Section 2: Wastewater and Emissions from Mercury Cell Chlor-Alkali Operations
- 2.1 Wastewater
- 2.2 Emissions
- 2.3 Solid Waste
The main contaminant streams from mercury cell chlor-alkali operations may be classified as wastewaters, emissions, and solid wastes. These streams, due to the use of mercury, are invariably contaminated with mercury and require some form of collection and either reuse within the plant or treatment before being released to the receiving environment.
Water is used extensively at mercury cell plants for noncontact cooling, tail gas scrubbing, cell washing, floor washing, equipment maintenance, and caustic soda production (in the denuder) and as brine makeup. Invariably, either a process wastewater, wash wastewater, or blowdown will be produced. The degree of mercury contamination determines the treatment used.
Table 5 summarizes the main sources of wastewater from mercury cell plants, their characteristics, and the practices followed to control them.
The main sources of mercury emissions to the atmosphere from mercury cell chlor-alkali plants are the
- cell room ventilation air (cell maintenance)
- hydrogen by-product stream
- cell end box ventilation system
- exhaust gases from the retort
- exhaust gases from tanks
Cell room ventilation air includes cell operation and cell maintenance, which is conducted on cells on an as-required basis. With the installation of dimensionally stable anodes at all plants in Canada, cells now require less maintenance, which has resulted in reduced mercury losses.
Table 6 summarizes the main sources of emissions from mercury cell plants, associated contaminants, and emission control practices.
The principal sources of solid waste (also referred to as sludge) generated at mercury cell chlor-alkali plants are
- impurities from brine saturators
- impurities from recycled brine
- caustic soda product from the denuder cell
- sludge from the wastewater treatment plant
- solids from cell maintenance, treated mercury butter, and retort products
Table 7 summarizes the general characteristics and contaminants present in these solid wastes/sludges and the disposal practices employed.