Leachate Recirculation Research Articles

Investigations into the landfill behaviour of raw and treated wastes

Bioreactor landfills (BLFs) basically involve recirculation of leachate in controlled quantities back into the bioreactor landfill to boost biodegradation of municipal solid wastes thereby improving its efficiency. This augmented biodegradation leading to faster and improved stabilization of landfill waste is being showcased by a study on two anaerobic bioreactors. One bioreactor is being loaded with raw wastes having high organic content causing an impediment in the biogas production and biodegradation and on the other hand, there is a bioreactor of same configuration loaded with windrow compost as treated waste having lower polluting potential. An attempt is made to showcase a comparative analysis to investigate the impact of treatment on biodegradation in both raw and treated MSWs. Over a 9–10 month study period which is currently under progress, data from the first 3 months (13 weeks) is presented. Treated wastes have given better results as compared to raw MSW due to lower polluting potential in terms of both leachate quality as well as biogas production. Speculations are being made that treated wastes will give better results for the whole study period in terms of environmental sustainability.

Technological assessment of waste value change: implementation of CE concepts for implementing loop economy

ABSTRACT The Municipal Solid Waste Management (MSWM) system has been used as a unit of study to apply the Life Cycle Assessment (LCA) approach. Kanjur waste processing facility Mumbai, India was selected for technological performance assessment. The paper analyses multiple strategies for managing the MSW and the comparison of strategies is done to study impact on Global Warming Potential (GWP), Eutrophication Potential (GW) and Acidification potential (AP), which are the critical impact areas of MSW processing. The scenarios included were transportation, material recovery, direct landfill with the recovery of LFG, composting of the source-separated organic fraction with landfilling and biomining. Landfilling and the release of LFG (Landfill Gas), electricity generation from LFG, flaring of LFG were other assessed interventions. The scenarios were modelled using the CML impact characterisation method. The results highlight that sorting, biomining, composting, landfilling with energy recovery has the minimal impact on the environment compared to strategies where direct landfilling was considered. On a life cycle view, the transportation of waste to the processing site caused a significant global warming impact and is a hotspot, which can be considered for impact mitigation. Initiatives like RDF reuse, leachate recirculation, LFG recovery, biomining are other circular practices that lead to a significant reduction in GWP, EP and AP.

Extracting metal ions from basic oxygen steelmaking dust by using bio-hydrometallurgy

This study aimed to optimise metal extraction from secondary hazardous sources, such as basic oxygen steelmaking dust (BOS-D). Initially, three batch systems approaches, including bioleaching using Acidithiobacillus ferrooxidans, chemical leaching using choline chloride-ethylene glycol (ChCl-EG) and a combined approach were compared. Then, scaling up was evaluated through a semi-continuous bioleaching column system with varied leachate recirculation over 21 days, focusing on Y, Ce, Nd, Li, Co, Cu, Zn, Mn, and Al. Bioleaching outperformed the control experiments within 3 days in the batch, demonstrating the key role of A. ferrooxidans. Chemical leaching conducted with a solid concentration of 12.5 % (w/v) successfully dissolved over 50 % of all metals within 2 h. For rare earth elements (REE), both bioleaching and hybrid leaching outperformed chemical leaching. However, considering factors such as process duration, overall efficiency, and ease of extraction, chemical leaching was the most effective method. Leachate recirculation reached a plateau after 11 days, resulting in extraction efficiency of 39 % when semi-continuous column set-up was used. Interestingly, variations in recirculation rates did not influence the extraction efficiency. Overall, this study emphasizes the considerable potential of bioleaching for metal recovery, but also highlights the need for further studies for enhancing permeability for percolation methods and optimisation, particularly in parameters such as aeration rate, when transitioning to larger scale systems.

Influence of the presence of a pathogen and leachate recirculation on a bacterial competition

Influence of the presence of a pathogen and leachate recirculation on a bacterial competition

Waste-to-energy power plants: Multi-objective analysis and optimization of landfill heat and methane gas by recirculation of leachate

Elevated thermal energy trapped in landfill voids is a potential threat to humans since, fires might get ignited, eventually releasing poisonous gases, contaminated fluids (leachate), and abnormal quantity of heat. This study explores the practical potential of landfills to produce heat and methane gas through a leachate recirculation process, which involves returning nutrient-rich fluids to landfills to maximize electricity generation. This paper presents an experimental investigation of the physio-chemical properties of landfills by recirculating leachate to achieve sustainable performance characteristics of landfill models. Five input parameters i.e. waste particle size (WPS in mm), waste addition (WA in Ktoe), inorganic matter content (IO in %), leachate recirculation rate (LRR in liters/day), and age of landfill (LA in years) each at five levels is considered. The investigation is accomplished on the central composite rotating design (CCRD) matrix with a 5-level factor. The results reveal that WPS at D10, WA at 52.32 Ktoe, IO at 2%, LRR at 300 l/day, and LA at 4.07 year is the optimal setting of the input parameters that produce optimum values of the output responses considered simultaneously. An innovative method is studied for simultaneously lowering the internal temperature of landfills to ideal levels while also enhancing the rate of methane production. Energy transfer to the ORC system is 2.3 GJ in winters while 1.5 GJ in summers. Landfills equipped with leachate recirculation facilities provide 2.2 times more energy with stabilization occurring in 4th year with an energy content of 950 MJ/m3 of waste.

Application of Electrical Resistivity Tomography in Geotechnical and Geoenvironmental Engineering Aspect

Electrical resistivity tomography (ERT) has turned out to be one of the most applied and user-friendly geophysical methods in geotechnical and geoenvironmental research. ERT is an emerging technology that is becoming popular nowadays for investigating subsurface conditions. Multiple attributes of the technology using various electrode configurations significantly reduce measurement time and are suitable for applications even in hardly accessible mountain areas. It is a noninvasive test for subsurface characterization and a very sensitive method used to determine geophysical properties, i.e., structural integrity, water content, fluid composition, etc. This paper aimed to elucidate the ERT technique’s main features and applications in geotechnical and geoenvironmental engineering through four case studies. The first case study investigated the possible flow paths and areas of moisture accumulation after leachate recirculation in a bioreactor landfill. The second case study attempted to determine the moisture variation along highway pavement. The third case study explored the slope failure investigation by ERT. The fourth case study demonstrated the efficiency of the ERT method in the landfill evapotranspiration (ET) cover to investigate moisture variation on a broader scale and performance monitoring. In all of the four cases, ERT exhibited promising performance.

Mathematical Investigation for Two-Bacteria Competition in Presence of a Pathogen With Leachate Recirculation

Mathematical Investigation for Two-Bacteria Competition in Presence of a Pathogen With Leachate Recirculation

Performance evaluation of bioreactor landfills with leachate recirculation: an experimental study

Performance evaluation of bioreactor landfills with leachate recirculation: an experimental study

Anaerobic digestion of the organic fraction of municipal solid waste in a simulated bioreactor to improve predictive modeling of landfill systems

Municipal solid waste (MSW) generation is increasing globally, containing up to 57 % organic matter. Trapping and extraction of methane (CH4) produced via anaerobic digestion (AD) of the organic fraction of MSW (OFMSW) reduces CH4 released from landfills into the atmosphere. To estimate CH4 production from OFMSW, mathematical models are frequently used, but their accuracy varies under the non-ideal conditions that are inevitable in real landfilling scenarios. This work calibrates first-order decay (FOD) and Gompertz models for predicting CH4 production from the OFMSW based on experimental results from a pilot-scale landfill bioreactor operating under non-ideal conditions, namely under dry and mesophilic conditions with low leachate recirculation inteded to represent landfills in developing countries. This study achieved a 73 % and 66 % reduction in volatile solids (VS) and total solids (TS), respectively, demonstrating successful organic degradation. Models were calibrated using laboratory data, showing high correlation and accuracy >80 % in a Chemical Oxygen Demand (COD) mass balance. The experiment produced 104.3 mL CH4 g−1 VS with accurate predictions from calibrated models Non-calibrated models, however, overestimated methane production by 75 %. Work highlights the importance of modifying models for non-ideal conditions, and results provide useful information for landfills in developing countries.

Natural and anthropogenic dissolved organic matter in landfill leachate: Composition, transformation, and their coexistence characteristics

A large number of natural and anthropogenic wastes were landfilled, and dissolved organic matter (DOM) were formed during landfill. However, the composition, transformation, and coexistence characteristics of natural and anthropogenic DOM in leachate remain unclear. Fourier transform ion cyclotron resonance mass spectrometry, size exclusion chromatography, gas chromatography coupled with mass spectrometry, and three-dimensional excitation-emission matrix spectrum were employed to clarify comprehensively the abovementioned question. The results showed that natural DOM in young leachate constituted mainly straight-chain organic acids, protein substances, and building blocks of humic substances (BB). Straight-chain organic acids vanished in old leachates, and the concentration of protein substances and BB decreased from 44% to 26% and from 47% to 12%, respectively, while CHON and CHONS were degraded to CHO and CHOS during the process. As to anthropogenic DOM, its types and relative content in leachate increased during landfill, and aromatic acids, terpenes, halogenated organics, indoles, and phenols became the main organic components in old leachate. Compared to natural DOM, anthropogenic DOM was degraded slowly and accumulated in leachate, and some of the natural DOM facilitated the dechlorination of dichlorinated organic compounds. This study demonstrates that landfill led to an increase in humic substances and halogenated organic compounds in old leachate, which was intensified with concentrated leachate recirculation.

Experimental investigation and multi-performance optimization of the leachate recirculation based sustainable landfills using Taguchi approach and an integrated MCDM method

Landfill leachates contain harmful substances viz. chemicals, heavy metals, and pathogens, that pose a threat to human health and the environment. Unattended leachate can also cause ground water contamination, soil pollution and air pollution. This study focuses on management of leachate, by recirculating the rich, nutrient-filled fluid back into the landfills, turning it to a bioreactor, thereby maximising the performance parameters of landfills favourable for electricity production by the waste to energy plants. This study demonstrates a sustainable alternative method for utilising the fluid, rather than treating it using an extremely expensive treatment process. Further, it also experimentally investigates the effect of varying levels of five input parameters of the landfill including waste particle size, waste addition, inorganic content in waste, leachate recirculation rate, and landfill age, each at five levels, on the multiple performance of the landfill using Taguchi’s L25 standard orthogonal array. Experimental results are analysed using an integrated MCDM approach i.e. MEREC-PIV method and statistical techniques such as analysis of mean (ANOM) and analysis of variance (ANOVA). The results indicate that the optimal setting of the input parameters is waste particle size at 9 ppm, waste addition at 80 Ktoe, inorganic content in waste at 2%, leachate recirculation rate at 250 l/day and landfill age at 3 years. Further, inorganic content waste is found to be the most significant parameter for the multiple performance of the landfill. This study presents a novel approach to produce input parameters for power plants which may enhance their profitability and sustainability.

Prediction and control of elevated temperatures within landfills under aeration and recirculation based on the thermal non-equilibrium model

Aeration is an effective approach to sustainable landfilling but may lead to elevated temperatures within landfills, resulting in landfill fires or explosions. Therefore, aeration is usually combined with leachate recirculation to control the elevated temperatures within landfills. To predict landfill temperatures during aeration and recirculation, a local thermal non-equilibrium model is developed considering the heat generation of biodegradation, the heat removal due to evaporation and leachate-gas flow, and the effects of the capillary. The solver is implemented in OpenFOAM based on the finite volume method and validated against a waste-column experiment and an in-situ aeration test. The simulation results demonstrate that the assumption of local thermal equilibrium will distinctly overestimate the temperature, maximally by 15 °C in the studied case. The model is then used to simulate a typical aerobic landfill unit to investigate the formation of explosive gas mixtures and elevated temperatures under different operating conditions. The simulation results of gas composition suggest that aeration will not result in explosive gas within landfills. A reasonable recirculation method for temperature control with corresponding operating parameters under a group of values of aeration pressure (2000–4000 Pa) and recirculation rate (0.0001–0.0008 m/s) are proposed, which can provide some guides for the design of an aeration and recirculation combined system. For a given total volume of added leachate, a higher recirculation rate does not always mean better cooling, and the cooling effect of continuous recirculation is better than that of intermittent recirculation.

Micro-aeration and leachate recirculation for the acceleration of landfill stabilization: Enhanced hydrolytic acidification by facultative bacteria

The long duration of landfill stabilization is one of the challenges faced by municipalities. In this paper, a combination of micro-aeration and leachate recirculation is used to achieve rapid degradation of organic matter in landfill waste. The results showed that the content of volatile fatty acids (VFAs) in the hydrolysis phase increased significantly and could enter the methanogenic phase quickly. Until the end of the landfill, the removal rates of chemical oxygen demand (COD), total phosphorus (TP) and ammonia nitrogen (NH4+–N) by micro-aeration and leachate recirculation reached 80.17 %, 48.30 % and 48.56 %, respectively, and the organic matter degradation rate reached 50 %. Micro-aeration and leachate recirculation enhanced the abundance of facultative hydrolytic bacteria such as Rummeliibacillus and Bacillus and the oxygen tolerance of Methanobrevibacter and Methanoculleus. Micro-aeration and leachate recirculation improved the organic matter degradation efficiency of landfill waste by promoting the growth of functional microorganisms.

Isothermal Dual-Phase Flow Modeling to Assess the Impact of Gas Collection on Geotechnical and Hydraulic Performance of Landfills.

Liquid addition to landfilled municipal solid waste (MSW) is a practice employed to accelerate the biodegradation of the organic fraction of MSW and ensuing gas generation. Pore landfill gas (LFG) and leachate pressure from the added moisture and enhanced gas generation are expected to impact the geotechnical stability of landfill slopes. The impact of moisture addition and gas collection on the stability of landfills was numerically modeled using transient isothermal dual-phase flow and slope stability modeling. The temporal variation in the factor of safety (FS) for slope stability analysis was estimated for the simultaneous flow of LFG and leachate with and without gas collection and leachate recirculation for varying LFG generation rates and waste moisture contents. A significant decline in the FS for landfill slope stability was observed when recirculating leachate without active gas collection. Even without pressurized leachate recirculation, a significant decline in the FS value was observed for landfills with relatively high in situ moisture content without active gas collection. In some modeled scenarios without LFG collection, the FS value was lower than 1. The analysis suggests that the landfill side slope stability analysis should incorporate LFG generation and the resultant pressure for landfills containing high-moisture-content waste and for the landfill with pressurized leachate recirculation. The analysis suggests that an efficient gas collection system plays a critical role in the geotechnical stability of the slope of wet landfills and the performance of leachate recirculation trenches.

Evaluation of biogas production rate and leachate treatment in Landfill through a water-energy nexus framework for integrated waste management

The aim of this study was to investigate the simultaneous biogas generation and leachate treatment using municipal waste and its polluted leachate at Mashhad landfill in northeast Iran. The research focused on examining the kinetic model of CH4, CO2, CO, H2S and O2 production with and without leachate recirculation (LR) through control/test wells. The findings from both wells showed an increase in logarithmic CH4 production rate, with the coefficient related to the rate of increase in methane concentration ranging from 0/52-0/64 in the control well and 0/47-0/55 in the test well, respectively. Under LR conditions, it was observed that the CH4 production rate was slower, taking an average of 120 minutes to reach 50% concentration, compared to just 15 minutes without LR. Using first-order equations, the CH4 production coefficients were measured to be 2/17 h−1 and 0/9 h−1 for the control and test wells, respectively. The analysis of recirculated leachate revealed a significant decrease (∼30%) in the total volume of leachate with 72% COD removal, which could help manage overloaded leachate problems in the landfill. The COD removal coefficient was found to be 0/036 day−1 in the control well, whereas the test well with leachate recirculation showed a more rapid decrease from 50 g.l−1 to about 14 g.l−1 with a removal coefficient of 0/012 day−1, three times higher than the control well. Additionally, nitrogen content analysis indicated that although the amount of ammonia content increased with LR, the increase was relatively low in comparison to conditions without LR, equivalent to 1394 ppm and 1000 ppm in control and test wells, respectively. This study aligns with the water-energy-nexus concept by offering a sustainable solution for waste management and energy generation, while also addressing water management challenges associated with landfill operations.

Assessing moisture contributions from precipitation, waste, and leachate for active municipal solid waste landfills

Precipitation, evapotranspiration (ET), waste tonnage, landfill gas (LFG), and leachate data were aggregated from public sources to perform a 5–10 year water balance and estimate the contributions of three water sources (precipitation, incoming waste, and leachate recycling) for 36 active municipal solid waste (MSW) landfills in Ohio, USA. Uniquely, the water balance incorporated waste decomposition, using gas collection data to inform mass loss from biodegradation. Moisture contents of 20–30% for incoming waste indicate that entrained water is the largest source of landfill moisture. Infiltration of precipitation into the landfill after ET was the second largest source. Even at facilities where a majority of the leachate generated was recirculated, it did not significantly affect the moisture content in that year. Using the water balance approach, it appears leachate recirculation is unlikely to increase moisture content above 40% by mass, a regulatory threshold in the US, which would impose stricter air pollution control requirements. However, poor stormwater management could easily allow for “bioreactor” conditions to develop. The calculated landfill moisture content was significantly affected by the assumed runoff coefficient (CRO) parameter. CRO values below 20% and above 50% produced unrealistically high or low moisture contents, respectively. This approach can assist operators and regulators in understanding the contribution of different sources to a landfill's moisture profile and avoid future operational problems.

Impact of Leachate Recirculation on the Stabilization of Municipal Solid Waste in Anaerobic Bioreactors of Different Compositions

The aim of the current study is to determine the impacts of leachate recirculation on the degradation of three compositions of municipal solid waste in anaerobic bioreactors. The study was completed by using six columns with equal volume (0.042m3) containing different densities and compositions of solid waste, in order to follow waste degradation over a limited time. Three compositions of waste were studied: simulated fresh waste of standard composition, simulated fresh waste of fermentable composition, and actual aged waste. Measurements of the significant parameters including pH, leachate conductivity, Chemical Oxygen Demand (COD), and waste settlement, were carried out. The quantity of oxidized organic matter was increased by the leachate recirculation, and the degradation period was reduced by using leachate recirculation. After 300, 150, and 480 days, waste stabilization seemed to be reached for fresh, aged, and fermentable waste, whereas the organic content decreased to 650, 480, and 4000mg COD/L, respectively.

Geophysical Monitoring of Leachate Injection in Pretreated Waste Landfill

Landfill leachate recirculation is applied to manage the landfill as a bioreactor to enhance biogas production, limiting the impact due to greenhouse gas emissions and optimizing the energy recovery from biogas. This study deals with the geophysical monitoring of the leachate recirculation within the waste of a pretreated waste landfill. For this aim, electrical resistivity tomography (ERT) was adopted, detecting the main distribution of moisture within the waste both through the surface and through several boreholes. The electrical resistivity of waste mainly depends on water content, leachate salinity and temperature. The method is sensitive to the transient phenomena associated with leachate flow within the waste; moreover, the ERT long-term monitoring data suffer from anomalous and unexpected polarization phenomena induced by the measurements themselves. Results demonstrated the reliability of this approach to qualitatively detect the landfill volume affected by the leachate circulation. The effects of moisture changes by leachate infiltration on biogas production are still challenging, notwithstanding a positive effect on methane concentration in biogas itself is evident.

Experimental investigation of water retention curves of municipal solid wastes with different paper contents, dry unit weights and degrees of biodegradation

This paper investigates the drying and wetting water retention curves (WRCs) of municipal solid wastes (MSWs) with different paper contents, dry unit weights and degrees of biodegradation (DOBs). Fresh synthetic samples were prepared based on the field composition of the MSWs at Mugga Lane Landfill, the Australian Capital Territory (ACT), Australia. The degraded samples were prepared in simulators with MSWs of different initial dry unit weights and decomposition periods with leachate recirculation. The water retention curves (WRCs) of the MSWs were determined using pressure plate tests, in both drying and wetting phases. The outflow from MSWs was analysed using Gardner’s method to obtain the unsaturated hydraulic conductivity. The results indicate that the WRCs of the MSWs are greatly affected by the DOB, paper content and dry unit weight. When DOB < 30 %, as DOB increases, the air-entry pressure of MSWs with paper increases, and the residual moisture content decreases regardless of paper content. With DOB > 30 %, the air entry pressure and residual water content depend on the balance between organic matter and highly decomposed organic constituents. The paper content affects the WRCs of MSWs due to its water retention capacity and change in the particle size distribution with decomposition. The increase in the dry unit weight of MSWs significantly increases the air entry pressure and residual moisture content, similar to the borehole samples with combined effects of biodegradation and increase in stress level from literature. Hysteresis effects have been observed during the drying and wetting of MSWs. The hysteresis of WRCs increases with the paper content and DOB.

Microbial community dynamics of a sequentially fed anaerobic digester treating solid organic waste.

A 50-kg scale, high solids anaerobic digester (AD) comprising six sequentially fed leach beds with a leachate recirculation system was operated at 37°C for 88 weeks. The solid feedstock contained a constant fibre fraction (a mix of cardboard, boxboard, newsprint, and fine paper) and varying proportions of food waste. Previously, we reported on the stable operation of this digestion system, where significantly enhanced methane production from the fibre fraction was observed as the proportion of food waste increased. The objective of this study was to identify relationships between process parameters and the microbial community. Increasing food waste led to a large increase in the absolute microbial abundance in the circulating leachate. While 16S rRNA amplicons for Clostridium butyricum were most abundant and correlated with the amount of FW in the system and with the overall methane yield, it was more cryptic Candidatus Roizmanbacteria and Spirochaetaceae that correlated specifically with enhanced methane from the fiber fraction. A faulty batch of bulking agent led to hydraulic channeling, which was reflected in the leachate microbial profiles matching that of the incoming food waste. The system performance and microbial community re-established rapidly after reverting to better bulking agent, illustrating the robustness of the system.