Protection of methanogenic bacteria from low pH and toxic materials by immobilization using polyvinyl alcohol

Abstract

The applicability of cell immobilization to the anaerobic treatment process using the polyvinyl alcohol (PVA)-boric acid method was investigated. The acetate-utilizing methanogens were cultivated, concentrated and immobilized. The beads formed were stable for one year maintaining methanogenic activity. The possible advantage of immobilized cells over non-immobilized cells for low pH shock and for the presence of toxic substances was examined. The immobilized cells recovered their methanogenic activity faster than the non-immobilized cells from the inhibition caused by transient low pH (5.0) for 12–48 h in a continuously fed reactor. Formation of a pH gradient within the bead due to the consumption of acetic acid inside the bead is a possible mechanism of relief of the inhibitory effect. Batch experiments showed that the inhibitory effect of phenol, oleic acid, nickel, sulfide and propionic acid on the methanogenic bacteria was also reduced by immobilizing the bacteria. Formation of a pH gradient or the adsorption of toxic materials by PVA are likely mechanisms of this relief of inhibition.