A prefabricated packaged treatment plant (constructed offsite) from Spirac has enabled a water company in the north of England to make much-needed improvements to its inlet works, and in doing so, keep its carbon footprint to a minimum.

For the wastewater treatment plant that serves a population of 25,000, Spirac designed and built three of its proven Fineguard screens at its manufacturing plant so that there was minimal civils and no concrete pouring on site.

Spirac’s new treatment system sits on a reinforced precast concrete pad, supported by a galvanized steel support structure, elevated over 16 feet above ground level.  This allows flows to gravitate easily to the downstream process units.

Prior to the installation, the inlet could no longer cope with the volumes it was receiving. Rags were constantly bypassing the old screens and getting into the secondary treatment area.


Part of a $15 million upgrade, the new treatment process has already resulted in key improvements to the quality of water being released into the local river, helping the environment and fish population. Before the new investment, ammonia discharge was at 13 parts per million, but this has now been reduced to just 0.1 parts per million.

Spirac’s three Fineguard screens are capable of passing a maximum flow of 150 gallons per second of sewage at a design water depth of 1m downstream. Each screen consists of a band of perforated screen panels that are secured to drive chains on either side of the panels. On reaching the discharge section of the screen, a self-adjusting brush mechanism (with water spray jets) cleans the screen panels of debris. This ensures that the oncoming flow always meets unsullied panels for maximum performance. Furthermore, the screen panels are secured so that replacement of any individual units can be achieved with a minimum of effort and downtime.

Screenings are transferred from the screens via a launder trough system. Spirowash units then wash out the organic material, reducing the volume and weight of the screenings by compaction before delivering them to a skip via a press tube.

A grit vortex unit also removes suspended grit from the sewage flow. This consists of a pre-fabricated grit vortex chamber capable of handling up to a maximum 628 l/sec of screened raw sewage flow. The grit is extracted by means of a grit pump, and is fed to a Spirac Sandsep grit separator unit capable of handling up to 5 gallons per second of grit slurry. The Sandsep unit dewaters and discharges grit into a skip.


We are seeing far more focus and demand from water companies and Tier One contractors to provide a complete package, with minimal site time and use of civils materials, especially concrete.

With the comprehensive range of screens and grit removal solutions that we design and manufacture, we also have the capacity to create significant savings for our customers. Offsite build, testing and wiring is a big benefit for wastewater projects. 


For over forty years, Spirac has been market leaders in shaftless spiral (screw) conveyor systems and inlet works packages. With offices located around the world, Spirac can provide the best solids material handling solutions developed with the benefit of international and local experience. The company’s diverse product range and experienced team of engineers offer solutions for the smallest to largest WWTP. Spirac is also a major supplier of sludge silo systems, offering complete design, fabrication, and installation services for the efficient, clean, and odor-free handling of large or small capacity systems. For more information, visit www.spirac.com.

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