Study of atrazine degradation in subsurface flow constructed wetland under different salinity

To evaluate the treatment capability of subsurface flow constructed wetland (SFCW) and the effect of salinity on the degradation of atrazine, the degradation of atrazine in SFCW was studied. Under the static condition, the degradation of atrazine in SFCW followed first-order kinetics: c = 0.09679 exp(−0.0396t) (c, residue concentration, mg l−1; t, retention time, d), with a half-life of approximately 17.5 days. The atrazine degradation kinetic functions were established for salinities of 1.5, 3.0, 5.0, 10.0 and 15.0 g l−1, respectively, which appeared to approach first-order kinetics. The effect of salinity on the atrazine treatment efficiency showed an exponential inhibition: ln k = 3.204 + 0.04991C (k, degradation constant; C, NaCl concentration, mg l−1). The attenuation of atrazine in SFCW cannot be a result of hydrolysis or sorption process. It was considered that some bacteria in the wetland system degraded atrazine into deethylatrazine (DEA) and deisopropylatrazine (DIA) and sequentially into CO2 and H2O. Salinity impacted on the growth of bacteria resulting in a switch of the microbial community. With the increase of salinity, Shannon–Wiener Diversity Index in the SFCW system declined. The relationship between atrazine degradation constant (k) and Shannon Index was established as shown in linear phase, y = −0.07286 + 0.0363x. The positive correlation between them indicated that microbial community played an important role in the atrazine degradation process.