Minimal site installation time, but new screens revitalise inlet works

A prefabricated packaged treatment plant — constructed off-site — from SPIRAC has enabled a water company in the north of England, UK, to improve its inlet works and keep its carbon footprint to a minimum with a £12.3m upgrade. Ammonia discharge was reportedly reduced from 13mg/L to 0.1mg/L after the new investment as the upgrade improved the water quality being released into the local river, helping the environment and fish population.

For the wastewater treatment plant (WTP) that serves a population of 25,000, SPIRAC designed and built three of its FINEGUARD screens at its manufacturing plant so that there was minimal civils and no concrete pouring on-site. The SPIRAC new treatment system sits on a precast concrete pad, is supported by a galvanised steel support structure and is elevated 5m above ground level to allow flows to gravitate 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.

Installation of SPIRAC new FINEGUARD screens meant minimal civils and no concrete pouring on-site
A SPIRAC SANDSEP dewaters and discharges grit into a skip

SPIRAC’s three FINEGUARD screens are capable of passing a maximum flow of 566L/sec of sewage at a design water depth of 1m downstream. Each screen consists 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 to ensure oncoming flow meets unsullied panels. Furthermore, the screen panels are secured so that any individual units can be replaced with minimum 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.

SPIROWASH units wash out the organic material, reducing the volume and weight of screenings

A grit vortex unit also removes suspended grit from the sewage flow. This consists a prefabricated grit vortex chamber capable of handling up to a maximum 628L/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 handling up to 20L/sec of grit slurry. The SANDSEP unit dewaters and discharges grit into a skip.

Speaking for SPIRAC, Shyam Mallen said, “We are seeing demand from water companies and Tier One contractors to provide a complete package, with minimal site time and use of civils materials, especially concrete. Off-site build, testing and wiring are benefits for wastewater projects.”