(BAT) Reference Document for the Production of Chlor-alkali ...

Chapter 3
Emission factors of heavy metals to water are determined by the purity of the salt used. Apart
from their co-precipitation during brine purification, no additional techniques for their removal
are used.
Some of the heavy metals such as cadmium, nickel and lead are priority substances under the
Water Framework Directive [ 74, Directive 2008/105/EC 2008 ]. Metals and their compounds
are also included in Annex II to the Industrial Emissions Directive [ 77, Directive 2010/75/EU
2010 ].
3.4.2.3.7 Halogenated organic compounds Chlorinated hydrocarbons
Chlorinated hydrocarbons (CxClyHz) Halogenated organic compounds are formed in a reaction
between organic contaminants in the electrolyser or the brine system and free oxidants. Organic
contaminants may originate from the raw materials (salt and water) and the equipment used.
One or more of the C–H bonds are attacked by the chlorine and a C–Cl bond is formed.
Examples of chlorinated hydrocarbons which can be found in the effluent of chlor-alkali plants
are chloroform (CHCl3 CCl3H), dichloromethane (CH2Cl2 CCl2H2), carbon tetrachloride (CCl4)
and tetrachloroethylene (C2Cl4), but other chlorinated and also brominated compounds may be
found [ 17, Dutch Ministry 1998 ] [Dutch report, 1998]. Halogenated organic compounds in
water are usually measured as AOX (adsorbable organically-bound halogens) and EOX
(extractable organically-bound halogens). Reported emission concentrations and factors are
summarised in Table 3.16. Volatile halogenated organic compounds may be transferred from
the brine to the gas phase during electrolysis and especially during brine dechlorination.
Table 3.16: Emissions of halogenated organic compounds to water from chlor-alkali plants in
EU-27 and EFTA countries in 2008/2009
Parameter
Emission concentrations
in mg/l ( 1 ) ( 2 ) ( 3 )
Emission factors in g
per tonne of annual
chlorine capacity ( 1 ) ( 3 )
Cell
technique
Salt source
0.04 – 0.40
(average 0.31)
0.02 – 0.25
(average 0.2)
M V
0.100 – 0.500 0.5 M V
AOX
0.5 – 3.5 0.2 – 1.4 Hg V
0.6 – 1.0 Hg V
0.026 – 0.11 0.3 M SMB, O
< dl – 2.5 M R
EOX
0.01 – 0.05
0.4 – 11
0.015
0.24 – 7
M
M
V
SMB
VOX 0.020 – 0.130 0.025 M V
( 1 ) Coverage: all three cell techniques; both brine recirculation and once-through brine plants.
( 2 ) Data refer to the outlet of the electrolysis plant prior to mixing with other waste water.
( 3 ) All of the reporting plants perform periodic measurements (semi-monthly, monthly, quarterly, semi-yearly).
Averaging periods reported were a few minutes, daily and monthly.
NB: AOX = adsorbable organically-bound halogens; dl = detection limit; EOX = extractable organically-bound
halogens; Hg = mercury cell plant; M = membrane cell plant; O = other salt sources; R = rock salt; SMB =
solution-mined brine; V = vacuum salt; VOX = volatile organically-bound halogens.
Source: [ 57, EIPPCB 2011 ]
WORKING DRAFT IN PROGRESS
The emissions of halogenated organic compounds chlorinated hydrocarbons from chlor-alkali
plants have decreased significantly after the switch from graphite to metal anodes, The releases
of chlorinated hydrocarbons is normally low but can be higher for plants that destroy the
produced bleach in the chlorine destruction unit and discharge the remaining liquid. Discharges
to water of the sum of these components (measured as EOX, extractable organic halogens) were
found in the range of 0.03 – 1.16 g/tonne chlorine capacity, where the higher figure is reported
from a plant with bleach destruction [Dutch report, 1998]. Emissions depend primarily on the
92 December 2011 TB/EIPPCB/CAK_Draft_1