Journal of Environmental Engineering

Manganese (Mn) in a drinking water distribution system can cause multiple aesthetic problems including discolored water and fouling or scaling of fixtures. Oxidation and solid-liquid separation processes are typically employed at a treatment plant to limit the concentration of Mn entering the distribution system. Potassium permanganate (KMnO₄) is commonly used to oxidize the manganous ion (Mn⁺²) to manganese oxide (MnO₂). In this study, a mechanistic model is applied to the oxidation of manganese at a treatment plant. Literature kinetic constants (determined with artificial water) are compared with the values obtained for the plant's natural water. The solution and surface phase oxidation rate constants determined with the natural water are two to six orders of magnitude less than those determined with the artificial water. The reduced oxidation rate in the natural water is attributed to the presence of dissolved organic matter, which can exert a competitive demand on the oxidant and interfere with the oxidation by complexing Mn⁺². The development of an additional rate constant for the oxidation of dissolved organic matter improves the modeling results for KMnO₄ concentration versus time, but only marginally explains the Mn⁺² oxidation rate differences.

A treatment strategy is examined whereby organic compounds in the aqueous phase are first removed by fixed-bed adsorption, followed by off-line regeneration of spent adsorbent using saturated steam (160°C) and cleanup of steam condensate using fixed-bed photocatalysis. This treatment strategy is examined with the following organic compounds: Tetrachloroethylene (PCE), carbon tetrachloride (CCl₄), p-dichlorobenzene (p-DCB), o-chlorobiphenyl (o-PCB), and methyl ethyl ketone (MEK). For six cycles of adsorption and regeneration, the steaming process is effective to regenerate the adsorbent exhausted with PCE, p-DCB, CCl₄, or MEK. In the case of o-PCB, there is about 20% loss in adsorbent capacity after the first cycle; however, the adsorption capacity for Cycles 2–6 is almost the same. Fixed-bed photocatalysis is examined for decontamination of steam condensate carrying the desorbed organics, and it is observed to be effective for mineralization of aqueous phase PCE, p-DCB, CCl₄, and o-PCB. In the case of MEK, although 97% of the compound was removed, only 16% removal of total organic carbon was observed, thereby suggesting that some by-products were produced that were refractory to oxidation.

Titanium-supported titania-based photoelectrodes were prepared either by sol-gel processes or by thermal oxidation. Catalytic activities and stabilities of these photoelectrodes were monitored by photooxidizing formic acid in aqueous NaCl during three successive experiments under identical conditions. Although electrodes coated with either titania (higher activity) or zirconia-titania (lower activity) and heated at 300°C were less active initially than similar electrodes heated to higher temperatures, electrodes heated at 300°C were more stable. Activities of titania electrodes were increased by depositing the titania at a higher withdrawal speed (21.5 versus 1.5 cm min⁻¹) and by depositing more layers of titania. Stabilities of multilayer electrodes were improved by depositing the sol faster. Applying positive electrical potentials across electrodes also increased their activities. In particular, while activities diminished considerably in relatively high concentrations of NaCl if no potential was present, activities decreased only slightly under an electrical field. Activities of photoelectrodes prepared by heating metallic titanium plates at 300°C were low. Activities of photoelectrodes prepared by heating titanium at 500°C (giving a rutile coating) were similar to activities of photoelectrodes prepared by sol-gel techniques, but only when potentials were applied.

The rate of inactivation of Cryptosporidium parvum oocysts by ozone in 0.05 M phosphate buffer at pH 6, 7, and 8 was studied at 22 ± 1°C in batch reactors. Infectivity in neonatal CD-1 mice was used as the criterion for oocyst viability. Ozone inactivation data were fitted to the Incomplete gamma Hom (I.g.H.) and Chick-Watson (n = 1) model, both of which incorporate a first-order rate constant for the disappearance of aqueous ozone during the contact time. For a 0.05 M phosphate buffer ranging in pH from 6 to 8, a single I.g.H. model was found to adequately describe the kinetics of Cryptosporidium inactivation by ozone at 22°C. The I.g.H. model for pH 6–8 was found to provide a significantly better fit to the ozone inactivation data when compared with the Chick-Watson model. The effect of pH on ozone inactivation kinetics was associated with ozone residual stability over the pH range of 6–8. The sensitivity of Cryptosporidium to ozone at 22°C was therefore not statistically different at pH 6 when compared with pH 8. The inactivation behavior of Cryptosporidium by ozone was characterized by a tailing-off effect, with approximately equal importance of ozone concentration and contact time. The I.g.H. model for pH 6–8 can be used as an aid in the design of ozone disinfection systems, and this robust fitted model was used to formulate ozone design criteria—the initial oxone residual required for a given contact time for 1, 2, and 3 log units inactivation of Cryptosporidium at 22°C. Uncertainty associated with the ozone design criteria for 2 log units inactivation was quantified using inverse prediction intervals. An ozone design criterion was established that gives a 95% probability of achieving 2 log units inactivation of Cryptosporidium at 22°C, corresponding to an approximate safety factor of 0.7 log units.

The volatile organic compound, polycyclic aromatic hydrocarbon, dioxin, and metallic components released from incineration threaten human health. These pollutants, appearing in a molecular state, cannot be effectively removed by baghouse and electrostatic precipitators through capture and filtration mechanisms. Previous studies indicate that activated carbon is conventionally used to remove organic compounds from gas at low temperatures (less than 30°C). However, the adsorption characteristics of organic compounds from a gas phase at high temperatures (over 120°C) are seldom mentioned. Moreover, the complex compositions of flue gas cause the adsorption characteristics of organic compounds and heavy metals on adsorbent tubes to be more complicated. This research examines the adsorption characteristics of organic compounds and heavy metals at various incineration conditions. The evaluated parameters include: (1) the operating temperatures; (2) the characteristics of adsorbents (activated carbon and zeolite); and (3) waste compositions and the presence of heavy metals. The results indicate that activated carbon has a high adsorption capacity compared with zeolite.

Organic and inorganic components in natural waters are intimately interrelated and constitute a dissolved material matrix (DMM). The objective of this study was to systematically investigate the distribution and recovery of both organic and inorganic components in chemically fractionated natural waters. Untreated and previously coagulated natural waters were fractionated into hydrophobic and hydrophilic acid, base, and neutral DMM fractions using a resin exchange based protocol. Mass balances on nonpurgable dissolved organic carbon, aluminum, iron, and manganese were used to evaluate DMM component recovery. Quantitative recovery of dissolved organic matter was achieved, whereas, aluminum, iron, and manganese recoveries were largely incomplete (30–92%). Coagulation increased the recovery of all metals examined. Incomplete metals recovery was attributed to imperfect elution from MSC-1 cation exchange resin and appeared related to the distribution coefficient K_d of each metal with this resin. DMM component distribution among chemical fractions was altered by coagulation, with dissolved organic matter preferentially removed in the hydrophobic acid fraction. Unrecovered metals appeared to consist primarily of colloidal mineral (hydr)oxides solubilized by acidic pH conditions imposed during fractionation.

Municipal solid waste (MSW) recycling targets have been set nationally and in many states. Unfortunately, the definitions of recycling, rates of recycling, and the appropriate components of MSW vary. MSW recycling has been found to be costly for most municipalities compared to landfill disposal. MSW recycling policy should be determined by the cost to the community and to society more generally. In particular, recycling is a good policy only if environmental impacts and the resources used to collect, sort, and recycle a material are less than the environmental impacts and resources needed to provide equivalent virgin material plus the resources needed to dispose of the postconsumer material safely. From a review of the existing economic experience with recycling and an analysis of the environmental benefits (including estimation of external social costs), we find that, for most communities, curbside recycling is only justifiable for some postconsumer waste, such as aluminum and other metals. We argue that alternatives to curbside recycling collection should be explored, including product takeback for products with a toxic content (such as batteries) or product redesign to permit more effective product remanufacture.

A simple mathematical model was developed to simulate solid waste decomposition in landfills. Two processes were taken into account: (1) The exchange of the organic matter between the solid and the liquid phases; and (2) the depletion of the dissolved organic matter due to biological decomposition and flushing. Two equations using first-order kinetics were employed to describe these processes. The landfill was considered as a single fully mixed reactor. The model, which has a smaller set of parameters than other models proposed in the literature, was calibrated using the results obtained from six pilot laboratory-scale lysimeters. The fitting accuracy is indicative of the model reliability. Values for the kinetic parameters are proposed for characteristic types of solid wastes and landfill management practices.

This work investigates the constant-pressure consolidation characteristics of three different sludge samples, with particular emphasis on the tertiary consolidation stage. The refined Terzaghi-Voigt rheological model is applied to interpret the data and, in doing so, to evaluate the model parameters. Experimental results indicate that the tertiary consolidation stage is commonly found in sludge that contains a large amount of bound water. In addition, it was found that consolidation pressure and polymer conditioning would markedly affect the moisture distribution. Results obtained from conventional analysis are compared with those of the refined model.

Design and operation of saline wastewater treatment systems are difficult because of adverse effects of salt on microbial flora. Quantification and modeling of salt inhibition effects are essential in designing biological treatment processes for saline wastewater. Synthetic wastewater containing 0–10% salt (NaCl) was treated in a rotating biodisc contactor (RBC) unit operating in a continuous mode. Effects of important process variables such as the A/Q ratio, COD loading rate, and salt concentration on COD removal rate and efficiency were investigated. The system's performance improved with an increasing A/Q ratio; however, performance decreased with an increasing COD loading rate and salt content. The liquid phase was aerated to keep suspended cells active at high feed COD concentrations such as S₀ = 5,000 mg/L. A mathematical model was developed to describe the system's behavior. Model parameters were determined by using the experimental data. Salt inhibition was found to be significant for salt concentrations larger than 2% NaCl. The experimental results and mathematical model may be used in design of RBC units treating saline wastewater.

The ex situ remediation of heavy metals-contaminated industrial sludge (pH = 10.35, Zn = 3,500 mg/kg) by electroreclamation (I = 2.5 A) was studied at pilot scale (42.5 kg of sludge). This research focused on acidification of sludge and electrochemically induced migration of metals, emphasizing their partitioning prior to electroreclamation. The sludge was preacidified to an initial pH of 4.5. After treatment, a very low anode reservoir pH (near 0) was reached, and the average sludge pH was 2. Addition of 1 M HNO₃ to the cathode reservoir prevented basic conditions in the sludge. In accordance with selective sequential extraction results, a low migration of Zn and Cu was obtained. In the anode region, Zn and Cu concentrations decreased by 33 and 39%, respectively, and increased in the cathode region by 33 and 26%, respectively. These metals were concentrated in the cathode area but were not effectively transported onto the cathode. Mn appeared to be more mobile than other metals. After 10 days of current application, a layer mainly composed of Ca, Fe, and Mn appeared on the cathode surface.

A 5-year cooperative study of the Cumberland River at Nashville by consulting engineers, university researchers, Tennessee regulatory agency officials, federal agencies, and a citizens advisory committee produced results that allowed Nashville to alter its combined sewer overflow (CSO) control plan, eliminate two major detention tanks, and save $106,000,000. The data showed that dissolved oxygen depletion was not a problem, nor was toxic material discharges. Fecal coliform bacteria were a problem, but it was short term and near field, and would not be solved by planned detention tanks, or even by eliminating all CSOs. Other changes are being implemented that will greatly reduce CSO discharges at lower capital cost than the original plan.

The wash-off algorithm in the Storm Water Management Model has been widely used to simulate the wash off of sediment and pollutants from impervious areas. This algorithm indicates an exponential relationship between pollutant wash off and runoff volume. To simulate water quality, the initial mass of sediment or pollutant at the beginning of the storm and an empirical wash-off coefficient need to be determined. A simple analytical technique is developed for evaluating these parameters from measured water quality and runoff data. The proposed method is based on an expression of the exponential wash-off equation in terms of concentration rather than pollutant mass, and it can be applied to parameter evaluation without recourse to complex numerical models or optimization techniques.