Economic Considerations

Abstract

There are several difficulties at once apparent in attempting a useful comparison of the basic reactor types discussed in the preceding chapters: one problem pertains to the characterisation of system design, the demarcation between various bioreactor types being unclear and overlap of many features occurring. The major difference, for example, between the contact and the carrier-assisted contact processes is the presence of a small quantity of inert media as support particles in the latter, a situation easily produced in the former by the introduction of nonbiodegradable suspended solids with the influent; the floc structures of both reactor configurations are practically indistinguishable. The anaerobic sludge blanket and the contact reactor have likewise many similar features, the design differences themselves being in the placement of the settling unit, i.e., internal or external to the reaction vessel. In the case of the fixed-film processes, the borderline between expanded and fluidised bed reactors is indefinite and dependent almost exclusively upon the degree of fluidisation of the carrier particles, which in turn is governed by particle density, porosity and size, and by the fluid flow rate. Other elements must necessarily enter into any qualitative comparisons made between reactor design and mode of operation: these include the strength and complexity of the waste to be treated, the influent flow rate, temperature and pH, and diurnal, seasonal or other temporal variations of these factors. Differences between reactor performances and efficiencies therefore, are not as straightforward as may be expected from design and operational variations.