Capture rates ranged from 96.3% to 97.6%


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polymer dose used for the Volute and centrifuge was between 2 and 4kg/Tds. Volute solids capture rate ranged from 96.3% to 97.6%, which was equivalent to between 670- 1030 mg/l.


Due to the constraints on polymer dosing (type and dose rate), both the cake dry solids and filtrate results for anaerobic sludge should be considered sub- optimal. For any future trial it is advised a suitable poly dosing unit that can prepare and dosing branch chain powder polymer be used. Sludges from potable water treatment works were imported into the sludge holding tank for dewatering.


The lagoon sludge was tested instead of fresh iron sludge because, for operational reasons, it was not possible to disturb the process stream at the time of the trial.


The lagoon sludge will contain micro-organisms from biological degradation which is likely to make it more difficult to dewater that fresh potable water sludge. The % dry solids achieved provides indicative evidence that a cake of over 25% dry solids can be produced by the Volute from Iron sludge which is fresh from the process.


The DAF sludge was a particularly problematic sludge that had persistently blinded plates of a plate and frame press on the potable water site. In addition to producing a 20.6% dry solids cake, the Volute achieved a solids capture rate of 99.8%.


The trial demonstrated that the Volute can effectively dewater surplus activated, anaerobic and clean


water sludge to a transportable cake.


For dewatering conventional SAS only, the Volute produced a transportable cake of 20.8% DS, whilst adding primary sludge to produce a 90:10 SAS: raw mixture provided a cake of 22.5% DS.


For the trials on SAS, the source sites were of interest because they do not have PSTs and so have no indigenous raw sludge on site, meaning that raw


sludge needs to be imported in order to produce a >20% DS cake. As evidenced by the trial, using the Volute for SAS dewatering would require a lower proportion of raw sludge imports, thus reducing sludge haulage costs.


With many rural sites spread over a large area, the reductions to sludge processing made possible by the Volute are potentially significant.


The trial provided evidence that raw sludge import requirements, polymer dosing, and storage are all reduced for the Volute compared to a centrifuge.


Phosphorus


A further perceived benefit of reducing the process steps is shorter storage times meaning less release of phosphorus from biological cells that can increase during long periods of storage, especially in anaerobic conditions. Any released phosphorus ultimately ends up in the filtrate to be returned to the head of the works. With increasing pressures to reduce P levels in final effluent, reducing the re- release of phosphorus would be beneficial in terms of compliance risk.


Low solids in the Volute filtrate will reduce pressure on treatment processes. As mentioned above, liquors from dewatering equipment are traditionally returned to the head of the treatment works and if the solid load is high, this can negatively impact on operation and in the worst case, can affect compliance. Although not measured directly during the trial, energy input requirements for the Volute are around 80% lower than for centrifugation.


The Volute reduces polymer demand and, perhaps more importantly, reduces the amount of raw sludge required to be imported into cake production centres. This


means that raw


sludge can instead be transported directly to sludge treatment centres for anaerobic digestion, thus avoiding double handling and significant transport costs. ■


I WholehearTeDly reCoMMenD The ShoW For qualITy FaCe-To-FaCe TIMe WITh poTenTIal buSIneSS anD exISTInG ClIenTS


SIMON ASPINALL, VERDER UK LTD


IWEX is the live event for the water, wastewater and effluent treatment industries and is the place to inform and connect with powerful decision makers. It offers a unique opportunity to showcase products and services to a highly targeted and receptive audience of international visitors looking for sustainable solutions across the water lifecycle including: ●


Water Treatment Technology ● ● Filtration & Separation ●


Industrial Water & Wastewater Treatment Groundwater & Drainage Technology ● Water Conservation & Management


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December 2013 | WET News | 19


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