Scottish Water needed to replace two scrapers in a sewage treatment plant near Glasgow. They hired GMJV as the main contractor, who solicited bids for the refurbishment. Xm Services was awarded the contract. The original scrapers were failing due to issues with the scum skimming arrangement. Xm Services designed new scrapers with a robust scum skimming arrangement supported by the rotating scraper arm. They worked closely with suppliers and GMJV during manufacturing, which included factory acceptance tests. Xm Services then decommissioned and removed the old scrapers, and installed and commissioned the new scrapers, completing the project on time.

1. Turnkey Solutions – Case Study Refurbishment of ø20m fixed half bridge column mounted primary settlement tank scrapers

2. Introduction Scottish Water urgently needed to replace two scrapers that had fallen into disrepair at a sewage treatment works near Glasgow. A main contract was awarded to GMJV who sourced tenders from the marketplace for the refurbishment of the scrapers. As a result Xm Services became involved in the tendering process and was eventually awarded a contract to undertake the refurbishment.

3. Poorly performing primary settlement tank scraper

4. Primary settlement tank scraper with collapsed scum skimming device Sep Oct Nov Dec Jan Feb

5. The root cause of poor performance in primary treatment process was the use of peripheral rollers and scum board to support scum skimming arrangement. The peripheral rollers derailed from the scum board generating excessive forces at the point where the scum skimmer arrangement was fixed to the centrally located diffuser drum causing it to collapse.

6. Detailed Design In order to improve the robustness of the scraper the scum skimming arrangement was designed so that it is supported by the rotating scraper arm

7. Manufacture of Scrapers Xm Services worked closely with both its suppliers and GMJV throughout the manufacturing phase: Conducting regular project schedule reviews and updates to monitor and control the manufacturing process Perform factory acceptance tests to ensure conformance with: design documentation WIMES 2.01 data sheets EC standards

8. Manufacture of Scrapers

9. Scraper Refurbishment Decommissioning, removal and disposal of existing scrapers: Preparation of site risk assessments, method statements and lift plan for inclusion within the contract H&S file Site supervision and induction of all personnel Provision of confined space qualified personnel to work inside the settlement tank Provision of qualified first aider Conducting daily toolbox talks Daily issuing and closure of permits to work Cranage and execution of contract lift Scrap disposal

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14. Scraper Refurbishment Installation and commissioning new scrapers: Unloading, unpacking and storage of equipment Assembly Installation No load site acceptance tests Full load commissioning tests Customer acceptance and handover

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