# High Rate Stormwater Treatment for Water Reuse and Conservation--Review
## 2 Research Background  
### Stormwater Technologies Rural and Semi-Urban Areas  
Stormwater management often employs technologies like bioretention, biofiltration, constructed wetlands, rain gardens, swales, and permeable pavements to address dissolved pollutants [4; 5; 6; 7]. These methods work through mechanisms such as plant absorption, enhanced infiltration that reduces runoff, decomposition facilitated by microbes and plant roots, and adsorption. Although systems like constructed wetlands and bioretention rely on nature-based processes, they are best suited to semi-urban or rural areas due to their larger space requirements. Additionally, their treatment consistency measured in terms of suspended solids (SS), total phosphorus (Tot-P), total nitrogen (TOT-N), and _E. coli_ varies (see Table 2) and may fall short of standards required for water reuse. In rural areas, stormwater treatment primarily focuses on treatment for protection of environmental protection instead of producing water of a quality suitable for reuse [8]. Treatment goals emphasize removal of litter and sediment together with nutrients. Water destined for reuse also requires removal of heavy metals, pathogens, etc., which are generally not prioritized in stormwater treatment systems. In urban water, a study conducted by [PERSON] et al. [9] on the performance of horizontal subsurface flow constructed wetlands showed a BOD\({}_{5}\) and COD removal of 61-63% and 59-66%, respectively. Constructed wetland: Large-scale stormwater harvesting projects often use constructed wetlands due to their cost-effectiveness in treating substantial volumes of collected stormwater [10]. Unlike biofililtration systems that generally need separate water storage post-treatment, constructed wetlands offer integrated water storage within the wetland itself. These systems efficiently remove suspended solids, metals, and nutrients [11] and help reduce fecal coliform concentrations, though their effectiveness in this regard can be variable. [PERSON] et al. [12] reviewed the applicability of wetland systems across many locations in the USA, Australia, New Zealand, Singapore, and Greece. The performance shown highlights high variability in pollutant removal. For instance, total-P removal ranged from 15% to 90%, Tot-N from 10% to 82%, and total SS from 55% to 95%. [PERSON] et al. [13] conducted a floating treatment wetland (FTW) study on a pilot scale for treating stormwater runoff in Singapore. They observed the removal of 39% and 68% \begin{table}
\begin{tabular}{c c c c c} \hline
**Stormwater Treatment Method** & **SS** & **Tot-P** & **Tot-N** & _E. coli_ \\ \hline Gross Pollultant Tape (GPT) & 0–70\% & 0–30\% & 0–15\% & Negligible removal \\ Swale & 55–75\% & 25–35\% & 5–10\% & Negligible removal \\ Bioretention & 70–90\% & 50–80\% & 30–50\% & \(-\)58–95\% \\ Pond & 50–75\% & 25–45\% & 10–20\% & 40–90\% \\ Wieland & 50–90\% & 35–65\% & 15–30\% & \(-\)5–99\% \\ \hline \end{tabular}
\end{table} 
Table 2: Pollultants removal range by different treatment methods (modified from [PERSON] et al. [8]). for total-P and Tot-N, respectively, when _Typha angustifolia_ was used as a floating plant. When _Polygonum barbatum_ was used as a plant, the removal was reduced to 19% and 41% for total-P and Tot-N, respectively. An in situ study conducted in New Zealand with _Carex virgata_ as a plant led to 50% removal for tot-P [14]. A relatively large, controlled outdoor FTW experiment (Mesocosm) conducted in the USA with the _Schoenopictus tabernaemontani_ plant led to higher removal of 50% and 68% for total-P and Tot-N, respectively [15]. [PERSON] et al. [16] conducted a full-scale FTW study in France using _Androposon geradii_, _J. effusus_, _Carex stricta_, and _Hibiscus Moscheutos_ as plants and obtained the removal of 78%, 40%, and 49% for SS, total-P, and Tot-N, respectively. A pilot study FTW conducted in Australia with _Carex appressa_ as the plant led to a removal of 18% and 53% for total-P and Tot-N, respectively [17]. A field-scale study conducted by [PERSON] et al.