WE KEEP ALAMEDA COUNTY GREEN®

Vermitopias

The worm boxes, or vermitopias, house thousands of red wrigglers. These voracious worms are capable of eating 16 pounds of food per bin per day. Over twenty vermitopias were made out of reused hinges from the local salvage yard, recycled paint for weather protection, and recycled wood. Food waste is mixed with composted horse manure from a local stable, and then it is dumped from the top of the box. The material that has been processed by the worms is collected from the bottom of the vermitopia. This system (called 'continuous flow') saves us from the hassles of separating worms from the finished product. Nylon string, woven back and forth across the box, supports the weight of about two feet of moist vermicompost. Finished compost, called worm castings, falls through the ropes. None of the original vermitopias are in use. This summer we are constructing new bins using the same model. We have some rough plans and more information about how the vermitopias held up over the years.

Empty bin with the top dumping lid and bottom harvesting door open

Stringing a new worm bin

Strong rope!

Earth tub

Built by Green Mountain Technologies, the Earth Tub was kindly donated to us after we tested their prototype. Food waste mixed with a small amount of straw, or preferably wood chips, is fed into the tub through a hatch on the top. An electric motor turns an auger, which churns and chops the material. While the auger is spinning, we rotate the entire earth tub by pushing on handles mounted on opposite sides of the tub. This mixes and aerates the decomposing material. A small tube at the bottom drains leachate, or nasty compost liquid. A bio-filter with a fan pulls the outflow air through a box of wood chips, eliminating odor. When in full use, the earth tub processes 10-15% of our food waste. Currently the fan on the bio-filter is broken, so we are not using it.

The earth tub

A helpful diagram

Finished compost is removed from this side hatch

Windrows

These are hot piles (or "thermophilic composting systems"). These long, rectangular mounds currently compost all of the food waste that we collect every week. Between the summer of 2002 and the spring of 2004, we were not permitted to use exposed windrow piles. This was due to a series of pest and odor problems in the spring of 2002. We have overcome pests and odors with our current windrows. The windrows increase in size each week as new layers of food waste, woodchips and straw are added to them. Our mixer truck chops, churns, and applies the food waste to the piles. All other materials are layered by hand. We mix the upper section of the piles with a pitchfork before and after adding the layer of food waste. The wood chips act as a bulking agent and a carbon source while the straw creates an outer shell for extra protection. Both the wood chips and the straw absorb moisture and odors. We build the piles to about four feet high. Windrows take about a month after reaching this height to cool. During the dry California summer months we cover the windrows with tarps. This helps maintain good moisture levels. This method was adopted from a similar composting project at the Federal University of Santa Catarina in Florianópolis. Click here to view a photo gallery of their operation.