O trabalho consiste em uma análise experimental comparativa do processo de combustão e de transferência de calor ao longo de uma fornalha flamotubular. Os combustíveis utilizados são o óleo diesel e o biodiesel proveniente de óleo de fritura. Uma outra parcela deste trabalho é investigar os níveis de emissões gasosas no processo de combustão do biodiesel em fornalha flamotubular. Não seria possível realizar esta pesquisa sem uma fornalha flamotubular dotada de câmaras calorimétricas, janelas de observação e extração de gás, e totalmente instrumentada. Assim, foi efetuado em paralelo o projeto e a construção de uma fornalha calorimétrica flamotubular. Os parâmetros utilizados para se analisar os combustíveis na fornalha são: rendimento térmico, taxa de fluxo mássico, temperatura de chama e perda de carga. Observou-se que o óleo diesel apresentou maior taxa de transferência de calor para a maioria das seções expostas à chama. Na região onde o corpo da chama não está presente, a taxa de transferência de calor do biodiesel torna-se ligeiramente superior. Em relação às emissões gasosas observaram-se baixos níveis de poluentes / This work consists in a comparative experimental evaluation of the process of combustion and heat transfer along a flame tube furnace. The fuels used are diesel oil and ethyl ester from waste vegetable oil (biodiesel). Another part of this work investigates the percentage of pollutants and emissions of gases in the flame tube furnace. It would not be possible to carry out this research without a flame tube furnace endowed with calorimetric chambers, windows of observation and extraction of gases, and totally instrumented. Thus, the project and the construction of a flame tube calorimetric furnace were done parallel. The parameters used to analyze the fuels in the furnace are: thermal efficiency, mass flow rate, temperature of flame and draught loss. It was observed that diesel oil presented higher heat transfer rate in most parts of the furnace that was near the flame. In the region where the body of flame is not present, the heat transfer rate of biodiesel becomes a little higher. In relation to emission of gases, it was observed low indexes of pollutants

This thesis centers around an electric arc furnace (EAF) at a steel mini-mill in Wilton, IA. First, the thesis replicates previous optimization attempts. Next, the modeling is greatly altered to produce a much improved steel-melting model. Then, a new optimal control system is created and used to reduce energy and fuel costs over the melting process. Finally, results are presented. This thesis shows that when the new optimal control is simulated, the system shows significant energy and fuel savings.

The present work focuses on mineral reactions and slag formation of LKAB olivine iron ore pellets (MPBO) subjected to reducing conditions in the LKAB experimental blast furnace (EBF). The emphasis is on olivine reactions with surrounding iron oxides. Many factors influence the olivine behaviour. The study was performed by use of micro methods; optical microscopy, micro probe analysis, micro Raman and Mössbuer spectroscopy and thremodynamic modeling. During manufacturing, in oxidising atmosphere at high temperature (1350°C), olivine alterations occur through slag formation and rim reactions with iron oxides and other additives. To be able to describe olivine behaviour in the rather complex blast furnace reduction process one has to consider factors such as reactions kinetics, reduction degree of iron oxides, vertical and horizontal position in the furnace and reactions with alkali. Samples were collected from the EBF both from in shaft probing during operation and from excavation following quenching of the EBF. The initial slag forming olivine consist of primary forsterite – (Mg1.9Fe0.1)SiO4 – with inclusions of hematite and an amorphous silica rich phase, a first corona with lamellae of magnesioferrite, olivine and orthopyroxene, a second corona of amorphous silica and magnesioferrite. During reduction in the upper shaft in the EBF (700-900°C) Fe3+ reduces to Fe2+. The amorphous silica in the second corona absorbs alkali, Al, Fe2+, Mg, and Ca and form glasses of varying compositions. The lamellae in the first corona will merge into a single phase olivine rim. With further reduction the glasses in the second corona will merge with the olivine rim forming an iron rich olivine rim and leaving the elements that do not fit into the olivine crystal lattice as small silicate glass inclusions. Diffusion of magnesium and iron between olivines and iron oxides increase with increasing temperature in the lower shaft of the EBF (750-1100°C). In the cohesive zone of the EBF (1100-1200°C) Fe2+ is not stable any longer and Fe2+ will be expelled from the olivine as metallic iron blebs, and the olivine will form a complex melt with a typical composition of alkali-Al2O3-MgO-SiO2. Alkali plays an important role in this final olivine consumption. The quench time for samples collected with probes and excavation are minutes respectively hours. A study of the quench rate’s effect on the phases showed no differences in the upper shaft. However, in the lower shaft wüstite separates into wüstite and magnetite when wüstite grows out of its stability field during slow cooling of excavated samples. There is also a higher alkali and aluminium deposition in the glass phases surrounding olivines in excavated pellets as a result of alkali and aluminium gas condensing on the burden in the EBF during cooling. Coating applied to olivine pellets was studied in the EBF with the aim to investigate its behaviour, particularly its ability to capture alkali. The coating materials were kaolinite, bauxite, olivine and limestone. No significant reactions were observed in the upper shaft. In the lower shaft a majority of the phases were amorphous and reflecting the original coating compositions. Deposition from the EBF gas phase occurs and kalsilite (KAlSiO4) is found in all samples; coating used for binding alkali is redundant from a quality perspective.

Modern manufacturing systems need new types of scheduling methods. While traditional scheduling methods are primarily concerned with sequencing of jobs, modern manufacturing environments provide the additional possibility to process jobs in batches. This adds to the complexity of scheduling. There are two types of batching namely: (i) serial batching (jobs may be batched if they share the same setup on a machine and one job is processed at a time. The machine which processes jobs in this manner is called as discrete processor) and (ii) parallel batching (several jobs can be processed simultaneously on a machine at a time. The machine which processes jobs in this manner is called as batch processor or batch processing machine). Parallel batching environments have attracted wide attention of the researchers working in the field of scheduling. Particularly, taking inspiration from studies of scheduling batch processors in semiconductor manufacturing [Mathirajan and Sivakumar (2006b) and Venkataramana (2006)] and in steel casting industries [Krishnaswamy et al. (1998), Shekar (1998) and Mathirajan (2002)] in the Management Studies Department of Indian Institute of Science, this thesis addresses a special problem on scheduling batch processor, observed in the steel casting manufacturing. A fundamental feature of the steel casting industry is its extreme flexibility, enabling castings to be produced with almost unlimited freedom in design over an extremely wide range of sizes, quantities and materials suited to practically every environment and application. Furthermore, the steel casting industry is capital intensive and highly competitive. From the viewpoint of throughput and utilization of the important and costly resources in the foundry manufacturing, it was felt that the process-controlled furnace operations for the melting and pouring operations as well as the heat-treatment furnace operations are critical for meeting the overall production schedules. The two furnace operations are batch processes that have distinctive constraints on job-mixes in addition to the usual capacity and technical constraints associated with any industrial processes. The benefits of effective scheduling of these batch processes include higher machine utilization, lower work-in-process (WIP) inventory, shorter cycle time and greater customer satisfaction [Pinedo (1995)]. Very few studies address the production planning and scheduling models for a steel foundry, considering the melting furnace of the pre-casting stage as the core foundry operation [Voorhis et al. (2001), Krishnaswamy et al. (1998) and Shekar (1998)]. Even though the melting and pouring operations may be considered as the core of foundry operations and their scheduling is of central importance, the scheduling of heat-treatment furnaces is also of considerable importance. This is because the processing time required at the heat treatment furnace is often longer compared to other operations in the steel-casting foundry and therefore considerably affects the scheduling, overall flow time and WIP inventory. Further, the heat-treatment operation is critical because it determines the final properties that enable components to perform under demanding service conditions such as large mechanical load, high temperature and anti-corrosive processing. It is also important to note that the heat-treatment operation is the only predominantly long process in the entire steel casting manufacturing process, taking up a large part of total processing time (taking up to a few days as against other processes that typically take only a few hours). Because of these, the heat-treatment operation is a major bottleneck operation in the entire steel casting process. The jobs in the WIP inventory in front of heat-treatment furnace vary widely in sizes (few grams to a ton) and dimensions (from 10 mm to 2000 mm). Furthermore, castings are primarily classified into a number of job families based on the alloy type, such as low alloy castings and high alloy castings. These job families are incompatible as the temperature requirement for low alloy and high alloy vary for similar type of heat-treatment operation required. These job families are further classified into various sub-families based on the type of heat treatment operations they undergo. These sub-families are also incompatible as each of these sub-families requires a different combination of heat-treatment operation. The widely varying job sizes, job dimensions and multiple incompatible job family characteristic introduce a high degree of complexity into scheduling heat-treatment furnace. Scheduling of heat-treatment furnace with multiple incompatible job families can have profound effect on the overall production rate as the processing time at heat-treatment operation is very much longer. Considering the complexity of the process and time consumed by the heat treatment operation, it is imperative that efficient scheduling of this operation is required in order to maximize throughput and to enhance productivity of the entire steel casting manufacturing process. This is of importance to the firm. The concerns of the management in increasing the throughput of the bottleneck machine, thereby increasing productivity, motivated us to adopt the scheduling objective of makespan. In a recent observation of heat-treatment operations in a couple of steel casting industries and the research studies reported in the literature, we noticed that the real-life problem of dynamic scheduling of heat-treatment furnace with multiple incompatible job families, non-identical job sizes, non-identical job dimensions, non-agreeable release times and due dates to maximize the throughput, higher utilization and minimize the work-in-process inventory is not at all addressed. However, there are very few studies [Mathirajan et al. (2001, 2002, 2004a, 2007)] which have addressed the problem of scheduling of heat-treatment furnace with incompatible job families and non-identical job sizes to maximize the utilization of the furnace. Due to the difference between the real-life situation on dynamic scheduling of heat-treatment furnace of the steel casting manufacturing and the research reported on the same problem, we identified three new class of batch processor problems, which are applicable to a real-life situation based on the type of heat-treatment operation(s) being carried out and the type of steel casting industry (small, medium and large scale steel casting industry) and this thesis addresses these new class of research problems on scheduling of batch processor. The first part of the thesis addresses our new Research Problem (called Research Problem 1) of minimizing makespan (Cmax) on a batch processor (BP) with single job family (SJF), non-identical job sizes (NIJS), and non-identical job dimensions (NIJD). This problem is of interest to small scale steel casting industries performing only one type of heat treatment operation such as surface hardening. Generally, there would be only a few steel casting industries which offer such type of special heat-treatment operation and thus the customer is willing to accept delay in the completion of his orders. So, the due date issues are not important for these types of industries. We formulate the problem as Mixed Integer Linear Programming (MILP) model and validate the proposed MILP model through a numerical example. In order to understand the computational intractability issue, we carry out a small computational experiment. The results of this experiment indicate that the computational time required, as a function of problem size, for solving the MILP model is non-deterministic and non-polynomial. Due to the computational intractability of the proposed MILP model, we propose five variants of a greedy heuristic algorithm and a genetic algorithm for addressing the Research Problem 1. We carry out computational experiments to obtain the performance of heuristic algorithms based on two perspectives: (i) comparison with optimal solution on small scale instances and (ii) comparison with lower bound for large scale instances. We choose five important problem parameters for the computational experiment and propose a suitable experimental design to generate pseudo problem instances. As there is no lower bound (LB) procedure for the Research Problem1, in this thesis, we develop an LB procedure that provides LB on makespan by considering both NIJS and NIJD characteristics together. Before using the proposed LB procedure for evaluating heuristic algorithms, we conduct a computational experiment to obtain the quality of the LB on makespan in comparison with optimal makespan on number of small scale instances. The results of this experiment indicate that the proposed LB procedure is efficient and could be used to obtain LB on makespan for any large scale problem. In the first perspective of the evaluation of the performance of the heuristic algorithms proposed for Research Problem 1, the proposed heuristic algorithms are run through small scale problem instances and we record the makespan values. We solve the MILP model to obtain optimal solutions for these small scale instances. For comparing the proposed heuristic algorithms we use the performance measures: (a) number of times the proposed heuristic algorithm solution equal to optimal solution and (b) average loss with respect to optimal solution in percentage. In the second perspective of the evaluation of the performance of the heuristic algorithms, the proposed heuristic algorithms are run through large scale problem instances and we record the makespan values. The LB procedure is also run through these problem instances to obtain LB on makespan. For comparing the performance of heuristic algorithms with respect to LB on makespan, we use the performance measures: (a) number of times the proposed heuristic algorithm solution equal to LB on makespan (b) average loss with respect to LB on makespan in percentage, (c) average relative percentage deviation and (d) maximum relative percentage deviation. We extend the Research Problem 1 by including additional job characteristics: job arrival time to WIP inventory area of heat-treatment furnace, due date and additional constraint on non-agreeable release time and due date (NARD). Due date considerations and the constraint on non-agreeable release times and due date (called Research Problem 2) are imperative to small scale steel casting foundries performing traditional but only one type of heat treatment operation such as annealing where due date compliance is important as many steel casting industries offer such type of heat treatment operations. The mathematical model, LB procedure, greedy heuristic algorithm and genetic algorithm proposed for Research Problem 1, including the computational experiments, are appropriately modified and\or extended for addressing Research Problem 2. Finally, we extend the Research Problem 2 is by including an additional real life dimension: multiple incompatible job families (MIJF). This new Research Problem (called Research Problem 3) is more relevant to medium and large scale steel casting foundries performing more than one type of heat treatment operations such as homogenizing and tempering, normalizing and tempering. The solution methodologies, the LB procedure and the computational experiments proposed for Research Problem 2 are further modified and enriched to address the Research Problem 3. From the detailed computational experiments conducted for each of the research problems defined in this study, we observe that: (a) the problem parameters considered in this study have influence on the performance of the heuristic algorithms, (b) the proposed LB procedure is found to be efficient, (c) the proposed genetic algorithm outperforms among the proposed heuristic algorithms (but the computational time required for genetic algorithm increases as problem size keeps increasing), and (d) in case the decision maker wants to choose an heuristic algorithm which is computationally most efficient algorithm among the proposed algorithms, the variants of greedy heuristic algorithms : SWB, SWB(NARD), SWB(NARD&MIJF) is relatively the best algorithm for Research Problem 1, Research Problem 2 and Research Problem 3 respectively.

The aim of the present thesis was to study the heat flows in the blast furnace hearth lining by experimental measurements and numerical modeling. Thermocouple data from an operating furnace have been used throughout the work, to verify results and to develop methodologies to use the results in further studies. The hearth lining were divided into two zones based on the thermocouple readings: a region with regular temperature variations due to the tapping of the furnace, and another region with slow temperature variations. In an experimental study, the temperatures of the outer surfaces of the wall and bottom were measured and compared with lining temperature measured by thermocouples. Expressions to describe the outer surface temperature profiles were derived and used as input in a two-dimensional steady state heat transfer model. The aim of the study was to predict the lining temperature profiles in the region subjected to slow temperature variations. The methodology to calculate a steady state lining temperature profile was used as input to a three-dimensional model. The aim of the three-dimensional model was primarily to study the region with dynamic lining temperature variations caused by regular tappings. The study revealed that the replacement of original lining with tap clay has an effect when simulating the quasi-stationary temperature variations in the lining. The study initiated a more detailed study of the taphole region and the size and shape of the tap clay layer profile. It was concluded, that in order to make a more accurate heat transfer model of the blast furnace hearth, the presence of a skull build-up below the taphole, erosion above the taphole and the bath level variations must to be taken into consideration. / QC 20100706

The influence of supplementary materials such as slag, metakaolin and limestone in steam-cured ternary and quaternary cement blends on physical and chemical hydration mechanisms was studied by analyzing the evolution of non-evaporable water content, hydration products and compressive strength. The role of limestone in hydration reactions of cement was also investigated. These properties were studied through the use of differential thermal and thermogravimetric analyses, as well as the loss-on-ignition, X-ray diffraction and compressive strength tests at 1, 3, 7, and 28 days. Research findings revealed that it is possible to replace up to 40% cement with other materials and still achieve compressive strengths similar to mixtures with a 25% cement replacement at 0.34 w/b ratio. Additionally, ternary limestone mixtures exhibited superior mechanical properties to ternary metakaolin mixtures. Lastly, limestone powder was determined to behave as inert filler, accelerating hydration at early ages through heterogeneous nucleation.

A mathematical model to simulate the reaction kinetics of dust–carbon composite agglomerates in an RHF was developed. Major chemical, thermal and physical phenomena taking place during RHF treatment were formulated and the corresponding equations were solved to yield the trend of solid composition, temperature and gas composition of the agglomerates. The model calculation results indicate that the pellet reduction is accelerated by the reducing gas from high–volatile reductants if the gas is released after the pellet temperature is sufficiently high for reduction. The reduction of zinc oxide can also be represented using the model by implementing its small particle size caused by the inherent vaporization/re–oxidization process that zinc comes through in a melter. It was demonstrated that the proposed model can be used as an engineering tool to determine the optimum operating conditions for the RHF process to promote recycling a wide range of waste materials.

The influence of supplementary materials such as slag, metakaolin and limestone in steam-cured ternary and quaternary cement blends on physical and chemical hydration mechanisms was studied by analyzing the evolution of non-evaporable water content, hydration products and compressive strength. The role of limestone in hydration reactions of cement was also investigated. These properties were studied through the use of differential thermal and thermogravimetric analyses, as well as the loss-on-ignition, X-ray diffraction and compressive strength tests at 1, 3, 7, and 28 days. Research findings revealed that it is possible to replace up to 40% cement with other materials and still achieve compressive strengths similar to mixtures with a 25% cement replacement at 0.34 w/b ratio. Additionally, ternary limestone mixtures exhibited superior mechanical properties to ternary metakaolin mixtures. Lastly, limestone powder was determined to behave as inert filler, accelerating hydration at early ages through heterogeneous nucleation.

A mathematical model to simulate the reaction kinetics of dust–carbon composite agglomerates in an RHF was developed. Major chemical, thermal and physical phenomena taking place during RHF treatment were formulated and the corresponding equations were solved to yield the trend of solid composition, temperature and gas composition of the agglomerates. The model calculation results indicate that the pellet reduction is accelerated by the reducing gas from high–volatile reductants if the gas is released after the pellet temperature is sufficiently high for reduction. The reduction of zinc oxide can also be represented using the model by implementing its small particle size caused by the inherent vaporization/re–oxidization process that zinc comes through in a melter. It was demonstrated that the proposed model can be used as an engineering tool to determine the optimum operating conditions for the RHF process to promote recycling a wide range of waste materials.

Phosphorus (P) is one of the essential nutrients for living organisms; however, excess P in aquatic systems often causes environmental and ecological problems including eutrophication. Removal of P from domestic wastewater, industrial wastewater, and agricultural organic-waste systems is required to minimize loading of P to receiving water bodies. A variety of sorbents or filter materials have previously been evaluated for P removal, including natural materials, industrial byproducts, and synthetic products. Among these materials industrial byproducts were reported as most effective. However, only a few of these studies were based on field experiments. Pharmaceutically active compounds (PhACs) and acesulfame-K (an artificial sweetener) are emerging contaminants observed in wastewater. The removal of PhACs in conventional wastewater treatment systems has been studied; however, few studies on alternative treatment systems are available. Studies related to the removal of acesulfame-K are even more limited. This thesis was focused on evaluation of basic oxygen furnace slag (BOFS), a byproduct from the steel manufacturing industry, as a potential reactive media for P removal from surface water and wastewater. The removal of PhACs and acesulfame-K in wastewater treatment systems containing BOFS as a treatment component was also evaluated. The effectiveness of BOFS for removing P from lake water was evaluated in a three year pilot-scale hypolimnetic withdrawal P treatment system at Lake Wilcox, Richmond Hill, Ontario. Phosphate concentrations of the hypolimnion water ranged from 0.3 to 0.5 mg L-1. About 83-100% P was removed during the experiment. The reactive mixtures were changed each year to improve the performance of the treatment system. Elevated pH (9-12) at the effluent of the treatment system was adjusted by sparging CO2(g) to near neutral pH. Elevated Al was removed through this pH adjustment. Elevated concentrations of V were removed in a column containing 5 wt% zero valent iron (ZVI) mixed with sand (0.5 m3) at the end of the BOFS based column. Removal of P in the BOFS based media is attributed to adsorption and co-precipitation at the outer layer of BOFS. Geochemical modeling results showed supersaturation with respect to hydroxyapatite, ß-tricalciumphosphate, aragonite, and calcite. Solid phase analyzes of the BOFS based reactive media collected after completion of the year 2 experiment (spent media) through combination of scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and X-ray absorption near edge structure spectroscopy (XANES) support the presence of calcium phosphate minerals on the outer layer of the spent media. A multistep wastewater treatment experiment was carried out in an indoor facility at the Center for Alternative Wastewater Treatment, Fleming College, Lindsay, Ontario, Canada. This experiment evaluated the removal of P, ammonia, cBOD5, COD, E. coli, total coliform, and trace metals in a series of treatment cells including a mixing cell, a vertical subsurface flow aerobic cell, a vertical subsurface flow P treatment cell containing BOFS, and a horizontal subsurface flow anaerobic cell. About 97-99% removal of P, NH3, cBOD5, E. coli, and total coliform; and ~72% removal of COD were achieved in the treatment system. The mixing cell and the aerated cell reduced the concentrations of P, ammonia, cBOD5, E. coli, and total coliform significantly and the P treatment cell provided additional treatment. However, the primary objective of the P treatment cell was to reduce P concentrations to the acceptable range according to the water quality guidelines. The P treatment cell had successfully fulfilled this objective. Elevated concentration of Al and V were also observed in the P treatment cell effluent. The concentration of Al decreased to below the guideline value of 0.075 mg L-1 after introducing a pH adjustment unit between the P treatment cell and the anaerobic cell. The concentration of V was decreased in the anaerobic cell effluent. However, the effluent concentration of V was much higher than the guideline value. Geochemical speciation modeling results showed supersaturation with respect to hydroxyapatite, ß-tricalciumphosphate, aragonite and calcite along the flow path. Accumulation of P on the outer layer of the spent BOFS media was identified by energy dispersive X-ray spectroscopy (EDX). Although X-ray photoelectron spectroscopy (XPS) can provide information to a depth of 5-7 nm from the outer layer of the spent media, both Ca and P were positively identified in some of the samples. Accumulation of P at the edge of the grains of the spent media was clearly identified on the element map of polished cross-sections and corresponding FTIR spectra. The phosphate and carbonate functional groups were identified by the distribution of different vibrational frequencies through FTIR spectroscopy. The presence of calcite and hydroxyapatite were inferred based on the wave numbers assigned for these minerals in the literature. Finally, X-ray absorption near edge structure spectroscopy (XANES) on the outer layer samples from the spent BOFS media and corresponding linear combination fitting analysis indicated the presence of ß-tricalciumphosphate, hydroxyapatite, and calcium phosphate dibasic. Based on the observations from the indoor wastewater treatment experiment, a multistep demonstration-scale outdoor wastewater treatment experiment was conducted to investigate the applicability of the integration of the P treatment technology and engineered wetland technology at a relatively large scale prior to a full-scale field installation. The anaerobic treatment cell was not included in this outdoor system because this unit did not efficiently remove ammonia and metals (e.g. V) from the Cell 4 effluent in the indoor system. A 10 cm layer of zero valent iron was placed at the bottom part of the down flowing P treatment cell to address the elevated V in the P treatment cell effluent observed in the indoor system and also to treat PhACs in the effluent. More than 99% removal of P, E. coli, and total coliform; >82, >98, and >76% removal of ammonia, cBOD5, and COD were achieved in this treatment system. The effluent pH (10.88±1.47) was neutralized and the concentration of V remained < 0.006 mg L-1. The Al concentration was adjusted to <0.075 mg L-1 with the neutralization of pH. Geochemical speciation modeling results showed the supersaturation of hydroxyapatite, ß-tricalciumphosphate, octatricalciumphosphate, aragonite, and calcite. The FTIR and XANES spectra showed the presence of calcium phosphate minerals on the outer layer of the spent media. Removal of the PhACs, including caffeine, ibuprofen, carbamazepine, naproxen, and sulfamethoxazole, and acesulfame-K was monitored in the demonstration-scale outdoor wastewater treatment system, which consisted of five different treatment cells including a horizontal subsurface flow constructed wetland, a vertical subsurface flow aerated cell, a vertical subsurface flow BOFS cell, and a pH neutralization unit. Significant removal of caffeine (>75%) and ibuprofen (50-75%), and moderate removal of sulfamethoxazole and naproxen (25-50%) were observed. The removal of carbamazepine was less effective with <25% removal observed. Acesulfame-K was also persistent along the flow path with <25% removal. This study demonstrated that removal of P from lake water and wastewater in excess of 95% could be achieved using BOFS as a reactive media. Integration of this media into an engineered wetland system enhances its performance in removing nutrients and other wastewater contaminants.