Physico-chemical and biological aspects of a serially connected lab-scale constructed wetland-stabilization tank-GAC slow sand filtration system during removal of selected PPCPs

A serially connected lab-scale Greater duckweed constructed wetland (CW)-stabilization tank (ST)-GAC sandwich slow sand filtration system was tested to remove four widely detected pharmaceuticals and personal care products (PPCPs) from natural water with a spiked concentration of 25 mu g/L. High removals were achieved rapidly (93.5-100%), being on average 95.9%, 99.1%, 98.1% and 97.4% for DEET, paracetamol, caffeine and triclosan (n = 3), respectively. Except for DEET, no significant difference was observed between overall removals with and without artificial aeration in CW tank (p > 0.05), showing good stability of the system. COD was considerably removed under aeration and final TOC removal was 64.7%. Nitrite, nitrate, ammonia and phosphate were not detected at the end of the test (day 26). The microbial community structure in three connected units of the tested system showed differences and good stability after the aerators were removed. Proteobacteria was the most dominant phylum among the 47 phyla found. Microbes attaching to the Greater duckweed contributed more to the microbial community structure in CW and ST tanks than original natural water. However, at the end of the run, the structural differences among three units decreased. After aeration stopped, phylum composition became more stable in ST tank while CW tank showed small structural variation throughout the test. Various correlations were found between detected phyla, among which Proteobacteria and Bacteroidetes showed a significant negative correlation (R = -0.73, p < 0.001, FDR corrected). Good removal of target PPCPs and stability of the system show the potential application of this combined treatment process.