Performance evaluation of waste stabilization ponds in the removal of pharmaceutically active compounds : a case of Lubigi wastewater treatment plant

Abstract

Waste stabilization ponds (WSPs) have been extensively used for the treatment of wastewater due to their simplicity and cost-effectiveness. This study evaluated the performance of WSPs in removing Pharmaceutically Active Compounds (PhACs) at the Lubigi sewage and wastewater treatment plant. Three wastewater streams were sampled; the inlet for the domestic wastewater stream, the point of discharge for cesspool empties containing faecal sludge from septic tanks, and the gulper station receiving faecal sludge from pit latrines. Additionally, samples were collected at different treatment stages i.e. the inlet to the anaerobic pond, the outlet from the anaerobic pond, and the discharge point to the facultative pond. Fresh and dried sludge samples were also collected. Sample analysis was performed using Liquid Chromatography Mass spectrometry (LC-MS-MS). PhACs were present in median concentrations of 19.223 μgL-1 in wastewater from the sewer network, 13.429 μgL-1 in septage and 18.641 μgL-1 in faecal sludge from pit latrines respectively, with average concentrations of in the three source streams of up to 5300 μgL-1. WSPs exhibited the ability to remove a variety of PhACs from wastewater at an overall removal efficiency of 76.15% with the highest removal efficiency of 70-99.99% for chlortetracycline, sulfapyridine, ampicillin, gentamicin, albendazole, ibuprofen, sulfachloropyridazine, sulfaquinoxaline, and penicillin, the moderate removal efficiency was 50-70% for like paracetamol, chloramphenicol and enrofloxacin, and the lowest removal efficiency of 1-40% for sulfadiazine, oxytetracycline, diclofenac, and ciprofloxacin. PhACs like sulfamethoxazole sulfamerazine and amoxicillin were more recalcitrant exhibiting negative removal efficiencies. The study found that faecal sludge (FS) from pit latrines (3.35 ton/year) and conventional sewer network systems (1.63 ton/year), contribute to substantial volumes of wastewater entering the Lubigi sewage treatment plant and therefore consequently reduce the treatment efficiency of WSPs in removing these PhACs as compared to septic tanks (0.74 ton/year). This study recommends the substitution of pit latrines with source-separated technologies, the addition of maturation ponds and other tertiary treatment mechanisms and the use of advanced treatment technologies to effectively remove PhACs, routine monitoring of PhACs, proper disposal and management of pharmaceutical waste, and further research on the behaviour and fate of PhACs particularly regarding their transformation and potential impacts when discharged into wetland environments.