Analysis of pharmaceutical biodegradation of WWTP sludge using composting and identification of certain microorganisms involved in the process

Highlights: • Ten PhCs were analysed during wastewater treatment, and increased in the sewage sludge. • Composting degraded some pharmaceuticals depending on the C/N ratio. • Minimal microbiological cultures were applied to isolate degrading microorganisms. • Strains that metabolize azithromycin, ibuprofen, and irbesartan were isolated. Pharmaceuticals (PhCs) are organic contaminants that have been detected in wastewater, surface water, and soils throughout the world. The presence of 10 commonly used PhCs in Spain (azithromycin, benzylpenicillin, citalopram, fluconazole, fluoxetine, ibuprofen, irbesartan, olanzapine, telmisartan, and venlafaxine) was analysed at four wastewater treatment plants, and the changes in their concentrations during treatment were assessed. Although certain some PhCs were degraded in the treated water, their presence in sewage sludge increased in all cases. The sewage sludge was composted using rice straw to degrade the PhCs, and the composting efficiency was modified by changes in the relative C/N ratio of the composting blend. Using a simple microbiological culture process for enrichment, 11 different strains of microorganisms that degraded specific PhCs were identified. Ibuprofen and azithromycin were metabolized by one and four strains, respectively, and both PhCs were used as a carbon source; in addition, six strains used irbesartan as a nitrogen source.