SUSTAINABILITY OF HYBRID FLOW CONSTRUCTED WETLAND TREATMENT FOR COFFEE WASTEWATER: THE CASE OF KEGE WET COFFEE PROCESSING PLANT, GIDABO RIVER WATERSHED, ETHIOPIA

Abstract

Constructed wetlands (CWs) are treatment systems for treating wastewater with natural methods using wetland plants. This study evaluated the sustainability of hybrid flow-constructed wetlands (HFCW) planted with vetiver grass for coffee wastewater at the Kege Coffee Processing Plant. The wetland carried a hydraulic loading rate of 64m3 /d and it was evaluated for six different detention times(DT) which were 0.5 days, 1 day, 2 days, 3 days, 4 days, and 5 days. Samples were collected starting from November to January of the year 2021 which is the dry season of the study area. IBM SPSS was used for the analysis of data with One-way statistical analysis of variance (ANOVA) and descriptive analysis. The treatment of the HFCW was tested by analyzing water quality parameters; temperature, turbidity, electrical conductivity (EC), pH, TSS, TDS, DO, BOD5, COD, NH3-N, NO3- N, PO4 3- , and NO2-N. The effluent concentrations of these parameters from the constructed wetlands significantly became to the standard limit with an increase in detention time for pH, DO, TSS, turbidity, PO4 3- , NH3-N, BOD5, and COD at p≤ 0.05. But for temperature, EC, TDS, NO2-N, and NO3-N effluent concentration were not significantly changed (p>0.05). Additionally, percentage concentration removal was increased for TSS, turbidity, BOD5, and COD. However, temperature, EC, TDS, PO4 3- , NH3-N, NO2-N, and NO3-N ensure variation with DT. On the other hand, river water quality parameters revealed statistically non-significance (p>0.05) values between upstream and downstream of the river. River water quality parameter results were below the FAO irrigation water standards except for temperature. Furthermore, from the survey conducted 85.40% of the respondents have awareness of the importance of constructed wetlands and from the total 103 respondents 98.4% of them were recognized to socially accept the CW and 63.11% of them state that the environmental pollution decreases through the constructed wetland. From the respondents, 85.49% of them described that the CW has an economical purpose too (they sell the grass for purposes of house cover, local bed, and animal forage) in addition to the treatment of wastewater (WW). However, 71.43% of the CPP owners responded that the CW was not efficient to carry the WW discharge per day as their processing capacity increases year to year and its sustainability may be at risk due to this. Finally, CW treatment for coffee processing wastewater with an engineered design should be a way out for the current pollution of the Gidabo river watershed