The all-important dosing system

Published:  06 November, 2015

The accurate and consistent dosing of chemicals in wastewater treatment requires a pump technology that delivers the chemicals in a manner that optimises their usage and effectiveness. A chemical dosing skid employing either peristaltic or metering pumps attached to pipework built into a cabinet containing a dedicated control system provides the most effective solution for this process. PWE spoke to Verder Pumps about its approved dosing pump technology.

The effectiveness of the dosing system is all-important, for when wastewater is being discharged from a plant it must comply with all relevant environmental regulations and standards. The Water Industry Act of 1991 states that any liquid produced wholly or in part from any trade or business activity carried out on trade premises qualifies as trade effluent and therefore requires consent from a utility company. Trade effluent control applies to all businesses from large multi-nationals to small and medium-sized enterprises.

The main effluent treatment methods employ the precipitation of impurities, separation of solids from the liquid and pH adjustment. Non-compliance with effluent waste consent levels inevitably cause high levels of pollution and can result in prosecution, fines and even the closing down of plants. There are several types of reagents that can be used in the various stages of wastewater treatment; the most commonly used being lime, caustic soda, sodium hypochlorite, polymers and magnesium hydroxide.

To be truly effective, these reagents need to be dosed exactly, either in continuous or in batch processes. The flow of effluent may impact on the rate at which a reagent will need to be added. This is best managed by the use of a purpose-built chemical dosing system.

This has been recognised by Lhoist, the UK-based manufacturers of Neutralac SLS45, which has established an informal relationship with Verder Pumps. The company explained the relationship offers a cost-effective approach to the provision and application of this liquid lime product.

“Neutralac SLS45 is a 45% strength liquid lime developed specifically to have a low viscosity, low settlement rate and high reactivity due to its high strength,” explained Xavier Mear, Lhoist’s Neutralac specialist. “It is highly proficient at neutralising acid-based effluents, maintaining a steady pH and removing heavy metals, precipitating sulphate, phosphate and fluoride as well as treating fat, oil and greases.” According to Lhoist it offers both significant technical and economical benefits, being an alternative to powdered lime, caustic soda and magnesium hydroxide slurries. It delivers more efficient operation of the treatment plant and greatly reduces costs as it is a single ready-to-use reagent. Furthermore, Neutralac SLS45 lends itself to dosing using peristaltic pumps, making it an ideal fit for Verder’s chemical dosing packages.

Neutralac SLS45 is manufactured at the Lhoist plant in Buxton where there is very pure limestone. “It is used for industrial effluent, wastewater treatment, sludge treatment, food waste treatment and for increasing pH in digested sludge for agricultural uses”, added Mear.” Furthermore, being a suspension the most appropriate pumping technology is the peristaltic pump.”

Verder told PWE it has been building and supplying chemical dosing packages to wastewater treatment plants in a wide range of industry sectors around the world for many years. The collaborative approach adopted by Verder and Lhoist identified the Dura skid-mounted system as being a suitable vehicle for demonstrating the effectiveness of Neutralac SLS45 to potential customers.

Verder’s small-scale dosing rigs connected to IBCs tend to operate at low doing rates around 20lt/hr and the integrated package is designed around the Dura peristaltic pump. The Dura hose pump is a close-coupled compact pump offering flow rates of between 1lt/hr and 15.3m³/hr and pressures from 8bar to 16bar and is the perfect choice for this dosing package. Typically the Dura dosing package comes with a duty and standby pump configuration, pH monitor, control electronics, agitator for an IBC and any necessary pipework connections. Being lightweight, it is an easily transportable system that is ideal for temporary small-scale pilot applications. However, it is suitably robust to meet the demands of challenging environments, which is another reason why it appealed to Lhoist.

On trial

Introducing a new product into an established and rather conservative market is always a challenge, and for Lhoist the initial challenge was to convince potential Neutralac SLS45 customers of its benefits. “Lhoist offer the rig as part of a risk-free trial, and we are running it alongside existing systems so that comparisons can be made,” says Mear. “If something should go wrong, then the customer can simply switch over to their existing system. Most customers see the rig as impressive. Feedback indicates that Neutralac SLS45 is a far more effective product for enhanced flocculation, pH control, improved removal of heavy metals and COD level.”

Lhoist recognised that instead of installing a pump on a floor and attaching it to an IBC, it was more cost-effective to integrate all the elements in a single, compact rig. There was also the issue that in many instances robust industrial peristaltic pumps would be needed as they could be exposed to the elements, or operate in confined and environmentally challenging areas. Lhoist had indentified what they needed and that is what Verder could provide. Not only that, Verder could provide a complete package that offered the flexibility to satisfy the requirements of sites where both low dosage from IBCs was needed or for continuous operations typically encountered at much larger sites.

Verder explained that its connection came about back in 2013 when Lhoist needed a dosing system incorporating storage facilities, electronic control and instrumentation that could accurately deliver Neutralac SLS45. All companies discharging wastewater have to control the pH content at the point of discharge. Other considerations include BOD, COD and heavy metals. “The majority of the potential users for our product have their own treatment plants on site and are very much aware of discharge consent levels,” says Mear. “It is companies that are experiencing issues with existing caustic or lime dosing systems that are contacting us. In many existing plants the dosing technology is outdated or possibly not functioning as well as expected, which is why we are replacing an existing system with Neutralac SLS45 and a highly effective dosing system.”

This is where the trials unit comes into its own. “In our opinion the Verder rig provides better dosing control with a peristaltic pump, coupled with better pH control by using a high specification pH controller,” comments Mear. “This is generally better than the equipment that their customers may have been running for many years. One of the reasons why we work with Verder is that the pump company is very accommodating and co-operative. When approached for a trial pump to go onsite and the application is outside the range of the small unit, Verder is prepared to lend pumps for specific applications.” Although Lhoist says that they tend not to get much feedback on the pumps, they do get positive comments on how impressed they are with the rigs.

Markets

Using lime is an old technology but still widely used in the water treatment, metals production, food processing, chemicals processing and surface finishing industries, to name just a few. There are many companies still using caustic soda where a simple diaphragm pump will suffice, but this and other alkali alternatives do present more of a safety problem where ageing dosing systems tend to show wear and lack true dosing accuracy when handling liquid lime.

“Many older dosing systems use fixed speed pumps and are inefficient when there is not a requirement for continuous dosing,” explains Mear. “The Verder peristaltic pump is accurate, energy efficient, very reliable and is easy to speed up and slow down as circumstances demand and will follow a pH variation very easily. In addition, it is simple to operate and maintain.”

It is older sites where investment in dosing systems has been held back which offer the greatest opportunities for Lhoist to demonstrate the effectiveness of their products in conjunction with the Verder rigs. As effluent treatment is not necessarily a profit-making activity for many companies there is understandable reluctance to invest capital in new equipment. However, when it is pointed out that by changing to Neutralac®SLS45 and using an efficient dosing system, considerable savings can be made, and that the risks of breaking consent levels and any subsequent fines are eliminated, opinions change.

Although designed for trial purposes, the rigs built by Verder are rugged and use materials and pumps that have a proven track record of operating in harsh conditions over long periods. Thus, if a trial user wants to keep the rig at the end of the set period, it does not need to be removed. Lhoist and Verder explain they will tailor rigs to meet the exact requirements of the customer once the rig is taken as a permanent fixture. Alternatively, Lhoist will undertake a site survey with additional engineering consultancy provided by Verder when a rig is being installed.

For further information please visit: www.verder.co.uk

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