Wet landfill decomposition rate determination using methane yield results for excavated waste samples

An increasing number of landfills are operated to accelerate waste decomposition through liquids addition (e.g., leachate recirculation) as a wet landfill. Landfill design and regulation often depend on utilizing landfill gas production models that require an estimate of a first-order gas generation rate constant, k. Consequently, several studies have estimated k using collected gas volumes from operating wet landfills. Research was conducted to examine an alternative approach in which k is estimated not from collected landfill gas but from solid waste samples collected over time and analyzed for remaining gas yield. To achieve this goal, waste samples were collected from 1990 through 2007 at two full-scale landfills in Florida that practiced liquids addition. Methane yields were measured from waste samples collected over time, including periods before and after leachate recirculation, and the results were applied to a first-order decay model to estimate rate constants for each of the sites. An initial, intensive processing step was conducted to exclude non-biodegradable components from the methane yield testing procedure. The resulting rate constants for the two landfills examined were 0.47 yr(-1) and 0.21 yr(-1). These results expectedly exceeded the United States Environmental Protection Agency's rate constants for dry and conventional landfills (0.02-0.05 yr(-1)), but they are comparable to wet landfill rate constants derived using landfill gas data (0.1-0.3 yr(-1)).     

SPATIAL VARIATIONS OF WATER LOSS DURING DROUGH A CASE STUDY1

ABSTRACT: A regional water conservation system for drought management involves many uncertain factors. Water received from precipitation may stay on the ground surface, evaporate back into the atmosphere, or infiltrate into the ground. Reliable estimates of the amount of evapotranspiration and infiltration are not available for a large basin, especially during periods of drought. By applying a geographic information system, this study develops procedures to investigate spatial variations of unavailable water for given levels of drought severity. Levels of drought severity are defined by truncated values of monthly precipitation and daily streamflow to reflect levels of water availability. The greater the truncation level, the lower the precipitation or streamflow. Truncation levels of monthly precipitation are recorded in depth of water while those of daily streamflow are converted into monthly equivalent water depths. Truncation levels of precipitation and streamflow treated as regionalized variables are spatially interpolated by the unbiased minimum variance estimation. The interpolated results are vector values of precipitation and streamflow at a grid of points covering the studied basin. They are then converted into raster‐based values and expressed graphically. The image subtraction operation is used to subtract the image of streamflow from that of precipitation at their corresponding level of drought severity. It is done on a cell‐by‐cell basis resulting in new attribute values to form the spatial image representing a spatial distribution of potential water loss at a given level of drought severity.     

Occurrence of organic pollutants in recovered soil fines from construction and demolition waste

The objective of this study was to characterize recovered soil fines from construction and demolition (C&D) waste recycling facilities for trace organic pollutants. Over a period of 18 months, five sampling trips were made to 14 C&D waste recycling facilities in Florida. Screened soil fines were collected from older stockpiles and newly generated piles at the sites. The samples were analyzed for the total concentration (mg/kg) of a series of volatile organic compound (VOCs) and semi-volatile organic compounds (semi-VOCs). The synthetic precipitation leaching procedure (SPLP) test was also performed to evaluate the leachability of the trace organic chemicals. During the total analysis only a few volatile organic compounds were commonly found in the samples (trichlorofluoromethane, toluene, 4-isopropyltoluene, trimethylbenzene, xylenes, and methylene chloride). A total of nine VOCs were detected in the leaching test. Toluene showed the highest leachability among the compounds (61.3-92.0%), while trichlorofluoromethane, the most commonly detected compound from both the total and leaching tests, resulted in the lowest leachability (1.4-39.9%). For the semi-VOC analysis, three base-neutral semi-VOC compounds (bis(2-ethylhexyl)phthalate, butyl benzyl phthalate, and di-n-butyl phthalate) and several PAHs (acenaphthene, pyrene, fluoranthene, and phenanthrene) were commonly detected in C&D fines samples. These compounds also leached during the SPLP leaching test (0.1-25%). No acid extractable compounds, pesticides, or PCBs were detected. The results of this study were further investigated to assess risk from land applied recovered soil fines by comparing total and leaching concentrations of recovered soil fines samples to risk-based standards. The results of this indicate that the organic chemicals in recovered soil fines from C&D debris recycling facilities were not of a major concern in terms of human risk and leaching risk to groundwater under reuse and contact scenarios.     

OPTIMIZATION OF INTERMITTENT PUMPING SCHEDULES FOR AQUIFER REMEDIATION USING A GENETIC ALGORITHM1

ABSTRACT: Using a genetic algorithm (GA), optimal intermittent pumping schedules were established to simulate pump‐and‐treat remediation of a contaminated aquifer with known hydraulic limitations and a water miscible contaminant, located within the Duke Forest in Durham, North Carolina. The objectives of the optimization model were to minimize total costs, minimize health risks, and maximize the amount of contaminant removed from the aquifer. Stochastic ground water and contaminant transport models were required to provide estimates of contaminant concentrations at pumping wells. Optimization model simulations defined a tradeoff curve between the pumping cost and the amount of contaminant extracted from the aquifer. For this specific aquifer/miscible contaminant combination, the model simulations indicated that pump‐and‐treat remediation using intermittent pumping schedules for each pumping well produced significant reductions in predicted contaminant concentrations and associated health risks at a reasonable cost, after a remediation time of two years.     

Queen–worker–brood coadaptation rather than conflict may drive colony resource allocation in the ant Temnothorax curvispinosus

Conflicts of interest among genetically heterogeneous nestmates in social insect colonies have been emphasized as driving colony resource allocation. However, potential intracolonial conflicts may not actually be realized so that resource allocation could be shaped primarily by among-colony selection that maximizes colony productivity. To elucidate the causal basis of patterns of resource allocation, I experimentally manipulated three fundamental aspects of colony social structure (relatedness among workers, relatedness among larvae, and queen presence) in the ant Temnothorax curvispinosus and measured effects on colony resource allocation to new workers, gynes, and males. The experimental manipulations had widespread effects on patterns of colony resource allocation, but there was little evidence for realized conflicts over the sex ratio and caste ratio. Decreasing nestmate relatedness caused decreased colony productivity, suggesting that more closely related nestmates have more favorably interacting phenotypes. Together, these results suggest that resource allocation in T. curvispinosus may be shaped more by among-colony selection than intracolonial conflict, leading to queen–worker–brood coadaptation.     

Evaluation of cleaning and disinfection protocols for commercial farm equipment following a foreign animal disease outbreak

This study evaluated the microbiocidal efficacy of a cleaning and disinfection (C&D) treatment using stainless-steel coupons applied to three common types of animal mortality transport vehicles when exposed to agricultural conditions. Metal test coupons, inoculated with bacteriophage MS2, were affixed to the undercarriage of three types of animal mortality transport vehicles at various locations. Coupons were grimed by maneuvering the test vehicles down a series of wet dirt roads. Coupons were attached and extracted at various points to evaluate C&D performance with and without grime. C&D efficacy using a water-supplied pressure washing system and a dilute sodium hypochlorite (NaOCl) solution was determined by comparing the difference in recovered viable virus between positive control coupons and test coupons. The results demonstrated a relatively high surface decontamination efficacy, with all but one location showing >5 log reduction of MS2. Coupons located on the roll-off truck's inside-back bumper contained the highest level of grime and resulted in a 4 log reduction of MS2. There was no significant difference in C&D efficacy across vehicle types, but locations impacted by grime and lack of accessibility achieved lower efficacies on average. These findings suggest that common C&D protocols, when applied to farm mortality transport vehicles, are effective. Hard-to-access locations containing high levels of grime may be candidates for additional targeted treatment.     

Factors affecting TCLP lead leachability from computer CPUs

The factors impacting lead leachability from computer central processing units (CPUs) during the toxicity characteristic leaching procedure (TCLP) were investigated. Several CPUs were disassembled and their component materials were decreased in size to meet the requirements of the TCLP. The impact of CPU composition was examined by leaching different combinations of the CPU components. The ferrous metal content of the mixture greatly impacted lead leaching. TCLP lead concentrations of CPUs predicted by leaching the lead-bearing printed wire boards alone were much greater than those measured when the ferrous metal of the CPU was included in the mixture. The leaching of iron and zinc from the galvanized steel components of the CPU created electrochemical conditions where lead was less soluble. Additional size reduction beyond that required by the TCLP did not result in additional lead leaching. As the volume of head space above the leaching solution increased, the concentration of lead measured increased as well.     

Mitigating Impact of Devils Lake Flooding on the Sheyenne River Sulfate Concentration

Devils Lake is a terminal lake located in northeast North Dakota. Because of its glacial origin and accumulated salts from evaporation, the lake has a high concentration of sulfate compared to the surrounding water bodies. From 1993 to 2011, Devils Lake water levels rose by ~10 m, which flooded surrounding communities and increased the chance of an overspill to the Sheyenne River. To control the flooding, the State of North Dakota constructed two outlets to pump the lake water to the river. However, the pumped water has raised concerns about of water quality degradation and potential flooding risk of the Sheyenne River. To investigate these perceived impacts, a Soil and Water Assessment Tool (SWAT) model was developed for the Sheyenne River and it was linked to a coupled SWAT and CE‐QUAL‐W2 model that was developed for Devils Lake in a previous study. While the current outlet schedule has attempted to maintain the total river discharge within the confines of a two‐year flood (36 m³/s), our simulation from 2012 to 2018 revealed that the diversion increased the Sheyenne River sulfate concentration from an average of 125 to >750 mg/L. Furthermore, a conceptual optimization model was developed with a goal of better preserving the water quality of the Sheyenne River while effectively mitigating the flooding of Devils Lake. The optimal solution provides a “win–win” outlet management that maintains the efficiency of the outlets while reducing the Sheyenne River sulfate concentration to ≤600 mg/L.     

Growth of Dehalococcoides spp. and increased abundance of reductive dehalogenase genes in anaerobic PCB-contaminated sediment microcosms

Polychlorinated biphenyls (PCBs) contaminate 19% of US Superfund sites and represent a serious risk to human and environmental health. One promising strategy to remediate PCB-contaminated sediments utilizes organohalide-respiring bacteria (OHRB) that dechlorinate PCBs.

However, functional genes that act as biomarkers for PCB dechlorination processes (i.e., reductive dehalogenase genes) are poorly understood. Here, we developed anaerobic sediment microcosms that harbor an OHRB community dominated by the genus Dehalococcoides. During the 430-day microcosm incubation, Dehalococcoides 16S rRNA sequences increased two orders of magnitude to 10⁷ copies/g of sediment, and at the same time, PCB118 decreased by as much as 70%. In addition, the OHRB community dechlorinated a range of penta- and tetra-chlorinated PCB congeners including PCBs 66, 70?+?74?+?76, 95, 90?+?101, and PCB110 without exogenous electron donor. We quantified candidate reductive dehalogenase (RDase) genes over a 430-day incubation period and found rd14, a reductive dehalogenase that belongs to Dehalococcoides mccartyi strain CG5, was enriched to 10⁷ copies/g of sediment. At the same time, pcbA5 was enriched to only 10⁵ copies/g of sediment. A survey for additional RDase genes revealed sequences similar to strain CG5’s rd4 and rd8. In addition to demonstrating the PCB dechlorination potential of native microbial communities in contaminated freshwater sediments, our results suggest candidate functional genes with previously unexplored potential could serve as biomarkers of PCB dechlorination processes.

     

Hurricane Harvey and Greater Houston households: comparing pre-event preparedness with post-event health effects,event exposures,and recovery

Most disaster studies rely on convenience sampling and ‘after-only’ designs to assess impacts. This paper, focusing on Hurricane Harvey (2017) and leveraging a pre-/post-event sample of Greater Houston households (n=71) in the United States, establishes baselines for disaster preparedness and home structure flood hazard mitigation, explores household-level ramifications, and examines how preparedness and mitigation relate to health effects, event exposures, and recovery. Between 70 and 80 per cent of participants instituted preparedness measures. Mitigation actions varied: six per cent had interior drainage systems and 83 per cent had elevated indoor heating/cooling components. Sixty per cent reported home damage. One-half highlighted allergies and two-thirds indicated some level of post-traumatic stress (PTS). Three-quarters worried about family members/friends. The results of generalised linear models revealed that greater pre- event mitigation was associated with fewer physical health problems and adverse experiences, lower PTS, and faster recovery. The study design exposed the broad benefits of home structure flood hazard mitigation for households after Harvey.