Estimation of effect of sugarcane bagasse biochar amendment in landfill soil cover on geotechnical properties and landfill gas emission

In a sanitary landfill, the final cover plays an important role in reducing the landfill gas emission to the atmosphere and in preventing the ingress of rainwater into the dumped waste. The present study investigated the suitability of sugarcane bagasse biochar as an amendment to the cover soil to improve the required landfill liner properties. The amended cover soil sugarcane bagasse (SSB) was tested for its stability and effectiveness, in terms of both geotechnical properties and methane mitigation efficiency. The effects of amending 15%, 20%, and 25% of sugarcane bagasse biochar (passing through 300 micron Indian Standard sieve) on the geotechnical properties of the SSB indicated that the SSB with 25% biochar showed the required values as per the standard with maximum dry density of 1.57 grams per cubic centimeter (g/cm³), liquid limit, plasticity index, and percentage of fines 48.5%, 16.3%, and 74.7%, respectively, and permeability of 0.9 × 10^?7. A column study that was conducted to determine the methane emission from the cover soil showed a 65.8% reduction in the methane emission compared to that of a column without SSB cover, with a cumulative methane emission of 410 milliliters (mL) at the end of 200 hours (h). On the other hand, the volume of methane emitted after 310 h from the column without cover and with the SSB cover was 1850 mL and 692 mL, respectively. The difference between these two values is found to be 22% of the total methane that the cover would have handled in its lifetime (5267 mL). Thus, there is an increase in the percentage of methane adsorption by soil cover from 15% to 22% when the soil was amended with 25% sugarcane bagasse biochar.     

Methane oxidation in two Swedish landfill covers measured with carbon-13 to carbon-12 isotope ratios

The release of methane (CH4) from landfills to the atmosphere and the oxidation of CH4 in the cover soils were quantified with static chambers and a 13C-isotope technique on two landfills in Sweden. One of the landfills had been closed and covered 17 years before this investigation while the other was recently covered. On both landfills, the tops of the landfills were compared with the sloping parts in the summer and winter. Emitted CH4, captured in chambers, was significantly enriched in 13C during summer compared with winter (P < 0.0001), and was enriched relative to anaerobic-zone methane. The difference between emitted and anaerobic zone delta 13C-CH4 was used to estimate soil methane oxidation. In summer, these differences ranged from 9 to 26@1000, and CH4 oxidation was estimated to be between 41 and 50% of the produced CH4 in the new landfill, and between 60 and 94% in the old landfill. In winter, when soil temperature was below 0 degree C, no difference in delta 13C was observed between emitted and anaerobic-zone CH4, suggesting that there was no soil oxidation. The temperature effect shown in this experiment suggests that there may be both seasonal and latitudinal differences in the importance of landfill CH4 oxidation. Finally the isotopic fractionation factor (alpha) varied from 1.023 to 1.038 and was temperature dependent, increasing at colder temperatures. Methanotrophic bacteria appeared to have high growth efficiencies and the majority of the methane consumed in incubations did not result in immediate CO2 production.     

Environmental factors influencing attenuation of methane and hydrochlorofluorocarbons in landfill cover soils

The influence of different environmental factors on methane oxidation and degradation of hydrochlorofluorocarbons (HCFCs) was investigated in microcosms containing soil sampled at Skellingsted Landfill, Denmark. The soil showed a high capacity for methane oxidation resulting in a maximum oxidation rate of 104 microg CH4 g(-1) h(-1) and a low affinity of methane with a half-saturation constant of 2.0% v/v. The hydrochlorofluorocarbons HCFC-21 (dichlorofluoromethane) and HCFC-22 (chlorodifluoromethane) were rapidly oxidized and the oxidation occurred in parallel with the oxidation of methane. The maximal HCFC oxidation rates were 0.95 and 0.68 microg g(-1) h(-1) for HCFC-21 and HCFC-22, respectively. Increasing concentrations of HCFCs resulted in decreased methane oxidation rates. However, compared with typical concentrations in landfill gas, relatively high HCFC concentrations were needed to obtain a significant inhibition of methane oxidation. In general, the environmental factors studied influenced the degradation of HCFCs in almost the same way as they influenced methane oxidation. Temperature had a strong influence on the methanotrophic activity giving high Q10 values of 3.4 to 4.1 over the temperature range of 2 to 25 degrees C. Temperature optimum was around 30 degrees C; however, oxidation occurred at temperatures as low as 2 degrees C. A moisture content of 25% w/w yielded the maximum oxidation rate as it allowed good gas transport together with sufficient microbial activity. The optimum pH was around neutrality (pH = 6.5-7.5) showing that the methanotrophs were optimally adapted to the in situ pH, which was 6.9. Copper showed no inhibitory effect when added in relatively high concentrations (up to 60 mg kg(-1)), most likely due to sorption of copper ions to soil particles. At higher copper concentrations the oxidation rates decreased. The oxidation rates for methane, HCFC-21, and HCFC-22 were unaltered in ammonium-amended soil up to 14 mg kg(-1). Higher ammonium concentrations inhibited the oxidation process. The most important parameters controlling oxidation in landfill cover soil were found to be temperature, soil moisture, and methane and oxygen supply.     

Attenuation of methane and volatile organic compounds in landfill soil covers

The potential for natural attenuation of volatile organic compounds (VOCs) in landfill covers was investigated in soil microcosms incubated with methane and air, simulating the gas composition in landfill soil covers. Soil was sampled at Skellingsted Landfill at a location emitting methane. In total, 26 VOCs were investigated, including chlorinated methanes, ethanes, ethenes, fluorinated hydrocarbons, and aromatic hydrocarbons. The soil showed a high capacity for methane oxidation resulting in very high oxidation rates of between 24 and 112 microg CH4 g(-1) h(-1). All lower chlorinated compounds were shown degradable, and the degradation occurred in parallel with the oxidation of methane. In general, the degradation rates of the chlorinated aliphatics were inversely related to the chlorine to carbon ratios. For example, in batch experiments with chlorinated ethylenes, the highest rates were observed for vinyl chloride (VC) and lowest rates for trichloroethylene (TCE), while tetrachloroethylene (PCE) was not degraded. Maximal oxidation rates for the halogenated aliphatic compounds varied between 0.03 and 1.7 microg g(-1) h(-1). Fully halogenated hydrocarbons (PCE, tetrachloromethane [TeCM], chlorofluorocarbon [CFC]-11, CFC-12, and CFC-113) were not degraded in the presence of methane and oxygen. Aromatic hydrocarbons were rapidly degraded giving high maximal oxidation rates (0.17-1.4 microg g(-1) h(-1)). The capacity for methane oxidation was related to the depth of oxygen penetration. The methane oxidizers were very active in oxidizing methane and the selected trace components down to a depth of 50 cm below the surface. Maximal oxidation activity occurred in a zone between 15 and 20 cm below the surface, as this depth allowed sufficient supply of both methane and oxygen. Mass balance calculations using the maximal oxidation rates obtained demonstrated that landfill soil covers have a significant potential for not only methane oxidation but also cometabolic degradation of selected volatile organics, thereby reducing emissions to the atmosphere.     

Evaluation of alternative landfill cover soils for attenuating hydrogen sulfide from construction and demolition (C&D) debris landfills

Hydrogen sulfide (H(2)S) generated from C&D debris landfills has emerged as a major environmental concern due to odor problems and possible health impacts to landfill employees and surrounding residents. Research was performed to evaluate the performance of various cover materials as control measures for H(2)S emissions from C&D debris landfills. Twelve laboratory-scale simulated landfill columns containing gypsum drywall were operated under anaerobic conditions to promote H(2)S production. Five different cover materials were placed on top of the waste inside duplicate columns: (1) sandy soil, (2) sandy soil amended with lime, (3) clayey soil, (4) fine concrete (particle size less than 2.5 cm), and (5) coarse concrete (particle size greater than 2.5 cm). No cover was placed on two of the columns, which were used as controls. H(2)S concentrations measured from the middle of the waste layer ranged from 50,000 to 150,000 ppm. The different cover materials demonstrated varying H(2)S removal efficiencies. The sandy soil amended with lime and the fine concrete were the most effective for the control of H(2)S emissions. Both materials exhibited reduction efficiencies greater than 99%. The clayey and sandy soils exhibited lower reduction efficiencies, with average removal efficiencies of 65% and 30%, respectively. The coarse concrete was found to be the least efficient material as a result of its large particle size.     

城市生活垃圾填埋场甲烷气资源的产量估算及其利用

本文论述了填埋场甲烷气体的产生过程及影响因素，介绍了三种产气量估算方法及其主要特点、适用范围，并指出运用数学模型对产气量作出预测，为垃圾填埋场气体收集与处理系统的设计提供可靠的依据。同时，论述了甲烷气体的减排和综合利用措施。     

Monitoring of Gin Drinkers' Bay landfill,Hong Kong: II. Gas contents,soil properties,and vegetation performance on the side slope

This second part of the study concerned the plant cover, gas contents, and soil properties of the side slope area of the landfill, which is not protected against gas infiltration. Five different sites on the slope and a control site outside the landfill were chosen, and pipes were installed in the region. Gas contents were tested, and plant cover recorded by quadrat analysis Over 20 species of grasses, herbs, and vines were present on the slope The relative adaptabilities of the species were ranked according to the abundance of the plants Plant cover was found to be negatively correlated with landfill gas contents. The landfill soil had elevated contents of nitrogen, organic carbon, and extractable metals Total nitrogen, ammonia nitrogen, and extractable lead were further identified to be negatively correlated while available phosphate was positively correlated with plant cover     

Soil and plant characteristics of landfill sites near Merseyside,England

An ecological survey of the plant and soil characteristics was carried out on three landfill sites near Merseyside, England. It was discovered that bare ground at two of the landfill areas had high levels of methane contained in the soil air (Sefton Meadows landfill: 6–8% at 35 cm and 16–35% at 65 cm below soil surface; Coalgate Lane landfill: 1–24% at 35 cm and 39–45% at 40 cm below soils surface), causing the appearance of dark grey reduced regions in the soil, a phenomenon similar to flooded soil. The wellvegetated areas at the two sites had lower levels of methane (under 7%).In areas relatively free of methane, the concentrations of mineralized N and NO₃ ^– had significant correlations with the dry weights of vegetation (r = 0.71 withp<0.01;r=0.61 withp<0.02 accordingly), indicating the necessity of applying available nitrogen fertilizer.     

Volatilization and degradation of soil-applied dimethylselenide

Dimethylselenide (DMSe) is a highly volatile gas that is produced by indigenous microorganisms in seleniferous soils and sediments; however, little is known about the soil conditions that affect the persistence of DMSe and its transport to the atmosphere. In this study we investigated the effect of moisture content, temperature, and organic amendments on the degradation of soil-applied DMSe. The degradation of DMSe was entirely a result of biological mechanisms, but changes in temperature (20-40 degrees C) and soil moisture content (30-70% of the maximum water holding capacity) had little influence on the degradation rate. In contrast, amending soil with either 1% casein or gluten (by weight) had an inhibitory effect on the degradation of DMSe. After 18 d, 2.1 times more DMSe was present in the casein-amended soil and 2.6 times more DMSe was present in the gluten-amended soil. The transport of DMSe in packed soil columns was also investigated. Increasing the depth to soil surface was found to significantly decrease the amount of DMSe transported to the air. After 6 d, 57% of DMSe injected 10 cm below the soil surface was volatilized. At an injection depth of 20 cm the cumulative emissions were reduced by 38% and at 30 cm the cumulative emissions were reduced by 51%. In columns containing 1% casein or gluten in the top 5 cm of soil the cumulative loss of DMSe was about 9% higher than in unamended soil. Increasing our understanding of the soil conditions that influence the gaseous diffusion of DMSe should help in determining the feasibility of using Se volatilization as a remediation technique.     

Developing risk models of Cryptosporidium transport in soils from vegetated, tilted soilbox experiments

Transport of Cryptosporidium parvum through macroporous soils is poorly understood yet critical for assessing the risk of groundwater contamination. We developed a conceptual model of the physics of flow and transport in packed, tilted, and vegetated soilboxes during and immediately after a simulated rainfall event and applied it to 54 experiments implemented with different soils, slopes, and rainfall rates. Using a parsimonious inverse modeling procedure, we show that a significant amount of subsurface outflow from the soilboxes is due to macropore flow. The effective hydraulic properties of the macropore space were obtained by calibration of a simple two-domain flow and transport model that accounts for coupled flow in the matrix and in the macropores of the soils. Using linear mixed-effects analysis, macropore hydraulic properties and oocyst attenuation were shown to be associated with soil bulk density and rainfall rate. Macropore flow was shown to be responsible for bromide and C. parvum transport through the soil into the underlying pore space observed during the 4-h experiments. We confirmed this finding by conducting a pair of saturated soil column studies under homogeneously repacked conditions with no macropores in which no C. parvum transport was observed in the effluent. The linear mixed-effects and logistic regression models developed from the soilbox experiments provide a basis for estimating macropore hydraulic properties and the risk of C. parvum transport through shallow soils from bulk density, precipitation, and total shallow subsurface flow rate. The risk assessment is consistent with the reported occurrence of oocysts in springs or groundwater from fractured or karstic rocks protected only by shallow overlying soils.     

Monitoring of Gin Drinkers' Bay landfill,Hong Kong: I. Landfill gas on top of the landfill

The present study centered on the composition of landfill gas and its effects on soil and plants at the Gin Drinkers' Bay (GDB) landfill in Hong Kong This first part of the study was a whole-year monitoring of landfill gas composition in the gas ventilation system installed on top of the landfill Methane, carbon dioxide, oxygen, and ethylene were measured It was shown that gas generation was positively correlated with the amount of precipitation and air temperature and negatively correlated with atmospheric pressure     

Waste Management and Climate Change

Waste management has at least five types of impacts on climate change, attributable to: (1) landfill methane emissions; (2) reduction in industrial energy use and emissions due to recycling and waste reduction; (3) energy recovery from waste; (4) carbon sequestration in forests due to decreased demand for virgin paper; and (5) energy used in long-distance transport of waste: A recent USEPA study provides estimates of overall per-tonne greenhouse gas reductions due to recycling. Plausible calculations using these estimates suggest that countries such as the US or Australia could realise substantial greenhouse gas reductions through increased recycling, particularly of paper.     

PHOSPHORUS RELEASE AND ASSIMILATORY CAPACITY OF TWO LOWER MISSISSIPPI VALLEY FRESHWATER WETLAND SOILS1

ABSTRACT: Phosphorus fluxes and water quality functions of a bottomland hardwood and freshwater marsh wetland soil were compared. The effect of soil physicochemical conditions, phosphorus loading rate, and diffusive exchange between soils and the overlying food water column on phosphorus release and retention were studied. The predominantly mineral swamp forest soil displayed greater phosphorus sorption potential than the organic freshwater marsh soil. Moreover, due to its low bulk density (0.11 g cm^?3), the freshwater marsh soil surface area required for phosphorus retention is very large compared to the bottomland hardwood wetland soil. For both wetlands, soil redox status affected P release and assimilatory capacity. The more reducing the soils, the smaller their phosphorus retention capacity (greater their release). Phosphorus removal from the overlying water column into the wetland soils followed a first-order kinetic model. Under similar hydrological conditions, phosphorus was found to diffuse 1.2 times faster to the bottom. land hardwood soil than in the freshwater marsh soil. Results indicate that while the bottomland hardwood wetland soil will serve as a sink for phosphorus entering such wetland, phosphorus will be released and exported from the freshwater marsh soil into adjacent ecosystems.     

In vitro methane removal by volcanic pumice soil biofilter columns over one year

Soil methane (CH(4)) biofilters, containing CH(4)-oxidizing bacteria (methanotrophs), are a promising technology for mitigating greenhouse gas emissions. However, little is known about long-term biofilter performance. In this study, volcanic pumice topsoils (0-10 cm) and subsoils (10-50 cm) were tested for their ability to oxidize a range of CH(4) fluxes over 1 yr. The soils were sampled from an 8-yr-old and a 2-yr-old grassed landfill cover and from a nearby undisturbed pasture away from the influence of CH(4) generated by the decomposing refuse. Methane was passed through the soils in laboratory chambers with fluxes ranging from 0.5 g to 24 g CH(4) m(-3) h(-1). All topsoils efficiently oxidized CH(4). The undisturbed pasture topsoil exhibited the highest removal efficiency (24 g CH(4) m(-3) h(-1)), indicating rapid activation of the methanotroph population to the high CH(4) fluxes. The subsoils were less efficient at oxidizing CH(4) than the topsoils, achieving a maximum rate oxidation rate of 7 g CH(4) m(-3) h(-1). The topsoils exhibited higher porosities; moisture contents; surface areas; and total C, N, and available-P concentrations than the subsoils, suggesting that these characteristics strongly influence growth and activity of the CH(4)-oxidizing bacteria. Soil pH values and available-P levels gradually declined during the trial, indicating a need to monitor chemical parameters closely so that adjustments can be made when necessary. However, other key soil physicochemical parameters (moisture, total C, total N) increased over the course of the trial. This study showed that the selected topsoils were capable of continually sustaining high CH(4) removal rates over 1 yr, which is encouraging for the development of biofilters as a low-maintenance greenhouse gas mitigation technology.     

Effects of landfill gas on subtropical woody plants

An account is given of the influence of landfill gas on tree growth in the field at Gin Drinkers' Bay (GDB) landfill, Hong Kong, and in the laboratory. Ten species (Acacia confusa, Albizzia lebbek, Aporusa chinensis, Bombax malabaricum, Castanopsis fissa, Liquidambar formosana, Litsea glutinosa, Machilus breviflora, Pinus elliottii, andTristania conferta), belonging to eight families, were transplanted to two sites, one with a high concentration of landfill gas in the cover soil (high-gas site, HGS) and the other with a relatively low concentration of gas (low-gas site, LGS). Apart from the gaseous composition, the general soil properties were similar. A strong negative correlation between tree growth and landfill gas concentration was observed. A laboratory study using the simulated landfill gas to fumigate seedlings of the above species showed that the adventitious root growth ofAporusa chinensis, Bombax malabaricum, Machilus breviflora, andTristania confera was stimulated by the gas, with shallow root systems being induced.Acacia confusa, Albizzia lebbek, andLitsea glutinosa were gas-tolerant, while root growth ofCastanopsis fissa, Liquidambar formosana, andPinus elliottii was inhibited. In most cases, shoot growth was not affected, exceptions beingBombax malabaricum, Liquidambar formosana, andTristania conferta, where stunted growth and/or reduced foliation was observed. A very high CO₂ concentration in cover soil limits the depth of the root system. Trees with a shallow root system become very susceptible to water stress. The effects of low O₂ concentration in soil are less important than the effects of high CO₂ concentration.Acacia confusa, Albizzia lebbek, andTristania conferta are suited for growth on subtropical completed landfills mainly due to their gas tolerance and/or drought tolerance.     

Potential for enhanced phytoremediation of landfills using biosolids – a review

Despite the use of recyclable materials increasing worldwide, waste disposal to landfill remains the most common method of waste management because it is simple and relatively inexpensive. Although landfill disposal is an effective waste management system, if not managed correctly, a number of potential detrimental environmental impacts have been identified including soil and ground water contamination, leachate generation, and gas emissions. In particular, improper post-closure treatment of landfills or deterioration of the conventional clay landfill capping were shown to result in land degradation which required remediation to secure contaminants within the landfill site.Phytoremediation is an attractive technology for landfill remediation, as it can stabilize soil and simultaneously remediate landfill leachate. In addition, landfill phytoremediation systems can potentially be combined with landfill covers (Phytocapping) for hydrological control of infiltrated rainfall. However, for the successful application of any phytoremediation system, the effective establishment of appropriate, desired vegetation is critical. This is because the typically harsh and sterile nature of landfill capping soil limits the sustainable establishment of vegetation. Therefore, the physicochemical properties of landfill capping soils often need to be improved by incorporating soil amendments. Biosolids are a common soil amendment and will often meet these demanding conditions because they contain a variety of plant nutrients such as nitrogen, phosphate, potassium, as well as a large proportion of organic matter. Such amendment will also ameliorate the physical properties of the capping soils by increasing porosity, moisture content, and soil aggregation. Contaminants which potentially originate from biosolids will also be remediated by activities congruent with the establishment of plants and bacteria.     

Waste Management and Climate Change

Waste management has at least five types of impacts on climate change, attributable to: (1) landfill methane emissions; (2) reduction in industrial energy use and emissions due to recycling and waste reduction; (3) energy recovery from waste; (4) carbon sequestration in forests due to decreased demand for virgin paper; and (5) energy used in long-distance transport of waste: A recent USEPA study provides estimates of overall per-tonne greenhouse gas reductions due to recycling. Plausible calculations using these estimates suggest that countries such as the US or Australia could realise substantial greenhouse gas reductions through increased recycling, particularly of paper.     

Radiative Forcing Due to Anthropogenic Greenhouse Gas Emissions from Finland: Methods for Estimating Forcing of a Country or an Activity

The objective of this study was to assess the radiative forcing due to Finnish anthropogenic greenhouse gas emissions in three scenarios. All the Kyoto Protocol gases, i.e., CO₂, CH₄, N₂O, and fluorinated gases, were included. The calculations showed that forcing due to Finnish emissions will increase in the case of all gases except methane by the year 2100. In 1990, radiative forcing due to Finland's emission history of all Kyoto Protocol gases was 3.2 mW/m², of which 71% was due to carbon dioxide, 17% to methane, and the rest to nitrous oxide. In 1990 the share of fluorinated gases was negligible. The share of methane in radiative forcing is decreasing, whereas the shares of carbon dioxide and of fluorinated gases are increasing and that of nitrous oxide remains nearly constant. The nonlinear features concerning additional concentrations in the atmosphere and radiative forcing due to emissions caused by a single country or activity are also considered. Radiative forcing due to Finnish emissions was assessed with two different approaches, the marginal forcing approach and the averaged forcing approach. The impact of the so-called background scenario, i.e., the scenario for concentration caused by global emissions, was also estimated. The difference between different forcing models at its highest was 40%, and the averaged forcing approach appeared to be the more recommendable. The effect of background concentrations in the studied cases was up to 11%. Hence, the choice of forcing model and background scenario should be given particular attention.     

Influence of Landfill Gas on the Microdistribution of Grass Establishment Through Natural Colonization

Many revegetated landfills have poor cover including bare areas where plants do not grow. This study, on the Bisasar Road Landfill site in South Africa, assessed grass species preferences to microhabitat conditions in a mosaic of patches of well-established grassed areas and bare, nonvegetated areas. Factors, including soil CO₂, CH₄, O₂, nutrients, and other general soil conditions, were measured in relation to species distribution and grass biomass in the field. Cynodon dactylon was the dominant grass in the established grass areas but was less abundant in the areas bordering the bare areas where Paspalum paspalodes and Sporobolus africanus were common. A number of soil factors measured were significantly correlated with grass biomass and these included Mg, Ca, Zn, Mn, K, temperature, moisture, and CO₂. However, a laboratory bioassay using the growth of C. dactylon with soils removed from the landfill indicated that there were no differences in the soils from the bare areas and those that supported high plant biomass. Thus, no nutrient deficiency or chemical toxicity was inherent in the soil in the laboratory. The results of the field investigation and bioassay indicated that soil CO₂ as a result of landfill gas infiltration into the root zone was probably the main factor causing bare areas on the landfill where no grass species could colonize and grow and that C. dactylon was more sensitive to elevated soil CO₂ than other grass species such as P. paspalodes and S. africanus.     

Controlling greenhouse gas emissions through landfill in situ aeration

Landfills and old waste deposits are some of the major anthropogenic sources of methane (CH₄) emissions worldwide. Despite the fact that during the last 15 years the amount of carbon dioxide equivalent (CO₂-eq.) emitted from German landfills was reduced by approximately two thirds, estimates show that currently more than 10 Mtonnes are still being emitted annually. As a case study, the in situ aerated former Kuhstedt Landfill (District of Rotenburg (Wümme), Germany) was assessed regarding the possibility of reducing the emitted amounts of greenhouse gases (GHG; here methane). The assessment was based on both a model calculation of the landfill gas emissions that should occur under anaerobic conditions (reference scenario) as well as using monitoring data plus extrapolations to determine the actual emissions from the landfill. It was demonstrated that more than 72% of the total GHG emissions occurring under anaerobic conditions could be avoided by altering the ambient aerobic/oxidizing conditions. By means of subsequent thermal treatment (regenerative thermal oxidation, RTO) of the extracted off-gases during the aeration process, the amount of CO₂-eq. savings, as calculated from the amount of emitted methane taking into account secondary emissions for energy production, could be further increased to 96%.