Manipulating the sludge flow to increase methane production and to reduce effluent pollution in wastewater treatment plants

The present work deals with the manipulation of the sludge in a wastewater treatment plant. Concretely, this is done by varying wastage flow rate (Qw) and external recycle flow rate (Qr). Benchmark Simulation Model No. 2 is used as testing scenario. The objective of the proposed implementation is to reduce costs and/or limits violations of pollutants in the effluent. Ammonium and ammonia nitrogen (SNH) in the effluent (SNH, e) and total nitrogen (SNtot) in the effluent (SNtot, e) are the pollutants that are more difficult to be kept below the limits. Due to this reason, the manipulation of Qw and Qr is based on these pollutants. In the case of Qw, its variation must consider a relationship between the sludge that is led to the anaerobic digester for methane production and the sludge that remains in the biological treatment. As Qw variation needs time to produce an effect on the variables of the plant, Qw is manipulated based on the maximum SNH and SNtot values estimated for the next two days. On the other hand, the variations of Qr have faster effects than Qw. On basis to this fact, Qr is manipulated to reduce SNH, e and SNtot, e peaks, but only when a risk of effluent limits violations is detected. This risk is detected by an artificial neural network based on some variables of the plant.