Evaluation of Constructed Wetlands and Conventional Wastewater Treatment Systems in Selected Kenyan Tea Factories

Abstract

Environmental pollution due to discharge of untreated or poorly treated industrial wastewaters has become a major source of concern with respect to the safety of our environment. Wastewaters from processing of black tea contain harmful substances just like any other industrial effluent and therefore pre-treatment is necessary prior to release. The purpose of this study was to evaluate conventional and constructed wetlands wastewater treatment systems used in Kenya tea factories to establish the most effective system. Eberege tea factory which has a conventional effluent treatment plant and Chinga tea factory using constructed wetlands for effluent treatment were used to represent the two wastewater treatment systems. Test parameters of interest as per the National Environment Management Authority guidelines were: Biological Oxygen Demand, Total Suspended Solids, pH, fecal coliform, Chemical Oxygen Demand, color, organic nitrogen, flow, copper, zinc and surfactants. These parameters were analyzed in both treated and untreated effluent from the selected two factories using approved US EPA testing methods for wastewater analysis. The results obtained from the untreated effluent in both factories had high levels of >48.6mg/L BOD, >150.3mg/L COD and >29.3mg/L TSS while the treated effluent registered a major decrease of pollutants levels with readings of <25.5mg/L BOD, <70.4mg/L COD and <28.8mg/L TSS. Color in the untreated effluent gave readings of >15 hazen units while the treated effluent recorded <12 hazen units with the conventional treatment plant giving the most clear effluent of <6 hazen units. Organic nitrogen levels in the untreated effluent were >7.8 mg/L while the treated effluent levels were <2.8 mg/L with the constructed wetland registering the lowest values. Copper and zinc levels were below the detection limit in all untreated effluent samples with an exception of one sample which recorded zinc levels of 0.543mg/L but was effectively treated since the result of the treated effluent was <0.001mg/L. Surfactants were found to be below detection level in both untreated and treated effluent samples. Fecal coliform bacteria was also absent in all samples. The conventional wastewater treatment plant is recommended for tea factory wastewater treatment since it gave a clearer and the less toxic treated effluent compared to that from the constructed wetland. Further studies should major on designing upgraded treatment plants which combine both conventional and biological modes of treatment while eliminating the disadvantages that come with conventional plants especially the high cost of setting up and maintenance.