Effluent treatment with peroxygens

Applications chiefly include removal of reduced sulphur and nitrogen compounds, of cyanides or thiocyanates, and of toxic organic compounds including phenols and halo-organics. In many cases, more than one of the above pollutants may be present in an effluent. The following sections describe these uses in more detail. 

1 Sulphide. Hydrogen peroxide reacts with sulphide at below pH 7 to form sulphur [314]  

This is because the sulphur first formed is able to disproportionate under alkaline conditions before precipitation  

it is usual to employ mildly acidic conditions to destroy sulphides in solution in order to minimise the amount of H2O2 required. In the gas phase, hydrogen sulphide can be removed by scrubbing the gas stream with a hydrogen peroxide solution. Here, alkaline conditions are more effective owing to better absorption of H2S and avoidance of sulphur precipitation in the scrubber. 

3 Sulphite. Sulphite is oxidised to sulphate by H2O2, rapidly in acidic or neutral media and at a declining rate as pH increases. Again, this chemistry is applicable to removal of gaseous SO2 by using acidic H2O2 in scrubber systems [322]. In addition to specific chemical processes. 

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Several different peroxygen-based systems exist, all of which are compatible with biological treatment. The peroxygen treatment can be used up- or downstream of the biotreatment unit, either as a pre-treatment to reduce toxicity and improve biodegradability or as a post/polishing treatment to remove remaining biorecalcitrant species from the effluent. All the peroxygen-based treatments can also be used as stand-alone processes for the total treatment of a waste stream. The most common AOPs are ... 

The bulk of this article will focus on this latter area of obtaining environmental benefits within the chemical processing industry. The main focus will be on used of peroxygen technology in the processes themselves with a short overview of the potential in effluent treatment. 

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