Innovative thinking and advanced technology are helping one infrastructure operator dispose of excess water, while giving another a more sustainable supply.
Energy production uses water. A lot of water. In urban environments in particular, that water is not easily sourced, often having to be transported from outside the city at high cost. Until recently, a steam power plant for district energy in downtown San Francisco was one of the city’s biggest consumers of freshwater – particularly precious in water-stressed California. At the same time, the neighbouring subway had to deal with, and pay for, the disposal of a large amount of leaching foundation water. The intelligent application of water treatment technology connected the two circularly, with the energy company, Clearway Energy, teaming up with the San Francisco Public Utilities Commission (SFPUC), and DuPont Water Solutions in a public-private partnership that turns this polluted runoff water into a valued resource.
When the site commenced operation in July of 2019, Mayor London N Breed said, “In San Francisco, and throughout California, we need to continue to prepare for the effects of climate change by being more resourceful when it comes to our water supply. We are committed to environmental sustainability and protecting our scarce natural resources, and this innovative and groundbreaking project will help us conserve millions of gallons of clean drinking water.”1
In fact, this onsite water reuse project saves a staggering 30 million US gallons (114 million litres) of drinking water annually (equivalent to 45 olympic swimming pools) by using an advanced membrane system to treat not only water drained from the subway, but also from alternative sources such as the utility water supply, groundwater and rainwater, as availabilities fluctuate. The heart of the solution is closed-circuit reverse osmosis (CCRO), a game-changing system which purifies the varying qualities of water with a very high recovery rate, autonomously adjusting to changing conditions. Up to 95 per cent of the water can be reclaimed by a CCRO, with only a small proportion of highly concentrated discharge, reducing the cost of complicated brine disposal significantly. Furthermore, the system’s robustness keeps the critical supply of water flowing continuously to the steam power plant, while a high degree of automation means that on-site staff do not have to also become water system experts to keep the system running.
The investment makes sense economically, as well as ecologically. While the project had a cost of $3.75 million, annual savings alone amount to $1.8 million, giving a return on the investment within three years. The energy plant now uses fewer chemicals and has proudly received LEED (Leadership in Energy and Environmental Design) recognition from the US Green Building Council for the “sustainable steam” it produces for district heat.
This CCRO technology became part of DuPont Water Solutions during a series of recent acquisitions by the corporation. “As a global leader in innovative water technologies, we are continually expanding our technology portfolio of high-quality solutions to help our customers purify, conserve and reuse precious water resources,” said HP Nanda, Global Vice President & General Manager, DuPont Water Solutions, commenting on the 2019 acquisition of four companies including Desalitech which brought CCRO into the “toolkit”, as he describes it. Further acquisitions of inge, Memcor and OxyMem have added to what was already one of the industry’s broadest portfolios to help cater for evolving water treatment needs and allow DuPont to even better apply its own technology in innovation solutions such as the one for Clearway Energy and SFPUC.
Projects like this are connecting urban infrastructure to save precious resources and create circular economy approaches in neighbourhoods such as central San Francisco around the world.
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