Catalyzes the hydrolysis of 4,6-nonanedione, a beta-diketone compound. Also mediates hydrolysis of oxidized polyvinyl alcohol (PVA) in the second step in the degradation of polyvinyl alcohol. Not active toward the monoketone structure. H2O + nonane-4,6-dione = butanoate + H(+) + pentan-2-one Monomer. Belongs to the peptidase S9A family.