This paper describes the development and application of design tables for the hydraulic design of perforated pipes used in horizontal injection trenches in bioreactor landfills. It outlines the computational approach adopted and the pipe physical and operational characteristics analyzed. The results, presented through design tables, address the issue of selection of appropriate pipe diameter and length, perforation diameter and spacing, and inlet hydraulic head and flow rate required to achieve uniform discharge of liquid from the perforations along the length of the line, subject to typical design conditions. Design limits for pipe physical and operational characteristics were established through sensitivity analysis. An illustrative example is provided to demonstrate the use of the design tables and impact of perforated pipe design on other bioreactor landfill components.

The current practice of leachate collection and removal system (LCRS) design for sanitary landfills has limitations because of the uncertainties associated with a key design parameter, leachate production rate. The traditional techniques for determining leachate generation are accurate only to within one order of magnitude. One of the drawbacks is the inability of these techniques to account for short-term fluctuations in leachate generation rate caused by heavy rainfall events or leachate recirculation events. This paper presents a rational method to account for fluctuations in leachate generation by incorporating a correction factor to leachate generation rates determined from traditional techniques. The correction factor known as the peak leachate factor (PLF) is developed from landfill lysimeter and pilot scale test cell studies. It is defined as the ratio between peak and average daily leachate generation rate, and is proposed to be used in conjunction with the output from a leachate generation model such as the hydrologic evaluation of landfill performance model to generate a design leachate generation rate. The potential of applying PLF in the design of a LCRS in full scale landfills is evaluated by studying the scale up possibility of the hydrological behavior of laboratory lysimeters to a field scale landfill test cell. The results demonstrated that the hydrologic behavior of the field test cell is similar to that of the lysimeters. The results indicated that various categories of landfill cells will require the adoption of PLFs depending on the type of waste landfilled and climatic conditions and operational characteristics of the landfills. PLF could be an important design parameter for LCRS in landfills cells, especially those operated with continuous leachate recirculation or located in tropical climates subjected to frequent high intensity rainfall events.

Intensive research has focused on the biodegradation of the typical municipal solid waste in bioreactor landfills, but relatively little attention has been given to the biodegradability of individual refuse components. The objective of this paper is to examine and compare the degree of biodegradation of different waste fractions, textile, paper, and mixed waste, through measuring the change in the physical properties and settlement characteristics of waste and leachate quality, in six bench-scale bioreactor landfills operated under anaerobic conditions. Also, the impact caused by waste density increase in the form of subsequent waste layers on the same bioreactors is investigated. Two groups of bench-scale anaerobic bioreactor landfills operated for $125\text{days}$ . The first group was designed to study the anaerobic biodegradability, leachate quality, change in physical properties, and settlement of textile, paper, and mixed waste. The second group operated with the addition of $40\mathrm{kg}$ of load per cell to represent the overburden stresses provided by subsequent layers of waste. Mixed cells achieved about four times total wet weight reduction more than textile cells and about three times total wet weight reduction more than paper cells. Chemical oxygen demand, biological oxygen demand, volatile fatty acids, and total solids concentrations exhibited a classical peak in paper and mixed bioreactors followed by an asymptotic decline. Mixed waste experienced the highest settlement (27.2%) compared to paper and textile waste, which exhibited a maximum settlement of about 9.0%. Significant difference in the waste settlement between Group 1 (no load application) and Group 2 (load application and higher waste density) was noted. However, increasing waste density had a small effect on the leachate quality and the physical properties of waste.

Although there are advantages of bioreactor landfills over traditional sanitary landfills, the operation of bioreactor landfills is not without problems. A number of operational problems may arise when leachate is either diverted laterally or perched above low permeability layers within a landfill cell. This paper presents results from laboratory studies undertaken to determine the effects of the presence of daily/intermediate covers constructed of low permeable soils on leachate migration within a flushing bioreactor landfill. The quantities of leachate diverted laterally under a variety of soil-waste interface conditions were determined using a laboratory-scale flume of dimensions $0.2\mathrm{m}$ width, $1.5\mathrm{m}$ length, and $1.2\mathrm{m}$ depth. Two types of cover materials, silty loam and sand, were tested in combination with simulated municipal solid waste materials of two different compaction densities of 350 and $550\mathrm{kg}∕{\mathrm{m}}^3$ , and three different slopes of 0, 2, and 5%. When silt loam was used, less than 1% of leachate produced seeped through the cover layer, while when sand was used, 100% of the leachate generated seeped through the cover with no lateral migration. The ratio of hydraulic conductivities of the compacted waste and the cover soil determines the amount of lateral leachate flow observed.

The kinetic parameter of a composting process along with the effect of various parameters of composting mechanism on Michaelis Menten constant $\left(K_m\right)$ and maximum or limiting velocity constant $\left(K_3\right)$ has been evaluated in the present work. The results exhibit comparable variations in the kinetic constants $K_m$ and $K_3$ under varying parameters during the entire composting process. The deviations in the computed values of kinetic constants $K_m$ and $K_3$ helped to assess the dominant effect of various parameters during the composting process. It was also observed that the encapsulation of soil insulation has a detrimental effect on the extent of degradation. The overall assessment of kinetic data for windrows with soil insulation and variable parameters showed enhancement of degradation during the composting process.

Patterns of methane $\left(\mathrm{C}{\mathrm{H}}_4\right)$ oxidation were investigated under various combinations of environmental factors including temperature, moisture content, and fertilizer addition (as an additional nutrient source) in two types of existing landfill cover soils. In all the experimental runs, $\mathrm{C}{\mathrm{H}}_4$ and oxygen concentrations decreased with time, while carbon dioxide concentration increased suggesting that biological $\mathrm{C}{\mathrm{H}}_4$ oxidation was taking place. The highest $\mathrm{C}{\mathrm{H}}_4$ oxidation rates ( $6.4–12.3\mu \mathrm{g}$ $\mathrm{C}{\mathrm{H}}_4{\mathrm{h}}^{-1}{\mathrm{g}}_{\text{dry}\text{soil}}^{-1}$ ) were achieved at $35°\mathrm{C}$ . The lowest oxidation rates ( $3.3–4.7\mu \mathrm{g}$ $\mathrm{C}{\mathrm{H}}_4{\mathrm{h}}^{-1}{\mathrm{g}}_{\text{dry}\text{soil}}^{-1}$ ) were obtained for experiments conducted at $5°\mathrm{C}$ without adding the fertilizer. For both types of soil, without adding fertilizer, the soil with 20% moisture content (MC) showed consistently higher oxidation rates compared to soil samples containing 25 or 30% MC, for different operating temperatures. Adding the fertilizer as the nutrient source to the two soils samples with 30% moisture content resulted in enhanced $\mathrm{C}{\mathrm{H}}_4$ oxidation rates in a range of 44–145% at tested temperatures in the range between 5 and $35°\mathrm{C}$ .

A $30\text{-}\mathrm{cm}$ -thick biofilter was constructed with compost, which was obtained from Leon County Landfill (Florida). The compost was sieved with $7\text{-}\mathrm{mm}$ mesh sieve. The compost consisted of chipped yard waste that was windrowed for about $5\text{years}$ . Methane was then continuously supplied to the bottom of the biofilter, simultaneously the outflow of methane from the top and the extent of methane oxidation inside the biofilter were periodically measured. A one-dimensional dynamic numerical simulation model was then developed to simulate the methane transport and oxidation within a compost biofilter. This model was designed to incorporate dynamic parameters, such as gas permeability, diffusion coefficient, methanotrophic growth, and viscosity, as functions of water content and temperature. General agreement of methane outflux and oxidation was obtained between model simulations and experimental data. Additional simulations showed that outflux and oxidation had high correlations with temperature, whereas their relationship with water content depended on other factors, such as the influx boundary and the air-filled porosity.

In countries where resources are limited, especially in developing countries, it is important to use all available resources effectively and efficiently for the mitigation of environmental impacts caused by waste disposal sites. The aim of this paper is to present a tool for supporting decision making on environmental impact mitigation options. The proposed tool is designed to maximize short-term environmental improvements at waste disposal sites according to available resources. The process involves identifying environmental impacts caused by waste disposal activities and prioritizing these impacts using the analytical hierarchy process. The process then identifies mitigating options for each environmental impact with cost of mitigation and potential environmental improvement for each option. Using an optimization method it then determines the maximum achievable environmental improvement based on the affordability of relevant local authorities who maintain the disposal sites. This tool will provide decision makers with information on the cost effectiveness of various environmental improvement options. This tool also has the potential to use in new landfill site selection to determine the most cost-effective site. Relevant examples are provided in the paper to illustrate the use of the tool.

Curbside collection of municipal solid waste (MSW) constitutes a substantial portion of waste management cost. The utilization of operations research tools for the reduction of MSW collection costs in the Township of Millburn, N.J., was investigated. This research identified network models, specifically the Chinese postman problem algorithm as one of the approaches that could be used to evaluate the truck routes and the optimum sequence of each of these vehicles needed to collect the generated waste. The Township of Millburn has a population of 20,000 in approximately 7,000 households. The township divides the service area into three sections and collects waste twice a week from curbsides of single-family and two-2 family units using up to four trucks. Additional data, such as the number of houses per street and distances between intersections, were obtained from the Township and from Google Earth. Then with the aid of commercial software, the optimum routes for each of the trucks were obtained. Results from this optimization study were then compared with the current waste collection practice. Based on the case study results improvements to the current MSW collection procedure were proposed to the Township of Millburn, N.J.