Journal of Environmental Engineering

A long‐time‐scale, large‐space‐scale model of fate and bioaccumulation of PCB homologues in striped bass is constructed for the Hudson River estuary Of the total of 270 Mg (595,000 lb) of PCB discharged to the estuary proper from approximately 1947 through 1987, an estimated 66% volatilized, 6% went to sediment storage, and the remainder was lost by dredging and boundary transport. The striped‐bass model indicated that more than 90% of the fish PCB concentration is due to food‐chain effects. The upstream load from above Troy, New York, is estimated to be contributing about 20% to the current striped‐bass PCB concentrations.

A no‐action alternative indicates that 50% of the 3–6 year average striped bass in the mid‐ to lower Hudson would be below an action level of 2 μg/g (wet) by about 1992 and 95% by 2004. A simulation of removing all upstream PCB load does not change the time to reach the 95th percentile because of the increasingly small effect of upstream loading.

A methodology to assess the impact of a hydropower facility on downstream water quality is described. Negative impacts can result from the substitution of discharges aerated over a spillway with minimally aerated turbine discharges that are often withdrawn from lower reservoir levels, where dissolved oxygen (DO) is typically low. Three case studies illustrate the proposed method and problems that can be encountered. Historic data are used to establish the probability of low‐dissolved‐oxygen occurrences. Synoptic surveys, combined with downstream monitoring, give an overall picture of the water‐quality dynamics in the river and the reservoir. Spillway aeration is determined through measurements and adjusted for temperature. Theoretical computations of selective withdrawal are sensitive to boundary conditions, such as the location of the outlet relative to the reservoir bottom, but withdrawal from the different layers is estimated from measured upstream and downstream temperatures and dissolved‐oxygen profiles. Based on field measurements, the downstream water quality under hydropower operation is predicted. Improving selective withdrawal characteristics or diverting part of the flow over the spillway provided cost‐effective mitigation solutions for small hydropower facilities (less than 15 MW) because of the low capital investment required.

A dichloromethane‐degrading bacteria population is selected from sewage sludge. The microorganisms are employed in a fluidized‐bed reactor for regeneration of dichloromethane‐containing activated carbon. Bubble‐free oxygenation of the reactor was executed by means of polydimethylsiloxane tubes. Three run modes of the reactor were investigated: (1) Aeration of dichloromethane‐containing activated carbon without biomass; (2) treatment of the carbon with biomass and oxygenation by low gas flows of pure oxygen; and (3) biodegradation of the adsorbed dichloromethane under conditions of “dead‐end” oxygenation, i.e., oxygenation via closed polydimethylsiloxane tubes and addition of pressure impulses of pure oxygen when the oxygen concentration in the reactor fell below 2 mg/L. The third mode was the most advantageous because no exhaust gas was produced and the dichloromethane was degraded totally to HCl and carbon dioxide. The bioregenerated activated carbon exhibited the same adsorption capacity as fresh, untreated activated carbon.

Forward‐angle light‐scatter (FALS) particle counting is investigated as a means to quantify and improve filtered‐water quality in drinking‐water treatment. In the laboratory, FALS particle counts are found to be precise and reproducible by multiple analysts when proper sample handling procedures are followed. In FALS counts of water samples with added Giardia cysts, FALS categorizes Giardia cysts as equivalent to spheres of 1–5 μm in diameter, demonstrating the importance of using a particle counter to size particles of interest prior to selecting size ranges for routine monitoring. In full‐scale water‐treatment plant trials, FALS particle counts are used to show that particles in filtered water are substantially reduced when filter operation is changed from intermittent, fixed rate, 60‐hour filter runs to continuously operated, variable rate, with 48 hours between backwashes. Filtered‐water quality is also higher in stage 2 of the Bearspaw Water Treatment Plant than in stage 1 under all operating conditions. Turbidity measurements follow trends in particle counts in most cases. Further improvements in filtered‐water quality can likely be made by using FALS particle counting to optimize backwashing procedures and filter‐ripening strategies.

For highly urbanized cities where there is a scarcity of available land for landfilling, incineration may be a better method of solid‐waste disposal. After incineration about 20% by weight of ash and other residues are produced. Both the washed clinker and fly ash collected from the refuse‐incineration plant have the prerequisite properties for use in geotechnical applications. The washed clinker is essentially a granular material of irregular shape. Fly ash is predominantly silt‐sized, spherical particles. The specific gravities of the washed clinker and fly ash are 2.67 and 2.45 respectively. Both materials exhibit high strength and are relatively free‐draining, typical of granular materials. The fly ash could be used as an admixture in the stabilization of soft soil. The clay samples treated with fly ash show substantially improved shear strengths and lower compressive properties.

The disposal of sludge from wastewater treatment process presents increasingly difficult problems to highly urbanized cities. Incineration might be a feasible alternative solution for sludge disposal, providing a means of producing a reduced volume of sterile, odorless, inorganic ash. The feasibility of using de‐watered sludge mixed with lime to produce a cementlike material after incineration is studied, and the properties of cement made from sludge are investigated. Evaluation of compressive strengths of the mortar cubes indicates that it is possible to produce cement from sludge that will satisfy the strength requirements in the ASTM standard for masonry cement.

Both granular activated carbon (GAC) and packed tower aeration (PTA) are designated as best‐available treatment technology in the volatile‐organic‐chemicals (VOC) regulations. The constant‐pattern‐homogeneous‐surface‐diffusion model (CPHSDM) is used to predict liquid‐phase GAC use rates for selected single‐solute VOCs. Preliminary cost estimates for liquid‐phase GAC treatment systems are developed for a range of plant sizes, empty bed contact times (EBCTs), and carbon bed lives. A cost and performance model is developed to examine various scenarios for controlling VOCs by packed tower aeration, including off‐gas treatment. A comparison is made between liquid‐phase GAC and PTA treatment alternatives. This analysis exposes the sensitivity of GAC and PTA costs to variations in design and operating parameters.

This technical note estimates the possible effects on calculated critical dissolved oxygen deficits of using reaeration equations as compared to measured reaeration rates. Differences between observed and calculated reaeration coefficients can produce changes of about 30 percent in the calculated critical dissolved oxygen deficits. The uncertainty in dissolved oxygen concentrations, due to the use of reaeration equations rather than measured reaeration coefficients, are probably on the order of tenths to one part per million. This technical note deals with the effects of using equations rather than indications of the adequacy of the equations to represent reaeration coefficients.