 % showing an increase of 9.8 %.

Klebsiella pneumoniae sp. LZU10 degrades oil in food waste and enhances methane production from co-digestion of food waste and straw

High content of lipid in food waste (FW) often causes inhibition on anaerobic digestion (AD) and methane production. To facilitate the transformation of oily FW to biogas, a bacterial strain Klebsiella pneumoniae sp. LZU10 (hereafter LZU10) which could degrade waste cooking oil to soluble chemical oxygen demand (sCOD) was isolated from restaurant FW-contaminated soil. The strain also demonstrated high resistance to heavy metals, whose level were found elevated in FW. Thus LZU10 was used to pretreat FW prior to anaerobic co-digestion (coAD) with straw. Results showed that after pretreatment by LZU10 the lipid content decreased from 59.6% to 39.5%, and sCOD increased by 25.03%. The methane production and methane recovery rate were increased by 41% and 58%, respectively, after pretreatment with LZU10, compared with those of untreated FW. The present study suggests that pretreatment of lipid-rich FW with lipolytic bacteria is a promising solution to reduce lipid inhibition and enhance methane production.

Characterisation of volatile organic compounds (VOCs) released by the composting of different waste matrices

The complaints arising from the problem of odorants released by composting plants may impede the construction of new composting facilities, preclude the proper activity of existing facilities or even lead to their closure, with negative implications for waste management and local economy. Improving the knowledge on VOC emissions from composting processes is of particular importance since different VOCs imply different odour impacts. To this purpose, three different organic matrices were studied in this work: dewatered sewage sludge (M1), digested organic fraction of municipal solid waste (M2) and untreated food waste (M3). The three matrices were aerobically biodegraded in a bench-scale bioreactor simulating composting conditions. A homemade device sampled the process air from each treatment at defined time intervals. The samples were analysed for VOC detection. The information on the concentrations of the detected VOCs was combined with the VOC-specific odour thresholds to estimate the relative weight of each biodegraded matrix in terms of odour impact. When the odour formation was at its maximum, the waste gas from the composting of M3 showed a total odour concentration about 60 and 15,000 times higher than those resulting from the composting of M1 and M2, respectively. Ethyl isovalerate showed the highest contribution to the total odour concentration (>99%). Terpenes (α-pinene, β-pinene, p-cymene and limonene) were abundantly present in M2 and M3, while sulphides (dimethyl sulphide and dimethyl disulphide) were the dominant components of M1.

Investigating hydrothermal pretreatment of food waste for two-stage fermentative hydrogen and methane co-production

The growing amount of food waste (FW) in China poses great pressure on the environment. Complex solid organics limit the hydrolysis of FW, hence impairing anaerobic digestion. This study employed hydrothermal pretreatment (HTP) to facilitate the solubilization of FW. When HTP temperature increased from 100 to 200°C, soluble carbohydrate content first increased to a peak at 140°C and then decreased, whereas total carbohydrate content was negatively correlated with increasing temperature due to the enhanced degradation and Maillard reactions. Protein solubilization was dramatically promoted after HTP, whereas protein degradation was negligibly enhanced. The hydrogen and methane yields from hydrothermally pretreated FW under the optimum condition (140°C, 20min) through two-stage fermentation were 43.0 and 511.6mL/g volatile solids, respectively, resulting in an energy conversion efficiency (ECE) of 78.6%. The ECE of pretreated FW was higher than that of untreated FW by 31.7%.

Mass Loss Controlled Thermal Pretreatment System to Assess the Effects of Pretreatment Temperature on Organic Matter Solubilization and Methane Yield from Food Waste

The effects of thermal pretreatment (TP) on the main characteristics of food waste (FW) and its biochemical methane potential (BMP) and distribution of volatile fatty acids (VFAs) under mesophilic condition (35 ⁰C) were investigated. The TP experiments were carried out at 80 °C, 100 °C, 120 °C for 2 hour and 140 °C for 1 hour. The designed TP set-up was able to minimize the organic matter loss during the course of the pretreatments. Soluble organic fractions evaluated in terms of chemical oxygen demand (COD) and soluble protein increased linearly with pretreatment temperature. In contrast, the carbohydrate solubilization was more enhanced (30 % higher solubilization) by the TP at lower temperature (80 °C). A slight increment of soluble phenols was found, particularly for temperatures exceeding 100 °C. Thermally pretreated FW under all conditions exhibited an improved methane yield than the untreated FW, due to the increased organic matter solubilization. The highest cumulative methane yield of 442 (± 8.6) mL/gVSadded, corresponding to a 28.1 % enhancement compared to the untreated FW, was obtained with a TP at 80 °C. No significant variation in the VFAs trends were observed during the BMP tests under all investigated conditions.

Effect on Ca(OH)2 pretreatment to enhance biogas production of organic food waste

This study investigated the effect of calcium hydroxide, Ca(OH)2 pretreatment in optimizing COD solubilisation and methane production through anaerobic digestion process. Two different parameters, chemical concentration (40-190 mEq/L) and pretreatment time (1-6 hours) were used to pretreat food waste. A central composite design and response surface methodology (RSM) was applied in obtaining the optimized condition for COD solubilisation. Result showed COD solubilisation was optimized at 166.98 mEq/L (equivalent to 6.1 g Ca(OH)2/L) for 1 hour. These conditions were applied through biomethane potential test with methane production of 864.19 mL/g VSdestructed and an increase of 20.0% as compared to untreated food waste.

Enhanced anaerobic digestion of food waste by thermal and ozonation pretreatment methods

Treatment of food waste by anaerobic digestion can lead to an energy production coupled to a reduction of the volume and greenhouse gas emissions from this waste type. According to EU Regulation EC1774/2002, food waste should be pasteurized/sterilized before or after anaerobic digestion. With respect to this regulation and also considering the slow kinetics of the anaerobic digestion process, thermal and chemical pretreatments of food waste prior to mesophilic anaerobic digestion were studied. A series of batch experiments to determine the biomethane potential of untreated as well as pretreated food waste was carried out. All tested conditions of both thermal and ozonation pretreatments resulted in an enhanced biomethane production. The kinetics of the anaerobic digestion process were, however, accelerated by thermal pretreatment at lower temperatures (<120 °C) only. The best result of 647.5 ± 10.6 mlCH4/gVS, which is approximately 52% higher as compared to the specific biomethane production of untreated food waste, was obtained with thermal pretreatment at 80 °C for 1.5 h. On the basis of net energy calculations, the enhanced biomethane production could cover the energy requirement of the thermal pretreatment. In contrast, the enhanced biomethane production with ozonation pretreatment is insufficient to supply the required energy for the ozonator.

Anaerobic digestion of autoclaved and untreated food waste

Anaerobic digestion of autoclaved (160°C, 6.2bar) and untreated source segregated food waste (FW) was compared over 473days in semi-continuously fed mesophilic reactors with trace elements supplementation, at organic loading rates (OLRs) of 2, 3, 4 and 6kg volatile solids(VS)/m3d. Methane yields at all OLR were 5–10% higher for untreated FW (maximum 0.483±0.013m3 CH4/kgVS at 3kgVS/m3d) than autoclaved FW (maximum 0.439±0.020m3 CH4/kgVS at 4kgVS/m3d). The residual methane potential of both digestates at all OLRs was less than 0.110m3 CH4/kgVS, indicating efficient methanation in all cases. Use of acclimated inoculum allowed very rapid increases in OLR. Reactors fed on autoclaved FW showed lower ammonium and hydrogen sulphide concentrations, probably due to reduced protein hydrolysis as a result of formation of Maillard compounds. In the current study this reduced biodegradability appears to outweigh any benefit due to thermal hydrolysis of ligno-cellulosic components.

Single and combined effect of various pretreatment methods for biohydrogen production from food waste

Four individual pretreatment methods: ultrasonication, heat, acid, and base and three combined pretreatment methods comprising ultrasonication with heat (UH), ultrasonication with acid (UA), and ultrasonication with base (UB) were applied on the food waste. The effect of the seven pretreatment methods on food waste solubilization was first evaluated, and then batch experiments were conducted for biohydrogen production without using extra seed. UB pretreatment achieved the highest increase in soluble chemical oxygen demand (SCOD) and soluble protein of 33% and 40%, respectively. The highest increase in soluble carbohydrate of 31% was observed for UA pretreatment. Among the four individual pretreatment methods, ultrasonic pretreatment produced the highest hydrogen yield (as mL hydrogen per g initial volatile solid) of 97 mL/g VS initial, while the lowest hydrogen yield of 46 mL/g VS initial was observed for base pretreatment. In case of combined pretreatment methods, UA pretreatment had a positive effect on hydrogen production reflected by the highest hydrogen yield of 118 mL/g VS initial. While UH and UB pretreatments had a negative impact on hydrogen yield reducing it from 97 mL/g VS initial for ultrasonic only to 78 mL/g VS initial for UH pretreatment and to 67 mL/g VS initial for UB pretreatment. A hydrogen yield of 42 mL/g VS initial was observed for the untreated food waste. UA had the highest final volatile fatty acids (VFAs) concentrations of 16,900 mg COD/L as well as highest acetate to butyrate (HAc/HBu) molar ratio of 1.87, while base pretreatment had the lowest final VFAs of 9700 mg COD/L and the lowest HAc/HBu ratio of 0.61.

Hydrogen fermentation of food waste without inoculum addition

A novel batch process that produces H 2 without inoculum addition was devised based on two facts: (1) the abundant indigenous microflora found within organic solid wastes and (2) batch H 2 production completion times being in the same range with hydraulic retention times at continuous processes. Food waste successfully served not only as a substrate but also as a source of H 2-producing microflora when heat (90 °C for 20 min), acid (pH 1.0 for 1 d), or alkali (pH 13.0 for 1 d) treatment was applied. Among the three pretreatments, the heat treatment showed the best performance. The role of the pretreatment was the selection of microbial population rather than the enhancement of hydrolysis. Polymerase chain reaction-denaturing gradient gel electrophoresis analysis showed that lactic acid bacteria were the most abundant species in untreated food waste while H 2-producing bacteria were dominant in the pretreated food wastes. The increase of pretreatment temperature depressed the lactate production while increased the H 2/butyrate production. Repeated batch operation performances were impressive and reliable, achieving a very high H 2 yield of 2.05 mol H 2/mol hexose consumed with a margin of 17% error. As this invented method is simpler than those of existing continuous systems, and does not require a start-up period, this method is thought to be practically applicable.