Optimizing granular anammox retention via hydrocycloning during two-stage deammonification of high-solid sludge anaerobic digester supernatant

High-solid sludge anaerobic digestion leads to increased organic matters in digester supernatant, which pro-motes heterotrophic competition and reduces anaerobic ammonium oxidation (anammox) retention. This re-search demonstrated effective anammox retention by hydrocycloning during a two-stage deammonification. Anammox retention was evaluated by dividing large (>0.425 mm), medium (0.25 to 0.425 mm), and small (<0.25 mm) aggregate fractions via a sieve, whereby Candidatus Kuenenia abundance in each size aggregate was measured to be 16.8%, 5.0%, and 0.9% respectively. After hydrocyclone separation, large particles took up only 1.7% to 2.7% in the overflow discharge (upper discharge from the reactor), whereas its initial proportion was 19.4%, indicating limited anammox loss. The volume ratio change of large particles to total aggregates was defined for particle breakdown evaluation. Breakdown (23% to 32% large particles) occurred mainly during pumping (influenced by pump frequency and type), while little happened in the hydrocyclone. This research provided methods to use a sieve to evaluate anammox retention by hydrocyclone during high-solid sludge anaer-obic digester supernatant deammonification, and information for reducing particle breakdown, pumping selec-tion, and separation optimization. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

High-solid sludge anaerobic digestion can lead to increased organic matters in digester supernatant, which promotes heterotrophic competition and reduces anaerobic ammonium oxidation (anammox) retention. This study demonstrated effective anammox retention by hydrocycloning during a two-stage deammonification, providing information for reducing particle breakdown, pumping selection, and separation optimization.