Performance of a small-scale constructed wetland for the removal of antibiotics and antibiotic resistant bacteria from hospital wastewater

Abstract

Hospital wastewater is a reservoir for high load of antibiotics, heavy metals and antibiotic-resistant bacteria which are of public health concern and should be removed. Horizontal subsurface-flow constructed wetland (HSCW) is one of the most important green and environment-friendly technologies for removal of pollutants from wastewater. This study explored the efficiency of HSCW for removing antibiotics, antibiotic resistant bacteria and heavy metals from hospital wastewater of Tikur Anbessa Specialized Referral Hospital. Wastewater samples were taken periodically for five months in 2018 and fed into the influent of a HSCW in the CNCS, Addis Ababa University, with a flow rate of 0.72 L/hr and hydraulic retention time of 4 days. Influent and effluent samples were collected and analyzed for BOD, COD, Nitrogen and Phosphorus species, heavy metals, antibiotics and antibiotic resistant bacteria. The average BOD and COD values of the raw wastewater from the hospital were 243 and 1,312 mg/L, respectively, and mean total nitrogen and total phosphorus were 62.0 and 6.4 mg/L, respectively. Removal of TP was highest in cells planted with P. karka (95%) than the cell planted with the combination of the two plants (74%). Highest removal of TN was observed in the cell planted with T. latifolia (94%) than with combined plants (86%). P. karka showed high removal efficiency for Nickel (73%) and Zinc (86%). Heterotrophic bacteria exhibited resistance to ciprofloxacin and cefotaxime antibiotics but counts decreased in all cells of the CW compared to the influent. The removal efficiency observed for ciprofloxacin and cefotaxime was generally low in all cells, and requires further study for process optimization. The mean concentration of ciprofloxacin and cefotaxime residue in the influent were 1.23 ppm and 17 ppm, respectively, and were very high compared to literature reports. Strong positive correlation (r²=0.98, P=0.11) was found between cefotaxime concentration and bacterial count resistant to cefotaxime in the influent and the water treated with T. latifolia and strong negative correlation in unplanted control, P. karka and the combined plants (r²=−0.746, p=0.464). It is concluded that HSCW pretreatment schemes should be in place for removal of hospital wastewaters containing antibiotics and heavy metals.