Removal of phosphate from wastewaters for further utilization using electrocoagulation with hybrid electrodes – Techno-economic studies

• Electrocoagulation (EC) of synthetic wastewater containing phosphate optimized.
• Successful scale up of synthetic wastewater treatment with EC.
• Real phosphate-containing mining and dairy wastewaters treated successfully.
• Economic values of the EC process evaluated.
• Utilizing sludge as an additive in granulated bio ash-based fertilizers discussed.

The electrocoagulation (EC) process employed in the removal of phosphate from synthetic wastewater (SWW, 30 mg/l) was optimized, followed by successful scale-up experiments. The optimum process conditions (96% phosphate removal) for laboratory-scale SSW were found to be: anode/cathode = Al/Fe (although Fe/Al performed similarly), initial pH = 5, current density = 100 A/m2, treatment time = 15 min, supporting electrolyte = 1.0 g/l NaCl and electrode gap = 7 mm.Real industrial phosphate-containing mining wastewater (MWW) and dairy wastewater (DWW) were also treated with EC, with high pollutant removal efficiencies (optimal phosphate removal of 79% and 93% in 30 min and 60 min, respectively) achieved over the wide initial pH range studied. Electricity consumption and operating costs values in optimum conditions were low for all wastewaters: 0.75 kWh/m3 and 0.17 €/m3 for SSW (laboratory scale), 2.11 kWh/m3 and 0.28 €/m3 for MWW, and 1.46 kWh/m3 and 0.31 €/m3 for DWW. To summarize, the feasibility of using EC in removing phosphate from the wastewater types studied was proven. Utilization of the resulting EC sludge – a potentially valuable phosphorus source in the future (especially in granulated bio ash-based fertilizer products) – was also studied and is discussed.