Compact treatment for 'Venice's Garden'

The filtration system for a wastewater treatment plant on the Venetian island of Sant'Erasmo required a special configuration, says Darren Reed, business development manager of PCI Membranes.

High-throughput filtration membranes are at the heart of an extremely compact wastewater treatment plant on Isola di Sant'Erasmo, a 4km long island in the Venice lagoon. The sidestream bioreactor configuration has been engineered by Italian wastewater specialist, CP Srl, and is one of around 100 in the Venice area alone.

The system processes 1,000m3/d and employs advanced filtering technology from PCI Membranes - a business unit of ITT Flow Control, based in Hampshire. Venice's wastewater treatment network is highly distributed, with many small processing plants handling groups of houses or buildings, or single large installations such as hotels.

The plant on Sant'Erasmo processes all of the wastewater treatment for the population of the mainly agricultural island, known as 'Venice's Garden', which is renowned for artichokes and produces fruit and vegetables for the city's population. It also treats wastewater from the densely-populated residential island of Burano.

For this application, CP chose to Each A37 module houses 37 tubular polymeric membranes within a 100mm diameter, 3660mm long, stainless steel housing. The modules each provides a 5m2 cross-flow filtration surface area. As the membranes will operate with a pressure of up to seven bar (102 PSI), multiple modules can be connected in series and driven by pumps to achieve high throughputs.

MBR treatment
The system for Sant'Erasmo is a membrane bioreactor - a wastewater treatment system combining biological oxidation with activated sludge and a filtration system.

An underground basin handles the sedimentation, de-nitrification and nitrification treatment stages, while the pressurised sidestream filtering system separates the solid and liquid phases.

The particular filtration configuration designed for this application is a pumped system with two parallel processing lines constructed using 45 tubular A37 modules each, providing some 450m2 of filtration area in total. These two processing lines are assembled with U-bend components to form compact processing stacks.

The approach allows the complete filtration system to sit on a footprint of less than 5 It is cycled through the These solids are sent back to the bioreactor until they can no longer be degraded, and are periodically removed for a final dewatering phase and then disposal. Separated particle-free effluent is ozone polished before being reused for irrigation.

Sensitive environments
CP also employs special processing techniques which reduce the energy consumption of sidestream membrane bioreactor configurations by up to 50-60%. Sidestream membrane systems are much easier to access and maintain than submersed filtration systems, and are also ideal for sensitive environments such as Venice, because there is no need for lifting equipment, which in this case would have increased building height.

These attributes, and the system engineering by CP, mean that the Sant'Erasmo installation fits into a single-storey building, allowing the plant to blend unobtrusively into the flat farming landscape. The CP engineer who worked on the Sant'Erasmo plant, Silvano Levorin, says: "Sidestream membrane systems are advantageous for many of the wastewater treatment plant projects we handle, which are in sensitive and conservation areas. We like using PCI Membranes filtration because of the ease with which its tubular-mounted modules can be built into systems and maintained."


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