Ultra-compact wastewater plant in Venice lagoon

The sidestream bioreactor configuration employed is one of around 100 in the Venice area employing this filtering technology. 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 is on an even larger scale. It processes all of the wastewater treatment for the population of the mainly agricultural island –  which produces fruit and vegetables for the city's population –  as well as wastewater from the densely-populated island of Burano. For this application, which handles up to 1000 m3 a day or the equivalent wastewater output of around 4000 people, the Italian owners, CP Control of Pollution Srl, use PCI Membranes' largest stainless steel tubular system, the A37 module. Housing 37 tubular polymeric membranes within a 100 mm diameter, 3.66 m long stainless steel housing, each A37 module provides a cross-flow filtration surface area of 5 m3. 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. The system for Sant'Erasmo is a membrane bioreactor. An underground basin handles the sedimentation, de-nitrification and nitrification treatment stages, while the pressurized 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 450 square metres of filtration area in total. These two processing lines are assembled with U-bend components to form compact processing stacks. This approach allows the complete filtration system to sit on a footprint of less than 5 x 5 m, with a height of 2.8 m. "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", says Darren Reed of PCI Membranes. "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."