Comparative evaluation on the performance of bio-rack and shallow pond systems for domestic wastewater treatment.

Constructed wetlands have been used successfully for treatment of wastewater during the last decades. The bio-rack and shallow pond systems are well engineered wetland process in wastewater treatment. The aim of this study is to compare the potential use of bio-rack and shallow pond systems for domestic wastewater treatment either in presence of high total dissolved solids (TDS) or heavy metal salts. The sewage treatment performance indicates 75.15% & 80.93% chemical oxygen demand (COD), 86.59% & 90.90% biological oxygen demand (BOD5), 27.54% & 15.98% total dissolved solids (TDS), 73.13% & 70.31% total suspended solids (TSS), 8.86% & 3.61% Chlorides, 70.22% & 74.18% ammonia nitrogen (NH3-N), 31.71% & 41.24% phosphate (PO4-P), 92.11% & 96.45% most probable number (MPN) and 93.05% & 98.24% total viable count (TVC) reduction at 10 & 21 h hydraulic retention time (HRT) in bio-rack and shallow pond system respectively. Likewise, the Phragmites sp. and water hyacinth can tolerate TDS up to 9000 and 2000 mg/L. The reduction in TDS is minor (14 & 19%) at the highest tolerable limit whereas the heavy metal reduction is 68 & 65%, 69 & 67%, 67 & 63%, 71 & 69% for Cd, Cu, Ni and Zn in bio-rack and shallow pond system respectively. The overall studies indicate the better treatment efficiency in bio-rack system at low foot print area (91 m2) compared to shallow pond system.