Struvite Mitigation in Anaerobic Digesters

Struvite (MgNH4PO4*6H2O) precipitation is a common recurring problem in anaerobic digesters. This paper evaluates the effectiveness of different struvite control approaches to mitigate and/or remove struvite formation and accumulation in anaerobic digesters. Metal salt addition alone or in conjunction with struvite harvesting can eliminate struvite formation. Struvite harvesting upstream and downstream of the anaerobic digesters reduces the anaerobic digester struvite formation potential by 65 to 70 percent and 35 percent respectively. Life cycle evaluation shows the most cost effective manner to mitigate struvite formation in anaerobic digesters is labor intensive cleaning with high pressure water sprays, jetting pipe lines and physical hammering or brushing. If long term operations show mechanical cleaning does not provide reliable operations or results in excessive equipment repair, ferric chloride addition should be added to control struvite formation. Post–digestion processes, should consider either diluting the flow stream with water, or adding a metal salt (ferric chloride), struvite inhibiting chemicals, or hydrochloric acid to keep struvite from forming.