The existence of a biological equilibrium in a trickling filter for waste gas purification

Clogging is a well-known phenomenon in the application of a biological trickling filter for both waste gas and wastewater treatment. Nevertheless, no such observations or even significant changes in pressure drop have ever been recorded during the long-term processing of a waste gas containing dichloromethane (DCM) as a sole carbon source. To obtain more information about this phenomenon, a detailed investigation into the carbon balance of this system has been performed. During a period of operation of about 200 days the rate of DCM elimination and the overall rate of CO, production in a continuously operating filter were therefore recorded daily, thus allowing an evaluation of the overall conversion process. Furthermore pseudo-steady-state measurements were carried out on a regular basis. These experiments reveal more detailed information on the actual DCM conversion by Hyphornicrobiurn GJ21 within the biofilm. The combined results of the experiments de-scribed in this article show that on an overall basis a so-called biological equilibrium, i.e., a situation of no net biomass accumulation, is obtained in the course of time. It appeared that the overall rate of CO, production slowly increased until, after some 200 days, it finally counterbalanced the conversion rate of DCM on a molar basis. As opposed to this result, all pseudo-steady-state experiments indicated that about 60% of the eliminated primary carbon source is converted into biomass. This is in good agreement with results from microkinetic experiments. Based on these results and evaluation of the experimental data, it is concluded that interactions between several microbial populations are involved in this biological equilibrium. These interactions include both biomass growth and biomass degradation

THE USE OF MICROSENSORS TO DETERMINE POPULATION-DISTRIBUTIONS IN UASB AGGREGATES.

Glucose and pH microprofiles in UASB aggregates were interpreted with respect to the population distribution of fermentative and methanogenic bacteria. In order to map the activity distribution of these bacteria, microprofiles were measured with different substrates (glucose, propionate and acetate) and at varying buffer capacities of the medium. The measurements were compared to calcd. microprofiles, in which the spatial location of the activities was varied. The results suggested an inhomogeneous activity distribution in the aggregates investigated: fermentative were located dominantly at the outer 200-300 mm whereas methanogens were homogeneously distributed over the aggregate. [on SciFinder (R)

Microelectrode Measurements of the Activity Distribution in Nitrifying Bacterial Aggregates

Microelectrodes for ammonium, oxygen, nitrate, and pH were used to study nitrifying aggregates grown in a fluidized-bed reactor. Local reactant fluxes and distribution of microbial activity could be determined from the microprofiles. The interfacial fluxes of the reactants closely reflected the stoichiometry of bacterial nitrification. Both ammonium consumption and nitrate production were localized in the outer shells, with a thickness of approximately 100 to 120 μm, of the aggregates. Under conditions in which ammonium and oxygen penetrated the whole aggregate, nitrification was restricted to this zone; oxygen was consumed in the central parts of the aggregates as well, probably because of oxidation of dead biomass. A sudden increase of the oxygen concentration to saturation (pure oxygen) was inhibitory to nitrification. The pH profiles showed acidification in the aggregates, but not to an inhibitory level. The distribution of activity was determined by the penetration depth of oxygen during aggregate development in the reactor. Mass transfer was significantly limited by the boundary layer surrounding the aggregates. Microelectrode measurements showed that the thickness of this layer was correlated with the diffusion coefficient of the species. Determination of the distribution of nitrifying activity required the use of ammonium or nitrate microelectrodes, whereas the use of oxygen microelectrodes alone would lead to erroneous results

In situ structure/function studies in wastewater treatment systems

As an example of the importance and the potential of in situ structure/function studies, nitrifying aggregates from different zones of a lab-scale fluidised bed reactor were analysed by microelectrode measurements of O-2, NH4+, NO2-, and NO3- and in situ hybridisation targeting the 16S rRNA of the nitrifying bacteria. A shift from an ammonia oxidising to a nitrite oxidising community is present along the reactor. In the single aggregates an active nitrifying shell of about 100 mu m could be related to the maximum abundance of nitrifiers in this zone. Interestingly, the main actors in this system are not representatives of the well-described genera Nitrosomonas and Nitrobacter but some other ammonia oxidisers from the beta subclass of Proteobacteria and a thus far unknown nitrite oxidising population. (C) 1998 IAWQ. Published by Elsevier Science Ltd