Comparative performance and 16S amplicon sequencing analysis of deep and shallow cells of a full scale HFCW having sequentially decreasing depths reveals vast enhancement potential

The performance and microbial community characteristics of a full-scale horizontal flow constructed wetland (HFCW), comprising sequential cells of different depths (1.5 m to 0.8 m), treating domestic wastewater from a residential complex located at Roorkee, India was analysed. The BOD, COD, NO3-N, TN, and PO4 removal efficiencies of the system were found to be 89.9 %, 89.1 %, 72.7 %, 67.1 %, and 53.3 %, respectively. The areal removal rate constants kBOD, kTN and kTP for BOD, total nitrogen and total phosphorus removal were found to fit well with the optimized k values calculated using secondary data of 74 HSSF CWs. Comparative 16S rRNA amplicon sequencing revealed widely varying bacterial communities in the deep and shallow cells of the wetland with several communities being exclusively present in the deep cell. Abundant heterotrophic nitrifiers, aerobic denitrifiers, and phosphate accumulating bacteria demonstrate the utility of such deep HFCW systems for the combined organics and nutrients removal. [Display omitted] •Performance data of different cells of NIH-CW with varying depth analysed.•Removal rate coefficients (K) for BOD, NH4-N, TN and TP were calculated.•K values of low OLR cells found to be within range of optimized K values.•Bacterial diversity found to be different in deep vs. shallow cell.•N and P removal corroborated by relative abundances of respective genera.