characteristics and variability of the effluent to be treated

In sections urban effluent, industrial effluent and then general municipal effluent was characterised by its origin (produced during dry or wet weather), by the effect of any industries connected into the system and, more specifically, by:

• quantity expressed as a daily or hourly volume with the variability generated by human or industrial activities, weather conditions and other seasonal effects (week-ends, holidays, etc.), together with any additional aspects, in terms of importance and frequency, in order to optimise a system;
• contamination expressed as the suspended solids, organic matter ( BOD and COD ), nitrogen ( TKN ), phosphorous ( TP ) loading as well as the concentration of other components (including pathogenic micro-organisms). However, in section wastewater typology it was demonstrated that these general parameters were not sufficient and that a more detailed typology of the water to be treated was highly desirable;
• allowing for external inputs (waste outlets, waste from mains cleaning or grease transfer);
• the nature of the effluent may have an effect on its routing to the treatment site and, therefore, precautions will be required at the plant inlet (septicity, sulphide content, etc.). Thus, knowledge about the type of mains network (combined, separate or mixed system), its length and its hydraulic profile, will be of great value when forecasting its effects on the plant.

Furthermore, the emergence of new sensors, whose precision and reliability are continuously increasing with time, allows the development of new tools enabling new control algorithms to be deployed providing better real time control of processes.

Thanks to these new advanced sensors and control systems, knowledge on the variability of the types of effluent to be treated (in amount, frequency and quality) is improving. Forever shorter time frames enable processes to be better fine tuned and in the end managed more efficiently.

In this context, the discernment of the interdependence of the sewer network and the wastewater treatment plant is improving. This is why the optimisation in design and operation and the assessments of environmental impact increasingly cover the entire wastewater system (muncipal sewer network + stormwater tanks + overflows + treatment plant + receiving bodies).