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:
