ENGINEERING STREAMBEDS TO DRIVE HYPORHEIC EXCHANGE AND IMPROVE STREAM WATER QUALITY

Many urban and agricultural activities have impacted the water quality of streams and lead to high levels of nutrients, pesticides, metals, and pathogens. Non-point source pollution caused by these activities is difficult to identify and treat, preventing the rehabilitation of such streams. This research project aims to evaluate the removal of such constituents from within urban streams using Biohydrochemical Enhancements for Streamwater Treatment (BEST) engineered streambeds. This technology is also relevant for treating wastewater and agricultural runoff in both developing and developed settings.

The BEST water treatment system utilizes impermeable blocks to force water in and out of the hyporheic zone (streambed), which acts as a natural biofilter for streams. Both benchtop-scale tanks and pilot-scale streams were used to evaluate the performance of the BEST steam. Both systems consist of two artificial streambeds, one containing the triangular impermeable BEST modules and the other being a control stream. The water used in the experiments is recycled water pumped from a membrane bioreactor. The indoor benchtop-scale tank is a clear acrylic tank containing two adjacent streams both with controlled flow rates. The tank’s clear wall allowed for a red dye tracer test to visibly display the flow paths in both the control and the BEST streams. A time lapse video of both the control and the BEST demonstrated that the BEST modules markedly increased the hyporheic exchange and residence times in the BEST tank. Electrical conductivity tracer tests were performed on the larger outdoor pilot scale streams where results again concluded that the BEST modules provided noticeably greater hyporheic exchange than the control stream. Initial results from a similar tracer tests conducted with the indicator compound resazurin suggest that BEST hyporheic exchange also leads to contaminant attenuation.

Column and batch tests have also been used to evaluate several biochars for incorporation into the BEST system. Incorporating biochar into the BEST system is expected to improve the system’s removal of stormwater and recycled water contaminants. Preliminary results suggest that adding biochar to the sand media within BEST modules may improve the technology’s effectiveness in treating non-point source pollution.