Non-conventional structural forms for concrete sludge digesters

A recent programme of research at the University of Cape Town has focussed upon the structural feasibility of non-conventional sludge digesters in the form of thin shells of revolution constructed in concrete. Such forms are usually referred to in the literature as “egg-shaped”, and the advantages of these over conventional digesters of the wide-cylindrical type are well-documented: superior mixing efficiency, less accumulation of deposits at the bottom, easier removal of bottom deposits and surface crust, reduced heat losses, and so forth. With the aim of exploring the structural feasibility of certain non-conventional forms for concrete sludge digesters, and making available usable analytical data and practical guidelines for the design of such thin shell structures, a number of theoretical studies have recently been undertaken, and these have covered conical assemblies, spherical assemblies and parabolic ogival configurations. The purpose of the present paper is to bring the findings of these separate studies together, draw comparisons regarding relative structural efficiencies and functional suitability, and make appropriate conclusions and recommendations.