Oxidation units for aerating raw water routes
Modernised drinking water treatment – Cooperation with the Brokstedt waterworks
Drinking water is aerated in the waterworks so that via oxidation reactions iron ions separate as iron hydroxide (Fe(OH)3) – i.e. form particles that can be filtered out. For this purpose, air or technical oxygen is added to the raw water. At many waterworks facilities, the amount is determined by experience and is manually adjusted by the water master depending on the pressure and flow rate, which is quite time-consuming.
It is not harmful for health if too much is added, but the water becomes sparkling white and either more technical oxygen is used than is actually necessary or compressors run for an unnecessarily long period of time. Both scenarios are costly. Insufficient dosing leads to build-up in pipelines and containers, which in turn results in high costs for labour-intensive cleaning works.
Control system for optimal iron removal from raw water
This is done with the help of automated control systems that measure the iron content and accordingly adjust the amount of oxygen or air, the flow rate of the raw water, and the pressure in order to ensure optimal iron removal. It is possible to switch over to a cost-saving solution without interrupting operation.
The Brokstedt waterworks in the Schleswig-Holstein district of Steinburg is designed solely to work with groundwater, has four 60-metre production wells and has been in operation since 1978. It is part of the Mittleres Störgebiet water supply association (WBV) and, together with another waterworks in Nordoe, supplies ca. 17.500 inhabitants in 33 municipalities with approx. 1,1 million litres of drinking and process water annually. Modernisation of the water infrastructure and treatment process is always on the agenda. The waterworks employees reached out to Bürkert for this purpose in 2019 at a trade fair.
“In this context, removing the iron from our raw water also became an issue; we were looking for a more practical alternative for the air feed. We have been in good contact with the fluidics experts for many years now. With the previous manual compressor ventilation, solenoid valves, for example, demonstrated their value, and we also wanted to use German quality goods for a new, automated iron removal solution with a controlled air volume.”
Oxidation boxes for pressure-independent aeration
The Bürkert Systemhaus in Menden tailored its design of oxidation units to the specific application, and these units are now installed on each of the three raw water lines. Despite the dynamic water behaviour, these units always ensure precisely dosed aeration, regardless of the filter condition and, most importantly, the primary pressure of the raw water, which can vary significantly depending on the number and type of well pumps running at a given moment.
Since the air is added as needed, there is a reduction in the run time of the compressors and thus also in energy expenses. The tailor-made control system avoids the costly waste of resources due to overdosing and ensures consistent water quality – manual settings are no longer required. The reproducible, documented process prevents build-up in lines and containers, which significantly reduces cleaning work. The new oxidation units were delivered as a turnkey complete solution. They can either be placed in a stainless steel cabinet or on a mounting plate, like at the Brokstedt waterworks.
Mass flow controllers, proportional valves and water protection system
At the heart of the oxidation units are the mass flow controllers (MFCs). They are responsible for “intelligently” controlling and dosing the amount of air. Their thermal MEMS sensors ensure very short response times, a direct acting proportional valve as the control element ensures high response sensitivity and the integrated PI controller offers excellent control characteristics. Calibrated specifically to each application, the MFCs are combined with other components depending on the application.
Since conventional systems often suffer damage from back-pressure water in instances of compressor failure, Bürkert’s MFCs have a very robust design and are additionally protected with a water protection system. There is also an integrated bypass for manual operation. So even if there is a failure of the MFC or controller, the system can continue to be operated manually, thus preventing system downtime. The new oxidation units were delivered on a mounting plate as a turnkey complete solution. The plate dimensions were chosen to ensure that they fit into the cabinets already in place on the raw water lines. This made the installation and start-up of the control and dosing system quite simple and quick.
“All of the old was swapped out 1:1 for new, everything worked immediately and has continued to do so – to our complete satisfaction.”
Valve islands – compact, reliable and intelligent
Also the valve islands responsible for the pneumatic control unit of the process valves and flaps at the waterworks had to be replaced at the end of 2019. They had been in use for over 20 years; they kept malfunctioning and it was getting harder and harder to find spare parts. A failure of these key automation units would have brought the waterworks to a halt. With its extremely compact valve islands Type 8652, Bürkert delivered a future-proof substitute. They were installed in robust control cabinets which could easily be accommodated in the system, thanks to their small dimensions (W/D/H: 400 x 210 x 500 mm). At present, there are six of these cabinets installed in close proximity to the process valves.
Old for new – a quick swap.
The standard AirLINE Quick adapter plate simplified installation and reduced the use of pneumatic hoses and cables, thereby saving on costs and minimising potential leakage points. The automatic monitoring of pressure, wire breaks and slide run times detects defects – before they cause system failure! – and thus increases safety. Error messages are shown on the display in user-friendly plain text. There is also a manual emergency override and the individual valves can be replaced without interrupting operation. The valve islands communicate with the higher-level controller and the control system of the waterworks via Profinet.
Also the start-up of the new valve islands went off without a hitch. The automation contractor responsible for such was also satisfied with the good cooperation. Bürkert coordinated the software and protocols with the contractor in advance. The new valve islands could be integrated into the system and put into operation as plug-and-play complete solutions within a short period of time without disturbing the drinking water production. While one section of water was being switched over, operations on the other continued without interruption.
“Despite the technology used, the new solution is very clear and readily usable by any employee – e.g. in the event of a fault. Thanks to an additional floating flow rate meter, everyone can see at a glance whether everything is working reliably.”