Rajesh Seth

Simulating the response of metal contaminated lakes to reductions in atmospheric loading using a modified QWASI model

The changes in metal concentration following significant reductions in atmospheric metal loading of two nickel and copper contaminated lakes in Coniston Valley of the Sudbury Basin of Ontario, Canada were simulated by using steady-state and dynamic versions of a modified Quantitative Water Air Sediment Interaction (QWASI) Model. Metal partitioning and precipitation processes were quantified with the aid of US EPAs MINTEQA2 Model. The dynamic model successfully described the recovery of the two lakes and identified key input, loss and partitioning processes. A useful modelling strategy is to develop one or more steady-state models that give an approximate representation of conditions at defined times, then extend this to a dynamic version which can take into account the differing rates of response of components of the system. This modelling strategy can be used for designing and assessing remediation programs for metal contaminated lakes and watersheds.

Effect of Media on Biofilter Performance Following Ozonation of Secondary Treated Municipal Wastewater Effluent: Sand vs. GAC

Ozone has been shown to be effective in the transformation of several chemicals of emerging concern that escape the wastewater treatment process, but there is concern whether toxic transformation products are formed. Two parallel biofilter columns with granular activated carbon (GAC) and filter sand following a pilot-scale ozone unit to treat secondary treated municipal wastewater were studied. Results show reduced wastewater genotoxicity following ozonation and further reduction following biofiltration. The BAC biofilter outperformed the sand biofilter in terms of reduction in both organics and genotoxicity. Biofilter performance correlated with biological indicators (dissolved oxygen reduction and effluent E. coli counts) but not with ATP bioactivity measurements. Limited bacterial (E. coli) regrowth was observed in treated effluent from both biofilters.

The Role of Mass Balance Modelling in Impact Assessment and Pollution Prevention

The paper first addresses the applicability of steady-state mass balance models for evaluating the fate of a chemical in a multi-media environment as part of the process of impact assessment and pollution prevention. It is suggested that such models can be used to deduce concentrations in a variety of environmental compartments, including media such as air, water and foodstuffs, which are important vehicles for chemical exposure to humans and wildlife. The models can be applied both to continuous fluxes of chemicals into the environment (e.g. 100 kg/day of benzene from a petroleum refinery) and to pulses of chemicals associated with the use of functional units within an LCA framework (e.g. 100 g of volatile solvent from a can of paint). An Index for Potential Toxic Impact (IPTI) for comparing pollution prevention alternatives of consumer products and manufacturing processes is presented. The index brings together steady-state emissions or pulse LCA emissions, substance partitioning and persistence properties, inter-media transfer rates, exposure pathways and toxicity in an overall evaluation of potential toxic impacts. The use of the EQC Level III Multi-Media Model for this purpose is illustrated for both flux and pulse discharges in the hope that it may encourage the use of such models for impact assessment and pollution prevention.

Reaction Kinetics of Ozone with Selected Pharmaceuticals and Their Removal Potential from a Secondary Treated Municipal Wastewater Effluent in the Great Lakes Basin

Oxidation kinetics of selected pharmaceutical compounds and their degradation during ozonation of secondary treated municipal wastewater effluent (MWWE) was investigated. The apparent second-order rate constants for the reaction between chlorotetracycline (CTC), enrofloxacin (ENR), gemfibrozil (GEM) and ozone ranged between 6.82 – 52.7 × 104 M−1s−1. The measured second-order hydroxyl radical rate constants were several orders of magnitude higher at 8.4 × 109 – 13.1 × 109 M−1s−1 with a reactivity sequence of GEM > CTC > ENR. Overall degradation of CTC, ENR and GEM in secondary treated municipal wastewater effluent was >76 % at ozone doses of 0.33 mg O3/mg DOC or higher.

Evaluation of the gas stripping technique for calculation of Henry's law constants using the initial slope method for 1,2,4,5-tetrachlorobenzene, pentachlorobenzene, and hexachlorobenzene.

Henrys law constant (HLC) is an important factor used in environmental risk assessment and fate and transport models to describe mass transfer of chemical between water and air. HLCs and structure-property relationships were assessed for 1,2,4,5-tetrachlorobenzene (TeCB), pentachlorobenzene (PeCB), and hexachlorobenzene (HCB). HLCs were determined using the volatilization rate (kv) of sparged chemical at 25 °C. Despite the assumption that kv should be constant throughout the stripping duration, results indicated that kv decreased over time according to three separate slope regions. Results of ANCOVA indicate that kv is statistically different in the third slope region, which leads to the conclusion that use of the entire stripping data set would lead to biased HLCs. This decrease in kv may be attributed to desorption from sparger surfaces, which has not been considered widely in the literature. Statistical analysis was possible because of the robustness of the current experimental procedure which included numerous replications (15 total spargers) and extensive data points available to discern key slope changes. HLCs determined using the gas stripping technique were 57, 33, and 30 Pa m(3) mol(-1) for 1,2,4,5-TeCB, PeCB, and HCB, respectively. In comparison to literature values, current TeCB and HCB HLCs were within wide reference ranges spanning approximately an order of magnitude for each chemical. PeCB HLC of the current study was two times lower than the lowest reference data.

EVALUATION OF A MICRO CARRIER WEIGHTED COAGULATION FLOCCULATION PROCESS FOR THE TREATMENT OF COMBINED SEWER OVERFLOW

Modified bench scale jar tests were conducted to evaluate a treatment strategy for combined sewer overflow (CSO) generated during wet-weather conditions in Windsor, Ontario, Canada. Alum and an anionic polymer (Polymer A-3330) were used as a primary coagulant and coagulant aid, respectively. Commercially available silica sand was employed as the micro carrier. Under the operating conditions optimized in the study, alum dose of 9.7 – 17.8 mg l-1 as Al3+ and polymer dosage of 1.0 – 1.8 mg l-1 were observed to be the most effective in solids removal. Addition of the micro carrier (MC) up to 3 g l-1 significantly increased the settleability of suspended solids, and about a five-fold increase in settleability was observed with 3 g l-1 MC. In the size range of < 300 μm and at 3 g l-1 concentration, the effect of MC size on the performance of the process was observed to be insignificant. Using the developed process, suspended solids and BOD removal efficiencies of > 98% and > 60%, respectively, were obtained with wet-weather flow after 8 minutes of settling, under both low and high suspended solids conditions.

Oxidation of Emerging Contaminants during Pilot-Scale Ozonation of Secondary Treated Municipal Effluent

The transformation of 41 target emerging contaminants in secondary treated municipal wastewater effluent in Canada was examined at pilot-scale, at transferred ozone doses of 2.8 mg/L (0.46 O3/mg DOC) and 4.4 mg/L (0.72 mg O3/mg DOC). In general, transformation efficiencies of CECs either increased or were retained at the higher ozone dose. The higher ozone dose of 0.72 mg O3/mg DOC (Zspec = 0.6 mg O3/mg DOC) was sufficient to transform 21 of the 31 detected CECs by over 80% as well as achieving the disinfection target of < 200 MPN E. coli per 100 mL.

Investigation of Hydrophobic Organic Carbon (HOC) Partitioning to 1 kDa Fractionated Municipal Wastewater Colloids

Natural organic matter from the aquatic environment passing a 1 kDa filter has been hypothesized to not contribute appreciably to hydrophobic organic compound (HOC) partitioning; however, to our knowledge this limit has not been verified experimentally for any sorbate/sorbent system. Presently, colloidal organic carbon (COC) < 1 kDa approached 70% of the total COC (<1.5 μm) mass in primary effluent (PE) from a municipal wastewater treatment plant. Partitioning of HOCs 1,2,4,5-tetrachlorobenzene, pentachlorobenzene, and hexachlorobenzene to COC for both 1.5 μm and 1 kDa filtrates of PE was investigated using the gas-stripping technique. Contrary to the hypothesis, significant HOC-COC partitioning to the 1 kDa filtrate was observed with organic carbon-normalized partitioning coefficients (logKCOC) of 4.30, 4.36, and 3.74 for 1,2,4,5-TeCB, PeCB, and HCB, respectively. Further, partitioning to COC < 1 kDa dominated the overall partitioning of the three chlorobenzenes in the 1.5 μm filtrate, and the partitioning behavior did not follow the trend based on hydrophobicity (KOW). The results show that significant partitioning of HOC may occur to OC < 1 kDa and highlights the need for further experiments with other HOCs and COC characterization to better understand and explain the observed partitioning.

Toxic impact assessment of a manufacturing process: illustrative application to the automotive paint process

The paper discusses the application of steady‐state mass balance models for evaluating the fate of a chemical in a multi‐media environment as part of the process of impact assessment and pollution prevention in a manufacturing industry. The model results are integrated into an index that combines steady‐state emissions, substance partitioning and persistence properties, inter‐media transfer rates, exposure pathways and toxicity. The index, called the Index of Potential Toxic Impact (IPTI), can then be used as part of the relative toxic impact assessment of industrial processes. The approach is applied to evaluate the relative toxic impact to human health of solvent selection in the automotive paint process using a four‐stage toxicological impact assessment process.

Wastewater Colloidal Organic Carbon: Characterization of Filtration Fractions Using 1H NMR.

The current study separates colloidal organic carbon (COC) of municipal wastewater using membrane and ultrafiltration filters followed by characterization using 1H nuclear magnetic resonance (NMR) and UV absorbance with the goal of determination of size-specific characteristics, which may be used to correlate contaminant partitioning to natural COC. Passing fractions included 49.7, 44.8, 39.3, and 33.1 mg/L COC for filter sizes 1.5 μm, 0.45 μm, 100 kDa, and 1 kDa, respectively. The methodology used for processing COC prior to 1H NMR characterization was novel and successful in concentrating COC without modification of structures, which is the general drawback of other separation techniques such as resin extractions. This concentration technique is quite simple (i.e., not dependent on specialized instrumentation) and allows much shorter NMR experimental durations saving time and cost of analysis. Further work using NMR techniques will allow for greater understanding of COC molecular characteristics and be valuable for use in predictive modeling improvements.