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

Chapter 3
When measuring chlorine in water samples, several oxidising species are included due to the
analytical method employed. According to the European standards EN ISO 7393–1, –2 and –3,
free chlorine includes hypochlorite, hypochlorous acid and dissolved elementary chlorine while
total chlorine also includes organic and inorganic chloramines. In addition, other oxidising
species such as hypobromite, hypobromic acid, dissolved elementary bromine and bromamines
are included in the parameters free and total chlorine [ 162, CEN 2000 ], [ 163, CEN 2000 ],
[ 164, CEN 2000 ]. These oxidants may be present in the brine purge. Free oxidants include
halogenated components with a high reactivity: Cl2, Br2, OCl - , OBr - and NHxBry. Free oxidants
are toxic to aquatic biota and are found in water streams which have been in direct contact with
chlorine and bromine.
The purge from the brine purification is normally treated before being discharged to discharging
into the environment. Reported emission concentrations and factors are summarised in Table
3.12. A concentration of 10 mg/l is generally observed.
Table 3.12: Emissions of free oxidants to water from chlor-alkali plants in EU-27 and EFTA
countries in 2008/2009
Concentrations of free oxidants in mg/l ( 1 ) ( 2 ) ( 3 )
Value
reported ( 4 10th 25th
Min.
)
percentile percentile Median
75th 90th
Max.
percentile percentile
Min. ( 5 ) 0.030 ND 0.10 0.10 0.10 ND 75
Max. ( 6 ) 0.050 0.090 0.18 5.0 16 95 300
Free oxidants emission factors in g per tonne annual chlorine capacity ( 1 ) ( 3 )
Value
reported ( 4 10th 25th
Min,
)
percentile percentile Median
75th 90th
Max.
percentile percentile
Min. ( 7 ) 0.0003 and 0.01 and 0.01 and 103
Max. ( 8 ) 0.015 ND 0.055 0.32 2.7 ND 240
Average ( 9 ) 0.020 ND 1.3 3.2 16 ND 300
( 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 ) Most of the reporting plants perform periodic measurements (often daily and monthly) while a few perform
continuous measurements. Averaging periods reported were mostly daily.
( 4 ) Some plants reported ranges with minimum and maximum values, some reported average values and some
reported both.
( 5 ) 6 data from 6 plants. In addition, 11 plants reported values below the detection limit, 1 plant a value of
< 0.01 mg/l, 1 plant a value of < 0.1 mg/l, 1 plant a value of < 0.2 mg/l and 1 plant a value of < 2 mg/l.
( 6 ) 19 data from 19 plants. In addition, 1 plant reported a value of < 0.1 mg/l and 1 plant a value of < 0.2 mg/l.
( 7 ) 4 data from 4 plants. In addition, 3 plants reported values below the detection limit, 1 plant a value of
< 0.08 g/t and 1 plant a value of < 1 g/t.
( 8 ) 6 data from 6 plants. In addition, 1 plant reported a value below the detection limit, 1 plant a value of
< 0.08 g/t and 1 plant a value of < 1 g/t.
( 9 ) 7 data from 7 plants. In addition, 1 plant reported a value of < 0.008 g/t.
NB: ND = not enough data.
Source: [ 57, EIPPCB 2011 ]
WORKING DRAFT IN PROGRESS
The highest emission concentrations of free oxidants were observed for plants which reported
that no specific waste water treatment takes place at the plant level apart from the generally
applied partial dechlorination using a vacuum [ 57, EIPPCB 2011 ]. In the case of membrane
cell plants, the depleted brine is always totally dechlorinated (see Section 2.5.4). The release of
free oxidants is higher for plants that destroy the produced bleach in the chlorine destruction
unit and discharge the remaining liquid, which may contain significant amounts of free oxidants
[ 17, Dutch Ministry 1998 ] [Dutch report, 1998].
Free oxidants are toxic to aquatic biota. If waste water containing free oxidants becomes acidic,
chlorine is released. Moreover, the mixing of waste water containing free oxidants with other
waste water containing organic substances may lead to the formation of halogenated organic
compounds. Substances which may form halogenated organic compounds in the aquatic
TB/EIPPCB/CAK_Draft_1 December 2011 87