Teaching Eco-Friendliness


Teaching Eco-Friendliness


Malima, who has a PhD from MIT, also swims with dolphins

An excellent person to ask about the topic of ‘recycling systems’ is former MIT scholar and researcher, Malima I. Wolf. 

Malima completed her PhD in Mechanical Engineering from MIT in 2011, and went on to become a Rocca Fellow at the Politecnico di Milano, in Italy.

She continues to research recycling systems extensively. She presented her work at The International Symposium on Sustainable Systems and Technologies in 2010.

Just One Question

Malima, can you break down the concepts you have researched into frameworks that we can easily apply?

Response from Malima

Karim, there are so many places I could go with this question!

First, let me explain the role of recycling in the larger picture of resource conservation. About a third of world energy use (and consequently, a third of world carbon emissions) comes from manufacturing. The majority of the energy in the manufacturing sector is used to make raw materials before they are turned into recognizable products.

Chemicals, steel, cement, paper, plastics, and aluminum are some of the top material sectors for energy consumption. We expend all this energy on making materials, so why throw away the materials when a product doesn’t work anymore?

Recycling can capture these materials, which can then be incorporated into new production, preventing the need to make new materials. Besides the energy and emissions savings, there are also the more tangible environmental benefits, including reductions in ore mining, deforestation, the chemicals released to the environment, and the rate of land-filling. And as you mention, recycling is a great entrance into being green-minded. In most industrialized nations recycling is something anyone can do, and paying more attention to your trash helps you think about your consumption.

Now, that makes recycling sound like a rosy proposition, but there are complications:

Collecting materials, separating them, and refining them into a state where they can be used to substitute for new production requires money and resources.

Some materials aren’t worth recycling because it takes too much energy, some products contain too many mixed materials to separate, some ways of collecting materials for recycling are too expensive.

Sorting it all out is complicated, so I figured I would share some answers to questions about recycling I have received in the past.


What happens after I put my recycling bin on the curb?

Let me first say, recycling works differently in different places. Like trash collection, it’s dependent on your municipality:

If you live in a town where you put all your recyclables in one bin, a recycling truck comes to collect the recyclables and take them to a local first stage recycling facility. Again, what these look like on the inside depend on your municipality. In some places workers hand sort recyclables, but newer systems often use specialty equipment to take the place of hand labor, including density separators, magnets, metal detectors, eddy current separators that target non-ferrous metals, and computer vision and sensor systems that can discern between different kinds of plastics.

Separated recyclables are sent out from the facility to specialty handlers that either separate the products further or refine the old materials into new. What gets made out of these recycled materials can vary: almost all steel in products contain some recycled portion, while most recycled plastics are used in downgraded applications. Some portion of materials at each of these stages will be deemed unusable, because they don’t belong in the recyclables stream in the first place or are misidentified into the wrong stream, and will be sent to landfills.

Should I put tetra packs, small appliances, batteries in curbside recycling bins?

Where you should drop off different recyclables, how they are collected, and how they are processed are different everywhere. Check out your town’s utilities website for a description of what waste products go where, and try to follow it as closely as you can.

(But you probably shouldn’t put batteries in your curbside recycling!)

Does recycling cost my local government a lot of money?

The cost (or profit) of recycling varies from town to town. The added costs for recycling come from the additional collection infrastructure needed, but recyclables have a sale value. In my town, the local government sells its collected curbside recyclables to the local recycling facility at a price based on the commodities market, while it has to pay (roughly $80 per ton) to send trash to landfill. So my town saves money by recycling. The traits that correlate with your town saving money through recycling are large sized, green-minded populations, and a distance from cheap landfill.

Which are the most effective things to recycle?

Well, if I have to pick just one category of things that I think you should never skip on recycling, I’d say metal products, like cans.

The technology for metals recycling is well developed, so metals you put in the recycling should be re-used in new production. The energy savings from using recycled metals is quite large, to the point that even with the added energy, environmental, and economic costs from transportation, sorting, and refining; the outcome is almost always beneficial in all three of those aspects.

What’s the deal about plastic bags?

My city says not to put plastic bags in the recycling…

Plastic bags are actually recyclable, but not by conventional methods.

The problem is, plastic bags are thin films. The automatic techniques used to identify and separate heavier gauge plastic products like bottles and containers don’t work well on the thin bags. They can often get sorted into paper product recyclables streams because of their light weight. On top of that, plastic bags are stretchy and tough, they get wound around moving parts, jamming recycling equipment. Shut downs to clear these plastic bags are frequent, even with dedicated facility employees plucking plastic bags out of the incoming stream. Grocery stores are starting to have drop off bins for just plastic bags, but otherwise they should be reused or thrown in the trash.

Recycling is an emerging field, and energy, environmental, and economic cost balances are improving for most products and materials.

My main message here to those living in industrialized areas is to participate fully in the recycling programs available to you through your city or town and through companies. For example, for manufacturer take-backs or specialty waste collections offered by retailers.

Participation is key for economies of scale and to push innovation in recycling.