Landfill Simulation Reactors Research Articles

LANDFILL MINING IN THE FRAMEWORK OF INTEGRATED WASTE MANAGEMENT: CASE STUDY OF AN ITALIAN LANDFILL

A remediation project involving landfill mining (LFM) was designed and is ongoing at the 40-year-old Villadose landfill in Rovigo, Italy. The original natural clay lining the bottom of the old landfill is being recovered and used as technical material. Meanwhile newly constructed landfill sectors, designed to contained more than four times more waste than previously are being filled with both excavated waste and fresh municipal solid waste. A laboratory scale experiment was conducted to simulate the expected landfill conditions and analyse the effects of different waste fractions on emissions. The fresh municipal waste although pretreated at a mechanical biological treatment plant shows a significant residual emission potential, in terms of TOC, and NH4. A landfill housing such quality of waste would not be expected to have achieved final storage quality by the end of its aftercare life. The joint disposal of this waste fraction and the substantially degraded excavated waste may contribute to shortening this timeline. This paper reports the landfill mining operation, an assessment of the emissions from the landfill simulation reactors and the implications for the expected landfill behaviour.

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.

Applying the 15N labelling technique to material derived from a landfill simulation experiment to understand nitrogen cycle processes under aerobic and anaerobic conditions

Reactive nitrogen (N) species, such as ammonium (NH4+), nitrate (NO3) and gaseous nitrous oxide (N2O), are released into the environment during the degradation of municipal solid waste (MSW), causing persistent environmental problems. Landfill remediation measures, such as in-situ aeration, may accelerate the degradation of organic compounds and reduce the discharge of ammonium via leachate. Nonetheless, the actual amount of N in the waste material remains relatively constant and a coherent explanation for the decline in leachate ammonium concentrations is still lacking. Hence, the present study aimed to elucidate the dynamics of N and its transformation processes during waste degradation. To this end, the gross rates of organic N mineralization and nitrification were measured using 15N pool dilution in waste material derived from a landfill simulation reactor (LSR) experiment. The results revealed a high potential for N mineralization and nitrification, the latter of which declined with the diminishing amount of extractable ammonium (after aeration). The analysis of the concentration and isotopic composition of N2O formed confirmed incomplete denitrification as the main source for N2O. Moreover, the natural abundance of 15N was investigated in various waste N pools to verify the conclusions drawn from the 15N tracing experiment. δ15N values of total waste N increased during aeration, indicating that nitrification is the major driver for N losses from aerated waste. The application of stable isotopes thereby allowed unprecedented insights into the complex N dynamics in decomposing landfill waste, of their response to aeration and their effect on hydrological versus gaseous loss pathways.

Municipal Solid Waste Management through Sustainable Landfilling: In View of the Situation in Karachi, Pakistan.

Open disposal is the most common technique used for municipal solid waste (MSW) management due to the absence of sanitary landfills in Pakistan. The major cities and small towns in Pakistan have become a showcase of negligence and mismanagement of MSW, which results in deterioration of the environmental and social-life quality. Moreover, research has proved that inefficient handling (disposal) of MSW results in uncontrolled emissions of greenhouse gases (GHGs), mainly methane, and adds a significant share in global climate change. This study aims to estimate methane emissions from MSW disposed of at dumpsites and compare the GHG mitigation potential of different landfill strategies in specific climate and waste compositions in Karachi. The GHG estimations are based on lab-scale investigations conducted by simulating landfill conditions through the landfill simulation reactor (LSR) experiment. The synthetic MSW sample representing the composition of MSW generated in Karachi was used in the LSR experiment. Environmental sustainability and GHG mitigation potential of different landfilling strategies was evaluated by analyzing gas formation potential (GP21) and respiration activity (RI4) at the end of the experiment. This study revealed that the quantity of solid waste annually disposed of at dumpsites in Karachi possesses the potential to release about 3.9 Mt CO2-eq. methane (with specific methane potential of 1.8 tCO2-eq./tonne DM disposed) due to the biological decomposition of the organic fraction. Results show that the fresh waste disposed of at landfill sites in Karachi possesses about 92% and 94% higher GP21 and RI4, respectively, than the German allocated criteria for mechanically and biologically treated (MBT) waste for landfills Furthermore, sanitary landfills with post-aeration conditions showed higher GHG mitigation potential and low biological activity in the waste. The second highest GHG mitigation potential and lowest biological activity of the waste was noticed from bioreactor landfills with post-aeration conditions. The third number in GHG mitigation and reduced waste activity was noticed in the waste sampled from bioreactors without aftercare approach. The least GHG mitigation potential was noticed from the uncontrolled waste dumping (existing) approach with high residual gas potential and respiration index level. This lab-scale landfill simulation study can provide baseline data for further research and planning the development of new sustainable landfills in Karachi, Pakistan and in the region.

The microbial metabolic activity on carbohydrates and polymers impact the biodegradability of landfilled solid waste

Biological waste degradation is the main driving factor for landfill emissions. In a 2-year laboratory experiment simulating different landfill in-situ aeration scenarios, the microbial degradation of solid waste under different oxygen conditions (treatments) was investigated. Nine landfill simulation reactors were operated in triplicates under three distinct treatments. Three were kept anaerobic, three were aerated for 706 days after an initial anaerobic phase and three were aerated for 244 days in between two anaerobic phases. In total, 36 solid and 36 leachate samples were taken. Biolog® EcoPlates™ were used to assess the functional diversity of the microbial community. It was possible to directly relate the functional diversity to the biodegradability of MSW (municipal solid waste), measured as RI4 (respiration index after 4 days). The differences between the treatments in RI4 as well as in carbon and polymer degradation potential were small. Initially, a RI4 of about 6.5 to 8 mg O2 kg−1 DW was reduced to less than 1 mg O2 kg−1 DW within 114 days of treatment. After the termination of aeration, an increase 3 mg O2 kg−1 DW was observed. By calculating the integral of the Gompertz equation based on spline interpolation of the Biolog® EcoPlates™ results after 96 h two substrate groups mainly contributing to the biodegradability were identified: carbohydrates and polymers. The microbial activity of the respective microbial consortium could thus be related to the biodegradability with a multilinear regression model.

Influence of moisture content and leachate recirculation on oxygen consumption and waste stabilization in post aeration phase of landfill operation

Sustainable completion of municipal solid waste landfills requires post-closure care after a time when utilization of landfill gas produced from biodecomposition of organic waste be not possible/or economically feasible. Research proved that in-situ aeration is a promising approach employed for landfill aftercare. The application of post aeration operation is targeted to achieve accelerated waste stabilization to avoid long term environmental and public health impacts from landfills. In in-situ aeration operation, consumption of supplied oxygen has significant influence on biological stabilization of solid waste placed in the landfills. The consumption of oxygen is regulated by operation parameters of landfill – one of the important is presence of moisture in landfill ecosystem. This research aims to assess the influence of moisture content and leachate recirculation on the oxygen consumption during post aeration phase of landfill operation. The effect of oxygen consumption on the extent of waste stabilization achieved after experiment was also assessed. Three lab-scale landfill simulation reactors (LSRs) were used – in two of three reactors (LSR-1 and LSR-3) operation was carried out in two phases: Anaerobic and post-aeration. One reactor (LSR-2) was operated under anaerobic condition throughout the experiment and used as control. To compare the oxygen consumption, conventional landfill (CLF) conditions without excess water addition and leachate recirculation were simulated in LSR-1 and the bioreactor landfill conditions (BRLF) with excess water injection and leachate recirculation were simulated in LSR-3. In CLF 46.4% of supplied oxygen was consumed during post aeration phase while in BRLF only 0.96% of oxygen consumption was noticed. In result of higher oxygen consumption, biostabilization rate of waste in CLF was 7% higher than BRLF at the end of experiment. This study demonstrated that, in presence of low moisture in landfill ecosystem optimal air distribution can be realized which results in enhanced waste oxidization and stabilization.

Test investigation of percolation through municipal solid waste (MSW) with a triple function physical model

In this study, municipal solid waste (MSW) was considered as a three-phase structure including a waste body with a given field capacity and permeability, preferential channels with high permeability and impermeable sections. Hence, a landfill simulation reactor (LSR) consisting of rockwool and Sand (as the waste body), copper pipes (as preferential channels) and plastic pieces (as impermeable sections) was operated to analyze the leachate percolation from a landfill site. Waste permeability and field capacity were formulated as a function of two operating variables (impermeable sections and preferential channels) using response surface methodology (RSM). The results indicated that the preferential channels increased the MSW permeability; however, they did not affect the field capacity significantly. It was also found that even small changes in the impermeable sections severely affected both the permeability and the field capacity of MSW. The obtained experimental data and the actual leachate data of full-scale cells in Tehran Landfill were used to calibrate the landfill parameters. According to the calibration results, the estimated volume of impermeable sections in the landfill was 15.05% per cubic meter MSW, of which, 10% is activated in recirculation and intense precipitations (as secondary field capacity). Besides, the ratio of leachate discharge through preferential channels (instantly) to the total discharge was estimated at 0.26 and the travel time of leachate through the waste body was approximately 46 days.

Environmental Sustainability Enhancement of Waste Disposal Sites in Developing Countries through Controlling Greenhouse Gas Emissions

Sustainable management of municipal solid waste is one of the major challenges for authorities in developing countries. Current waste disposal methods in Pakistan and other developing countries are not meeting standards of any proper waste management system opted for in the developed world. This mismanagement of waste is leading to serious environmental problems at local as well as global levels. This study aims to investigate the methane emissions from waste dumpsites in the city of Karachi, Pakistan, and to propose an effective approach to enhance their environmental sustainability. The methane emissions from waste disposal sites were assessed by simulating four different landfill situations during the landfill simulation reactor experiment. The residual methane reduction potential of each waste disposal approach was assessed by a biochemical methane test of waste after the experiment. It is estimated that in the present situation, about 11,500 tons of CO2-eq methane is released annually from waste disposal sites in Karachi. The convectional anaerobic landfill with methane capturing facilities and post-aeration operation was found to be the most environmentally sustainable approach with controlling 65% of residual methane emissions in comparison with the present scenario. For the development of new landfill sites, we recommend the bioreactor landfill approach with methane recovery and post-care (in-situ aeration).

Statistical modelling and assessment of landfill leachate emission from fresh municipal solid waste: A laboratory-scale anaerobic landfill simulation reactor study.

Quantification, measurement of quality, post-treatment, and leachate control has been a significant problem due to the dumping of waste in an unscientific manner across the globe, and especially in developing countries like India. In this context, the objective of this study was to investigate the degradation of fresh mixed municipal solid waste (MSW) in an anaerobic landfill reactor operated with rainfall addition in laboratory conditions. Experiments were carried out in a landfill reactor of 1 m length × 1 m width × 1.1 m height. The reactor was simulated with 50 years weighted average actual rainfall rate of India. It contained the waste composition of 73% wet waste (food and kitchen) and 27% dry waste (paper, plastic, wood, textiles, and others). The leachate parameters were continually monitored for 39 weeks. In the fresh MSW landfill reactor it was evident that concentrations of leachate parameters were high initially, and there was a significant decrease in BOD5 (7041-39310 mg L-1), COD (15692-71630 mg L-1) and TS (9077-33200 mg L-1) in leachate. Therefore, rainfall had a direct influence on leachate quality. The developed first-order decay models were used for BOD5, COD, and total solids with adjusted R2 of 0.83, 0.92, and 0.96, respectively. Therefore, this model can be applied for leachate strength estimation at any given time from the period of deposition of waste under similar rainfall and waste compositions, and is largely applicable in India and tropical areas. This study is expected to be a good simulation for cities with the waste composition of high wet waste (>70%) as the estimations of important design parameters such as BOD5, COD, VFA, and NH4+-N were studied in this research. As the importance of moisture (precipitation) has been established in this study, some moisture additions can be designed in areas with low rainfall, such as arid zones.

Effects of char from biomass gasification on carbon retention and nitrogen conversion in landfill simulation bioreactors.

The application of char from biomass gasification as a filling material in landfill simulation reactors was investigated to evaluate the effect of char on carbon retention and nitrogen leaching, nitrogen denitrification, and waste stabilization. Landfill simulation columns filled with fine fraction of aged refuse (AR) and solid fraction of digestate (SFD) were used, with two char application methods: embedding a char layer between AR and SFD layers and mixing char with the SFD. The experimental results show that char application increased the biodegradable organic matter content as the respiration index (RI4) of the mixture char-SFD increased up to 37.7%, which could enhance the heterotrophic denitrification. Moreover, 12.3% of ammonia leaching was avoid by applying the SFD mixed with char. These results indicate that char from biomass gasification poses a significant enhancement on nitrogen and carbon retention which might increase the denitrification capacity of the SFD in the long run. Although high nitrogen removal rates were achieved (up to 23.1mgN/kg-TS day), the addition of char from biomass gasification has little effect on the nitrate removal.

Influence of the void fraction and vertical gas vents on the waste decomposition in semi-aerobic landfill: Lab-scale tests

The waste classification has not been carried out worldwide, especially in developing countries. The high content of water in the kitchen waste will definitely affect the amount of air flowing into waste layer from leachate collection pipe. In this experiment, three lab-scale landfill simulation reactors were established. Reactor A and B are semi-aerobic landfill modes, while reactor C has no vertical gas vent. The void fraction in the waste of reactor B was increased by adding gravel serve as part of the waste. The waste sample used in landfill reactor mainly included kitchen waste (58%). The waste decomposition conditions in the landfill were investigated using temperature sensors embedded in the waste, by determining the velocity and gas flow direction and by measuring the volume and composition of leachate produced. The results showed that the void fraction of waste in reactor A and C was 29.79% and 30.86% respectively, and that of waste in reactor B 34.96%. Compared with reactor A, reactor B had its temperature increase earlier. In addition, the temperature distribution in vertical gas vent of the reactor A and B is higher than in the leachate collection pipe. The gas flux of vertical gas vent increased with the temperature of gas vent. Reactor A and B had significantly lower concentration of chemical oxygen demand (COD) and ammonia nitrogen (NH3+-N) than that of reactor C. It was concluded that landfill decomposition can be accelerated by increasing the void fraction in the waste and keeping a vertical gas vent open.

Optimization of operations for nitrous oxide production and mitigation in aerobic and Aerobic-Anaerobic landfill method on MSW degradation

N2O is a potent greenhouse gas, induced by aeration coupled with leachate recirculation in Municipal Solid Waste (MSW) landfills. In this study, N2O emission was measured in the aerobic and Aerobic-Anaerobic Landfill Method (AALM) with or without leachate recirculation at two aeration rates in synthetic MSW. The experiment was carried out for six Plexiglass® landfill simulation reactors. Low aeration (1.6 l/kg-DM/h) was supplied in RLA, RLAA (Recirculatory) and LAA (non-recirculatory) reactors, while an aeration rate three times higher (4.8 l/kg-DM/h) was performed for RHA, RHAA, and HAA reactors. Based on the supplied leachate quantity, leachate recirculation was performed in five different phases. The results showed that a significant amount of N2O was produced in all reactors. The largest N2O emission of 0.11 and 0.13 g/kg-DM were observed in the RHA and RHAA reactors, respectively. Higher N2O and cumulative GHG was produced in high aeration reactors compared to the low aeration reactors. Recirculated leachate promoted waste stabilization, as reflected in the diminishing CH4 production and other leachate pollutant parameters, especially NH4+-N. It has been evaluated that in the operative or newly placed waste landfill, in-situ aeration with leachate recirculation exhibits the significant N2O production. However, lower amount of leachate in the later stage beneficial to inhibit the N2O production. It is recommended that in-situ aeration will become more effective after the recovery of CH4 from newly placed waste in an operative landfill for net GHG reduction, especially N2O reduction and early stabilization of landfills.

Heavy metals in municipal waste: the content and leaching ability by waste fraction

Today, heavy metals remain crucial pollutants in municipal waste due to their danger and leaching behavior. The purpose of this study is to analyze the sources of heavy metals in mixed municipal waste, including from recently introduced products, and to identify their composition and leaching properties in various fractions. The author has measured the concentration of four heavy metals (lead, cadmium, nickel, and chromium) in various fractions sampled from an operational municipal waste facility in the town of Pirna (Saxony, Germany). Batteries and waste electrical and electronic equipment (WEEE) were found to be the main sources of heavy metals in municipal waste, while a relatively high metals’ content was also detected in the rubber fraction. To assess leaching behavior, landfill simulation reactors were used to simulate conditions over several decades. The metals’ weight in the input and output waste was compared. The lowest leaching rate was found for lead, while the highest was found for cadmium and chromium. In addition, it was confirmed that the degree of leaching depended on the humidity and organic matter in the landfill: the higher the moisture and organic matter, the more heavy metals are leached from the waste.

Anaerobic/aerobic conditions determine antibiotic resistance genes removal patterns from leachate by affecting bacteria taxa-genes co-occurrence modules

Landfill treatment of municipal solid waste treatment produces a large amount of leachate, which has been an important hotspot of ARGs. This study aimed to investigate the ARGs removal potential, kinetics and mechanism from leachate in aerobic and anaerobic conditions. Simulated landfill reactors showed the efficacy in reducing ARGs, and the removal efficiencies depended on ARGs types and aerobic/anaerobic conditions. The ARGs tetQ and blaCTX-M were more likely to attenuate with the log-removal efficiencies of 1.50–3 order of magnitude. The ARGs removal kinetic was well fitted by modified Collins-Selleck model, and aerobic condition showed better removal capacities and kinetics than anaerobic condition. Among the ARGs with great removal performance, sul2, aadA1and blaCTX-M were eliminated from leachate and refuse simultaneously, but tetM, ermB, and mefA were removed from leachate but enriched in refuse. Aerobic/anaerobic states might drive the bacterial community shift of leachate and refuse, and topology property comparison of co-occurrence networks suggested that refuse had a closer non-random host relationship between ARGs and microbial taxa than leachate. Further module analyses revealed that ARGs removal efficiencies depended on the taxonomy of host bacteria in leachate, while the refuse taxa-ARGs correlation determined ARGs removal patterns. By selecting distinct bacteria cluster in different conditions, aerobic treatment benefited ARGs reduction in leachate and refuse, while anaerobic treatment enhanced the enrichment of ARGs in refuse. These findings can potentially foster the understanding of ARGs removal mechanism in biological treatment processes.

Denitrification of Mature Landfill Leachate with High Nitrite in Simulated Landfill Columns Packed with Solid Digestate from Organic Fraction of Municipal Solid Waste

PURPOSE: The management of solid digestate (SD) from organic fraction of municipal solid waste is essential component of sustainable biogas plants. Beyond land use, this study aims to evaluate the application of digestate in simulated landfill columns to enhance nitrogen conversion of partially nitrified landfill leachate (PNL). METHODS: Two identical simulated landfill reactors filled with SD were setup and PNL was fed through the columns. The PNL characteristics were 1004 mg N–NO₂⁻/L, 428 mg N–NO₃⁻/L, and 434 mg N–NH₄⁺/L. RESULTS: After 109 days of operation, the average N–NO₂⁻and N–NO₃⁻ removal efficiencies were 92.6% and 85.8%, respectively. The high concentrations of nitrite did not significantly inhibit methane production during denitrification in the digestate-added landfill columns as the average specific methane production yield was 20.1 normal liter (NL) CH₄/kg VS. CONCLUSIONS: These results suggest that the novelty of applying SD in a landfill can achieve denitrification in a carbon limited environment observed in mature landfill leachate and stabilization of the digestate.

Influence of operations on leachate characteristics in the Aerobic-Anaerobic Landfill Method

Landfill aeration is an effective technique for the controlled and sustainable conversion of conventional anaerobic landfills into a biologically stabilized state associated with a significantly lowered or the near elimination of the landfill gas emission potential. For in-situ leachate treatment recycling back the generated leachate in the bioreactor is also a promising technique for reducing pollutants and cost of ex-situ treatment as well. This research has been conducted to ascertain the in-situ treatment of leachate in Aerobic Anaerobic Landfill Method (AALM) compared with aerobic landfill and evaluated the impacts of various leachate recirculation regimes on MSW degradation and to provide data for successful operation in landfill sites. The experiment was conducted using six Plexiglass® landfill simulation reactors with a height of 100 cm and a diameter of 15 cm. Air was injected at the rates of 1.6 l/kg DM/h (Low aeration rate) for reactors R-LA, R-LAA (recirculatory) and LAA (non-recirculatory) and 4.8 l/kg DM/h (High aeration rate) in R-HA, R-HAA (recirculatory), and HAA (non-recirculatory) until day 242. It has been evaluated that R-HAA at high aeration rate achieved higher leachate quantity reduction (36.9%) than low aeration rate reactor R-LAA (19.6%) and AALM provides a better solution to control the temperature within the landfill body. The final NH4+-N concentration in R-HA (214.5 mg/l) was eight times lower than in the R-LA (1741.0 mg/l) reactor, and R-HAA (842.5 mg/l) was about three times lower than R-LAA (2315.4 mg/l) reactor on day 242. The change in leachate recirculation amount at varying moisture content positively affected the stabilization process and in-situ leachate treatment efficiency. The combination of both technologies (intermittent aeration and leachate recirculation) is a feasible way for in-situ leachate treatment, decrease the cost of further ex-situ leachate treatment as well as a viable and cost-saving alternative to continuous aeration.

Prediction of heavy metals concentration in the leachate: a case study of Ukrainian waste

A lifetime of landfill with the waste composition and conditions specific to big and small towns of Ukraine is reproduced with landfill simulation reactors in 12-week period. The heavy metals concentrations (lead, nickel, chromium, cadmium) and physico-chemical parameters affecting (pH, reduction potential, conductivity, DOC, COD) are measured in the leachate formed during the reactors exploitation. The results show a quite high content of the heavy metals. Higher concentrations are found where more organic fraction is present in the waste. There are conditions inside the reactors, especially acidity, which are crucial at the early stages. Further, a significant impact can be caused by unequal distribution of heavy metals in the waste body. Also due to accelerated water regime in the reactors, the heavy metals concentrations in a landfill leachate are predicted up to 50–55 years. Forecast shows multiple (2–18 times) exceeding the allowable concentrations of all heavy metals.

Release behavior of chloride from MSW landfill simulation reactors with different operation modes

The chloride ion (Cl−), a very common monatomic anion, has high ecological toxicity at high concentrations because of its non-biodegradability, and can easily migrate from landfill site into the surrounding environment. Four lab-scale landfill simulation reactors were established to investigate Cl− release behavior: the anaerobic landfill mode (R1), the semi-aerobic landfill mode (R2), the anaerobic landfill with leachate re-circulation mode (R3), and the semi-aerobic landfill with leachate re-circulation mode (R4). The landfill operation modes had a great influence on the release of Cl−. In 256 days, the cumulative release amounts of Cl− in the four reactors were 64.52, 132.07, 56.10, and 33.1 g for R1–R4, respectively. Once air enters anaerobic landfill, the leachate Cl− concentration may sharply increase. The highest leachate Cl− concentrations were 6.6 g L−1 in anaerobic reactor and 18 g L−1 in semi-aerobic reactor. However, the leachate re-circulation can maintain the release of Cl− at dynamic equilibrium state. Theoretically, the Cl− release behavior from anaerobic landfill with leachate re-circulation (R3) will be continuous. In contrast, under the other conditions, it can be anticipated to occur once the leachate recirculation stops (R1) or when the landfill encounters air incursion (R2 and R4). The semi-aerobic operation modes had significantly lower COD/Cl and NH4-N/Cl ratios than the anaerobic modes. This indicates that the Cl− pollution risk from semi-aerobic modes is lower than that from anaerobic modes.

FRACTIONATION OF ZINC IN MUNICIPAL SOLID WASTE LANDFILL LEACHATE: EFFECT OF LEACHATE RECIRCULATION

Two sets of simulated landfill reactors, namely conventional landfill (CL) and leachate recirculated landfill (RL) were operated to investigate the effect of leachate recirculation on the fractionation of Zn in municipal solid waste (MSW) landfill leachate. Zn in landfill leachate was fractionated into three fractionations: particulate and colloidal matter >0.45 m, non-labile complexes 0.45 m and non-labile complexes at the end of the study, for both of landfills. The recirculation of leachate could facilitate the transformation of the fractionation of Zn. Moreover, large amounts of Zn mainly present as free cations/labile complexes and non-labile complexes were leached out from CL, while only small amounts of Zn mainly present as was particulate and colloidal matter >0.45 m were leached out from RL all through the study. It suggested the leachate recirculation not only reduced total leaching amounts of Zn, but also decreased the bioavailability and toxicity of the leached Zn.

Biocomplex textile as an alternative daily cover for the simultaneous mitigation of methane and malodorous compounds

Space-saving biocomplex textiles, which can be used as covers or rolled up as needed, have been demonstrated as alternative daily covers for the simultaneous mitigation of greenhouse gases (GHGs) and odors in landfills. The biocomplex textiles were made by inserting inorganic biocarriers (perlite (P), tobermolite (T) and their mixture (P/T)) between nonwoven fabrics. Methane (CH4) and dimethyl sulfide (DMS) were used as model compounds for GHGs and odors, and a CH4 and DMS co-degrading microbial consortium was used as an inoculum source. CH4 and DMS could be biologically degraded by methanotrophs and sulfur-oxidizing bacteria in the biocomplex textiles. Both biocomplex textiles made with either P or T were able to maintain the removability for CH4 and DMS after storage for 70 days, although their removal efficiencies for CH4 and DMS were 70–71% and 62–65% of those before storage, respectively. CH4 and DMS were simultaneously removed in lab-scale landfill simulation reactors employed with the biocomplex textiles. After 17 days of starvation, only 2–3 days were needed to recover their removability. Among the 3 kinds of biocarriers evaluated, the biocomplex textile generated using the P/T showed the highest removability and was the most stable. The maximum elimination capacities of the biocomplex textile generated with the P/T were 11.5 g-CH4·m−2-fabric·d−1 and 0.5 g-DMS·m−2-fabric·d−1, respectively. These results suggest that the biocomplex textiles are promising alternative daily covers to mitigate the emission of greenhouse gas and odor in operational landfills.