We were building a wastewater treatment system of the 2nd degree, and received treated wastewater of the 3rd degree

We built a 2nd level wastewater treatment system and got 3rd level purified wastewater.

Donji Miholjac, a town of 10,000 inhabitants on the Drava River, needed to improve its wastewater treatment system to preserve the quality of the Drava River, protect the habitats of wild animals, and ultimately ensure a better quality of life for people living in the area.

Any use of tap water for different purposes pollutes water and changes its physical, chemical and biological properties. Wastewater generated in this way, be it industrial, domestic, agricultural, or rainwater, must be collected, purified, and transported to a receiver without harming the environment.

The treatment of wastewater and the construction of purification devices at the end of the city sewage system, as well as within the framework of the industrial plant before entering the city sewage system, are almost imperative today for every developed or rural environment.

From an outdated plant with a small capacity to a new plant that covers all the needs of residents

When we took over the project, the wastewater treatment facility (WWTP) of the city of Donji Miholjec was only performing the function of the 1st stage of wastewater treatment (sedimentation and mechanical treatment), which still returned water polluted by biological substances to nature and water resources. and smaller particles.

The primary treatment (1st stage) starts from the inlet pumping station where, with the help of a coarse and fine grate, the process of extracting large impurities and large particles of sludge and sediment, fat and sand is carried out on the sand and oil extraction device.

The reconstruction provided for the upgrading and expanding functionality to the level of the 2nd stage of wastewater treatment (biological treatment, secondary sedimentation and sludge treatment).

Secondary treatment (2nd stage) is based on biological processes for removing biodegradable organic substances. The procedure occurs inside an elliptical biological pool (Orbal) with rotating biological discs and two secondary sedimentators.

The wastewater is constantly mixed with a specific volume and concentration of sludge, and the sedimentation of activated sludge (secondary sludge) occurs, while part of the sludge is returned to the biological pool to make the most of its ability to decompose. The rest of the sludge is treated and discharged in a mechanical dehydration facility.

For the protection of employees, but also more efficient operation of the plant, our task was to design a complete one

Monitoring and control system with SCADA system consisting of:

• management distributor,
• PLC electrical installation
• measuring instrumentation

The designed load of the device after the reconstruction is 8,000 population equivalent (ES).

Four units of the supervision and management system

First, the complete electrical installation of the plant was carried out with the installation of the fundamental grounding device, lightning protection installation, potential equalization installation, cable installations and cable routes, so that ATO could guarantee the safety and durability of the system.

After the preparatory work on the electrical installations, we proceeded with the implementation of the automation and monitoring of the control system.

The complete solution of the monitoring and control system is installed on a SIEMENS SIMATIC 317PN-DP processor with a SIMATIC-ET200M distributed peripheral.

Each of the four segments has its sensor system, a system for ensuring and monitoring correct functioning according to the settings of the devices included in that system and checking the transfer of water and sludge step by step.

All activities are monitored in parallel from the control room. Communication between the control room and the distributed peripherals occurs via an optical redundant ring.

The implemented SCADA system is based on the Siemens WinCC platform with a special control module for managing water treatment plants.

The work units we have structured are:

1. Distribution of the power supply of the facility with the aggregate station,
2. management of the input first stage of purification (input pumping station),
3. management of biological treatment,
4. sludge treatment and dehydration management.

The results are better than expected – the water is disinfected and free of nitrogen and phosphorus residues.

After we started the plant, in cooperation with the Investor’s technologist, we adjusted and refined the operating parameters of the biological pool, which, with its construction, significantly improved wastewater treatment compared to the original project.

Examination of samples at the plant exit showed the results of the 3rd stage of wastewater treatment, which means the removal of nitrogen and phosphorus, and the disinfection of treated wastewater.

Which means that the water is polluted with fertilizers and pesticides,

That’s how the ATO works – the results often turn out to be better than planned.