Study of the odorous impact of the sewage treatment plants
Latest generation forecasting models to safeguard public health
It is well known that one of the most important impacts of waste water treatment plants is the emission and spread of smell. Various parameters are used to describe smell, including the hedonic tone, i.e. the feeling of pleasure or distaste accompanying a smell, and this decides whether an odorous source is actually a disturbance or not. In the specific case of purification plants, the sludge treatment areas generate the most relevant emissions and, on their own, these account for about 50% of odorous emissions.
During plant modification or renewal authorisation procedures, management bodies are required to produce studies forecasting the emissions of the purifier paying special attention to the smell-producing type, a critical element for nearby residential areas.
NET Engineering drafted the study of the odorous impact generated on the surrounding area for the Marco Simone (at Guidonia Montecelio, Rome), Massimina (at Malagrotta) and Colle delle Mele (at Fiuggi, Frosinone) purification plants. These are all biological, activated sludge plants; the first has a project potential of the equivalent of 35,000 inhabitants while the second has a project potential of the equivalent of 72,000 inhabitants although, at present, only one line equivalent to 36,000 inhabitants is operational.
The CALMET/CALPUFF/CALPOST suite, created to manage CALPUFF, the well-known multi-source, non-stationary gaussian model, developed on behalf of the California Air Resources Board and adopted as the reference model of the U.S. Environmental Protection Agency, was used for the calculations of diffusion of the odour-generating field in the environment. Application of the CALPUFF system requires the preparation of specific input data.
The calculation grids are set based on orographic data, land use (distribution of receptors) meteorological data (speed and direction of wind, air temperature, atmospheric pressure, humidity etc) and data on emissions (structural data of the source and emission factors). As a consequence, the area of influence of smell diffusion of the plant is established.
NET Engineering were aware of the impact that the plants in the study can have on public health and sociability and carried out very detailed analyses, developing numeric simulations in both the base scenario (most frequent plant operating situation and representative of the trend for the year) and the worst case, using reference forecasting models in the market so that the client was given the most accurate yet precautionary output.