An evaluation of clay minerals as support materials in anaerobic digesters

The use of different clay minerals as support materials in anaerobic digestion has been studied. The support materials were evaluated in a batch microdigester and their effect on the digestion process was measured at the beginning of the process (startup) and at an intermediate point of the digestion process when the maximum differences between support materials were observed (working digester). All the systems with support were more efficient than the control (support-free). The following order of purification was established: STARTUP: Bentonite > talc > vermiculite > nontronite > montmorillonite > pyrophyllite > stevensite > sepiolite. WORKING DIGESTER: Sepiolite > stevensite > talc > nontronite > bentonite > montmorillonite > vermiculite > pyrophyllite. Bentonite, montmorillonite, talc and vermiculite were favourable for startup, as they rapidly released Ca2+ or Mg2+ to the medium. The best COD removal efficiencies were obtained with sepiolite and stevensite which release Mg2+ progressively to the medium. The presence of Fe3+, Co2+ and Ni2+ in the structure of the mineral stimulated anaerobic digestion.