For the past 22 years in the Netherlands, the behavior of Hg in coal-fired power plants has been studied extensively. Coal from all over the world is fired in Dutch power stations. First, the Hg concentrations in these coals were measured. Second, the fate of the Hg during combustion was established by performing mass balance studies. On average, 43 +/- 30% of the Hg was present in the flue gases downstream of the electrostatic precipitator (ESP; dust collector). In individual cases, this figure can vary between 1 and 100%. Important parameters are the Cl content of the fuel and the flue gas temperature in the ESP. On average, 54 +/- 24% of the gaseous Hg was removed in the wet flue-gas desulfurization (FGD) systems, which are present at all Dutch coal-power stations. In individual cases, this removal can vary between 8% (outlier) and 72%. On average, the fate of Hg entering the power station in the coal was as follows: <1% in the bottom ash, 49% in the pulverized fuel ash (ash collected in the ESP), 16.6% in the FGD gypsum, 9% in the sludge of the wastewater treatment plant, 0.04% in the effluent of the wastewater treatment plant, 0.07% in fly dust (leaving the stack), and 25% as gaseous Hg in the flue gases and emitted into the air. The distribution of Hg over the streams leaving the FGD depends strongly on the installation. On average, 75% of the Hg was removed, and the final concentration of Hg in the emitted flue gases of the Dutch power stations was only -3 microg/m3(STP) at 6% O2. During co-combustion with biomass, the removal of Hg was similar to that during 100% coal firing. Speciation of Hg is a very important factor. An oxidized form (HgCl2) favors a high degree of removal. The conversion from Hg0 to HgCl2 is positively correlated with the Cl content of the fuel. A catalytic DENOX (SCR) favors the formation of oxidized Hg, and, in combination with a wet FGD, the total removal can be as high as 90%.

The focusing on the discharge of nitrogen compounds to aquifers has put pressure on power plants to look into removal of nitrogen compounds from the gas scrubbing liquors (DESOx and DENOx). The scrubber liquor has a high salinity, a high chloride content and a temperature of about 40°. Initial laboratory tests to evaluate the possibility of performing biological nitrification and denitrification showed promise and a pilot-scale test unit was established at one of the Danish coal-fired combined heat and power plant (AVEDØRE 1). The pilot plant was operated under varying conditions with regard to temperature and chloride concentration. Maximum nitrification and denitrification rates were measured. At 30°C and 20 g Cl−/l, maximum nitrification and denitrification rates of 2 and 3 mg N/g VSS·h respectively were measured. In the effluent, concentrations of inorganic nitrogen were below 8 mg N/l. Twice during the test period, inhibition of the biomass activity was caused by high concentrations of heavy metals. The high content of heavy metals was due to malfunction of pH control in the heavy metal removal plant. The nitrification process was more sensitive to heavy metals than the denitrification process, and during the two toxic events the nitrification rate decreased to zero. The influence of rapid changes in the chloride and nitrite contents on nitrification was also examined. The results from the performed tests can be applied on other wastewaters with similar characteristics as these scrubber liquors i.e. with salinity. As an example fertilizer and pharmaceutical industries can be mentioned.

Wastewater from wet lime(stone)-gypsum flue gas desulphurisation (FGD) processes in coal-fired power plants contains nitrate. Where case selective catalytic reduction (SCR) of NOx is applied the wastewater can also contain ammonia. For the removal of both nitrate and ammonia, biological processes are an attractive option. A bottle-neck for application of biological processes might be the high chloride concentration and relatively high temperature of the wastewater. Therefore research work was performed in fluid-bed reactors at pilot-plant scale for both biological nitrification and denitrification. Biological nitrification was studied up to 34 gCl−/l and nitrite was the main product formed. Biological denitrification was effective up to at least 45 gCl−/l. Both nitrate and nitrite were removed effectively.

Bank filtration schemes for the production of drinking water are increasingly affected by constituents such as sulphate and organic micropollutants (OMP) in the source water. Within the European project AquaNES, the combination of bank filtration followed by capillary nanofiltration (capNF) is being demonstrated as a potential solution for these challenges at pilot scale. As the bank filtration process reliably reduces total organic carbon and dissolved organic carbon (DOC), biopolymers, algae and particles, membrane fouling is reduced resulting in long term operational stability of capNF systems. Iron and manganese fouling could be reduced with the possibility of anoxic operation of capNF. With the newly developed membrane module HF-TNF a good retention of sulphate (67–71%), selected micropollutants (e.g., EDTA: 84–92%) and hardness (41–55%) was achieved together with further removal of DOC (82–87%). Fouling and scaling could be handled with a good cleaning concept with acid and caustic. With the combination of bank filtration and capNF a possibility for treatment of anoxic well water without further pre-treatment was demonstrated and retention of selected current water pollutants was shown.

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