Influence of operating parameters on phosphate removal from water by electrocoagulation using aluminum electrodes

• Rate of phosphate removal by electrocoagulation is governed by precipitation of AlPO4(s) and/or adsorption on Al(OH)3.
• Kinetics of phosphate removal is depending only on electrical charge whatever the time of treatment and the current density.
• Electrical consumption is lower at low current density because of the limited ohmic voltage drop.
• pH variation depends on production of OH- at the cathode and its reaction with Al3+.

Treatment of water containing phosphate by electrocoagulation has been studied in a laboratory batch reactor. The effect of operating parameters on both phosphate removal efficiency and pH evolution has been investigated. Influence of distance between electrodes, current density, initial pH, temperature and conductivity has been extensively studied in a wide range of values. The results show that the removal efficiency depends on the electrical charges; the same efficiency is obtained with low current density with long time of treatment, or higher current intensity with short treatment time. The time evolution of the pH during the treatment strongly depends on the operating conditions but the final pH is more or less the same due to the buffering effect of Al(OH)3/Al(OH)4- mixture. Effects of the temperature, often disregarded in the literature shows that treatment rate is strongly increased with temperature whereas conductivity near 1 mS/cm is enough to ensure reasonable treatment rate. The electrical energy consumption (around 4 Kw/m3) is acceptable to achieve 90% of conversion but lower current density is preferable because of the lower voltage drop.