Gore(tm) composting system
The Timaru District Council’s GoreTM Cover Compost System
The GoreTM cover compost facility is the first of its kind in the Southern Hemisphere.
- Each kerbside collection truck assembles the contents of 240-litre green-lid bins per day.
- Numbers of bins collected by a truck ranges from 600 – 850 bins per day depending on urban density and distance to travel.
- Each bin weighs on average 18kg and contains lawn clippings, garden waste, food waste and dirty paper.
- Kerbside trucks deliver their greenwaste to the Timaru Eco Compost Facility.
- Greenwaste is also received from commercial contractors and from transfer stations.
Material delivered to the site in the green bins is ground into smaller pieces using a large shredder. The Crambo shredder is very powerful and can even break down large tree stumps.
Loader Building a Windrow
Water is added to the shredded material. A loader then places this into a 50m long row of organic material, called a windrow, which is 8m wide and 3.8m high. Each windrow contains 750 m3, which reduces in volume by 30% during the composting process.
The windrows are covered with GoreTM covers, using a large cover winding machine. The covers help to speed up the compost process, maintain moisture, allow the windrow to “breathe” under aerobic conditions and reduce odours.
The composting site accommodates eight windrows. New material is placed on pads 1 – 4 for four weeks. The cover is then removed, and the windrow is moved to pads 5 or 6 and covered for two more weeks. This process is then repeated with material moved to pads 7 and 8, but no cover is used.
The custom-built cover winder machine enables easy laying and removing of covers. A single cover weighs nearly a tonne! The machine will only operate in calm conditions.
Oxygen levels, temperature and moisture are keys to the composting process. Oxygen and temperature probes assisted by a computer keep track of conditions in the windrow. The compost needs to be kept at a minimum temperature of 550C for at least 3 days to kill weed seeds and pathogens. Temperatures up to 800C have been recorded in the windrows.
Underneath the windrows are two air channels that blow air into the compost to ensure that the compost process is kept aerobic and high temperatures are maintained
After 8-10 weeks material is tested to make sure it meets the New Zealand Composting Standard before it is sieved through the trommel to produce fine, nutrient-rich compost.