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testing, Amiad asked Chester University to validate the per- formance of its high efficiency media filter technology and, in particular, its Double Vortex Filter (DVF). The aim of the test was to validate several of Ami- ad's R&D findings, including: The removal efficiency of the DVF filter system at varying filtration velocities includ- ing up to four times that of a standard media filter The removal efficiency in a single pass through the filter by sampling inlet and outlet water flow Examining the TSS removal rate and the influence the filter would have on differ- ing particle size ranges. This was carried out through par- ticle analysis of the samples as well as the standard industry gravimetric test Our tests were carried out to industry standards which meant using Arizona test dust as a source contaminant. The standard test dust used throughout conformed to ISO 12103-1:2016 A2 Fine – Arizona Simulate (Particle Technology, UK) and contained silica parti- cles in the 1–100μm range (SG 2.65). The particle analysis equip- ment used was a Spextrex laser particle counter, size/ count analysis in the 1–100μm (Spectrex, US). This was cho- sen to mimic the in-house lab- oratory facility in Amiad UK so data from field operational plants with organic challenges as well as Chester laboratory results could be combined to establish practical predictive performance for clients. The conclusions included: Chester University confirmed that operation of the filter at a flux rate of 40m3/m2 had no impact on filter perfor- mance. This had been con- firmed previously by the Amiad R&D department. Thus, meaning smaller foot- prints were possible for comparative flow of conven- tional media filters. This goes against traditional fil- ter design belief Mineral TSS loads of up to 292mg/l were applied with- out unexpected impact on backwash frequency A combination of Chester 12 WET NEWS NOVEMBER 2017 Don't bury your head in the sand T he numerous ways in which sand filtration can be combined mean that if you asked 'how fine does it fil- ter?', you would expect to get a straightforward answer if the supplier knows its stuff. What you would not want is a barrage of questions such as 'is your load mineral or organic?'; 'what is the filtration flux rate (veloc- ity through the filter bed)?' etc. If you take the time to dig deep enough, some suppliers will eventually give a filtration performance figure usually expressed in micron size as to the expected solid size that will be removed, or an antici- pated reduction in turbidity. This lacklustre, possibly unsci- entific response then defines the selection process against what could be a significant investment. All of this causes market confusion as to what to specify and what to expect in terms of operational results. Whether to procure a basic shallow bed fil- ter o¤en seen in domestic before backwashing?' Amiad UK supports its cli- ents with a laboratory facility in the UK that answers these questions. The graph (Fig 1) shows the impact of solids removed based on the starting point of efficiency. Both filters are similar in performance just before backwashing but just a¤er there is a considerable difference in what is removed by the higher efficiency filter. If the challenge is to remove suspended solids, what really needs to be asked is: "At a given micron size performance what is the efficiency of removal?" This is usually expressed as a percentage, i.e 5 micron removal at a typical efficiency of 50%, or as a per- centage of the total solids removed. If we assume either a mineral or organic load, a con- stant TSS load, this gives a real performance measure when comparing media filter tech- nologies. Materials of con- struction are far easier to assess, if we consider the nature of the liquid we are fil- tering in that industry, most of us have to make material com- patibility decisions daily. We also need to consider how much water is put to waste over time to regenerate the filters as this brings con- siderable saving in terms of waste stream processing or disposal. Combine this with media bed replacement and disposal costs, and a true pic- ture of the real Opex costs of the investment is created. Despite having conducted its own extensive internal research and development laboratory and Amiad field results concluded the DVF was an effective 1 micron fil- ter with efficiency ranges of removal at 1 micron of up to 80% being viable with some clients reporting higher than this What has also become clear is that every application is dif- ferent and differing challenges produce different results. How- ever, what is important to Amiad is the ability to effec- tively predict performance when presented with a client's individual process conditions. At this point, it has to be clear that the DVF is not a standard media filter. Rather than using a flat filter bed, the DVF activates the top layer of the filter bed releasing the lighter contaminates and allowing them to be retained in a vortex which operates above the filter bed surface. It has long been recognised that a flat filter bed produces the best profile for filtration. However, traditional media fil- tration with challenging influ- ent are prone to biofouling due to the static nature of the bed. This also limits the size of the filter media that can be incor- porated as finer media only accentuates this problem and promotes the biofouling pro- cess. Nevertheless, flatbed configurations can optimise performance. Tangential inlets have been introduced in recent years to create a vortex, activate the bed surface and create a sur- face scouring action. However, this re-profiles the bed and fluid, taking the easiest route, shortcuts the deepest part of the bed where the optimum fil- tration takes place. Several devices have been incorpo- rated to continuously flatten the bed using various designs of nozzles but these also bring with them their own issues. The nozzles very o¤en incorpo- rate fine jets and, as the water they distribute contains the solids from the filter inlet, this results in additional mainte- nance to maintain the nozzles performance. Creating a vortex above the filter bed can have its own issues in that a quiet zone is created above the vortex where Fig 1: The graph highlights the impact of solids removed based on the starting point of efficiency A test programme for Amiad's Double Vortex Filter was initiated using a test rig swimming pools, or a deep multimedia system designed specifically for a set purpose, the choices are innumerable. Combine this with some sup- pliers who will state that a fil- ter has 5 micron performance (when it only actually removes a few 5 micron particles with every pass) together with the need to consider if the perfor- mance claimed is based on a single pass or multi-pass though the filter (in which case the difference in comparative performance is immense) at best you can expect to have to wade through a minefield at worst you are potentially head- ing for a commercial disaster. And, of course, there are many more complex questions that need to be asked when specifying process water filtra- tion technology. Questions such as 'what time during the filtration cycle is the perfor- mance measured, i.e when the bed is at its least efficient, directly a¤er backwashing?' or 'when is it at its optimum just • INSIGHT Filtration & screening Sand filtration has been applied to municipal and industrial water processes for 200-plus years. But, says Amiad UK, a lack of evidence means there is still confusion as to what the technology can achieve. 120 100 80 60 40 20 0 DVF Sand Filter

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