Journal of Environmental Engineering

In this paper, a quantitative model of coagulation with inorganic polymer flocculants (IPFs) was investigated, using polyauminum chloride (PACl) as an example. Application of a modified precipitation charge-neutralization model (M-PCNM) was examined and discussed, including variation of dose, pH, and $B$ value on the resulting coagulation diagram. The model was modified by using measured Al fractions as model inputs. The experimental results show that there exists a remarkable difference in coagulation with various PACl formulations in accordance with the different species being preformed. This indicates that the assumption of all the surface species consisting of the same aluminum hydroxide solids is not correct, and some modification of the PCNM is therefore needed. By invoking different final hydroxide precipitates, the M-PCNM can be used quite well to predict the general behavior of coagulation with IPF-PACl.

A model of adsorption and thermal desorption was built and validated from experiments performed under various operating conditions. The abatement increased with the reduction in the inlet concentration and with the increase of bed height. Particles at the end of adsorption step were saturated although their pores were not completely filled with acetone. Adsorption yielded an increase of the bed temperature at the beginning of the tests, where the separation rate had the maximum value nearly equal to 100%, but the temperature rise of the bed remained much smaller than that obtained in fixed-bed adsorption for similar conditions. Simulations of a process operating with successive cycles of adsorption and thermal desorption was then performed. Desorption appeared to have a reasonable duration compared to adsorption. Calculations proved that a third reactor for transient states from adsorption to desorption or from desorption to adsorption that would achieve the cooling or the heating of particles was not necessary. Results show the feasibility of the adsorption–desorption process of volatile organic compounds in fluidized beds of granular activated carbon.

A procedure for the optimization of an unstructured first-order kinetics model of cyclically operated biological reactors for the biodegradation of a single pollutant is developed using a combination of analytical and numerical tools. Asymptotic analytical profiles for the substrate and biomass for each steady cycle are obtained, which allow the formulation of an analytical design equation that relates the concentration of the pollutant at the end of a steady cycle to all the operating parameters of the bioreactor such as space-time, pollutant feed concentration, filling time, and ratio of minimum to maximum reactor volume. This analytical design equation is used for the systematic construction of practical bifurcation diagrams showing the variations of the pollutant concentration at the end of a cycle with the bioreactor operating parameters. The design equation also allows the formulation of a variety of optimization problems such as the maximization of volumetric efficiency as well as the minimization of the end-of-cycle pollutant concentration. In all cases it is shown that optimal parameter value sets exist. Implications of these results for the optimization of waste-treatment facilities are discussed.

The aim of this research was to use activated carbon fibers (ACFs) to adsorb 16 polycyclic aromatic hydrocarbon (PAH) species from flue gas emissions during incineration. The operation conditions included the presence of three activated carbon fibers, the adsorption temperature (200, 300, and $340°\mathrm{C}$ ), and the weight of the ACFs. The removal efficiencies of the gaseous and solid-state PAHs were evaluated respectively. It was found that the BET surface area did not affect PAH removal when the BET surface area was enough for PAH removal and micropore volume was the determinant parameter for PAHs removal. The best adsorption temperature in this study was 300°C. The removal efficiency of PAHs was proportional to the weight of ACFs.

The dilution method has been accepted widely as the standard procedure for determining biochemical oxygen demand (BOD). A mass-balance approach was used to analyze four equations for computing BOD: two involving external seed correction methods (Standard Methods) and two involving internal correction methods (Sawyer and McCarty in 1978 and Kline and Gibbs in 1979). Five testing conditions were identified as being pertinent to the underlying assumptions: seed addition method, uniform BOD bottle volume, uniform initial dissolved oxygen (DO), seed uptake linearity, and data handling method. The results of this study showed that internal methods may provide more reproducible results, primarily due to the inherent correction for dilution water demand and better data handling (regression) technique to cope with the variation in BOD bottle volume and initial DO. However, internal methods may violate the requirements imposed by Standard Methods for minimum final DO $(1\mathrm{mg}∕\mathrm{L})$ for the high spike runs and minimum $5\text{day}$ DO depletion $(2\mathrm{mg}∕\mathrm{L})$ for the low spike runs. Recommendations are also made to improve the reliability of these methods.

Proper use or disposal of wastewater solids is an important responsibility of wastewater treatment plants. At present, there are several options for wastewater solids, including agriculture, forestry, and mine reclamation reuse; production of marketable products such as compost and dried pellets; and disposal in landfills and incinerators. Land application of biosolids products is beneficial as part of recycling efforts on local farms, forests, tree farms, and mines and has gained greater acceptance of late. Coupled with these beneficial aspects are odors, which must be managed relative to the receiving populations. In this paper we present several statistical models that predict biosolids odor levels based on processing and management variables as well as ambient conditions. Such models are useful to managers at advanced wastewater treatment plants in helping them to better forecast the biosolids odors and minimize the “odor footprint,” thus making these biosolids products better received.

Sodium carbonate softening at pH 10.3 is a viable method of removing the inorganic contaminants arsenic, barium, chromium, strontium, and vanadium from drinking water sources. A broad survey revealed that removals varied widely and were dependent on solution composition. Median removals of As, Ba, Cr, Sr, and V were 24, 100, 92, 99, and 60%, respectively. Linear and nonlinear empirical models were fit for crudely estimating the removal of these contaminants in the presence of other elements that are typically removed in the softening process (i.e., calcium, magnesium, silicon, iron, and aluminum). Boron was removed to a much lesser extent (median removal 2%) indicating soda ash softening is not a promising treatment option for this purpose.

Incinerator fly ash from municipal solid waste is considered as a hazardous waste and can release toxic metals such as Pb and Cd into the environment. This research verifies the performance of a sequential, closed circuit treatment process involving chemical leaching (alkaline washings followed by an acid washings) and precipitation (neutralization at $\mathrm{pH}=5$ and 7). This method also includes the recirculation of treated leachates during the acid washing steps. In total, ten recirculation loops were executed in laboratory pilot scale. The three alkaline leaching steps effectively solubilized the leachable Pb. Two acid leaching steps were required to solubilize Cd, Al, and Zn. Toxic metals, Cd and Pb, were removed from the fly ash at 72 and 30%, respectively. The toxicity characteristic leaching procedure (TCLP), the synthetic precipitation leaching procedure (SPLP), and a simple test using neutral water were conducted on the treated ash in order to validate the process. The results obtained were below the norm for the TCLP and near $0.01\mathrm{mg}∕\mathrm{L}$ of Cd and Pb in solution for the other two tests. The removal efficiency during the precipitation step were 21% Cd, 99% Pb, 100% Al, and 63% Zn. The metallic residue produced at $\mathrm{pH}=7$ contained 23% Zn which is potentially recyclable in the metallurgical industry. The recirculation of treated leachates reduced water consumption for the decontamination process by 60%.

Understanding that there is a significant presence of extracellular polymeric substances at the biofilm/wastewater interface and that the primary constituent of chemical oxygen demand (COD) in domestic wastewaters is organic particulates, this research describes the kinetics of particulate removal in a pilot-scale trickling filter (TF) and the role of bioflocculation in the removal process. Recent research has described the role of bioflocculation on particulate COD (PCOD) removal in suspended growth biological wastewater treatment systems. However, no research pertaining to PCOD removal by bioflocculation in attached growth systems was identified prior to this study. For this study, experiments were conducted using both bench- and pilot-scale biofilm reactors and provided evidence that the removal of organic and inorganic particulate matter in a TF bioreactor follows a first-order bioflocculation rate equation. The statistical analysis of data obtained from the pilot TF fits the dispersion model to suspended solids and PCOD remaining in the pilot TF.

Direct Red 83 $\left(10\mathrm{\mu }\mathrm{M}\right)$ was electrolytically treated with a graphite anode paired with a stainless steel cathode at $0.05\mathrm{mA}∕{\mathrm{mm}}^2$ . Electrolyte composition was varied from 0 to $0.05\mathrm{N}$ sodium chloride in increments of $0.01\mathrm{N}$ , using sodium sulfate as a makeup salt to keep the total electrolyte strength at $0.05\mathrm{N}$ . Fraction of dye remaining was plotted versus time, and first order curves were fitted to the data. Apparent first order rate constants ranged from $3.96\times {10}^{-5}$ to $1.24\times {10}^{-3}{\mathrm{s}}^{-1}$ . Both direct oxidation by applied current and indirect oxidation by electrolytically formed chemical species were responsible for color removal. The rate of indirect oxidation was slower than the rate of chlorinated oxidizing species production above $0.01\mathrm{N}$ sodium chloride concentration. Decolorization rate increased with increasing chloride concentration to a rate-limited point occurring at $0.04\mathrm{N}$ sodium chloride in the system studied.

Experiments on the permeation of several chlorinated and aromatic hydrocarbons through high-density polyethylene (HDPE) geomembranes were conducted using the ASTM F-739 standard test method. The diffusion coefficients were estimated by a one-dimensional diffusion equation based on Fick’s second law, and the solubilities of the solvents in HDPE were determined by the steady state permeation rates. The one-dimensional transient model was able to simulate the permeation concentrations and implied that equilibrium partition between organic solvent and HDPE geomembrane was not achieved during the initial permeation. The solubilities of organic solvents in the HDPE geomembranes obtained by immersion tests or weight gain methods of permeation experiments were not an appropriate boundary condition for the model simulation of permeation. It was found that the diffusion coefficients and solubilities of organic solvents correlated well with their molecular weights and dipole moment, respectively. The present work provides information on the extent of organic compounds permeations through HDPE geomembranes as applied in hazardous waste landfills.

Nitrate reduction in an iron/nitrate/water system with or without an organic buffer was investigated using multiple batch reactors under strict anoxic conditions. Nitrate reduction was very limited $(<10\%)$ at near-neutral pH in the absence of the organic buffer. However, nitrate reduction was greatly enhanced if the system: (1) had a low initial pH $(\sim 2–3)$ ; (2) was primed with adequate aqueous ${\mathrm{Fe}}^{2+}$ ; or (3) was in the presence of the organic buffer. In Cases (1) and (3), nitrate reduction usually was involved in three stages. The first stage was quick, and ${\mathrm{H}}^{+}$ ions directly participated in the corrosion of iron grains. The second stage was very slow due to the formation of amorphous oxides on the surface of iron grains, while the third stage was characterized by a rapid nitrate reduction concurrent with the disappearance of aqueous ${\mathrm{Fe}}^{2+}$ . Results indicate that reduction of nitrate by ${\mathrm{Fe}}^0$ will form magnetite; ${\mathrm{Fe}}^{2+}$ (aq.) can accelerate reduction of nitrate and will be substoichiometrically consumed. Once nitrate is exhausted in the system, no more ${\mathrm{Fe}}^{2+}$ will be consumed. In the presence of nitrate, ${\mathrm{Fe}}^{2+}$ (aq) will be adsorbed onto the surface of iron grains or iron oxides; the surface-complexed Fe(II) (extracted by acetate with $\mathrm{pH}=4.1$ ) might be oxidized and become structural Fe(III), resulting in a steadily increasing ratio of $\mathrm{Fe}\left(\mathrm{III}\right)∕\mathrm{Fe}\left(\mathrm{II}\right)$ in the oxides formed. The transformation of nonstoichiometric amorphous iron oxides into crystalline magnetite, a nonpassive oxide, triggers the rapid nitrate removal thereafter.

Data from a pilot study, in which renewable energy was used for low-temperature subsurface heating in a northern climate, suggests that such an approach may be useful for remediating low permeable soils. Low-temperature soil heating is expected to enhance remediation effectiveness by increasing contaminant volatility, diffusion, desorption, and microbiological activity. Direct and indirect solar energy was harvested with a hybrid photovoltaic/wind electric system. The electrical energy generated by the hybrid renewable energy system was distributed to the subsurface using a control system and wire, then converted to heat energy using a resistive element emplaced in an unsaturated silty layer $2.3\mathrm{m}$ below grade. Renewable energy system performance, soil temperature, and environmental data were collected. Ambient soil temperatures fluctuated seasonally within the silt layer from $4\text{to}15°\mathrm{C}$ . The small renewable energy system performed as predicted and injected $441\mathrm{kWh}$ of energy into the soil over the eight-month study. This energy input translated to increased soil temperatures ranging from $7.7\text{to}19.4°\mathrm{C}$ and from $3.3\text{to}4.3°\mathrm{C}$ above ambient at distances 0.3 and $0.9\mathrm{m}$ from the heating well, respectively. The system supplied sufficient heat to maintain soil temperatures above ambient even in winter in Vermont, where low direct solar energy was available and sustained low ambient temperatures prevail.

This study compares electrocoagulation and chemical precipitation for heavy metals removal from acidic soil saline leachate (SSL) at the laboratory pilot scale. The electrocoagulation process was evaluated via an electrolytic cell [12 cm (width) $\times$ 12 cm (length) $\times$ 19 cm (depth)] using mild steel electrodes (10 cm width $\times$ 11 cm high), whereas chemical precipitation was evaluated using either calcium hydroxide $\left[\mathrm{Ca}{\left(\mathrm{O}\mathrm{H}\right)}_2\right]$ or sodium hydroxide (NaOH). By comparison with chemical precipitation at a pH varying between 7 and 8, electrocoagulation was more effective in removing metals from SSL having a relatively low contamination level ( $124\mathrm{mg}\mathrm{Pb}∕\mathrm{L}$ and $38\mathrm{mg}\mathrm{Zn}∕\mathrm{L}$ ). For SSL enriched with different heavy metals (each concentration of metals was initially adjusted to 100 mg/L) and treated at a pH lower than 8.5, with the exception of Cd, the residual metal concentrations at the end of the experiments were below the acceptable level recommended for effluent discharge in urban sewage works (less than 4 mg/L of each residual metal concentration was recorded) using electrocoagulation, contrary to chemical precipitation using NaOH (more than 15 mg/L of each residual metal concentration was recorded). By comparison, chemical precipitation using $\mathrm{Ca}{\left(\mathrm{O}\mathrm{H}\right)}_2$ was effective in reducing Cr, Cu, Ni, and Zn under the permissive level, but not for Cd and Pb. However, both chemical precipitation processes needed to be operated at higher pH values (around 10.0) to be more effective in reducing metals from SSL and, therefore, required a pH adjustment of the effluent before discharge, whereas electrochemical treatment had a practical advantage of producing an effluent having a pH close to the neutral value and suitable for stream discharge in the receiving water. On the other hand, electrocoagulation was also found to be very efficient for removing Pb from very contaminated solutions (250–2,000 $\mathrm{mg}\mathrm{Pb}$ /L). At least 94% of Pb was removed regardless of the initial Pb concentration in the SSL. Electrochemical coagulation involves a total cost varying from 8.67 to 13.00 $/tds, whereas 0.84 to 16.73 $/tds is recorded using chemical precipitation. The cost included only energy consumption, chemicals consumption, and metallic sludge disposal.

Iron powder has previously been demonstrated to be a potential dry cleansing agent for oiled feathers, whereby both the oil ad(b)sorbing particles and the contaminant may be harvested magnetically. Previous studies on feather clusters have only been able to achieve 97.4% removal. While impressive, this is not considered to be entirely satisfactory for wildlife rehabilitation in practice. Reported in this Technical Note is a series of experiments designed to establish whether a grade of iron powder can be identified that is capable of achieving 100% removal and to identify those characteristics responsible for such improvement. To this end, the abilities of nine different grades of iron powder to remove four different contaminants (three crude oils and a crude oil/seawater emulsion) from feather clusters have been compared, as have the relative physical characteristics of the different iron powders. It has been established that the efficiency of remediation is indeed related to certain physical attributes of the particles (the “grade”). Specifically, a spongy superfine iron powder has been identified that is capable of achieving 100% removal (within experimental error) for all four contaminants tested. This represents an important proof of principle that makes the development of a practical field device a real possibility.

This work looks at several new abiotic treatment methods for transformation of DDT in an aqueous solution. Various combinations of calcium peroxide $\left(\mathrm{Ca}{\mathrm{O}}_2\right)$ , zero-valent iron $\left({\mathrm{Fe}}^0\right)$ , iron sulfide (FeS), and hydrogen peroxide $\left({\mathrm{H}}_2{\mathrm{O}}_2\right)$ were utilized to promote the abiotic transformation of 1,1,1-trichloro-2,2-bis( $p$ -chlorophenyl)ethane (DDT) in electrolyte, hydroquinone, and nonionic surfactant (Triton X-114) systems. Treatment with $\mathrm{Ca}{\mathrm{O}}_2$ resulted in 86% DDT mass reduction within $10\text{days}$ of treatment with only traces of 1,1-dichloro-2,2-bis( $p$ -chlorophenyl)ethane (DDD) , 1,1-dichloro-2,2-bis( $p$ -chlorophenyl)ethylene (DDE), and 1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene (DDMU) being generated. Treatments with 1:1 mixtures of ${\mathrm{Fe}}^0:\mathrm{Ca}{\mathrm{O}}_2$ and $\mathrm{Fe}\mathrm{S}:\mathrm{Ca}{\mathrm{O}}_2$ resulted in 86 and 85% DDT mass transformation, respectively, within $8\text{days}$ . A mixture of $0.75\mathrm{g}{\mathrm{Fe}}^0:0.1\mathrm{g}\mathrm{Ca}{\mathrm{O}}_2$ showed similar results with 79% DDT mass transformed within $8\text{days}$ . A mixture of $0.75–0.1\mathrm{g}$ of ${\mathrm{Fe}}^0:\mathrm{Fe}\mathrm{S}$ resulted in 85 and 97% transformation in the total mass of DDT in an electrolyte solution and a hydroquinone solution, respectively. The treatment of DDT in aqueous solution by $\mathrm{Ca}{\mathrm{O}}_2$ , in the presence of Triton X-114, resulted in the transformation of 97% of the total mass of DDT within $30\text{days}$ , albeit, large amounts of DDE $\left(402\mu \mathrm{M}\right)$ were generated.