IMPACT OF THE MAIN PHENOLIC-COMPOUNDS OF OLIVE MILL WASTE-WATER (OMW)ON THE KINETICS OF ACETOCLASTIC METHANOGENESIS

Bench-scale tests were conducted to assess the impact of the most repr esentative phenolic compounds present in olive mill wastewater (OMW), two cinnamic acid derivatives (p-coumaric and caffeic acids) and two b enzoic acid derivatives (p-hydroxybenzoic and protocatechuic acids), o n the kinetics of acetoclastic methanogenesis. Phenolic compounds were added to cultures transferred from an acetate-enriched seed culture r eactor. A control without phenolic compound was included as a basis fo r comparison. Unacclimated cultures were used to minimize the biodegra dation of the toxic organic chemicals during the test. A finite-differ ence, non-linear, least-squares algorithm was used to estimate kinetic parameters by obtaining a best fit of the experimental data to the cl assical Monod growth and substrate utilization model. Resulting kineti c coefficients revealed substantial changes in both the maximum rate o f acetate conversion, k, and the half-velocity coefficient, K-s, when both cinnamic and benzoic acid derivatives were used. The relative eff ect of the phenolic compound was manifested in a decrease in the value of k or an increase in the value of K-s as the phenolic compound conc entration increased. Therefore, mixed inhibition was occurring. In add ition, the toxic effects were clearly related to the molecular structu re of the phenolic compound in each pair of toxicants studied, the inh ibitory impact being greater for the ortho-diphenols (caffeic and prot ocatechuic acids) in relation to their corresponding monophenolic comp ounds (p-coumaric and p-hydroxybenzoic acids, respectively). Copyright (C) 1996 Elsevier Science Ltd