Evaluation of four mathematical models to describe dissipation kinetics of 4-n-nonylphenol and bisphenol-A in groundwater-aquifer material slurry

The performance of four mathematical models (hockey stick, biexponential, first-order double exponential decay, and first-order two-compartment) was evaluated to describe the dissipation kinetics for 4-n-nonylphenol (4-n-NP) and bisphenol-A (BPA) in groundwater-aquifer material slurry under aerobic and anaerobic conditions conducted under controlled laboratory conditions. The fit of each model to the measured values under both conditions was tested using an array of statistical indices to judge the model's ability to fit the measured datasets. Corresponding 50% (DT(50)) and 90% (DT(90)) dissipation values for each compound were numerically obtained and compared against each model. The model derived DT(50) values in groundwater-aquifer material ranged from 1.06 to 1.24 (4-n-NP) and 0.341 to 0.568 days (BPA) under aerobic condition, while they were 2- to 4-fold higher under anoxic condition. DT(90) values for 4-n-NP ranged anywhere between 2.3 and 4.45 days under both conditions, while DT(90) values for BPA ranged from around 1 day to as high as 12 days under both conditions tested. A visual examination of the measured and fitted plots as well as the statistical indices showed that, with the exception of the hockey stick model, the models performed satisfactorily. Despite having only 3 parameters, the biexponential model could describe the dissipation kinetics very well and this was supported by the statistical indices generated for each case.