# High Rate Stormwater Treatment for Water Reuse and Conservation--Review
## 5 High-Rate Stormwater Treatment Technologies  
Systems such as wetlands, biofilters, and PPS are popular for treating stormwater. However, the existing stormwater treatment systems do not consistently deliver the water quality suitable to meet standards for recycling. Additionally, given the high volume of stormwater discharge, they typically incorporate storage components that occupy significant land areas, which can be limited in urban inner-city environments. An alternative approach involves storing stormwater before treatment, similar to traditional management systems. However, untreated stormwater in storage holds little value and can deteriorate under both anaerobic and anoxic conditions. Incorporating pre-treatment can enhance the quality of stored water, making it more suitable for beneficial reuse. Physico-chemical treatment systems, including fiber filters, deep bed filters, and granular activated carbon (GAC) filters, can effectively remove pollutants at high rates (see Table 7). High-rate systems are designed to improve water quality to meet at least non-potable standards. A brief overview of these systems is provided below. Fiber Filter: High-rate fiber filters have been effectively utilized in tertiary wastewater treatment. Unlike traditional sand filters, these systems use filters consisting of fine polyamide fibers shaped in the form of U-shaped bundles. Fiber filters operate at filtration velocities that are over five times faster than conventional rapid sand filters and possess a specific surface area that is more than double that of sand [51; 52; 53]. The unique packing of the fibers provides a large specific surface area and is highly porous (exceeding 90%). This means that the pressure drop across the filter is low while maintaining a high removal efficiency, even at elevated filtration velocities [53]. The inline addition of flocculants can further enhance the system's capacity to remove dissolved organics and trace metals. Deep Bed Filter: Deep bed filtration, also known as media or rapid filtration, is extensively employed in water treatment for particle removal as the last clarification step. This method is effective for eliminating various particles in both water and wastewater. Deep bed filters are particularly suitable for clarifying dilute suspensions with particle concentrations below 500 mg/L and sizes ranging from approximately 0.1 to 50 \(\upmu\)m [52]. These filters can operate under pressure or gravity, with filtration velocities typically ranging from 5-20 m/h. Deep bed filters can be configured as either single-media or dual-media systems, with dual-media setups enabling the influent to flow through one type of media before moving on to another. Membrane Filtration and Hybrid Systems: Pilot studies in low-pressure membrane technologies, including microfiltration (MF) and ultrafiltration (UF), have led to their growing use in stormwater treatment, thanks to their effectiveness, ease of operation, and compact size [52]. Microfiltration membranes usually have pore sizes between 0.1 and 0.2 \(\upmu\)m. In comparison, ultrafiltration membranes typically have smaller pore sizes, ranging from 0.005 to 0.05 \(\upmu\)m or less. Microfiltration is effective at removing particles, clays, and bacteria, while ultrafiltration is designed to eliminate macro-molecules, proteins, polysaccharides, and viruses. Operating pressures for MF vary from 100-200 KPa, whereas UF generally requires pressures above 200 KPa. Membrane filtration is often preceded by pre-treatment methods (e.g., fiber filters, deep bed filters), resulting in hybrid systems that significantly improve overall removal efficiency and produce good quality water that meets water quality standards for reuse [52]. GAC Biofilter: This is an adsorption biofiliter generally consisting of a column packed with support media that promotes microbial growth. During the initial operation phase, the main mechanism is the adsorption of different substances, including microorganisms.