A group of five TTL members visited Cumberlow Green Composting facility on 3 October, togged up in our wellies ready for a wet farm yard visit. We were met by Mark Simpkins (Contract Manager for Hertfordshire County Council) and James Hodge (the owner of the site), who both gave us a tour. We were seeing the site which for obvious reasons was after the day’s work had finished and the workers gone home.
Each day the collecting lorries take their morning’s collection straight onto the weighbridge at the front of the site. HCC pays for the weight of each load delivered and the operation thereafter is what James can make pay by turning the green waste into either agricultural or horticultural grade soil improver.
Once weighed in, the waste is deposited in an enclosed building and the first operation is for litter pickers to manually remove items that can easily be seen not to be green waste, while smaller sundry matter gets through and is only removed at the end of the processing.
The day’s load is taken by a conveyor belt to a machine that shreds the green waste, before being moved to the next stage of the process. The 2nd stage involves placing the waste in two barriers of sealed concrete vessels (tunnels), where air is constantly pumped in to ensure aerobic decomposition takes place. The temperature naturally rises as decomposition takes place, monitored by probes to ensure that the correct temperature is reached and maintained, thus ensuring the destruction of both plant and animal pathogens in line with government Animal Bi-Products regulations. Once the material reaches 65 c or above for more than 3 days, it can then be transferred into the next barrier of tunnels , where this process is repeated.Once the materials have reached the required temperatures in both sets of tunnels, the load will be removed from the tunnel and added to a ‘windrow’ for the composting to continue for approx. 8 – 10 weeks . Windrow composting is a more traditional way to compost green material and the smell was discernible; a bit like silage, I thought.
Earlier this year residents in North Herts were prepared for the arrival of a purple bin and the new regime; cardboard was no longer to go with green waste in the brown bin – which to those of us who compost at home, was very anti-intuitive. Mark showed some bits of cardboard that had survived the process almost intact because it was backed up with straw board; other cardboard was laminated with plastic and won’t break down hence the change in collection arrangements, which we learned had been responded to very successfully in North Herts despite protests in The Comet.
So now the last process was reached where the composted material was sieved to remove the persistent un-compostable materials and pushed though a 40mm sieve for agricultural use and a 10mm sieve for horticulture, known to us as Ace of Hearts Soil Conditioner. Quite a lot of debris that should never have been in the brown bin remains and for which James can find no use and sadly has to go to landfill.
I had strong misgiving about Ace of Hearts before this visit as I only used my brown bin as a last resort to dispose of woody material I couldn’t compost. Mark told us that not everyone is keen on home composting for a number of reasons and that North Herts produces approximately 15,000 tonnes of green material per year. I also felt that I knew what was in New Horizon Organic and Peat Free but I didn’t know what a soil conditioner was. I was a bit stunned to learn that Ace of Hearts has a wide range of trace elements which are obviously very valuable if added to improve the soil but if used neat (!) it would actually burn and possibly kill plants because of the strength of the phyto nutrients. Now I know this I may pay the bit extra for the bumper sized bag and improve the quality of my beds. I’m left feeling that perhaps Ace of Hearts is a secret waiting to get out.