Systems and methods for determining liquid phase turbidity of multiphase wastewater. A turbidity sensor is provided with multiphase wastewater, such as by placement of the sensor in a reaction chamber, and generates a signal in response to a detected turbidity of the wastewater. The generated signal is sampled to produce a plurality of signal samples. The samples are compared to a threshold, and a turbidity of the wastewater is determined based on samples falling within the threshold. The threshold may be determined based on a statistical analysis of the plurality of samples, or may be set to a predetermined value. The wastewater may be provided by placing the turbidity sensor in a flocculation chamber, and a control signal generated based on the determined turbidity of the wastewater. This control signal may be used to adjust the amount of a chemical, such as a coagulant, introduced into the wastewater.