WET News

18 WET NEWS JULY 2014 Circular sludge settlement tanks are iconic in the industry. However, they can be odorous and have high energy requirements. The challenge: Plotting a revolution in sludge scraping INSIGHT SEWAGE & SLUDGE TREATMENT Checking out the drive ring on a site visit to the most recent installation completed this spring at Getteröverket in Sweden Z ickert sludge and scum scraping technology has been available in the UK for rectangular settlement tanks for well over 20 years and is al- ready proven in use by water companies across the UK, in- cluding Thames Water, South- ern Water, Anglian Water, Scot- tish Water and United Utilities. The circular tank, an iconic and ubiquitous symbol of wastewater treatment plants, are used in a number of settle- ment processes in sewage treat- ment including primary, humus and final settlement. At least 90% of sludge settle- ment tanks are estimated to be circular. However, until now, the proven benefits of Zickert for odour control, higher sludge-throughput, energy effi- ciency and lower maintenance have not been available for them. The quality and efficiency of primary settlement treatment in particular affects the efficiency of downstream processes by removing suspended solids and BOD from wastewater. Inade- quate final treatment processes, such as discharges that exceed permitted limits for pollutants or Biological Oxygen Demand (BOD), can result in operators incurring punitive fines. On the other hand, a reduced BOD level allows smaller tanks to be used for aerobic treatment of the water in the secondary stage. Primary treatment, when done well, can significantly reduce the energy requirements for secondary treatment. More efficient sludge settlement, con- centration and collection can also increase the sludge feed- stock and leads to greater out- puts for energy recovery via anaerobic digestion or for pro- ducing dewatered sludge for incineration. Traditional solutions for sol- ids consolidation and removal from circular settlement tanks generally involve large struc- tural mechanisms, typically travelling bridges which strad- dle the large circular tanks and are seen at most treatment works. However, these tradi- tional travelling bridge scrapers have high power requirements and need frequent service and maintenance. They can also be prone to wear and mechanical breakdown. Odour control Reducing the odours from pri- mary settlement processes is becoming an increasing con- cern for operators who are look- ing for more efficient, minimal THE CONCEPT • A new way of removing sludge from circular tanks • Peripheral drive • Rotation via drive ring and circular ladder rail around the tank wall perimeter • Static electrical connection point – no sliprings • Scraper section is supported on wheels to allow the drive ring and central support to hold the scraper in the optimal position with minimum stress THE VERDICT "The Zickert Rotating Sludge Scraper has great potential to upgrade the UK's installed base of circular settlement tanks for both retrofitting and new construction. In particular it offers opportunities for water companies to save operating and energy costs and improve odour control." Keith Hutchings, group wastewater product manager, Hydro International • disturbance treatment and eas- ily enclosable plant. Covering the tanks and extracting the air reduces odours but has a high energy demand. Therefore min- imising the headroom with a low-cover profile is desirable. Travelling bridge scrapers need platforms to allow access by operatives to the drives, motors and electrical connec- tion points located at centre of the structure. A bridge greatly increases the height at which odour control covers can be installed, creating a significant extra volume of air to be removed by odour control sys- tems, resulting in far greater energy consumption and cost. For AMP6, UK water compa- nies are being encouraged to demonstrate performance based on best totex. Wastewater treatment plant operators must consider the cost benefits of their investment in plant and process efficiency both in the capital outlay and the ongoing costs of operation, energy con- sumption and through-life maintenance. Therefore, find- ing a more efficient and produc- tive solution for sludge settle- ment and removal in circular tanks would offer advantages to many water companies. n NEED TO KNOW • No need for a travelling bridge • Low profile for odour control covers • Low wear and maintenance • Operation to suit sludge load and tank • High sludge throughput "The technical diligence was undertaken to fully understand all design, mechanical and maintenance aspects..." Keith Hutchings, Hydro The Zickert 3700 Rotating Sludge Scraper has a peripheral drive and rotating scraper design, eliminat- ing the need for a bridge or a moving electrical connection point JULY 2014 WET NEWS 19 Circular sludge settlement tanks are iconic in the industry. However, they can be odorous and have high energy requirements. A solution: Taking the cost out of sludge scraping H ydro International is the sole UK distributor for Swedish manufacturer Nordic Water Products, and had the opportunity to be involved in the development process and in- troduce the new Zickert sludge scraping technology for circular tanks. The Zickert 3700 Rotating Sludge Scraper is a new way of removing sludge from circular settlement tanks. It features an innovative peripheral drive and rotating scraper design, so there is no need for a bridge or a mov- ing electrical connection point. The circular tank scraper's electric drive is located on the perimeter tank wall with a static electrical connection point meaning no sliprings are needed. The neoprene bottom scraper blades of the new Zick- ert 3700 are rotated via a circular ladder rail inside the tank wall, moving settled sludge to the col- lection point. The scraper section is sup- ported by its own wheels, there- fore allowing the drive ring and central support to hold the scraper in position without addi- tional stresses. There is no fixed rail above the tank rim making concrete construction easier. Where surface scum has to be skimmed off, the scraper frame is equipped with an additional top blade which directs scum to a scum beach and trough on the tank perimeter. With full stainless steel con- struction and few moving parts, Zickert Rotating Sludge Scrapers require less frequent mainte- nance and are less subject to mechanical wear than conven- tional bridge scrapers. By removing the need for a bridge, the Zickert Rotating Sludge Scraper also has a lower profile design, which reduces the space under odour control HUBER TECHNOLOGY Sludge Thickening and Dewatering Solutions Small footprint with enclosed design. Low power, polymer and washwater consumption. Wide product range suitable for thin/difficult sludges. Containerised, mobile or skid mounted. Low OPEX – due to slow drum rotation. Transport costs reduced with onsite processing. Sizes suitable for small, medium and large throughput application sites. covers. With only the motor / gearbox assembly protruding above the tank wall, low profile covers can be easily deployed so there is less air to be purified and energy costs are reduced. Scrutiny Hydro's product management team carried out extensive tech- nical diligence on the new Zick- ert scraper before recommend- ing introducing the technology for the UK market. The technol- ogy was already installed in pri- mary and secondary tanks inter- nationally and had been in full scale operation for more than 12 months. . A site visit to the most recent installation completed this spring at Getteröverket in Swe- den gave the team a chance to view the latest design with the tank drained down. Hydro's Group wastewater product man- ager Keith Hutchings explains: "Hydro always undertakes full engineering and commercial scrutiny before every new prod- uct introduction. The technical diligence was undertaken to fully understand all design, mechanical and maintenance aspects of the Zickert Rotating Sludge Scraper throughout its lifespan. "It was important for us to fully review the engineering design decisions made by Nor- dic Water for the product, in particular so we could assess where design and installation adaptations might be needed for introduction by UK operators. Our visit to the most recent installation in Sweden also demonstrated that the Zickert 3700 had been further improved in the light of early experience. "We also received assurances about patent protection and the availability of CE and ATEX cer- tifications. n Built off-site for rapid delivery and start-up, Ovivo's new standard range of RBC's offer a competitive alternative in wastewater treatment. The Ovivo standard RBC's are based on serving Population Equivalents: 300, 400, 500, 600, 700 and 800 based on 180l/hd/day for 95%ile 20:30 (BOD:SS) assuming 30% BOD reduction in primary settlement. Units can be added for larger populations or to achieve tighter discharge consents. CONTACT OVIVO TO FIND OUT HOW THE NEW AFFORDABLE OVIVO RBC TECHNOLOGY CAN BENEFIT YOU. DESIGNED TO MEET YOUR NEEDS... • Low capital cost wastewater treatment • Reduced operating cost • Simple maintenance • Built off-site • Reliable process WE FOUND THE RIGHT SOLUTION TO MAKING OUR HIGH QUALITY RBC'S COMPETITIVE. Call: 01249 705 350 or visit: www.ovivowater.co.uk/rbc © 2014 GLV Inc. All rights reserved. SYSTEMATIC INNOVATIVE THINKING Ovivo ® RBC DESIGNED TO MEET YOUR NEEDS... • Low capital cost wastewater treatment • Reduced operating cost WE FOUND THE RIGHT SOLUTION TO MAKING OUR HIGH QUALITY SYSTEMATIC INNOVATIVE THINKING THINKING C M Y CM MY CY CMY K RBC Launch Ad 0514_PRINT READY.pdf 1 27/05/2014 11:55:25 AM

• Cover