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Sewage treatment works (STWs) are routes through which treated wastewater effluents often containing myriads of chemicals are passed into receiving waters due to incomplete removal processes as have been identified in several studies. The current work aimed to determine the levels of these chemicals in the effluents from Stoke Bardolph STW, Nottingham and to determine the fate and behaviour of compounds by conducting degradation batch studies under different treatment conditions. The selection of representative illicit compounds; cocaine and its metabolite benzoylecgonine, heroin and its metabolites 6-monoacetylmorphine and morphine and a pharmaceutical (diazepam) was based on their presence in the STW effluent. The results obtained using solid phase extraction gas-chromatography technique (SPE-GCMS) showed thirteen compounds detected at concentrations between 1.9 and 3147 ng L-1 in effluents from Stoke Bardolph STW. Procaine, bromacil, codeine, lidocaine, ibruprofen, caffeine, nicotine and diazepam were the most abundant compounds in the final effluent with concentrations of 99.2, 1806.8, 33.5, 71.8, 3147, 213.4, 252.5 and 105.2 ng L-1, respectively. The percentage recoveries ranged from 74.5 – 109.6%, with the instrumental limits of detection (LODs) ranges of 0.2 – 12.7 ng L-1, and relative standard deviation (RSD) values of 0.6 – 4.7% were achieved for all the compounds. The batch tests enabled determination of the degradation of the compounds at different temperatures and times, using various sludge types after characterization. Removal rates of cocaine (91.0%), benzoylecgonine (90.6%), heroin (97.9%), morphine (99.7%), 6 monoacetylmorphine (93.3%) and diazepam (99.7%) were measured after 3 hours equilibration; partition coefficients (Kd) for these six substances ranged from substances ranged from substances ranged from substances ranged from substances ranged from 1.2 – 68.1 Kg L-1. The degradation of compounds at 19 ± 0.5o C was relatively greater but it still occurred slowly at 4 ± 0.5o C, at between 5 and 10%. Mass balances for two STW (Molesworth, Cambridgeshire, U.K. and Stoke Bardolph) were constructed using the removal rate data from these batch studies. Final effluent concentrations of 110.0110.0 ng L-1 (cocaine), 690.0(cocaine), 690.0 ng L-1 (benzoylecgonine), 10.0 (morphine), 80.0 ng L-1 (6 -monoacetylmorphine), and 0.7 ng L-1 (diazepam) were found in effluents after a total of 8 hour hydraulic times (8 HRT) from an initial influent concentration of 50 mg L-1. Projected influent concentrations of cocaine (14, 471 ng L-1) and benzoylecgonine (23, 907.1 ng L-1) at Stoke Bardolph were derived from back-calculating measured final effluent concentrations using this same mass balance approach. Work encompassed in this study directly measures illicit drug removal rates in laboratory studies for the first time. The application of removal rates in calculating mass balances in sewage works is an improvement over prior studies where assumptions on removal rates at STW were made. |
