This study was carried out at Mahallet Ziad wastewater treatment plant in El-Gharbia Province during a period extending between Feb. 2018 and Jan. 2019. Major planktonic groups and certain physico-chemical parameters were investigated monthly at this water plant to elucidate its performance efficiency in treating and enhancing the wastewater. It was apparently that protozoa and rotifers represent the major groups in that wastewater treatment plant. Protozoa are represented by three major phyla (Sarcodina, Mastigophorea and Ciliophora)  where the ciliated protozoans prevail the other two phyla. The numerical densities of sessile peritrich ciliates were less abundant than other ciliated protozoan types (crawling and swimming ciliates). It was proved that the maximal and minimal numerical densities of total protozoans of the present investigation exhibited 6956 and 1716x 10²/L during March and December, respectively. Simultaneously, the uppermost numerical values of sarcodines, flagellates and ciliates were 565, 2211 and 5631²/L during May, February and April, while the lowest ones were 30, 87 and 1716x 10²/L on September, July and December, respectively. Different types of protozoan were proved to be significantly influenced to varying levels with certain physico-chemical parameters.
From the technological point of view, it was proved that the performing efficiency of the activated sludge of the present study is more or lessparallel to those of other wastewater treatment plants in different provinces of Egypt which gives an indication that there is a critical strategic need for the government to have more treated water to be used in agricultural and industrial activities.