Properties of biochars from conventional and alternative feedstocks and their suitability for metal immobilization in industrial soil

In contaminated soils, excessive concentrations of metals and their high mobility pose a serious environmental risk. A suitable soil amendment can minimize the negative effect of metals in soil. This study investigated the effect of different biochars on metal (Cu, Pb, Zn) immobilization in industrial soil. Biochars produced at 300 and 600 °C from conventional (MS, maize silage; WP, wooden pellets) and alternative (SC, sewage sludge compost; DR, digestate residue) feedstocks were used as soil amendments at a dosage of 10 % (w/w). The type of feedstock and pyrolysis temperature affected the properties of the biochars and their ability to immobilize metal in soil. Compared to production at 300 °C, all biochars produced at 600 °C had higher pH (6.2–10.7), content of ash (7.2–69.0 %) and fixed carbon (21.1–56.7 %), but lower content of volatile matter (9.7–37.2 %). All biochars except DR biochar had lower dissolved organic carbon (DOC) content (1.4–2.3 g C/L) when made at 600 °C. Only MS and SC biochars had higher cation exchange capacity (25.2 and 44.7 cmol/kg, respectively) after charring at 600 °C. All biochars contained low concentrations of Cd, Cu, Ni, Pb and Zn; Cd was volatilized to the greatest extent during pyrolysis. Based on FTIR analysis and molar ratios of H/C and O/C, biochars had a greater degree of carbonization and aromaticity after charring at 600 °C. The efficiency of the biochars in metal immobilization depended mainly on their pH, ash content, and concentration of DOC. SC and DR biochars were more effective for Cu and Zn immobilization than MS and WP biochars, which makes them attractive options for large-scale soil amendment.     

Modeling methane oxidation in landfill cover soils as indicator of functional stability with respect to gas management

A performance-based method for evaluating methane (CH₄) oxidation as the best available control technology (BACT) for passive management of landfill gas (LFG) was applied at a municipal solid waste (MSW) landfill in central Washington, USA, to predict when conditions for functional stability with respect to LFG management would be expected. The permitted final cover design at the subject landfill is an all-soil evapotranspirative (ET) cover system. Using a model, a correlation between CH₄ loading flux and oxidation was developed for the specific ET cover design. Under Washington’s regulations, a MSW landfill is functionally stable when it does not present a threat to human health or the environment (HHE) at the relevant point of exposure (POE), which was conservatively established as the cover surface. Approaches for modeling LFG migration and CH₄ oxidation are discussed, along with comparisons between CH₄ oxidation and biodegradation of non-CH₄ organic compounds (NMOCs). The modeled oxidation capacity of the ET cover design is 15 g/m²/day under average climatic conditions at the site, with 100% oxidation expected on an annual average basis for fluxes up to 8 g/m²/day. This translates to a sitewide CH₄ generation rate of about 260 m³/hr, which represents the functional stability target for allowing transition to cover oxidation as the BACT (subject to completion of a confirmation monitoring program). It is recognized that less than 100% oxidation might occur periodically if climate and/or cover conditions do not precisely match the model, but that residual emissions during such events would be de minimis in comparison with published limit values. Accordingly, it is also noted that nonzero net emissions may not represent a threat to HHE at a POE (i.e., a target flux between 8 and 15 g/m²/day might be appropriate for functional stability) depending on the site reuse plan and distance to potential receptors.

Implications: This study provides a scientifically defensible method for estimating when methane oxidation in landfill cover soils may represent the best available control technology for residual landfill gas (LFG) emissions. This should help operators and regulators agree on the process of safely eliminating active LFG controls in favor of passive control measures once LFG generation exhibits asymptotic trend behavior below the oxidation capacity of the soil. It also helps illustrate the potential benefits of evolving landfill designs to include all-soil vegetated evapotranspirative (ET) covers that meet sustainability objectives as well as regulatory performance objectives for infiltration control.     

Increased bioavailability of metals in two contrasting agricultural soils treated with waste wood-derived biochar and ash

Recycled waste wood is being increasingly used for energy production; however, organic and metal contaminants in by-products produced from the combustion/pyrolysis residue may pose a significant environmental risk if they are disposed of to land. Here we conducted a study to evaluate if highly polluted biochar (from pyrolysis) and ash (from incineration) derived from Cu-based preservative-treated wood led to different metal (e.g., Cu, As, Ni, Cd, Pb, and Zn) bioavailability and accumulation in sunflower (Helianthus annuus L.). In a pot experiment, biochar at a common rate of 2 % w/w, corresponding to ～50 t ha^?1, and an equivalent pre-combustion dose of wood ash (0.2 % w/w) were added to a Eutric Cambisol (pH 6.02) and a Haplic Podzol (pH 4.95), respectively. Both amendments initially raised soil pH, although this effect was relatively short-term, with pH returning close to the unamended control within about 7 weeks. The addition of both amendments resulted in an exceedance of soil Cu statutory limit, together with a significant increase of Cu and plant nutrient (e.g., K) bioavailability. The metal-sorbing capacity of the biochar, and the temporary increase in soil pH caused by adding the ash and biochar were insufficient to offset the amount of free metal released into solution. Sunflower plants were negatively affected by the addition of metal-treated wood-derived biochar and led to elevated concentration of metals in plant tissue, and reduced above- and below-ground biomass, while sunflower did not grow at all in the Haplic Podzol. Biochar and ash derived from wood treated with Cu-based preservatives can lead to extremely high Cu concentrations in soil and negatively affect plant growth. Identifying sources of contaminated wood in waste stream feedstocks is crucial before large-scale application of biochar or wood ash to soil is considered.     

Comprehending adsorption of methylethylketone and toluene and microwave regeneration effectiveness for beaded activated carbon derived from recycled waste bamboo tar

ABSTRACT

Beaded activated carbons (BACs) were derived from waste bamboo tar through carbonization (500°C for 2 hr) followed by physical activation using carbon dioxide (800–900°C for 2–4 hr). The adsorbent was examined for their physical and chemical properties, adsorption capacities toward methylethylketone (MEK) and toluene, and regenerabilities under microwave heating. It was found that the maximum total surface area reached for bamboo-tar-derived BAC after physical activation was 1364 m² g^?1, and more than 95% of the area was attributed to the microporous structures. Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models were applied to the adsorption isotherm fitting, and the minimum R² for each model was 0.986, 0.915, and 0.943, respectively. The isosteric heats of adsorption calculated based on D-R parameters for methylethylketone and toluene were 44.04 to 51.50 and 45.88 to 73.27 KJ mol^?1, respectively. They were slightly over the range of physisorption and increased with adsorbate loading, which might be related to the micropore filling mechanism. Microwave regeneration under 600 W of power output removed most of the adsorbate (>93.03%) within 8 min. The results of this study are intended to benefit future study on waste-derived adsorbent in environmental applications.     

Effects of ammonia on methane oxidation in landfill cover materials

The effects of ammonia (NH₃) on CH₄ attenuation in landfill cover materials consisting of landfill cover soil (LCS) and aged municipal solid waste (AMSW), at different CH₄ concentrations, were investigated. The CH₄ oxidation capacities of LCS and AMSW were found to be significantly affected by the CH₄ concentration. The maximum oxidation rates for LCS and AMSW were obtained at CH₄ concentrations of 5 % and 20 %(v/v), respectively, within 20 days. CH₄ biological oxidation in AMSW was significantly inhibited by NH₃ at low CH₄ concentrations (5 %, v/v) but highly stimulated at high levels (20 % and 50 %, v/v). Oxidation in LCS was stimulated by NH₃ at all CH₄ concentrations due to the higher conversion of the nitrogen in NH₃ in AMSW than in LCS. NH₃ increases CH₄ oxidation in landfill cover materials.     

Modeling landfill gas potential and potential energy recovery from Thohoyandou landfill site,South Africa

ABSTRACT

The increase in solid waste generation has been a major contributor to the amount of Greenhouse gases (GHGs) present in the atmosphere. To some extent, a great chunk of these GHGs in the atmosphere is from landfill. This study assesses two theoretical models (LandGEM and Afvalzorg models) to estimate the amount of landfill gas (LFG) emitted from Thohoyandou landfill site. Also, the LFGcost Web model was used to estimate the cost and benefits of the implementation of an LFG utilization technology. The Thohoyandou landfill started operations in the year 2005 and it is proposed to reach its peak at approximately in the year 2026. The LandGEM calculates the mass of landfill gas emission using methane generation capacity, mass of deposited waste, methane generation constant and methane generation rate. Meanwhile, the Afvalzorg model determines the LFG emissions using the Methane correction factor, yearly waste mass disposal, waste composition, Degradation Organic Carbon, methane generation rate constant, LFG recovery efficiency. The study findings indicate that the methane (CH₄) and carbon dioxide (CO₂) emitted from the landfill estimated from LandGEM will peak in the year 2026 with values of 3517 Mg/year and 9649 Mg/year, respectively. Results from the Afvalzorg model show that CH₄ emission will peak in the year 2026 (3336 Mg/year). The LandGEM model showed that the total LFG, CH₄ and CO₂ emitted from the landfill between 2005 and 2040 are 293239.3 Mg/year, 78325.7 Mg/year and 214908.6 Mg/year, respectively. The simulation from the Afvalzorg model found that the CH₄ emitted from the years 2005– 2040 is 74302 Mg/year. The implementation of an LFG utilization technology was economically feasible from consideration of the sales of electricity generated and Certified Emission Reductions (CER) (carbon credits).     

Methane balance of a bioreactor landfill in Latin America

This paper presents results from a methane (CH4) gas emission characterization survey conducted at the Loma Los Colorados landfill located 60 km from Santiago, Chile. The landfill receives approximately 1 million metric tons (t) of waste annually, and is equipped with leachate control systems and landfill gas collection systems. The collected leachate is recirculated to enable operation of the landfill as a bioreactor. For this study, conducted between April and July 2000, a total of 232 surface emission measurements were made over the 23-ha surface area of the landfill. The average surface flux rate of CH4 emissions over the landfill surface was 167 g x m(-2) x day(-1), and the total quantity of surface emissions was 13,320 t/yr. These values do not include the contribution made by "hot spots," originating from leachate pools caused by "daylighting" of leachate, that were identified on the landfill surface and had very high CH4 emission rates. Other point sources of CH4 emissions at this landfill include 20 disconnected gas wells that vent directly to the atmosphere. Additionally, there are 13 gas wells connected to an incinerator responsible for destroying 84 t/yr of CH4. The balance also includes CH4 that is being oxidized on the surface of the landfill by meth-anotrophic bacteria. Including all sources, except leachate pool emissions, the emissions were estimated to be 14,584 t/yr CH4. It was estimated that less than 1% of the gas produced by the decomposition of waste was captured by the gas collection system and 38% of CH4 generated was emitted to the atmosphere through the soil cover.     

Utilisation of chemically stabilized arsenic-contaminated soil in a landfill cover

The aim of the study was to determine if an As-contaminated soil, stabilized using zerovalent iron (Fe⁰) and its combination with gypsum waste, coal fly ash, peat, or sewage sludge, could be used as a construction material at the top layer of the landfill cover. A reproduction of 2 m thick protection/vegetation layer of a landfill cover using a column setup was used to determine the ability of the amendments to reduce As solubility and stimulate soil functionality along the soil profile. Soil amendment with Fe⁰ was highly efficient in reducing As in soil porewater reaching 99 % reduction, but only at the soil surface. In the deeper soil layers (below 0.5 m), the Fe treatment had a reverse effect, As solubility increased dramatically exceeding that of the untreated soil or any other treatment by one to two orders of magnitude. A slight bioluminescence inhibition of Vibrio fischeri was detected in the Fe⁰ treatment. Soil amendment with iron and peat showed no toxicity to bacteria and was the most efficient in reducing dissolved As in soil porewater throughout the 2 m soil profile followed by iron and gypsum treatment, most likely resulting from a low soil density and a good air diffusion to the soil. The least suitable combination of soil amendments for As immobilization was a mixture of iron with coal fly ash. An increase in all measured enzyme activities was observed in all treatments, particularly those receiving organic matter. For As to be stable in soil, a combination of amendments that can keep the soil porous and ensure the air diffusion through the entire soil layer of the landfill cover is required.     

Cr(VI) and COD removal from landfill leachate by polyculture constructed wetland at a pilot scale

Four subsurface horizontal-flow constructed wetlands (CWs) at a pilot scale planted with a polyculture of the tropical plants Gynerium sagittatum (Gs), Colocasia esculenta (Ce) and Heliconia psittacorum (He) were evaluated for 7 months. The CW cells with an area of 17.94 m² and 0.60 m (h) each and 0.5 m of gravel were operated at continuous gravity flow (Q?=?0.5 m³ day^?1) and a theoretical HRT of 7 days each and treating landfill leachate for the removal of filtered chemical oxygen demand (COD_f), BOD₅, TKN, NH₄ ⁺, NO₃ ^?, PO₄ ^3?–P and Cr(VI). Three CWs were divided into three sections, and each section (5.98 m²) was seeded with 36 cuttings of each species (plant density of six cuttings per square metre). The other unit was planted randomly. The final distributions of plants in the bioreactors were as follows: CW I (He-Ce-Gs), CW II (randomly), CW III (Ce-Gs-He) and CW IV (Gs-He-Ce). The units received effluent from a high-rate anaerobic pond (BLAAT®). The results show a slightly alkaline and anoxic environment in the solid-liquid matrix (pH?=?8.0; 0.5–2 mg L^?1 dissolved oxygen (DO)). COD_f removal was 67 %, BOD₅ 80 %, and TKN and NH₄ ⁺ 50–57 %; NO₃ ^? effluents were slightly higher than the influent, PO₄ ^3?–P (38 %) and Cr(VI) between 50 and 58 %. CW IV gave the best performance, indicating that plant distribution may affect the removal capacity of the bioreactors. He and Gs were the plants exhibiting a translocation factor (TF) of Cr(VI) >1. The evaluated plants demonstrated their suitability for phytoremediation of landfill leachate, and all of them can be categorized as Cr(VI) accumulators. The CWs also showed that they could be a low-cost operation as a secondary system for treatment of intermediated landfill leachate (LL).     

The size distribution of organic carbon in headwater streams in the Amazon basin

Despite the strong representativeness of streams in the Amazon basin, their role in the accumulation of coarse particulate organic carbon (CPOC), fine particulate organic carbon (FPOC), and dissolved organic carbon (DOC) in transport, an important energy source in these environments, is poorly known. It is known that the arboreal vegetation in the Amazon basin is influenced by soil fertility and rainfall gradients, but would these gradients promote local differences in organic matter in headwater streams? To answer this question, 14 low-order streams were selected within these gradients along the Amazon basin, with extensions that varied between 4 and 8 km. The efficiency of the transformation of particulate into dissolved carbon fractions was assessed for each stream. The mean monthly benthic organic matter storage ranged between 1.58 and 9.40 t ha^?1 month^?1. In all locations, CPOC was the most abundant fraction in biomass, followed by FPOC and DOC. Rainfall and soil fertility influenced the distribution of the C fraction (p?=?0.01), showing differentiated particulate organic carbon (POC) storage and DOC transportation along the basin. Furthermore, the results revealed that carbon quantification at the basin level could be underestimated, ultimately influencing the global carbon calculations for the region. This is especially due to the fact that the majority of studies consider only fine particulate organic matter and dissolved organic matter, which represent less than 50 % of the stored and transported carbon in streambeds.     

A comparison of CH4, N2O and CO2 emissions from three different cover types in a municipal solid waste landfill

High-density polyethylene (HDPE) membranes are commonly used as a cover component in sanitary landfills, although only limited evaluations of its effect on greenhouse gas (GHG) emissions have been completed. In this study, field GHG emission were investigated at the Dongbu landfill, using three different cover systems: HDPE covering; no covering, on the working face; and a novel material-Oreezyme Waste Cover (OWC) material as a trial material. Results showed that the HDPE membrane achieved a high CH₄ retention, 99.8% (CH₄ mean flux of 12 mg C m^-2 h^-1) compared with the air-permeable OWC surface (CH4 mean flux of 5933 mg C m^-2 h^-1) of the same landfill age. Fresh waste at the working face emitted a large fraction of N₂O, with average fluxes of 10 mg N m^-2 h^-2, while N₂O emissions were small at both the HDPE and the OWC sections. At the OWC section, CH₄ emissions were elevated under high air temperatures but decreased as landfill age increased. N₂O emissions from the working face had a significant negative correlation with air temperature, with peak values in winter. A massive presence of CO₂ was observed at both the working face and the OWC sections. Most importantly, the annual GHG emissions were 4.9 Gg yr^-1 in CO₂ equivalents for the landfill site, of which the OWC-covered section contributed the most CH₄ (41.9%), while the working face contributed the most N₂O (97.2%). HDPE membrane is therefore, a recommended cover material for GHG control.

Implications: Monitoring of GHG emissions at three different cover types in a municipal solid waste landfill during a 1-year period showed that the working face was a hotspot of N₂O, which should draw attention. High CH₄ fluxes occurred on the permeable surface covering a 1- to 2-year-old landfill. In contrast, the high-density polyethylene (HDPE) membrane achieved high CH₄ retention, and therefore is a recommended cover material for GHG control.     

Geotechnical Engineering Properties of Incinerator Ash Mixes

Abstract

The incineration of solid waste produces large quantities of bottom and fly ash. Landfilling has been the primary mode of disposal of these waste materials. Shortage in landfill space and the high cost of treatment have, however, prompted the search for alternative uses of these waste materials. This study presents an experimental program that was conducted to determine the engineering properties of incinerator ash mixes for use as construction materials. Incinerator ash mixes were tested as received and around optimum compacted conditions. Compaction curves, shear strength, and permeability values of fly ash, bottom ash, and their various blends were investigated. Bottom ash tends to achieve maximum dry density at much lower water content than does fly ash. The mixes displayed a change in their cohesion and friction angle values when one of the two mix components was altered or as a result of the addition of water. The permeability of bottom ash is quite comparable to that of sand. The permeability of fly ash lies in the range of those values obtained for silts and clays. A 100% bottom ash compacted at the optimum water content has a lower density value and yields a higher friction angle and cohesion values than most construction fills. This would encourage the use of bottom ash as a fill or embankment material because free drainage of water will prevent the buildup of pore water pressures.     

Natural deep eutectic solvent mediated pretreatment of rice straw: bioanalytical characterization of lignin extract and enzymatic hydrolysis of pretreated biomass residue

The present investigation demonstrated pretreatment of lignocellulosic biomass rice straw using natural deep eutectic solvents (NADESs), and separation of high-quality lignin and holocellulose in a single step. Qualitative analysis of the NADES extract showed that the extracted lignin was of high purity (>90 %), and quantitative analysis showed that nearly 60?±?5 % (w/w) of total lignin was separated from the lignocellulosic biomass. Addition of 5.0 % (v/v) water during pretreatment significantly enhanced the total lignin extraction, and nearly 22?±?3 % more lignin was released from the residual biomass into the NADES extract. X-ray diffraction studies of the untreated and pretreated rice straw biomass showed that the crystallinity index ratio was marginally decreased from 46.4 to 44.3 %, indicating subtle structural alterations in the crystalline and amorphous regions of the cellulosic fractions. Thermogravimetric analysis of the pretreated biomass residue revealed a slightly higher T _dcp (295 °C) compared to the T _dcp (285 °C) of untreated biomass. Among the tested NADES reagents, lactic acid/choline chloride at molar ratio of 5:1 extracted maximum lignin of 68?±?4 mg g^?1 from the rice straw biomass, and subsequent enzymatic hydrolysis of the residual holocellulose enriched biomass showed maximum reducing sugars of 333?±?11 mg g^?1 with a saccharification efficiency of 36.0?±?3.2 % in 24 h at 10 % solids loading.     

Geotechnical engineering properties of incinerator ash mixes

The incineration of solid waste produces large quantities of bottom and fly ash. Landfilling has been the primary mode of disposal of these waste materials. Shortage in landfill space and the high cost of treatment have, however, prompted the search for alternative uses of these waste materials. This study presents an experimental program that was conducted to determine the engineering properties of incinerator ash mixes for use as construction materials. Incinerator ash mixes were tested as received and around optimum compacted conditions. Compaction curves, shear strength, and permeability values of fly ash, bottom ash, and their various blends were investigated. Bottom ash tends to achieve maximum dry density at much lower water content than does fly ash. The mixes displayed a change in their cohesion and friction angle values when one of the two mix components was altered or as a result of the addition of water. The permeability of bottom ash is quite comparable to that of sand. The permeability of fly ash lies in the range of those values obtained for silts and clays. A 100% bottom ash compacted at the optimum water content has a lower density value and yields a higher friction angle and cohesion values than most construction fills. This would encourage the use of bottom ash as a fill or embankment material because free drainage of water will prevent the buildup of pore water pressures.     

Adsorption of lead onto smectite from aqueous solution

The purpose of this research is to study the effect of a new method of adsorption using membrane filtration to determine the maximum amount of lead adsorbed by clay and investigate the behavior of the clay after adsorption of the said metal. Treatment of wastewater contaminated with heavy metals depends on the characteristics of the effluent, the amount of final discharge, the cost of treatment, and the compatibility of the treatment process. The process of adsorption of heavy metals by clays may be a simple, selective, and economically viable alternative to the conventional physical–chemical treatment. This is justified by the importance of the surface developed by this material, the presence of negative charges on the said surface, the possibility of ion exchange taking place, and its wide availability in nature. The removal of lead from wastewater was studied by using the adsorption technique and using clay as the adsorbent. A method was optimized for adsorption through a membrane approaching natural adsorption. This new method is simple, selective, and the lead adsorption time is about 3 days. The various properties of clay were determined. It was observed that the cation exchange capacity of the clay was 56 meq/100 g of hydrated clay for the raw sample and 82 meq/100 g for the purified sample. The total surface area determined by the methylene blue method was equal to 556 and 783 m²/g for the raw and purified samples, respectively. The adsorption kinetics depends on several parameters. The Pb(II) clay, obeys the Langmuir, Freundlich, and the Elovich adsorption isotherms with high regression coefficients. The use of this adsorbent notably decreases the cost of treatment. It was concluded that clay shows a strong adsorption capacity on Pb(II), the maximum interaction occurring with purified clay treated at high concentration of lead. It is proposed that this adsorption through a membrane be extended for the treatment of effluents containing other metals.     

Numerical model for static chamber measurement of multi-component landfill gas emissions and its application

The quantitative assessment of landfill gas emissions is essential to assess the performance of the landfill cover and gas collection system. The relative error of the measured surface emission of landfill gas may be induced by the static flux chamber technique. This study aims to quantify effects of the size of the chamber, the insertion depth, pressure differential on the relative errors by using an integrated approach of in situ tests, and numerical modeling. A field experiment study of landfill gas emission is conducted by using a static chamber at one landfill site in Xi’an, Northwest China. Additionally, a two-dimensional axisymmetric numerical model for multi-component gas transport in the soil and the static chamber is developed based on the dusty-gas model (DGM). The proposed model is validated by the field data obtained in this study and a set of experimental data in the literature. The results show that DGM model has a better capacity to predict gas transport under a wider range of permeability compared to Blanc’s method. This is due to the fact that DGM model can explain the interaction among gases (e.g., CH₄, CO₂, O₂, and N₂) and the Knudsen diffusion process while these mechanisms are not included in Blanc’s model. Increasing the size and the insertion depth of static chambers can reduce the relative error for the flux of CH₄ and CO₂. For example, increasing the height of chambers from 0.55 to 1.1 m can decrease relative errors of CH₄ and CO₂ flux by 17% and 18%, respectively. Moreover, we find that gas emission fluxes for the case with positive pressure differential (?P_in-out) are greater than that of the case without considering pressure fluctuations. The Monte Carlo method was adopted to carry out the statistical analysis for quantifying the range of relative errors. The agreement of the measured field data and predicted results demonstrated that the proposed model has the capacity to quantify the emission of landfill gas from the landfill cover systems.

     

Electricity generation from landfill gas in Turkey

Landfill gas (LFG)-to-energy plants in Turkey were investigated, and the LFG-to-energy plant of a metropolitan municipal landfill was monitored for 3 years. Installed capacities and actual gas engine working hours were determined. An equation was developed to estimate the power capacity for LFG-to-energy plants for a given amount of landfilled waste. Monitoring the actual gas generation rates enabled determination of LFG generation factors for Turkish municipal waste. A significant relationship (R = 0.524, p < 0.01, two-tailed) was found between the amounts of landfilled waste and the ambient temperature, which can be attributed to food consumption and kitchen waste generation behaviors influenced by the ambient temperature. However, no significant correlation was found between the ambient temperature and the generated LFG. A temperature buffering capacity was inferred to exist within the landfill, which enables the anaerobic reactions to continue functioning even during cold seasons. The average LFG and energy generation rates were 45 m³ LFG/ton waste landfilled and 0.08 MWhr/ton waste landfilled, respectively. The mean specific LFG consumption for electricity generation was 529 ± 28 m³/MWhr.

Implications: The paper will be useful for local authorities who need to manage municipal waste by using landfills. The paper will also be useful for investors who want to evaluate the energy production potential of municipal wastes and the factors affecting the energy generation process mostly for economical purposes. Landfills can be regarded as energy sources and their potentials need to be investigated. The paper will also be useful for policymakers dealing with energy issues. The paper contains information on real practical data such as engine working hours, equation to estimate the necessary power for a given amount of landfilled waste, and son on.     

Removal of Cu, Zn, and Cd from aqueous solutions by the dairy manure-derived biochar

Purpose

Biochar derived from waste biomass is now gaining much attention for its function as a biosorbent for environmental remediation. The objective of this study was to determine the effectiveness of biochar as a sorbent in removing Cd, Cu, and Zn from aqueous solutions.

Methods

Biochar was produced from dairy manure (DM) at two temperatures: 200°C and 350°C, referred to as DM200 and DM350, respectively. The obtained biochars were then equilibrated with 0–5 mM Cu, Zn or Cd in 0.01 M NaNO₃ solution for 10 h. The changes in solution metal concentrations after sorption were evaluated for sorption capacity using isotherm modeling and chemical speciation Visual MINTEQ modeling, while the solid was collected for species characterization using infrared spectroscopy and X-ray elemental dot mapping techniques.

Results

The isotherms of Cu, Zn, and Cd sorption by DM200 were better fitted to Langmuir model, whereas Freundlich model well described the sorption of the three metals by DM350. The DM350 were more effective in sorbing all three metals than DM200 with both biochars had the highest affinity for Cu, followed by Zn and Cd. The maximum sorption capacities of Cu, Zn, and Cd by DM200 were 48.4, 31.6, and 31.9 mg g^?1, respectively, and those of Cu, Zn, and Cd by DM350 were 54.4, 32.8, and 51.4 mg g^?1, respectively. Sorption of the metals by the biochar was mainly attributed to their precipitation with PO ₄ ^3? or CO ₃ ^2? originating in biochar, with less to the surface complexation through –OH groups or delocalized π electrons. At the initial metal concentration of 5 mM, 80–100 % of Cu, Zn, and Cd retention by DM200 resulted from the precipitation, with less than 20 % from surface adsorption through phenonic –OH complexation. Among the precipitation, 20–30 % of the precipitation occurred as metal phosphate and 70–80 % as metal carbonate. For DM350, 75–100 % of Cu, Zn, and Cd retention were due to the precipitation, with less than 25 % to surface adsorption through complexation of heavy metal by phenonic –OH site or delocalized π electrons. Among the precipitation, only less than 10 % of the precipitation was present as metal phosphate and more than 90 % as metal carbonate.

Conclusions

Results indicated that dairy manure waste can be converted into value-added biochar as a sorbent for sorption of heavy metals, and the mineral components originated in the biochar play an important role in the biochar's high sorption capacity.     

N2O emissions at municipal solid waste landfill sites: Effects of CH4 emissions and cover soil

Municipal solid waste landfills are the significant anthropogenic sources of N₂O due to the cooxidation of ammonia by methane-oxidizing bacteria in cover soils. Such bacteria could be developed through CH₄ fumigation, as evidenced by both laboratory incubation and field measurement. During a 10-day incubation with leachate addition, the average N₂O fluxes in the soil samples, collected from the three selected landfill covers, were multiplied by 1.75 (p < 0.01), 3.56 (p < 0.01), and 2.12 (p < 0.01) from the soil samples preincubated with 5% CH₄ for three months when compared with the control, respectively. Among the three selected landfill sites, N₂O fluxes in two landfill sites were significantly correlated with the variations of the CH₄ emissions without landfill gas recovery (p < 0.001). N₂O fluxes were also elevated by the increase of the CH₄ emissions with landfill gas recovery in another landfill site (p > 0.05). The annual average N₂O flux was 176 ± 566 μg N₂O–N m^?2 h^?1 (p < 0.01) from sandy soil–covered landfill site, which was 72% (p < 0.05) and 173% (p < 0.01) lower than the other two clay soil covered landfill sites, respectively. The magnitude order of N₂O emissions in three landfill sites was also coincident by the results of laboratory incubation, suggesting the sandy soil cover could mitigate landfill N₂O emissions.     

Development of a reference artificial sediment for chemical testing adapted to the MELA sediment contact assay

Most persistent organic pollutants, due to their hydrophobic properties, accumulate in aquatic sediments and represent a high risk for sediment quality. To assess the toxicity of hydrophobic pollutants, a novel approach was recently proposed as an alternative to replace, refine and reduce animal experimentation: the medaka embryo–larval sediment contact assay (MELAc). This assay is performed with Japanese medaka embryos incubated on a natural sediment spiked with the compound being tested. With the aim of improving this assay, our study developed a reference exposure protocol with an artificial sediment specifically designed to limit natural sediment composition uncertainties and preparation variability. The optimum composition of the new artificial sediment was tested using a model polycyclic aromatic hydrocarbon (PAH), fluoranthene. The sediment was then validated with two other model PAHs, benz[a]anthracene and benzo[a]pyrene. Various developmental end points were recorded, including survival, embryonic heartbeat, hatching delay, hatching success, larval biometry and abnormalities. The final artificial sediment composition was set at 2.5 % dry weight (dw) Sphagnum peat, 5 % dw kaolin clay and 92.5 % dw silica of 0.2- to 0.5-mm grain size. In contrast with natural sediments, the chemical components of this artificial matrix are fully defined and readily identifiable. It is totally safe for fish embryos and presents relatively high sorption capacities for hydrophobic compounds. Studies with other hydrophobic and metallic contaminants and mixtures should be performed to further validate this artificial sediment.