The Center for Sustainable Infrastructure Blog

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The Center for Sustainable Infrastructure Blog

The Carbon Benefits of Loop® Biosolids

December 10th, 2015 · No Comments · Waste

Thanks to Guest Contributor Kate Kurtz, Loop Biosolids Project Manager for King County.

Loop® biosolids is a natural soil conditioner and fertilizer replacement created by King County. The County has been recycling wastewater solids for this innovative purpose for over 40 years now. By using the Loop soil amendment, farmers can help to close the nutrient loop: plants pull nutrients from the soil, humans consume these nutrients and return them back to the soil through the use of Loop.

Kate is pictured here tending to her home vegetable garden where the soil is amended with compost made with Loop.

Kate is pictured here tending to her home vegetable garden where the soil is amended with compost made with Loop.

Loop represents an endlessly renewable resource able to continually restore carbon, phosphorus, nitrogen, and other nutrients back to the land. It not only provides a fuller suite of macro and micronutrients compared with synthetic fertilizers, but also offers the added benefit of improving soil structure, therefore reducing runoff, and preventing erosion.

This recycled product has been proven safe used alone or as an ingredient in GroCo compost since 1976; it is held to strict standards by both the EPA and WA State. King County processes about 175 million gallons of raw wastewater each day resulting in 120,000 wet tons of Loop extracted from wastewater per year. The bulk of this represents an excellent source of carbon and other beneficial nutrients for the soil and plants, which would otherwise be incinerated or dumped in a landfill.

Forester Brian Vrablick assessing a stand where Loop biosolids have been used as a fertilizer

Forester Brian Vrablick assessing a stand where Loop biosolids have been used as a fertilizer

Producing synthetic fertilizers uses significant amounts of energy, contributing to higher levels of greenhouse gases in the atmosphere, not only through the input of energy in manufacturing processes, but also through the mining of phosphates and pelletizing of nitrogen gas. By using recycled products, we can avoid many of these environmental costs. Moreover, the production of Loop, rather than consuming energy, actually creates it in a usable form via the capture of methane gas. Methane is emitted by the microbes that process waste inside anaerobic digester tanks at King County’s wastewater treatment facilities. Some of this methane is used to power the treatment plants themselves, and the rest can be sold to local utilities.

A handful of rich soil amended with Loop

A handful of rich soil amended with Loop

Using 100% of the Loop biosolids produced each year dramatically helps King County Wastewater Treatment Division reduce its carbon footprint by sequestering carbon in the soil and offsetting the emissions associated with commercial fertilizer production. In fact, over 80% of the utility’s emissions are offset by the strategic use of Loop. That’s the equivalent of taking over 8,000 cars off the road each year. Recent research in WA State has shown that using biosolids offsets emissions in three main ways:

1. Some of the carbon in biosolids will stay in the soil for a very long time.
2. Biosolids increase plant growth, which means that more roots and leaves are being deposited into the soil, further increasing the amount of carbon in the soil.
3. Biosolids are used as a fertilizer replacement, which means that the carbon emissions associated with manufacturing synthetic fertilizer are offset.”

People understandably have concerns about a product that is made from processed wastewater. Because of these concerns, biosolids-based soil amendments have been extensively studied for decades. Based on the results of thousands of studies, the safety of using biosolids as a soil amendment has been repeatedly demonstrated. Because it has been extensively studied, the production process has benefited from improved management practices and treatment methods. This science has pointed toward many previously unknown benefits of using biosolids and provided a foundation for the establishment of regulations.

Check out the images below or visit to learn more about the environmental and carbon benefits of this innovative product!





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