The promulgation of the 10 μg/L arsenic MCL will require some utilities to implement new, or to modify existing, treatment processes. Arsenate removal is commonly performed by adsorption to hydrous ferric oxide during sweep-floe conventional treatment, and can be improved through enhanced coagulation modification options. An integrated process model including detailed process chemistry was developed and used to investigate the effect of water composition, influent pH, and silica competition on operating conditions for arsenic removal to produce a 10 μg/L effluent arsenic concentration. Additionally, two different sets of arsenate and silica adsorption constants were used to assess qualitatively the impacts of model structure uncertainty. In general, the background inorganic concentrations, influent pH, and (for one model) silica competition increased the range of conditions under which treatment modification is required to improve removal efficiency. The treatment modifications considered include additional ferric chloride dose, acid addition, or both. For additional treatment cases, an optimization approach was used to determine the least-cost modification option to improve removal efficiency. When silica competition was not considered, the additional ferric chloride dose option was determined to be the least-cost modification for both models. When silica competition was considered, the model that predicts significant silica competition selects acid addition or both modification options at high pH and background inorganic concentrations; the other model continued to suggest only the additional ferric chloride dose option.
- Enhanced coagulation
ASJC Scopus subject areas
- Environmental Chemistry
- Waste Management and Disposal