Waste Treatment

Waste Treatment
It is nearly impossible to eliminate waste completely, but it is essential to remove or degrade harmful material before it is discharged or disposed of. On many sites ground water must also be collected and processed, as it may contain traces of the chemicals made and used on the site. In the event of accidental spillage this collection is essential.

It is common for all the waste to be treated together in one plant, rather than treating waste from each process separately. This "end of pipe" treatment can be achieved by physical, chemical or biological means.

Physical Materials are separated using a range of methods including filters, distillation, centrifugation, membrane techniques and "steam stripping" (volatile substances removed using steam).
Chemical The type of reaction depends on the nature of the waste, but may involve neutralisation of acids/alkalis, oxidation of toxic substances, or electrochemical reduction of metal ions. In some cases the treatment results in a useful product.
Biological Microorganisms degrade many materials. The process may be aerobic (with oxygen) or anaerobic. Aerobic treatment results in the production of carbon dioxide from respiration, but anaerobic treatment results in both carbon dioxide and methane (which can be collected and used as a fuel).
As treatment is generally more economic in larger quantities, some chemical manufacturers will choose to have their solid and liquid waste collected and treated off-site by a specialist company. This may be by a company that specialises in recovering energy by the blending of solvent wastes for use as a fuel - more details can be found in the Energy Reduction section
Novel Waste Treatment
Some materials are particularly difficult to break down. This is often the case with waste from pharmaceutical manufacturing. Research into the use of ultrasound (high frequency sound) is giving promising results. In liquids the sound waves can produce very high temperatures and pressures in short-lived bubbles - several thousand °C and several hundred atmospheres - while the bulk of the liquid remains cool. These conditions are sufficient to break down contaminants into degradable products.

Supercritical fluids have also been used to remove contaminants from soil. Researchers have used supercritical carbon dioxide to remove organic waste, including the pesticide DDT, from soil.

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