Scraping a living

Installation underway at the Mogden site.
ODOUR reduction is one of the tasks for sludge handling technology installed at a Thames Water sewage works in London.
The water company has invested in the Zickert equipment from Hydro International in record-breaking contracts totalling £24m. The continuous bottom scraping and surface scum removal kit will collect sludge from a total of 53 primary settlement tanks at Beckton, Crossness and Mogden sewage works. The projects are designed to increase sewage treatment capacity, improve operating efficiency and reduce odour.
At Beckton STW, 24 existing sedimentation tanks will use the new scrapers, adding to eight existing primary tanks already converted to the Zickert system. The entire £16.5m installation will cover more than 56,000 sq. metres.
Thames Water made the decision to invest in the Zickert top and bottom scrapers based on the performance of existing installations. The equipment is said to offer significant advantages over conventional sludge scraping technology, with lower operating and infrastructure costs. A gentle action produces a higher yield of sludge while the higher throughput reduces the amount of secondary treatment required and produces more primary sludge with a higher calorific value for incineration. And because the tank design requires lower headroom than other sludge collection equipment, it reduces the volume of air to be treated for odour removal in the tank enclosures.
At Mogden the requirement was to retrofit eight primary settlement tanks and to equip five new tanks. Work there is part of Thames’s £140m upgrade to increase sewage treatment capacity by 50%. At Crossness, eight primary settlement tanks are being built as part of the £220m upgrade to boost sewage treatment capacity by 44%. The Zickert equipment will provide energy-efficient odour control and deliver sludge to provide 20% of the plant’s energy needs.
The Beckton project was awarded to Hydro by main contractor GBM, the joint venture of Galliford Try, MWH Treatment and Mott Macdonald. GBM’s project manager Phil Muir explained: “Thames Water decided to use Zickert scrapers for primary treatment to replicate the good performance and reliability of the existing Zickert tanks installed at Beckton in 2007 and 2009. They recognised that the Zickert process was a good one for wider upgrade of the facility.”
Chris Day, operations director of Hydro International’s wastewater division, added: “These contracts together are a record breaker, the largest ever placed with Hydro,” said. “It’s a true vote of confidence in Zickert technology which has been proven in use in the UK for 15 years. We are expecting other water companies in the UK to follow suit.”
In addition, the first Scottish installation of the Zickert technology is underway at a waste water treatment works in Lanarkshire for Scottish Water Solutions.