Pretreated Food Waste Research Articles

Sustainable Extraction of Micronutrient of Food Waste by Thermal Treatment under Elevating Temperature

Food waste management by biological treatment is widely used due to the eco-friendly and more attractive than physical and chemical treatment. However, the use of biological treatment takes longer time for the food waste to degrade. To overcome this problem the pretreatment of food waste is proposed. The aim of this study is to determine the characteristic of food waste when subject to pretreatment, to determine the effect of thermal pretreatment on chemical compositions of food waste, and to determine the relationship between the effect of temperature and time on food waste carbon to nitrogen ratio, pH and micronutrient by using statistical analysis. The water bath method was carried out in this experiment. The parameter measured were Carbon to Nitrogen ratio (C;N), pH and micronutrient with the effect of temperature and time. The result of the food waste before treatment and after pretreatment was compare. The laboratory results showed that the chemical composition of the food waste was affected by the thermal pretreatment of water bath method for C:N and pH which in the range 11.18 to 25.94 and 5.32 to 5.72 respectively. The statistical analysis indicates that the interaction effect between retention time and temperature was not significant for pH, Fe, Cu and Mn except for C:N (F = 4.394, P = 0.003). Overall, the thermal pretreatment applied on the food waste revealed that temperature below 100 °C did not suitable to use as a pretreatment before the biological treatment, in order to expedite the degradation process. Instead, high temperature which above 100°C and long heating duration are beneficial for the release and reduction of organic compounds.

Optimization of urban waste fermentation for volatile fatty acids production

The problem of waste disposal has recently focused on practices for waste recycling and bio-resources valorization. Organic waste produced in urban context together with biological sludge produced in wastewater treatment plants (WWTPs) can be used as renewable feedstock for the production of building blocks of different products, from biopolymers to methyl esters. This paper deals with the optimization of the fermentation process in order to transform urban organic waste (a mixture of pre-treated food waste and biological sludge) into added-value volatile fatty acid (VFA) rich stream, useful for biological processes within a biorefinery technology chain. Different temperatures, pH, hydraulic retention times (HRTs) and organic loading rates (OLRs) were tested both in batch and continuous trials. Batch tests showed the best working conditions at 37 °C and pH 9, using the bio-waste feedstock thermally pre-treated (76 h at 72 °C). These conditions were applied in continuous process, where higher HRT (6.0 d) and lower OLR [7.7 kg VS/(m3 d)] gave the best performances in terms of process yield and maximum VFA level achieved: 0.77 CODVFA/VS(0) and 39 g CODVFA/L. An optimized fermentation process is crucial in a biorefinery perspective since it has to give a final stream of constant composition or tailored products suitable for further applications.

Ultrasonic pretreatment of food waste to accelerate enzymatic hydrolysis for glucose production

Recovering valuable materials from food waste by applying the concept of a bio-refinery is attracting considerable interest. To this effect, we investigated the possibility of enhancing the enzymatic hydrolysis of food waste using ultrasonic technology. The effect of pre-treating blended food waste with high-intensity ultrasound (20 kHz) on subsequent hydrolysis by glucoamylase was investigated as a function of sonication time and temperature. Particle sizing by laser diffraction, and imaging via scanning electronic microscopy showed that ultrasonic pre-treatment could reduce the particle size of the blended food waste significantly, resulting in a better interaction with the enzyme. As a consequence, the glucose yield of enzymatic hydrolysis was ∼10% higher for food waste pre-sonicated using the most intensive ultrasonication conditions studied (5 min sonication at a power of 0.8 W/mL at 20 °C) than for the untreated control. In addition, the time required to achieve high yields of glucose could be more than halved using ultrasonic pre-treatment. This could enable the hydrolysis reactor size or the enzyme usage to be reduced by more than 50%. Therefore, an ultrasound-assisted bioconversion process from food waste into a value-added product has been demonstrated.

Biochemical and microbial changes reveal how aerobic pre-treatment impacts anaerobic biodegradability of food waste

Aerobic pre-treatment of food waste (FW) was performed at different oxygen concentrations (0%, 5%, 10% and 21%O2) and different durations (1, 2, 3 and 4 days) to investigate its impact on biochemical and microbial community characteristics of the waste and its ability to improve anaerobic biodegradability. Whatever the duration, the highest effect of pre-treatment was observed at full aerobic pre-treatment (21%O2) while 5%O2 and 10%O2 showed lower transformation performances. Biochemical variations at 21%O2 were mainly a decrease of simple carbohydrates, volatile fatty acids (VFA) and low molecular weight water soluble compounds and an increase of high weight water soluble compounds. Microbial community analysis showed a clear modification of populations after 21%O2 aerobic pre-treatment, changing from an initial dominance of lactic acid bacteria to a final dominance of VFA consumers (like Acetobacter) and a higher presence of Fungi. Enzymatic tests showed an increase of exoenzymes content and a higher presence of protein and carbohydrates degrading enzymes. Finally, the aerobic pre-treatment did not negatively impact methane potential of FW (496 NLCH4·kgVS−1) which remained unchanged after two days of pre-treatment at 21%O2. These latter optimal pre-treatment conditions are proposed to be tested in future investigation of anaerobic digestion (AD) process with low inoculum to substrate ratio in order to assess their ability to avoid acidification risk during AD of FW.

Dry anaerobic co-digestion of food waste and cattle manure: Impact of total solids, substrate ratio and thermal pre treatment on methane yield and quality of biomanure

The objective of the present study is to assess the impact of TS concentration, substrate mixing ratio (co digestion) and thermal pretreatment on biogas production, methane yield, VS reduction (%) and quality of biomanure through dry anaerobic digestion (DAD) of food waste (FW) and cattle manure (CM). Results divulged that the optimum methane yield and biomanure of 0.18 and 0.21 m3 CH4/(kg VS reduced) and 3.15 and 2.8 kg/kg waste was obtained from FW at TS of 25% and 30% at an HRT of 41 and 31 days respectively whereas it was 0.32 and 0.43 m3 CH4/(kg VS reduced) and 2.2 and 1.15 kg/kg waste from pretreated FW at an HRT of 16 and 20 days correspondingly. Improvement of methane from 62 to 81% was obtained due to thermal pretreatment. The highest nutrient recovery in terms of N, P, K was found to be 5.14, 2.6 and 3.2 respectively.

Production of lactic acid from thermal pretreated food waste through the fermentation of waste activated sludge: Effects of substrate and thermal pretreatment temperature

Valorization of organic-rich waste stream to lactic acid by the mixed microbial consortium has attracted tremendous research interests in recent years. In this study, thermal pretreatment was involved in co-fermentation of food waste (FW) and waste activated sludge (WAS) to enhance lactic acid production. First, sole FW was observed as the most suitable substrate employing thermal pretreatment for the generation of lactic acid. The fermentation time for reaching the maximal plateau was significantly shortened at a corresponding thermal pretreatment temperature. The mechanism study found that the enhancement of lactic acid yield was in accordance with the acceleration of solubilization and hydrolysis. Furthermore, the physicochemical characteristics of fermentative substrate and surface morphology of the fermentation mixture varied with the pretreatment temperatures. Further investigations of microbial community structure also revealed that the proportions of key microorganisms such as Bacillus and Lactobacillus were changed by the thermal pretreatment.

Ethanol Production from Acid Pretreated Food Waste Hydrolysate Using Saccharomyces cerevisiae 74D694 and Optimizing the Process Using Response Surface Methodology

Ethanol production from acid pretreated food waste hydrolysate using immobilized Saccharomyces cerevisiae 74D694 was investigated under different conditions in a batch experiment. Ethanol yield was measured at different time intervals (38, 48, 72, 96 and 105 h) using different immobilized bead ratios (25:100, 30:100, 40:100, 50:100 and 54:100, w/v). Food waste was pretreated using dilute sulphuric acid and the hydrolysate was filtered. The dry food waste had an initial reducing sugar content of 46% (w/w). After dilute acid pretreatment, reducing sugar content increased to 62%. The present study utilized liquid hydrolysate for ethanol production. The process was optimized using central composite design (CCD) a statistical tool used for optimization in response surface methodology (RSM). RSM predicted a maximum ethanol yield of 0.044 g/g of soluble solid in liquid hydrolysate at 40 h fermentation time and immobilized bead ratio of 54:100 (w/v). An experiment was run at the optimal condition and an ethanol yield of 0.047 g/g of soluble solid in liquid hydrolysate was obtained. The predicted result was thus experimentally verified.

Energy and exergy optimization of food waste pretreatment and incineration.

With the aim of upgrading current food waste (FW) management strategy, a novel FW hydrothermal pretreatment and air-drying incineration system is proposed and optimized from an energy and exergy perspective. Parameters considered include the extracted steam quality, the final moisture content of dehydrated FW, and the reactor thermal efficiency. Results show that optimal working condition can be obtained when the temperature and pressure of extracted steam are 159°C and 0.17MPa, the final moisture content of dehydrated FW is 10%, and the reactor thermal efficiency is 90%. Under such circumstance, the optimal steam energy and exergy increments reach 194.92 and 324.50kJ/kg-FW, respectively. The novel system is then applied under the local conditions of Hangzhou, China. Results show that approximately 2.7 or 11.6% (from energy or exergy analysis perspective) of electricity can be additionally generated from 1ton of MSW if the proposed novel FW system is implemented. Besides, comparisons between energy and exergy analysis are also discussed.

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%.

Pretreatment of food waste with high voltage pulse discharge towards methane production enhancement

Anaerobic batch tests were performed to investigate the methane production enhancement and solid transformation rates from food waste (FW) by high voltage pulse discharge (HVPD) pretreatment. The total cumulative methane production with HVPD pretreatment was 134% higher than that of the control. The final volatile solids transformation rates of FW with and without HVPD pretreatment were 54.3% and 32.3%, respectively. Comparison study on HVPD pretreatment with acid, alkali and ultrasonic pretreatments showed that the methane production and COD removal rates of FW pretreated with HVPD were more than 100% higher than the control, but only about 50% higher can be obtained with other pretreatments. HVPD pretreatment could be a promising pretreatment method in the application of energy recovery from FW.

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.

Lifecycle assessment of a system for food waste disposers to tank – A full-scale system evaluation

An increased interest for separate collection of household food waste in Sweden has led to development of a number of different collection-systems – each with their particular benefits and drawbacks. In the present study, two systems for collection of food waste in households were compared; (a) use of food waste disposers (FWD) in kitchen sinks and (b) collection of food waste in paper bags for further treatment. The comparison was made in relation to greenhouse gas emissions as well as primary energy utilization. In both cases, collected food waste was treated through anaerobic digestion and digestate was used as fertilizer on farmland. Systems emissions of greenhouse gases from collection and treatment of 1ton of food waste (dry matter), are according to the performed assessment lower from the FWD-system compared to the reference system (−990 and −770kgCO2-eq./ton food waste dry matter respectively). The main reasons are a higher substitution of mineral nitrogen fertilizer followed by a higher substitution of diesel. Performed uncertainty analyses state that results are robust, but that decreasing losses of organic matter in pre-treatment of food waste collected in paper bags, as well as increased losses of organic matter and nutrients from the FWD-system could change the hierarchy in relation to greenhouse gas emissions. Owing to a higher use of electricity in the FWD-system, the paper bag collection system was preferable in relation to primary energy utilization. Due to the many questions still remaining regarding the impacts of an increased amount of nutrients and organic matter to the sewage system through an increased use of FWD, the later treatment of effluent from the FWD-system, as well as treatment of wastewater from kitchen sinks in the reference system, was not included in the assessment. In future work, these aspects would be of relevance to monitor.

음폐수 산발효 조건에 따른 바이오가스 생산량에 관한 연구

This study performed acid fermentation pre-treatment to improve production efficiency of methane that is produced as a product in case of anaerobic fermentation by using food waste leachate, and attempted to confirm the acid fermentation optimum through the BMP test by using pre-treated food waste leachate to increase the yield of methane. As a result of the BMP experiment by using acid fermented food waste leachate, the highest yield of methane of 0.220 L/g VS was confirmed in the HRT three-day condition, and in the initial BMP test by pH, pH 6 was 19,920 mg/L that the highest VFA and acetic acid/TVFA(76.2%) were shown. At this time, it was confirmed that the yield of methane was mostly within 10 days that was reduced to around one-third compared to the general methane fermentation (within 30 days). As the yield of methane was 0.294 L/g VS, it showed a high efficiency of around 1.3 times compared to the control group.

Importance of food waste pre-treatment efficiency for global warming potential in life cycle assessment of anaerobic digestion systems

A need for improvement of food waste (FW) pre-treatment methods has been recognized, but few life cycle assessments (LCA) of FW management systems have considered the pre-treatment with respect to input energy, loss of organic material and nutrients for anaerobic digestion (AD) and/or further treatment of the refuse. The objective of this study was to investigate how FW pre-treatment efficiency impacts the environmental performance of waste management, with respect to global warming potential (GWP). The modeling tool EASETECH was used to perform consequential LCA focusing on the impact of changes in mass distribution within framework conditions that were varied with respect to biogas utilization and energy system, representing different geographical regions and/or different time-frames. The variations of the GWP due to changes in pre-treatment efficiency were generally small, especially when biogas and refuse were substituting the same energy carriers, when energy conversion efficiencies were high and slurry quality good enough to enable digestate use on land. In these cases other environmental aspects, economy and practicality could be guiding when selecting pre-treatment system without large risk of sub-optimization with regards to GWP. However, the methane potential of the slurry is important for the net LCA results and must be included in the sensitivity analysis. Furthermore, when biogas is used as vehicle fuel the importance of pre-treatment is sensitive to assumptions and approach of modelling marginal energy which must be decided based on the focus and timeframe of the study in question.

Effect of Oil Content on Dry Anaerobic Digestion of Food Waste under Mesophilic Conditions

The variations of daily biogas yields, cumulative biogas yields, biogas composition analysis, total solids (TS) and volatile solids (VS) were studied in the process of mesophilic and dry anaerobic digestion of food waste under different oil contents (0%, 2%, 4%, 6%, 8%, 10%) at 35 °C. The gas production raised and then went down with the oil content, followed by 243.14, 245.64, 256.09, 269.25, 276.54, 284.22mL /g TS respectively. The research provided a reference for the pretreatment of food waste in follow-up continuous fermentation. Results showed that the period of the process of mesophilic dry anaerobic digestion under oil content of 0% was the shortest, with the total biogas production of 1275.5mL. During the process of the digestion, methane content of the biogas raised and then went down, up to a maximum of 77.62%. The removal rate of TS and VS in food waste with the oil content of 6% was the highest, obtained as 11.2% and 13.2%, respectively.

Aerobic decomposition of food waste with different ratios of solids at ambient temperatures and evaluation of CO2 emissions

The aim of this study was to investigate the recycling of organic matter in the food waste by degrading aerobically and evaluation of the CO2 emissions. With this aim, food waste with the content of 5–7–10 % TS was degraded aerobically. The pH in all the reactors was observed within the range of 6.5–7. The highest CO2 production rate was obtained from 5 % TS. Removal was achieved at the rates of 5 % TS and 57 % in COD and TOC. CO2 production rate was calculated as 38.53 g CO2/h/kg TOCw. Moreover, CO2 production potential of the food waste was identified. A batch, single-stage reactor was used to determine the food waste pre-treatment. Finally, food waste in landfill areas was recycled and evaluated by without taking.

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.

Effect of acid-pretreatment on hydrogen fermentation of food waste: Microbial community analysis by next generation sequencing

This work presents the effect of acid-pretreatment on H2 fermentation of food waste with detailed microbial information by next generation sequencing. The pretreated food waste at pH 1.0–4.0 was cultivated under mesophilic conditions without external inoculum addition. From the food waste acid-pretreated at pH 1–3, H2 yields in the range of 1.37–1.74 mol H2/mol hexoseadded were achieved, attaining the highest value at pH 2. Clostridium sp. such as Clostridium acetobutylicum ATCC 824 and Clostridium perfringens occupied more than 70% of total number of sequences at pH 1–3. On the other hand, in the control (no pretreatment) and at pH 4, lactic acid bacteria such as Lactobacillus and Streptococcus were found to be the dominant genus (>90% of total number of sequences), resulting in a low H2 yield. In addition, the effect of substrate concentration on H2 fermentation was investigated, and the maximum H2 productivity was estimated to be 27.2 L H2/L/d by Andrew's model.

Improving production of volatile fatty acids from food waste fermentation by hydrothermal pretreatment

Food waste (FW) was pretreated by a hydrothermal method and then fermented for volatile fatty acid (VFAs) production. The soluble substance in FW increased after hydrothermal pretreatment (⩽200°C). Higher hydrothermal temperature would lead to mineralization of the organic compounds. The optimal temperature for organic dissolution was 180°C, at which FW dissolved 42.5% more soluble chemical oxygen demand than the control. VFA production from pretreated FW fermentation was significantly enhanced compared with the control. The optimal hydrothermal temperature was 160°C with a VFA yield of 0.908g/g VSremoval. Butyrate and acetate were the prevalent VFAs followed by propionate and valerate. FW fermentation was inhibited after 200°C pretreatment. The VFAs were extracted from the fermentation broth by liquid–liquid extraction. The VFA recovery was 50–70%. Thus, 0.294–0.411g VFAs could be obtained per gram of hydrothermally pretreated FW (in dry weight) by this method.

Evaluation of hydrogen producing cultures using pretreated food waste

In order to enhance bio-hydrogen production from food waste, pretreatment methods are widely used. The influence of the initial pH and autoclaving were investigated in batch experiments. Fermentative studies showed that pure cultures like Clostridium beijerinckii could directly utilize raw food waste to produce hydrogen, while other cultures (Clostridium butyricum and Clostridium pasteurianum) could produce hydrogen only after pH adjustment. In this case, the optimal starting pH of the culture was found to be 7. Autoclaving could further enhance hydrogen yields due to increased hydrolysis of food waste. The maximum hydrogen yield was achieved by C. butyricum (38.9 mL-H2/g-VSadded) after autoclaving food waste with pH adjustment at 7. In addition, the ratio acetic to butyric acid was decreased by autoclaving pretreatment, because butyrate metabolic pathway was favored in the fermentation process. However, suitable pH for bacteria growth and the low ammonia production could be achieved from autoclaving food waste.