Does every facility have the same classification scheme? No. In fact it’s better if they don’t. The classification scheme can follow regulatory categories (hazardous, radioactive) but large facilities usually have more categories than that. The waste manager determines which categories are appropriate.
Waste management is difficult partly because the waste is heterogeneous. Variety increases costs for collection, storage, treatment, and disposal. Segregation, one of the principles of medical waste management, is important, and having different categories supports segregation, but there is a trade-off as more categories increase complexity.
This is a judgement call. More categories results in the waste within each category being more homogeneous and offers more potential for reducing costs in treatment and disposal. But past a certain point there are diminishing returns. The downsides include too many containers, too much cognitive load on the employees (in the segregation), and too many opportunities for accidental cross-contamination.
For legal reasons, you should have separate streams for
If you normally generate these types.
And for economic (cost-saving) reasons you should have separate streams for
Some other potential streams (evaluate for your facility):
Richness is a simple count of the number of different types. The boundaries of different types of waste are not straightforward necessarily, but are drawn from a combination of judgment calls (from experienced engineers/waste managers), formal regulations, and industry norms. Types of treatment may inform waste categories, but should not dictate categories by themselves. Ways to characterize waste include:
So richness is just a count of different types. One facility may produce four categories of waste, and another six categories. The second facility is more rich in waste. The word “rich” implies that richer is better than less rich, and in the field of ecology this is generally true. But it is not true in the field of waste management. Richness makes things more complicated and expensive.
We can get a more nuanced characteristic of waste diversity if we factor in the amounts of each type of waste. The Shannon Index, borrowed from information science, takes into account variety (richness) and quantities (however measured) to come up with a measure of diversity. Also called the Shannon Wiener index.and Shannon-Weaver index. Related measures include Renys entropy and the Simpson Index.
How useful are these indices in waste management? For day-to-day activities, not useful. But for long-term planning, strategic planning, it can possibly be of use, especially when comparing situations at different facilities. Or in planning locations of facilities. If you can put operations in locations such that the diversity index is lower, all other things being equal, you win.
A set of waste streams with high richness but low diversity can be said to be even. Evenness is neither good nor bad from a waste management standpoint.
Is it OK to use the term “toxic waste” occasionally?
No, as waste management professionals we need to be precise in our language. Waste is ‘toxic’ only if, when it is biologically harmful or fatal to a living organism when it gets inside the body. The US federal government definition of hazardous waste, RCRA, lists four characteristics that might make a waste hazardous, and toxicity is one of them. So while it might be technically correct to call a material toxic waste, most potentially harmful waste you encounter is probably not toxic. Stick to the familiar categories just to be safe.