San Diego gives green light to potable reuse plan

San Diego's city council has given the green light to the construction of a 415Ml/d facility for direct potable reuse of wastewater costing up to US$ 3.5 billion. The reverse osmosis recycling scheme is expected to meet as much as a third of San Diego's daily drinking water requirement by 2035 making it the second largest potable reuse plant in the US.

The scheme - known as the Pure Water Plan - will be built in three stages in different parts of the city. The first stage, scheduled for 2023, will be a 75 Ml/d facility at the North City Reclamation plant where trials for the scheme have been carried out. A second 75 Ml/d facility is planned at the South Bay Reclamation Plant also for 2023, with a 265 Ml/d per day facility on the grounds of a former Naval Training Centre scheduled for completion in 2035.

The system has been subject to extensive testing at a trail installation. It comprises pre- treatment with micro filtration followed by reverse osmosis and disinfection with ultraviolet light and hydrogen peroxide treatment.

The programme could avert the need for upgrades to the Point Loma wastewater treatment plant needed to bring it up to federal standards for secondary treatment and costed at about US$ 2 billion. The plant currently treated sewage from 16 towns and cities at a rate of 900 Ml/d and discharges into the Pacific.

Current thinking calls for the purified water to be mixed with supplies in San Vicente reservoir to be piped to customers. An alternate strategy would be to allow the city to pipe the water direct to water distribution systems and into users' homes and businesses. Either approach would require changes to state regulations.

San Diego has put a construction cost on the project of US$ 1.5 billion to US$ 2.5 billion. Interest payments would take that to up US$ 3.5 billion. Officials have estimated that the city would have to increase the price of water by 1-3% for most of the contraction of the plants. They plan to cover between a quarter and a third of the cost with state and federal grants. They are seeking money from a recently passed $7.5 billion state water bond and earlier state water measures as well as grants from the Environmental Protection Agency (EPA).

The city is claiming support for the Pure Water project from local taxpayer and environmental groups. Earlier public support for direct potable reuse was poor in San Diego. The city, this summer, hired public relations form Katz on a US$ 1 million, two-year contract to improve the perception of what was dubbed "toilet to tap" technology.

Preliminary planning and design for the Pure Water scheme are underway. The start of construction awaits approval from the EPA and other regulators.


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