Smart Air injection (SAI) is a new sludge pumping system that is offering wastewater treatment plants (WWTP) a cost-effective and energy-efficient solution. Here we look at how this technology is reducing the carbon footprint of the Hetlingen WWTP, near Hamburg, Germany, which is now saving around 20–25 percent of energy in thick sludge pumping alone.

Environmental and economic considerations play a decisive role when municipal water utilities are considering the purchase of new pumping technology. Worldwide, SEEPEX’s energy-efficient and low-maintenance SAI-system ensures that thick sludge reaches its destination at low pressure, even for distances longer than 1km.

Two conveying technologies for a customised solution

SAI is a customised system solution that uses a combination of progressive cavity pumping and dense phase pneumatic conveying to discontinuously transport short plugs of highly dewatered sludge in a particularly energy efficient manner. In principle, it’s just like the good old pneumatic mail.

As a result, friction losses only occur along these plugs and not in the entire pipe, resulting in numerous unique advantages, such as the ability to transport sludge for up to 1km with a low-pressure pump and PN10 piping.

For water utilities in Australia, SAI poses an alternative to conventional processes, and has been tried and tested overseas for years. The energy saving it provides means that SAI can quickly pay for itself, and more than 80 customers already benefit from this innovation, which is patented in Europe, the US and China.

Implementation at the Hetlingen WWTP

Located north-west of Hamburg, Germany, the Hetlingen WWTP serves more than 40 towns and communities, treats more than 31 million cubic metres of wastewater per year and processes about 46,000Mg of sludge per year – which is anaerobically stabilised, dewatered in centrifuges and pumped into silos.

After anaerobic stabilisation, the digested sludge is dewatered in centrifuges in a separate building and then falls through a hopper into the pump cellar. From there, it was previously pumped by two piston pumps to two silos located 60m away and 30m higher. The dewatered sludge was then trucked to an off-site incinerator for thermal recovery.

When the centrifuges were replaced in a planned rebuild, the piston pumps were found to be undersized. In addition, maintenance requirements and energy costs were very high. Hetlingen WWTP turned to SEEPEX when it needed to improve its solids handling technology following the replacement of centrifuges and feed pumps.

The main challenge was to find a new thick sludge conveying system that would fit into the existing infrastructure along with the re-planning of the thickening sludge silos. The result, as envisioned by the plant operators, was a system that would minimise maintenance and energy costs, as well as downtime for servicing. The goal was to significantly reduce the total cost of ownership (TCO) in direct comparison to installed piston pumps.

In addition, the wastewater authority wanted a much more flexible system that would be suitable for future upgrades. As the centrifuges for dewatering had already been ordered, a quick solution had to be found to transport the 5–15m³/h of sludge to the two silos within the existing infrastructure and without interrupting operations.

Smart Air Injection including sensors, compressed air connections and lubricant injection points.

After extensive consultation and a comprehensive review of the plant’s specific conditions, SEEPEX experts set about developing a solution that was perfectly tailored to the plant. In the end, SEEPEX was chosen as the general contractor to supply and install two redundant systems. The scope of supply included installation, piping and cabling.

Delivery was completed within six months. The bespoke SAI system was supplied with a hopper pump (BTHE 130-12) with a moveable stuffing part for easy removal and access to the rotor side joint and screw conveyor (Rotor Joint Access), a dosing pump for lubricant supply, a compressed air system consisting of a compressor and air receiver, and a control cabinet with integrated control.

In addition, SEEPEX installed two separate pipelines (PN16, DN250 in stainless steel) over a length of 90m (60m horizontal, 30m vertical), including the necessary sensors and isolation valves. The integrated automation technology (SAI controller) allows the two outdoor silos to be fed as required.

Pneumatic dense phase conveying with supporting lubricant minimised friction losses in the pipeline. The characteristic pressure behaviour of SAI is also evident in Hetlingen, where the pipeline pressure in operation is only 2–3bar. In contrast, hydraulic operation using a piston pump was achieved at up to 70bar.

By reducing the operating pressure, it was possible to use a PN16 stainless steel pipeline. Due to the low pressure level compared to conventional solutions with much higher operating pressures, it was possible to save costs in the purchase of piping.

In addition, the low operating pressure significantly increases the service life of all pump and pipework components. Overall, SAI saves around 20–25 per cent of energy per year compared to a piston pump. The Rotor Joint Access maintenance concept, with its moveable stuffing part, simplifies pump maintenance and saves costs.

It allows quick and easy access to the rotor-side joint for easy maintenance without dismantling the pressure branch or stator. In this way, the innovative SAI system solution greatly simplifies maintenance. With these new pumps up and running, the Hetlingen WWTP will have to intervene less frequently during operation and the entire operational side runs more smoothly.

Significant energy savings during pump operation will reduce the plant’s carbon footprint, boosting their climate protection measures.

SEEPEX is one of the world’s leading specialists in the field of pump technology. Its product portfolio includes progressive cavity pumps, pump systems and digital solutions. SEEPEX also offers innovative solutions for conveying aggressive or abrasive media with low to high viscosities. Since 2021, SEEPEX has been part of the Ingersoll Rand Group, a global supplier of mission-critical flow creation and industrial solutions, consisting of more than 40 renowned brands. Ingersoll Rand Inc. (NYSE:IR), driven by an entrepreneurial spirit and ownership mindset, is dedicated to helping make life better for our employees, customers and communities. For more information, contact SEEPEX or visit 

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