December 19, 2005 | General

Vermicomposting In Urban Settings

BioCycle December 2005, Vol. 46, No. 12, p. 44
California project evaluates commercial composter for key factors – air flow, feedstocks that include food residuals, and impact on moisture content.
Maria de la Fuente, Rosa Maria Gordillo, Michele Young, Sarah Smith and Mickey Neff

IN LOOKING for a mid-size vermicomposting unit that would be appropriate for diverting food residuals from schools, buildings, restaurants and businesses, the University of California Cooperative Extension-Santa Clara County, California (UCCE SCL), the Santa Clara County Home Composting Education Program, and the City of San Jose Environmental Services Department have teamed up to test the BioSystem 500®.
In 2002, the BioSystem 500 vermicomposting unit was identified as a good fit for a system that was easy to operate, clean looking, and allowed for frequent or heavy loading. It is a two-drawer cabinet system, built with sturdy plastic, and includes a 120 Volt built-in fan/heating system, located behind the bottom drawer, to remove excess moisture. The cost per unit is $1,250.
The Santa Clara County Home Composting Education Program received a BioSystem unit to process cafeteria waste generated from the County Service Center in San Jose. The Program had already been working with the cafeteria at this location for several years, and estimated it was diverting approximately 1,134 kg of food waste/year from the garbage stream into vermicomposting units.
The Program managers decided not to power the fan in the BioSystem unit to test a limited input system. The drawers were loaded with earthworms (Eisenia foetida). Food residuals consisted of coffee grounds and salad bar trimmings, plus a bedding of shredded office and newspapers. It was estimated that 20 gallons of food waste were processed every month. Due to reduced ventilation in the system, leachate tended to accumulate in the collection drawer and one quart or more had to be discarded every other week. The vermicompost harvested was very wet, almost anaerobic, and was removed periodically from the collection trays. The unit received regular maintenance by BioSystem Solutions technical personnel. Despite these attempts, the Program decided to discontinue the use of the system after two years, and return to wood boxes.
A second BioSystem 500 unit was installed in a small barn at Royal Oaks Mushrooms Farm in Morgan Hill, California, where UCCE SCL has other vermicompost research projects. Due to the operational challenges with the unit, it was decided to test the performance of the fan system to prevent excessive moisture accumulation in the modules. Power was not available in the barn, so a solar-panel system was installed to power the fan. The solar power system included (one each): Deep cycle 12 Volt DC battery; 15 Watt /1 Amp ICP Solar Panel (used to charge the battery); ICP Charge Controller (used to control the battery charging rate); and 400 Watt Power Inverter (to convert the 12 Volts DC to 120 Volts AC).
With this configuration, the battery voltage was dropping below the input requirement of the 400-Watt Power Inverter which was then eliminated. Instead, the original 120 Volt AC fan/heating system was replaced by a 12 Volt DC/1.5 Watt fan (80 mm fan with an equivalent air flow), and the fan operation controlled by a timer-switch (7-day, battery powered, 4 Amp). The solar system worked well with two circuits: Circuit 1 going from the solar panel, to the charge controller, to the deep cycle battery. Circuit 2 going from the deep cycle battery, to the 7-day timer, to the fan. The system consumed on average 1.5 Watts from the 15 Watts supplied by the solar panel. The battery-voltage was maintained between 13.0 and 14.2 Volts DC.
The drawers in the unit were then loaded with earthworms (Eisenia foetida), as well as shredded office paper and newspaper for bedding. The worms received mushroom waste available from the farm and some coffee grounds. Mushroom waste consisted of stumps removed during harvesting and deformed or broken fruiting bodies (culls). The evaluation of the system’s performance required running the fan for different lengths of time (1-7 hours). With the fan running for 4 hours a day, it was observed the bedding of the bottom drawer reached acceptable moisture level but the moisture in the top drawer was still excessive. Compost harvested from the top drawer had 63 percent moisture content, and 38 percent in the bottom drawer. These results reflect how the flow of air was not effective in removing excessive moisture from the top drawer.
In an attempt to improve the airflow through the unit, the 12 Volt/1.5 Watt fan was replaced with a 12 Volt/2.0 Watt fan. Two and 4 hours a day running time were tested. Two hours did not provide enough aeration, and 4 hours a day caused excessive dryness in the bottom drawer and a drop in the earthworm population (desiccated earthworms were found in the collection tray), but it still did not reduce the wetness in the top drawer. The next modification considered required cutting a hole in the cabinet structure to install a second fan, closer to the top drawer. A 12 Volt/2.0 Watt fan (80 mm) was inserted at two inches from the top of the cabinet. In the location of the original fan (behind bottom drawer), the 12 Volt/1.5 Watt fan was re-installed. Testing of the new fan system included running the fans simultaneously and independently.
The two-fan system provides now more possibilities to moderate the airflow according to the food waste load, stage of composting, etc. The timers also allow running each fan one or more times a day, and for different lengths of time. For example, after loading the drawers with fresh materials and earthworms, running the top fan alone for two hours a day or on alternate days provided excellent moisture conditions in both drawers, more so than running both fans for 2 or 4 hours every day, which resulted in excessive dryness.
The findings from operating two BioSystem 500 units suggest: a) A fan system needs to be operating for optimum performance; b) Installation of a second fan in the unit improved the flow of air and the conditions in the vermicomposting drawers considerably; c) In areas where the units cannot be powered, a small solar panel system can provide the power to operate the fans. The cost of the solar system and the modifications to the BioSystem 500 unit here described was approximately $360 (tax not included).
Table 1 summarizes the inputs (feedstock) and vermicompost produced from the BioSystem 500 unit operated by UCCE-SCL, while adjusting the fan performance.
Maria de la Fuente is with the University of California Cooperative Extension in Santa Clara County; Rosa Maria Gordillo, Sarah Smith and Mickey Neff are also with UCCE Santa Clara County program. Michele Young is in the San Jose Environmental Services Department.

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