Phosphorus Removal Research

Mimicking Nature to Remove Phosphorus in Leach Fields

Presented at NOWRA, 2013

Iron-rich ‘B-horizon’ soil is formed naturally by precipitation of oxides of iron leached from the overlying ‘A-horizon’ soil. Reactive phosphorus dissolved in septic tank effluent passing through B-horizon soil adsorbs onto and binds chemically to surfaces of iron oxides and hydroxides. These Fe-P mixtures transform into stable iron-phosphate minerals such as vivianite and strengite, which have very low solubilities in aerobic and anoxic environments. Total phosphorus (TP) is thus removed from the hydrologic cycle, out of groundwater and adjacent surface water bodies.

Advances in Understanding Phosphorus Removal in Septic Systems

Presented at NOWRA, 2014

Removal of phosphorus in residential septic systems to over 95% is now being attained using electrochemistry (Waterloo EC-PTM, patents pending) to introduce iron or aluminum into sewage to react with phosphorus and form insoluble P-based mineral cements. Conventional leach fields made of clear sand remove perhaps 15 – 35% of phosphorus from septic tank effluent, but if it is only loosely adsorbed onto surfaces of other minerals and is susceptible to being leached out at a later date.

Removal of Sewage Phosphorus by Adsorption and Mineral Precipitation, With Recovery as Fertilizing Soil Amendment

Published by Water Science & Technology, 2018

Sand filters loosely adsorb 15 – 35% total phosphorus from septic tank effluent, with likely more adsorbed by soils in septic system leach fields. Although iron oxide and clay minerals in soils increase adsorption, P adsorbed by minerals may still be readily mobilized. Mineral forms of P are desirable to ensure stability, and do occur in certain soils when first adsorbed. The Waterloo EC-P method mimics processes that lead to P immobilization in mineral soil, but bypasses the
intermediary step of adsorption onto minerals.