Division BAT 15 In order to reduce emissions to water from flue-gas treatment, BAT is to use an appropriate combination of the techniques given below, and to use secondary techniques as close as possible to the source in order to avoid dilution.

United Kingdom

Technique		Typical pollutants prevented/abated	Applicability
The descriptions of the techniques are given in Section 8.6
Primary techniques
a.	Optimised combustion (see BAT 6) and flue-gas treatment systems (e.g. SCR/SNCR, see BAT 7)	Organic compounds, ammonia (NH₃)	Generally applicable
Secondary techniques^f1
b.	Adsorption on activated carbon	Organic compounds, mercury (Hg)	Generally applicable
c.	Aerobic biological treatment	Biodegradable organic compounds, ammonium (NH₄ ⁺)	Generally applicable for the treatment of organic compounds. Aerobic biological treatment of ammonium (NH₄ ⁺) may not be applicable in the case of high chloride concentrations (i.e. around 10 g/l)
d.	Anoxic/anaerobic biological treatment	Mercury (Hg), nitrate (NO₃ ^–), nitrite (NO₂ ^–)	Generally applicable
e.	Coagulation and flocculation	Suspended solids	Generally applicable
f.	Crystallisation	Metals and metalloids, sulphate (SO₄ ^2–), fluoride (F^–)	Generally applicable
g.	Filtration (e.g. sand filtration, microfiltration, ultrafiltration)	Suspended solids, metals	Generally applicable
h.	Flotation	Suspended solids, free oil	Generally applicable
i.	Ion exchange	Metals	Generally applicable
j.	Neutralisation	Acids, alkalis	Generally applicable
k.	Oxidation	Sulphide (S^2–), sulphite (SO₃ ^2–)	Generally applicable
l.	Precipitation	Metals and metalloids, sulphate (SO₄ ^2–), fluoride (F^–)	Generally applicable
m.	Sedimentation	Suspended solids	Generally applicable
n.	Stripping	Ammonia (NH₃)	Generally applicable

The BAT-AELs refer to direct discharges to a receiving water body at the point where the emission leaves the installation.

Table 1

BAT-AELs for direct discharges to a receiving water body from flue-gas treatment

Substance/Parameter		BAT-AELs
Either the BAT-AEL for TOC or the BAT-AEL for COD applies. TOC is the preferred option because its monitoring does not rely on the use of very toxic compounds.
This BAT-AEL applies after subtraction of the intake load.
This BAT-AEL only applies to waste water from the use of wet FGD.
This BAT-AEL only applies to combustion plants using calcium compounds in flue-gas treatment.
The higher end of the BAT-AEL range may not apply in the case of highly saline waste water (e.g. chloride concentrations ≥ 5 g/l) due to the increased solubility of calcium sulphate.
This BAT-AEL does not apply to discharges to the sea or to brackish water bodies.
Substance/Parameter		Daily average
Total organic carbon (TOC)		20–50 mg/l^f2 ^f3 ^f4
Chemical oxygen demand (COD)		60–150 mg/l
Total suspended solids (TSS)		10–30 mg/l
Fluoride (F^–)		10–25 mg/l
Sulphate (SO₄ ^2–)		1,3–2,0 g/l ^f5 ^f6 ^f7
Sulphide (S^2–), easily released		0,1–0,2 mg/l
Sulphite (SO₃ ^2–)		1–20 mg/l
Metals and metalloids	As	10–50 μg/l
	Cd	2–5 μg/l
	Cr	10–50 μg/l
	Cu	10–50 μg/l
	Hg	0,2–3 μg/l
	Ni	10–50 μg/l
	Pb	10–20 μg/l
	Zn	50–200 μg/l

Annotations

f1: The descriptions of the techniques are given in Section 8.6
f2: Either the BAT-AEL for TOC or the BAT-AEL for COD applies. TOC is the preferred option because its monitoring does not rely on the use of very toxic compounds.
f3: This BAT-AEL applies after subtraction of the intake load.
f4: This BAT-AEL only applies to waste water from the use of wet FGD.
f5: This BAT-AEL only applies to combustion plants using calcium compounds in flue-gas treatment.
f6: The higher end of the BAT-AEL range may not apply in the case of highly saline waste water (e.g. chloride concentrations ≥ 5 g/l) due to the increased solubility of calcium sulphate.
f7: This BAT-AEL does not apply to discharges to the sea or to brackish water bodies.