Changes in the physicochemical and microbial quality of wastewater from a wastewater treatment plant

Abstract

The discharge of wastewater directly into the environment could constitute serious health hazards to humans and other life forms. This study aimed at determining the changes in the physicochemical and bacteriological quality of wastewater from a treatment process plant. Wastewater samples were aseptically collected at 10 different points of a treatment plant and bacterial isolates were obtained from them. Isolates were identified using biochemical technique and API 20E identification system. The isolates were assessed for resistance to common antibiotics using Kirby-Bauer disk diffusion method from which the Multiple Antibiotic Resistance (MAR) Index was calculated. There was improvement in the physicochemical parameters analyzed. The biological oxygen demand, dissolved oxygen, pH, temperature, turbidity, salinity, sulphate and heavy metal concentrations were within acceptable wastewater effluent limits at point of discharge. The total heterotrophic bacterial population, total coliforms and total heterotrophic fungi ranged from 1.4 x 107 to 4.0 x 102 , 3.2 x 104 to 2.0 x 10 2 and 5.6 x 104 to 2.5x 102 cfu ml -1 at the point of entry and discharge to the environment respectively. Thirteen bacterial species were detected from the wastewater samples collected which include Enterobacter species (3), Escherichia spp. (3), Klebsiella species (3), Enteric group 69 (1), Rahnella aquatilis (1), Edwardsiella tarda (1) and Buttiauxella ferraguitiae (1). None of the isolates had 100% susceptibility to the antibiotics investigated. The most prevalent multiple antibiotic resistance phenotype observed among the isolates were tetracycline, gentamicin and cotrimoxazole. The MAR values ranged from 0.16 to 0.83. The result proved that the treatment process was effective in reducing the final concentrations of the physicochemical parameters, microbial load and pathogen discharged into the environment. Keywords: Antibiotics, coliforms, metals, physicochemical, wastewater.