Leachate Recirculation Research Articles

Physical, geotechnical and biochemical behaviours of municipal solid waste in field and laboratory bioreactors

This paper investigates the effects of degrees of compaction (initial dry unit weights), recirculation liquid and rate, and environmental temperature on the long-term physical, geotechnical, and biochemical properties of municipal solid wastes (MSWs) biodegraded for approximately 800 days. Four field bioreactors were filled with fresh MSWs collected from a landfill site. Three laboratory bioreactors were filled with synthetic MSWs with the composition same as that used in the field bioreactors. The bioreactors were recirculated with water or leachate at different rates. Compared to water recirculation, leachate recirculation further promotes the settlement of the MSWs and methane generation. Increasing the recirculation rate does not significantly increase the settlement of the MSWs. The biocompression ratio increases with the environmental temperature. The MSWs with lower dry unit weights are more sensitive to the change in temperature, especially with leachate recirculation. However, opposite to common sense, the decomposition of MSWs may not significantly contribute to the settlement after analysing the relationship between the degrees of biodegradation and settlement of the MSWs. Over 90 % of the settlement during the test period was completed within 25 % degrees of biodegradation. The major change in the physical, geotechnical, and biochemical properties occurs at low (less than20 %) degrees of biodegradation. A new equation is proposed to describe the nonlinear variation in the methane generation rate. The modelled methane generation rate and accumulated volume of methane well match the test results from the laboratory scale bioreactors and other studies.

Increasing recovery opportunities of metal(loid)s from municipal solid waste via landfill leachate recirculation

The recovery of 12 critical raw materials (CRM) from municipal solid wastes (MSW) via leachate recirculation was evaluated using a 4 L semi-pilot scale column percolation. The results showed that the recovery of the metal(loid)s was mainly influenced by order of importance: pH > organic content > type of metal(loid)s > age of the waste > redox potential. Among the CRM, Cd and Ni were the most mobile elements, while As and Cr were the least mobile. A comparison of leachate from the leachate recirculated columns before and after the initiation of recirculation indicates an increase in the concentrations of certain CRM and metalloids. The first recirculation cycle supported achieving 100 % recovery. CRM and metalloids in leachate can be recovered; however, the concentrations of CRM and metalloids are usually below 1 mg/L. In this regard, leachate recirculation may enhance the increasing concentration of CRM in landfill leachate. For example, after first recirculation cycle, Ni concentration increased from 0.05 mg/L to 0.11 mg/L. The results obtained from this study can develop further methodologies for the potential recovery of CRM and help foster further research into overcoming limitations for recovering CRM in landfill leachate.

Landfill leachate treatment by a combination of a multiple plant hybrid constructed wetland system with a solar photoFenton process in a raceway pond reactor

The sustainable and green treatment of landfill leachate (LL), produced by municipal solid waste, represents one of the most relevant challenges in the integrated waste management systems. Accordingly, in this work a green solution was investigated by coupling an innovative hybrid constructed wetland (HCW) to a solar photo-Fenton (SPF) process. A multiple layers HCW pilot plant including different medium substrates (sand, solid compost and carriers) and plant species (Phragmites australis, Arundo donax and A. plinii) was designed. The HCW was functionalised with compost tea solution to simultaneously provide high nutrient content for plants and increase the microorganism biodiversity. Process efficiency was investigated using different real LLs (young and mature) in terms of chemical oxygen demand (COD), nitrogen compounds, chlorides and metals. Removals in the range 75–95% were observed for all the parameters after ten days of leachate recirculation in the pilot plant. Subsequently, the SPF process was carried out in a raceway pond reactor (RPR) as polishing step, significantly improving COD removal (further 49%). HCW combined with SPF in RPR would allow to meet the corresponding limits according to the final use/fate of the effluent by modulating the main parameters of the process.

ENHANCED IN-SITU REDUCTION OF LEACHATE PARAMETERS DUE TO AERATION AND LEACHATE RECIRCULATION IN PILOT SCALE MSW BIOREACTOR LANDFILL MODELS IN TROPICAL CLIMATE

The processes for optimizing toxicity removal of leachate from pilot scale Municipal Solid Waste bioreactor landfills were attempted. Landfill models were simulated in Fibre Reinforced Plastic tanks of size 1.5m x 1.0m x 1.0m by applying interventions like aeration and leachate recirculation. It was found that the Chemical Oxygen Demand and Biochemical Oxygen Demand values increased till 46th week after which the values started reducing. On 89th week after closure of landfill, the aerobic landfill model showed the minimum values for COD (10,200 mg/l) and both anaerobic and aerobic models with leachate recirculation had the lowest BOD (4934 mg/l). By 116th week the least concentrations of COD and BOD were in anaerobic landfill model with leachate recirculation (64 and 22 mg/l). Ammonia Nitrogen was the least in aerated model with leachate recirculation by 116th week from closure (281 mg/l). Conductivity was less in the landfill models with leachate recirculation (4.2 and 5 mS/cm for anaerobic and aerobic respectively).

The effect of climate change on the potential for landfill gas generation at the Vinča landfill site

Climate change projections indicate that Republic of Serbia and the Western Balkans will face a high probability of continuing temperature increases, climatic extremes are projected to become more common, including a significant increase in the number of extreme heat events. Heavier precipitation events are expected in the winter months, whilst summers are projected to become even drier. This paper aims to analyse effect of precipitation changes on landfill gas generation on the Vinča landfill, the biggest landfill in Serbia. Quantities of generated landfill gas and methane have been estimated by using LandGem model. Site specific methane generation rate has been calculated according to GMI methodology for Central Eastern Europe. Sensitivity analyses is performed to determine influence of a precipitation regimes on the methane generation rate on the site. Any increase in precipitation (in range 10-30%) may increase landfill gas production for 4.3%. The paper shows the difference in gas emissions, with the same composition of waste, and different precipitation regimes. Changes in precipitation regimes due to climate change can affect the dynamics of landfill gas emissions. This information is significant for the possible re-circulation of leachate from the landfill which could result in an increased production of landfill gas.

Influence of Leachate Recirculation on Landfill Degradation and Biogas Production

Population growth combined with the rising standard of living of people around the world is the reason for the ever-increasing production of waste which management is costing states a lot of money for its disposal. Among available waste treatment techniques, landfill is one of the most promoted waste management techniques with the emergence of the bioreactor concept. However, the control of biodegradation parameters in order to accelerate waste stabilization is an important issue. For environmental and economic reasons, the technique of leachate recirculation by injection into the waste is increasingly used to improve the degradation of landfilled waste. The injection of leachate is possible using vertical boreholes, horizontal pipes, infiltration ponds or a combination of these. Indeed, moisture is the main factor in waste degradation and biogas production. The migration of leachate to the bottom of the landfill creates low moisture in the upper areas of the landfill reducing the growth of microbial populations. This results in low or no biogas production. The main objective of the present work is to develop a numerical model of leachate recirculation by injection into the waste to rewet the waste and restart biological activity. The analysis of the results shows that the diffusion of the wet front increases with time and depth. The lateral widening of the wet front is slow in relation to the progression of the wet front towards the bottom of the waste cell. This indicates the predominance of gravity effects over diffusion phenomena. The results reveal that the distributed re-injection is the best mode of leachate recirculation because the moisture distribution on the whole waste mass is totally satisfactory and the biogas generation is more important. Leachate recirculation campaigns should be done periodically to rewet the waste, boost microbial activity and hope for a quicker stabilization of the landfill.

Mathematical modeling for anaerobic digestion under the influence of leachate recirculation

<abstract><p>In this paper, we proposed and studied a simple five-dimensional mathematical model that describes the second and third stages of the anaerobic degradation process under the influence of leachate recirculation. The state variables are the concentration of insoluble substrate, soluble substrate, produced hydrogen, acetogenic bacteria and hydrogenotrophic-methanogenic bacteria. The growth rates of used bacteria will be of general nonlinear form. The stability of the steady states will be studied by reducing the model to a 3D system. According to the operating parameters of the bioreactor described by the added insoluble substrate, soluble substrate and hydrogen input concentrations and the dilution rate, we proved that the model can admit multiple equilibrium points and we gave the necessary and sufficient assumptions for their existence, their uniqueness and their stability. In particular, the uniform persistence of the system was satisfied under some natural assumptions on the growth rates. Then, a question was answered related to the management of renewable resources where the goal of was to propose an optimal strategy of leachate recirculation to reduce the organic matter (either soluble or insoluble) and keep a limitation of the costs of the recirculation operation during the process. The findings of this work were validated by an intensive numerical investigation.</p></abstract>

Effect of increased temperature and leachate recirculation on biogas production and settlement of municipal solid waste.

This study evaluated the effects of increased temperature and leachate recirculation on volatile solids (VS), biogas, hydrogen sulphide (H2S) leachate quality (pH and chemical oxygen demand) and the settlement of municipal solid waste (MSW). Three large-scale tests were conducted with no leachate recirculation at 21°C, weekly leachate recirculation at 20°C and weekly leachate recirculation at 50°C. Leachate recirculation and increased temperature accelerated biodegradation and pushed forward the onset time (from 27 to 8 days). The increase of biodegradation activity was reflected in the change of biogas production, VS and settlement. Compressibility index , increased from 0.71 and 0.77 at 21°C to 0.83 when the temperature was 50°C. In addition, leachate recirculation and high temperature reduced H2S concentration levels by inhibiting the growth of sulphate-reducing bacteria and leachate recirculation lowered H2S production by dissolving the high H2S presence. The results showed that MSW can have significantly changed mechanical and biochemical behaviour under different temperatures and saturations. The results help understand the processes in landfills for more effective short-term and long-term design and management.

An integrated leachate bed reactor – anaerobic membrane bioreactor system (LBR-AnMBR) for food waste stabilization and biogas recovery

This study developed an integrated LBR – AnMBR system for efficient stabilization and biogas recovery from food waste (FW) at room temperatures (21–22 °C). First, the leachate recirculation rate (4.4–13.2 L/h) was optimized to maximize hydrolysis and acidification yields. The maximum hydrolysis yield of 551 gSCOD/kg VSadded was achieved at recirculation rate of 13.2 L/h. The VFA concentrations in the FW leachate was as high as 12.5–16.0 g/L, resulting in a high acidification of 468 g CODVFA/kg VS. The solubilized FW was further stabilized by feeding the leachate to AnMBR. Different hydraulic (HRT) and solids retention times (SRT) were tested to achieve high COD removal and methane yields. High COD removal of 86 ± 3% was obtained in the AnMBR at HRT of 13 and SRT of 75 days. High biogas recovery of about 850 kWh per ton FWtreated was achieved along with high quality of AnMBR permeates containing low COD concentration but advantageously high concentration of nutrients (NH4+-N 317–403 mg/L, total phosphate 23–213 mg/L) without any particulates, which can be reused for landscape or liquid fertilizer.

Enhanced landfill process based on leachate recirculation and micro-aeration: A comprehensive technical, environmental, and economic assessment

The landfill is still the primary waste treatment method in developing countries. Due to the long stability time and long-term occupation of a large amount of land, the landfill poses a significant threat to the ecological environment and affects the process of urbanization. This study conducted a landfill simulation reactor (LSR) experiment to achieve rapid landfill stabilization through micro-aeration and leachate recirculation. More than 60 % of the degradable organic carbon in the enhanced process (LSR-IV contains 24 % of the retained carbon) can be relatively quickly converted to a gaseous state, which is nearly half higher than the degradation efficiency of the traditional process (LSR-I contains 59.3 % of the retained carbon). A comprehensive environmental assessment is developed for the enhanced process, and better environmental benefits are obtained from the whole landfill process. Compared with conventional treatment process, the enhanced process is applied to the actual landfill to analyze the economic cost. In terms of the total cost, the enhanced process cost (60.1 CNY) is about 44 % lower than the conventional landfill process cost (107.6 CNY). The enhanced process saves nearly half of the time cost and reduces the cost of land acquisition. This study can provide a reference for governmental and municipal administrations to carry out the technological transformation of traditional landfills from the aspects of technology, economy and environment.

Mechanistic study of the effect of leachate recirculation ratios on the carboxylic acid productions during a two-phase food waste anaerobic digestion

Food waste (FW) bioconversion to valuable carboxylic acids in leach bed reactors (LBRs) has received increasing attention over the years. Wherein, leachate recirculation is a specific factor when operating LBR to facilitate solid waste degradation. However, its impact and mechanism on the regulation of soluble metabolic products (SMPs) production remain underexplored. Aiming to comprehend the effect of leach recirculation ratio selection on manipulating FW acidogenesis, this study investigated the changes in SMPs production and the corresponding mechanisms in LBRs under different leachate recirculation ratios (LRRs), i.e., 0%, 25%, 50% and 75%. The results showed that the total SMP production increased by approximately 2.3–4.2 folds concurrently with the increasing LRR when compared to that without leachate recirculation. Besides, the SMPs distribution was also ratio-dependent. Mechanistic investigation revealed that the application of leachate recirculation not only alleviated the microbial loss but also improved the abundance of functional gene encodings on fatty acids biosynthesis by 38.5–65.4%, enhancing the SMP production. Moreover, the leachate recirculation at different levels significantly changed the key bacteria responsible for SMPs production. By increasing the LRR, the main functioning acid producer mainly altered from Lactobacillus to Clostridium, Bifidobacterium, Megasphaera and Caproicoproducens. Consequently, the dominated SMP was changed from lactate to butyrate and/or medium-chain fatty acids. Together, this study offers a mechanistic insight into the role of the LRR on FW acidogenesis and emphasize the significance of leachate recirculation on enhancing and manipulating SMP production.

Performance of a percolation reactor integrated to solid-state anaerobic garage-type digesters with leachate recirculation for organic fraction of municipal solid waste treatment

Solid-state anaerobic digestion (SSAD) systems have been used for the sustainable treatment of the organic fraction of municipal solid waste (OFMSW). Unlike previous reports considering lab-scale SSAD systems as a unique system, the present study aims to deeper evaluate only the complementary percolation reactor (PR) integrated into the first semi-industrial scale SSAD system in Latin America. An innovative methodology was developed based on the probability function analysis of the monitoring data with target values reported in the literature and a linear correlation matrix to address the relation between different operating parameters. The results indicate that under a maximum organic loading rate of 1.9 kg VS.m−3.d−1, PR achieved a VS removal efficiency of 56 %, producing a highly stabilized inoculum (VS/TS ratio of 0.43). A maximum methane yield of 0.06 m3 CH4.kg VS−1removed and biogas CH4 content up to 76.5 % were reached during the long-term operation of 730 days.

Evaluation of Leachate Recirculation as a Stabilisation Strategy for Landfills in Developing Countries

This study evaluated leachate recirculation (LR) as a stabilisation strategy for landfills using bioreactor experiments with excavated waste from a tropical landfill in Colombia. The experimental evaluation was performed in two 115 L bioreactors, one simulating the operation of a landfill with LR, Br2, where the leachate produced was recirculated at a rate of 0.8 L d−1, and a control system without LR, Br1. Both systems reached stabilisation indicator values on a dry matter (DM) basis for volatile solids VS (<25% DM) and a biochemical methane potential BMP (≤10 mL CH4 g−1 DM). Likewise, towards the end of the experiment, the leachate generated in Br2 reached stabilisation indicator values for BOD5 (<100 mg L−1) and the BOD (biological oxygen demand)/COD (chemical oxygen demand) ratio (<0.1). Although the stabilisation criterion for COD was not met in any bioreactor (<200 mg L−1), LR helped to release 19% more oxidisable organic matter in Br2 than in Br1, indicating a reduction in the contaminating potential of the waste in the case of uncontrolled discharges of leachate to the environment. Regarding biogas production, the generation of CH4 in Br2 was more intense and its cumulative production was 34.5% higher than Br1; thus, Br2 achieved CH4 emission rates, indicating waste stabilisation (<1.0 L CH4 m−2 h−1) sooner than Br1, showing an accelerating effect of LR on waste degradation. A carbon mass balance indicated that waste degradation, in terms of the initial total organic carbon mineralisation and the C gas discharge via CH4, was greater in Br2. These results demonstrate the LR potential to accelerate the stabilisation of a landfill but also to reduce greenhouse gas emissions in final disposal sites where biogas is also captured and utilised for energy production; a key aspect when improving the sustainability of landfill operations in developing countries.

Influence of Hydraulic Conductivity and Moisture Retention Characteristics of Waste on the Performance of Leachate Recirculation System

Influence of Hydraulic Conductivity and Moisture Retention Characteristics of Waste on the Performance of Leachate Recirculation System

Bioavailability reduction of heavy metals through dual mode anaerobic Co-landfilling of municipal solid waste and industrial organic sludge

Heavy metal physiology during landfilling process defines its overall efficacy. In this study, bioavailability of heavy metals (Cu, Pb, Cr, Ni, Cd and Zn) was investigated using Tessier’s sequential extraction method during co-landfilling of pressmud and municipal solid waste performed in dry tomb – bioreactor landfilling as dual mode. Pressmud and municipal solid waste were mixed in three distinct proportions in separate landfill reactors, viz., 1:3, 1:1 and 3:1 against control reactor with sole municipal solid waste disposal. As bioreactor operation, periodic leachate recirculation was performed in all the reactors, after 192 days of dry tomb landfilling. The results revealed that dry tomb – bioreactor landfilling approach of landfilling induced significant reduction in bioavailability of heavy metals. Moreover, addition of pressmud as industrial organic sludge in simulated landfills, further enhanced the immobilization of heavy metals. In particular, landfill reactor with equal co-disposal ratio, achieved highest increments in stable residual fractions (Cr, Ni, Pb, Cu, Cd and Zn by 4.69%, 8.45%, 6.80%, 6.84%, 3.40% and 4.35%, respectively) of each heavy metal after 300 days of dual mode landfilling operation. Other co-disposed landfill reactors also attained significant reductions in bioavailability of heavy metals, unlike control reactor. The variations in species of heavy metals were reliant on co-disposal proportions of pressmud and municipal solid waste. In addition, correlation analysis between physico-chemical parameters and speciation of heavy metals also advocated dependency of landfilling environment on variation of heavy metals and their potential transformation into relatively stable states.

Effect of Zeolite on the Methane Production from Chicken Manure Leachate

This study demonstrates the leachate characteristics derived from bench-scale leach-bed reactors (LBRs) filled with chicken manure (CM) and zeolite. Zeolite was used to maintain the necessary porosity for the leaching process and to adsorb ammonia. Fresh water was added for leachate production and removed daily, in order to estimate the readily leachable organic and nitrogen matter of the CM. Tests were conducted at two ratios of zeolite to bed (10% and 3.5% v/v CMbed). Other operating parameters studied were the amount of water added in the LBRs, the leachate recirculation rate, and the hydraulic retention time (HRT). A control LBR with river pebbles at a similar size and ratio (10% v/v) with zeolite was also studied. Some experiments were repeated with CM, which had different characteristics. Compared to the control test, the LBR with zeolite at 10% v/v yielded leachate with less NH3 and a higher biochemical methane potential (BMP). However, free ΝH3 in the control experiment was below the inhibition threshold, proving that zeolite contributes to the higher BMP of leachate, and that this effect is not only due to NH3 adsorption.

Intermittent aeration reducing N2O emissions from bioreactor landfills with gas–water joint regulation

Landfills are important emission sources of atmospheric N2O, especially bioreactor landfills with leachate recirculation. In this study, N2O emissions were characterized in four bioreactor landfills with different ventilation methods, including intermittent (2-h aeration per 12 h or 4 h/d in continuous) and continuous aeration (20 h/d), in comparison to a traditional landfill without aeration. During the experiment, the N2O emissions from the landfill reactors with intermittent aeration were 7.48 and 7.15 mg, accounting for only 20.8% and 19.9% of those with continuous aeration, respectively. Continuous aeration was more favorable for the biodegradation of organic matter than intermittent aeration in the landfilled waste and leachate. Intermittent and continuous aeration could both effectively remove total nitrogen (TN) and NH4+-N with removal efficiencies above 64% in the leachate. In the experimental landfill reactors with gas–water joint regulation, the proportion of N2O-N to TN loss ranged from 0.02% to 0.75%. Luteimonas, Pseudomonas, Thauera, Pusillimonas and Comamonas were the dominant denitrifying bacteria in the landfill reactors. The denitrifying bacterial community in the landfilled waste was closely related to its degree of stabilization and nitrogenous compound concentrations in the landfilled waste and leachate. The NO3–-N and NO2–-N concentrations of leachate were the most important environmental factors affecting the succession of nirS-type and nirK-type denitrifying microbial communities in the landfilled waste. These findings indicated that intermittent aeration was an economical and effective way to accelerate the stabilization of landfilled waste and reduce the pollutants in leachate and N2O emissions during landfill mining and reclamation.

Enhanced Landfill Process Based on Leachate Recirculation and Micro-Aeration: A Comprehensive Technical, Environmental and Economic Assessment

Enhanced Landfill Process Based on Leachate Recirculation and Micro-Aeration: A Comprehensive Technical, Environmental and Economic Assessment

Enhanced Landfill Process Based on Leachate Recirculation and Micro-Aeration: A Comprehensive Technical, Environmental and Economic Assessment

Enhanced Landfill Process Based on Leachate Recirculation and Micro-Aeration: A Comprehensive Technical, Environmental and Economic Assessment

Enhanced Landfill Process Based on Leachate Recirculation and Micro-Aeration: A Comprehensive Technical, Environmental, and Economic Assessment

Enhanced Landfill Process Based on Leachate Recirculation and Micro-Aeration: A Comprehensive Technical, Environmental, and Economic Assessment