The island of Sant'erasmo uses high-throughput side-stream systems, processing enough for two islands
High-throughput filtration membranes are at the heart of an extremely compact wastewater treatment plant on the island of Sant'Erasmo in Venice, Italy. Engineered by CP Srl, the side-stream bioreactor configuration employed is one of around 100 in the area alone employing advanced filtering technology from PCI Membranes, a business unit of ITT Flow Control.
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 the island 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 cu m a day, CP chose to 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 sq m.
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 pressurized side-stream filtering system separates the solid and liquid phases.
In operation, wastewater flows into an activated sludge biological treatment basin or bioreactor for breakdown of the organic material. It is cycled through the ultrafiltration plant to remove the sludge and high molecular weight solids. These solids are sent back to the bioreactor until they can no longer be degraded, and are periodically removed for a final de-watering phase and then disposal. Separated particle-free effluent is ozone polished before being re-used for irrigation.