Start-up and experimental analysis of a pilot-scale SBR as a basis for the design and economic evaluation of full-scale plants

Wastewater treatment is strictly regulated in Italy and Europe to prevent the pollution of the natural water bodies. At European level the law was recently updated in the EU directive 2024/3019 of the European Parliament and of the Council of the 27 of November 2024. The majority of the plants for domestic wastewater treatment consist of a conventional activated sludge process (CAS), that comprehends an aerated tank in which the degradation of the organic matter is carried out by microorganisms in steady state conditions. Sequencing Batch Reactor technology emerges as an innovative way to treat wastewater, that switches from a continuous flow to a batch system that evolutes in time and not in space; this helps with process flexibility and allows to avoid the settlers, since sedimentation can occur directly inside the reactor, saving a lot of space and energy. In this context, a laboratory experience with a pilot scale SBR was carried out to deeply investigate the work of this type of technology. All the devices that constitute the reactor are interfaced with an Arduino, which acquires all the signals and sends them to a computer. A Matlab code controls the system by processing the data and sending commands to the devices. Thanks to this automation, it is possible to let the reactor work continuously through the four phases that it manages, that are biological phase, sedimentation, discharge and charge phase. The evaluation of the efficiency of the COD removal is encouraging, since is almost always over 90%, with a concentration of COD that respect BAT limits. A calibration test was performed to estimate the parameters that govern the microbial activity, following the Activated Sludge Model 3, but the results were bad, highlighting the need of further investigations. The rate of microbial growth was investigated through a solids analysis, to make an estimation of the sludge retention time to manage the periodical discharge of the sludge. Even a brief analysis on nitrogen removal has been carried out, but this aspect needs more time to be studied. As a conclusion, since the efficiency of removal is good, a comparison between a CAS and a SBR at industrial scale was carried out, to quantitatively demonstrate the economic advantages of SBR, revealing that it would guarantee a 23% of land saving and 3400 €/y saved during operational phase.