David K. Gattie

Stability and quality of municipal solid waste compost from a landfill aerobic bioreduction process

Solid waste compost product from an aerobic bioreduction process at a full-scale landfill was characterized. The landfill was sampled after 5 months of aerobic bioreduction for spatial variations in biological stability. The product after 14 months of bioreduction was excavated and screened in three different ways to improve product quality. After 5 months of bioreduction, the stability index (SI) of solid waste in the landfill ranged from low activity (0.15–0.67 mg g−1 h−1) in the 6.1–7.6-m depth layer to high activity (1.42–2.14 mg g−1 h−1) at the 4.6–6.1-m depth layer. After 14 months of bioreduction, the 9.5-mm trommel screen provided a superior product among those tested and resulted in total inert content of 3.5% compared to 9.0% (dry basis) when using a 19.1-mm screen. Product SI ranged from 0.39 to 0.55 mg g−1 h−1, indicating stability. Regulated heavy metals were below EPA exceptional quality compost levels. Lead, nickel, chromium and zinc were at relatively higher levels than other metals.

Interactions of pathogens and irritant chemicals in land-applied sewage sludges (biosolids)

BackgroundFertilisation of land with processed sewage sludges, which often contain low levels of pathogens, endotoxins, and trace amounts of industrial and household chemicals, has become common practice in Western Europe, the US, and Canada. Local governments, however, are increasingly restricting or banning the practice in response to residents reporting adverse health effects. These self-reported illnesses have not been studied and methods for assessing exposures of residential communities to contaminants from processed sewage sludges need to be developed.MethodsTo describe and document adverse effects reported by residents, 48 individuals at ten sites in the US and Canada were questioned about their environmental exposures and symptoms. Information was obtained on five additional cases where an outbreak of staphylococcal infections occurred near a land application site in Robesonia, PA. Medical records were reviewed in cases involving hospitalisation or other medical treatment. Since most complaints were associated with airborne contaminants, an air dispersion model was used as a means for potentially ruling out exposure to sludge as the cause of adverse effects.ResultsAffected residents lived within approximately 1 km of land application sites and generally complained of irritation (e.g., skin rashes and burning of the eyes, throat, and lungs) after exposure to winds blowing from treated fields. A prevalence of Staphylococcus aureus infections of the skin and respiratory tract was found. Approximately 1 in 4 of 54 individuals were infected, including 2 mortalities (septicaemia, pneumonia). This result was consistent with the prevalence of S. aureus infections accompanying diaper rashes in which the organism, which is commonly found in the lower human colon, tends to invade irritated or inflamed tissue.ConclusionsWhen assessing public health risks from applying sewage sludges in residential areas, potential interactions of chemical contaminants with low levels of pathogens should be considered. An increased risk of infection may occur when allergic and non-allergic reactions to endotoxins and other chemical components irritate skin and mucus membranes and thereby compromise normal barriers to infection.

Characterization of microbial populations in landfill leachate and bulk samples during aerobic bioreduction

Abstract Aerobic microbial populations in landfill leachate and bulk material were characterized during an engineered aerobic bioreduction process in a test cell of a municipal landfill in Atlanta, Georgia, USA. Assessment of the microbial ecology (bacterial numbers, species, and substrate utilization patterns) of this engineered system was undertaken to determine its biological status during the progression of the remediation process. Counts of aerobes in leachate increased by two orders of magnitude during the first 5 months of air injection. Bacterial counts in solid samples collected from various depths in the cell varied more than three orders of magnitude during the fifth month of treatment, exceeding counts in leachate by as much as three log units. In the ninth month of treatment, bacterial counts in bulk material were non-detectable in some cases, suggesting stability of the degraded waste material. Although bacterial species in leachate and bulk samples varied with sample collection date, eight species were identified in samples from multiple sampling dates. Only two Gram positive and six Gram negative species were isolated from both leachate and bulk material, and none of the yeast (Candida sp. or Cryptococcus sp.) isolated from solid samples was found in leachate. Analysis of the substrate utilization patterns of individual bacteria isolated from leachate collected on sequential sampling dates indicated a decrease in the percentage of Gram negative bacteria able to metabolize selected sugars with a concomitant increase in the percentage of Gram positive bacteria able to metabolize them. The amino acids tested were not readily utilized by Gram positive or Gram negative bacteria from either sample type. The observed decrease in percentage of bacteria able to metabolize specific substrates may have resulted from a decrease in substrate availability as waste stabilization, which was the goal of the project, began.

Human domination of the biosphere: Rapid discharge of the earth-space battery foretells the future of humankind

Earth is a chemical battery where, over evolutionary time with a trickle-charge of photosynthesis using solar energy, billions of tons of living biomass were stored in forests and other ecosystems and in vast reserves of fossil fuels. In just the last few hundred years, humans extracted exploitable energy from these living and fossilized biomass fuels to build the modern industrial-technological-informational economy, to grow our population to more than 7 billion, and to transform the biogeochemical cycles and biodiversity of the earth. This rapid discharge of the earth’s store of organic energy fuels the human domination of the biosphere, including conversion of natural habitats to agricultural fields and the resulting loss of native species, emission of carbon dioxide and the resulting climate and sea level change, and use of supplemental nuclear, hydro, wind, and solar energy sources. The laws of thermodynamics governing the trickle-charge and rapid discharge of the earth’s battery are universal and absolute; the earth is only temporarily poised a quantifiable distance from the thermodynamic equilibrium of outer space. Although this distance from equilibrium is comprised of all energy types, most critical for humans is the store of living biomass. With the rapid depletion of this chemical energy, the earth is shifting back toward the inhospitable equilibrium of outer space with fundamental ramifications for the biosphere and humanity. Because there is no substitute or replacement energy for living biomass, the remaining distance from equilibrium that will be required to support human life is unknown.

Engineering Education as a Complex System.

This paper presents a theoretical basis for cultivating engineering education as a complex system that will prepare students to think critically and make decisions with regard to poorly understood, ill-structured issues. Integral to this theoretical basis is a solution space construct developed and presented as a benchmark for evaluating problem-solving orientations that emerge within students’ thinking as they progress through an engineering curriculum. It is proposed that the traditional engineering education model, while analytically rigorous, is characterised by properties that, although necessary, are insufficient for preparing students to address complex issues of the twenty-first century. A Synthesis and Design Studio model for engineering education is proposed, which maintains the necessary rigor of analysis within a uniquely complex yet sufficiently structured learning environment.

A High-Level Disinfection Standard for Land-Applied Sewage Sludges (Biosolids)

Complaints associated with land-applied sewage sludges primarily involve irritation of the skin, mucous membranes, and the respiratory tract accompanied by opportunistic infections. Volatile emissions and organic dusts appear to be the main source of irritation. Occasionally, chronic gastrointestinal problems are reported by affected residents who have private wells. To prevent acute health effects, we recommend that the current system of classifying sludges based on indicator pathogen levels (Class A and Class B) be replaced with a single high-level disinfection standard and that methods used to treat sludges be improved to reduce levels of irritant chemicals, especially endotoxins. A national opinion survey of individuals impacted by or concerned about the safety of land-application practices indicated that most did not consider the practice inherently unsafe but that they lacked confidence in research supported by federal and state agencies

Interactions of pathogens and irritant chemicals in land-applied sewage sludges (biosolids).

Fertilization of land with processed sewage sludges, which often contain low levels of pathogens, endotoxins, and trace amounts of industrial and household chemicals, has become common practice in Western Europe, the United States, and Canada. Local governments, however, are increasingly restricting or banning the practice in response to residents reporting adverse health effects. These self-reported illnesses have not been studied and methods for assessing exposures of residential communities to contaminants from processed sewage sludges need to be developed. Methods: To describe and document adverse effects reported by residents, 48 individuals at ten sites in the United States and Canada were questioned about their environmental exposures and symptoms. Information was obtained on five additional cases where an outbreak of staphylococcal infections occurred near a land application site in Robesonia, Pennsylvania. Medical records were reviewed in cases involving hospitalization or other medical treatment. Since most complaints were associated with airborne contaminants, an air dispersion model was used as a means for potentially ruling out exposure to sludge as the cause of adverse effects. Results: Affected residents lived within approximately 1 km of land-application sites and generally complained of irritation (e.g., skin rashes and burning of the eyes, throat, and lungs) after exposure to winds blowing from treated fields. A prevalence of Staphylococcus aureus infections of the skin and respiratory tract was found. Approximately one in four of 54 individuals were infected, including two mortalities (septicemia, pneumonia). This result was consistent with the prevalence of S. aureus infections accompanying diaper rashes in which the organism, which is occasionally found in the lower human colon, tends to invade irritated or inflamed tissue. Conclusions: When assessing public health risks from applying sewage sludges in residential areas, potential interactions of chemical contaminants with low levels of pathogens should be considered. An increased risk of infection may occur when allergic and non-allergic reactions to endotoxins and other chemical components irritate skin and mucous membranes and thereby compromise normal barriers to infection.

A network model of distributed and centralized systems of students

The body of knowledge in active and cooperative learning lacks an analytical model to determine the emergent patterns of distributed (active, student centered) and centralized (traditional, teacher centered) networks of students. To address the complexity of learning systems a network modeling approach based on Social Network Analysis and Ecological Network Analysis is proposed as an appropriate scientific construct for developing analytical techniques for studying and understanding learning systems. Models were developed, designed, and interpreted for two configurations, one with four actors and another with 16 actors. A preliminary analysis was performed on a 12 actor model to determine the optimal cluster size to maximize indirect effects within the system. In the future, network models can be utilized to further understand learning systems through network properties that are not directly observable. It is the aim of the authors to provide an additional lens to view, assess, and optimize student learning.

Watershed Assessment within a Georgia Coastal Plain Municipality

Heightened concern regarding the impact of land-use changes on ecological systems has prompted state and federal regulatory agencies to require water quality monitoring and modeling as well as biological assessments at a watershed scale prior to issuance of NPDES permits for new facilities or renewal of existing permits. The watershed assessment process integrates physical traits, biological diversity, and water quality of streams with watershed and water quality models. Biological assessment results and recommendations are a product of the EPA’s Rapid Bioassessment Protocols while modeling techniques, results and suggestions are a product of a variety of pollutant (SWMM, SWAT) and water quality (WASP, QUAL2E) models. The focal points of a watershed assessment are to give municipalities feasible options for watershed protection, viable alternatives for long-term development, planning and effective education for citizens on the preservation of their watersheds.