The diurnal dynamics of the upstream biological wastewater treatment processes (e.g. activated sludge process) have been addressed since the introduction of dynamic simulations; however in the available literature, the process conditions of water purification have mostly been discussed and investigated under diurnal steady-state conditions. In fact, the downstream water purification facility inherits environmental variations that occur in the upstream wastewater reclamation influent. Even though part of these variations is attenuated through the wastewater treatment processes, abrupt or gradual variations are observed in the water purification influent during different hours of a diurnal period. The variable parameters, can include: hydraulic load, pollutant loads (i.e. suspended solids and dissolved solids), and water temperature. The variations in theses environmental parameters affect the process parameters, and consequently create a dynamic energy footprint during the diurnal cycle.

Dynamics of MF Operating Cycle

The results of our study indicate that from midnight until noon, when the MF influent load is lower, the time between backwash events (tc) could be much longer compared to the maximum and average load operating condition. For example, from 6–9 a.m., when the hydraulic and constituent loads are at a minimum, the MF operating cycle could be 2.2-times longer compared the operating cycle required at the maximum load and 1.5-times longer compared to the operating cycle required for the average load.

Dynamics of RO Feed Pump Energy Consumption

The diurnal power variations in an AWP facility are mostly the result of the load fluctuations of the RO feed water. The results presented in Fig. 2 indicate that while the hydraulic and constituent loads (i.e., represented here by conductivity) fluctuate 56% and 13%, respectively, the RO power required for the feed pumps varied 74% during a typical diurnal period. Between midnight and noon, the power variation is dominated by the flow variation. From afternoon until midnight the feed water flow is stable and thus, the power variation is dominated by the variation in conductivity.

The data revealed that the required power for RO pumping decreases at midnight until 7 a.m., due to the simultaneous decrease of the RO feed flow and electrical conductivity. After 8 a.m., flow and conductivity increase and the required power starts to rise. During the afternoon, the feed flow stabilizes, however the conductivity increases and thus, a steady increase in required power occurs until approximately 5 p.m. After this, the required power decreases until midnight when the feed water conductivity in the feed flow decreases.

Figure 1. Diurnal variations of flow and turbidity in the MF process

Figure 1. Diurnal variations of flow and turbidity in the MF process

 

Figure 2. Diurnal variations of RO required power caused by fluctuations of RO hydraulic and constituent (i.e., conductivity) loading

Figure 2. Diurnal variations of RO required power caused by fluctuations of RO hydraulic and constituent (i.e., conductivity) loading