This paper provides a procedure for comparing the performance of different biofilm carrier medias and their surrounding suspended biomass through oxygen uptake rate (OUR) tests. For in situ OUR measurements three identical lab scale biofilm reactors were set up at the El Gouna wastewater treatment plant (WWTP). In this setup two options of media for moving-bed biofilm reactors (MBBR) and one media for fixed-bed biofilm reactors (FBBR) were compared. The WWTP also used the same carrier in a real scale hybrid application to analyze how the interactions between the carrier type and the suspended biomass influences the overall performance. The in situ OUR approach is recommended to measure the contribution of the biofilm fixed biomass under side specific conditions. Especially settleability and diffusion limitations are here the two opposite poles that for warm climate conditions can’t be sufficiently predicted based on literature. A biofilm carrier application can add but actually can also reduce the capacity in a hybrid activated sludge system: Added MBBR-media are able to grind down sludge flocs forming a badly settleable suspended biomass. Added FBBR-media can lead to EPS rich biofilms that contribute very little as substrate and oxygen are unavailable for the biofilm organisms. In this application of the comparison procedure, Kaldnes K1 like MBBR media was compared with a recycling MBBR carrier option (poly propylene bottle caps) and Jäger Envirotech “BioCurlz™” FBBR media. The study showed higher average rates for the MBBR but decreased settleability. The FBBR showed higher peak rates when flushed to break up the biofilm and well settleable sludge. The determination of OUR per gram of volatile solids (SOUR) showed equal results for all carriers and that in warm conditions only the capacity to accommodate biomass, determines the contribution of the carrier.
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