Combined use of coagulation (M. oleifera) and electrochemical techniques in the treatment of industrial paint wastewater for reuse and/or disposal

• Published in: Water research (Oxford) 2018-11, Vol.145, p.153-161
• Main Authors: Barbosa, Andreia D., da Silva, Larissa F., de Paula, Heber M., Romualdo, Lincoln L., Sadoyama, Geraldo, Andrade, Leonardo S.
• Format: Article
• Language: English
• Subjects: Boron-doped diamond electrode; Coagulation-flocculation; Moringa oleifera; Paint manufacturing wastewater; Water reuse
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2018.08.022

In this work, water-based paint (WBP) wastewater was treated using a natural coagulant, Moringa oleifera aqueous extract (MOAE), fortified with Ca2+ (from nitrate and chloride salts). In order to improve the quality of the treated wastewater and render it suitable for disposal, an electrolytic flow process was associated with the wastewater treatment using a filter-press reactor with a boron doped diamond (BDD) electrode. The feasibility of the treatment was evidenced by the reuse of the treated wastewater in the production of a new paint (manufactured by the company supplying the raw wastewater), whose quality was compatible with the water used by the manufacturer. The best conditions for the coagulation-flocculation process involved the use of 80 mL of MOAE (50 g/L of MO and 0.125 mol/L of Ca2+) for every 1.0 L of wastewater at pH 6.5. The limiting current density (35 mA/cm2) and an electrolysis time of 90 min (charge passed of 3.68 A h/L) were used in the electrochemical treatment. Biotoxicity assays using the brine shrimp Artemia salina revealed that the mortality (in %) of microcrustaceans was reduced from 100% (raw wastewater) to only 11% at the end of the electrolysis process, in addition to eliminating the strong odor and 85% of the organic load. Moreover, microbiological tests showed that the number of mesophiles decreased by more than six orders of magnitude and there was no growth of thermotolerant coliforms (TC). [Display omitted] •M. oleifera (biocoagulant) meets the quality control requirements for reuse proposal.•Calcium ions potentiate the coagulating effect of the protein contained in M. oleifera.•Reuse is only possible if Ca2+ ions (from a NO3− salt) are added into biocoagulant.•Electrochemical treatment wastewater is required for water discharge proposal.•The quality of the paints produced with recycled water was similar to the marketed.