Evaluation of manganese adsorption onto GAC using isotherms and RapStech® service
Severn Trent Water Ltd
Jan’06 to Mar’07
Manganese in some surface waters can be adsorbed onto Granular Activated Carbon (GAC) filters at Water Treatment Works (WTWs) which can assist with meeting the final drinking water PCV of 50µg/l. A WTW was planning to introduce changes to the coagulation process upstream of the GAC filters by the alteration of pH and needed to determine if this would impact on manganese adsorption within the GAC.
Laboratory scale investigations were conducted using field spent, recently regenerated and virgin GAC from the WTWs with site water in batch isotherm tests at different pHs and Rapid Small Scale Column Testing (RSSCT) using the RapStech® service.
Comparison of the isotherm and the RSSCT data has highlighted the strengths and weakness of the two methods. Manganese adsorption is greater under isotherm conditions (batch tests utilising long contact times) and RSSCT indicates the adsorption of manganese which is likely to occur onsite with continuous flow system and specific velocity. Isotherm analysis using site water and also laboratory water, provided evidence for competitive adsorption, as adsorption of manganese was greater for the isotherms using just laboratory water spiked with manganese.