This anaerobic pretreatment plant is proposed as an alternative to conventional primary treatments as decantation. In this process, organic load is reduced (minimizing energy consumption in the next aerobic process) and biogas is produced in the anaerobic digestion. This biological process is carried out by microorganisms that integrate the sludge of the reactor. Those microorganisms are able of uptake the nutrients from the wastewater to grow and generate a biogas rich in biomethane, which could be further used.

A pulse feeding system (PUSH, European Patent EP 3009408), developed by Aqualia, will be applied to increase the mixing in the UASB reactor independently of hydraulic retention time (HRT). Using a pulse feeding system will improve the sludge-wastewater contact, avoid channeling and dead zones, and thus use the entire reactor volume efficiently. The influent wastewater distribution device enables feeding the UASB reactor by gravity, without recycling effluent and comprises a feeding tank located over the reactor water level and inlet manifold which distributes wastewater over the bottom of the reactor through several strings and injection nozzles. Pulses are generated by filling the tank with pumps and draining it with automatic valves.

a) UASB (pretratamiento anaerobio); b) Búffer UASB

The anaerobic pretreatment with an UASB reactor offers several advantages compared to other primary treatments:

• Excellent clarification due to efficient solids settling by static clarification between pulses.
• System suitable for both granular or flocculant sludge.
• High solids removal, which are entrapped into the sludge bed with further hydrolysis and anaerobic degradation.
• Low energy requirements, minimized by the application of the PUSH system.
• Lower sludge production due to anaerobic conditions. 

Thanks to the previous experience of Aqualia on designing, installing and operating UASB systems, the construction of this plant will be efficiently performed in the shortest time. Aqualia developed its knowledge in UASB systems on previous European projects such as FP7 AllGas and H2020 Incover.

Both the operational data logging and the plant control will be carried out by a PLC, which will centralize all the information from the different measurements probes, analyzers and control equipment installed in the plant. With this aim, a SCADA system will be developed to manage all the information received from different equipment and to send the necessary control actions to the field elements that are in charge of the control.

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