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.
