The City of Corvallis wants to harvest and recycle nutrients from landfill leachate to create a revenue stream for the city while cleaning up its wastewater. Last year, a College of Engineering senior project team worked with Multiform Harvest, Inc. and the City of Corvallis Wastewater Reclamation Plant to make a fertilizer called struvite from landfill runoff at the Coffin Butte Landfill. However, the 2011 team discovered that excess calcium was interfering with the reclamation process, so this year’s team addressed that issue.
Phosphate is one of the key components of struvite, but 2011 tests revealed that high levels of calcium interfere with struvite formation by reducing phosphate levels. As landfill capping efforts at Coffin Butte improve, calcium levels are expected to increase in the coming years, making it essential to address the issue of excess calcium formation to achieve the goal of capturing and selling struvite.
The current solution for reducing calcium is simply to add phosphate to the leachate. Kristina Schmunk, Michael Jue, and Abhishek Yadav tested an alternative approach that involves adding oxalic acid as a pretreatment step, which lowers calcium ion levels. The team investigated the optimal oxalic acid feed ratio, characterized precipitate formed in the leachate, and measured overall calcium removal.
Funding will be available in the first quarter of 2013 to implement the new reclamation system at Coffin Butte. Information gathered through the efforts of Oregon State University environmental engineering project teams in 2011 and 2012 will provide valuable data to optimize the reclamation process.