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28 May 2014

There’s gold in them thar compost piles – pilot study helps convert to a covered aerated static pile to increase compost throughput

Bernardini_CASP-grinderI’ve been working for the past few years with a Waste Management landfill in northern California to help convert a classic windrow composting facility (in which compost is piled up outdoors and periodically turned) to a covered aerated static pile (CASP) composting facility, where larger piles undergo aeration using on-grade piping. The landfill currently produces an Organic Management Research Institute (OMRI)-approved compost product that is sold to local farmers and vineyards and wants to increase throughput and continue to provide OMRI-approved material by converting to a CASP facility. Read on to see how a recent pilot study I was a part of helped us design a flexible, inexpensive, and efficient large scale CASP facility.

The windrow facility composted 150 tpd of feedstock, mainly green waste material (yard waste and approximately 5 percent residential food waste), and the CASP facility is permitted for a 514 tons per day (tpd) throughput. They received an approval to increase material throughput based on decreasing emissions due to converting windrow operation to CASP. The emission decreases come from elimination of the windrow turning (which creates particulates) and from placing a biofilter layer over the aerated piles to collect emissions. So, the landfill was looking for the best process, materials, and set-up for the facility that would be able to manage the higher feedstock volume, which will come from increased intake of green waste, as well as a small percentage of commercial food waste that is not used in the current windrow composting operation.

To help evaluate options, we began with a pilot study, building five full-scale piles with dimensions as large as 90-ft long, 30-ft wide, and 12-ft high. We constructed the piles in an extended CASP fashion, or “piggy-backed” onto each other to create one large extended compost pile, so we could evaluate the effect of the overlapping piles. On-site personnel constructed the blowers and piping.

Bernardini_CASP-processed-compost-aerationWe conducted aeration over a 4-week period, and monitored over a period spanning winter to the end of summer, so we got great information on the seasonality of the green waste, and we could also get a good look at changes in temperature and precipitation and their effects on aeration of the piles.

We monitored the piles every morning and afternoon during the four week aeration period, getting a treasure trove of information on temperature, oxygen, moisture, bulk density and porosity. We also performed Seal of Testing Approval (STA) tests at the conclusion of the aeration period for each pile. The STA tests provided information on the compost’s carbon dioxide evolution and maturity, which we used to compare the aerated piles to the existing windrow composting piles.

The pilot study gave us room to experiment, and we looked at a variety of conditions, including aeration schemes; levels of material moisture conditioning; percentages of commercial grade food waste; and the size and spacing of the aeration piping underlying the piles. We started out thinking we would evaluate both negative and positive aeration during the pilot, but later switched to looking only at positive aeration following a decision that the full-scale facility would use positive aeration.

We used the pilot study findings to design a flexible, inexpensive, and efficient large scale CASP facility. We found that devising and testing compost recipes by varying the percentage of commercial food waste within the recipes was important, as was spacing and size of the piping that provides aeration to the piles. The CASP facility’s grand opening is coming up this summer and there are plans in the work for a second facility to be constructed at another Northern California WM facility.

Do you have any experience on composting using the CASP method?


Categories: Landfill Engineering and Design, Organics, Solid Waste, Transfer/Recycling/Processing Facilities
Posted By Jessica Bernardini, PE at 11:15 AM  |  No Comments on There’s gold in them thar compost piles – pilot study helps convert to a covered aerated static pile to increase compost throughput

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