Treatment of printing industrial wastewater: application of acidification, coagulation and flocculation for dewatering

Printing industrial wastewater (PIW) contains high levels of non-biodegradable organic compounds, particularly from surfactant-laden cleaning of ink cartridges. It presents a waste challenge due to its dark coloration and toxic content. Current treatments of PIW include coagulation and flocculation, which are suitable for high-solids-content waste, followed by advanced oxidation processes for polishing. This study investigates the application of acidification, coagulation and flocculation for dewatering PIW using lab-scale and pilot-scale setups, focusing on the efficiency of pH adjustment, ferric chloride (FeCl₃) coagulation, and biobased flocculants like cationic starch alongside a synthetic polymer. Acidification combined with cationic polyacrylamide or starch produced filter cakes with dry matter contents of up to 79 % w /w for 24 h consolidation, with a residual dye and aromatic compound reduction of over 99 %. FeCl₃ coagulation followed by flocculation is a cost-effective treatment for small-scale facilities, enhancing effluent quality, while producing a cake dry matter upwards of 55 % at 2 bar pressure. Implementing these approaches could reduce disposal costs significantly and enable water reuse, supporting sustainability in wastewater management for the printing industry. • Coagulation-flocculation removed >99.9 % dye and > 99.5 % aromatics from PIW. • Acidification produced a filter cake with up to 79 % dry matter content. • Biobased and synthetic flocculants showed comparable treatment performance. • FeCl₃ coagulation was cost-effective and enhanced effluent clarity for reuse.