Stormwater Treatment

Stormwater capture, treatment, and reuse
Stormwater capture, treatment, and reuse

Green infrastructures such as rain garden, green roofs, and bioinfiltration systems are increasingly being used in urban areas to harvest stormwater for reuse or groundwater replenishment, but the fate of stormwater contaminants in these systems is not well understood. In particular, it is not clear if these systems could sustainably remove contaminants during extreme events. These treatment systems are traditionally designed to increase infiltration of stormwater runoff. Although they have shown to remove some of the stormwater contaminants, many contaminants pass through the system and go on to contaminate the receiving water resource. In particular, bacteria in stormwater or urban runoff cause widespread contamination of surface water and groundwater. The study under this category aims to improve the design of bioinfiltration system to achieve better bacterial removal.

To learn more about the stormwater research conducted at the center for ReInventing the Nation’s Urban Water Infrastructure (ReNUWIt), where I worked previously, see the video below:

Collaborators:

Selected publications in this category are provided below.


Engineering solutions to improve bacterial removal from stormwater

Increasing saturation and addition of iron oxide coated sand or geomedia that promote strong attachment of bacteria increase the bacterial removal capacity of bioinfiltration system
Increasing saturation and addition of iron oxide coated sand or geomedia that promote strong attachment of bacteria increase the bacterial removal capacity of bioinfiltration system

This study examined the mechanism of bacterial removal in bioinfiltration system during intermittent infiltration of stormwater. The results show that intermittent flow can mobilize some of the attached bacteria from traditional bioinfiltration geomedia, thereby making the bioinfiltration system as a net source (instead of a sink) of bacteria. Increasing saturation and augmenting bioinfiltration geomedia with iron oxide coated sands increase removal and decrease detachment of bacteria during intermittent infiltration of stormwater, although iron oxide coated sands become ineffective in the presence of dissolved organic carbon. This work is published at Environmental Science and Technology herePDF.


Biochar for stormwater treatment: Effect of intermittent flow and dissolved organic carbon

Improved bacterial removal in bioinfiltration system in the presence of biochar.
Improved bacterial removal in bioinfiltration system in the presence of biochar.

This study examined the use of biochar—a low cost, carbonaceous engineered geomedia derived from waste biomass—to improve the bacterial removal capacity of bioinfiltration system. The results show that addition of small quantity of biochar not only improved bacterial removal capacity of bioinfiltration systems but also decreased the remobilization of the attached bacteria during intermittent infiltraiton of stormwater. Unlike iron oxide coated sand, biochar consistently removed nearly 90% of bacteria from stormwater in the presence of dissolved organic carbon. The study also revealed the mechanism of bacterial removal in biochar. This work is published at Water Research herePDF.


Biochar for stormwater treatment: Effect of infiltration rate, initial bacterial concentration, biochar particle size, and presence of compost

Biochar has potential to remove bacteria from stormwater under a wide range of bacterial loading and stormwater infiltration rate, but for biochar to be effective, the size should be small and biochar should be applied without compost.
For biochar to be effective, the size should be small, and biochar should be applied without compost.

This work shows that bacterial removal capacity of biochar-augmented bioinfiltration systems could remain high despite increases in infiltration rate (or rainfall intensity) and bacterial loading. However, a decrease in biochar particle size and presence of compost significantly reduced bacterial removal. Thus, for biochar to be effective adsorbent, biochar size should be small, and it should be applied without compost. This work is published at Environmental Science and Technology here.  PDF.


Biochar for stormwater treatment: Effect of physical and chemical weathering

Weathering conditions affect the mobility of fine biochar particles and removal of bacteria in biochar-augmented bioinfiltration system.
Weathering conditions affect the mobility of fine biochar particles and removal of bacteria in biochar-augmented bioinfiltration system.

This work examined whether the bacterial removal capacity of biochar-augmented bioinfiltration systems would remain consistent as the biochar weathers during intermittent exposure to stormwater under dry-wet and freeze-thaw cycles. Biochar particles were mobilized during intermittent infiltration of stormwater, but the mobilization depended on temperature and antecedent conditions. Chemical weathering (or exposure to natural organic carbon in stormwater) decreased bacterial removal capacity of the bioinfiltration system partly due to exhaustion of attachment sites by NOM adsorption, but intermediate drying cycle helped replenish some of the attachment sites. Overall, these results indicate that physical weathering has a net positive effect on bacterial removal by biochar-augmented biofilters. This work is published at Water Research herePDF.


Acknowledgements

The studies were supported through by the U.S. National Science Foundation-funded Engineering Research Center for Re-inventing the Nation’s Urban Water Infrastructure (Grant# EEC-1028968).

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