The behaviour, fate and removal of pharmaceuticals in biological nutrient removal sewage treatment
Student thesis: Doctoral Thesis
Pharmaceuticals that are intended for human use are frequently detected in the aquatic environment. This is predominantly from the excretion of pharmaceuticals by patients, in their urine and faeces, which subsequently enter sewage treatment plants. Sewage treatment provides a final opportunity for pharmaceutical removal, prior to discharge into the environment, however, removal is often incomplete. Once in the environment, pharmaceuticals have the potential to cause effects on aquatic organisms. Sewage treatment plants, that are designed to meet statutory discharge consents for nutrients, are increasing in number. These plants, capable of biological nutrient removal, are understudied for the removal efficiencies of pharmaceuticals. This thesis presents research findings on the behaviour, fate and removal of selected pharmaceuticals in a bespoke laboratory rig, and in operational biological nutrient removal sewage treatment plants. Pharmaceuticals possessing a broad range of physical and chemical properties were selected for this research, they included: salicylic acid, caffeine, propranolol, diclofenac and carbamazepine. Sensitive chromatographic methods were developed to quantify the analytes in a laboratory sequencing batch reactor rig and in operational plants. Radiolabelled 14C isotopes of salicylic acid, caffeine, propranolol and diclofenac were dosed into the laboratory rig. The compounds exhibited different behaviours during a simulated sewage treatment process. Salicylic acid and caffeine produced the highest amount of biodegradation, with 25.2% and 14.5% of the radiolabel mineralised to 14CO2 in the rig. However, parent degradation is likely to have been higher, since neither compound could be detected in the effluent by specific chemical analysis. These findings were replicated in the operational sewage treatment plants, with > 97% removal of both pharmaceuticals, in all three plants investigated. Propranolol and diclofenac were less affected by biodegradation processes, and produced 3.7% and 0.2% mineralisation, respectively, in the laboratory rig. Furthermore, 33.8% of the radioactivity associated to 14C propranolol was detected in the rig solids. These compounds showed insignificant removal from two operational plants; 6.8% and 20.9% (propranolol) and -0.9% and -39.4% (diclofenac). Monitoring of operational plants showed that concentrations of propranolol were highest in the activated sludge tanks at all three sites. This supports the findings from the rig, that propranolol interacts with the sludge, which might be more significant in plants with lower sludge wastage rates, such as sequencing batch reactors. This could have implications for the terrestrial environment, and therefore, terrestrial risk assessments should be refined accordingly. Monitoring of the operational sewage treatment plants highlighted the widespread presence, and recalcitrant behaviour, of carbamazepine during biological sewage treatment. Future work should focus on investigating the mechanisms of removal, of this pharmaceutical in the laboratory sequencing batch reactor. This work highlighted the problems biological systems face in effectively removing recalcitrant pharmaceuticals. Advanced wastewater treatment should be considered, if complete removal is desired.
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