Utilizing Waste Eggshells as a Calcium Precursor for Contact Precipitation of Phosphorus from Digested Sludge Centrate

Abstract

Phosphorus (P) recovery from wastewater is an essential component of the global P cycle. A contact precipitation process using eggshells as a calcium (Ca) precursor was used to recover P from synthetic wastewater and real digested sludge centrate. Up to 96.4% of P could be recovered from the digested sludge centrate after three repeated cycles of the contact precipitation process. In addition, 36.1% of total chemical oxygen demand and 37.6% of total ammonia nitrogen were removed from the centrate. Finally, most of the precipitates could be collected by a simple washing step. Scanning electron microscopy–energy dispersive spectroscopy and x-ray diffraction results indicated that the eggshells played three roles in this process: Ca source, precipitation template, and filter medium. Precipitates were mainly brushite. This research provides a new perspective on P recovery from wastewater using waste eggshells, and if further optimized, has a potential for practical future applications.

Keywords: Phosphorus recovery, Contact precipitation, Calcium phosphate, Eggshells, Digested sludge centrate