Robert K. Ham

Methane production from municipal refuse: A review of enhancement techniques and microbial dynamics

Methane is recovered from about 100 municipal solid waste landfills in the U.S. in saleable volumes, although yields are 1 to 50% of the methane potential of refuse based on biodegradability data. Studies on the microbiology of refuse decomposition and efforts to enhance refuse methanogenesis are reviewed here. Results of studies on the effects of leachate recycle and neutralization, a reduction in refuse particle size, the addition of anaerobic sewage sludge or old refuse as a seed, nutrient addition, calcium carbonate addition, and moisture on methane production are examined in consideration of new findings on landfill microbiology. A four‐phase description of refuse decomposition with leachate recycle, including an aerobic phase, an anaerobic acid phase, an accelerated methane production phase, and a decelerated methane production phase, is proposed. Mass balances and pumping tests may be used to estimate the methane potential of a sanitary landfill. The use of empirical, zero, and first‐order models t...

The effect of lignin and sugars to the aerobic decomposition of solid wastes

A series of experimental runs were conducted from 1995 to 1999 in Madison (WI, USA) with the goal to investigate the biodegradation process of seven (7) solid waste components and mixtures of them under near optimal aerobic conditions. It was shown that substrates with high initial lignin contents or high initial HWSM contents were observed to have relatively low and high degradation extents, respectively. Two linear equations were derived that correlate degradation extent (as indicated by the volatile solids reduction) to initial lignin and initial HWSM contents separately. The lignin equation was compared to a similar equation previously developed for anaerobic environments by Chandler et al. (Predicting methane fermentation biodegradability. In: Biotechnology and Bioengineering Symposium No. 10 (1980) New York: John Wiley & Sons). With comparison to the Chandler formula, lignin was found to be less inhibitory to the overall substrate decomposition in aerobic environments compared to anaerobic ones. Cellulose loss contributed to a higher than 50% to the overall dry mass loss for all substrates studied. In addition, the cellulose to lignin (C/L) ratio appeared to be a relatively accurate compost maturity indicator, since it reduced to a value less than 0.5 for most substrates that had reached their degradation extent.

Gas Production Parameters in Sanitary Landfill Simulators

Abstract The decomposition of shredded municipal refuse was studied in 19 drums (208 l). Gas production and composition were monitored for two years. The addition of old, anaerobically degraded refuse as a seed of anaerobic bacteria and the neutralization of the refuse were the two techniques which stimulated methane production. Yields of 80–150 l of methane per kilogram of dry, grindable, volatile solids were measured. The addition of anaerobic sewage sludge, acetate, and the initial removal of oxygen from a drum, were not stimulatory. Initially, it was the development of the methanogen population and not polymer hydrolysis which limited methane production.

Life Cycle Management of Municipal Solid Waste

Life-cycle assessment concepts and methods are currently being applied to evaluate integrated municipal solid waste management strategies throughout the world. The Research Triangle Institute and the U.S. Environmental Protection Agency are working to develop a computer-based decision support tool to evaluate integrated municipal solid waste management strategies in the United States. The waste management unit processes included in this tool are waste collection, transfer stations, recovery, compost, combustion, and landfill. Additional unit processes included are electrical energy production, transportation, and remanufacturing. The process models include methodologies for environmental and cost analysis. The environmental methodology calculates life cycle inventory type data for the different unit processes. The cost methodology calculates annualized construction and equipment capital costs and operating costs per ton processed at the facility. The resulting environmental and cost parameters are allocated to individual components of the waste stream by process specific allocation methodologies. All of this information is implemented into the decision support tool to provide a life-cycle management evaluation of integrated municipal solid waste management strategies.

Life‐cycle inventory of a modern municipal solid waste landfill

The Environmental Research and Education Foundation (EREF), in conjunction with Ecobalance and researchers from the University of Wisconsin and North Carolina State, is nearing completion of a comprehensive 2-year project on the life-cycle inventory (LCI) of a modern municipal solid waste (MSW) landfill. Data for the model came from both primary (over 100 landfills world-wide) and secondary data sources. Partners in the project included waste management companies from North America and Europe (including Waste Management Inc., SITA and CREED). In addition to the landfill LCI model, the project also includes the development of a software tool. The final report will provide a sound basis for assessing, on a life-cycle basis, the emissions and resource consumption associated with a modern MSW landfill. The model and report can be used to assess the importance of: ( 1 ) the various stages in the life- cycle system; (2) the time horizon selected; and (3) the air and water management techniques selected.

Effects of moisture movement on methane production in solid waste landfill samples

Abstract Increasing interest in methane gas extracted from landfills stems from its being a valuable resource and its potential economical availability for use as a fuel. This study indicated that moisture movement through a decomposing solid waste sample appears to increase methane gas generation rates by 25 to 50% over methane gas rates observed during minimal moisture movement but at the same overall moisture content levels. This points out the difference between moisture content and moisture movement as two separate variables affecting methane generation rates. The results are of importance in predicting gas flow and understanding measured gas production rates at full-scale landfills, especially with regard to local climatic effects.

Microbial chemical and methane production characteristics of anaerobically decomposed refuse with and without leachate recycling

Abstract Microbial and chemical characteristics of refuse in an active state of methane production, incubated in the laboratory with and without leachate recycle, were compared. There were no significant differences in the total anaerobic population or the sub-populations of cellulolytic, hemicellulolytic, acetogenic or methanogenic (based on acetate or H 2 CO 2 utilization) bacteria in refuse incubated with or without leachate recycle. Therefore, leachate recycle may be used to accelerate refuse decomposition in laboratory-scale test lysimeters without changing the microbial composition of the aforementioned trophic groups. Differences in soluble constituent concentrations and methane production patterns between leachate recycle and non-leachate recycle containers were attributed to the mixing associated with leachate recycle. Under certain circumstances, leachate recycle is a useful technique for acceleration of refuse decomposition in the laboratory, thus reducing the period of time required to study the effect of an addition to the refuse ecosystem on methane production.

A laboratory method to investigate gaseous emissions and solids decomposition during composting of municipal solid wastes.

A laboratory method was developed to quantify CO2, NH3 and VOC yields and to follow solids decomposition during composting of MSW or its components. All organic substrates were shredded, water and nutrients were added to near optimum levels prior to composting, and composting was continued until feed materials reached approximately the full extent of decomposition. Twenty five L stainless steel digesters were used and aluminum packing was mixed with the wastes to facilitate airflow. Thermophilic temperatures were maintained and air supplied in excess. Nutrients were added to reach an initial C/N ratio of approximately 30. CO2 and NH3 gases in the exit air stream were captured in alkaline and acidic solutions, respectively, and quantified through titration on a cumulative basis. VOC traps, prior to the gas traps, captured emitted volatile organic compounds, which were quantified on a cumulative basis. Solids were analyzed for hot water soluble matter, fats and lipids, cellulose, hemicellulose and lignin/humus. Food wastes, yard wastes and mixed paper produced approximately 368, 220 and 153 g C-CO2/dry kg and approximately 40.5, 4.6 and 2.0 g N NH3/dry kg of starting material, respectively. VOC volatilization profiles had a decreasing trend with composting. Partially composted MSW produced 8.2 mg/dry kg of 8 selected VOCs. CO2, NH3 and VOC recovery tests resulted in efficiencies of 98.6%, 97.6% and 94.6% respectively. Reproducibility of the solids decomposition and gaseous emissions measurements was observed. Carbon and nitrogen mass balance closures ranged from 85.5% to 117.1% and 32.2% to 175% respectively.

Household food waste to wastewater or to solid waste? That is the question

Decision makers need sound analyses of economic and environmental impacts of options for managing household food waste. Food waste impacts public health (it rots, smells, and attracts rodents) and costs (it drives collection frequency). A life cycle inventory is used to quantify total materials, energy, costs and environmental flows for three municipal solid waste systems (collection followed by compost, waste-to-energy or landfill) and two wastewater systems (kitchen food waste disposer followed by rural on-site or municipal wastewater treatment) for food waste management. Inventory parameters are expressed per 100 kg of food waste (wet weight) to place data on a normalised basis for comparison. System boundaries include acquisition, use and decommissioning. Parameters include inputs (land, materials, water) and output emissions to air, water and land. Parameters are ranked simply from high to low. Ranking highest overall was the rural wastewater system, which has a high amount of food waste and carrier water relative to the total throughput over its design life. Waste-to-energy was second; burning food waste yields little exportable energy and is costly. Next, municipal wastewater tied with landfill. Municipal wastewater is low for land, material, energy and cost, but is highest for food waste by-product (sludge). Landfill ranks low for air emissions and cost. Compost ranks lowest; it has the lowest material and water inputs and generates the least waste-water and waterborne waste.

Inhibition of methane formation from municipal refuse in laboratory scale lysimeters

Changes in chemical composition and population development of key groups of bacteria (hydrolytic, acetogenic, and methanogenic) were measured in a laboratory scale simulation of refuse decomposition from the time of initial incubation through the methane production phase. Inhibition of methane production appeared to be characteristic of refuse decomposition. It was observed in 20 of 32 leachate recycle containers and all 19 control containers. Inhibition was not owing to an absence of indigenous microorganisms, toxic concentrations of carboxylic acids or cations, or insufficient ammonia. Characteristics of inhibited and successful containers are compared.