We needed to base the development of a new pumping station design on real data concerning the operation of the current wastewater treatment plant. The quickest way of obtaining the real data without interfering with the wastewater treatment plant control system was to connect the eWON router to the PLC SIMATIC S7-300 equipment with a subsequent setting that enabled collection and archiving of selected values of variables from the PLC into the eWON modem internal memory.

All wastewater from the plant flows into two storage tanks from where it is pumped into the original wastewater treatment plant. In addition to the total daily volume of waste water, we needed to know the pH values, the minimum and maximum inflows, the water level in the storage tanks, the engine hours of the individual pumps, etc. We used the eWON modem purchased from FOXON, Ltd. In order to obtain the most accurate data for further processing, the period for the saving of measured data was set to one minute. The customer is located nearly 200 km from the company working on the design; therefore the UMTS 3G mobile operator service was used to transfer data between the company and the eWON modem. To obtain the required information, the eWONrouter needed to be installed in the switchboard for a few days only; it was then returned to the company. The entire installation consists of connecting the 24 V DC supply voltage, a 3G GSM antenna, and an MPI connecting cable between the PLC and the modem, and inserting the mobile operator's SIM card. Finally we obtained a full set of information on the operation of the wastewater treatment plant.

Fig. 1. Water level position in the first storage tank

 

Figure 1 shows a chart displaying the eWON modem in a web browser. The picture concerns the water level in one of the tanks. The user connects to the modem locally or remotely, selects the monitored values and then selects the time period to be displayed on the chart. The readings from the chart show that, at a particular moment during the cleaning in service mode, the tank was drained to the bottom. The water level was almost zero at that time. When the quantity of water flowing in was large, the water level was 110 cm at the most. The maximum water level in the storage tank amounts to 160 cm. Each pumping station of the original wastewater treatment plant has three pumps (Picture on the right) that switch on in a cascade as the water level progresses.

Over a longer period that we monitored, we discovered that the required water level could easily be reached with only one pump. It is therefore not necessary to use three pumps for the renovation and replicate the situation as it is today; one main pump and a backup pump used in the event of main pump failure are largely sufficient.

Fig. 2. Combined chart of water level and amount of pumped water: red - totalizer for flotation machine No. 1 (m3), green - totalizer for flotation machine No. 2 (m3), blue - water level in storage tank N1 (cm), purple - water level in storage tank N2 (cm)

The chart in Figure 2 provides a comprehensive overview of the water levels and the total amount of pumped wastewater (m3). It is obvious at first glance how uneven the input flow into the pumping stations is. Obtaining a picture of the inflows during the day was of key importance. A high unevenness would greatly affect the operation of the new wastewater treatment plant. The charts show that this is exactly what happens every day. Between 10 a.m. and 4 p.m., the inflow increase is a multiple of the average, while in the morning and evening hours it is far below it (Fig. 3). The great advantage is that the company was already able to deal with this negative factor prior to the implementation, which is a much cheaper procedure than launching a solution only after the manufacture and start-up of the new wastewater treatment plant. Had it relied exclusively on the data received from the customer, which only indicated the average flow rate, this would have led to a majorproblem. The second key factor that had to be monitored was the unevenness of inflow on different days. The pumping station was monitored for seven days in order to compare the situation on different days of the week. On Sunday, the maximum flow amounted to 6.3 m3 / h, and on Monday it exceeded 20 m3 / h. During this period, the mobile operator services associated with data transmission cost us about 50 CZK.

Fig. 3. The inflow increase between 10 a.m. and 4 p.m

The data collected using the eWON modem helped to ascertain that two pumps instead of the original three will be sufficient for the renovation. The economy in each pumping station represents one pump, which amounts to a financial saving of approximately 70000.- CZK in one pumping station. The eWON modem is a very efficient tool for monitoring the operation of equipment, as well as data collection and data evaluation. The modem enabled remote access to the PLC Simatic S7-300 equipment via the UMTS 3G network and gave the company the opportunity to choose the values that would be monitored and archived.