PROTECTION OF BIOFILMS AGAINST TOXIC SHOCKS BY THE ADSORPTION AND DESORPTION CAPACITY OF CARRIERS IN ANAEROBIC FLUIDIZED-BED REACTORS

The aim of this study was to select a support medium for an anaerobic biofilm fluidized bed reactor (AFBR) for waste water treatment. Six ma terials, shale, pumice, porous glass, quartz sand, activated carbon an d anthracite were used as carriers for the biofilm. The reactors were operated in parallel for several months with vapour condensate from a sulfite cellulose process as feed. The criteria used for the evaluatio n were: a) Reproducibility of the reactor performance, b) performance of the different carriers under various loading rates, c) stability ag ainst toxic shock loadings using 2,4,6-trichlorophenol (TCP) as toxica nt, d) recovery capacity after intoxication and starvation, e) adsorpt ion/desorption behavior of the carriers. A comparison between four run s showed good reproducibility of the steady state removal rates. The p erformance of the reactors and the stability of the degradation rates were tested for a range of loading conditions. Unbuffered, buffered an d pH controlled conditions were compared. The pumice carrier was best with respect to the degradation rate achieved per carrier mass. The re sponse of the reactors to massive TCP step loadings was tested. Loadin gs less than 1.5 kg TCP/m3d resulted in initially normal gas productio n rates for all the systems, except the activated carbon, whose gas pr oduction was partially inhibited from the start. After increasing the load to 1.5 kg TCP/m3d the gas production rates of all the other react ors fell abruptly to zero. Restarting after 2 months, all reactors sho wed methanogenic activity without requiring new inoculum. Adsorption a nd desorption experiments with TCP showed that only the anthracite and activated carbon adsorbed appreciable amounts. The activated carbon h ad the greatest adsorption capacity but did not release the TCP by des orption, as did the anthracite. A bicomponent (pumice and anthracite) carrier mixture was compared in biological experiments with pumice and anthracite carrier alone, with and without TCP loading. The pumice an d the carrier-mix performed equally well under non-toxic loading condi tions. With TCP toxic loading, the performance of the anthracite was s uperior. The anthracite carrier could be regenerated, owing mainly to its capacity for desorption.