Division 3 Generation of waste water
United Kingdom
BAT 4: In order to reduce the generation of waste water, BAT is to use a combination of the techniques given below.
| Technique | Description | Applicability | |
|---|---|---|---|
| a | Brine recirculation | The depleted brine from the electrolysis cells is resaturated with solid salt or by evaporation and fed back to the cells. | Not applicable to diaphragm cell plants. Not applicable to membrane cell plants using solution-mined brine when abundant salt and water resources and a saline receiving water body, which tolerates high chloride emission levels, are available. Not applicable to membrane cell plants using the brine purge in other production units. |
| b | Recycling of other process streams | Process streams from the chlor-alkali plant such as condensates from chlorine, sodium/potassium hydroxide and hydrogen processing are fed back to various steps of the process. The degree of recycling is limited by the purity requirements of the liquid stream to which the process stream is recycled and the water balance of the plant. | Generally applicable. |
| c | Recycling of salt-containing waste water from other production processes | Salt-containing waste water from other production processes is treated and fed back into the brine system. The degree of recycling is limited by the purity requirements of the brine system and the water balance of the plant. | Not applicable to plants where an additional treatment of this waste water offsets the environmental benefits. |
| d | Use of waste water for solution mining | Waste water from the chlor-alkali plant is treated and pumped back to the salt mine. | Not applicable to membrane cell plants using the brine purge in other production units. Not applicable if the mine is located at a significantly higher altitude than the plant. |
| e | Concentration of brine filtration sludges | Brine filtration sludges are concentrated in filter presses, rotary drum vacuum filters or centrifuges. The residual water is fed back into the brine system. | Not applicable if the brine filtration sludges can be removed as dry cake. Not applicable to plants that reuse waste water for solution mining. |
| f | Nanofiltration | A specific type of membrane filtration with membrane pore sizes of approximately 1 nm, used to concentrate sulphate in the brine purge, thereby reducing the waste water volume. | Applicable to membrane cell plants with brine recirculation, if the brine purge rate is determined by the sulphate concentration. |
| g | Techniques to reduce chlorate emissions | Techniques to reduce chlorate emissions are described in BAT 14. These techniques reduce the brine purge volume. | Applicable to membrane cell plants with brine recirculation, if the brine purge rate is determined by the chlorate concentration. |