Matt C. Smith

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.

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.

A quantitative approach for measuring N and P concentration changes in surface runoff from a restored riparian forest wetland

A recently restored riparian wetland is being evaluated as a bioremediation site for nutrients moving downslope from an animal waste application site. In question is the short-term effectiveness of the restored wetland in enhancing the quality of the water leaving the site. Networks of shallow ground-water wells and surface runoff collectors are being used to monitor nutrients concentrations and nutrient assimilation as surface and grounds water moves through the wetland. A 450-mm H-flume at the wetland outlet measures the quantity and quality of surface-water discharged from the wetland. Runoff is sampled at two locations entering the wetland and at two locations near the stream flow. At each location, the runoff is collected in a gutter, passed through a flume, and redistributed through a slotted gutter. Composite samples from each runoff event are collected with a low-cost automated sampler and analyzed for NO3-N, NH4-N, TKN, PO4-P, Total P, and Cl. Recorded hydrographs are used to determine total runoff volume and peak runoff rates of each runoff event. The runoff collectors have operated reliably and seem to be quantifying both hydrologic characteristics of runoff events and nutrient concentration changes in surface runoff as it migrate through the wetland. The simple design, low cost, and dependability of the runoff collection and automated sampling system make it suitable for a variety of research and industrial applications.

Water quality in catfish ponds subjected to high stocking density selective harvesting production practice

Abstract Nine 0·1-ha earthen ponds were stocked with 12500, 25000, and 37500 channel catfish ( Ictalurus punctatus ) fingerlings/ha in three replicates. Ponds were fed daily with a commercial feed at a rate up to 3% of the fish weight determined by sampling. They were periodically harvested to remove marketable fish weighing more than 0·25 kg. The harvested fish were replaced by fingerlings. Water quality of all ponds was monitored weekly by analyzing chemical parameters including nitrite-N, nitrate-N, total ammonia-N (TAN), total Kjeldahl nitrogen (TKN), total phosphorus, chloride, chemical oxygen demand (COD), and total and dissolved solids. Concentrations of nitrite-N, nitrate-N, TAN, and total phosphorus were not significantly different among stocking densities at any given time but were significantly different over time. The values of TKN and COD were significantly affected by treatments as well as time. The amounts of total solids were significantly higher for the highest stocking density treatment but the dissolved solids concentrations did not change significantly with stocking density or time. Ranges for chemical parameters were 7·0 to 8·4 for pH, 0·4 to 2·7 mg/litre for NH 3 N, 1·3 to 28·5 μg/litre for NO 2 N, 10·6 to 771·9 μg/litre for NO 3 N, 2·2 to 85·5 mg/litre for TKN, 28·2 to 150·0 mg/litre for COD, and 0·05 to 0·6 mg/litre for total phosphorus. The amount of total solids ranged from 105 to 262 mg/litre. The feed-to-weight-gain ratios were 1·66, 1·64, and 1·82 for high, medium, and low density treatments respectively.

Sediment Oxygen Demand of Coastal Plain Blackwater Streams

Sediment Oxygen Demand (SOD) has become and integral part of modeling dissolved oxygen within surface water bodies. Because very few data on SOD are available, it is common for modelers today to take SOD values from the literature for use with dissolved oxygen (DO) models. SOD is such an important parameter in modeling DO that this approach may lead to erroneous results. This paper reports on an extensive study to quantify SOD in blackwater streams of the Georgia coastal plain. In-situ SOD measurements are made in the Upper Suwannee, Alapaha, Little River, and Withlacoochee river basins. The subwatersheds within which SOD measurements are taken are chosen to vary from 3000-7000 ha in area and are classified as predominantly forested or predominantly agricultural. SOD is measured using four in-situ chambers. In addition to SOD measurements, a particle size analysis is completed on the sediment and water flow is measured at each site. The result of this paper connects SOD values to specific sediment composition and land use properties. By recording percent sand, silt, clay, organics, and flow, SOD values recorded in one region may be applied to similar conditions in another region. Results from this study will be used by the Georgia Department of Natural Resources – Environmental Protection Division as input data to their Georgia DO Sag model which is used to develop DO TMDLs or evaluate already developed DO TMDLs in the Georgia coastal plain.

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.