High-value reuse of lime from drinking water softening is sustainable and profitable

At the end of 2015, the TKI Water Technology research project ‘Marketing Dutch lime pellets’ was successfully completed. It demonstrated the feasibility of reusing (following processing) of the lime pellets, which are released from the drinking water softening process, as feedstock (seeding material) in the same softening process. By using part of the created lime instead of garnet sand as seeding material, a higher quality residual is produced, which can for instance be used in the production of carpets and, in the future, possibly also paper, white glass, plastic and feed/food.

The partners in ‘Marketing Dutch lime pellets’ were Waternet, Reststoffenunie, Dunea, PWN, WML, Brabant Water and KWR. The research was partly financed by the premium of the Top Consortia for Knowledge and Innovation (TKI) programme of the Ministry of Economic Affairs. The concept has since been implemented at Waternet’s Weesperkarspel water production plant, an experience the company wants to repeat at its plant in Leiduin.

Higher value reuse is possible

The softening of drinking water using pellet reactors produces lime pellet residuals. These lime pellets are already finding useful applications in different markets. But by improving the quality of the lime pellets, new high-value applications open up, such as in the production of white glass, paper, carpets, plastics and feed/food. The improvement requires that the sand nucleus in the lime pellet – the seeding material – be replaced by a calcite nucleus. This creates a lime pellet that consists almost entirely of lime. The calcite used as seeding material can, in principle, be produced from the process’s own lime pellets. The process therefore involves the reuse of residuals, the valorisation of residuals and possible sustainability benefits, because of the reduced extraction of primary lime and transport. But the reuse of the material in drinking water production is only possible if it meets strict microbiological and chemical quality standards to safeguard drinking water quality.

Hoogwaardig hergebruik van kalk uit drinkwaterontharding is duurzaam en winstgevend

Good quality and operational management

Mineral raw material suppliers processed (i.e., dried, ground, sieved) several batches of lime pellets into seeding material. The quality of calcite throughout the supply chain was carefully measured. The results show that the microbiological and chemical quality requirements for calcite in drinking water can be met. The calcite produced has indeed been successfully used in several endurance tests at Waternet’s Weesperkarspel water production plant.

Net returns and sustainability are sensitive to scale

Different alternatives for the implementation of the concept have been defined, varying from production and application at the level of the softening reactor to a centralised processing by an independent party, whereby several water companies would participate. The risks to water quality and the associated certification requirements were determined for each of the alternatives. A cost-benefit analysis was also carried out, while sustainability was determined through Life-Cycle Analysis. This multi-criteria analysis shows that the net returns are favourable in the case of the large-scale alternative, but that the sustainability benefits decrease as scale increases. The smaller scale alternatives produce greater sustainability benefits, but the net returns are less favourable. Read more on the TKI Water Technology project page.

In relation to this research, in 2015 the chainpartners Reststoffenunie, Waternet, Ardagh Glass and Desso received the prestigious  IWA-KWR Award for Best Practices on Resource Recovery from Water for the valorisation and high-value application of calcite pellets. Jury chairman Willy Verstraete handed out the prize during the first  IWA Resource Recovery Conference in Ghent.