Methane production from food waste leachate in laboratory-scale simulated landfill

Due to the prohibition of food waste landfilling in Korea from 2005 and the subsequent ban on the marine disposal of organic sludge, including leachate generated from food waste recycling facilities from 2012, it is urgent to develop an innovative and sustainable disposal strategy that is eco-friendly, yet economically beneficial. In this study, methane production from food waste leachate (FWL) in landfill sites with landfill gas recovery facilities was evaluated in simulated landfill reactors (lysimeters) for a period of 90 d with four different inoculum–substrate ratios (ISRs) on volatile solid (VS) basis. Simultaneous biochemical methane potential batch experiments were also conducted at the same ISRs for 30 d to compare CH₄ yield obtained from lysimeter studies. Under the experimental conditions, a maximum CH₄ yield of 0.272 and 0.294 L/g VS was obtained in the batch and lysimeter studies, respectively, at ISR of 1:1. The biodegradability of FWL in batch and lysimeter experiments at ISR of 1:1 was 64% and 69%, respectively. The calculated data using the modified Gompertz equation for the cumulative CH₄ production showed good agreement with the experimental result obtained from lysimeter study. Based on the results obtained from this study, field-scale pilot test is required to re-evaluate the existing sanitary landfills with efficient leachate collection and gas recovery facilities as engineered bioreactors to treat non-hazardous liquid organic wastes for energy recovery with optimum utilization of facilities.     

Potential methane yield of food waste/food waste leachate from the biogasification facilities in South Korea

This study was to find out potential of methane yield on food waste and food waste leachate as biomass in Korea. The seven biogasification facilities were selected for comparison of theoretical methane yield and actual methane yield. The theoretical methane yield was calculated based on organic constituents (carbohydrate, protein, fat) and based on element analysis. The actual methane yield was investigated based on volatile solids and CODcr. Theoretical methane yields by organic constituents were 0.52 Sm³CH₄/kg VS and 0.35 Sm³CH₄/kg CODcr and these by element analysis were 0.53 Sm³CH₄/kg VS and 0.36 Sm³CH₄/kg CODcr. Actual methane yields were 0.36 Sm³CH₄/kg VS_in and 0.26 Sm³CH₄/kg CODcr_in. Considering the average removal efficiency of organic materials of seven FWL biogasification facilities, actual methane yields were 0.48 Sm³CH₄/kg VS_rem and 0.33 Sm³CH₄/kg CODcr_rem. Methane yield by organic constituents is very similar to that by element analysis and actual methane yields of volatile solids and CODcr were similar to theoretical value. The actual methane yield in this study showed approximated boundary values with previous other references which conducted in lab-scale or biochemical methane potential (BMP) tests. In conclusion, Korean food waste and food waste leachate have sufficient potential of methane yield in the ongoing biogasification facilities.     

Anaerobic digestion of food waste: comparing leachate exchange rates in sequential batch systems digesting food waste and biosolids

Over 35,000 tonnes of food waste are generated from high concentration point sources (i.e., restaurants, hospitals and markets) in metropolitan Adelaide (Australia) each year. Anaerobic digestion is a preferred method of treatment to degrade highly putrescible waste streams such as food waste due its high methane potential. To maximise methane yield, a sequential batch anaerobic system was chosen as the most appropriate system. Two sets of sequential batch systems consisting of mature and start-up reactors in triplicate exchanged leachate. One set exchanged twice as much leachate by volume as the other set to determine the effects of different leachate exchange volumes. Results show that by increasing the leachate volume between mature and start-up reactors, the time to degrade feedstock decreases, but total methane generation yields did not markedly differ, being 229LCH4 kg(-1) VSadded and 214LCH4 kg(-1) VSadded. Process parameters used to determine when to cease leachate exchange in start-up reactors were a pH of 6.5 and methane generation rate of >0.5LCH4 kg(-1) VSadded day(-1). Changes in carbon dioxide and methane biogas composition in the mature reactors reflected process stress caused by the addition of leachate with high VFA concentrations from the start-up reactors and indicate there may be limits to leachate exchange rates and subsequent loading of mature reactors.     

Solid waste characterization and recycling potential for a university campus

Integrated waste management systems are one of the greatest challenges for sustainable development. For these systems to be successful, the first step is to carry out waste characterization studies. In this paper are reported the results of a waste characterization study performed in the Campus Mexicali I of the Autonomous University of Baja California (UABC). The aim of this study was to set the basis for implementation of a recovery, reduction and recycling waste management program at the campus. It was found that the campus Mexicali I produces 1ton of solid wastes per day; more than 65% of these wastes are recyclable or potentially recyclable. These results showed that a program for segregation and recycling is feasible on a University Campus. The study also showed that the local market for recyclable waste, under present conditions - number of recycling companies and amounts of recyclables accepted - can absorb all of these wastes. Some alternatives for the potentially recyclables wastes are discussed. Finally some strategies that could be used to reduce waste at the source are discussed as well.     

Enhanced methane recovery by food waste leachate injection into a landfill in Korea

The current food waste leachate (FWL) disposal practice in Korea warrants urgent attention and necessary action to develop an innovative and sustainable disposal strategy, which is both environmentally friendly and economically beneficial. In this study, methane production by FWL injection into a municipal solid waste landfill with landfill gas (LFG) recovery facility was evaluated for a period of more than 4 months. With the target of recovering LFG with methane content ~50%, optimum LFG extraction rate was decided by a trial and error approach during the field investigation in five different phases. The results showed that, upon FWL injection, LFG extraction rate of ~20 m(3)/h was reasonable to recover LFG with methane content ~58%. Considering the estimated methane production potential of 31.7 m(3) CH(4) per ton of FWL, methane recovery from the landfill was enhanced by 14%. The scientific findings of this short-term investigation indicates that FWL can be injected into the existing sanitary landfills to tackle the present issue and such landfills with efficient liner and gas collection facility can be utilized as absolute and sustainable environmental infrastructures.     

Effect of leachate recirculation on mesophilic anaerobic digestion of food waste

The effects of using untreated leachate for supplemental water addition and liquid recirculation on anaerobic digestion of food waste was evaluated by combining cyclic water recycle operations with batch mesophilic biochemical methane potential (BMP) assays. Cyclic BMP assays indicated that using an appropriate fraction of recycled leachate and fresh make up water can stimulate methanogenic activity and enhance biogas production. Conversely increasing the percentage of recycled leachate in the make up water eventually causes methanogenic inhibition and decrease in the rate of food waste stabilization. The decrease in activity is exacerbated as the number cycles increases. Inhibition is possibly attributed to accumulation and elevated concentrations of ammonia as well as other waste by products in the recycled leachate that inhibit methanogenesis.     

The potential environmental gains from recycling waste plastics: Simulation of transferring recycling and recovery technologies to Shenyang, China

With the increasing attention on developing a low-carbon economy, it is necessary to seek appropriate ways on reducing greenhouse gas (GHG) emissions through innovative municipal solid waste management (MSWM), such as urban symbiosis. However, quantitative assessments on the environmental benefits of urban symbiosis, especially in developing countries, are limited because only a limited number of planned synergistic activities have been successful and it is difficult to acquire detailed inventory data from private companies. This paper modifies and applies a two-step simulation system and used it to assess the potential environmental benefits, including the reduction of GHG emissions and saving of fossil fuels, by employing various Japanese plastics recycling/energy-recovery technologies in Shenyang, China. The results showed that among various recycling/energy-recovery technologies, the mechanical waste plastics recycling technology, which produces concrete formwork boards (NF boards), has the greatest potential in terms of reducing GHG emissions (1.66 kg CO₂e/kg plastics), whereas the technology for the production of refuse plastic fuel (RPF) has the greatest potential on saving fossil fuel consumption (0.77 kgce/kg-plastics). Additional benefits can be gained by applying combined technologies that cascade the utilization of waste plastics. Moreover, the development of clean energy in conjunction with the promotion of new waste plastics recycling programs could contribute to additional reductions in GHG emissions and fossil fuel consumption.     

Anaerobic co-digestion of food waste and landfill leachate in single-phase batch reactors

In order to investigate the effect of raw leachate on anaerobic digestion of food waste, co-digestions of food waste with raw leachate were carried out. A series of single-phase batch mesophilic (35 ± 1 °C) anaerobic digestions were performed at a food waste concentration of 41.8 g VS/L. The results showed that inhibition of biogas production by volatile fatty acids (VFA) occurred without raw leachate addition. A certain amount of raw leachate in the reactors effectively relieved acidic inhibition caused by VFA accumulation, and the system maintained stable with methane yield of 369–466 mL/g VS. Total ammonia nitrogen introduced into the digestion systems with initial 2000–3000 mgNH₄–N/L not only replenished nitrogen for bacterial growth, but also formed a buffer system with VFA to maintain a delicate biochemical balance between the acidogenic and methanogenic microorganisms. UV spectroscopy and fluorescence excitation–emission matrix spectroscopy data showed that food waste was completely degraded.We concluded that using raw leachate for supplement water addition and pH modifier on anaerobic digestion of food waste was effective. An appropriate fraction of leachate could stimulate methanogenic activity and enhance biogas production.     

An experimental study on fermentative H2 production from food waste as affected by pH

Batch dark fermentation experiments were performed on food waste and mixtures of food waste and wastewater activated sludge to evaluate the influence of pH on biological H₂ production and compare the process performance with and without inoculum addition. The effect of a preliminary thermal shock treatment of the inoculum was also investigated as a means to harvest the hydrogenogenic biomass. The best performance in terms of both H₂ generation potential and process kinetics was observed at pH = 6.5 under all experimental conditions (no inoculum, and untreated or thermally treated inoculum added). H₂ production from food waste was found to be feasible even without inoculum addition, although thermal pre-treatment of the inoculum notably increased the maximum production and reduced the lag phase duration. The analysis of the fermentation products indicated that the biological hydrogen production could be mainly ascribed to a mixed acetate/butyrate-type fermentation. However, the presence of additional metabolites in the digestate, including propionate and ethanol, also indicated that other metabolic pathways were active during the process, reducing substrate conversion into hydrogen. The plateau in H₂ generation was found to mirror the condition at which soluble carbohydrates were depleted. Beyond this condition, homoacetogenesis probably started to play a role in the degradation process.     

VFA and ammonia from residential food waste as indicators of odor potential

Research was conducted to determine suitable chemical parameters as indicators of odor from decomposing food wastes. Prepared food scraps were stored in 18 l plastic buckets (2 kg wet weight each) at 20 °C and 8 °C to reproduce high and low temperature conditions. After 1, 3, 7, 10 and 14 days of storage, the odor from the buckets were marked to an intensity scale of 0 (no odor) to 5 (intense) and the corresponding leachate analyzed for volatile fatty acids, ammonia and total organic carbon. A linear relationship between odor intensity and the measured parameter indicates a suitable odor indicator. Odor intensified with longer storage period and warmer surroundings. The study found ammonia and isovaleric acid to be promising odor indicators. For this food waste mixture, offensive odors were emitted if the ammonia and isovaleric acid contents exceeded 360 mg/l and 940 mg/l, respectively.     

Formulating a VET roadmap for the waste and recycling sector: A case study from Queensland, Australia

Vocational Education and Training (VET) is an essential tool for providing waste management and recycling workers with the necessary skills and knowledge needed to beneficially influence their own employment and career development; and to also ensure productivity and safe working conditions within the organisations in which they are employed. Current training opportunities within Queensland for the sector are limited and not widely communicated or marketed; with other States, particularly Victoria and New South Wales, realising higher numbers of VET enrollments for waste management courses. This paper presents current VET opportunities and trends for the Queensland waste management sector. Results from a facilitated workshop to identify workforce requirements and future training needs organised by the Waste Contractors and Recyclers Association of Queensland (WCRAQ) are also presented and discussion follows on the future training needs of the industry within Queensland.     

Energy recovery and greenhouse gas reduction potential from food waste in Japan

Waste-to-energy is one effective waste management approach for a sustainable society. The purpose of this study was to clarify the potential for energy recovery and greenhouse gas (GHG) reduction that could be achieved by introducing anaerobic digestion (AD) facilities in the process of reconstructing aging incineration facilities in Japan. Using statistical data from 1068 incineration facilities, four future scenarios were considered and compared with the current situation. As results, compared with the current situation the amount of electricity generated could increase by 60 % in 2030, by combining AD facilities for food waste with new, high-efficiency incineration facilities for remaining municipal solid waste (MSW). From a life cycle perspective, net energy recovery in 2030 was approximately three times greater than in 2011, and GHG emission could be reduced by 27 %. The introduction of AD facilities is attractive for small authorities, which currently treat <100 t/day of MSW through incineration facilities without energy recovery. An AD facility is also beneficial for large authorities. On the contrary, in middle-scale authorities that treat 100–299 t/day of MSW, the reconstruction of incineration facilities to include electricity production capabilities requires careful consideration, because it will significantly influence energy recovery and GHG reduction effects.     

Assessment of the recycling potential of fresh concrete waste using a factorial design of experiments

Recycling of industrial wastes and by-products can help reduce the cost of waste treatment prior to disposal and eventually preserve natural resources and energy. To assess the recycling potential of a given waste, it is important to select a tool capable of giving clear indications either way, with the least time and work consumption, as is the case of modelling the system properties using the results obtained from statistical design of experiments. In this work, the aggregate reclaimed from the mud that results from washout and cleaning operations of fresh concrete mixer trucks (fresh concrete waste, FCW) was recycled into new concrete with various water/cement ratios, as replacement of natural fine aggregates. A 3² factorial design of experiments was used to model fresh concrete consistency index and hardened concrete water absorption and 7- and 28-day compressive strength, as functions of FCW content and water/cement ratio, and the resulting regression equations and contour plots were validated with confirmation experiments. The results showed that the fresh concrete workability worsened with the increase in FCW content but the water absorption (5–10 wt.%), 7-day compressive strength (26–36 MPa) and 28-day compressive strength (32–44 MPa) remained within the specified ranges, thus demonstrating that the aggregate reclaimed from FCW can be recycled into new concrete mixtures with lower natural aggregate content.     

Evaluating the biogas potential of the dry fraction from pretreatment of food waste from households

At the waste handling company NSR, Helsingborg, Sweden, the food waste fraction of source separated municipal solid waste is pretreated to obtain a liquid fraction, which is used for biogas production, and a dry fraction, which is at present incinerated. This pretreatment and separation is performed to remove impurities, however also some of the organic material is removed. The possibility of realising the methane potential of the dry fraction through batch-wise dry anaerobic digestion was investigated. The anaerobic digestion technique used was a two-stage process consisting of a static leach bed reactor and a methane reactor. Treatment of the dry fraction alone and in a mixture with structural material was tested to investigate the effect on the porosity of the leach bed. A tracer experiment was carried out to investigate the liquid flow through the leach beds, and this method proved useful in demonstrating a more homogenous flow through the leach bed when structural material was added. Addition of structural material to the dry fraction was needed to achieve a functional digestion process. A methane yield of 98 m³/ton was obtained from the dry fraction mixed with structural material after 76 days of digestion. This was in the same range as obtained in the laboratory scale biochemical methane potential test, showing that it was possible to extract the organic content in the dry fraction in this type of dry digestion system for the production of methane.     

The influence of sodium on biohydrogen production from food waste by anaerobic fermentation

Anaerobic fermentation of food waste for hydrogen production was performed in serum bottles with various linear alkylbenzene sulfonate (LAS) dosages (7.1–21.4 g/l) and sodium concentrations (5.03–28.7 g/l). LAS can effectively inhibit the activity of hydrogen-consuming bacteria, and the maximum hydrogen yield of 109.2 ml/g volatile solid (VS) was obtained at an LAS dosage of 14.3 g/l without added sodium. The feasible pH for hydrogen production is 5.0–6.0, and the process will slow down or stop when the pH is below 5.0.The hydrogen production potential increased when the sodium concentration increased in the range 5.03–14.41 g/l. The maximum hydrogen yield was 154.8 ml/g VS, and then the hydrogen production began to decrease when the sodium concentration increased further. A sodium chloride concentration of 20 g/l and higher will enhance the osmotic pressure and make bacteria inert. In the effluent, acetic acid is the major by-product. The results indicated that the hydrogen production from the anaerobic fermentation of food waste could clearly be increased with the additives and a sodium concentration less than 20 g/l.     

Potential of biogas production from mixed leaf and food waste in anaerobic reactors

Anaerobic digestion of mixed leaf (MLW) and food wastes (FW) was used to explore the potential use of MLW as an accelerator for FW digestion in two parts for biogas production and as a waste management option in a university community. The effects of the single substrate of FW, co-digestion, ratio of MLW and FW (3:2 and 2:3) and ratio of waste feed to inoculum: F/I (0.1 and 0.4), and feeding frequency (every other day and every 2 days) were evaluated in two neutralized anaerobic reactors. The results showed that different mixture ratios with the same F/I ratio were the major factor on biogas (39.87 m³/kg VS_added) and CH₄ yield (25.99 m³/kg VS_added), including %COD removal (84.50%). Co-digestion had the same effect as F/I on biogas production. Only FW provided the lowest biogas and CH₄ yield. The use of a MLW:FW 2:3, F/I 0.4 mixture with every 2 days feeding provided higher biogas production and %COD removal than with every other day feeding. Two neutralized anaerobic reactors were suitable for digestion with a high F/I, and a wider interval feeding. This finding affirms the possibility of biogas production using MLW as the co-substrate with FW, as opposed to using FW alone.     

Microbial nitrogen transformation potential in surface run-off leachate from a tropical landfill

Ammonium is one of the major toxic compounds and a critical long-term pollutant in landfill leachate. Leachate from the Jatibarang landfill in Semarang, Indonesia, contains ammonium in concentrations ranging from 376 to 929 mg N L⁻¹. The objective of this study was to determine seasonal variation in the potential for organic nitrogen ammonification, aerobic nitrification, anaerobic nitrate reduction and anaerobic ammonium oxidation (anammox) at this landfilling site. Seasonal samples from leachate collection treatment ponds were used as an inoculum to feed synthetic media to determine potential rates of nitrogen transformations. Aerobic ammonium oxidation potential (<0.06 mg N L⁻¹ h⁻¹) was more than a hundred times lower than the anaerobic nitrogen transformation processes and organic nitrogen ammonification, which were of the same order of magnitude. Anaerobic nitrate oxidation did not proceed beyond nitrite; isolates grown with nitrate as electron acceptor did not degrade nitrite further. Effects of season were only observed for aerobic nitrification and anammox, and were relatively minor: rates were up to three times higher in the dry season. To completely remove the excess ammonium from the leachate, we propose a two-stage treatment system to be implemented. Aeration in the first leachate pond would strongly contribute to aerobic ammonium oxidation to nitrate by providing the currently missing oxygen in the anaerobic leachate and allowing for the growth of ammonium oxidisers. In the second pond the remaining ammonium and produced nitrate can be converted by a combination of nitrate reduction to nitrite and anammox. Such optimization of microbial nitrogen transformations can contribute to alleviating the ammonium discharge to surface water draining the landfill.     

Feasibility of producing ethanol from food waste

Food waste generated in Korea is rich in carbohydrate as high as 65% of total solids. Using the food waste, the feasibility of ethanol production was investigated in a lab-scale fermentor. Pretreatment with hydrolyzing enzymes including carbohydrase, glucoamylase, cellulase and protease were tested for hydrolysis of food waste. The carbohydrase was able to hydrolyze and produce glucose with a glucose yield of 0.63 g glucose/g total solid. Enzymatic hydrolysis and ethanol fermentation by using carbohydrase and Saccharomyces cerevisiae were conducted in the batch mode. For separated hydrolysis and fermentation (SHF), ethanol concentration reached at the level corresponding to an ethanol yield of 0.43 g ethanol/g total solids. For simultaneous saccharification and fermentation (SSF), the ethanol yield was 0.31 g ethanol/g total solids. During the continuous operation of SHF, the volumetric ethanol production rate was 1.18 g/lh with an ethanol yield of 0.3g ethanol/g total solids. For SSF process, the volumetric ethanol production rate was 0.8 g/lh with an ethanol yield of 0.2g ethanol/g total solids.     

Assessment of long-term pH developments in leachate from waste incineration residues.

Environmental assessment of residue disposal needs to account for long-term changes in leaching conditions. Leaching of heavy metals from incineration residues are highly affected by the leachate pH; the overall environmental consequences of disposing of these residues are therefore greatly influenced by changes in pH over time. The paper presents an approach for assessing pH changes in leachate from municipal solid waste incineration (MSWI) air-pollution-control (APC) residues. Residue samples were subjected to a stepwise batch extraction method in order to obtain residue samples at a range of pH values (similar to common pH-dependence tests), and then on these samples to determine leaching of alkalinity as well as remaining solid phase alkalinity. On a range of APC residues covering various pretreatment and disposal options, this procedure was used to determine leachable and residual alkalinity as a function of pH. Mass balance calculations for typical disposal scenarios were used to provide data on pH as a function of the liquid-to-solid (L/S) ratio in the leaching system. Regardless of residue type and pretreatment, pH was found to stay above 7 for L/S ratios up to about 2000 L kg(-1) corresponding to about 100,000 years in typical landfill scenarios. It was found that pH changes were mainly governed by alkalinity decreases from leaching processes rather than neutralization reactions. The results suggest that leaching testing for assessment purposes should be carried out in the alkaline range, for example, at pH 9. The paper offers a thorough basis for further modelling of incineration residue leaching and for modelling the environmental consequences of landfilling and utilization of these residues.