Welcome to SOCRRA’s virtual tour of the Rochester Hills Compost Site.  In this tour, we will be exploring the various operations that take place to convert leaves and grass into rich organic garden compost or “humus”. 

 Beginning in spring, large trucks pull into the Compost Site and deposit grass clippings adjacent to a long row of leaves (called a “windrow”).  These leaves came in the previous fall and were moved around by front-end loader to form the neat windrows seen here.  The loads of nitrogen-rich grass clippings are deposited next to the rows of carbon-rich leaves for a ratio of one part grass to 3 parts leaves.   

 After the trucks dump the fresh grass, the old leaf row is pushed over the grass clippings.

If large logs or branches are present, they are removed because it takes too long for them to decompose and they tear up the machinery that turns the windrows.

 After the new row is formed, a huge piece of farming equipment—called a SCARAB Compost Turner--- makes four passes per row to mix the material. The SCARAB has a large revolving drum that has 154 knives on it, so that the grass clippings and leaves get thoroughly mixed and chopped with each pass. If the windrows give off a foul odor upon turning, woodchips are spread over the turned row, which acts as a biological odor filter.

 The primary purpose of turning a row is to maintain optimal temperature, oxygen and moisture levels.  For grass clippings and leaves to be converted to garden humus, many types of microorganisms have to participate in the decomposition process.  As these microbes do their work, they consume oxygen in the row and produce high temperatures from the energy process.  Most biological activity occurs when temperatures are in the 120-degree plus range.  To ensure weed seed destruction, the internal temperature of a row must reach 140^oF for a few days.  Turning a row with the SCARAB allows the inner hot and anaerobic material to be mixed with the cooler/aerobic material from the outside of the row.  In addition to this mixing, turning also shreds the material and provides more surface area from which the microbes can multiply.

 If the moisture level is too high, an insufficient amount of oxygen will reach the core of the row and it will go anaerobic, giving off strong noxious odor.  This situation rarely occurs in Michigan, however, so, as a practical matter, rows will be turned about every other week until the decomposing material reaches a consistency of garden humus. After about four months, the leaf and grass mixture will be decomposed into humus and will be ready for screening.  A loader fills the dump truck with the humus, then it is sent to the screener.   

Here, a loader fills the screener with humus.  The humus passes through a large rotating sift where the screen removes anything larger than 3/4-inch by 3/4-inch.  The reject is carried out by conveyer belt and stored in these piles.  Reject includes sticks, rocks, debris and large clumps of material that did not decompose.  Reject material is then loaded in a semi truck where it is sent to a landfill. The good/screened compost is sent by conveyer belt out of the screener and is stockpiled over winter for curing. During curing, microbes that thrive in cooler temperatures provide the finishing touches so that the decomposition results in what gardeners call “black gold”. 

 Once the process is complete and the compost has cured, it is then ready for sale to landscaping firms and for delivery to the DPW yards at SOCRRA member communities.  Anyone can come to the Site and purchase compost for a fee of $7 per cubic yard.

 This concludes SOCRRA’s virtual tour of the Rochester Hills Compost Site.  Thank you for watching and we hope you enjoy our finished garden compost product.

Copyright © 2007 [SOCRRA]. All rights reserved.
Revised: February 01, 2008.