Real time control schemes for improving water quality from bioretention cells

Abstract

Extreme weather and the proliferation of impervious areas in urban watersheds increases the frequency of flood events and deepens water quality concerns. Bioretention is a type of green infrastructure practice developed to mitigate these impacts by reducing peak flows, runoff volume, and nutrient loads in stormwater. However, studies have shown inconsistency in the ability of bioretention to manage some pollutants, particularly some forms of nitrogen. Innovative sensor and control technologies are being tested to actively manage urban stormwater, primarily in open water stormwater systems such as wet ponds. Through these cyber-physical controls, it may be possible to optimize storage time and/or soil moisture dynamics within bioretention cells to create more favorable conditions for water quality improvements. A column study testing the influence of active control on bioretention system performance was conducted over a 9-week period. Active control columns were regulated based on either maintaining a specific water level or soil moisture content and were compared to free draining (FD) and internal water storage standards. Actively controlled bioretention columns performed similarly, with the soil moisture-based control showing the best performance with over 86% removal of metals and total suspended solids (TSS) while also exhibiting the highest ammonium removal (43%) and second highest nitrate removal (74%). While all column types showed mostly similar TSS and metal removal trends (median 94 and 98%, respectively), traditionally FD and internal water storage configurations promoted aerobic and anaerobic processes, respectively, which suggests that actively controlled systems have greater potential for targeting both processes. The results suggest that active controls can improve upon standard bioretention designs, but further optimization is required to balance the water quality benefits gained by retention time against storage needs for impending storms.

Nature-based solutions and Real-time control: Challenges and opportunities

“…Free draining have shown good results at literature, but are domintated by aerobic conditions and lack to perform both nitrification and denitrification [42][43][44]. Therefore, bioretention cells with interal water storage promote aerobic and anaerobic conditions favoring both nitrification and denitrification [13,45].…”

“…The author used two low-cost implementation strategies for both new cells and for cells already built and found that bioretention with RTC can mitigate the negative effects of short and long dry periods and mitigate the influence that large inflow volumes have on the treatment of faecal microbes. [13] analyzed several RTC schemes in bioretention columns to improve water quality. The most notable water quality improvement was related to nutrients, while the static system performed best to ammonium by more than 40% and columns with internal water storage removed more nitrate by more than 73%.…”

“…LIDs stand out for providing reduction of peak flow and diffuse pollution through related physical-chemical process such as filtration and drainage layers at the systems [10]. However, dispite the most varied designs, these systems are projected to function passively, i.e they are not adapted for internal storage (formation of a saturated layer) or free drainage to optimize aerobic, anaerobic and/or hydraulic process at the layers [13].…”

Nature-Based Solutions and Real-Time Control: Challenges and Opportunities

“…In a historical context, LID initially aimed to reintegrate excess runoff into the hydrological cycle [10]. With the advances of techniques, LID incorporated objectives of mitigating the impacts caused by climate change, in addition to proposing to reintegrate the runoff volume into the catchment through local reuse [11,12]. Therefore, incorporating medium-and long-term time scales, considering the increased occurrence of extreme flood and drought events and aiming at the recycling and co-management of resources, LIDs can contribute to several United Nations Sustainable Development Goals (UN SDG), specifically, the objectives of zero hunger (SDG 2), clean water and sanitation (SDG 6), affordable and clean energy (SDG 7), sustainable cities and communities (SDG 11) and climate action (SDG 13).…”

“…LID practices provide reductions in peak flow and diffuse pollution through physicalchemical processes, such as filtration and drainage layers at the systems [10]. However, despite the most varied designs, these systems are projected to function passively, i.e., they do not adapt the system configurations over time to optimize aerobic, anaerobic and/or hydraulic processes at the layers [12].…”