AWWA MTC57600

At the end of 1999 United Utilities (formerly North West Water) started up two microfiltration drinking water plants in the Lake District region of North West England, at Ennerdale 59 Ml/d (16 MGD) and Cornhow 32 Ml/d (8 MGD). This formed part of a strategy to provide protection against Cryptosporidium. The plants are fed from two separate oligotrophic lake sources located within the Lake District National Park. Ennerdale is now the longest running microporous membrane plant for drinking water production in the United Kingdom. There were a number of significant design challenges. No liquid waste discharges are permitted on the sites, so a secondary membrane system is provided as a concentration step. There are seasonal algal blooms in the sources and pronounced temperature variation between summer and winter (2 - 20 C), which directly affect membrane performance. The paper describes how these factors have been reflected in the first 2 to 3 years of operation. Plant operational data tracks the clear seasonal impact on the membranes of temperature and summer plankton growth over two summers. Changes in backwash and Clean in Place (CIP) efficiencies are analyzed, membrane resistances are related to the fouling characteristics of the source, and approaches for successfully dealing with problems that arise are described. The effects of an inadvertent bypass of algae mass from the micro-strainers acting as pre-screens and how they were overcome are illustrated. The secondary membranes operate in conjunction with a coagulation and sedimentation process using polyaluminium chloride and receive higher solids loading. This system handles CIP waste as well as backwash. The plant originally experienced some periods of disturbance related to the intermittent presence of chemicals from cleaning operations. This impacted performance, and design adjustments to allow for this are described. Operational data is analyzed and compared. Operational costs are analyzed and opportunity for future optimization is identified. Includes 6 references, tables, figures.