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

Sustainable management of food waste; pre-treatment strategies, techno-economic assessment, bibliometric analysis, and potential utilizations: A systematic review

Food waste (FW) contains many nutritional components such as proteins, lipids, fats, polysaccharides, carbohydrates, and metal ions, which can be reused in some processes to produce value-added products. Furthermore, FW can be converted into biogas, biohydrogen, and biodiesel, and this type of green energy can be used as an alternative to nonrenewable fuel and reduce reliance on fossil fuel sources. It has been demonstrated in many reports that at the laboratory scale production of biochemicals using FW is as good as pure carbon sources. The goal of this paper is to review approaches used globally to promote turning FW into useable products and green energy. In this context, the present review article highlights deeply in a transdisciplinary manner the sources, types, impacts, characteristics, pre-treatment strategies, and potential management of FW into value-added products. We find that FW could be upcycled into different valuable products such as eco-friendly green fuels, organic acids, bioplastics, enzymes, fertilizers, char, and single-cell protein, after the suitable pre-treatment method. The results confirmed the technical feasibility of all the reviewed transformation processes of FW. Furthermore, life cycle and techno-economic assessment studies regarding the socio-economic, environmental, and engineering aspects of FW management are discussed. The reviewed articles showed that energy recovery from FW in various forms is economically feasible.

Cross-Comparison of the Impact of Grass Silage Pulsed Electric Field and Microwave-Induced Disintegration on Biogas Production Efficiency

Lignocellulosic biomass is included in the group of renewable energy sources. Its calorific value is high, owing to which it can be successfully used in the production of second-generation fuels, e.g., biogas. However, its complex structure makes it necessary to apply a pretreatment in order to increase the biogas output. This study presents the usability of a pulsed electric field in grass silage pretreatment in methane fermentation and compares it with microwave-induced disintegration. The experiment shows that substrate disintegration with a pulsed electric field (PEF) results in an increase in methane output. The productivity of methane from PEF pretreatment silage increased by 20.1% compared to the untreated control. The application of microwave disintegration, with the assumption that the same energy is used for the pretreatment, resulted in a methane output increase of 6% compared to the control. The highest biogas production output in PEF-pretreated samples was 535.57 NL/kg VS, while the highest biogas output from substrates pretreated with microwaves was 487.18 NL/kg VS.

Disintegration of sewage sludge using pulsed electrical field technique: PEF optimization, simulation, and anaerobic digestion

A Pulsed Electrical Field (PEF) reactor was developed to process biological sludge as a pretreatment method prior to anaerobic digestion. This study focuses on the effects of operational parameters such as applied voltage, pH, conductivity, flow-rate, and temperature affecting the treatment of waste active sludge (WAS) by PEF, the simulation of reactor process conditions and anaerobic biodegradation of PEF pretreated sludge. The effects of the sludge conductivity, flow-rate, and temperature on the Soluble Chemical Oxygen Demand (SCOD) of WAS treated by PEF reactor were investigated by using a Box-Wilson statistical experiment design. Simulations of the PEF process conditions were performed to verify experimental results. After PEF optimization study, the PEF operational conditions for maximum SCOD were obtained at 4 mS/cm conductivity, 5 mL/min flow-rate, and 40 °C temperature during PEF treatment. The measured and predicted SCOD showed a good consistency (R²= 0.92). After it was pretreated by the PEF, the SCOD, total nitrogen, total phosphorus, polysaccharide and protein contents of WAS increased. However filterability property also decreased. In the anaerobic digestion study, the reactor fed with the PEF pretreated WAS provided 1.70 times higher methane production compared with raw sludge. In addition to this situation, 18% and 19% improvements, respectively, were observed in SCOD and VSS reductions when it was compared with raw sludge in the 23 days of anaerobic operation. Sixteen percent decrease in CST showed that the PEF enhanced the filterability of WAS during the anaerobic stabilization.

Increasing the Biogas Potential of Rapeseed Straw Using Pulsed Electric Field Pre-Treatment

Due to the high availability of lignocellulosic biomass, which can be obtained from terrestrial plants, agricultural waste biomass, and the agro-food, paper or wood industries, its use for energy production by methane fermentation is economically and environmentally justified. However, due to their complex structures, lignocellulosic substrates have a low conversion factor to biogas. Therefore, scientists are still working on the development of new methods of the pre-treatment of lignocellulosic materials that will increase the biogas productivity from lignocellulosic biomass. The presented research focuses on the use of a pulsed electric field (PEF) to disintegrate rapeseed straw prior to the methane fermentation process. Scanning electron microscopy observation showed that, in the disintegrated sample, the extent of damage to the plant tissue was more severe than in the control sample. In the sample disintegrated for 7 min, the chemical oxygen demand increased from 4146 ± 75 mg/L to 4920 ± 60 mg/L. The best result was achieved with a 5-min PEF pre-treatment. The methane production reached 290.8 ± 12.1 NmL CH4/g VS, and the biogas production was 478.0 ± 27.5 NmL/g VS; it was 14% and 15% higher, respectively, compared to the control sample.

Inhibition of N-Vanillylnonanamide in anaerobic digestion of lipids in food waste: Microorganisms damage and blocked electron transfer

To study the inhibited degradation metabolism and anaerobic digestion of typical lipids in food waste, an artificially produced capsaicin, N-Vanillylnonanamide, a typical soluble component in waste lipids, was added to a glycerol trioleate anaerobic digestion system. The microorganisms damage and blocked electron transfer caused by N-Vanillylnonanamide during anaerobic digestion were further clarified. Scanning electron microscopy and transmission electron microscopy images demonstrated that N-Vanillylnonanamide (≥4 wt%) structurally damaged microorganisms via cell membrane breakage, which impair their function. N-Vanillylnonanamide inhibited the activities of the key enzyme CoA, AK, F₄₂₀, and CoM, which are relevant for both degradation metabolism and anaerobic digestion. 16S rRNA analysis showed that dominant bacterial and archaeal communities markedly decreased after anaerobic digestion of glycerol trioleate with N-Vanillylnonanamide (≥4 wt%). For example, the proportion of Methanosarcina decreased from 30 % to 6 %. Current-voltage curves indicated that the electron transfer rate in the community of microorganisms decreased by 99 % from 4.67 × 10^-2 to 5.66 × 10^-4 s^-1 in response to N-Vanillylnonanamide (40 wt%). The methane yield during anaerobic digestion of glycerol trioleate decreased by 84.0 % from 780.21-142.10 mL/g-total volatile solids with N-Vanillylnonanamide (40 wt%).

Using an expended granular sludge bed reactor for advanced anaerobic digestion of food waste pretreated with enzyme: The feasibility and its performance

The high content of solid organics in food waste (FW) results in a low and unstable anaerobic digestion (AD) efficiency. Improving methane production rate and process stability is attracting much attention towards advanced AD of FW. The feasibility of advanced AD of FW pretreated with enzyme was investigated by batch experiments and 164 days running of an expanded granular sludge bed (EGSB) reactor. Simulation study based on the results of batch experiments indicates it is possible to treat enzymatically pretreated FW using an EGSB reactor. During the running of an EGSB reactor, the organic loading rate went up to 20 g chemical oxygen demand (COD)/L.d, and the total COD removal rate reached 88%. The significance of this study is to achieve an advanced AD of enzymatically pretreated FW with a stable and efficient methane production with biogas residue being reduced greatly.

Insight into Pretreatment Methods of Lignocellulosic Biomass to Increase Biogas Yield: Current State, Challenges, and Opportunities

Lignocellulosic biomass is recalcitrant due to its heterogeneous structure, which is one of the major limitations for its use as a feedstock for methane production. Although different pretreatment methods are being used, intermediaries formed are known to show adverse effect on microorganisms involved in methane formation. This review, apart from highlighting the efficiency and limitations of the different pretreatment methods from engineering, chemical, and biochemical point of views, will discuss the strategies to increase the carbon recovery in the form of methane by way of amending pretreatments to lower inhibitory effects on microbial groups and by optimizing process conditions.

Co-digestion of food waste and sewage sludge for methane production: Current status and perspective

Food waste (FW) is a valuable resource which requires sustainable management avenues to reduce the hazardous environmental impacts and add-value for better economy. Anaerobic digestion (AD) is still reliable, cost-effective technology for waste management. Conventional AD was originally designed for sewer sludge digestion, is not effective for FW due to mainly high organics and volatile fatty acid (VFA) accumulation, hence better technical aptitudes and biochemical inputs are required for optimal biogas production. Besides, to overcome these challenges, FW co-digestion with complementary organic waste e.g. sewage sludge (SS) mixed which complement each other for better process design. The main aim of this article is to summarize the recent updates and review different holistic approaches for efficient anaerobic co-digestion (AcoD) of FW and SS to provide a comprehensive review on the topic. Moreover, to demonstrate the status and perspectives of AcoD at present scenario for Hong Kong and rest of the world.

Pretreatment of food waste for methane and hydrogen recovery: A review

Food waste (FW) management by biological process is more attractive and eco-friendly approach than thermo-chemical conversion or landfilling. However, FW composition and physico-chemical and biological characteristics affect the overall biological process in terms of product yield and degradation rate. To overcome this major bottle-neck, the pretreatment of FW is proposed. Therefore this review aims to provide a comprehensive summary of the importance of pretreatment of FW with respect to FW management by anaerobic digestion (AD) and dark fermentation (DF). It also reviews the existing knowledge gaps and future research perspectives for better integration of FW pretreatments for AD and DF, which should include (i) the preservation of carbon mass through freeze and thaw, or drying; and (ii) improve the carbon accessibility through particle size reduction and thermal pretreatments for high-rate bioenergy recovery.

Food loss and waste management in Turkey

Food waste can be an environmental and economic problem if not managed properly but it can meet various demands of a country if it is considered as a resource. The purpose of this report is to review the existing state of the field in Turkey and identify the potential of food waste as a resource. Food loss and waste (FLW) was examined throughout the food supply chain (FSC) and quantified using the FAO model. Edible FLW was estimated to be approximately 26milliontons/year. The amount of biodegradable waste was estimated based on waste statistics and research conducted on household food waste in Turkey. The total amount of biodegradable waste was found to be approximately 20milliontons/year, where more than 8.6milliontons/year of this waste is FLW from distribution and consumption in the FSC. Options for the end-of-life management of biodegradable wastes are also discussed in this review article.