Clogging of reactive filters for phosphorus removal - A review

The objective of this paper is to present a comprehensive review of clogging that is associated with reactive filters applications aimed at phosphorus removal. Reviewed studies used various inlet design strategies: water flow direction (vertical or horizontal), influent pressurization (pressurized by pumps or gravity-fed by overflow) and feeding distribution types (point, water spraying, distribution pipes or coarse surface layers). They used operational strategies including prefilters, filters in series, regeneration of media, optimization of hydraulic retention time, concealment from the air, chemical additions and backwashing. Media mixes and different particle sizes in series were used as media selection strategies for clogging mitigation. Small reactive media size (0-10 mm) was used in most reviewed applications of reactive filters, while larger particle size was used to improve water distribution. While guidelines for particle size selection do exist, most authors did not systematically evaluate the suitability of the media for flow. Bicarbonate inputs from wastewater or from atmospheric CO₂ were found to impact significantly the filter lifetime by chemical precipitation. However, most reviewed studies did not report the alkalinity or inorganic carbon concentration in the feeding wastewater and did not report the level of atmospheric concealment. The authors recommend to systematically report the following parameters in future studies on RFs: wastewater alkalinity; level of sealing from atmospheric CO₂; complete description of operational parameters such as feeding pressure, presence of overflows, evolution of pressure over time, impact of maintenance events, feeding mode, wastewater distribution mode; and particle size stability.