Impact of approach used to determine removal levels of drugs of abuse during wastewater treatment

In this study the levels of 19 drugs of abuse were estimated throughout a wastewater treatment plant using polar organic chemical integrative samplers (POCIS), 24 h composite samples and grab samples. Overall removal efficiencies and removals in between each treatment unit were calculated using load data for each sampling technique as well as removals that take into account the hydraulic residence time distribution of the treatment plant (time-shifted mass balancing approach). Amphetamine-type stimulants, cocaine and its major metabolite, benzoylecgonine and opioid levels determined with 24 h composite samples were generally comparable to those obtained with POCIS and grab samples. Negative mass balances resulting from the estimation of overall removal efficiencies by POCIS, day-to-day mass balancing of 24 h composite and grab sample data did not occur when the hydraulic retention time (HRT) distributions of the plant were taken into account for calculation. Among the compounds investigated, cocaine exhibited the highest overall removal (90%) while codeine had the lowest with 13%, respectively. Sampling between the treatment units revealed that highest removal occurs during biological treatment as compared to primary or secondary clarification. Methylenedioxyamphetamine (MDA), fentanyl, dihydrocodeine and heroin were not detected in wastewater at any of the sampling locations at the treatment plant regardless of the sampling technique. The study demonstrates the benefits of applying the time-shifted mass balancing approach to the calculation of removals of drugs of abuse during wastewater treatment.