FILTRATION & SEPARATION FEATURE THE FACTS & FIGURES


Amiad UK’s Double Vortex Filter has undergone tests at Chester University which confirm it’s performance in terms of efficiency, cost savings and ROI


and filtration has been applied to municipal and industrial water processes for over 200 years. Despite this there is still confusion as to what sand filtration technology can actually achieve, mainly due to lack of reliable evidence. The numerous ways in which sand


S


filtration can be combined mean that if you ask ‘how fine does it filter’, you would expect to get a straightforward answer. What you wouldn’t then want to face is barrage of questions such as ‘is your load mineral or organic?’; ‘what is the filtration flux rate (velocity through the filter bed)?’ etc. Eventually, some suppliers will give a filtration performance figure usually expressed in micron size as to the expected solid size that will be removed, or an anticipated reduction in turbidity. This very lack lustre, possibly unscientific response, then defines our selection process of 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. Some unscrupulous suppliers may state that a filter has 5 micron performance (when it only actually removes a few 5 micron particles with every pass), while specifiers also need to consider if the performance claimed is based on a single pass or multipass though the filter. And of course there are many more


complex questions that need to be asked, such as ‘what time during the filtration cycle is the performance measured, i.e when the bed is at its least efficient, directly after backwashing’ or ‘when is it at its optimum just before backwashing’? This is why Amiad UK supports its clients


with a laboratory facility here in the UK that answers these awkward questions for you. The Graph (above, right) shows the impact of solids removed based on the starting point of efficiency. You will see both filters are similar in performance just before backwashing but just after there is a considerable difference in what is removed by the higher efficiency filter. Given all of this, if our challenge is therefore to remove suspended solids, what we really need to be asking 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 percentage of the total solids removed. If we assume either a mineral or organic load, a constant TSS load, this


gives us a real performance measure when comparing media filter technologies. Materials of construction are far easier to assess, if we consider the nature of the liquid we are filtering. We also need to consider how much water we put to waste overtime to regenerate the filters as this brings with it saving in terms of waste stream processing or disposal. Combine this with media bed replacement and disposal costs, we begin to get a true picture of the real OPEX costs. Amiad UK encourages clients to ask the


efficiency % removal question of its competitors and they are often given reasons as to why that information cannot be predicted. Despite internal research and development testing, Amiad asked Chester University to independently validate the performance of the high efficiency media filter technology and in particular the Double Vortex Filter (DVF). A test program was initiated using a test rig as described in the schematic below. The purpose was to confirm and validate a number of Amiad’s R&D findings, the main ones being: 1. The removal efficiency of the DVF


filter system at varying filtration velocities including up to 4 times that of a standard media filter. 2. The removal efficiency in a single pass


through the filter by sampling inlet and outlet water flow. 3. Establishing the impact that our patented inlet system had on the filtration cycle period over time, quantifying the loading capability of the filter. 4. Examining the Total Suspended Solids


(TSS) removal rate as well as the influence the filter would have on differing particle size ranges. This was carried out through particle analysis of the samples as well as the standard industry gravimetric test. Tests were carried out to industry standards which meant using Arizona test dust as a source contaminant, and the


A test program was initiated using a test rig as described in the schematic below. The purpose was to confirm and validate a number of Amiad’s research and development findings


The graph above shows the impact of solids removed based on the starting point of efficiency


Amiad has proven not only the benefits of using a quality media but also, thanks to the external research with Chester University, provides customers with the facts and figures on what they should expect from their filtration processes in terms of efficiencies, cost savings and return on investment


particle analysis equipment used was a Spextrex laser particle counter, size/count analysis in the 1 – 100 μm. Some interesting conclusions: • Chester University confirmed that operation of the filter at a flux rate of 40m3


/m2 had no impact on filter


performance. This had been confirmed previously by the Amiad research and development department. Thus meaning smaller footprints were possible for comparative flow of conventional media filters. This goes against traditional filter design belief. • The impact of the patented inlet was


contributory to extending the periods between the requirement to backwash, with the bed accepting significant mineral solids loading levels. • Mineral TSS loads of up to 292mg/l


were applied without unexpected impact on backwash frequency. • A combination of Chester laboratory and Amiad UK field results concluded the DVF was an effective 1 micron filter with efficiency ranges of removal at 1 micron of up to 80% being viable with some clients reporting higher than this. At this point, we have 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 above the filter bed surface. Amiad UK’s inlet design incorporates a vortex generating system. This ensures the vortex effect is maintained throughout the upper part of the filter vessel, ensuring balanced dynamics within the whole top section of the vessels without causing a quiet zone. In addition, when it comes to filter media, Amiad uses activated glass, as this resists microbiological fouling. Amiad’s DVF’s backwash nozzle


minimises backwash volumes yet further. These also act as a physical barrier to prevent media migrating downstream with the finest media being larger than the retention capability of the nozzles. The media is drinking water approved, so can be used in sensitive applications.


Amiad UK www.amiaduk.com


 PROCESS & CONTROL | MAY 2018 33


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