Assessing the Capacity of Iron-Amended Biochar to Remove Phosphorus from Wastewater

Location

PANEL: Biological and Environmental Chemistry
Science Center A154
Moderator: Gaybe Moore

Document Type

Presentation - Open Access

Start Date

5-1-2026 2:30 PM

End Date

5-1-2026 3:30 PM

Abstract

Ecologically engineered constructed wetlands (CW) incorporate components of natural wetland ecosystems, such emergent and floating vegetation to treat wastewater. “Tertiary treatment” or removal of the key macronutrients nitrogen (N) and phosphorus (P) from the wastestream, is a key feature and design goal of CW systems. Removing these nutrients is crucial to preventing the eutrophication of downstream bodies of water. Unlike N, P can not be converted to a gaseous form; removing it from the water column necessitates long term storage within the CW system or that it be physically removed from the system for example in plant biomass, sediment or other other absorptive materials. The Oberlin College “Living Machine”(LM) is a CW system that uses a series of anaerobic and aerobic tanks, some with vegetation, and then a final marsh system to break down organic matter (secondary treatment) and remove nutrients. A long term assessment conducted in 2024 demonstrated that the LM has become increasingly less effective at removing P over its 25 year history and concluded that absorptive capacity of rock media in the CW are likely saturated (Ferry & Fink, 2024). Recent studies show that amended biochar, a porous, carbon-rich substance with high ion exchange capacity, has potential in efficient removal of P from wastewater when amended with metal salts such as ferric chloride. We designed a laboratory study to quantitatively assess the extent to which locally produced biochar might be used for P-removal. Using LM effluent water, we compared P uptake (mg/L) over time in experimental systems that used an aquarium pump to circulate water through small bags of biochar in 1 L reaction vessels. As hypothesized, biochar amended with ferric chloride removed P. We observed no overall change in P in unamended biochar or in a control that contained no biochar. We also observed amended biochar removed N from wastewater, although the rate of and overall removal of P was substantially greater. We intend to engage in further study to determine the replicability of these results, to assess how much phosphorus can be taken up per unit of biochar, and to determine whether an iron-amended biochar is a feasible and practical solution for use in constructed wetlands.

Keywords:

Wastewater, Biochar, Phosphorus

Notes

Presenters: Anjali Vuksanaj and Ella Kavanaugh

Major

Environmental Science

Project Mentor(s)

John Petersen, Environmental Studies

2026

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May 1st, 2:30 PM May 1st, 3:30 PM

Assessing the Capacity of Iron-Amended Biochar to Remove Phosphorus from Wastewater

PANEL: Biological and Environmental Chemistry
Science Center A154
Moderator: Gaybe Moore

Ecologically engineered constructed wetlands (CW) incorporate components of natural wetland ecosystems, such emergent and floating vegetation to treat wastewater. “Tertiary treatment” or removal of the key macronutrients nitrogen (N) and phosphorus (P) from the wastestream, is a key feature and design goal of CW systems. Removing these nutrients is crucial to preventing the eutrophication of downstream bodies of water. Unlike N, P can not be converted to a gaseous form; removing it from the water column necessitates long term storage within the CW system or that it be physically removed from the system for example in plant biomass, sediment or other other absorptive materials. The Oberlin College “Living Machine”(LM) is a CW system that uses a series of anaerobic and aerobic tanks, some with vegetation, and then a final marsh system to break down organic matter (secondary treatment) and remove nutrients. A long term assessment conducted in 2024 demonstrated that the LM has become increasingly less effective at removing P over its 25 year history and concluded that absorptive capacity of rock media in the CW are likely saturated (Ferry & Fink, 2024). Recent studies show that amended biochar, a porous, carbon-rich substance with high ion exchange capacity, has potential in efficient removal of P from wastewater when amended with metal salts such as ferric chloride. We designed a laboratory study to quantitatively assess the extent to which locally produced biochar might be used for P-removal. Using LM effluent water, we compared P uptake (mg/L) over time in experimental systems that used an aquarium pump to circulate water through small bags of biochar in 1 L reaction vessels. As hypothesized, biochar amended with ferric chloride removed P. We observed no overall change in P in unamended biochar or in a control that contained no biochar. We also observed amended biochar removed N from wastewater, although the rate of and overall removal of P was substantially greater. We intend to engage in further study to determine the replicability of these results, to assess how much phosphorus can be taken up per unit of biochar, and to determine whether an iron-amended biochar is a feasible and practical solution for use in constructed wetlands.