Impact of Iron Salt Addition on Solids Production and Operations

Wastewater agency management and staff are often in the position of evaluating their options to control struvite formation, manage digester gas hydrogen sulfide concentrations, limit phosphorus levels in plant effluent or solids processing systems, or control upstream or plant sulfide for odor/corrosion control. These and other objectives can be managed with an iron salt chemical addition program. However, non-chemical options are also usually available and the owner needs to consider and evaluate all reasonable alternatives using the best information available. This paper brings together information about iron salt addition theory and experiences so that accurate and informed comparisons can be developed for alternative evaluations. Chemical dosing calculation examples are included to relate how iron salt dosing and feed rates are determined and to describe the type and extent of additional chemical solids that may be produced with certain levels of chemical feed. Additional tools used in the industry are discussed including chemical equilibrium modeling, and related testing work. Key observations from previous work on iron salt programs is included.