Antibiotic resistant bacteria removal of subsurface flow constructed wetlands from hospital wastewater

Eight horizontal subsurface flow pilot scale artificial wetlands were constructed to evaluate their effectiveness in the removal of antibiotic-resistant bacteria from hospital wastewater. A total of 40 composite samples were collected from the inlet and outlet of wetlands, transported and processed for enumeration of indicator organisms, bacteriological identification and susceptibility testing following standard procedure. The treatment wetlands achieved 7.1 logs10 and 5.1 logs10 removal of total and fecal coliforms. Among the total samples, 159 bacterial isolates were detected, of these 45 (28.3%) were from hospital wastewater and 114 (71.7%) from the outlets of wetlands. The most frequently isolated bacteria from hospital wastewater samples were found to be Staphylococcus sp 12 (26.6%) followed by E.coli 11(24.4%), Klebsiella sp 9(20%) and Shigella sp 5(11.1%). Similarly, the overall isolates in treated wastewater samples were E.coli 45(39.5%), Staphylococcus (35.1%) and Klebsiella sp 35 (30.7%). Among bacterial isolates from hospital wastewater, 100% of Salmonella isolates were found to be resistant to ampicillin and 75% to doxycycline, erythromycin, ceftazidime, cefoxitin, and chloramphenicol. E.coli was also found to be 81.8% resistant to ampicillin and 72.7% to cotrimoxazole and amoxicillin-clavulanic acid. Significantly (P < 0.005) higher removal (80.8% to 93.2%) of antibiotic-resistant bacteria was recorded in vegetated wetlands. In contrary, no significant difference between the vegetated and non-vegetated wetlands was observed in the removal of indicator and pathogenic bacteria. Constructed wetlands could help to solve the problem of the cost-effective disposal of hospital wastewater and be promoted in a strategy to reduce water pollution in low-income countries like Ethiopia.