Implement a computerized raw material inventory tracking system. Maintain product inventory to minimize changeovers for batch operations. Purchase raw materials in totes and other reusable containers. Purchase raw materials with lower impurity levels. Practice first-in/first-out inventory control. Housekeeping Practices
Recycle and reuse wooden pallets used to store drums. Implement procedures to segregate solid waste from aqueous discharges. Implement procedures to segregate hazardous waste from nonhazardous waste. Segregate and weigh waste generated by individual production areas. Drain contents of unloading and loading hoses into collection sumps.
Change filters based on pressure-drop measurements rather than operator preferences. Increase relief valve set pressure to avoid premature lifting and loss of vessel contents. Optimize reflux ratio for distillation columns to improve separation. Optimize batch reaction operating procedures to minimize venting to process flares. Optimize electrostatic spray booth coater stroke and processing line speed to conserve coating. Implement a nitrogen conservation program for processes that commonly use VOCs. Minimize the duration for which charging hatches are opened on VOC-containing vessels. Use vent condensers to recover solvents when boiling solvents for vessel cleaning purposes. Reduce the number or volume of samples collected for quality control purposes. Develop and test new markets for off-spec products and other waste. Blend small quantities of off-spec product into the salable product. Cleaning Procedures
Use mechanical cleaning methods instead of organic solvents.
Operate solvent baths at lower temperatures and cover when not in use.
Reduce the depth of the solvent layer used in immersion baths.
Reduce the frequency of the solvent bath change-out.
Use deionized water to prepare cleaning and washing solutions.
Develop written operating procedures for cleaning and washing operations.
Source: Chadha, 1994.
The metal finishing industry uses a variety of physical, chemical, and electrochemical processes to clean, etch, and plate metallic and nonmetallic substrates. Chemical and electrochemical processes are performed in numerous chemical baths, which are following by a rinsing operation.
Various techniques for recovering metals and metal salts, such as electrolysis, electrodialysis, and ion exchange, can be used to recycle rinse water in a closed-loop or open-loop system. In a closed-loop system, the treated effluent is returned to the rinse system. In an open-loop, the treated effluent is reused in the rinse system, but the final rinse is accomplished with fresh water. An example of a closed-loop system is shown in Figure 3.3.6.
Due to the cost associated with purchasing virgin solvents and the subsequent disposal of solvent waste, onsite recycling is a favorable option. Recycling back to the generating process is favored for solvents used in large volumes in one or more processes.
Some companies have developed ingenious techniques for recycling waste streams that greatly reduced water consumption and waste regeneration. At a refinery, hydrocarbon-contaminated wastewater and steam condensate are first reused as washwater in compressor aftercoolers to prevent salt buildup. The washwater is then pumped to a fluid catalytic cracker column to absorb ammonium salts from the vapor. The washwater, now laden with phenol, hydrogen sulfide, and ammonia, is pumped to a crude column vapor line, where organics extract the phenol from the wastewater. This step reduces the organic load to the downstream end-of-pipe wastewater treatment process which includes steam stripping and a biological system (Yen 1994).
A general pollution prevention option in the paper and pulp industry is to use closed-cycle mill processes. An example of a closed-cycle bleached kraft pulp mill is shown in Figure 3.3.7. This system is completely closed, and water is added only to the bleached pulp decker or to the last
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