Seeing how others do it!
Like you I have been to my local Household Waste Recycling site several times in recent weeks with twiggy prunings which I can't compost at home and I often wondered what happens to all the green waste they collect. Last week I was fortunate enough to join a group visiting a commercial composting facility and can report a truly interesting and eye-opening experience.
Shown round by delightful Jane we were treated to an explanation of the whole process from green waste being tipped from large lorries to the final graded products.
Tipped into huge green mountains the very first thing to happen is sorting to remove any contamination not suitable for the composting process. It is quite amazing and a bit shocking to see the odd garden fork, bits of wire and garden plastic in the general heap not to mention disposable nappies sometimes too!
When contamination has been removed the remaining green waste is put through a large (noisy!) industrial shredder. The shredded material is then transferred to the large, steaming, prism-shaped piles known as windrows. This is when the composting process really begins. Windrow composting which has three main phases:
Phase 1 is the sanitisation phase taking 2 weeks. During this time a high temperature of 65 - 80 degrees C must be maintained if the weed seeds and pathogens are to be killed off. Daily monitoring of the heaps ensures both the temperature and moisture content stay high with a temperature over 65 degrees C for a minimum of 7 consecutive days! Where does the heat come from? It's generated by the microbes and bacteria breaking down the garden waste. During this time the compost is turned a minimum of twice to maintain aerobic decomposition throughout the heap (windrow).
Phase 2 is the stabilisation phase - a further 7 weeks of actively managed composting where temperatures are maintained at 55 degrees C. During this time the compost is turned at least 6 more times and is monitored regularly too.
At the end of these first two phased the compost is ready for screening to remove all the un-composted oversize green waste. This is returned to be re-shredded.
Phase 3 is the maturation phase. Waiting in stock piles for a minimum of 2 weeks before it can be used for gardens and farmers' fields across the country.
My memorable visit means I will never need to wonder again about what happens to the green waste at Household Waste Recycling sites! Annie
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