Engineered pine nut shell powdered activated carbons for advanced drinking water treatment

Abstract

The presence of micropollutants in natural waters, as pharmaceutical compounds (PhCs), natural organic matter (NOM) and cyanotoxins (naturally produced by cyanobacteria in drinking water source reservoirs under some conditions), that resist to conventional treatments, calls for the development of advanced drinking water treatment (DWT) processes. Activated carbon adsorption is considered one of the best available technologies to tackle these current water quality challenges. In this work, high-performing powdered activated carbons (PACs) were prepared by physical (steam or CO2) activation of carbonized pine nut shells (PNS) with particles < 150 μm. The particle size distribution of the obtained PACs, and of the as-received commercial PACs, NORIT SAE Super and NORIT SA-UF, was assessed and each fraction was characterized regarding textural properties, density, moisture content and pHPZC. Smaller particle sizes were generally associated with higher total and mesopore volumes, allowing faster kinetics and higher adsorption capacity under real competitive environments towards NOM, PhCs and microcystins (commonly produced hepatotoxic cyanotoxins). In assays with dechlorinated water spiked with PhCs and NOM surrogates the PNS-derived PACs (fraction < 20 μm) outperform the commercial ones towards PhC removal by more than 15 percentual points. The steam-activated PNS PACs presented the highest removal rate for carbamazepine (91%), followed by diclofenac (56%) and sulfamethoxazole (28%), for a contact time of 24 h and [PhC]0= 500 μg/L. The PNS-derived PACs are being tested with coagulation, flocculation, and sedimentation processes, for conventional DWT processes, and with membranes, as a hybrid adsorption-membrane technology, for advanced DWT.