Aerobic granular sludge reactor technology - Aerobic granulation with different substrates
Aerobic granular sludge is a promising alternative to traditional activated sludge basins in wastewater treatment plants (WWTP). Granular sludge has much better settling characteristics than activated sludge. Furthermore it can remove carbon, nitrogen and phosphorus within the same reactor. Aerobic granules can be formed in bubble column reactors (BCR) in sequencing batch mode (SB) by alternating anaerobic and aerobic phases. Our investigation consisted in running two reactors one with acetate as C-source, like in most studies, and one with propionate, to see if it is also possible to form granules with propionate. Propionate is assumed to favor the growth of phosphate accumulating organisms (PAO) over glycogen accumulating organisms (GAO). This is an important point for the removal performances, because in contrary to GAO, PAO can take up phosphate and may also denitrify (DPAO). A first objective was reached as we obtained stable, good settling granules with propionate. Concerning the reactor performances, we got 100 % of substrate removal, 83 % and 55 % of phosphate removal in the propionate and acetate reactor respectively, but only moderate ammonium removal. Based on these results we concluded that granule formation, C-removal and P-removal with acetate and also propionate as substrate is possible, but that further investigation is needed to cultivate nitrifying bacteria in the granules.