Assessment of Efficiency of Finlays Saosa Constructed Wetland for Treating Tea Extract Wastewater in Kericho, Kenya

Abstract

The release of partially treated tea extract wastewater poses serious environmental risks due to high pollutant loads, necessitating sustainable treatment solutions, such as constructed wetlands. Additionally, there is no published data on the operational efficacy of Finlays Saosa constructed wetland. Therefore, this study assessed the efficiency of Finlays Saosa constructed wetland for treating tea extract wastewater in Kericho, Kenya, from November 2024 to March 2025. Water samples were collected twice a month from seven sampling points and analyzed in the laboratory at the Department of Biological Sciences, Egerton University. American Public Health Association (APHA, 2017) Standard Procedures was used to analyze BOD, COD, NH₄⁺, TSS, tannin, TN, TP, SRP, NO₃⁻, and NO₂⁻, while parameters like pH, EC, DO, and water temperature were measured in situ using a calibrated multi-meter model HQ 40D (HACH). Above-ground biomass of macrophytes was determined by the harvest method, while nutrient allocation in the ground sample was estimated calorimetrically after acid digestion. Data was processed using IBM SPSS software version 28 and Microsoft Office Excel 2007, subjected to a normality test using the Shapiro test and homogeneity of variance using the Levene Test. ANOVA showed significant variation in physical, chemical, and nutrient parameters (p<0.05) except for DO. Additionally, Tukey’s HSD post hoc test differentiated between the groups of means across the sampling location. A t-test compared the mean loadings and concentrations in the inlet and outlet of the constructed wetland. On the other hand, descriptive statistics presented data about the physical, chemical, nutrient parameters, above-ground biomass, nutrient removal, vegetation cover, and removal efficiency. Pontederia cordata achieved the highest above-ground biomass (8986.01 ± 2.21 g/m²) and nitrogen removal rate (62.9 g/m²), while Colocasia esculenta recorded the highest phosphorus removal rate of 17.49 g/m². Canna indica had the lowest above-ground biomass (2592.13 ± 4.28 g/m²) and phosphorus uptake (4.15 g/m²), while Phragmites mauritianus recorded the lowest nitrogen uptake (5.75 g/m²). The constructed wetland showed a high removal efficiency for most pollutants with over 90% removal rate. TSS, TP and BOD5 met the National Environment Management Authority (NEMA) set standards. However, effluent concentrations of COD and TN did not meet NEMA set standards. The findings will provide practical insights for tea factories in improving their wastewater management and guide wetland designers in selecting efficient macrophytes for nutrient removal, thereby enhancing the operation and maintenance of the constructed wetland.