How to Manage Rainfall and Leachate on Compost Piles

Last week I was in North Idaho winterizing soil piles from a foundation excavation for a new house I am building near Coeur d’Alene. It took 4 hours to cover the piles by myself using large 28’ by 48’ recycled vinyl billboards. North Idaho does not usually get big thunderstorms in late summer, but just 2 hours after I covered the 4 large soil piles, a big one hit. It reminded me of how hard it is to manage for rainfall and snow while staying in constant production at composting facilities. In short, you must always be ready for rain or snow, at least ready to respond in a way that will work for your operation. Each facility eventually has a plan to manage for large rainfall events, because they have spent too much time paying for not planning. Here are some of your options:

• Use large Tarps over windrows. This includes non-woven geotextiles (fleece), reinforced landfill covers with ultra-violet sun protection, recycled billboard vinyl, or silage bag systems. There are also high tech materials and systems which breath out gas while repelling water.
• Use large and deep piles. GMT found in our report to Portland Metro that this is the most common method of composting in the USA. However most operations have phased this out due to significant problems with fires and odors.
• Use Short and wide piles that are turned frequently. These are the Tabular or Trapezoidal shaped piles turned with side discharge turners like the TracTurn from Compost Systems, the Willibald TBU,  and Doppstadt’s Grizzley or Panda and move it right after a big rain event.
• Use a roof of a size and shape. You can manage the composting process the way you like to, and ignore the rain or snow. Remember about blown-in rain however! These big storms are rarely vertical.
• Keep your site very, very clean around the piles and access areas. Jerry Bartlett wrote a great article for Biocycle in 2006 regarding runoff quality research he did at Cedar Grove.

These options work for keeping the pile moisture controlled to varying degrees, and each has its own drawback in either cost or ease of operation or the total volume of stormwater they release. My next blog posting will cover my opinion regarding the best way to minimize cost while also minimizing the amount of water generated and costs. But all systems will produce dirty water around the edges of the piles and generate SOME leachate from rain or condensed vapor from the composting process itself. So how do you manage that which is generated?

Managing leachate from composting operations 

Leachate is usually very rich with nutrients and microbes go crazy trying to eat it all up. Trouble is when a pile has wet edges, collection ponds, tanks, or even catch basins can quickly go anaerobic if they are not managed well. Here are some rules of thumb to consider when managing leachate or leachate-soaked compost:

• Don’t let it sit, keep it moving and draining. Slope your paved surfaces by 1.5% to 2% and soil like surfaces by over 2%.
• Remove sediment and floatables. This is done by using weirs, filter berms, catch basin inserts, and infiltration swales.
• Aerate with bubblers or agitators or recirculation systems to keep oxygen levels above 1.0 mg/kg in the water. This is needed for at least 3 to 4 days before going to storage or further treatment. Biological Oxygen Demand (BOD) has been seen to exceed 20,000 mg O2/liter in compost runoff.
• Store enough of the treated leachate in a lined pond so that the piles can dry out and you can re-use the leachate, OR treat it further to meet your local waste-water discharge permit requirements.
• Apply leachate during the first 14 days of composting and then delay PFRP time and temperature procedures until after the last leachate is applied.

Choosing the Right Rainfall Solution 

Each composting site is unique. That’s why there is never a “one size fits all” solution when it comes to rainfall and leachate management. At Green Mountain Technologies, we work with over 300 sites worldwide, so we are used to the distinct challenges each operator faces. If you’re trying to get your site ready for the fall and winter months, give us a call today. With our consulting services, we can help find the best solution rainfall at your site, give us a call or email. Prepare for Fall and Winter, give GMT a call today!