Microbial evaluation of Al-Khobar wastewater treatment plants

Abstract

A one year study was conducted at the Al-Khobar Wastewater Treatment Plan to investigate the seasonal variations of temperature and flowrate on the fate of indicator microorganisms. The raw sewage, secondary effluent, chlorinated effluent, and dry sludge were analyzed for the detection and enumeration of five indicator microorganisms, namely; Standard Plate Count, total coliform, fecal coliform, coliphage, and Clostridium perfringens on a weekly basis. Multiple non-linear stepwise regression analysis was performed to correlate the microbial population with temperature and flowrate of wastewater, measured in the treatment plant to develop regressional models for all studied microorganisms at different stages. Verification of these models was performed on the basis of percent error and plot of measured Vs predicted values. The t-test performed on mean population densities of studied indicator microorganisms showed higher microbial populations during summer than winter. However, dry sludge showed a higher population density of total coliform, fecal coliform, and coliphage during winter while population density of Standard Plate Count and Colstridium perfringens showed no signifcant difference in their mean population densities during summer and winter. High percent removal of Standard Plate Count, total coliform and feecal coliform (99% to 99.9%) observed after secondary treatment as compared to coliphage removal of 83.6% and Clostridium perfringes removal of 55.5%. Whereas , after chlorination Standard Plate Count, total coliform, and fecal coliform were removed up to 99.7% compared to coliphage reduction of 52% and Clostridium perfringes removal of only 42% showing a high resistance against chlorination.