Antibiotic resistance and survival of faecal coliforms in activated sludge system in a semi-arid region (Beni Mellal, Morocco)

The activated sludge process is one of the biological treatment methods used in many countries to reduce the high levels of organic and mineral pollutants and pathogenic micro-organisms present in wastewater. The present work was undertaken to study the dynamic and antibiotic-resistance of faecal coliforms (FC) in the activated sludge system of Beni Mellal. This work has also as objective the study of the survival of FC, protozoan cysts, helminth eggs and FC antibiotic resistance in the sludge dehydrated in drying beds in order to know if the agricultural usage of sludge presents any problems to public health. The activated sludge treatment of Beni Mellal resulted in an average reduction of FC and faecal streptococci of 90.75 and 91.06%, respectively. The overall resistance (resistance to at least one antibiotic) of 111 FC strains isolated from the system was 72.07%. This treatment system did not increase the incidence of FC antibiotic resistance in treated wastewaters. The antibiotic resistance of FC was found to be similar in both raw (71.05%) and treated sewage (77.77%). High levels of antibiotic resistance were towards streptomycin (54.05%), ampicillin (42.34%), amoxicillin (42.34%) and amoxicillin-clavulanic acid (31.53%). The treatment of sludge in drying beds appeared to be efficient in eliminating pathogenic micro-organisms: FC, protozoan cysts and helminth eggs. Moreover, the FC antibiotic resistance did not change over time in sludge-drying bed. According to the standard norms, agricultural utilization of this sludge cannot be excluded. However, it is important to study in the receptor environment the survival and the behaviour of antibiotic-resistant FC present in sludge and water.