A study of two wastewater treatment plants in Cordoba, Spain evaluates the odorous impact of the technologies deployed in each.
The study appears to show that degrading wastewater pollution by means of mechanical aeration results in fewer odorous compounds than the use of intensive systems. A parallel study seemed to demonstrate that biofilters filled with pruning and sludge compost are efficient systems to minimize the odorous impact of sewage treatment plants.
The odour emitted by wastewater treatment plants in cities is one of the social problems that technology has been trying to solve for years. The control and management systems of this type of infrastructure have been concerned with minimizing the environmental and odorous impact of this waste, which directly affects the quality of life, especially for those who live near treatment plants. Among the latest systems to emerge from biotechnology research are two that are becoming more and more established: mechanical ventilation and biofiltration.
Both were evaluated in two separate, independent studies carried out by separate scientific teams at the University of Córdoba and published in the Process Safety and Environmental Protection journal. The first of these studies describe the work carried out at a real-world scale at the Wastewater Treatment Plants (WWTP) in two Cordoba towns: Espiel and Villaviciosa; while the second analyzed the operation of pilot-scale biofilters operated at the facilities of the Chemical Engineering area of the University of Córdoba.
In the first work, the analysis of different biological treatments of wastewater showed that the process known as the extended aeration of activated sludge, which is employed at the WWTP in Espiel, emits a slightly higher odour rate per inhabitant than the rotating disc system used in Villaviciosa. It was also found that the system in Espiel is more efficient and intensive for the treatment of wastewater, and generates a greater amount of sludge, a by-product that can be properly treated, thus providing a better marriage with aspirations towards supporting a circular economy. In addition, as the analysis of the sludge microbiome has shown, the presence of nitrifying and denitrifying bacteria allows for the elimination of nitrogenous contaminating compounds from wastewater.
The second publication analyzed the effectiveness of biofiltration in eliminating odoriferous compounds in systems filled with different variants of waste: pruning waste, exclusively, or mixed with sludge compost from the treatment plant itself. The work seems to show that when biofilters are used to remove acidic and water-soluble odorous compounds, such as butyric acid, they have a greater but more transient impact than in the removal of less water-miscible compounds, such as D-Limonene. Butyric acid is a compound that is generated in fermentation processes, and has a characteristic rancid odour. D-Limonene, on the other hand, is a compound whose odour is reminscent of citrus.
In any case, as María Ángeles Martín Santos, a professor of Chemical Engineering at the UCO, explained: “It must be taken into account that all the plants studied comply with the established discharge limits, and that the smell of a treatment station does not always reach the nearby populations. There is a whole process of transport and dilution of polluting odours through the environment that diminishes their perception. The wind, for example, can disperse them. Hence, an essential aspect in wastewater management is where treatment plants are located. The problem is that, as a result of urbanization and re-zoning, many sewage treatment plants are very close to towns, so they must be better outfitted with systems to reduce odor emissions.”