Wastewater treatment plants (WWTPs) are fundamental for water ecosystems conservation but when they are located in the proximity of residential areas may produce odour nuisance. One of the most common odours pollutants emitted in WWTPs is hydrogen sulphide (H2S) and release to the atmosphere (in waste-waterfalls, manholes), producing a strong unpleasant smell. In this work, field olfactometry and H2S measurement enabled to identify the main odour source, located in the inlet of the WWTP.

   The maximum H2S concentration in this emission point measured was 15 ppm and odour concentration was D/T 60, enough high to produce odour nuisance despite they were produced in open atmosphere. By means of a thorough data analysis of the essential variables involved, such as wind speed, wind direction and the H2S concentrations in its role as the central pollutant, it could be shown via contrasting annual, monthly and daily patterns, that the probability to be affected for these residential areas is the highest in summer from 19:00 hours.

  Odours are typically released into the atmosphere as diffuse emissions from area and volume sources, whose detailed quantification in terms of odour emission rate is often hardly achievable by direct source sampling. Indirect methods, involving the use of micrometeorological methods in order to correlate downwind concentrations to the emission rates, are already mentioned in literature, but rarely found in real applications for the quantification of odour emissions.

   The instrumentation needed for the development of micrometeorological methods has nowadays become accessible in terms of prices and reliability, thus making the implementation of such methods to industrial applications more and more interesting.


   In a non-hazardous waste landfill an integrated odour monitoring system comprised with 2 IOMS, 2 H2S continuous analyser and two automatic air samplers has been operating since 2018: automatic air samplers are activated when two consecutive measurements of 20 ppb at 5 min intervals are measured by H2S continuous analyser or when overall odour emission measured by IOMS exceeded 500 ouE/m3 for more than 5 min.

   Problems with odour emissions were noticed in May-August 2019 with almost a daily automatic samplers’ activation, often correlated with complaints of population; moreover, monitoring campaigns of biogas from the landfill surface showed significant increase of surface emissions for certain zones, implying that surface and fugitive emissions form landfill biogas (LFG) collecting system could have been responsible for such odour emissions. The LFG wellfield system of is comprised of a network of 301 vertical wells in the landfill, coupled with conveyance piping for the transport of LFG to energy recovery and 3 blowerflare facilities.

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