Steady-state design of horizontal systems for liquids addition at bioreactor landfills

The key parameters for designing a horizontal source (horizontal trenches, infiltration ponds, infiltration galleries or blankets) for steady state are the rate liquids can be added to the source, the lateral and vertical extents of the zone of impact of the source, and the liquids volume needed to wet the waste within the zone of impact at steady state. This paper presents charts that a designer can use to estimate these key parameters as functions of source dimensions, injection pressure, and municipal solid waste properties (porosity, hydraulic conductivity, and anisotropy) for designing a new or analyzing an existing horizontal source system for liquids addition to landfilled waste. SEEP/W was used to model liquids flow from a horizontal source in a range of conditions practically encountered for such systems. The governing equation (Richard’s equation) and the boundary conditions were analyzed to formulate dimensionless variables by normalizing the design parameters (flow rate, injection pressure, the lateral zone of impact, injection pressure, and the added liquids volume) with the waste properties and source dimensions. The simulation results were transformed to the respective dimensionless forms and presented in design charts to estimate the key design parameters as functions of the source dimensions, waste properties, and injection pressure. The presentation of the modeling results in the dimensionless form facilitates their use beyond the conditions modeled. A solved example is presented to demonstrate the use of the design charts. The approach presented in the paper should be considered as approximate and designers should use their judgement and experience when using these charts for designing a horizontal liquids addition system for a specific site.     

Transient design of landfill liquid addition systems

This study presents the development of design charts that can be used to estimate lateral and vertical spacing of liquids addition devices (e.g., vertical well, horizontal trenches) and the operating duration needed for transient operating conditions (conditions until steady-state operating conditions are achieved). These design charts should be used in conjunction with steady-state design charts published earlier by Jain et al., 2010a, Jain et al., 2010b. The data suggest that the liquids addition system operating time can be significantly reduced by utilizing moderately closer spacing between liquids addition devices than the spacing needed for steady-state conditions. These design charts can be used by designers to readily estimate achievable flow rate and lateral and vertical extents of the zone of impact from liquid addition devices, and analyze the sensitivity of various input variables (e.g., hydraulic conductivity, anisotropy, well radius, screen length) to the design. The applicability of the design charts, which are developed based on simulations of a continuously operated system, was also evaluated for the design of a system that would be operated intermittently (e.g., systems only operated during facility operating hours). The design charts somewhat underestimates the flow rate achieved and overestimates the lateral extent of the zone of impact over an operating duration for an intermittently operated system. The associated estimation errors would be smaller than the margin of errors associated with measurement of other key design inputs such as waste properties (e.g., hydraulic conductivity) and wider variation of these properties at a given site due to heterogeneous nature of waste.     

Uses and misuses of bioclimatic envelope modeling

Bioclimatic envelope models use associations between aspects of climate and species' occurrences to estimate the conditions that are suitable to maintain viable populations. Once bioclimatic envelopes are characterized, they can be applied to a variety of questions in ecology, evolution, and conservation. However, some have questioned the usefulness of these models, because they may be based on implausible assumptions or may be contradicted by empirical evidence. We review these areas of contention, and suggest that criticism has often been misplaced, resulting from confusion between what the models actually deliver and what users wish that they would express. Although improvements in data and methods will have some effect, the usefulness of these models is contingent on their appropriate use, and they will improve mainly via better awareness of their conceptual basis, strengths, and limitations.     

An integrated analytical framework for quantifying the LCOE of waste-to-energy facilities for a range of greenhouse gas emissions policy and technical factors

This study presents a novel integrated method for considering the economics of waste-to-energy (WTE) facilities with priced greenhouse gas (GHG) emissions based upon technical and economic characteristics of the WTE facility, MSW stream, landfill alternative, and GHG emissions policy. The study demonstrates use of the formulation for six different policy scenarios and explores sensitivity of the results to ranges of certain technical parameters as found in existing literature. The study shows that details of the GHG emissions regulations have large impact on the levelized cost of energy (LCOE) of WTE and that GHG regulations can either increase or decrease the LCOE of WTE depending on policy choices regarding biogenic fractions from combusted waste and emissions from landfills. Important policy considerations are the fraction of the carbon emissions that are priced (i.e. all emissions versus only non-biogenic emissions), whether emissions credits are allowed due to reducing fugitive landfill gas emissions, whether biogenic carbon sequestration in landfills is credited against landfill emissions, and the effectiveness of the landfill gas recovery system where waste would otherwise have been buried. The default landfill gas recovery system effectiveness assumed by much of the industry yields GHG offsets that are very close to the direct non-biogenic GHG emissions from a WTE facility, meaning that small changes in the recovery effectiveness cause relatively larger changes in the emissions factor of the WTE facility. Finally, the economics of WTE are dependent on the MSW stream composition, with paper and wood being advantageous, metal and glass being disadvantageous, and plastics, food, and yard waste being either advantageous or disadvantageous depending upon the avoided tipping fee and the GHG emissions price.     

Adaptive Management of Flows in the Lower Roanoke River, North Carolina, USA

The lower Roanoke River in North Carolina, USA, has been regulated by a series of dams since the 1950s. This river and its floodplain have been identified by The Nature Conservancy, the US Fish and Wildlife Service, and the State of North Carolina as critical resources for the conservation of bottomland hardwoods and other riparian and in-stream biota and communities. Upstream dams are causing extended floods in the growing season for bottomland hardwood forests, threatening their survival. A coalition of stakeholders including public agencies and private organizations is cooperating with the dam managers to establish an active adaptive management program to reduce the negative impacts of flow regulation, especially extended growing season inundation, on these conservation targets. We introduce the lower Roanoke River, describe the regulatory context for negotiating towards an active adaptive management program, present our conservation objective for bottomland hardwoods, and describe investigations in which we successfully employed a series of models to develop testable management hypotheses. We propose adaptive management strategies that we believe will enable the bottomland hardwoods to regenerate and support their associated biota and that are reasonable, flexible, and economically sustainable.     

Municipal solid waste in situ moisture content measurement using an electrical resistance sensor

Moisture content (MC) is a crucial parameter for degradation of solid waste in landfills. Present MC measurement techniques suffer from several drawbacks. A moisture sensor for measurement of in situ moisture content of solid waste in landfills was developed. The sensor measures the electrical resistance across the granular matrix of the sensor, which in turn can be correlated to moisture content. The sensor was also equipped with a thermocouple and tubing that permits simultaneous measurement of temperature and gas sampling. The electrical conductivity of the surrounding moisture and the temperature in the matrix both affect the resistance measurements. This paper describes the results of laboratory experiments designed to select the appropriate granular media particle size, measure the influence of moisture electrical conductivity and temperature, and develop calibration relationships between measured resistance and gravimetrically determined moisture content. With a few limitations, the sensor is able to detect MC of solid waste under conditions allowing moisture movement into the sensor. The application of this technique shows promise for use in bioreactor landfills where high moisture contents are expected and desired.     

Spatial and temporal patterns of Campylobacter contamination underlying public health risk in the Taieri River, New Zealand

New Zealand's freshwater ecosystems are subject to microbial contamination from a predominantly agricultural landscape. This study examines the spatial and temporal distribution of the human pathogen Campylobacter in the lower Taieri River, South Island (New Zealand). Enumeration of thermophilic Campylobacter from river samples was performed using a most probable number (MPN) method. Seasonal variation in Campylobacter levels was evident, with higher median levels detected in summer, when human exposure through recreational water use is maximal. Campylobacter levels varied significantly among the 10 sampling sites, increasing below a major tributary entering the river and then showing a downstream decrease. These changes probably resulted from inputs from adjacent farms and instream Campylobacter losses (settling, death). Two main peaks in the flux of Campylobacter were observed, one in winter and one in summer. A decrease in notified cases of campylobacteriosis in the human population was observed when levels of Campylobacter at the main recreational bathing site on the river were low. Continuing land use change and intensification in New Zealand may lead to further increases in microbial contamination of freshwaters, and an associated increase in waterborne enteric diseases such as campylobacteriosis.     

The Roles of Photooxidation and Biodegradation in Long-term Weathering of Crude and Heavy Fuel Oils

Although spilled oil is subject to a range of natural processes, only combustion, photooxidation and biodegradation destroy hydrocarbons and remove them from the biosphere. We present laboratory data that demonstrate the molecular preferences of these processes, and then examine some oil residues collected from previously documented releases to confirm the important roles that these processes play in removing spilled oil from both marine and terrestrial environments.     

Trace chemical partitioning in construction and demolition debris fines: process and market implications

Construction and demolition debris (CDD) fines, a residue generated from mechanized CDD recycling, can often be beneficially reused. Concentrations of chemicals of potential concern in CDD fines should be evaluated prior to being reintroduced into the environment to assess risk and make informed decisions about appropriate reuse opportunities. The distribution of trace chemicals in CDD fines as a function of particle size was measured to evaluate if concentrations in the bulk material can be reduced by removing certain particle size ranges through screening. Chemicals of potential concern, including arsenic, lead, sulfate and polycyclic aromatic hydrocarbons (PAH), were characterized in four different size fractions (19–4.8 mm, 4.8–0.84 mm, 0.84–0.3 mm, < 0.3 mm) of CDD fine samples collected from 12 US CDD recycling facilities throughout the US. Results revealed that aluminum, arsenic and chromium concentrations were distributed evenly throughout all four size fractions. As for the remaining chemicals, most samples had lower concentrations in the 19–4.8 mm size range. In some samples and for certain chemicals, removal of the finer size fractions reduced overall concentrations in CDD fines, suggesting that additional processing may be worth further investigation.