Indicator and Pathogen Removal by Low Impact Development Best Management Practices

Abstract

Microbial contamination in urban stormwater is one of the most widespread and challenging water quality issues in developed countries. Low impact development (LID) best management practices (BMPs) restore pre-urban hydrology by treating and/or harvesting urban runoff and stormwater, and can be designed to remove many contaminants including pathogens. One particular type of LID BMP, stormwater biofilters (i.e., vegetated media filters, also known as bioinfiltration, bioretention, or rain gardens), is becoming increasingly popular in urban environments due to its multiple co-benefits (e.g., improved hydrology, water quality, local climate and aesthetics). However, increased understanding of the factors influencing microbial removal in biofilters is needed to effectively design and implement biofilters for microbial water quality improvement. This paper aims to provide a holistic view of microbial removal in biofilter systems, and reviews the effects of various design choices such as filter media, vegetation, infauna, submerged zones, and hydraulic retention time on microbial removal. Limitations in current knowledge and recommendations for future research are also discussed.

Predictive Power of Clean Bed Filtration Theory for Fecal Indicator Bacteria Removal in Stormwater Biofilters

“…The influence of increasing biofilter age on FIB removal rate may reflect an increase in the number of ways FIB are removed by the biofilter as it ages, including "filter ripening" (where previously deposited particles serve as additional collectors in the absence of electrostatic interparticle repulsion), 67 biofilm formation (and associated increases in the attachment efficiency), 63 and/or the progressive growth of micro-and meso-faunal grazers over time. 19,37,38 The influence of ADP on FIB removal rate, however, may reflect the tendency of preferential flow paths (including fissures and macropores) to develop after long ADPs. 34,39 While preferential flow paths are associated with increased infiltration rates (an effect already accounted for by CBFT and hence incorporated into the value of k CBFT , see above), 34,39 by "short circuiting" the flow they can also reduce the number of FIB/collector collisions that can occur as FIB quickly pass through the biofilter (an effect not accounted for by CBFT and thus not included in k CBFT ).…”

“…We focused on the first-order removal rate because it is the more fundamental parameter; i.e., the overall removal rate achieved by a biofilter will depend on both the rate at which FIB are removed by one or more mechanisms (k obs ) and the advective and dispersive transport processes that determine the biofilter's residence time distribution. 47 Thus, plants can affect overall FIB removal in at least three potential ways: (1) creating new mechanisms by which FIB are removed in the biofilter, for example, by growing roots that serve as collectors for FIB, 40 creating habitat for micro-and meso-faunal grazers that remove FIB through predation, 19,37,38,62 and altering the survival rates of FIB through, for example, competition for nutrients; 34 (2) altering the single collector contact efficiency and attachment efficiency through promotion of biofilm growth, 63 generation of surface-active plant exudates, 64 and creation of preferential flow paths that limit stormwater/biofilter media interactions; 65,66 and (3) changing the infiltration rate which, in turn, alters the biofilter's residence time distribution, 66 the single-collector contact efficiency (see Figure 1), and ultimately the first-order filtration rate (see eq 5).…”

A review on microbial contaminants in stormwater runoff and outfalls: Potential health risks and mitigation strategies

“…The removal of pathogens varies from system to system and therefore, it may be useful to assess individual systems in-situ to account for local variability resulting from factors such as sedimentation, sunlight exposure, water temperature, and adsorption/desorption with biofilms . Peng et al, 2016 highlighted that most microbe focused studies of stormwater biofilters focus on FIB, which are measured by culturebased methods, and less frequently by molecular based methods. These studies may be difficult to extrapolate to pathogens.…”

“…There are few studies on the removal of pathogens, particularly viruses, in stormwater by biofiltration. Peng et al (2016) also noted the need for more studies that use field-based measurements, rather than laboratory settings, as it captures the more variable and complex features of the urban environment that influences how effective WSUD approaches are likely to be in reducing pathogen loads.…”

Removal of Heavy Metals from Urban Stormwater Runoff Using Bioretention Media Mix

“…Level I [16] 10.0 10.0 1.0 50.0 Level II [16] 1000.0 10.0 5.0 1000.0 Level III [16] 1000.0 50.0 50.0 1000.0 Beijing [13] In recent years, developed countries have used many ecological measures such as bioretention facilities, ecological tree boxes, and green roofs to control stormwater runoff pollution and have attempted to restore the hydrological conditions of urbanized areas to pre-development conditions [18,19]. Among these measures, bioretention technology can not only control water quality efficiently but also has an ecological function and positive effects on the landscape.…”