Pervious concrete and biochar system for nitrogen removal from urban stormwater runoff

Overview

Urban stormwater runoff carries significant nitrogen, phosphorus, fecal coliforms, and other pollutants into waterways, posing challenges for municipalities and developers seeking cost-effective treatment solutions. This research proposes an integrated green infrastructure system combining mix-optimized fly ash pervious concrete (PC) pavement with a removable biochar barrier to capture and remove multiple stormwater pollutants. The system is designed to function as a best management practice that easily integrates with existing stormwater treatment methods such as bioretention basins, offering a scalable approach for urban water quality improvement.

Technical specifications

System design:

• Three-compartment treatment train: PC slab with storage course, removable biochar barrier, and bioretention compartment planted with ryegrass
• PC mix optimized using supplementary cementitious materials (SCMs) for both structural strength and hydrological performance
• Biochar barrier amount and service life determined through kinetic and breakthrough experiments
• Simulated stormwater applied at flow rates of 1 to 2 gpm/ft²

Target pollutant removals (based on prior validation):

• Phosphorus removal of approximately 50% via the PC and bioretention combination
• Fecal coliform removal of approximately 99%
• Enhanced total nitrogen and phosphorus removals exceeding 75% and 60%, respectively, with biochar-mixed PC

Mechanisms of action:

• Adsorption, precipitation, and biotransformation pathways for nitrogen and other pollutants
• Response Surface Methodology applied to optimize fly ash replacement and water content for compressive strength and permeability

Technology readiness level

The technology is currently at laboratory validation stage (TRL 3–4). Prior work has demonstrated pollutant removal performance in lab-scale PC systems combined with bioretention basins, and biochar-mixed PC has been tested for total nitrogen, phosphorus, and COD removal in submerged conditions. The proposed future validation includes a continuous-flow lab-scale treatment train to be completed within one year at Texas State University, a minority-serving institution. This next phase will elucidate pollutant removal mechanisms—particularly for nitrogen—and quantify biochar service life, advancing the system toward field readiness.