Villaservice Industrial Site Visit and Commentary

Today we drove up to the Villaservice Plant, located just outside of Villacidro. After some confusion over parking, we disembarked and wandered inside for a presentation and video about the plant. Villaservice is a four part operation: landfilling, anaerobic digestion, composting, and waste water treatment.

It was originally a landfill. The first landfill was opened in 1993, and closed in 2006, this landfill accepted all of the municipal solid waste (MSW), as it was developed before the new laws were enforced. Once it was closed, a new landfill was opened. It currently only accepts the non-organic fraction of the waste, as well as the sludge from the anaerobic digestion plant. It is due to close in the next year, so a new one is currently under construction. The biogas is collected from the landfills, but because less organic fraction reaches the landfill, this is expected to decrease over time.

The anaerobic digestion plant began its service in 2002, and until 2009 accepted unsorted household waste. Once the regulations called for the separation of municipal solid waste, only the organic fraction was accepted. As of 2013, it was operating at an annual 12.3 Gg under capacity. Before the separation laws, the MSW was put through a rotating trammel screen and exposed to an electromagnet. This sorted the organic from the inorganic. Next, the waste went through wet mechanical treatment, which included the use of a hydro-pulper and a hydro-cyclone to create the organic slurry. From there, the slurry went through several centrifuges in order to produce biogas, liquid discharge (which is then sent to the wastewater treatment plant), and solid discharge (which is sent to the landfill).

The composting plant was functional in 2010, with a capacity of 51.3 Gg/yr. Its components are kitchen waste, green waste, sewage sludge, and digestate. As of 2013, it was operating 38 Gg/yr under capacity.   

This visit has left me with some questions:

Why are some parts of the plant operating under capacity? Is this a problem of collection? What is happening?

The total consumption of the plant is 3.7 million kWh of electricity, but the plant only produces 2.3 million kWh of electricity. Of that production, 639,000 kWh is transferred to the grid. How does the plant operate when it requires an additional 2 million kWh of electricity to function? Why do they sell their power, when their operation seems unsustainable?

The speaker mentioned problems heating the anaerobic digestion tanks, but if both the landfill and the digestion plant create biogas, why are their problems heating the tanks? Couldn’t the heat be collected and used to ensure optimum biogas production?  

Why does Villaservice landfill their mixed municipal solid waste, when it could otherwise be incinerated for energy recovery? Why did they stop placing the bails in distinct areas of the landfill, for ease of mining later?  

In terms of the composting plant, what sort of losses do they take per ton of compost? If the first composting plant took a loss of 118 euro per ton, what sort of loss does Villaservice take? Do they have plans for future profitability, in the event of the cancellation of government subsidies? Once the landfilling process is discontinued (either by reaching the third landfill’s capacity or by their illegalization), how does Villaservice plan to use its batches of compost?

Maybe I didn’t quite understand some of the points the speaker made, but there seems to be a lot going on at this plant. The potential for inefficiencies got my industrial engineering brain turning, and I came up with a scenario…

I think if I were to implement a system in the United States, I would create a waste management plant based on the layout of Disneyland. Walt Disney designed Disneyland with what has come to be known as a “hub and spoke” method. Given that the United States collects all of its MSW together (except in some places where they collect recyclables separately), I would place a receiving and sorting building in the middle as the hub, and place the managing plants around it. I would then decide the location of each of the separate managing facilities. I would plan to have composting, anaerobic digestion, landfilling, waste to energy, wastewater treatment, and recycling. Some things clearly need to be placed together, for this I made an activity relationship chart, and then a finalized suggested layout: