Dilution hazardous environments

Early decisions made purely for process reasons often can lead to problems of safety and health (and environment) which require complex and often expensive solutions. It is far better to consider them early as the design progresses. Designs that avoid the need for hazardous materials, or use less of them, or use them at lower temperatures and pressures, or dilute them with inert materials will be inherently safe and will not require elaborate safety systems. ... 

Refrigeration, like dilution, reduces the vapor pressure of the material being stored, reducing the driving force (pressure differential) for a leak to the outside environment. If possible, the hazardous material should be cooled to or below its atmospheric pressure boiling point. At this temperature, the rate of flow of a liquid leak will depend only on liquid head or pressure, with no contribution from vapor pressure. The flow through any hole in the vapor space will be small and will be limited to breathing and diffusion. 

The future will bring further increase in concern over the environmental impact of chemical operations. The liquid effluents must not only be controlled, they must also be rendered harmless to the environment. This requires removal of the hazardous substances. For many of the dilute waste solutions, solvent extraction has proved to be an effective process. This is even more true for recycling of mixed metals from various industries. Nevertheless, the increasing amounts of wastes from human activities require much more to be done in this field. 

Environment Canada recently developed an evaluation system based on effluent toxicity testing, capable of ranking the environmental hazards of industrial effluents [185]. This so-called Potential Ecotoxic Effects Probe (PEEP) incorporates the results of a variety of small-scale toxicity tests into one relative toxicity index to prioritize effluents for sanitation. In the index no allowance has been made for in-stream dilution, therefore the acmal risk for environmental effects is not modeled. The tests performed on each effluent are the following bacterial assay [V.fisheri (P. phosphoreum), Microtox], microalgal assay S. capricornutum) crustacean assay (C. dubiay, and bacterial genotoxicity test E. coli, SOS-test). 

Lactic acid is caustic in concentrated form and can cause burns on contact with the skin and eyes. It is harmful if swallowed, inhaled, or absorbed through the skin. Observe precautions appropriate to the circumstances and quantity of material handled. Eye protection, rubber gloves, and respirator are recommended. It is advisable to handle the compound in a chemical fume hood and to avoid repeated or prolonged exposure. Spillages should be diluted with copious quantities of water. In case of excessive inhalation, remove the patient to a well-ventilated environment and seek medical attention. Lactic acid presents no fire or explosion hazard but emits acrid smoke and fumes when heated to decomposition. 

One of the key concerns facing regulators is that any toxicity discharged will be recalcitrant ( hard ) and, even if initial toxicity is diluted below any PNEC, effects may occur as toxic material builds up in the environment. Consequently, some regulators are interested in reducing the potential of effluents to cause a problem by reducing the amount of toxicity discharged (a hazard based approach) irrespective of the risks posed. 

Determination of the concentrations of a hydrochloricInitric acid in a mixture. Prepare an external standard mixture for gas chromatographic analysis as follows. Add nitric acid (0.5 g) and hydrochloric acid (0.1 g) to dichloromethane (10 ml) followed by scrubber solution (10 ml). Stir for 15 min then dilute to 50 ml with dichloromethane. Generate a mixed acid vapour environment by placing a small beaker containing the acids in equal volume on a hot-plate stirrer inside a fume cupboard and heat gently. Sample the atmosphere as detailed in (a) but for 10 min. Note the volume sampled. Make 0.5 pi duplicate injections of standard and sample and hence determine the concentrations of the acids in the sample by direct comparison with peak areas of the standard (external standardisation). From this data and the volume of atmosphere sampled determine the short term exposure limit. By comparison with HSE recommended limits would this atmosphere pose a hazard (See Figures 9.15-9.17.)... 

After the patient treated with has been released from hospital, the in the body is excreted primarily in the urine, and ends up in the sewage system and further into the environment. In general the activities are very low, and the dilution and the time it takes from deposition in the soil and return to the food chain make the environmental risk very low. Environmental impact from I has not been measurable. With appropriate regulations, even without storage of urine, sewer disposal of excreta from patients diagnosed or treated with I has been within radiation dose Emits (ICRP-94, 2004) and poses fittle hazard to the public and sewage workers. 

X. Zhu. 2002. Removal of cyanide from dilute solution using a cell with three-phase three-dimensional electrode. J. Environ. Sci. Health A Tox. Hazard. Subst. Environ. Eng. 37(4) 715-24. 

The alkalinity of soluble silicates is their primary hazard. Contact exposure effects can range from irritation to corrosion. Inhaled or ingested sodium silicates are rapidly eliminated in the urine. Trace quantities of dissolved silica are essential to nutrition, but if normal dietary amounts are exceeded, siliceous urinary calculi may result. Dissolved silica is a minor but ubiquitous constituent of the environment. When dissolved silica becomes depleted in natural waters, diatoms are displaced by species that accelerate eutrophication. Commercial soluble silicates rapidly depolymerize upon dilution to molecular species indistinguishable from natural dissolved silica. 

---