Impact of carbon-dosing on micro-pollutants removal in MBBR post-denitrification systems

Dosing of methanol or ethanol is a common practice in post-denitrification steps during wastewater treatment by MBBR technology. The carbon-dosage impact on micro- pollutants removal, in terms of type (methanol or ethanol) and concentration was investigated. First, with continuous operation and indigenous micro-pollutants concentrations, different methanol and ethanol dosages were used to manipulate the carbon-to-nitrate ratio in two MBBRs. Atenolol, citalopram and trimethoprim were efficiently removed in both reactors. However, type or concentration of carbon did not correlate to micro-pollutant removal rates. Second, an anoxic-batch test with spiked micropollutants was conducted. The batch test showed that acetyl-sulfadiazine, atenolol, citalopram, propranolol and trimethoprim were easily removed in both reactors. Ibuprofen, clarithromycin,
iopromide, metoprolol, iohexol, iomeprol, venlafaxine, erythromycin and sotalol were moderately removed while diatrizoic acid, iopamidol, carbamazepine and diclofenac showed to be hardly biodegradable. The fact that both reactors gave similar removal rate constants for easily degradable compounds, could suggest that diffusion through the biofilm determined the removal of such compounds. In contrast, for moderately degraded micro-pollutants, the biofilm developed under methanol dosing presented the highest removal rate constants. This might mean that the primary metabolism of methanol improved the metabolism of these micro-pollutants. In general, postdenitrification with methanol or ethanol gave high and consistent removals of micro-pollutants.