Design Questions and Answers


Is there a difference between a waste autoclave and an autoclave for sterilizing equipment?

Yes. The equipment is similar or identical but you should keep autoclaves intended for deactivation of infectious waste separate from autoclaves for sterilization of scalpels.

For one thing, you don’t need to absolutely sterilize most biohazardous waste. You just need to disinfect it. The batch time does not have to be as long.

Good autoclave pages: https://ehs.umass.edu/sites/default/files/Biowaste%20poster_10-30-19.pdf and http://www.wvdhhr.org/wvimw/autoclave.asp

Can I use old tanks rather than buy new ones?

If the tanks function, do not leak, and will stand up to operating temperatures and pressures while full of process fluids, yes. You want to guard against leaks, though, and that means regular inspection of all vessels. If you are operating under pressure, get a boilermaker to come out and check out your equipment.

Do I have to use stainless steel vessels?

Stainless steel is expensive but it resists corrosion much better than regular steel (also called carbon steel or mild steel).

How likely is corrosion?

It depends on the content of the fluid in contact with the equipment. Aqueous solutions with very high or low pH are corrosive, but sometimes neutral pH fluids (such as seawater) can be corrosive, too. More on materials of construction.

Why can’t we just throw everything into an incinerator? Those are hot enough to kill anything.

Incinerators are indeed hot enough to kill all bacteria and fungi and disable all viruses. And although prions are not alive, experts feel exposure to temperatures over 1000 °F destroys prions so they cannot infect anything.

machine We are a fan of incineration technology but there are limits and downsides. For some waste streams incineration is not the best technology. And even when they are appropriate, incinerators are not always widely available.

Further it is often cheaper and safer to use chemical treatment as a treatment technology. It is overly simplistic to think incineration is always the best solution.

What do I do about prions?

Prions are difficult to destroy. They can withstand conventional sterilization processes, and although they are proteins, they can survive enzyme treatment that would denature other proteins. Call in a specialist if you need to handle prions.

Is entropy something to think about in waste treatment design?

Waste treatment by changing chemical or physical characteristics of waste. This is usually accompanied by an increase in entropy in the waste. Waste encapsulation often leaves the actual waste (and its entropy level) unchanged, but increases the overall entropy of the waste plus encapsulation unit. As a practical matter, the engineer usually ignores entropy in design consideration.

How do I know if my process worked?

If you run a batch process as opposed to a continuous one, you can test a sample of every completed batch. This might get expensive and time-consuming, so you have to consider whether it is worth doing.

IF YOUR FACILITY IS PERMITTED (such as by the EPA or a state agency), the permit will state how often you have to test treated waste. It might be every batch or it might be every 20 batches.

Common Abbreviations

IBC - Intermediate Bulk Container - A storage vessel commonly manufactured from high density poly-ethylene.

CIP - Clean in Place - A method of cleaning equipment without removing it. Standard for process equipment where it would be more practical and economical than removing the equipment for cleaning.

API - American Petroleum Institute - The API is the representative for America’s oil and gas industry, whose standards are commonly used as a global guideline for many engineering designs.

SS - Stainless Steel - An alloy of iron, chromium and sometimes nickel and other metals.

FDA - U.S. Food and Drug Administration - Regulatory body for America’s food, beverage and pharmaceutical industries.

EU - European Union - An economic and political union between 27 European countries.

ASME - American Society of Mechanical Engineers - A nonprofit membership organization promoting engineering and allied sciences. It develops mechanical engineering standards regarding the proper design, construction, and testing of many mechanical devices.

HMI - Human-Machine Interface - The interface between the processor machine and the operator. Usually screens, buttons, switches and levers.

PLC - Programmable Logic Controller - An industrial computer used in process control.

Process design.