Time for a change? Lessons learned while transitioning from windrow operations to aerated static pile composting
Last year I wrote a blog post about helping a Waste Management landfill in northern California 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 (or in-floor) piping. Fast forward a year, and I’m back with the sequel – the pros and cons we encountered, as well as changes we made during conversion.
First – a word on why we recommended the conversion to CASP for the landfill. The existing traditional windrow composting facility had a permitted capacity of 170 tons per day (tpd) of feedstock, consisting of green waste material (yard waste and approximately 5 percent residential food waste). With the California waste diversion goal of 75 percent and a goal to reduce GHG emissions, the landfill wanted to convert to a CASP to increase throughput while decreasing emissions and remaining within the existing composting facility footprint. The photo shows the existing feedstocks the site was taking, along with commercial foodwaste that they started taking during conversion.
We evaluated design options for managing a higher volume of feedstock with the goal of keeping capital costs low during conversion from windrow to CASP, managing handling issues that arose with increased feedstock, and limiting the creation of new infrastructure.
The pros and cons of transitioning into a large scale CASP operation
Ability to process more
Pro – Ability to process large volumes of material, since you have more leeway with emissions limits, equipment size, and pile size.
Con – More feedstock material means more space is needed – or the material must be neatly organized within the same footprint.
Pro – Design a less hands-on facility with more automation.
Con – Results in an increase in capital costs and a learning curve for existing operators.
Pro – Options to take in feedstocks not previously accepted, such as increased food waste.
Con – Additional feedstocks would require a review and update to existing permits.
Things to consider
Need to upgrade permits – For example, solid waste handling permits need to be revisited for accepting food waste.
Decrease in air emission – The elimination of windrow turning equipment eliminates particulate emissions significantly, allowing for increase in on-site material because static piles do not require turning during the active composting phase.
Increase in feedstock volume – Consider space and equipment needs for managing incoming feedstock during processing, active, curing, finished storage.
Recipe variations when changing from windrow to CASP – Consider accepting additional food wastes or additives.
Challenges typically encountered when increasing feedstocks
Leachate – Need to manage liquids in accordance with permits, requiring in-place storage and conveyance systems.
Odor – Need to facilitate timely processing and sufficient aeration.
Vectors – More material and the addition of foodwastes increases the attractiveness by vectors to the site. Features needed to keep birds, rats, and other vermin (who love food wastes!), for example, fences or hawks.
Stormwater management solutions –Stormwater from runoff, run-on, and contact waters may need to be managed differently.
Traffic and material management – Increasing feedstock may reduce working space and increase traffic, so traffic patterns and material storage need to be laid out early to ensure sufficient space.
Layout and space constraints when utilizing existing infrastructure.
Successes, lessons learned, and feedback from operators
Start simple, and ramp up feedstock intake slowly!
Make sure that the entire team (site managers and site operators) all have input on the facility, since they will have the hands-on day-to-day dealings with the system that is designed.
Identify your end-user needs to make sure that the feedstocks you accept meet the standards and quality your user is looking for.
We found that capital costs and infrastructure can be kept on the low end if you’re looking for a more simplistic and manual facility. Those looking to have less hands on interaction with the daily process can opt for a more sophisticated system, which translates to more capital costs.
The site had existing infrastructure that met the permit requirements, so they were reused, for example, the asphalt pad shown in the photo. Other aeration options include in-floor trenches, but they opted for on-grade piping with their existing infrastructure to keep capital costs low.
Overall, the project was a successful conversion from windrow to CASP. It highlights the benefits of composting at a landfill. Be sure landfill personnel are familiar with composting operations – and that the infrastructure is in place to address challenges that arise from on-site composting.
Do you have any thoughts on the pros and cons of the CASP method?
Jessica Bernardini, PE, is a project manager with more than eight years of experience in a range of solid waste related projects on a local, regional, and national level.
Categories: Air Quality, Landfill Engineering and Design, Organics, Solid Waste, Transfer/Recycling/Processing Facilities
Posted By Jessica Bernardini, PE at 11:30 AM | No Comments on Time for a change? Lessons learned while transitioning from windrow operations to aerated static pile composting
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