Monitoring the Efficiency of Automatic Screens Based on Computational Analysis of Wastewater Level Variations

The quantity of solid waste entering the sewage system is contingent on a number of factors, including the type of wastewater, the time of day and year, prevailing weather conditions, as well as the habits and awareness of users of the sewage infrastructure. In this regard, the water and sewerage company in Koszalin (northern Poland), where this study was conducted, initiated a long-term information campaign in 2019 under the slogan "Keep waste out of the sewer system". The objective of the campaign was to raise residents’ awareness of the detrimental consequences of improper use of the sewerage system, particularly in terms of the disposal of solid waste into the network that should not be there. This paper presents the findings of an investigation into alterations in the level of wastewater measured using an ultrasonic probe situated in front of automatic step gratings with a clearance width of 3 mm. The measurement data (comprising more than 186,000 records) were systematically recorded at a frequency of 10 seconds over a period of three weeks in the WinCC system of a municipal wastewater treatment facility. The number of grating engagements in each hour was then calculated based on the local minima of wastewater levels. Subsequent data analysis was conducted on a weekly basis, with a distinction made for each of the three independently operating screens. In the preliminary phase of the study, a hypothesis was formulated concerning the variations in the efficiency of the grilles, attributable to the duration since their most recent comprehensive overhaul. The results of the analysis confirmed the assumption of varying efficiency of pollutant separation, with screens displaying a higher degree of wear showing a lower number of engagements per hour, which may indicate a reduction in their efficiency. The findings of the study indicated that the implementation of an effective monitoring system to assess the efficiency of automatic screens used for the separation of solids from wastewater can be facilitated by the analysis of changes in the level of wastewater in front of the screens.