Replacing soda with lime

An alternative to caustic soda has been developed by Lhoist UK at Buxton in Derbyshire. Product manager Derek Thompson uses two examples to demonstrate its benefits

Dissolved air filtration (DAF) systems have shown themselves to be versatile pieces of equipment, as seen in use in a multitude of industries ranging from oil refineries to food processors. This flotation process is also established in the treatment of industrial wastewaters, and water treatment overall as it separates the suspended material from the liquid that is carrying it.

The basic DAF process of transporting suspended materials, such as oils and grease, to the surface is enhanced by the addition of pretreatment flocculants. The flocculant of choice needs to take into account the material being removed from the effluent stream, as well as the pH conditions in which it needs to operate.

DAF systems typically use an iron or aluminium salt based flocculant, which lowers pH, followed by an alkali to raise the pH to near neutral before the addition of a polymer to stabilise and densify the Floc. It is at this pH adjustment step that Neutralac SLS45 is proving a successful alternative to caustic soda, the common alkali in use today.

Neutralac SLS45 has been shown to improve the performance of contaminant removal in DAF processes by improving floc properties and hence the efficiency of contaminant removal, with the welcome addition of reducing often expensive polymers and flocculants.

As a reagent
As an innovative product designed to address the main objectives of reducing trade effluent charges and to achieve compliance for sewer discharge, it has been successfully applied to treat dairy waste, food effluent and other wastewaters. Neutralac SLS45 offers the advantages of using caustic soda, but provides superior technical performance as regards coagulation, settling velocity and the consequent dewatering of sludge.

Developed and manufactured by lime manufacturer Lhoist, Neutralac SLS45 is a versatile liquid lime that is a safe, environmentally friendly and highly costeffective alternative to caustic soda and magnesium hydroxide. It has displayed several advantages in many industries ranging from automotive to metal finishing applications, and has also seen success in combination with DAF plants at different processing sites.

Case study: Pet food production
A leading pet food manufacturer in central England needed to treat an acidic and cloudy effluent stream that resulted from its food treatment process. Before its final discharge, the effluent had to conform to specific criteria that required the effluent to be pH neutral, have limited solids content and be free from odour.

A new DAF process was installed as an upgrade to their existing effluent treatment plant, which utilises Neutralac SLS45 as a reagent for chemical pre-treatment, in order to optimise the level of fat, oil and grease removal.

Even during the trial phase, more responsive changes to the incoming effluent were immediately noted, and amounted to improved reagent usage. With its high concentration and high reactivity, Neutralac SLS45 exhibits unique liquid lime capabilities. As a ready-to-use reagent, its patented manufacturing technology delivers an alkali with an unmatched content of 45% Ca(OH)2 solids by weight, yet retaining a viscosity comparable to more traditional fluid reagents.

Having supplanted a standard liquid lime, reagent consumption fell by 60%, whilst expensive polymer additives and caustic soda have been replaced by the more favourably priced Neutralac SLS45 and alum.

The positive effects of Neutralac SLS45 were also noted further downstream, where an improved dewatering efficiency imparted by Neutralac SLS45 produced a drier sludge that consequently was cheaper to dispose of. In addition, the improved drying has been shown to lower energy costs, as well as improve sludge characteristics overall.

Case study 2: Malt processing
A food manufacturer in the South-east of England has used Neutralac SLS45 to replace its own lime slurry production from bagged lime.

In doing so, the need to run and maintain the slurry plant was eliminated.

Combined with its better handling properties and improved neutralisation potential, the immediate price advantage was in favour of Neutralac SLS45. In addition, it removed the risks to health associated with bagged lime, and its compatibility with existing plant equipment was shown in its easy integration with the pumping and dosing systems already present.

Consequently, a direct changeover was possible ensuring a smooth transition period and continued processing capacity. Minimal settling, combined with reduced blockages observed on site have shown how conveniently Neutralac SLS45 can be applied at existing and new plants.

A decrease in reagent volume was noted, as Neutralac SLS45 is much more responsive than a conventional liquid lime. Manufactured to dissolve completely, Ca2+ and OH- become immediately available, with these characteristics translating as meeting the requirements of increasingly strict environmental permits.

Treatment capacity
In many cases, the operational output of a plant increases at a rate at which the effluent treatment plant struggles to keep pace.

Without the space or capital expenditure to bring waste treatment operations in line with the remainder of the facility's competence, alternative solutions have been found. Some DAF units are designed to make use of parallel plate packing materials, which provides a significantly increased separation surface whilst occupying a disproportionately small footprint for the enhanced separation efficiency that has been made available through this method.

Together with Neutralac SLS45, a 2-in-1 reagent that offers both flocculation and pH adjustment capabilities, the optimum conditions for DAF processes can be ensured, whilst avoiding the potential large investment necessary to increase the capacity for treating effluent.

Furthermore, by reducing the need for coagulants or minimising the volume of sludge generated, Neutralac SLS45 helps in optimizing the overall processing costs.

Neutralac SLS45 is produced by Lhoist UK near Buxton in Derbyshire. In operating its own processing plant and quarry, Neutralac SLS45 is produced on demand, with a guaranteed secured supply always available at predictable prices.

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