Purification of thermal wastewater by membrane separation and ozonation

The aim of our work was to find a method with which to reduce the phenol content and the high ion concentration of thermal water used to heat greenhouses. Membrane separation techniques and ozone treatment were investigated. The most powerful membrane separation method was reverse osmosis which eliminated >90% of all compounds. Another effective method was nanofiltration, which demonstrated almost 10 times greater permeability values than those for reverse osmosis, and a relatively high (40%) purification efficiency. Ultrafiltration resulted in only slight decrease in concentrations measured. Ozone alone degraded phenolic and humic compounds, but only a slow decrease in the chemical oxygen demand was observed. The effect of preozonation on nanofiltration was also investigated. It was found that (in accordance with earlier experience [1]) normalized water permeability was decreased whereas the purification efficiency of nanofiltration was increased by ozonation.