Journal of Environmental Engineering

A continuous-flow coculture bioreactor with a phenol-degrading organism, Pseudomonas putida DMP-1, and a Cr(VI)-reducing species, Escherichia coli ATCC 33456, was developed for simultaneous removal of phenol and Cr(VI). Phenol was the sole energy and carbon source added to the coculture along with a basal medium and hexavalent chromium. The coculture bioreactor was operated under three liquid detention times (0.20, 0.31, and 0.52 days) with phenol and Cr(VI) loadings ranging from 2,500 to 8,200 mg/L/day and 4.5–33.2 mg/L/day, respectively. After 279 days of continuous operation, eight quasi-steady-state operation conditions were obtained with near complete removal of phenol and Cr(VI). Elevated levels of Cr(VI) and phenol were observed in the effluent under a high influent Cr(VI) concentration (16 mg/L) or a short liquid detention time (0.20 days). The system recovered from Cr(VI) toxicity after influent Cr(VI) level was reduced. Chromium mass balance analysis revealed that nearly all of the influent Cr(VI) was reduced to Cr(III) in the coculture bioreactor through biological activity. Spectra of UV-Vis and mass spectrometers suggested that phenol metabolites produced by P. putida were utilized by E. coli.

This paper embodies details on the extraction behavior of Cr(III) along with Al(III), Fe(III), Mg(II), Mn(II), Co(II), Ni(II), and Cu(II) from hydrochloric acid media employing the Cyanex 301-toluene system. All of these metals, except Cr(III), Mg(II), and Mn(II), are extracted into the organic phase. This property of the extractant has been used to separate Cr(III) from the binary mixtures. The partition data have been extended onto spent chrome liquor, and this waste has been treated in such a manner so that it becomes suitable for use in trivalent plating baths. The hydrolytic stability and recycling capacity has been reported. Because the concentration of Cr(III) in the waste is much lower than that required for chromium depositions in Cr(III) plating baths, a concentration step using MgO as a precipitating agent has been appended. To summarize, this paper envisages a new approach to tannery waste management that focuses on treating spent chrome liquors using a solvent extraction technique in such a manner that the waste becomes suitable for use in trivalent plating baths. This would not only help abate pollution but also recover the metal in a pure form.

This paper discusses the results of research into the pollutants in runoff from road pavement surfaces following natural rainfall events. Road runoff water quality was monitored at 21 sites centering around Brisbane, in southeast Queensland, Australia. The sites were selected according to traffic volumes, surrounding land use, pavement surface type, ease of access, and commercial vehicle percentage. Bridge sites were chosen for convenience of sample collection and minimized infrastructure modification. “First flush” grab samplers were permanently installed at each site to collect the first 20 L of runoff from one of the bridge drainage scuppers. The runoff samples were tested for a number of heavy metals, hydrocarbons, pesticides, and other physical characteristics. The observed results fall within the ranges of concentrations reported internationally and nationally but do not typically follow the “30,000 average annual daily traffic” results reported in the United States. Traffic volumes have not been found to be the best indicator of road runoff pollutant concentrations. Interevent duration has been found to be a statistically significant factor for pollutant concentrations. Sites incorporating exit lanes have recorded higher concentrations of acid-extractable copper and zinc, tending to support the hypothesis that brake pad and tire wear caused by rapid deceleration contributes to the concentrations of these metals in road runoff. Laser particle sizing has shown that a significant proportion of the sediment found in the runoff is <100 μm. However, these particulates do settle in water within 24 h, under laboratory conditions. This may be due to the presence of heavy metals.

Two wet detention ponds were investigated for their ability to remove pollutants, primarily phosphorus, from storm water runoff. The two ponds lie within the Phantom Lake watershed, a subbasin of the Lake Sammamish watershed in Bellevue, Wash., which is developed as a commercial and residential area with impervious surface area as high as 57%. There are design differences between the two ponds, yet both are comparable to design recommendations set forth by local agencies. One pond was built for flow attenuation and water quality treatment; the other serves only to improve water quality. Fifteen storms and two baseflows were successfully sampled during the Northwest's wet season from October 1996 through March 1997. Pollutant removals varied between one-fifth and one-half for phosphorus, and greater than one-half for total suspended solids and most of the analyzed metals. Removal efficiencies were consistently better in the pond designed primarily for water quality.

A computer model for epilithic algae and grazer biomass in streams is modified to better predict the effects of temperature and is calibrated for diatoms and mayflies. Mayflies are predicted to maintain low diatom biomass provided that (1) temperatures remain within their preferred range (10–20°C); and (2) mayfly populations are not adversely affected by floods. Algal blooms are predicted to occur in mayfly-dominated streams above 20°C—temperatures common in pasture streams over summer. We hypothesize that mobile bed streams are susceptible to blooms during summer low flows following floods because (1) they usually lack temperature tolerant snail grazers; and (2) mayfly recovery lags behind algal regrowth, and there is a short period when algae escape from “top-down” grazer control.

Copper and copper alloys have proven to be highly effective in preventing zebra mussel biofouling. The present laboratory measurements reveal that the rate of copper release (mg/m²/day) from surfaces in flowing lake water is inversely proportional to the number of zebra mussels adhering to similar surfaces in Lake Erie. Data are shown for copper, copper-nickel alloys (90:10, 80:20, and 70:30), a copper-epoxy coating, and galvanic couples of copper connected to zinc or aluminum.

The reaction of hydrogen peroxide (H₂O₂) and Fe(II) (Fenton's reaction) generates hydroxyl radicals (⋅OH) that can be used to oxidize contaminants in soils and aquifers. In such environments, several factors can limit the effectiveness of chemical oxidation, including reactions involving H₂O₂ that do not yield ⋅OH, ⋅OH reactions with nontargeted chemicals, and insufficient iron in the soil or aquifer. Consequently, site-specific studies may be necessary to evaluate the feasibility of chemical oxidation using H₂O₂. Here, the degradation of a contaminant analog, α-(4-pyridyl-1-oxide) N-tert-butylnitrone (4POBN), was used to estimate ⋅OH concentration and simplify testing procedures. A kinetic model was developed, calibrated using 4POBN degradation kinetics, and used to predict the disappearance of 2-chlorophenol (2CP), a representative target. Good agreement between predicted (Y) and measured (X) values for 2CP (Y = 0.95X) suggests that the kinetics of analog degradation can be used to predict the degradation rate of compounds for which the rate constant for reaction with ⋅OH is known.

The objective of this work is to provide a preliminary screening of the effectiveness of alternative sorbents for treating ground water contaminated with methyl tert-butyl ether (MTBE). Sorbents studied include synthetic carbonaceous resins, porous graphitic carbon, C18 silicas, and acrylic resins. Activated carbon was also tested for comparison purposes. Bottle point isotherms show that porous graphitic carbon and two synthetic carbonaceous resins have a greater capacity for MTBE than activated carbon. However, the required addition of a wetting agent to suspend and activate the porous graphitic carbon makes this sorbent unsuitable for drinking water purposes. The synthetic carbonaceous resins tested were found to have capacities three to five times greater than activated carbon at an MTBE concentration of 1 mg/L. The application of the Dubinin-Astakov isotherm to data for the synthetic carbonaceous resins suggests that the mechanism of adsorption is micropore filling. Additional bisolute experiments with m-xylene as a representative gasoline contaminant indicate that the m-xylene is preferentially sorbed, depleting the micropore volume available for MTBE sorption. The extent of this competitive adsorption was directly predicted from measured concentrations of the monoaromatic hydrocarbon.

Controlled precipitation of struvite from postdigestion, sludge lagoon supernatant was studied using a pilot scale fluidized bed reactor (FBR). The process effectively and rapidly removed struvite constituents from the supernatant and produced effluent significantly undersaturated for struvite. Recently published information on struvite thermodynamic and kinetic properties was incorporated into the FBR system design and selection of components. Struvite crystals were selected as seed media, which enabled precipitation of nearly pure crystals and allowed nucleation, with its associated lag time, to be bypassed. Mixing energy in the FBR was demonstrated to be sufficient to overcome transport limitations to struvite growth, allowing growth kinetics to be governed by the surface integration rate of constituent ions into the growing crystal lattice structure. Struvite removal was optimized by incorporating pH elevation into the FBR system. Process fluid was circulated in the pH adjustment tank/FBR system, which was configured as a continuous feed stirred-tank reactor. Struvite removal efficiency exceeded 80% in continuous feed experiments where the hydraulic detention time exceeded 1 h.

In situ bioremediation (ISB) has been shown to be an effective and cost-efficient method for remediating contaminated ground water and soil. One of the major disadvantages associated with this process is the lack of available kinetic information. The viability of respirometry to determine the relevant biokinetic parameters for degradation of contaminants in groundwater has been proven; however, little work has been done using soil systems. This work investigated the applicability of using respirometer data to determine the biokinetic parameters for soil systems. The specific soil investigated was contaminated with polycyclic aromatic hydrocarbons (PAHs), which contain 16 EPA priority pollutants. The work also investigated a logarithmic growth and modified Lineweaver-Burke approach for experimentally determining the maximum specific growth rate from batch degradation data. As expected, this research concluded that determining all biokinetic parameters from respirometer data was not a viable method for soil systems. Obtaining the maximum specific growth rate from batch degradation data provided more accurate results.

Soil-vapor extraction has become the most common innovative technology for treating subsurface soils contaminated with volatile and semivolatile organic compounds. This popularity is due partly to the low cost of vapor extraction and partly to the fact that mitigation is completed in situ. Previous applications of this technology have generally considered flow to either vertical or horizontal wells. However, vapor flow to a trench offers the advantages of a more uniform velocity field and lower construction costs at sites with shallow water tables. Therefore, an analytical solution is obtained for steady flow to a trench. The trench is assumed to partially penetrate an anisotropic aquifer and to have a finite horizontal length. The bottom aquifer boundary is assumed to be an impermeable water table, and the top boundary is a semipermeable aquitard. A comparison is made with field measurements to illustrate the application of the solution and to give confidence in its use.

Mechanical aerators, used in many industrial plants for wastewater treatment, are the largest energy consumers in biological reactors. A number of aerators of equal or different power may be used with aeration control achieved by selecting appropriate working aerator combinations, and by changing aerators' submergence, provided by a control weir lift at the exit of reactors. Effective control may be implemented by selecting an adequate combination of working aerators and control weir lift for achieving the necessary oxygen demand. In this paper an approximate method is proposed for determining the characteristics of aerators used for controlling the necessary oxygen supply. The method is based on an experimental determination of power characteristics of aerators under field conditions at different water levels in reactors, and on the use of known oxygen transfer rate under normal conditions and characteristics of weirs for water level control. Application of the proposed method has made it possible to obtain a mathematical model, which is used for the control of aeration in two biological reactors of Netanya Wastewater Treatment Works (Netanya, Israel).