Ground water coagulation using soluble stainless steel electrodes

This study dealt with colloids separation from ground water in the Eastern Province of Saudi Arabia. The water was found to have a conductivity of 4400 Rs/cm and chloride and sulfate concentrations of 834 and 550 mg/l, respectively. The turbidity of the water was increased to 76 nephlometric turbidity unit (NTU) by the addition of bentonite. The efficiency of using soluble stainless steel electrodes for the in-situ formation of ferric hydroxide has been investigated. The electrical current input was found to be inversely proportional to the residual turbidity in the test water. At a contact time of 5 min and a natural chloride content, the highest turbidity removal efficiency of 95% was achieved at a current of 1 A. When the current was reduced to 0.5 A and the contact time was increased to 10 min, the residual turbidity was reduced from 4.0 to 1.6 NTU. Furthermore, similar turbidity removals were achieved at a much shorter contact time (2 min) when 1 g/l sodium chloride was added to the test water. Due to the importance of pH variation with regard to coagulation, the phenomenon of voltage-induced hydrogen evolution was investigated as well. While the solutions final pH increased with the increase in current and contact time, it decreased with the increase in sodium chloride concentration. (C) 2002 Elsevier Science Ltd. All rights reserved.