Inhibition of anaerobic digestion by terephthalic acid and its aromatic by products

With 14.4 million tons produced in 1993, purified terephthalic acid (PTA) and dimethylterephthalate (DMT) are the main monomers used in the world polyester production. Even though there are ten industrial digestors treating the effluents of both products, little is known about the influence of their organic components, terephthalic (TA), p-toluic (p-tol), benzoic (BA) and phthalic (PA) acids as well as 4-carboxybenzaldehyde (4-CBA) on methanogenesis. This study shows that the concentrations of 4-CBA, p-tol and TA required to inhibit by 50% the hydrogenotrophic methanogenic activity are respectively 5.4, 34 and more than 100 mM. At the maximum concentration tested (10 mM), the inhibition of the acetoclastic methanogenic activity by the same compounds was less than 12%. The results indicate that at the concentration of TA, p-tol and 4-CBA found in PTA and DMT wastewater, no significant inhibition of the methanogenic activity should be observed for PTA but that the hydrogenotrophic activity could be reduced by as much as 30% in the case of DMT. The degradation of TA was completely inhibited by the presence of BA and glucose while the presence of phthalate had no effect. According to these results, it is concluded that it is at least possible to anaerobically treat the easily biodegradable compounds of these effluents (acetic, benzoic and formic acid) as they would not be significantly inhibited by TA, p-tol or 4-CBA.