Chemical processing of medical waste


process valve Chemical disinfection, primarily through the use of chlorine compounds, kills microorganisms in medical waste and can oxidize hazardous chemical constituents. Chlorine bleach has been used for disinfecting processes for years – you might use it to clean your underwear and kill the e.coli. Chlorine compounds are used in swimming pools to reduce the risk of disease transmission. Ethylene oxide treatment is another chemical process. It is used to disinfect or sterilize materials equipment that will be reused. It is too expensive to use on equipment or waste that will be sent to a landfill - incineration is better.

Both mechanical grinding and chemical processes are usually batch processes – which you may think of as similar to a washing machine at the laundromat. They can be run in fixed batch sizes and consistent processing times. Liquid medical waste treatnent tank medical waste is often best treated with chemicals, if the medical waste is aqueous; organic liquid waste does not mix well with bleach. But most liquid medical waste is aqueous.

The EPA identifies chemical processing as the most appropriate method to treat liquid medical waste. Treated liquid waste can usually be discharged into the sewer system. Sometimes it goes to a holding tank for testing before discharge.

Oxidation

There are many oxidants on the market. They can be used for liquid waste but can also be used for treatment of slurries and sludges. They may be best for low organic content waste as organic material will eat up the oxidant. The same oxidants are used to treat waste as are used for disinfection.

Reduction

Reduction is the flip side to oxidation, but in treatment it is less common than oxidation. One waste constituent treated by reduction is heavy metals ions, which are converted to a less toxic form or to precipitate

Some Reactants

Potassium permanganate - purchased as purple crystals. Mixed with wet waste to oxidize constituents.

Temp, C Solubility, g/L
0 28
20 65
40 125
60 230
80 350
100 500

Calcium hypochlorite Ca(OCl2

Contains 65 percent available chlorine. Sold as solid tablets or granular. Can be purchased from the pool supply store and industrial suppliers. Comes in 50, 75, and 100 lb fiber drums.

Hydrogen peroxide

Sold at 30 to 70 percent concentration. Special handling required, especially for high concentration solutions. Can decompose if impurities present in storage. Often sold with inhibitors mixed in so no decomposition.

Properties of 50 percent H2O2
Active oxygen, 23.5 wt percent
600 grams of H2O2 per liter
Density = 1.2 g/l
Boiling point = 237 °F
Freezing point = -62 °F

Hydrogen peroxide comes in 30- or 55-gal drums. Also large tankers.

Sodium hypochlorite NaOCl

Sold in aqueous solution - “bleach”. Available chlorine = measure of oxidizing power of active chlorine compared to elemental chlorine. This is not the same as concentration. 5.25 percent NaOCl has 5.0 percent available chlorine.

Reduction Agents

Sodium Borohydride NaBH4
Sold as 12 percent solution in 40 percent sodium hydroxide
Density is 1.4 g/ml

Used to reduce metals: lead, cadmium, mercury, copper, cobalt, nickel

Sulfur Dioxide and Ferrous Sulfate are also reduction agents.

Mechanical Processing

Mechanical treatment does not kill pathogens or disinfect equipment, but it can reduce waste volume and increase the surface area in preparation of further treatment or disposal. Crushers and milling machines break down solid pieces of waste. Mechanical shattering or splintering of waste can also alter its appearance, which can be useful in lessening the psychological impact of the waste on human observers. More on shredders.