Journal of Environmental Engineering

The aim of this study was to develop a simple biological system suitable for the treatment of dairy parlor wash waters. A novel horizontal-flow biofilm system with step feed was designed, constructed, and tested in the laboratory for organic carbon removal, nitrification, and denitrification of a synthetic dairy wastewater with average filtered chemical oxygen demand $\left({\mathrm{COD}}_f\right)$ of $\mathrm{2,060}\mathrm{mg}∕\mathrm{L}$ , total nitrogen (TN) of $288\mathrm{mg}∕\mathrm{L}$ , and ammonia nitrogen $\left({\mathrm{NH}}_4\text{–}\mathrm{N}\right)$ of $127\mathrm{mg}∕\mathrm{L}$ . The novel biofilm system consisted of two reactor units placed on top of one another, each comprising a stack of horizontal plastic sheets. Part of the wastewater was pumped onto Sheet 1 (top feed) and the remainder onto Sheet 11 (step feed) and flowed over the horizontal sheets down through the system. Three hydraulic loading rates were examined: 32.3, 25.1, and $19.3\mathrm{L}∕{\mathrm{m}}^2\mathrm{day}$ , based on the top plan area, and the respective removals of ${\mathrm{COD}}_f$ were 96, 96, and 97% and of TN, 86, 83, and 75% were achieved. The system was simple and cheap to construct and operate.

Collection conduits flowing full with nonuniform inflow (variable rate of increase in flow with distance along the conduit length) include well screens (vertical and directionally drilled); submerged effluent collectors; and certain types of inboard weir configurations for settling tanks. Certain subsurface drains used in environmental engineering applications and civil engineering more generally may be inadvertently designed for full-flowing conditions. Formulation of the problem for such collection conduits is presented in terms of the applicable differential equation, slope invariance, the frictionless solution for a general cross section, a uniform-inflow solution, and the difference formulation. The importance of checking inflow uniformity is discussed and exemplified. Dimensional analysis is then employed to demonstrate the relationship between variables, leading to a new generalized numerical solution. That solution is presented in a graphical form which provides further useful display of the relationships between variables and quantitative information for design and analysis. The detrimental effects of flowing-full conditions in subsurface drains is demonstrated, and it is noted that existing design methods may unintentionally cause such conditions to occur.

This paper analyzes cost data pertinent to the municipal wastewater treatment plants (MWTP) in Greece. First, data have been collected with onsite visits and contain the land size necessary for a MWTP, the construction cost, and the operation and maintenance cost of existing wastewater treatment facilities. Second, they come from analytical budgeting of natural wastewater treatment system units. Twelve equations of the form $\ln Y_i=A_{0i}+A_{1i}\ln X_i$ are estimated both with ordinary least squares (OLS) and fuzzy linear regression (FLR). The root mean square error and the mean absolute error are used as fitting measures for the comparison of the OLS with the fuzzy estimations. It is shown that the FLR did produce very similar estimates but slightly inferior to those of OLS in most of the cases for these particular datasets.

The impact of the assumption of linear sorption on retardation of nonlinearly sorbed solutes in porous media is numerically explored in this paper. Breakthrough data of nonlinearly sorbed solutes are generated using the BIO1D simulation code along with the Freundlich-type nonlinear sorption model. Retardation coefficients $\left(R\right)$ from generated breakthrough curves are estimated using first-moment analysis. Variations of $R$ with experimental conditions revealed that $R$ of a nonlinearly sorbed solute is a function of the input concentration, the injection period, and the pore–water velocity but is independent of the length scale. This study also showed that it is appropriate to estimate $R$ of a nonlinearly sorbed solute using a linearized isotherm if all soil particles experience sorption with liquid concentration equal to the induced concentration. Otherwise, the estimated linearized $R$ will be either under- or overestimated depending on the applied experimental conditions and Freundlich parameters. The study further revealed that inability to account for sorption nonlinearity may in some cases erroneously be interpreted as evidence of the presence of transport nonequilibrium. A method is suggested to determine nonlinear sorption parameters from miscible displacement experiments.

This study investigates the adverse effects of synthesized arsenic–iron hydroxide sludge, the by-product of arsenic removal by coagulation with ferric chloride, on unconfined compressive strength (UCS) and cement hydration of solidified/stabilized matrices. The results from both UCS tests and X-ray diffraction (XRD) implied that synthesized arsenic–iron hydroxide sludge might not be chemically inert in a cementitious environment, which could account for the retardation of cement hydration. The culprit for this retardation is likely to be the multiphase formation of calcium arsenic compounds suggested by the strong peak at $7.90\mathrm{\AA }$ $(11.2°2\theta )$ . This peak appeared when more than 20 and 13% of arsenic–iron hydroxide sludge were added to the solidification/stabilization $(S∕S)$ process of cement–water and cement-hydrated lime–water systems, respectively. The proposed mechanisms for the retardation of cement hydration by calcium–arsenic compounds are calcium complexation and, subsequently, surface precipitation due to the interaction between desorbed arsenate and hydration by-products in a cement porewater environment. The extent of the hydration retardation is qualitatively determined by the semiquantitative comparison of ${\mathrm{Ca}}_3\mathrm{Si}{\mathrm{O}}_5$ and ${\mathrm{Ca}}_2\mathrm{Si}{\mathrm{O}}_4$ remaining after $28\text{days}$ of hydration between the control $S∕S$ samples and that with various doses of the sludge added. When 20 and 33% of the sludge were added into the $S∕S$ matrices, the remaining ${\mathrm{Ca}}_3\mathrm{Si}{\mathrm{O}}_5$ and ${\mathrm{Ca}}_2\mathrm{Si}{\mathrm{O}}_4$ were more than that of the control sample by factors of 2 and 3.2, respectively.

Cadmium ion-selective microelectrodes and carbon fiber mercury film microelectrodes were fabricated and compared in this research. In order to determine whether either microelectrode could be used in biofilm microenvironmental profile studies, their performances were evaluated under different pH, buffer concentration, and ionic strength conditions. Both microelectrodes showed good linearity during calibration. pH did not have a significant impact on the ion-selective microelectrode, but significantly changed the performance of the carbon fiber mercury film microelectrode. Tris buffer was evaluated for pH control and found to increase readings of both microelectrodes. Ionic strength had a similar impact on both microelectrodes. Both microelectrodes had high selectivity for ${\mathrm{Cd}}^{2+}$ , but potential interferences should be considered when real samples are to be measured.

Water quality of highway stormwater runoff from an ultra-urban area was characterized by determining the event mean concentration (EMC) for several pollutants and by evaluating pollutant flushing. Thirty-two storm events were monitored between June 2002 and October 2003. Mean EMCs in mg/L were 0.035, 0.11, 0.22, 1.18, 420, 3.4, 0.14, 1.0, and 0.56 for Cd, Cu, Pb, Zn, total suspended solids (TSS), total Kjeldahl nitrogen (TKN), $\mathrm{N}{\mathrm{O}}_2–\mathrm{N}$ , $\mathrm{N}{\mathrm{O}}_3–\mathrm{N}$ , and TP. First flush as defined by flushing of 50% of the total pollutant mass load in the first 25% of the event runoff volume occurred in 33% of the storm events for $\mathrm{N}{\mathrm{O}}_2^{-}$ , 27% for TP, 22% for $\mathrm{N}{\mathrm{O}}_3^{-}$ and TKN, 21% for Cu, 17% for TSS, 14% for Zn, and 13% for Pb. Median values for the mass flushed in the first 25% of runoff volume were greater than the mass flushed in any 25% portion beyond the first for all pollutants. The mass in later 25% volume portions were greater than in the first 25% volume in at least 17% of the events for all pollutants, indicating that a significant amount of the pollutant load can be contained in later portions of the runoff volume. Nonetheless, management of the first $1.3\mathrm{mm}$ $(1∕2\mathrm{in.})$ of runoff was able to capture 81–86% of the total pollutant mass.

The objective of this study is to investigate the effect of the composition of anodic purging solutions on electroosmosis in an electrokinetic (EK) system. The effect of buffering capacity of anodic purging solutions on electroosmosis was first studied. With the increase of buffering capacity, soil pH and electric current increased, but the maximal cumulative electroosmostic flow (EOF) was achieved with $0.010\mathrm{mol}∕\mathrm{L}$ ${\mathrm{Na}}_2\mathrm{C}{\mathrm{O}}_3∕\mathrm{Na}\mathrm{H}\mathrm{C}{\mathrm{O}}_3$ buffer. ${\mathrm{Na}}_2\mathrm{C}{\mathrm{O}}_3∕\mathrm{Na}\mathrm{H}\mathrm{C}{\mathrm{O}}_3$ containing NaCl and ${\mathrm{Na}}_2\mathrm{S}{\mathrm{O}}_4$ , respectively, were used as anodic purging solutions to investigate the effect of cation concentration and anion type on electroosmosis. The increase of cation concentration led to the increase of soil pH and electric current but the decrease of EOF. At the same cation concentration, ${\mathrm{Na}}_2\mathrm{S}{\mathrm{O}}_4$ resulted in higher electric current and greater EOF than NaCl, but similar distribution of soil pH. The present study provides useful information for the selection of purging solution in the EK remediation of contaminated soils.

Adsorption tests of Congo Red, a commercial azo dye, by acid mine drainage (AMD) sludge were carried out at different pH, temperature, dye concentration, contact time, and adsorbent dosage. Precoat filtration was conducted to test if the dye could be removed during continuous filtration by a precoated AMD sludge layer. Adsorption of Congo Red onto AMD sludge followed the Langmuir isotherm model with a maximum adsorption capacity of $389.1\mathrm{mg}∕\mathrm{g}$ . Based on thermodynamic studies, adsorption was found to be exothermic, and an increase in temperature led to a decline in dye removal. Dye removal decreased with an increasing pH. Through metal leaching tests, it was observed that most metals associated with AMD sludge remained insoluble when adsorption occurred at pH 6–10. A rather rapid process was observed for the adsorption of Congo Red onto AMD sludge with more than 80% adsorption taking place within $5\min$ . Adsorption kinetics followed pseudo-second-order model. Precoat filtration continuously removed Congo Red from aqueous solution with success, and dye removal mechanism via precoat filtration was adsorption. The adsorption and precoat filtration studies showed dye removal could be a beneficial use of AMD sludge prior to its final disposal.

The photochemical degradation of 2,4,6-trichlorophenol (2,4,6-TCP) has been studied in the presence of a nonionic surfactant. A faster decay of 2,4,6-TCP could be achieved by the addition of surfactant depending on the pH levels. By examining the TCP decay at different solution pH and surfactant concentrations, the variations in photodecay rates were dominated by the existence of surfactant micelles. In water or when surfactant dosage was below the critical micellar concentration, the photodecay of 2,4,6-TCP was found to be faster at high pH levels, mainly due to the higher absorption of TCP and additional hydrogen source (from surfactant monomer). On the contrary, in the presence of micelles, faster decay of 2,4,6-TCP was obtained at lower pH levels. This was possibly due to the domination of both photochemical homolysis and electron transfer processes in acidic condition, but the latter was inhibited at alkaline condition. In addition, the cage effect of surfactant micelles may possibly hinder the $\mathrm{O}{\mathrm{H}}^{-}$ -catalyzed photohydrolysis in the solution, so the TCP decay in micellar solution was reduced at high pH levels.

A novel pilot-scale flow through photoreactor has been designed with the intent to apply it in the field. The photoreactor uses a new plastic coil, instead of the conventional quartz tube. The photoreactor consists of six ultraviolet (UV) lamps with five around the coil and one at the center. Laboratory investigations were conducted using the photoreactor to treat neat Aroclor 1254 in alkaline isopropanol (IPA). The photoreaction is fast and efficient, even though the UV transmittances of the three plastic tubes investigated were lower than that of quartz. The reaction kinetics of the practical mixtures are explored. An analysis of five different constituent congeners of Aroclor 1254 indicated that higher congeners dechlorinate producing some of the lower ones, which are subsequently dechlorinated. The dechlorination of Aroclor 1254 was faster when water was added to the alkaline IPA–Aroclor solution.

Effects of iron on the kinetics and stoichiometry of aerobic chemical sulfide oxidation in wastewater from two different sites were studied at pH 8 and 20°C. Iron(III) chloride was added to the wastewater in concentrations of up to $20\mathrm{g}\mathrm{Fe}{\mathrm{m}}^{-3}$ . The rate of aerobic chemical sulfide oxidation increased linearly with the iron(III) additions resulting in equal effects with wastewater from the two sites. Despite the significant effect of the iron(III) additions, the background concentrations of iron cannot explain the significant temporal and spatial variability of aerobic chemical sulfide oxidation kinetics reported in this study and in the literature. In this respect, other metals are probably also important. In addition to the impacts on the oxidation kinetics, the iron(III) additions resulted in a change of the oxidation stoichiometry. With increasing amounts of iron(III) added to the wastewater, less dissolved oxygen was required for the sulfide oxidation.

Chloride is used as conservative tracers to estimate hydrological pathways. Field data on treatment of municipal solid waste (MSW) leachate show that Cl is reduced in aerobic treatment. Here laboratory experiments simulating MSW leachate treatment are conducted to see if electrical conductivity (EC) reduction can be duplicated in the laboratory, and to find probable chemical or physical factors explaining EC and chloride reduction. The experiments include three leachate, eight artificial, and three control samples. Mean reduction of EC in the respirometers was 17% for the leachate and 25% in the artificial samples. There was close to zero reduction in the controls. Mean reduction of chloride was 45% in the artificial samples and 9% in the controls. The oxygen consumption was lower in the leachate samples during aeration, probably due to inhibitory compounds. There was no reduction in EC after chemical coagulation with Al and organic coagulants, 31% reduction in the aerobic system, and 46% in the anaerobic system. Total organic carbon significantly influenced the oxygen consumption. The reduction of chloride and EC depended on the acidity (pH) of the leachate. Centrifugation showed an effect on EC and chloride concentration. Based on these results it seems that the reduction of chloride in leachate treatment depends on the formation of organic precipitates.