THE COST of hazardous wastewater disposal could be reduced by 70% using a process based on freezing, its designers claim. Niro Freeze Concentration (NFC) reduces the water content of waste streams that must be incinerated, cutting energy demand and reducing costs.
The process, developed by Abingdon-based Niro, removes clean water from wastewater by growing ice crystals in the waste then extracting and melting them. The clean water can be reused or discharged safely. The remaining high-solids concentrate can be easily incinerated at a lower cost.
Small ice crystals are formed by pumping the unconcentrated liquid, typically with a solids concentration of 10%, into a heat exchanger. These crystals are pumped to a recrystalliser where they are mixed with larger ice crystals. The small crystals melt on the surface of the larger ones before refreezing, causing the large crystals to grow. The icy slurry is then pumped to a wash column where crystals are separated out to leave a concentrated solution behind for conventional disposal.
The process can recover water from solutions without the loss of other compounds. The technology was originally developed in the food industry for concentrating fruit juices. As the process creates pure water crystals the level of residual solids in the water is very low – less than 50 parts per million
NFC has been tested on waste solutions containing sodium hydroxide, sodium benzoate, magnesium sulphate and other organic and inorganic salts. It can also treat solutions that contain acetaldehyde, ethanol and methanol, Niro claims.
The company has already installed the process at two wastewater treatment plants, one for Seraya Chemicals in Singapore and the other for Basell – a BASF-Shell joint venture – in the Netherlands.