Novel Use of Dairy Processing Sludge Derived Pyrogenic Char (DPS-PC) to Remove Phosphorus in Discharge Effluents

Purpose: Pyrogenic char (PC) materials derived from the pyrolysis of dairy processing sludge (DPS) could be a cost effective option to develop carbonaceous adsorbent for phosphorus (P) removal from wastewater. The main objectives of the present work were to: (1) determine the efficacy of DPS derived PC (DPS-PC) to remove P from synthetic and dairy wastewater samples, (2) identify possible P removal mechanisms, and identify parameters that could be used to quickly identify the P removal capacity of a char and (3) propose a ranking system for the selection of DPS-PC which includes energy, char yield and P removal criterion. Methods: DPS-PC samples were obtained from the pyrolysis process (700 °C) of two sludge streams: (1) bio-chemically treated mixed sludge and (2) lime treated dissolved air floatation (DAF) sludge. Herein, 12 DPS-PC samples were assessed and pre-screened in batch experiments to determine the P removal efficacy from both synthetic and dairy wastewater solutions. The effect of solid to liquid dosage, contact time, pH and P concentration was investigated. Statistical regression and correlation analyses were performed to understand P removal mechanism. The quantitative assessment of char yield, energy balance and P removal performance were combined to propose a ranking system for DPS feedstock selection. Results: P removal varied across DPS-PC type and composition, with mixed sludge derived char exhibiting 85–98% P removal at a dose of between 10 and 50 g/L, whereas, those from DAF sludge removed > 99% at 3 g/L. The P removal process was associated with a number of strongly significant mineral phase correlations pertaining to mineral composition (i.e. availability of Ca, Mg and Si) of the DPS-PC samples. A quick water extractible P test together with knowledge of the major P locking minerals can be used to pre-screen the potential of PC for P removal application. This study also provides a physicochemical reference and ranking of DPS feedstock selection, which will be useful for future investigation on the pyrolysis of DPS at pilot-scale and subsequently, to develop PC based efficient adsorbent for application in wastewater treatment. Graphic Abstract: [Figure not available: see fulltext.].