Water & Wastewater Treatment

WASTEWATER TREATMENT 20 Water & Wastewater Treatment February 2014 W hen considering how to provide solids-liquid separation during treatment plants upgrade works, for example, when refurbishing the half-bridge scraper in a final settlement tank (FST), water companies have a number of options: • Install another settlement tank • Use existing redundancy (if available) • Hire in an additional FST – often technically impractical because of space constraints • Hire in a separate biological treatment process plant Alternatively, they could hire in dissolved air flotation (DAF) technology, which provides a cheaper and quicker solution to any of the above. DAF has been around for some time and whilst it is commonly used in industrial and potable water treatment, it is seldom used in municipal wastewater treatment, due to the perceived ongoing running costs. However, Siltbuster Process Solutions (SPS) has been working with a number of water companies during works to upgrade treatment plants, to provide temporary capacity whilst also ensuring consent compliance prior to and during the works. Two D100 lamella DAF units were recently supplied to joint venture contractor Barhale Trant Utilities (BTU) for a final effluent polishing application on a Southern Water wastewater treatment works (WwTW). Solids removal This is the third application of this type undertaken. The first was a couple of years ago on an Anglian Water site at Cottesmore where the DAF installation provided solids removal instead of two continuous backwash sand filters, which were struggling to achieve suspended solids consent. One of recent installations replaced drum filters to ensure compliance with a suspended solids limit. The SPS range of lamella DAF units are perfect for this type of application as the addition of lamella plates to a DAF allows a relatively high flow rate to be treated by a very compact unit. At Anglian Water, the 2.4m-wide x 6m-long unit was used to treat a peak flow rate of up to 144m 3 /h which, in combination with a small amount of flocculant, was able to reduce the discharge solids concentration to less than 5mg/l. At one Southern Water site, the requirement was slightly different. Here the problem was not suspended solids compliance, but iron. Iron removal Iron is added at the works to ensure compliance with a tight phosphorous consent. This iron can be bio-accumulated into the biological growth in the trickling filters. Over time the percentage of iron in the biomass increases, hence when the biomass comes off (sloughs), the solids discharge limit is put at risk, but more importantly, the iron limit is also put at risk. This is important as the iron is an 'upper tier' failure and if the iron limit is breached then works becomes a failed works, seriously affecting the water company's serviceability targets. The iron can also cause the solids to become finer and hence affect normal solids compliance as well. The standard temporary treatment is to use drum filters, however, because of the fineness of the filter media, these tend to blind. Consequently, the throughput can be reduced and a significant volume of backwash is generated. They considered using drum filters, but the footprint required would be too large. Hence DAF seemed obvious as an alternative solution. Having visited the site and tested the water samples at SPS's in-house laboratory, it was possible to reassure the client that this unusual DAF application would achieve the desired result. Once the solution was approved, we were able to mobilise the plant and commission the installation within days. The D100 DAFs have since achieved the required suspended solids reduction, which also ensured compliance with the total iron and phosphorus limits. Using DAF technology in a different way is saving water companies time and money Paul Lewis, managing director of Siltbuster Process Solutions explains Making a DAF decision Smart liquid lime www.neutralac.co.uk Derek Thompson Product Manager T: 01298 768 670 M: 07976 391 673 Lhoist UK, Hindlow Buxton, Derbyshire derek.thompson@lhoist.co.uk Non Compliance What could this mean to you? Pollution, closure, heavy fines, negative publicity, loss of profits? Industries treat acidic effluent in different ways, but many are now turning to Neutralac SLS45, the UK's fastest growing, high strength liquid lime. Utilities, Metals, Chemical and Food manufacturers are all under compliance pressure to meet increasingly stringent wastewater treament legislation - and why many are harnessing the benefits of Neutralac SLS45. Test the water with a no-risk FREE field trial. WASTEWATER TREATMENT 21 February 2014 Water & Wastewater Treatment Separation system The project with Kelda Water Services at Royal Marines Base Chivenor in North Devon was different again. Here, the project involved providing a temporary solids/liquid separation system whilst the existing final settlement tank was refurbished. Normally solids liquid/separation on an activated sludge plant is carried out using a FST. However, as this was only a temporary installation, a D100 portable DAF unit was provided instead. Whilst the use of DAF for sludge thickening applications is well documented, they are still relatively unused on municipal sites. DAFs are ideal for this sort of temporary application because they are small and portable – they can be brought to site and installed via a lorry-mounted crane. They are also ideal for emergency situations where fast and flexible deployment of kit is needed. For example, at Chivenor, due to access constraints the original intention was to install the unit using a crane. However on the agreed delivery day the wind speeds were too high for the crane to operate so the unit was delivered and installed using a lorry-mounted Hiab. This allowed the unit to be positioned via a low-level lift, out of the wind. Operator control DAF systems are easier to manage - the DAF operator is in control of the solids/liquids separation process, so the treated water clarity and density of the floated off sludge can be controlled. Compare this with a conventional clarifier where performance is dictated solely by the settlement characteristics of the sludge. For example, at Chivenor, the D100 was fed at a rate of 43m 3 /h of mixed liquors with a suspended solids concentration of 3,500mg/l and produced a treated water to meet the 30mg/l TSS site consent and a return activated sludge concentration of 3% solids. Maintenance-led programmes Moving into AMP6, water companies are becoming more and more maintenance-led and SPS is seeing more and more requests for assistance with the water companies to work with them to build such solutions into their programmes. When it comes to asset upgrade, they need to consider that solutions that are right for the long-term. Short-term fixes need to be small, quick, easy and cost effective – and DAF technology is a viable solution in many cases. DAF can provide additional treatment capacity during upgrade works and also ensure compliance is maintained, in a low-risk way. DAF also offers a short-term solution for water companies, buying them valuable time to consider the optimal long-term solution in terms of plant upgrade. nnn AB13-686 www.michael-smith-engineers.co.uk Runs Dry for Hours Guaranteed for Years Perfect Self-Priming PUMPS ✓ SP Series pumps are perfect for emptying IBC's, drums, tanks, sumps & bunds.If you need to transfer liquids that are clean, contaminated or dirty... ● Self-priming – up to 7.6 metre lift ● Flow rates up to 45 m3/hr ● Available in polypropylene or PVDF ● Magnet drive – leak free ...Choose FTI SP Pumps the safe and reliable choice Finish Thompson SP Series – the safe solution for all your liquid chemical transfer Temporary lamella DAF installation at Brockenhurst wastewater treatment works in Hampshire

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