AEROBIC-ANOXIC BIOPROCESS FOR THE TREATMENT OF MUNICIPAL WASTEWATER AND APPLYING THE EFFLUENT FOR IRRIGATING VEGETABLE CROPS

Abstract

This study was designed to evaluate the treatment performance of aerobic-anoxic bioprocess system for Arba Minch Town (AMT) municipal wastewater treatment. Wastewater sample were collected and characterized from nine purposively selected sampling stations. The treated effluent and influent wastewater were evaluated for growing three randomly selected vegetables (Lettuce, Cabbage and Tomato). Petridish and pot experiment set up were designed and analyzed using standard protocols for vegetables germination and physiological parameters test including shoot and root length, leaf number and area, fresh and dry biomass, chlorophyll content, heavy metal and pathogenic organism. Descriptive statistics and a one-way ANOVA followed by Duncan’s multiple range test with p<0.05 were used. The experimental results indicated that NH4 + -N, NO3 - - N, TN, PO4 -3 , COD and BOD5 removal efficiency from the aerobic-anoxic reactors were found 97.41, 93.46, 97.03, 86.48, 92.96 and 90.01%, respectively. The pH of the wastewater collected from different sites varied from 8.2-9.4. The order of heavy metals (mg/L) in wastewater were also found Fe>Pb>Zn>Mn>Cu>Cd, 5.1±0.1, 2.2±0.4, 0.38±0.07, 0.26±0.07, 0.1±0.0, 0.006±0.11, respectively. Moreover, the result showed that leaf number and area, chlorophyll, shoot and root length, dry and fresh weight of vegetable crops were significantly higher (p<0.05) in vegetables irrigated with treated wastewater (TWW) compared to untreated wastewater (UTWW). For vegetables irrigated with TWW, heavy metals were found significant lower (p<0.05) as compared with UTWW. Furthermore, the result showed, coliform bacteria and helminthes eggs were significantly higher in all vegetables irrigated with UTWW than irrigated with TWW (p<0.05). The overall results showed that most of the physicochemical characteristic of AMT wastewater has been above the recommended standards set by FAO and WHO, which needs treatment before applied for irrigation purpose. Due to the effectiveness of laboratory-scale aerobic- anoxic wastewater treatment plant which will be better to upscale to pilot plant is important for treating AMU municipal wastewater.