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Open Access Ferric/Ferrous Chloride Injection Optimization as Demonstrated by Regional Case Studies

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Abstract:

In southern California, the South Coast Air Quality Management District (AQMD) limits the concentration and mass of hydrogen sulfide (H2S) in gas from all sources (Rule 431.1). Many wastewater treatment plants are successfully applying iron salts to mitigate H2S concentrations in the biogas produced through the anaerobic digestion of biosolids. The iron salt usage at nine facilities was evaluated to assess chemical costs and determine the optimum injection locations. Findings indicate that relocation of the ferric chloride injection point from the primary influent channel to the digesters tends to reduce chemical dose and cost, improve plant aesthetics, and increase the downstream aeration demand. The type of metal salt specified affects location. Plants observed a dosage gain when injecting ferric into anaerobic environments. However, the presence of oxygen appears to improve ferrous performance and either form is appropriate for aerobic locations. The key parameter that controls effective injection is adequate mixing.

Keywords: AIR EMISSIONS; ANAEROBIC DIGESTION; BIOSOLIDS; CALIFORNIA CASE STUDIES; CHEMICAL INJECTION OPTIMIZATION; CORROSION POTENTIAL; FERRIC CHLORIDE; FERROUS CHLORIDE; HYDROGEN SULFIDE CONTROL

Document Type: Research Article

DOI: https://doi.org/10.2175/193317707X195999

Publication date: 2007-04-01

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