# High Rate Stormwater Treatment for Water Reuse and Conservation--Review
## 2 Research Background
### Stormwater Technologies in Urban Areas  
Wetlands find application in locations where land space is less constrained as they require several hectares to accommodate all their components. This space is not available in more urbanized settings, particularly in inner city areas. The essential features of wetlands have been captured in the form of a vegetated biofilter for application where land space footprint is a constraint. Vegetated Biofilter: In urbanized areas, biofilters are a more suitable alternative treatment, requiring less land than constructed wetlands and making it particularly suitable for local stormwater harvesting solutions. Laboratory experiments have shown that biofilters are effective at removing significant amounts of suspended solids and metals from stormwater [22; 23], and these findings have been largely validated in real-world applications [24; 25]. Although the removal of nutrients is another potential benefit [26; 27; 28], certain studies report biofilters as net contributors of nutrients, particularly nitrogen [22; 23; 29]. Tables 3 and 4 outline the main elements of stormwater biofilters and the processes involved in pollutant removal. \begin{table}
\begin{tabular}{c c} \hline
**Components** & **Function** \\ \hline Vegetation & Provides carbon to microbes, reduction of stormwater volume through transpiration, helps to maintain infiltration rates, provides cooling to nearby environment, aesthetic appearance, adsorbs stormwater pollutants, and treats through the microbes in the plant roots. \\ \hline Filter media & Offers particulate filtration, pollutant removal via adsorption and precipitation, fosters plant growth, and enhances stream health. \\ \hline \end{tabular}
\end{table} 
Table 3: Two key components of stormwater biofilters and their functions (modified from [PERSON] et al. [30]). Biofiltration works by improving water quality through biological filtering processes (Figure 1). These systems are called by various names, such as biofilters, bioretention systems, and rain gardens, and are integral to GSI as treatment methods that consume little energy and enhance both water quality and volume management. These systems are adaptable to a range of catchment sizes and settings, from small-scale applications like street trees and private gardens to larger installations along streets and in parking areas. A typical biofilter is made up of two layers, i.e., a vegetated basin or swale layered over a porous filter medium, usually sand. These drain into a porous pipe connected to the stormwater system. There is limited data available on pathogen removal in biofilters. A pilot study assessing vegetated biofilters with various plant species found that they achieved _E. coli_ removal rates ranging from 48% to 97% [29]. Additionally, experiments with different biofilter configurations showed pathogen removal of more than two to three log reductions [32]. Small stormwater harvesting systems in Kuring-Gai, New South Wales, Australia showed approximately a 1 log reduction in fecal coliforms. Influent water to this system (pre-treatment) is typically treated by biofilter. Although both constructed wetlands and biofilters have demonstrated significant potential in reducing pathogen levels, they are not yet recommended for compliance under Australian guidelines [2].