Effective treatment of the wastewater from ceramic industry using ceramic membranes

Emissions of organic compounds, heavy metals and chemicals used in the ceramic industry cause significant organic and inorganic pollution of water. The effluent must be treated before it is discharged into a water body. International and EU laws control the chemical oxygen demand (COD) of the wastewater. Conventional technologies, such as sedimentation, flocculation and biological treatment, have lots of drawbacks, whereas membrane technologies give many benefits, as they are chemical-free and allow a reduction of the treatment steps. One-step wastewater nanofiltration with ceramic membranes of 450 Da cut-off is able to reduce the COD of ceramic wastewater to a sufficient level. However, the working time without cleaning is limited and the rejection of membranes can be significantly reduced due to fouling. Multistage filtration can be the solution. Filtration experiments with various combinations (MF, UF and NF) of ceramic membranes were performed at a laboratory scale with single-channel membranes and at pilot scale with 7-, 19- and 151-channel membranes in order to permanently reach the limit value of a COD below 80 mg/L and to increase the operating time. Four types of membranes were sequentially tested in the cross-flow mode: MF (200 nm pore size), UF (2,000 Da), NF (450 Da) and NF (200 Da). 5-day Biological Oxygen Demand (BOD) tests were performed in order to examine the wastewater biodegradability. The test results with single-channel membranes showed that in terms of the highest COD rejection and the highest permeability, the best combination was that of MF and UF membranes. Here, UF membranes were sufficient to reach the limit values. As for the multi-channel membranes, the combination of MF and NF (450 Da) was the best and the final COD concentration ranged from 11 to 48 mg/L. 5-day BOD bottle tests showed a COD/BOD ratio of 3.8, which opened up possibilities for combined treatment.