Pulp mill sludge-derived carbon activated with an alternative source of chemicals and its application in wastewater treatment – An approach for byproducts valorization

Abstract

The purpose of this study was to investigate pulp mill by-products valorization through activated carbon (AC) production and its application in wastewater treatment. Bio-sludge is a known promising precursor for AC production. The mill's chemical recovery stage generates an effluent (electrostatic precipitator ash leachate - EPAL) with high levels of potassium and sodium, which motivate studies regarding its viability as a chemical source for carbon activation. Bio-sludge and EPAL are problematic by-products and this research line would allow their return to the productive chain, as an adsorbent for the wastewater treatment. Two carbonization heating rates (3.5, 15 °C/min), three activation agents (NaOH, KOH, EPAL) and two activator:bio-sludge ratios (1:1, 2:1) were used for AC production. The best ACs in terms of surface area were those produced at 3.5 °C/min, with KOH or EPAL in 2:1 proportion. ACs produced under these conditions and commercial activated carbon (CAC) were used in adsorption tests with industrial wastewater. For color removal, KOH-activated carbon presented the greatest efficiency (80.45 %), followed by CAC (76.74 %) and EPAL-activated carbon (70.13 %). For COD removal, EPAL-activated carbon presented greater efficiency (53.49 %), followed by CAC (40.84 %) and KOH-activated carbon (36.86 %). Freundlich's model best described the experimental adsorption data. The KOH results were expected to be satisfactory, since KOH is proven to be effective for carbon activation. The EPAL-activated carbon results were remarkable, especially for COD removal, showing that EPAL can be used as an activator and that the by-products have potential for valorization according to the circular economy principles.