Journal of Environmental Engineering

The purpose of this study was to quantify the potential level of protection that secondary disinfection may provide in response to an intrusion event. Although several uncertainties exist regarding intrusion events, this study presents an analysis of the inactivation provided by disinfectant residuals by using a distribution system model, inactivation and disinfectant decay models, and conservative assumptions based on available data. A variety of conditions were modeled, including a range of water quality parameters (pH, temperature); inactivation of two microorganisms, Giardia and E. coli O157:H7; and intrusion water dilution ratios. Despite the assumptions inherent in the model, several generalizations were derived from the study. A free chlorine residual of $0.5\mathrm{mg}∕\mathrm{L}$ may be insufficient to provide adequate control of disinfectant-resistant Giardia even at low pH (6.5) and high temperature $(25°\mathrm{C})$ conditions that enhance chlorine effectiveness. For E. coli, an organism of “average” disinfectant resistance relative to others, a residual of $0.5\mathrm{mg}∕\mathrm{L}$ may provide ample protection against intrusion even assuming that the chlorine residual is reduced within several minutes, such as would be predicted to occur with sewage intrusion at levels below 1% of the total flow. Importantly, chloramines may have a negligible benefit in terms of protecting against intrusion for even relatively susceptible organisms such as E. coli. Consequently, systems should consider protection against intrusion when choosing their secondary disinfectant.

A dynamic “two-site” model was formulated and tested for simulating the elution histories of copper $\left({\mathrm{Cu}}^{2+}\right)$ and lead $\left({\mathrm{Pb}}^{2+}\right)$ from a contaminated soil treated by poly(amidoamine) dendrimers. In the model, the metal sorption sites of the soil were divided into two compartments: one with a fast desorption rate and the other with a slow desorption rate. The model was tested for simulating and predicting ${\mathrm{Cu}}^{2+}$ and ${\mathrm{Pb}}^{2+}$ elution histories obtained from column experiments. Compared to the classical “one-site” model and the modified “gamma distribution” model, the “two-site” model not only provides much improved power for simulating the observed metal elution data, but also can more accurately predict the metal elution histories under various experimental conditions including initial metal concentration in soil, dendrimer concentration, and pH.

Several sources of uncertainty are considered in using field data to perform mass balance calculations to estimate nonpoint source (NPS) loads of total dissolved solids (TDS) and selenium (Se) to two reaches along the Lower Arkansas River in Colorado. This approach renders stochastic models of the mass balance equations for each river reach, where the input variables and their associated parameters are treated as random variables described by probability distributions. A data set collected in an intensive field effort conducted over several years is used in developing the models. Monte Carlo simulation solves the stochastic mass balance equations to describe distributions of possible values of the NPS loads. Results indicate that uncertainty in these calculated loads is sizeable. Annual average coefficient of variation (CV) in calculated total NPS TDS loads for sample periods within the two reaches ranges between 0.15 and 2.76, averaging about 1.1. For the Se mass balance along the downstream reach, the average CV in calculated loads is 0.23. The 90% prediction interval width for total NPS TDS load averaged over the 58 sample periods along the upstream reach is $\mathrm{13,691}(\mathrm{kg}∕\text{day})∕\mathrm{km}$ , compared to an overall average mean load of $\mathrm{8,383}(\mathrm{kg}∕\text{day})∕\mathrm{km}$ . It is $\mathrm{8,545}(\mathrm{kg}∕\text{day})∕\mathrm{km}$ averaged over the 61 sample periods downstream, compared to an overall average mean load of $\mathrm{11,183}(\mathrm{kg}∕\text{day})∕\mathrm{km}$ . For the Se load, the overall average 90% prediction interval width is also substantial compared to the overall average mean: $0.028(\mathrm{kg}∕\text{day})∕\mathrm{km}$ compared to $0.038(\mathrm{kg}∕\text{day})∕\mathrm{km}$ . Change in stored solute mass within the river over sample periods is found to be a major contributing factor to the calculation of NPS loads. Also, sensitivity analyses are performed that yield information on the relative influence that the degree of uncertainty in each random parameter has on the uncertainty in the calculated solute loads.

As more manufactured stormwater treatment devices enter the market, stormwater managers are searching for effective and rapid methods for evaluating device performance. Many agencies require vendors to test full-scale versions of their devices under controlled conditions. The most common parameter used to document performance is suspended solids for several reasons: (1) many pollutants attach to solids; (2) a solids simulant is relatively easy to generate; and (3) solids are comparatively easy and inexpensive to quantify. However, a controversy still exists in the profession and some regulatory agencies as to whether total suspended solids (TSS) or suspended sediment concentration (SSC), or both, should be measured. This paper focuses on the comparability of the two methods/protocols used for sample solids analysis, including lessons learned during recent evaluations of two manufactured treatment devices. Analysis of 215 sample pairs (where both TSS and SSC were measured on aliquots of the same sample) showed that statistically the TSS measured using the wide-bore pipet method and SSC results were indistinguishable from one another and from the original simulant mixture.

Recent investigations have demonstrated that it is feasible to utilize a combined technology, consisting of an upflow anaerobic sludge bed (UASB) reactor for anaerobic pretreatment, followed by aerobic posttreatment, to efficiently treat municipal wastewater. In the proposed system the excess sludge produced in the aerobic stage is recycled to the anaerobic unit for sludge stabilization. The proposed configuration is an attractive alternative for secondary wastewater treatment because the costs associated with sludge digestion are eliminated. The present paper compares two anaerobic pretreatment technologies, namely, the anaerobic fluidized bed reactor (AFBR) and the UASB, and demonstrates that both have similar performances with regard to chemical oxygen demand (COD) removal, suspended solids removal, and gas generation. Of the solids loading applied to the AFBR $[1.02\mathrm{kg}\text{suspended}\text{solids}\left(\mathrm{SS}\right)∕{\mathrm{m}}^3\text{day}]$ , $0.16\mathrm{kg}$ SS/ ${\mathrm{m}}^3\text{day}$ were consumed, and $0.17\mathrm{kg}$ SS/ ${\mathrm{m}}^3\text{day}$ accumulated in the bed and eventually would need to be removed. In comparison, of the solids load of $1.15\mathrm{kg}\text{total}\text{suspended}\text{solids}\left(\mathrm{TSS}\right)∕{\mathrm{m}}^3\text{day}$ applied to the UASB, $0.38\mathrm{kg}∕{\mathrm{m}}^3\text{day}$ were consumed, and $0.054\mathrm{kg}∕{\mathrm{m}}^3\text{day}$ accumulated in the unit. Therefore, a much more efficient sludge stabilization was achieved in the UASB. In addition, the UASB requires significantly lower energy requirements for effluent recirculation than the AFBR, and thus it would be more economical to operate. As in the case of the conventional wastewater treatment plants with separate sludge digestion, the costs associated with digested sludge dewatering and final disposal must be considered. However, the costs of having a separate sludge digester are eliminated, because the anaerobic reactor, in addition to being a pretreatment unit, plays the role of the sludge stabilization unit. The proposed UASB/SC process is not only effective for providing secondary wastewater treatment, but it also minimizes the surplus sludge production and produces a well-stabilized sludge.

In order to investigate the turbulent flow and mass transfer in primary settling tanks, numerical simulations are conducted by using a modified $k-\epsilon$ two-layer model based Boussinesq’s approximation to model the Reynolds stress in primary settling tanks, and solving the governing equations using a hybrid finite analytic method (HFAM). The simulation results obtained using the mathematical model are compared with the experimental data and simulation results available in the literature, and the results of comparison indicate that the profiles of the primary velocity field are in line with the experimental results and the flow-through curve obtained using the mathematical model are in good agreement with the curves based on experimental data. It is therefore concluded that the HFAM approach can be used to simulate the turbulent flow and mass transfer in a primary settling tank, and the modified $k-\epsilon$ two-layer model can be used to establish the velocity field distribution at the bottom of a primary settling tank.

Air injection systems have a wide range of environmental engineering applications. In this study, we conducted experiments on air injection in a relatively large water tank to investigate the effect of nozzle type, including single/multiple orifice nozzles and a porous airstone, on the characteristics of the bubbles and the induced flow structure. Measurements of bubble characteristics and flow field surrounding the bubble core were obtained using a double-tip optical probe and particle image velocimetry, respectively. The results revealed that bubble velocity did not change significantly with different nozzles, but bubble size decreased significantly while interfacial area, liquid entrainment rate, and kinetic energy of the mean and turbulent flow increased significantly by using the porous airstone instead of nozzles with large orifices. The results for a nozzle with multiple orifices of small diameter are comparable to those for the airstone, which suggests the suitability of its use for systems susceptible to clogging of the pores. Correlations using adequate length and velocity scales are also proposed to describe both bubble and liquid flow characteristics. Finally, applications of the results for different artificial aeration/mixing systems are presented.

Combined cultures were developed from anaerobic granular and suspended aerobic cultures in three upflow sludge blanket reactors aerated at $10\mathrm{mL}$ air/min $4\mathrm{h}∕\text{day}$ (R2), every other day (R3), and $24\mathrm{h}∕\text{day}$ (R4). The use of combined cultures was found to be advantageous compared to the anaerobic granules for the treatment of low-strength wastewaters. During municipal wastewater treatment at influent $5\text{-}\text{day}$ biochemical oxygen demand $\left({\mathrm{BOD}}_5\right)$ concentration of $53–118\mathrm{mg}∕\mathrm{L}$ (hydraulic retention time: $0.75\text{day}$ ), combined cultures in R2, R3, and R4 exhibited average ${\mathrm{BOD}}_5$ removal efficiencies of 52, 75, and 76%, respectively. The use of these cultures might be proposed as an alternative for municipal wastewater treatment due to their advantages such as achievement of required discharge standards, prevention of biomass loss/settleability problems unlike activated sludge systems and possible methanogenic activity, as well as high settling characteristics comparable to those of anaerobic granules.

A biodosimetric technique was used to verify the concentration-contact time (CT) values [ ${\mathrm{CT}}_{10}$ , CT integrated disinfection design framework (CT-IDDF), CT segregated flow analysis (CT-SFA)] of the ozone contactors of the DesBaillets water treatment plant (Montreal), using indigenous aerobic spore formers (ASFs) as indicators of disinfection efficiency. ASF measurement in ozonated water was performed using a large water sample concentration method. Four assays, completed over a $6\text{-}\text{week}$ period, involved the implementation of biodosimetric calibration curves using an ozone pilot apparatus and followed by full-scale verifications. ASF inactivation kinetics were well described by a simple Chick–Watson model. The most accurate data also indicated that the ${\mathrm{CT}}_{10}$ underestimates the effective CT (by 1.2–1.9-fold), whereas the CT-IDDF and CT-SFA overestimate it (by 1.0–1.7-fold and 0.9–1.5-fold, respectively). Underestimation from ${\mathrm{CT}}_{10}$ was more pronounced with increased ozone dose while overestimation from CT-IDDF and CT-SFA is most likely due to the difficulty in obtaining a representative ozone residual profile within the contactor. The use of segregated flow analysis provided the best estimate of disinfection performance. Biodosimetry is useful in measuring the effective CT transferred, in verifying model predictions, and in determining the influence of water quality on microbial inactivation.

The effects of oxygen on the pyrolysis of rice husk were investigated with a thermal gravimetric analysis (TGA) reaction system. Pyrolysis experiments of rice husk were carried out in ${\mathrm{N}}_2$ , 10% ${\mathrm{O}}_2$ , and air at the heating rates of 2, 5, and $10\mathrm{K}∕\min$ . The TGA curves indicated two principal reactions, distinguished by significant and distinct mass changes over the experimental range. Oxygen enhanced the pyrolysis reactions of intermediates, which was produced from the first stage reaction of rice husk. A simple kinetic model was proposed for the pyrolysis of rice husk in different oxygen concentrations. The corresponding activation energies, preexponential factors, and reaction orders were determined. The experimental results were satisfactorily fitted by the proposed kinetic model.

Relatively few reported works have dealt with wastewaters arising from amoxillin manufacture. To develop a treatment process for one such wastewater, several physicochemical methods such as coagulation, ultrafiltration, and Fenton oxidation (FO), have been investigated. Among these methods, FO proved effective. Consequently the method was further investigated to identify the appropriate ${\mathrm{H}}_2{\mathrm{O}}_2∕{\mathrm{FeSO}}_4$ ratio, ${\mathrm{FeSO}}_4$ and ${\mathrm{H}}_2{\mathrm{O}}_2$ concentrations, and reaction pH and temperature. In relation to the wastewater, a suitable ${\mathrm{H}}_2{\mathrm{O}}_2∕{\mathrm{FeSO}}_4$ weight ratio was 5:1 (molar ratio: 22.4:1) with ${\mathrm{H}}_2{\mathrm{O}}_2$ and ${\mathrm{FeSO}}_4$ concentrations at $20\mathrm{g}∕\mathrm{L}$ , $4\mathrm{g}∕\mathrm{L}$ , respectively. The corresponding pH range was 2.0–4.0 while the reaction temperature was $60°\mathrm{C}$ . Given these conditions, wastewater total organic carbon was reduced by 48.8–49.4%. After FO treatment, reverse osmosis (RO) effectively reduced the dissolved salt content. The contribution of FO and RO pretreatment improved the wastewater’s biodegradability thus making a downstream biotreatment polishing process viable.