| Abstract | An investigation of the applicability of ion exchange for removing hardness from waters found in metropolitan Bangkok was conducted using cationic resins in sodium form. The objective was to produce a water of approximately 20 mg/1 residual hardness- a highly softened water required
by several industries. Two resins were studied; a conventional cationic resin under the trade name Abelite IR-120 and a new macroreticular resin under the trade name Amber lite 200. Two waters, municipal water from
Bangkok and well water from Thonburi, were tested during the investigation. Using a laboratory model designed for the investigation, the total and breakthrough capacities of the two resins were determined. Optimum operating values of flow rate, regenerate concentration and regeneration
contact time were also investigated. Using these parameters, operating
guidelines were established for a prototype ion-exchange unit, including regenerant recovery and wastewater reuse.
Investigations showed that Amberlite IR-120 has a total exchange capacity of 4.62 meq/gm against 4.47 meq/gm for Amber lite 200. The
breakthrough capacities, which were found to be reduced by the presence of iron and manganese by about 20% per mg/1 of these impurities, amounted to 33.8 and 36.5 kgr/cu ft. of Amber lite IR-120 using well and municipal
waters respectively; 26.7 and 28.9 kgr/cu ft. of Amber lite 200 using well and municipal water respectively. Hence, Amber lite IR-120 had a higher capacity for removing hardness from waters used than Amber lite 200,
Clogging of the resin bed by iron and manganese precipitates limited the flow rate to 2 gpm/cu ft. of resin, requiring backwashing between each
exhaustion cycle. Optimum values of 10% NaC1 for regenerant concentration
and 60 minutes for regeneration contact time were obtained.
Under prototype operating conditions, one cubic foot of resin was estimated to produce a gross water yield of 1,210 gallons of softened well water and 1,310 gallons of softened municipal water. From this yield, 6-7% would be wasted in backwashing, regenerating and rinsing under optimum recovery and reuse conditions. Operating time per cycle would amount to
12 hours for the well water and 13 hours for the municipal water.
Due to reduced resin capacity and increased cyclic operating time, pretreatment of waters for both iron and manganese removal appears justified. |
