Water & Wastewater Treatment Magazine
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8 | OCTOBER 2017 | WWT | www.wwtonline.co.uk ooded, receive a rebate. The cost to the company of that penalty for a ooding incident can typically be £42,000, but the impacted customer gets hardly anything. So our current system is not designed to be equitable. So how could the introduction of a market for domestic water customers improve the system's alignment with these three principles? Competition will see service provision split into wholesale and retail components. This changes the relationship between customers and the wholesale business by introducing the retailer as an intermediary. A customer pays the retailer, and the retailer pays the wholesalers. This potentially gives a mechanism to move from charges based on a regional cost of providing service to ones based on a national cost of providing service. An individual retailer could be paying charges to 20 or more di erent wholesalers at di erent rates, with those rates set by Ofwat through the periodic review process. What if, instead, the retailers paid the national standard wholesale tari to a market operator, who paid the wholesalers depending on their regional cost of providing service, assessed through the periodic review process? The control that Ofwat has over charges and over the wholesale companies would be very similar to the current system. This would provide charges based on a national cost of providing service. It would be easier for the retailers, no more diƒ cult for Ofwat or the wholesalers, and the market operator would simply move money around in line with the Ofwat The Talk: opinion SPONSORED BY SPONSORED BY KWAN CHAN MANAGING DIRECTOR DEWLINK SLUDGE TREATMENT LTD The Next Generation of Sludge Dewatering The established equipment for dewatering sludge all comes with various pros and cons, but technology is now evolving for the better W astewater produced domesti- cally and commercially must be treated before it can be reused or returned to the water cycle. Sludge is a byproduct of wastewater treatment, which must also be treated before it is disposed of or recycled. The cost of sludge treatment can be astronomical, but dewatering is a technique used to reduce the volume of the sludge, thus reducing transportation and disposal costs. There are various systems available, and choos- ing the right technology is dependent on many variables. Operating and mainte- nance costs will be an important factor in the decision. One of the oldest dewatering devices available - dating back in the 1850s – is the ‰ lter press. It has a high solid capture rate, with the ability to dewater hard-to-dewater sludge, but it requires a large quantity of chemicals and the replacement of the ‰ lter media is expensive. The belt press is another common choice. It has a vast amount of applications such as mineral slurry, sewage, pharmaceutical, petrochemical, food processing and paper pulp waste. The throughput of a belt press is high, with a low capital and energy cost; however, the running costs can be expensive. Chemicals such as potassium permanganate are required to neutralize odour, and water is used for cleaning with frequent ‰ lter media changes. Another option is the centrifuge. It has been around for a long time, due to its many advantages and superior performance. It is reliable, with a small footprint, has low sta requirements, is easy to maintain, and boasts good odour containment. On the negative side, it consumes high levels of energy, with high polymer usage and is relatively noisy, with a lot of vibration. The screw press is a relatively new technology. Here, occulated sludge is fed into the rotating screw sha' , squeezing the sludge to separate liquid and solids. Traditionally, the running cost is low, but so too are the throughput and cake solid content. However, the advancement of the system in recent years has made it more attractive. Dewlink employs a screw-based system, with an interconnecting duel screw con‰ guration inside a single enclosure. It consists of two closely aligned screw sha' s with consecutive ‰ xed and moving rings. This con‰ guration further promotes the movement of the sludge. As the screw turns, sludge is pushed forward, and the moving rings, driven by external drive rods, generate a vertical up-down movement with a pendulum motion, cutting through the ‰ xed rings. This combination of screw structure and ring movement ensure that the moving rings cut through the ‰ xed rings e ectively, preventing any clogging between the gaps and also maximizing the shear e ect on the sludge, squeezing it and pushing it further forward, increasing throughput with a reduction in moisture content of the sludge cake. The system has a low operating cost, it consumes very little energy, cleaning is minimal and less chemicals are required. It can operate 24 hours fully automated, with little maintenance, and it can be easily integrated with any existing system in the wastewater treatment plant. For more information on the screw press dewatering system visit: www.dewlink.com