Domestic wastewaters causing pollution contain inorganic and/or organic materials. When the domestic wastewater outflows to the receiving waters, it causes physical, chemical, and biological pollution in them, and deteriorates the ecological balance of those waters. In the treatment of wastewater, various treatment methods are available depending on the pollution strength of the wastewater. Besides mechanical and biological methods, wastewater treatment with physicochemical methods is still one of the most effective and economical options. Particularly in wastewater with a high concentration of suspended solids, this method is very successful, and obtaining high suspended solids removal efficiencies are far possible. In this study, the effects of the use of coagulant and coagulant aid to be used in a treatment plant where domestic wastewater treatment is carried out are determined to increase the treatment efficiency of a biological treatment that comes later of the stages of the treatment. The effluent of the pre-settling tank may contain a lot of suspended solids. This presence of excess suspended solids decreases the efficiency at other levels of treatment and causes energy loss. In the experiments, the standard jar and inhibition tests are done as a method. As a result of the conducted studies, it is determined that the FeCl3, Synthetic coagulant LP 526, FeClSO4, and the combination of anionic polyelectrolyte yields the best results in the removal of the parameters of COD, TSS, and VSS. While FeCl3, APE 65, APE 85, Synthetic coagulant LP 526, and FeClSO4 did not show any inhibition effect in the sludge, APE 67, CPE 84, and (Al2(SO4)3 are found to cause inhibition in the sludge.