Combined phosphate and nitrogen removal in a sequencing batch reactor using the aerobic denitrifier, Microvirgula aerodenitrificans

A phosphate removal sludge was bioaugmented with the aerobic denitrifier, M icrovirgula aerodenitrificans in order to reduce the nitrate produced durin g the aerobic nitrifying-phosphate uptake phase. Fluorescent in situ hybrid ization (FISH) was used to follow the fate of the added strain. In order to maintain the pure strain in the complex ecosystem, diverse physiological a nd kinetic based strategies of bioaugmentation were tested under the sequen cing batch reactor (SBR) type culture. The nature of the M. aerodenitrifica ns inoculum (adapted to nitrate-aerobic conditions or to anoxic one) had no influence on the SBR performances and did not enhance aerobic denitrifying performances. The optimum quantity of the added strain (10% of the total b iomass) seemed to have much more positive influence on the long term mainte nance of the purl strain than on the SBR performances. A small but daily su pply of M. aerodenitrificans gave exactly the same result than a massive an d 1-day supply, i.e. no enhancement of performances and no amelioration of the length of maintenance. A continuous supply of carbon during the first h our of the aerobic phase combined to a 10% supply of M. aerodenitrificans g ave the best compromise in terms of phosphate removal, nitrification and ae robic denitrification performances. It was accompanied too by a decreased n umber of the ammonia and nitrite-oxidizing bacteria and a modification of t he nitrite-oxidizing flee structure. FISH on M. aerodenitrificans revealed that (i) before bioaugmentation, the strain was already present in the phos phate removal sludge and (ii) the added bacteria almost disappeared from th e reactor after 16 HRT. In a last experiment, M. aerodenitrificans embedded in alginate beads allowed enhancement of both aerobic denitrifying perform ances and length of strain maintenance. (C) 2000 Elsevier Science Ltd. All rights reserved.