Catch the WasteMarch 1, 2006 By: Stephanie vL Henkel, Sensors Sensors
Municipalities typically generate a large amount of compostable material as a byproduct of their wastewater treatment operations. The "green" cities turn this unappealing substance into something of benefit to everyone, but the transformation doesn't happen all on its own.
Automate temperature monitoring of municipal composting operations
Compost is made by first creating large windrows or piles of bio-solid waste material mixed with an amendment such as wood chips. The windrows are laid out in huge, covered warehouses or barns, or outdoors. Once a windrow is created, it is allowed to biodegrade in accordance with EPA guidelines. The temperature, moisture, and oxygen content of the compost during this exothermic process must be monitored and controlled to prevent the matter from spoiling or igniting.
Until recently, the only way to keep an eye on the compost's working entailed putting fixed, hardwired sensors or manual probes into the windrows. But the sensors were invisible to machine operators who came with rotating tillers to turn the piles and add water as needed, or to remove a composted windrow and replace it with new raw material. Goodbye, sensors! Manual monitoring requires someone to walk up and down the windrows, inserting a long probe here and there and writing down the data. Local "hot spots" make such data unreliable, and, if the compost is outside and the weather's bad, the job might not get done.
Embedding removable temperature sensors into the windrows to wirelessly monitor the composting process proved tricky. Compost absorbs radio waves, limiting both the communication range and acceptable sensor placement sites. And the sheer size of the processing barns keeps individual radio signals from sensors at the far reaches of the structure from reaching a central wireless communications hub.
Industrial Telemetry figured out a solution. The BioMESH system embeds wireless-enabled temperature probes into the compost piles. A mesh networking scheme designed by RF Monolithics sends the temperature readings to the next probe closer to the hub, which in turn relays the data on to the hub along with its own report. The sensors, from Reotemp Instruments (www.reotemp.com), are attached to a long metal pole. The tops of the sensors are painted so that the machine operators can readily see and remove them before turning or removing a windrow. And in time, community waste becomes food for community parks and gardens.
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