Process modification, waste reduction

Group 2 includes long-term reduction measures involving process modifications or process substitutions to eliminate problem wastes. This second group of corrective actions fall into two investment categories - moderate and high. Such projects... 

If the program continues and additional reductions are desired, more expensive and more complex projects begin to emerge (Phase II). These are often associated with equipment modifications, process modifications and process control and may include the addition or adaptation of auxiliary equipment for simple source treatment, possibly for recycle. This phase usually has little immediate ROI, and more inclusive approaches to assessing the economics of the operation (estimating costs for waste handling, long-term liability, risk) are needed to justify the continued pollution-prevention operation. 

Source reduction is usually the least expensive approach to minimizing waste. Many of these techniques involve housekeeping changes or minor inplant process modifications. 

It is not currently feasible to achieve a zero discharge of chemical pollutants from metal finishing operations. However, substantial reductions in the type and volume of hazardous chemicals wasted from most metal finishing operations are possible.8 Because end-of-pipe waste detoxification is costly for small- and medium-sized metal finishers, and the cost and liability of residuals disposal have increased for all metal finishers, management and production personnel may be more willing to consider production process modifications to reduce the amount of chemicals lost to waste. 

The petroleum industry requires very large, capital-intensive process equipment. Expected lifetimes of process equipment are measured in decades. This limits economic incentives to make capital-intensive process modifications to reduce wastes generation. Reductions in waste generation can be accomplished by process modifications ... 

The checklist is divided into three areas 1) Material Storage and Handling, 2) Production Processes and 3) Treatment Alternatives. Material degradation, samples, spills, storage, and inspections are addressed in the first section. Production processes include source reduction for process bath solutions and rinse systems, resource recovery and recycling, and solvent management. Treatment Alternatives focuses on process water pretreatment, modification of conventional wastewater treatment, and alternative waste treatment methods. Each of these subsections follow the question and answer format. 

For this paper, process modification for the purpose of source reduction in a plating operation will be defined as changes in equipment which lead to reduced generation of wastes. Purposely excluded are separation and concentration technologies covered elsewhere in this conference. The intent of this section is to list options, in rough order of simplicity of implementation, and provide information about each... 

Tables 14.18.1 and 14.18.2 give the reported solvent releases and transfers from the organie ehemieal industry. Large quantities of solvents are involved. The organic chemical industry produced the second largest quantity of VOC and the second largest releases and transfers. The industry is actively working to reduee solvent use because of the high costs (waste treatment, fines, liabilities, etc). There are many efforts under way to reduce environmental emissions and improve safe practices. The initiatives include process modifications such as a reduction in non-reactive materials (e.g., solvents) to improve process efficiency, a reduction in the concentration of chemicals in aqueous solution, and improved R D and process engineering. Equipment modifications are planned to reduce leaks, prevent equipment breakdown, and improve die efficiency of emission control devices.

The preferred option for preventing pollution is to avoid generating wastes whenever possible (source reduction). Examples include process modifications to reduce waste volumes and material substitution to reduce toxicity. From EPA s Exemption of oil and gas exploration and production wastes from federal hazardous waste regulations... 

Frequently, waste streams can be eliminated or reduced by process modifications or improvements. A notable example of this is the use of save-rinse and spray-rinse tanks in plating lines. This measure brings about a substantial reduction in waste volume and frequently a net reduction in metal dragout. 

Modifications of the manufacturing process can yield substantial waste reduction. Some such modifications are of a chemical nature. Changes in chemical reaction conditions can minimize the production of by-product hazardous substances. In some cases, potentially hazardous catalysts, such as those formulated from toxic substances, can be replaced by catalysts that are nonhazardous or that can be recycled rather than discarded. Wastes can be minimized by volume reduction, for example, through dewatering and drying sludge. 

Already, some U.S. companies have discovered how waste reduction can offer substantial benefits quickly at low cost. In the past, EPA s Industrial Pollution Control Program emphasized process modification to control industrial effluents." ... 

Reduced Emissions and Waste Minimization. Reducing harmful emissions and minimizing wastes within a process by inclusion of additional reaction and separation steps and catalyst modification may be substantially better than end-of-pipe cleanup or even simply improving maintenance, housekeeping, and process control practices. SO2 and NO reduction to their elemental products in fluid catalytic cracking units exemplifies the use of such a strategy (11). 

Its appeal Hes in the fact that synthesis gas can be produced from trash, municipal sewage, scrap wood, sawdust, newsprint, or other waste. The early work of Fischer and Tropsch on methanol synthesis showed that ethanol could be obtained in the process (165) and that by certain modifications the proportion of ethanol in the product could be increased (166). The Hterature concerning this method is extensive (167—176). The conditions that favor ethanol formation are 125—175°C and 1.42 MPa (14 atm) in the presence of reduction catalysts such as powdered iron. 

Source reduction includes any in-plant actions to reduce the quantity or the toxicity of the waste at the source. Examples include equipment modification, design and operational changes of the process, reformulation or redesign of products, substitution of raw materials, and use of environmentally benign chemical reactions. 

Selective catalytic reduction (SCR) and selective noncatalytic reduction processes (SNCR) are widely employed in large industrial and utility boiler plants, as well as in municipal waste incineration plants and other combustion processes. They are used to complement mechanical improvements (such as low NOx burners and furnace design modifications) as an aid to reducing the emission levels of NOx, S02, and other noxious gases into the atmosphere. 

It should be noted that in most cases wastestreams are composed not only of process chemistry but also of by-products of chemical reactions and electrolysis. This fact becomes important when attempting to recover and return those escaped" solutions (e.g., dilute metal-bearing rinse streams) which are often the focus of process and operation modification. It is usually not sufficient to stop generating waste simply by returning it to its source. Usually some type of purification or separation, themselves sources of waste generation, will eventually be required. This quickly puts the lie to the myth of "closed-loop" operations. While source reduction is powerful, it is only reduction, not elimination. 

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