Articles & Case Studies

New liquid lime delivers integrated sludge treatment solution for a major Southern based utility

Posted: Friday 14th June 2013

In a time when both economic and environmental issues are fast becoming high on agendas for many companies, it is encouraging that one utility company in the south of England is taking considerable strides in both directions.

Seeking an improved, integrated and sustainable solution for four waste treatment plants on the south coast, the utilities company turned to Buxton-based lime producer Lhoist Group, the largest manufacturer of lime products in the world.

The main issues centred on the treatment of raw sewerage that would enable the resultant, treated waste water to be safely recycled and for the remaining slurry be suitable and safe as a farm fertiliser.

In the past, waste sludge has been in danger of being insufficiently cleansed and disinfected, with the potential of retaining pathogens such as Campylobacter and Salmonella, which can cause food poisoning, contaminating the soil. This renders it inadequate as a fertiliser and therefore only suitable for landfill – a commercially and environmentally negative solution.

One solution is to use large gas powered drum driers which although effective are costly to run and expensive to maintain, a position this utility company found itself in. Therefore, after decommissioning the drying equipment, with unsustainably high running costs, an alternative method for disinfecting and dewatering the sludge had to be found.

Lhoist Group produces Neutralac® SLS45, a technologically advanced, high strength liquid lime with 45% solids. Its unique, high alkali content properties include retention of high levels of viscosity compared to competitive lime slurries with only half the concentration. These are perhaps the key factors when assessed by utilities companies as Neutralac® SLS45 was found to both solve a number of long-standing sewerage treatment process problems and proved easier to use from a viscosity perspective.

Traditionally, wastewater and slurry is separated using centrifugal technology to de-water the slurry. However, it was found that by pre-treating the waste with Neutralac® SLS45 before de-watering, its high alkaline content sufficiently neutralises the wastewater so it can be recycled back into the water course, and the slurry is cleansed and disinfected for use as farm fertiliser. The organic matter is enhanced for farming purposes due to the lowering of acidity, the removal of pathogens and subsequent high nitrate qualities.

The chemical reaction of Neutralac® SLS45 creates a sterile alkaline environment in excess of pH12 for sustained periods, effectively disinfecting the sludge by killing the wide spectrum of pathogens listed above.

Furthermore, the cost reductions in transporting both the treated water and disinfected slurry become significant while, at the same time, closing the environmental recycling loop. The disinfected farm slurry also offers an income stream previously not always available to utilities companies as it can then be sold to farmers.

A spokesperson for the utilities company commented: ‘We have been through a stringent process and our selection of Neutralac® SLS45 was not taken lightly. Our tests have shown a significant improvement in the lowering of acidity of waste, and the improvement and relevance of the resultant slurry as a fertiliser.

‘Also, it became apparent we required a tailored solution, including custom-built storage and dosing rigs, which we could integrate into our current system without too much disruption. The Lhoist team has worked hard to help us create this and integrate it into our SCADA computer-controlled system.’

Partnering with PCM, leading and recognised suppliers of chemical dosing equipment to the utilities industry, Lhoist is also installing 15 and 40 tonne dosing tanks on all four sites.

‘The project was not just about choosing the best liquid lime for the job, important though that is. We needed a liquid lime supplier who delivers on all fronts, including understanding our issues and setting up the treatment processes.

‘This integrated, sustainable solution closes the environmental loop while improving our processes and making significant cost savings,’ concluded the spokesperson.

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