Tour de Garbage: Grand Finale

Yesterday we had our third (and last) technical visit of the Dialogue. Each of the treatment facilities we have visited so far have focused on different waste streams, This one was no exception. Traveling to an industrial area only 20 minutes away from Cagliari, we actually saw three separate facilities. The first was a commercial composting operation for organic (food and yard) waste. The second was a waste-to-energy plant, which is basically just a fancy name for a trash incinerator. The third was an electronic waste recycling facility. The first two were part of a complex that also included a wastewater treatment plant and hazardous waste facility. The E-waste facility was 5 minutes down the road.

The first technical visit we made to Arborea had a composting facility, so this was very similar except on a much larger scale. The facility mixes precise ratios of food and yard waste, then stores them in cells to mature. The cells are 100 meters long, 4 meters wide, and 3 meters tall. Aeration vents embedded in the floor ensure the proper decomposition of the material, and as the compost ages it is transferred down the row of 15 cells until it reaches the end, where it is moved to piles to mature. One thing that I found interesting about the plant was the siting of the facility. The plant sits right next to acres and acres of protected wetlands, where flamingos and other important species live. In order to prevent any contamination, the whole complex is built over a plastic liner and elevated on a layer of soil. A collection system around the perimeter catches any water runoff, which is then treated.
Turns out hundreds of tons of rotting food STINKS. We got to observe the plant from the safety of the control room.
Our next stop on Tour de Garbage: the waste-to-energy (WTE) plant. The idea behind a WTE is essentially this: it's better to burn any combustible non-recyclable material and get energy than to place it in a landfill, where it will just sit. This decreases the amount of coal burned to produce electricity, and reduces the volume of waste placed in a landfill (ash from incineration is about 10% of the original size of the waste). Some quick numbers about the plant:

  • the plant has 4 ovens. 3 of them treat municipal waste, a fourth treats hazardous materials such as toxic industrial waste and hospital 
  • the plant generates 14.3 MW of electricity. 4.8 MW provide power to the composting plant, wastewater treatment facility, and offices of the facility. The remaining 9.5 are fed back into the grid
  • the plant incinerates 650 tons of waste per day. 500 of this is municipal, the additional 150 tons is hazardous. This amounts to waste from 700,000 people on the island
  • Over 200 trucks bring waste to the plant every day, dumping it into a massive storage bay that can hold 7,500 tons
  • Heat from incineration is used to dry sludge from the nearby wastewater treatment plant. The high-energy dried sludge can then be burned for more energy
The plant runs 24/7 to incinerate all of the waste, and 85 employees are on the site to keep it operational. Since constant use is hard on all of the equipment, it must be shut down for about a month every 2 years to hastily perform repairs. The plant was in this repair stage while we visited, so we didn't actually get to see it in action. It was still cool to walk around the facility and see just how massive the plant was.


The incineration plant, with smoke stack on the left and the building housing incinerators on the right. 
Mounds of waste sit in the storage bay. 
After touring the incineration plant and learning what some of the major components were, we hopped in the bus and went over to the electronic waste plant. The facility is designed to handle three different types of electronic waste: refrigerators, small appliances, and washing machines. The center handles 36 tons of waste per day, accounting for 80% of all Sardinia's electronic waste.

We spent most of our time checking out the refrigerator section.  Rows and rows of warehouse were filled with old and defunct refrigerators. Workers moved the refrigerators onto a conveyor belt, where components are disassembled before the fridge is shredded. One of the important steps in this process is capture of freon, the primary cooling agent. Freon is a chlorofluorocarbon (CFC) that harms the ozone layer. The workers had special clamps with hoses that attached to the cooling units, extracting the freon for disposal at another location. The pumps were then removed, drilled into, and the oil drained. The now-empty fridges were moved into a shredder, which separated bits of plastic and metal into separate collection bins by density.

Clamps with hoses remove the freon from ghosts of fridges past.

Pumps are drilled into, and then oil drained into the pan on the right. 
The final product of shredding- a container full of metal scraps will be recycled. 

Something that really stood out to me: at the end of the trip, someone asked who paid for the operation of the plant. The plant manager explained that due to an Enhanced Producer Responsibility policy in the EU, manufacturers of electronics are responsible for the lifetime of the whole product, including disposal.

Carbon Sequestration Technology
Today we had a lecture from Giovanna, a researcher at University of Cagliari. She shared some of the research she has been doing on climate change mitigation strategies. Essentially, CO2 emissions can be reduced by reacting them with an alkaline substance. The resulting carbonate is a natural material that is stable and will hold carbon dioxide that would otherwise be released into the atmosphere. She was looking specifically at the ability to use this technology in a metal refining process. One of the byproducts of the refining is an alkaline substance. When CO2 emissions from the process are passed over the alkaline, the carbon is captured and the resulting carbonate can actually be used as a construction material. Her results found that up to 16% of the carbon dioxide from the refining process can be removed if this technology is effectively implemented.

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