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Malodorous compounds arise at practically every stage of wastewater management, starting from the sewer network, via the technological sewage-treatment system, through to the sludge-management stage. The formation of hydrogen sulphide is a significant problem even while sewage remains in sewers, as anaerobic conditions prevalent in the network are conducive to wastewater putrefaction, and therefore contribute to increased malodorous emissions. The development of such anaerobic conditions is favoured by the oversizing of conduits or designs that feature inadequate gradients, causing wastewater in the network to stagnate. Where emissions to the air from wastewater occur, they are found to constitute a complex mixture of perhaps even 1000 different substances, produced under varying process conditions. Among those present are compounds of sulphur and nitrogen, chlorinated compounds, and other organics. In Poland, the issue of odour annoyance has not yet been subject to standardisation in either legal or methodological terms. Indeed, as only 11 EU Member States have regulations in place regarding air-quality standards, it is likely that such a law will soon be developed to try and resolve problems with odour annoyance, including those originating in the systems dealing with wastewater. This denotes a need to develop methods of counteracting the formation of odours, and those of a chemical nature are regarded as among the most effective, hence their growing popularity. They also abide by green-technology principles. Against that background, this article seeks to consider the process by which malodorous substances arise in sewer and wastewater-treatment systems, as well as to discuss methods of odour abatement. The work also presents the current legal regulations of relevance to the issue.

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Abstract:The work detailed in this study utilized 20 kHz ultrasonic irradiation as a mechanism of hydrogen peroxide production. The effects of various operating parameters were investigated, including ultrasonic intensity; solution pH; source of water; initial dibutyl phthalate concentration and the presence of hydrogen peroxide. During the irradiation, the H2O2 concentration was monitored. The results indicate that H2O2 is produced by cavitation during ultrasonic irradiation. An increase in ultrasonic intensity increases the amount of hydrogen peroxide produced. The initial pH of the solution does not affect the efficiency of processes substantially. H2O2 is regarded as one of the most effective additives enhancing the sonochemical production of hydroxyl radicals and hydrogen peroxide. Above a 0.1 mM dose of H2O2, the amount of H2O2 formed decreased as the concentration of H2O2 increased. Thus, the concentration of hydrogen peroxide plays a crucial role in the extent to which the effectiveness of the combined process is enhanced. The negative effect on reactions of the presence of additional components in the reaction solution was also confirmed. It was therefore concluded that the experimental evaluation of optimum parameters of hybrid processes is a matter of importance.