Waste Water Treatment Performance of Two Vertical Flow Constructed Wetlands for Agricultural Reuse in Jordan: Enhancing Nitrogen Removal

Abstract

This study demonstrates the treatment performance of two vertical flow constructed wetlands (VFCWs) for decentralized wastewater treatment plants in Jordan, for reuse purposes to meet the WHO regulations for reuse in agriculture and the Jordanian standards (JS 893/2006). The first system is a recirculating VFCW that has shown high removal efficiency of COD, TSS, and CBOD5 over the study period, conforming to the JS (Category A). Whereas, the Total Nitrogen (TN) and Nitrate (NO3-) removal were limited (55 and 44 mg/L) over the baseline monitoring, conforming to the JS Category-B (TN: 70 mg/L and NO3-N: 45 mg/L). Therefore, the system was modified by converting the recirculation tank into attach growth tank (using electric conduit pipes as plastic media). TN concentration reduced effectively of 40 mg/L, conforming to the JS category-A (TN: 45 mg/L), whereas, NO3–N concentration reduced to 37 mg/L, conforming to the JS Category-B (TN: 45 mg/L). Over the study period, E. coli reduction were constant, 2 log10 reduction, conforming to the JS category C (more than 1000 MPN/100 mL). The second system is two-stage VFCW that has shown high removal efficiency of COD, TSS, and BOD5, conforming to the JS Category-A over the study period. But, TN and NO3–N concentrations were limited (55 and 44 mg/L), conforming to the JS Category-B, due to insufficiency of carbon source to promote denitrification (high BOD5 removal by first filter). Thus, the two-stage VFCW was modified with raw wastewater step-feeding application to the intermediate pump shaft before the second stage filter. The results of operational modification showed a small significant improvement in TN removal (p = 0.005); TN and NO3–N concentrations were reduced to 52 and 50 mg/L, respectively; conforming to the JS Category-B. Higher E. coli removal was observed in the two-stage system than the recirculating system, with an overall average removal of 4.5 log10 units, conforming to the JS category B (less than 2.0 log10 units). While, E. coli reduction influenced negatively by step-feeding modification, conforming to the JS category C