Toxicity of acrylic acid to acetate-enriched Methanosarcina cultures

The microbial acclimation potential of acetate-enriched Methanosarcina cultures to acrylic acid was investigated. Acrylate-acclimated and unacclimated, acetate-enriched Methanosarcina cultures maintained at a nearly constant acetate concentration of 7,500 mg/L were used in batch and fed-batch serum bottles. The results revealed that the 6-d lag period observed before the onset of acrylic acid biotransformation for an unacclimated culture disappeared for a 150-d acrylate acclimated culture. Even though acrylic acid was notably inhibitory to an unacclimated Methanosarcina culture above slug-doses of 20 mg/L [0.019 mg acrylic acid/mg volatile suspended solids (VSS)], the toxic effects of acrylic acid could be significantly reduced through acclimation. The inhibition and recovery periods of the cultures were dependent on administration patterns. The activity level (or gas production) of a culture can be kept around a desired level by applying a predetermined acrylic acid administration strategy. Acclimation to acrylic acid could not be achieved below a threshold 40-d loading rate of 10 mg/L. Higher solids retention time (SRT) systems provided better tolerance to acrylic acid toxicity for the same acrylic acid loading. The acrylic acid inhibition was reversible but exposure to acrylic acid had a negative residual effect on the biomass that was manifested for over 30 d after the toxic supernatant was removed by centrifugation.