Journal of Environmental Engineering

This paper proposes a new approach to synthesize polymeric ferric sulfate (PFS). It was found that the basicity and stability of the synthesized PFS varied with the quantity of sulfuric acid used. The minimum amount of sulfuric acid needed for the synthesis of PFS to insure a residual ${\mathrm{Fe}}^{2+}$ concentration in the product lower than 0.1 wt% is about 31.0 wt% of the stoichiometric requirement. However, to produce a stable product which can be stored for six months, the amount of sulfuric acid should be 51.7 and 62.0 wt% of the stoichiometric requirement for PFS produced at 55 and 85°C, respectively. The structure of PFS depended on the synthesis temperature, as observed through x-ray diffraction and transmission electron microscopy. A comparison of the coagulation performance of PFS and ferric sulfate (FS) showed that PFS is, in general, more effective than FS in reducing the turbidity of Kaolinite suspensions for various conditions.

A two-dimensional numerical solute transport model was developed for simulating an enhanced in situ denitrification experiment performed in a nitrate-contaminated aquifer on Cape Cod, Massachusetts. In this experiment, formate $\left({\mathrm{HCOO}}^{-}\right)$ was injected for a period of 26 days into the carbon-limited aquifer to stimulate denitrification. Calibration of the vertical-profile site model was demonstrated through error analysis and comparison with formate, nitrate, and nitrite concentration data monitored along a transect of three multilevel groundwater sampling wells for 75 days after initial injection. Formate utilization rates were approximately 142 and 38 μM/day for nitrate and nitrite reduction, respectively. Nitrate and nitrite utilization rates were approximately 29 and 8 μM/day, respectively. Nitrate utilization rates under enhanced conditions were 1 order of magnitude greater than previously reported naturally occurring rates. The nitrite production rate was approximately 29 μM/day. Persistence of nitrite was attributed to a combination of factors, including electron donor (formate) limitation late in the experiment, preferential utilization of nitrate as an electron acceptor, and greater nitrite production relative to nitrite utilization.

The influence of supplemental acetate on in situ bioremediation for the removal of dissolved polycyclic aromatic hydrocarbons (PAHs) in groundwater was evaluated in laboratory sand columns. Sand columns, inoculated with a soil enrichment culture, were fed with dissolved PAHs (9 mg/L naphthalene, 0.8 mg/L phenanthrene, 0.09 mg/L pyrene), nutrients, and hydrogen peroxide to sustain aerobic microbial growth. Pore water PAH concentration profiles were obtained during the study. Determinations of viable biomass, carbohydrate, and PAH sorption capacity were obtained at the conclusion of the experimental runs. Pore water profiles indicated that PAH biodegradation capability became more quickly established after 45 days in sand columns amended with acetate versus the unamended control. The endpoint pore water PAH concentration profiles were similar for both acetate-amended and unamended columns. Higher biomass in acetate-amended columns increased the overall sorption capacity of the sand medium for PAHs by 24–47%. Supplemental acetate resulted in minimal biofouling of the sand medium as the final hydraulic conductivity of the acetate-amended treatments was 36–72% of the clean sand value.

A mathematical model was developed to simulate the performance of a pilot-scale ozone bubble-diffuser column. The reactor hydrodynamics was represented with the axial dispersion reactor model. An analytical solution was developed for the liquid and gas phase ozone mass balances in which dissolved ozone decomposes by first-order kinetics. Numerical approximations were provided for the mass balances for viable microorganisms and the more general case of dissolved ozone decomposition through a second-order reaction with fast ozone demand in natural organic matter. Model components required to predict the liquid and gas phase ozone concentration and viable microorganism number density profiles throughout the bubble-diffuser column included input parameters (liquid and gas flow rates, influent gas and dissolved ozone concentrations, temperature, and countercurrent or cocurrent operation mode), empirical correlations (dispersion number, volumetric mass transfer coefficient, Henry’s law constant), and batch or semibatch kinetic information (ozone decomposition rate constants and fast-ozone demand, and microorganism inactivation lag phase and rate constant). A sample model run for the case of first-order ozone decomposition revealed that the analytical and numerical solutions were practically identical.

The axial dispersion reactor (ADR) model developed in Part I of this study was successfully validated with experimental data obtained for the inactivation of C. parvum and C. muris oocysts with a pilot-scale ozone-bubble diffuser contactor operated with treated Ohio River water. Kinetic parameters, required to model the effect of temperature on the decomposition of ozone in treated Ohio River water and oocyst inactivation, were determined from batch and semibatch ozonation experiments. The ADR model was used to simulate the effects of operating conditions (feed-gas ozone concentration, liquid flow rate, and gas flow rate), and water quality related parameters (fast ozone demand, first and second order ozone decomposition rate constants, and temperature) on the performance of the pilot-scale contactor. The model simulation provided valuable insight into understanding the performance of ozone disinfection systems and recommendations for ozone contactor design and optimization. For example, the simulation revealed that meeting inactivation requirements for C. parvum oocysts would be more challenging at relatively lower temperatures.

A neural network approach was employed to relate risky Cryptosporidium and Giardia concentrations with other biological, chemical and physical parameters in surface water. A set of drinking water samples was classified as “risky” and “nonrisky” based on the concentrations of full and empty oocysts, and cycsts of Cryptosporidium and Giardia, respectively. Given the constraints associated with collecting large sets of microbial data, the study was aimed at identifying an effective training algorithm that would maximize the performance of a neural network model working with a relatively small dataset. A number of algorithms for training neural networks, including gradient search with first- and second-order partial derivatives, and genetic search were used and compared. Results showed that genetic algorithm based neural network training consistently provided better results compared to other training methods.

An integrated approach is presented for determining the harmonized optimal coastline from given options for large-scale coastal reclamation. The approach incorporates results from hydrodynamic, sediment transport, and water quality models and ecological impact considerations. These models predict reclamation impact on tidal flow, sediment deposition and erosion, and water quality under different scenarios. The impact on sensitive coastal ecosystems is considered indirectly in terms of the qualitative relationship to results from the sediment transport model. The analytical hierarchy process method is applied to determine the weights of various control factors and to integrate the model predictions. A sensitivity analysis is made to assess the effect on the final results of modeling errors and uncertainty in the weights assigned, and thus to enhance the reliability of decision making. Although the methodology given herein emphasizes reclamation in a bay with multifold functions, the procedure is potentially applicable to most coastal reclamation projects, except single-option schemes. An application to Deep Bay coastline is described in the companion paper.

In this case study, a harmonized optimal postreclamation coastline is determined from a set of proposed options for Deep Bay in South China, where large-scale reclamation work is under consideration. Within the framework of the integrated approach presented in the companion paper, hydrodynamic, sediment transport, and water quality models are calibrated, validated, and then used to predict reclamation impacts on tidal flow, sediment deposition and erosion, and water quality under different scenarios. The ecological impact due to reclamation is qualitatively interpreted in terms of changes in deposition and erosion rate, in addition to professional judgement. The analytical hierarchy process method is applied to determine weights for the various primary issues and control factors, and thus an integrated mark calculated for each option. A sensitivity analysis indicates that the priority order of three proposed options does not change for certain fluctuations in the values of assigned weights and grades. Hence, the choice of postreclamation coastline for Deep Bay may be regarded as reliable.

Off gas analyses of oxygen transfer efficiency (OTE) at Terminal Island Treatment Plant of Los Angeles document changing performance of fine-pore diffusers in an activated sludge plant from 1991 to 1998. Although the plant treats a challenging waste stream, the aeration tanks are little different from other plants. Recent sessions provided improved time and space resolution, compared to previous work. Samples were more closely spaced, and some samples were taken in the intervals between the aeration grids, at the ends of the tanks, and near the edges of the grids. Very short term fluctuations in the data were assessed by leaving the hood in the same position for 1–2 h. The 1998 efficiencies were low. Analysis of the measurements since 1991 shows effects expected from fouling, and there was also extensive deterioration of the air distribution system that has now been remedied by a refurbishment program. These measurements show the degree to which efficiency losses may grow unrecognized if OTE measurements are not done. Hence, this study may serve as a prototype for similar measurement programs at other plants.