Evaluation of Horizontal Subsurface Flow Constructed Wetland for Treatment of Tannery Wastewater in Kaduna, Nigeria

Abstract

Tannery wastewater is often characterized by their complexities in terms of contaminants and require specialized treatment technologies. Hence, the objective of this paper is to explore the performance evaluation of a laboratory-scale horizontal subsurface flow constructed wetland (HSSFCW) in the treatment of tannery wastewater in Kaduna, Nigeria using appropriate standard techniques. Out of the tree replica systems, two were respectively vegetated with Phragmites australis and Polygonum salicifolium + Ipomoea carnea, while the last was left un-vegetated and used to treat tannery effluent. Characteristics such as Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Nitrates (NO^-3), phosphates (PO₄^3-), suspended solids (TSS) and chromium (Cr) analyzed using standard methods were used as indicators of the treatment efficiency under a 6-day Hydraulic Retention Time.  The results showed that the system vegetated with Phragmites australis had the best performance in the removal of BOD, COD, NO^-3, PO₄^3- and Cr (97.9%, 94.2%, 54.4%, 44.1% and 98.4% respectively). The system vegetated with Polygonum salicifolium + Ipomoea carnea on the other hand had the best performance for SS removal (92.6%) while the system vegetated with Phragmites australis had a SS removal efficiency of 92.3%. The performance indices for unvegetated cell, Phragmites australis vegetated cell and Polygonum salicifolium + Ipomoea carnea vegetated cell were respectively, 4, 9 and 8 which shows that the cell vegetated with Phragmites australis had the best performance in the treatment of tannery wastewater. It also showed that the performance of the cell vegetated with Polygonum salicifolium + Ipomoea carnea was also comparable with that of Phragmites australis. This study demonstrated that the HSSFCW vegetated with both Phragmites australis and Polygonum salicifolium + Ipomoea carnea can effectively treat tannery wastewater. There is however a need to investigate the efficiency of the system over a longer period with consideration of microbial characteristics.