Technologies to Remove Phosphorus from Wastewater

This brief literature review examines treatment technologies available for wastewater treatment plants to remove phosphorus. Although it is not meant to be exhaustive or complete, it does include some of the newest available reports on P removal. Treatment technologies presently available for phosphorus removal include: Physical: filtration for particulate phosphorus membrane technologies Chemical: precipitation other (mainly physical-chemical adsorption) Biological assimilation enhanced biological phosphorus removal (EBPR) The greatest interest and most recent progress has been made in EBPR, which has the potential to remove P down to very low levels at relatively lower costs. Membrane technologies are also receiving increased attention, although their use for P removal has been more limited to date. The question of sludge handling and treatment of P in side streams is also being addressed. Assuming that 2-3% of organic solids is P, then an effluent total suspended solids (TSS) of 20 mg/L represents 0.4-0.6 mg/L of effluent P (Strom, 2006b). In plants with EBPR the P content is even higher. Thus sand filtration or other method of TSS removal (e.g., membrane, chemical precipitation) is likely necessary for plants with low effluent TP permits (Reardon, 2006). 2. Membrane technologies Membrane technologies have been of growing interest for wastewater treatment in general, and most recently, for P removal in particular. A recent 3 day national Water Environment Research Foundation (WERF) workshop on achieving low effluent nutrient levels devoted an entire session (4 papers) to this topic (WERF, 2006). In addition to 2 removing the P in the TSS, membranes also can remove dissolved P. Membrane bioreactors (MBRs, which incorporate membrane technology in a suspended growth secondary treatment process), tertiary membrane filtration (after secondary treatment), and reverse osmosis (RO) systems have all been used in full-scale plants with good results. Reardon (2006) reported on several plants achieving <0.1 mg/L TP in their effluent, and suggested the current reliable limits of technology are 0.04 mg/L for MBRs and tertiary membrane filtration, and 0.008 mg/L for RO. Chemical precipitation has long been used for P removal. The chemicals most often employed are compounds of calcium, aluminum, and iron (Tchobanoglous et al., 2003). Chemical addition points include prior to primary settling, during secondary treatment, or as part of a tertiary treatment process (Neethling and Gu, 2006). Song et al. 2006) generally agree, however, that the process is more complex than predicted by laboratory pure chemical experiments, and that formation of and sorption …