Alternative methods for dissolved oxygen removal from water: a comparative study

An experimental study was performed to assess the feasibility of recovering valuable chemicals from waste streams. The ammonia in the wastewater generated from the NH4Cl manufacturing could be recovered using an ion-exchange technique. After the ammonia-rich wastewater passed through cation exchange resin, regeneration with HCl was performed. The resultant regenerant soluton was composed of NH4Cl. This spent solution could be recycled into the upstream, i.e., drying process for the NH4Cl production. However, NH4Cl concentration in the regenerant solution was so little for drying that the direct recycling of the regenerant solution could not be valid. Therefore, pre-concentration of the regenerant was strongly proposed to increase the NH4Cl concentration. Typical concentration methods such as reverse osmosis, evaporation and electrodialysis were attempted to select an appropriate method for the pre-concentration. It was found that the electrodialysis was the most effective method to concentrate the regenerant NH4Cl solution. Since the ammonia concentration in the effluent of ion exchange was negligible, the effluent was able to be reused as process water or discharge directly. This new process makes it possible to recover the valuable material from the wastewater and to improve the effluent water quality. Consequently, it provides an environmentally sound alternative for manufacturing NH4Cl.