Date of visit: 11 August 2009.
Tour guide: Colin Marriage, Unit Manager,
Viridor.
Tour organiser: Deborah Wargate.
Background
Foxhall household waste recycling centre
is one of the 18 sites in Suffolk (new window)
that take household garden waste including grass cuttings, tree
and bush cuttings, weeds and plants. Once garden waste is put in
the green containers staff remove any obvious contamination that
can be reached and then the waste is compacted to increase the
bulk collected in each load. The waste (with additions from
landscape gardeners and councils in North Essex) is then taken
to a composting area at the adjoining landfill site, processed
and turned into Composting Association PAS100 soil conditioner
for agricultural use, landscape gardeners or for gardens.
Composting Association PAS100
Compost is now being used extensively in landscaping,
horticulture and agriculture. It is a good source of organic matter
and can be used as:
- a general soil improver for either sandy soil (enriches) or
clay soil (breaks it up);
- in turf establishment and maintenance;
- as a turf top dressing;
- for container, tree and shrub planting; and
- as a mulch.
It is also being used more and more as a key component in
manufactured topsoils.
BSI PAS 100 certification scheme has been set up to ensure that
compost producers are manufacturing a product that is consistent,
traceable, safe and reliable. One that does not contain weed seeds
(tested by adding water and light to a sample to see if anything
grows), that contains the right nutrients (tested by ensuring
tomatoes grow in it), and does not contain heavy metals.
Foxhall composting facility
The first stop was at the windrows which are formed from green
waste shredded to a suitable size to aid the composting process and
to ensure that biodegradation is achieved. It is the responsibility
of the man overseeing this process to remove any Horsetail,
Japanese Knotweed and other invasive plants (which are then
landfilled at least 5 metres below the surface) and treated
timber.
Windrows are banked up against the prevailing wind to reduce
odours being released beyond the plant and an odour suppression
system (Airborne 10, a sophisticated surfactant chemical in a water
carrier which interacts with odorous gases, absorbs them and
presents them to the environment to naturally biodegrade). Airborne
10 neutralises odours to remove them from the air, rather than
masking them, and scrubs dust particles from the atmosphere.
Temperature readings are taken initially on a daily basis and
then three times a week to ensure the windrows are warm enough to
kill weed seeds and harmful bacteria (between 60 and 80ºC in the
centre of the windrows), but not so hot that the necessary bacteria
dies off or that the pile spontaneously combusts.
The material is turned by a JCB making a hole in the centre of
the windrow and moving the stuff from the outside into that. This
increases oxygen to aid bacteria and adjusts temperatures. When
conditions are too dry, pumped groundwater is added using an
agricultural sprayer (the process uses on average 100,000 cubic
metres of water a year).
Composting takes about 13 weeks and the finished material is
screened through a 10mm sieve for compost and a 25mm sieve for soil
improver. This prevents contaminants such as pieces of plastic bags
from entering the final product. Any heavily contaminated material
is used to cover rubbish landfilled at the end of each day. Any
larger organic material left after screening, such as logs is set
aside for firewood, while larger roots and sticks are added to the
centre of a new windrow to continue composting and improve
aeration. These larger items aid oxygenation at the bottom of the
windrow via the air spaces that they trap.
Foxhall produces about 5 to 6,000 tonnes of soil improver per
year from the 10 to 15,000 tonnes of green waste received on the
site.
Foxhall landfill site
We saw the cell that has been closed for ten years, grassed and
trees planted in one corner. Ten ewes and lambs are grazed on this
in the spring when the grass is sufficiently long. A methane
extraction facility is in place and this produces 1MW of
electricity for exporting each year (enough to power 257 homes at a
consumption of 3880kWh per year).
We saw the new cell, capacity of 400,000 cubic metres, which
should be sufficient until at least 2021 and which cost £1.1million
(which explains the cost of skip hire and other waste related
activities). It is bentonite clay, lined with strong plastic and
the bottom covered in rounded stones below which are perforated
pipes - this all ensures that leachate does not contaminate
surrounding groundwater and is in fact reused to keep the waste
moist and the bacteria active.
Seagull activity is kept down by a bird controller who comes in
three days a week and by use of bird scarers.
We saw another landfill cell capped by bentonite and being
readied for landscaping.
Vehicles used are predominantly diesel due to the power needed
to shift waste. No other suitable low carbon vehicle currently
exists - electric is not only not powerful enough but needs cabling
which does not exist or a generator which is once again powered by
diesel.