ANTIBIOTIC-RESISTANT BACTERIA IN GREYWATER: IS THERE REASON FOR CONCERN?

Greywater (GW), household effluents that excludes wastewater from toilet flushing, is often contaminated with pathogens and require treatment before it can be safely reused for landscape irrigation. A recirculating vertical flow constructed wetland (RVFCW), is a useful treatment technology for GW. An emerging source of negative environmental impact associated with wastewater or greywater reuse is the spread of antibiotic-resistant bacteria (ARBs). Interestingly, there is very little information concerning the presence of ARBs in GW. Thus, the aim of the present study was to investigate the presence of ARB in GW and then to evaluate if there is a significant risk irrigating with the treated effluents.

Freshwater (FW) Raw and RVFCW-treated GW from three households were routinely examined for ARBs as well as respective irrigated soils. FW irrigated soil plots served as controls.

No ARB were detected from all freshwater samples. In all systems and in all sampling points along the RVFCW we detected ARB’s for the three tested antibiotics. Amoxicillin ARB’s were most abundant followed by kanamycin and ciprofloxacin ARB. The RVFCW treatment reduced all ARB’s by up to three logs. No significant differences were observed between ARB loads in soil irrigated with GW or FW. From the different locations, we isolated 27 strains with resistance for the different antibiotics. Flavobacterium occupied 36% of ARB isolated from water sources and soils. One of them, identified as Elizabethkingia meningoseptica, was highly resistant for the three antibiotics but was eradicated from GW by chlorination.

We suggest that the ARB in GW may originate from external surfaces of human bodies in the bath water or contaminated laundry or food. Pathogens resistant bacteria were not detected in the treated GW because they have been eliminated by the treatment. Thus, upon adequate treatment, ARBs are not expected to accumulate in soils because of GW irrigation.