Ever wondered what happens to your green waste and food waste?
The council are putting on a second free tour of the local composting facility in South Mimms, together with a look at the new Anaerobic Digester taking all our food waste – on March 7th 10.30 – 12.30pm.
The first trip during Sustainable StAlbans Week was fully booked, and was a surprisingly enjoyable experience: below Liz Sefton gives us a creative look into the tour:
Pedant Power for the Green Bin!
‘Two of my favourite things came together in the Sustainable St Albans’ tour of the Agrivert Composting facility at South Mimms: the magic of composting and an enduring love of heavy plant and machinery.
I have always wondered about those neat, steaming, but oddly unsmelly, heaps of brown stuff at the side of the M25. Then Stuart, the Sgt Major turned Eco-Warrior, who runs the Agrivert Composting facility, entered my life and a wonderful welly-wearing morning enjoying an industrial tour became a highlight of my year.
So, you ask, what happens at South Mimms?
Six men, with their big yellow scoopers and a straddle turner, plus the all-important grading machine, make tonnes of lovely compost out of the grass, leaves, and prunings in our green bins. In summer, they take in over 300 tonnes of green waste from 5 District Councils, including St Albans, and turn it into compost of a standard suitable for agricultural purposes – supplying nutrient and structure to local farmers’ fields. In winter it is reduced to 150 tonnes a day.
The Agrivert team knows exactly which streets put what in their green wheelie bins – because every lorry-load of green waste is checked in separately. Then the waste is tipped out into a huge bay, mixed, then piled neatly into one of the 15 large, long, insulated composting tunnels which meet optimum width and height requirements for good composting. Air is pulsed through each long heap to speed composting and the temperature is monitored to ensure that bugs and weed seeds are killed and to ascertain when the composting bacteria have slowed in their work. This process is repeated with remixed materials in a second set of tunnels where the composting bacteria become re-enlivened and the end-product further refined.
It is very cosy in the composting tunnels, and not at all smelly. However, after the warm-up comes the cool down!
The almost finished compost is stacked in long piles outside where a wonderful machine called a ‘straddle-turner’ – does what is says as the driver steers it back and forth along the piles. Large sticks and roots, and far too many alien items, remain in the compost at this stage.
Finally, the sifter and grader sorts the compost. It removes the foreign bodies (which should not have been in the green bins to start with), and the large odd bits of uncomposted woody material, and piles up lovely sweet-smelling, brown stuff which is all ready for the farmers’ fields.
The ‘should never have been included’ old shirts, shoes, toys, DIY rubbish, etc removed from the compost, is sent for landfill, and the ‘oversize’ woody material, which has been sifted out, is sent back to the beginning of the process: here it is useful in providing necessary aeration to compacted green waste, such as grass clippings, helping to speed the next batch of composting. They don’t waste much at Agrivert!
With their ‘green waste in and great compost out’ process the Agrivert site at South Mimms is a local asset we should all be proud of.
And now, understanding the industrial composting process better, I, am proud to be a total pedant about what goes into my green waste wheelie bin: it’s green garden waste and woody prunings only for me! ‘
Liz Sefton Feb 2017