Anaerobic treatment of petrochemical wastewater containing acrylic acid and formaldehyde
Description
Acrylic acid and formaldehyde are present in several industrial wastewaters including petrochemical wastes. The objectives of this study were to determine the anaerobic degradability of acrylic acid and formaldehyde in acidogenic and methanogenic systems and anaerobic treatability of petrochemical wastewaters containing acrylic acid and formaldehyde Acetate, propionate, and glucose enrichment cultures were used in serum bottle and chemostat studies. The results showed that the acrylic acid was degraded to propionate and acetate and without acclimation it completely inhibited propionate degradation and partially inhibited acetate degradation. In both the methanogenic and acidogenic chemostats, 98% of the acrylic acid was removed. However, the acidogenic chemostat had a significantly higher acrylic acid loading rate (416 mg/L-d) than the methanogenic chemostat (16.7-66.7 mg/L-d). Even at low acrylic acid loading rates, the propionate utilizers required a long time to acclimate to acrylic acid Formaldehyde showed severe toxicity to the acetate enrichment culture. As low as 10 mg/L of formaldehyde completely inhibited acetate utilization. Formaldehyde was, however, degraded while acetate utilization was inhibited. Degradation of formaldehyde (Initial concentration $\le$30 mg/L) followed Monod model with a rate constant, k, of 0.35-0.46 d$\sp{-1}$. At higher initial concentrations ($\ge$60 mg/L), formaldehyde degradation was inhibited and partial degradation was possible. The initial formaldehyde to biomass ratio, S$\sb0$/X$\sb0$, was useful to predict the degradation potential of high concentrations of formaldehyde in batch systems. The inhibition of formaldehyde degradation in batch systems could be avoided by repeated additions of low concentrations of formaldehyde (up to 30 mg/L). Methanogenic chemostats (14-day retention time) showed degradation of 1110 mg/L of influent formaldehyde with a removal capacity of 164 mg/g VSS-day. The results also showed that the acetate enrichment culture was not acclimated to formaldehyde even after 226 days The acetate enrichment culture, acclimated to acrylic acid and formaldehyde, successfully treated 25% of the 'Wastewater B' from a petrochemical plant containing high concentrations of acrylic acid (1650 mg/L) and formaldehyde (3330 mg/L) and other constituents. The removal efficiency for acetic acid, acrylic acid, formaldehyde, and COD were 99, 99, 99, and 91%, respectively. The unacclimated acetate enrichment culture can also be used to treat 'Wastewater A' containing low concentrations of acrylic acid (240 mg/L) and formaldehyde (30 mg/L). The system had 92, 99, 99, and 62% of removal efficiency for acetate, acrylate, formaldehyde, and COD, respectively