ASSESSMENT OF THE RELATIONSHIP BETWEEN MICROBIAL COMMUNITY STRUCTURE AND WATER QUALITY FROM THE ACTIVATED SLUDGE SYSTEM OF WASTEWATER TREATMENT PLANT

Abstract

This study aimed to evaluate water quality and investigate microbial diversity in the activated sludge system of the Water Quality Control Plant. Samples were collected from July 2024 to January 2025. Water quality parameters included temperature (14.9–26.0°C), pH (6.49–8.00), dissolved oxygen (6.81–7.34 mg/L), conductivity (400–730 µS/cm), biochemical oxygen demand (4.81–5.12 mg/L), total dissolved solids (198 mg/L), alkalinity (178–357 mg/L), hardness (300 mg/L), sludge volume index (60–250 mg/L), fat oil and grase (4-15 mg/L), phosphate (2-4 mg/L), nitrate (0.5 mg/L) nitrite and ammonia (0 mg/L), and coliform/fecal coliform  (>1,600 MPN/100mL). Dominant microorganisms observed under a microscope included Aphanocapsa sp., Microcystis sp., and Coleps elongatus, which showed the highest densities. Among them, Aphanocapsa and Microcystis are cyanobacteria known to cause eutrophication (algal blooms) under high phosphate and nitrogen conditions. Testate amoebae were abundant in early samples, indicating high organic content that later declined, possibly due to environmental shifts or microbial competition. Other phytoplankton, such as Scenedesmus sp., Navicula sp., and Chlorella sp., appeared in low abundance, suggesting suboptimal light or pH conditions related to inconsistent system control. Zooplankton, including Rotifera and Daphnia sp., were occasionally present, reflecting possible variations in dissolved oxygen or organic toxicity. Transient species such as purple sulfur bacteria indicated short-term anaerobic events. Overall, the study highlights the dynamic interactions between microbial communities and water quality parameters in the activated sludge process, emphasizing their potential as bioindicators for treatment efficiency.