Semi-aerobic Landfill Research Articles

Extraction and application of starch-based coagulants from sago trunk for semi-aerobic landfill leachate treatment.

Malaysia is one of the highest starch producers. In this study, sago starch was utilized as a natural coagulant aid to reduce the dosage of aluminum-based coagulant in leachate treatment. The potential of native sago trunk starch (NSTS) and commercial sago starch (CSS) was evaluated as sole coagulant and coagulant aid in the presence of polyaluminum chloride (PACl) in the removal of color, suspended solids (SS), NH3-N, turbidity, chemical oxygen demand, organic UV254, Cd, and Ni. Leachate was sampled from Pulau Burung Landfill Site, one of the semi-aerobic landfills in Malaysia. The optimum dosage for PACl in the presence of NSTS or CSS as coagulant aid was reduced from 3100 to 2000 mg/L. In the presence of 2000 mg/L PACl with 6000 mg/L NSTS and 2000 mg/L PACl with 5000 mg/L CSS, the removal performance for color, SS, and turbidity are 94.7, 99.2, and 98.9%, respectively. Similar results were obtained with the use of 3100 mg/L PACl alone. Therefore, CSS and NSTS can be used as coagulant aid.

Temporal and Spatial Distribution Characteristics of Nitrate Nitrogen in Leachate of the Semi-Aerobic Landfill Treatment

Contrast experiment was developed on the semi-aerobic and anaerobic landfill treatment. Leachate nitrate nitrogen concentrations in different landfill layers spatially were monitored regularly in two landfill equipments, and variations and differences of leachate nitrate nitrogen concentration of different landfills were discussed. The results showed that differences on the variation characteristics of nitrate nitrogen concentration in space and time were obvious in the landfill treatments with different structures. In 73 weeks of monitoring period, nitrate nitrogen concentration in the middle and the lower layer of semi-aerobic landfill treatment was in turn stable within 55.40 mg/L and 40.80 mg/L; The concentration fluctuations in both layers were small in general. Nitrate nitrogen concentration decreased respectively to 9.26 mg/L, 6.82 mg/L and 4.69 mg/L at the 73th week from 28.51 mg/L, 4.44 mg/L and 5.85 mg/L at the initial landfill stage in the lower , middle and the upper layer of anaerobic landfill treatment. When degradation of the landfill treatments went into relatively stable stage, nitrate nitrogen concentration in the upper, middle and the lower layer of semi-aerobic landfill treatment was located respectively in 30-240 mg/L, 2.5-11.0 mg/L and 5.5-13.5 mg/L respectively, and the spatial distribution difference of nitrate nitrogen concentration in the upper layer of semi-aerobic landfill treatment was relatively big, but those of the middle and the lower layer were relatively small, and they were both lower than the upper layer. Nitrate nitrogen concentration in the upper, middle and the lower layer of anaerobic landfill treatment was located in 1.6-7.4 mg/L, 3.8-7.2 mg/L and 7.5-15 mg/L respectively, and showing a performance of spatial nitrate nitrogen concentration that was the lower layer> the middle layer >the upper layer. Under the experimental conditions, seim-aerobic landfill treatment was favorable to the nitrification and denitrification of leachate in contrast with the anaerobic landfill treatment.

Effectiveness of the Vertical Gas Ventilation Pipes for Promoting Waste Stabilization in Post-Closure Phase

To make inside of the municipal solid waste (MSW) landfill aerobic as much as possible is thought to be preferable for promoting waste stabilization, reducing pollutant's load in leachate, minimizing greenhouse gas emission and shortening post-closure-care period. In Japan, installation of semi-aerobic landfill structure has widely spread in order to promote waste stabilization in MSW landfill from 1980s. In semi-aerobic landfill structure, outlet of main leachate collection pipe is opened to atmosphere. Heat generated by aerobic degradation of waste causes natural convection and natural aeration arises from the outlet of leachate collection pipe to the gas vents. It is so-called stack effect. This air flow is thought to be effective for purifying leachate flowing through drainage layer and leachate collection pipes. And it is also thought to be contributing to expanding aerobic region in waste layer in landfill. Recently, measures attempting the promotion of waste stabilization are taken at several landfills at where stabilization of waste delays, in which many vertical gas vents are newly installed and close structure to semi-aerobic landfill is created. However, in many cases, these gas vents are not connected to leachate collection pipes. Many vertical gas vents are just installed without scientific proof regarding whether they can contribute for waste stabilization. In this study, how such installation of gas vents is effective for waste stabilization and aerobization of waste layer was discussed by numerical analysis. In numerical analysis, heat transfer, gas movement by pressure, gas diffusion, biological degradation of organic matter, and heat generation by biodegradation were taken into account. Simulations were carried out by using the general purpose simulator of finite element method. Three types of landfill structure were assumed. As the results, the following information were obtained. In dig-down type landfill, installation of gas vents has no effect for changing air flow. On the other hand, in pile-up type landfill, installation of vertical gas vents can accelerate air invasion and significantly promote waste stabilization, if it has high permeable horizontal layer.

Life-cycle greenhouse gas emissions and economic analysis of alternative treatments of solid waste from city markets in Vietnam

We utilize life cycle assessment to trace conversion of degradable organic carbon (DOC) contained in organic waste from city markets in Da Nang, Vietnam. Our methodology makes explicit the process of conversion of DOC under aerobic and anaerobic conditions, as well as the balance of nutrients. Greenhouse gas emissions were calculated for six alternative scenarios: (i) anaerobic landfilling (current situation); (ii) semi-aerobic landfilling; (iii) landfill gas capture; (iv) composting; (v) pre-composting before landfill; and (vi) biogas production. We calculate that 1 t of waste in anaerobic landfilling emits 1.70 t CO2-eq. with life-cycle perspective. Lowest emission occurs in biogas scenario with 0.26 t CO2-eq./t. Composting occupies an intermediate position with 0.39 t CO2-eq./t. Likewise, we estimate that cost of emission reduction in solid waste sector of Vietnam is 15.13 US$/t CO2-eq., given by alternative of composting and taking anaerobic landfilling as reference. On the other hand, if social cost of carbon (SCC) is incorporated lowest cost to treat 1 t of waste is given by composting and semi-aerobic landfilling at discount rate of 5 %. However, using lower discount rates, and consequently higher values of SCC, composting and biogas production become the alternatives with lowest treatment costs.

Field assessment of semi-aerobic condition and the methane correction factor for the semi-aerobic landfills provided by IPCC guidelines

According to IPCC guidelines, a semi-aerobic landfill site produces one-half of the amount of CH4 produced by an equally-sized anaerobic landfill site. Therefore categorizing the landfill type is important on greenhouse gas inventories. In order to assess semi-aerobic condition in the sites and the MCF value for semi-aerobic landfill, landfill gas has been measured from vent pipes in five semi-aerobically designed landfills in South Korea. All of the five sites satisfied requirements of semi-aerobic landfills in 2006 IPCC guidelines. However, the ends of leachate collection pipes which are main entrance of air in the semi-aerobic landfill were closed in all five sites. The CH4/CO2 ratio in landfill gas, indicator of aerobic and anaerobic decomposition, ranged from 1.08 to 1.46 which is higher than the values (0.3–1.0) reported for semi-aerobic landfill sites and is rather close to those (1.0–2.0) for anaerobic landfill sites. The low CH4+CO2% in landfill gas implied air intrusion into the landfill. However, there was no evidence that air intrusion has caused by semi-aerobic design and operation. Therefore, the landfills investigated in this study are difficult to be classified as semi-aerobic landfills. Also MCF of 0.5 may significantly underestimate methane emissions compared to other researches. According to the carbon mass balance analyses, the higher MCF needs to be proposed for semi-aerobic landfills. Consequently, methane emission estimate should be based on field evaluation for the semi-aerobically designed landfills.

Onsite survey on the mechanism of passive aeration and air flow path in a semi-aerobic landfill

The semi-aerobic landfill is a widely accepted landfill concept in Japan because it promotes stabilization of leachates and waste via passive aeration without using any type of mechanical equipment. Ambient air is thought to be supplied to the landfill through a perforated pipe network made of leachate collection pipe laid along the bottom and a vertically erected gas vent. However, its underlying air flow path and driving forces are unclear because empirical data from real-world landfills is inadequate. The objective of this study is to establish scientific evidence about the aeration mechanisms and air flow path by an on-site survey of a full-scale, semi-aerobic landfill.First, all passive vents located in the landfill were monitored with respect to temperature level and gas velocity in different seasons. We found a linear correlation between the outflow rate and gas temperature, suggesting that air flow is driven by a buoyancy force caused by the temperature difference between waste in the landfill and the ambient temperature. Some vents located near the landfill bottom acted as air inflow vents. Second, we conducted a tracer test to determine the air flow path between two vents, by injecting tracer gas from an air sucking vent. The resulting slowly increasing gas concentration at the neighboring vent suggested that fresh air flow passes through the waste layer toward the gas vents from leachate collection pipes, as well as directly flowing through the pipe network. Third, we monitored the temperature of gas flowing out of a vent at night. Since the temperature drop of the gas was much smaller than that of the environment, the air collected at the gas vents was estimated to flow mostly through the waste layer, i.e., the semi-aerobic landfill has considerable aeration ability under the appropriate conditions.

Landfill Gas Detection in Leachate Pipe: A Consideration for Design Improvement of Leachate Piping and Gas Venting Systems

Landfill provides simple and economic means of solid waste disposal. However, it causes negative effects to the environment due to leachate generation and greenhouse gas emissions. Current trends in landfill design allow aerobic or semi aerobic processes to take place inside the landfill to speed up degradation process and reduce odour. In Malaysia, the semi aerobic system of landfill design is adopted. This paper presents the study of the gas venting system and leachate quality of the semi aerobic landfill. The gas samples were collected from the end of the leachate pipe and the gas vent of a sanitary landfill by the water displacement method. Raw leachate samples from the landfill leachate ponds were collected and the COD of the samples were measured. The concentration of methane gas escaping from the leachate pipe was found to be around 13%. The COD content of the raw leachate was found to be more than 15000 mg/l. The improvement of landfill gas collection in Malaysia is recommended.

Spatial patterns of methane oxidation and methanotrophic diversity in landfill cover soils of southern China.

Aerobic CH4 oxidation is an important CH4 sink in landfills. To investigate the distribution and community diversity of methanotrophs and link with soil characteristics and operational parameters (e.g., concentrations of O2, CH4), cover soil samples were collected at different locations and depths from the Mengzi semi-aerobic landfill (SAL) in Yunnan Province of southern China. Specific PCR followed by denaturing gradient gel electrophoresis and realtime PCR were used to examine methanotrophs in the landfill cover soils. The results showed that different locations did harbor distinct methanotroph communities. Methanotrophs were more abundant in areas near the venting pipes because of the higher O2 concentrations. The depth of 20-25 cm, where the ratio of the CH4 to O2 was within the range from 1.3 to 8.6, was more conducive to the growth of CH4-oxidizing bacteria. Type II methanotrophs dominated in all samples compared with Type I methanotrophs, as evidenced by the high ratio of Type II to Type I methanotrophic copy numbers (from 1.76 to 11.60). The total copy numbers of methanotrophs detected were similar to other ecosystems, although the CH4 concentration was much higher in SAL cover soil. Methylobacter and Methylocystis were the most abundant Type I and Type II methanotrophs genera, respectively, in the Mengzi SAL. The results suggested that SALs could provide a special environment with both high concentrations of CH4 and O2 for methanotrophs, especially around the vertical venting pipes.

Comparison of Solid Waste Stabilization and Methane Emission from Anaerobic and Semi-Aerobic Landfills Operated in Tropical Condition

Leachate quality and methane emission from pilot-scale lysimeters operated under semi-aerobic and anaerobic conditions were monitored for 650 days. Two semi-aerobic lysimeters were filled with un-compacted and compacted municipal solid wastes whereas two anaerobic lysimeters containing compacted wastes were operated with leachate storage at 50% and 100% of waste height, respectively. Despite having high moisture in wastes and operating under tropical rainfall events, leachate stabilization in semi-aerobic lysimeters took place much faster resulting in BOD reduction by 90% within 60 days, significantly shorter than 180?210 days observed in anaerobic lysimeters. Nitrogen concentration in leachate from semi-aerobic lysimeter could be reduced by 90%. In term of gas emission, semi-aerobic lysimeter with un-compacted wastes had much lower methane emission rate of 2.8 g/m2/day compare to anaerobic lysimeters (62.6 g/m2/day) through seasonal fluctuation was observed. Nevertheless, semi-aerobic lysimeter with waste compaction has similar performance to anaerobic lysimeter.

The dependence of the methylation of mercury on the landfill stabilization process and implications for the landfill management

Mercury species and other chemical characteristics of the leachate from anaerobic and semi-aerobic landfills were analyzed to investigate the factors that control mercury methylation during the landfill stabilization process. At the early landfill stage, the total mercury (THg) and the monomethyl mercury (MMHg) released rapidly and significantly, the THg concentration of the semi-aerobic landfill leachate was obviously higher than that of the anaerobic landfill leachate, while compared with the semi-aerobic landfill, the MMHg concentration in the anaerobic landfill was higher. As the landfill time increased, both of THg and MMHg concentration decreased quickly, the THg concentration in the anaerobic landfill was much higher than that in semi-aerobic landfill, while the MMHg concentration in the anaerobic landfill was lower than that in the semi-aerobic landfill. Generally, the concentrations of dimethyl mercury (DMHg) in the anaerobic landfill leachate were slightly higher than in the semi-aerobic landfill leachate during the stabilization process. A significant positive correlation was found between the DMHg concentrations and the pH value in anaerobic landfill leachate, but this correlation was opposite in the semi-aerobic landfill. The oxidative–reductive potential (ORP) condition was found to be the controlling factor of the methylation process during the early stage. However, the chemical characteristics, especially the TOC concentration, appeared to be the dominant factor affecting the methylation process as the landfill time increased.

Application of response surface methodology (RSM) for optimization of semi-aerobic landfill leachate treatment using ozone

The removal efficiencies for chemical oxygen demand (COD), ammoniacal nitrogen (NH3–N), and color, as well as ozone consumption (OC) from the Malaysian semi-aerobic landfill stabilized leachate using ozone reactor, were investigated. Central composite design with response surface methodology was applied to evaluate the interaction and relationship between operating variables (i.e., ozone dosage, COD concentration, and reaction time) and to develop the optimum operating condition. Based on statistical analysis, Quadratic models for the four responses (COD, NH3–N, color, and OC) proved to be significant with very low probability values (<0.0001). The obtained optimum conditions were 70 g/m3 ozone, 250 mg/l COD, and 60 min reaction time. The results obtained by the predicted model were 26.7, 7.1, and 92 % removal for COD, NH3–N, and color, respectively, with 9.42 (kgO3/kg COD) OC. The predicted results fitted well with the results of the laboratory experiment.

Initial Characterization of Semi-aerobic Landfill Leachate Based On Its Biodegradation

The characterization of landfill leachate has been well established. However, its biodegradation properties have not been well reported. Therefore, this research was undertaken to investigate the biodegradability of semi-aerobic sanitary landfill and the ratio of the biological oxygen demand (BOD) to chemical oxygen demand (COD) BOD5/COD, COD fraction on leachate from Pulau Burung landfill Site (PBLS). These parameters are important as they may provide appropriate and suitable treatment for this kind of leachate. In this research, leachate from two different ponds were studied i.e., the raw leachate from leachate collection pond and the leachate effluents of the treatment plant'. Five different measurement points were tested for each pond to understand the characterization for leachate. The soluble and particulate organic compound was separated by filtration using a 0.45μm pore size membrane filter. The results indicated that leachate in PBLS has low BOD5/COD ratio. The total COD (TCOD) ranged from 2040mg/L to 3160mg/L. The Biodegradable COD (BCOD), unbiodegradable COD (UBOD), soluble biodegradable (RBCOD), particlulate biodegradable (SBCOD), particulate inert (UPCOD), and soluble inert (USCOD) ranged from 53%-67%, 33%-47%, 38%-46%, 9%-25%, 12%-26%, and 18%-25%. This indicates, the leachate in Pulau Burung Landfill Site have different of COD fraction behavior compare with domestic wastewater. In which, leachate have low SBCOD, but relatively high in others COD fraction compare with domestic wastewater.

Potential of KMnO4 and H2O2 in treating semi-aerobic landfill leachate

Treatment of recalcitrant landfill leachate was carried out using hydrogen peroxide (H2O2) and potassium permanganate (KMnO4). The treatment performance was reported in terms of colour, chemical oxygen demand (COD) and ammoniacal nitrogen (NH4-N). The effect of oxidant dosages and pH was determined and optimum conditions were determined considering the removal of parameters of interest. The optimum dosage of both oxidants was similar in terms of COD removal; however, H2O2 gave better removal (42 %) and similar results were obtained for NH4-N (24 %). KMnO4 proved better in terms of colour with a reduction of 74 % compared to 43 % by hydrogen peroxide at pH 7. Acidic conditions (pH 2–5) proved conducive towards the removal of all parameters with the exception of COD removal by KMnO4 that exhibited a low removal at pH 5 and increased with increasing pH. The COD reduction at pH 3 was ~38 % for KMnO4 and H2O2, whereas the reduction in NH4-N was 22 and 28 % for KMnO4 and H2O2, respectively. The COD and NH4-N removal performance of H2O2 was better compared with KMnO4; however, consistently higher colour removal was obtained for KMnO4.

Proper Design of Leachate Collection Pipe in Semi-Aerobic Landfill by Two Dimensional Simulation

Semi-aerobic method is a standard type of landfill currently used in Japan. Semi-aerobic landfill system enables to enhance the stabilization of landfilled solid waste utilizing the self-purification capacity inherent in nature. Although semi-aerobic method has been developed for about 20 years, the mechanism has not widely understood in many countries. The objective of this study is to make clear the influence of the laying condition (pipe diameter, pipe placement distance) of leachate collection pipe on the stabilization of landfill through numerical simulation, by use of landfill model constructed in this study with consideration of the interactions of microbial activity and the transport process such as gas transport, heat transport and material transfer between gas and liquid phases.

Mitigating CH4 Emissions in Semi-Aerobic Landfills: Impacts of Operating Conditions on Abundance and Community Structure of Methanotrophs in Cover Soils

Methanotrophs are the most important sink of CH₄, which is a more highly potent greenhouse gas than CO₂. Methanotrophic abundance and community diversity in cover soils from two typical semi-aerobic landfills (SALs) in China were detected using real-time polymerase chain reaction (real-time-PCR) and denaturing gradient gel electrophoresis (DGGE) based on 16S rRNA genes, respectively. Real time-PCR showed that Type I methanotrophs ranged from 1.07 × 10⁶ to 2.34 × 10⁷ copies/g soil and that of Type II methanotrophs from 1.51 × 10⁷ to 1.83 × 10⁸ copies/g soil. The ratio of Type II to Type I methanotrophic copy numbers ranged from 5.61 to 21.89, indicating that Type II methanotrophs dominated in SAL. DGGE revealed that Type I methanotrophs responded more sensitively to the environment, changing as the community structure varied with different soil types and locations. Methylobacter, Methylosarcina, and Methylomicrobium for Type I, and Methylocystis for Type II were most prevalent in the SAL cover layer. Abundant interflow O₂ with high CH₄ concentration in SALs is the reason for the higher population density of methanotrophs and the higher enrichment of Type II methanotrophs compared with anaerobic landfills and other ecosystems, which proved a conclusion that increasing the oxygen supply in a landfill cover layer would greatly improve CH₄ mitigation.

The effect of aerobic conditions on the complexation ability between mercury and humic acid from landfill leachate and its implication for the environment

Three-dimensional excitation emission matrix (3DEEM) fluorescence spectroscopy was employed to investigate the structure and characteristics of humic acid (HA) from landfills at different stabilization processes. The results show that the HA in anaerobic landfill leachate stabilized more rapidly than that in semi-aerobic landfill leachate. There were strong interactions between HA and Hg, the S content as well as the oxygen-containing ligands of the HA played a key role in the complexation with mercury. The higher complexation capacity (CL) and stability constant (logK) of HA from anaerobic landfill leachate implies that it is important to strengthen the control of mercury transportation in anaerobic landfills during the early stabilization process. The logK and CL of HA from semi-aerobic landfill leachate increased with the landfill time indicate that control of leachate Hg contamination in the latter stage is of great significance in semi-aerobic landfills.

Preparation of banana frond activated carbon by microwave induced activation for the removal of boron and total iron from landfill leachate

The present work demonstrates the preparation of banana frond derived activated carbon (BFAC) by microwave induced KOH activation for the adsorptive removal of boron and total iron from the semi-aerobic landfill leachate. The physical and chemical properties of BFAC were evaluated by pore structural analysis, scanning electron microscopy and Fourier transform infrared spectroscopy. The effects of adsorbent dosage, contact time, solution pH and temperature on the adsorption performance were examined in a batch mode study. The experimental results manifested that the adsorptive removal of boron and total iron increased with increasing the adsorbent dosage, contact time and temperature, accomplished the adsorptive removal of boron and total iron of 93.56% and 95.14%, respectively. Equilibrium data was best confronted to the pseudo-second-order kinetic model, while the adsorptive removal of boron and total iron onto BFAC was satisfactory described by the Freundlich and Langmuir isotherm models. The findings illustrated the applicability of BFAC as an ideal on-site solution for the adsorptive treatment of boron and total iron from the contaminated landfill leachate.

Advanced Treatment of Landfill Leachate Effluent Using Membrane Filtration

Treatment of water by membrane filtration process has been well established. However, its application on landfill leachate effluent treatment is quite limited. This study was undertaken to investigate suitability of this process on leachate effluent treatment generated from Pulau Burung semi aerobic sanitary landfill. Three types of membrane namely Nylon, Resin and Poly-propylene (PP) were used in this study. The pore sizes were 1 µm and 5 µm. The effects of different filtration rates on leachate treatment were studied. The parameters studied were COD, colour, suspended solids (SS) and turbidity. A set of batch studies were carried out in order to evaluate the effectiveness of the membrane filtration process in leachate effluent treatment. The results indicated that Poly-propylene membrane with pore size 1 µm had the best performance in reducing all the parameters whereas the Resin membrane gave the poorest results. It can be deduced that the filtration rate of 10 mL/min exhibited the highest removal efficiency. Poly-propylene membrane with pore size 1 µm and at filtration rate of 10 mL/min was found to be the most effective membrane to remove COD, colour, SS and turbidity.

Spectroscopic studies of the effect of aerobic conditions on the chemical characteristics of humic acid in landfill leachate and its implication for the environment

Humic acids (HAs) that extracted from leachates from semi-aerobic and anaerobic landfills test field at different stabilization times were characterized by elemental composition, Fourier transform infrared spectroscopy (FTIR), and Carbon-13 Cross-Polarization Magic-Angle-Spinning Nuclear Magnetic Resonance (13C CP/MAS NMR). The higher sulfur (S) content of HA in the anaerobic landfill leachate after a short stabilization time showed that the S released from the organic matter degradation was more easily stabilized under anaerobic conditions, which indicate that HA from anaerobic landfill leachate was more chemically reactive and played a more important role in mobilizing heavy metal, especially mercury, at early landfill stabilization times. However, the S content of HA from the semi-aerobic landfill increased over time, suggesting that more S was stabilized in HA as the landfill stabilization time was extended. The analytical results for the FTIR and NMR showed that the HA from the anaerobic landfill contained more aromatic groups, while HA from the semi-aerobic landfill had more oxygen-containing groups. The aromatic components of the HA from both the anaerobic and semi-aerobic landfills increased over time, suggesting that the maturity and humification degree of HA increased during the stabilization process.

Batch adsorption of semi-aerobic landfill leachate by granular activated carbon prepared by microwave heating

In this work, tamarind fruit seed derived granular activated carbon (TSAC) was prepared by microwave heating for the adsorptive treatment of semi-aerobic landfill leachate. TSAC was examined by pore structural analysis and determination of surface acidity/basicity. The effects of adsorbent dosage, contact time, and solution pH on the adsorptive removal of color and non-biodegradable constituents, expressed in term of chemical oxygen demand (COD) were quantified. The experimental results manifested that the adsorptive removal of color and COD increased with increasing the adsorbent dosage and contact time, with the adsorptive removal of color and COD of 91.23% and 79.93%, respectively, at the adsorbent dosage of 6mg/200mL and pH 6. The adsorption kinetic was satisfactory fitted to the pseudo-second-order kinetic model. Equilibrium data were favorably described by the Langmuir isotherm model, showing a monolayer adsorption capacity for color and COD of 168.57Pt–Co/g and 64.93mg/g at 30°C, respectively.