Journal of Environmental Engineering

Many control strategies can be used to address health and comfort concerns posed by high levels of indoor air contaminants. Sufficient experience exists to develop models that estimate the effectiveness and cost of radon (Rn) mitigation strategies in single-family houses. In this paper, cost curves are developed that use one or several control strategies to achieve a range of concentration reductions. The results indicate preferred “cost-optimal” strategies at various mitigation levels. Rn control strategies considered include sealing, block-wall ventilation, subslab ventilation, drain-tile ventilation, ventilation with and without heat recovery, and water treatment. For a case-study residence typical of U.S. single-family homes, cost-effective control is provided by sealing soil-gas entry routes, block-wall ventilation, and heat-recovery ventilation. Other strategies can provide similar Rn reductions, but at higher costs. The sensitivity of results to climate and energy-price assumptions is explored. Identifying strategies that are cost-effective will help to increase their use and reduce risks.

This paper examines the use of falling water as an aerator for the oxidation-ditch process. The study was carried out in order to clarify the characteristics of this process and compare it with other oxidation-ditch processes. The method uses pumps that lift wastewater and cause it to develop a head, creating a cascade or waterfall. Application of this concept may reduce construction costs for wastewater treatment plants. Furthermore, nitrogen removal is made easier through simple control of pump speed, on-off functions, and change in the height of the waterfall. Aeration efficiency is similar to that of aerators used in other oxidation-ditch processes. The power input of this oxidation-ditch-aeration process was the lowest of all the oxidation-ditch processes. This oxidation-ditch process also provides various other advantages for waste-treatment plants.

The mechanisms of the reduction of fecal coliforms were investigated in pilot-scale and full-scale wastewater stabilization ponds under tropical climatic conditions. Field studies were conducted in pilot and large waste stabilization ponds with pond depths ranging from 1.0 to 1.82 m and hydraulic retention time between 4.3 and 11.2 d, to develop and verify the model. The observation made indicates that sunlight intensity, pond depth, and pH were the key input parameters to the model. In a multifactor developed model, the bacterial mortality rate constant for pH, k_pH was 0.0135 d ⁻¹ and the ratio of rate constant for the light mortality term to light attenuation coefficient k _s /K was 5.67 × 10 ⁻⁴ m cm ² /cal. The model was successfully verified by simulation with data obtained from field-scale pond systems in Tanzania and from two other pond systems reported in the literature. A brief model application, including the prediction of water pH, is given to aid the designer.

The upflow anaerobic-sludge blanket (UASB) process consistently removed 97–99% of chemical oxygen demand (COD) from wastewater containing concentrated mixed volatile fatty acids (VFA) at 37°C at loading rates of up to 24 g-COD/(L$\dot{s}$d), corresponding to a food/microorganism ratio of 0.78 g-COD/[g–volatile suspended solids (VSS)$\dot{s}$d]. It suggested that, with preacidification, the UASB process can be effective for a wide variety of wastewaters. The COD removal efficiency deteriorated at higher loading rates; there was no butyrate in the effluent, suggesting that butyrate degradation was not a rate-limiting step. Of the COD removed, 92.6% was converted to methane; the rest was converted to granular biomass with an average yield of 0.054 g-VSS/g-COD. The granules had a size of 1–2 mm and settled satisfactorily. Each gram of granule in the reactor was capable of converting a daily maximum of 0.86 g of COD into methane. The granules had a fluffy surface mostly composed of interwound filamentous Methanothrix -like bacteria. Syntrophic associations between Methanothrix-, Methanospirillum hungatei- , and Syntrophobacter -like bacteria were prevalent in the granule interior. The syntrophic relation between these species was elucidated by thermodynamics.

A model to predict the spatial and temporal variation of domestic dry weather flow in sewer networks was developed in this paper. A probabilistic framework was used to interpret intermittent appliance usage and methods for modeling the spatial distribution of inflow, and multiple appliances were developed. The concept of expected flow was introduced to overcome the problem of converting short-term, intermittent inputs into long-term, continuous baseflow suitable as an upstream boundary condition for a Muskingum-Cunge flow model. A small-scale domestic appliance usage survey was carried out to provide the necessary input data. The model was verified on a small combined sewer network in southeast England, using 25 days of dry weather flow data. The accuracy of mean daily and peak flows fell within ±10% of the measured values, and the overall fit of the data throughout the day was found to be good. The long-term variability of flow about its mean at any instant during the day was also successfully modeled.

Several chemical washing procedures were applied to a zinc(II) contaminated (artificially) soil column to determine metal-extraction efficiency. Specific extractants examined include acid solution, ethylenediaminetetraacetic acid (EDTA) and diethylenetriamine pentaacetic acid (DTPA) organic complexing agents, and chlorine, all at various concentrations. Effects of ionic strength, flow rate, and type of zinc contamination were also determined. These parameters affect metal removal via various physicochemical mechanisms. The most efficient washing occurred using the organic chelating agents at the lowest flow rate (essentially complete zinc removal), although nearly as much zinc could be removed at higher flow rates, requiring less washing time. The washing efficiency is strongly dependent on the form of the zinc contamination in the soil.

The waste slurry generated in fertilizer plants in India has been converted into a cheap carbonaceous adsorbent material. This product is a promising scavenger of some toxic metal ions and phenols in industrial effluents. The reported investigations deal with the chemical regeneration of the spent sorbent materials. Organic as well as inorganic regenerants were experimented with for the regeneration of exhausted carbon samples. Sorbent material was exhausted with 2,4,6-trinitrophenol, 4-nitrophenol, 4-chlorophenol, and 1,3-dihydroxybenzene. The results indicate that organic chemicals with solubilizing powers are better regenerants for spent carbon particles than inorganic elutants. The adsorbent material was used up to 28 cycles and the adsorbent, after regeneration with organic regenerants, retains more than 90% of the sorption capacity of virgin carbon.

A broad weir-aeration model was derived to predict downstream dissolved oxygen (DO) over a wide range of upstream DO concentrations and fall heights. This model was then used to construct a three-dimensional (3D) surface of downstream DO for a range of upstream DO concentrations and fall heights. A 3D surface for kW$\dot{s}$hr per ton of DO absorbed was constructed for a range of upstream DO concentrations and fall heights. This shows the asymptotic rise in energy per ton of DO absorbed as higher downstream DO concentrations are realized. The energy consumption per ton of DO absorbed for weir aeration is below that for surface aeration and above that for fine bubble diffusers, for downstream DO concentrations of 0–8 mg/L.