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Sludge treatment & disposal


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Hydro delivers water and wastewater treatment solutions to meet the demands of today’s ever- tougher operating environments.


Through innovative design, sustainable operation and planned maintenance and service, our focus is on achieving the best performance of your plant from the start to the end of its life.


Sustainable sludge dewatering


Dewatering secondary activated sludge (SAS) to a thicker sludge or transportable cake remains one of the key sludge handling challenges for UK water companies. The Volute dewatering screw press provides a solution.


A NUMBER of technologies exist for removing water from sludges to produce either a thicker sludge or a cake. Existing technologies used for this purpose include screw belt


drum presses, thickeners, around


thickeners, gravity and


centrifuges. Whilst all these technologies are widely used by UK water companies, issues


reliability,


blockages, maintenance, and energy costs, mean that there is a continual drive for innovation.


Centrifuges can be used for dewatering SAS but require the addition of sludge from Primary


Settlement


Hydro’s unique industry background, knowledge and R&D are encapsulated in HX: Hydro Experience – a stamp of quality and a mark of our commitment.


• Grit removal • Primary clarification


• Sludge scraper systems


• Sludge and CSO screening


• Tertiary treatment • Conveying systems • Flow control


• Overhaul, service and maintenance


For more information call 01353 645700 or visit www.hydro-int.com


Tanks


(PSTs), referred to as raw sludge, in order to produce a transportable cake. Before adding the raw sludge, the SAS first needs to be pre- thickened which requires a polymer dosing step. The raw sludge is then blended lending a more fibrous matrix to the sludge without which the centrifuge will be unable to produce a cake. Another dose of polymer is added to the mix prior to entering the centrifuge. An eight-month trial was recently conducted by a water company in England on a low energy dewatering process called the Volute dewatering screw press, supplied


by Evergreen Wastewater Solutions Turning Water Around...®


Engineering. The technology has been developed and used in Japan for 22 years and has 2,056 municipal and industrial installations spread over 56 countries worldwide. The Volute has a number of innovative design features that improve its functionality when compared with other screw press technology. The two main innovations are: • A funnel shaped inner screw that causes increased pressure on the sludge cake and leads


to dewatering


• Alternate moving and fixed rings that keep the Volute clog-free


o WetNews 369x45mm V2 AW.indd 1 18 | WET News | December 2013 18/3/13 10:38:33 improved


The Volute requires less energy input


The above design features mean that the Volute disc press can dewater a <1% dry solids sludge to a >19% dry solids cake in a single step, thus reducing the mechanical equipment and associated maintenance required, lowering polymer demand and storage requirements. The


Volute using also


requires lower energy input compared to other processes,


around


40% less energy than a belt press and 80% less energy that centrifuge (Amcon, 2008).


A joint research project conducted


by AMCON


and Bureau of Sewerage Tokyo Metropolitan Government over three years finished at the end of 2008 (AMCON, 2008). An ES351 model was used in the trial and a throughput of 300kgDS/h was achieved with a maximum cake solids achieved of 27%.


A Volute ES 131 unit was installed at a site in England. During the trial, different sludges were imported for


testing. A sludge holding tank with a mixer was filled with sludge for each trial. Liquid polymer was dosed via a Polymore dosing unit. Sludge from five different processes was imported into the sludge holding tank for processing through the Volute. The sludge type and processes on the five sites where the sludge was sourced were: • SAS from deep shaft activated sludge process (ASP)


• SAS from a site with traditional ASP


• Digested sludge post Enhanced Enzymic Hydrolysis and Anaerobic Digestion


• Digested sludge post Cambi Thermal Hydrolysis and Anaerobic Digestion


• Iron sludge from a


potable water treatment plant


Dry solids analysis was performed in an oven at 1050C for 24 hours on the feed sludge and cake. The filtrate was analysed


for Total Suspended Solids content. The polymer dose was adjusted to an optimum level and the dry solids recorded.


Influent solids for SAS ranged from 6,000- 15,000mg/l and tended to require higher polymer dose rates when the feed solids were lower. The polymer dose averaged around 6.5kg/Tds.


Pilot testing The Volute can be expected to achieve a range of solids capture of between 97.7% and 98.9% for SAS, which corresponded to 200 to 1,000mg/l during the trial. The higher solids capture of the Volute is thought to be due to a combination of lower shear (the Volute screw turns at between 1.5 and 2rpm) and the self cleaning discs that prevent solids escaping from the inner screw.


from


Anaerobic sludges advanced


digestion


processes were imported into the sludge holding tank for dewatering.


They dewater best using a branched polymer. These polymers are, however, only available in powder form, which were not suitable for use with the Polymore dosing unit supplied with the ES131 Volute model. For the Enhanced Enzymic Hydrolysis sludge, a ready mixed linear chain polymer, SNF Flopam ES 640 LH, was used instead of the branched powder poly. The optimum polymer dose for the Volute was 8.5kg/Tds. For comparison, the cake produced by the centrifuge using a branched polymer on the Monsal sludge was between 28 and 31% dry solids, at a polymer dose of around 6kg/Tds. Preliminary pilot testing was completed on Cambi sludge post digestion, the SNF Flopam ES 640 LH polymer failed to form a


good enough dewatering.


Containers of the mixed powder polymer used for centrifugation, BASF 8140, were


therefore collected and dosed manually. The


floc for


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