Treatment of Tannin waste water in baffled horizontal substance flow constructed wetland (BHSSFCW)

Tannin extracts are substances commonly used in leather production processes. Presences of polyphones in wastewaters make them toxic and recalcitrant, thus requiring more attention in treatment before discharging the same to the environment. The aim of this work was to study the feasibility of treating wattle tannin wastewater in a Baffled Horizontal Subsurface Flow Constructed Wetland (BHSSFCW).Three experiments were done in the constructed wetland (dilution ratios of 1:1, 3:1 for untreated tannin wastewater and 3:1 for pre-treated tannin wastewater respectively). The wetland was operated for 20 days for each run. Parameters, which were analyzed, include COD, Tannin concentration, electrical conductivity, pH and temperature. COD removal efficiency of 96.6% with outlet concentration of 20mg/L was obtained for the dilution ratio of 1:1. COD removal efficiency for the dilution ratio of 3:1 was 95.4% with outlet concentration of 47mg/While that for pre-treated tannin wastewater was 96.7% with outlet concentration of 32mg/L. For the dilution ratio of 3:1, tannin removal efficiency of 97.4% with outlet tannin concentration of 23mg/L was achieved while for the pre-treated tannin wastewater; tannin removal efficiency was about 95.6% with outlet tannin concentration of 31mg/L. With dilution ratio of 1:1, the concentration of tannin along the baffled cell as well as in the outlet was below detectable level. Based on the results it was concluded that BHSSFCW can be used to treat tannin wastewater to acceptable effluent quality if mixed with domestic wastewater.