Efficacy of Biomass Input into Main-Stream Treatment from Warm Sludge Liquor Treatment at Cold Temperatures

A laboratory-scale reactor study was conducted to evaluate the potential for biomass input to stabilize nitrification at low temperatures and allow shorter solids retention times. Recovery and enrichment of nitrifying microorganisms in a second-sludge side-stream reactor treating anaerobic digester supernatant in batch and continuously-fed configurations was evaluated. Complete oxidation of ammonia to nitrate was observed in all main-stream reactors, as expected, during the initial phase of the experiment conducted at room temperature. However, as temperature was reduced to 10°C nitrite accumulation was experienced in all reactors. Incomplete ammonia oxidation has also been experienced to a lesser extent. However, it appears that input of biomass from a batch-fed side-stream reactor to a batch-fed main-stream reactor is more beneficial to nitrification stability than input from a continuously-fed side-stream. The side-stream reactors have experienced upsets brought on by operator error resulting in nitrite accumulation likely due to reduced oxygen tension. A potential mechanism involves accumulation of free hydroxylamine.