Control of biological iron removal from drinking water using oxidation-reduction potential

Biological removal of iron to produce drinking water was established in a p ilot plant treating raw water with a pH of 5.7. The objective was to evalua te the use of oxidation-reduction potential (ORP) as a control tool and det ermine its relationship to dissolved oxygen (DO) and residual iron concentr ation in filtered water from an operating biological filter. Results showed that above a low minimum value of DO, residual iron concentration and ORP were not affected by varying the DO level. A non-linear regression was esta blished to correlate total residual iron concentration to ORP with an R-2 o f 0.8848. This correlation can be used to predict iron concentration when O RP is in the range 300 to 470 mV. Below this range, total residual iron is greater than or equal to 3 mg/l and above, total residual iron is less than the French regulation limit of 0.2 mg/l. Pilot plant operating conditions were implemented in the primary filter of an industrial plant in France, im proving iron elimination and doubling the length of the filtration cycle. ( C) 1998 Published by Elsevier Science Ltd. All rights reserved.