Wireless Loggers Monitor Composting Success

Green garden and kitchen waste is being recycled by Vital Earth to help save the peat bogs and address the UK’s landfill issues. The output is organic, peat free compost and the Tinytag Radio Data Logging System from Gemini Data Loggers (UK) monitors the temperature of the ‘green compost’ during processing. This £10 million site in the Derbyshire Dales is one of the most advanced in-vessel composting sites in the UK.

In the UK, 99 thousand tonnes of green waste, which would otherwise go to landfill, is collected over a 12-month period. This is cleaned of debris (glass, metal, plastic) and water added before being enclosed in a carefully controlled vessel, where it aerates. This process allows the friendly bacteria to heat up naturally while destroying weeds and disease causing pathogenic microorganisms. The temperature needs to exceed 60 degrees for 2 days on two occasions to satisfy DEFRA; Vital Earth ensures it reaches a minimum temperature of 65 degrees for PAS100 during the sanitisation stage. During the subsequent maturation stage, the Tinytag Radio system will track a rising temperature over a period of about 6 weeks and then a temperature levelling trend that informs when the material is stable and ready for the next stage. During this period, the material is housed in a 2- acre building called a Maturation Hall, which has the capacity for 14-thousand tonnes of material. Here it is heaped into 24 separate heaps called ‘windrows’ where it continues to aerate, cool and mature. Tinytag radio loggers and probes are placed in the windrows to track this process.

The Tinytag Radio loggers send their temperature readings to a computer in the control room via a receiver unit positioned in the roof of the Maturation Hall. This can then be accessed remotely by other computers on the same network. By monitoring the temperature in this way, the technical team at Vital Earth is able to follow the trend of the bacteria heating up, the compost maturing and then cooling. The radio system provides the reliability and accuracy essential in the aeration process, as well as convenience.

Commenting on the radio loggers, Vital Earth’s John Wakefield said: “The automatic collection of temperature data has saved a great deal of time and effort and has helped to ensure that we comply with PAS100. The system was simple to install and we have found the TinyTag products to be extremely flexible and reliable.”

The Tinytag Radio data logging system can also be integrated into a control process via a Modbus interface that provides read-only access to data logger configurations and instantaneous measurements. This data can then be used to control process equipment and a trial to control fans is the Maturation Hall is being considered.