Stormwater Recharged: Innovating with Electrical Flocculation

Abstract

The construction, operation, and maintenance of public infrastructure systems generate a variety of pollutants such as sediment, heavy metals, and nutrients, which are contaminants the U.S. Environmental Protection Agency (EPA) identifies as the most widespread in affecting the beneficial uses of the Nation’s rivers and streams. These contaminants degrade aquatic habitat, impair water quality, and reduce channel capacity, often requiring costly dredging or remediation. Growing urban development and increasingly severe storm events place additional strain on traditional drainage infrastructure, which must contend with both high flow volumes and elevated pollutant concentrations. In response, construction sites located near Waters of the United States, impaired waterbodies, or areas served by municipal separate storm sewer systems are required to implement stormwater pollution prevention plans, incorporating best‐management practices to minimize downstream impacts. Although conventional erosion and sediment control measures, such as sediment basins, check dams, and silt fences effectively capture coarse, gravitationally settleable solids, they are not necessarily designed to reduce turbidity from colloidal particles. Currently, chemical flocculants remain the primary enhancement method for turbidity control in the field of stormwater. However, these chemical flocculants typically require manual dosing, generate large sludge volumes, and require tailored products for specific soils. These challenges highlight the need for additional solutions to address high turbidity environments to improve downstream water quality. To address these limitations, this dissertation details the design, fabrication, and evaluation of a portable electrical flocculant generator, which employs in situ electrocoagulation to aggregate fine particulates without added chemicals. While electrocoagulation is well established in municipal and industrial water treatment, its application to construction and post‐construction stormwater has been limited. By branding the technology as “electrical flocculation,” this work introduces a familiar concept to stormwater practitioners and provides a foundation for broader field adoption. Research began with a comprehensive literature review to distinguish between chemical coagulation and electrical flocculation, identify common stormwater contaminants, and the parameters affecting electrical flocculation performance. Leveraging these insights, three prototypes (A, B, and C) were developed and tested in an intermediate-scale system across five evaluation categories, including fundamental performance evaluations, aluminum‐coagulant release, mixing, electrode longevity, and pollutant loading. Fundamental performance evaluations that compared series versus parallel electrode wiring (prototypes A and B), showed no significant difference in turbidity removal performance. Subsequently, aluminum release trials demonstrated that under conditions of 54.1 L/min (14.3 GPM), 750 Nephelometric Turbidity unit (NTU) influent, and 37 A/m2 (3.4 A/ft2), prototype C released 0.19 mg/L Al3+, which is below the EPA’s secondary drinking‐water standard of 0.20 mg/L. This indicated preliminary compliance; however, toxicity analysis must be completed to confirm this finding in future testing. Mixing experiments demonstrated that two minutes of mechanical stirring at 360 rotations per minute (RPM) optimizes settlement, and specific passive mixers can offer equal performance. Electrode‐longevity trials revealed a 33% performance decline over 100 hours without polarity reversal and showed that a 5-hour reversal interval did not improve current density or performance within a 30-hour test. Pollutant‐loading evaluations conducted under testing parameters of 37.9 L/min (10.0 GPM) and 38 A/m2 (3.5 A/ft2) achieved removals of 60% of cadmium, below detection limits for copper, 73% for iron, 82% for lead, 68% for phosphorus, and 33% for zinc. Field‐scale tests with prototypes C and D confirmed that performance is strongly influenced by both influent temperature and anodic surface area. These results establish a baseline performance for the retrofit electrical flocculant generator, demonstrating its lab‐ and field‐scale efficacy in removing turbidity and non‐sediment pollutants and quantifying its kinetics, energy use, and optimal current densities. This research provides a new approach to improving stormwater treatment by introducing a chemical-free, portable device that uses electrical flocculation to remove suspended solids and pollutants. By effectively reducing turbidity, heavy metals, and nutrients, the technology can help prevent the degradation of downstream waterbodies and support cleaner, healthier aquatic ecosystems. Its ability to operate without added chemicals also reduces the risk of harmful byproducts and makes it easier to implement at construction sites and other areas with stormwater challenges. Overall, this research offers a practical alternative solution to enhance water quality and advance sustainable stormwater management practices.