The U.S. is currently experiencing its worst drought in 56 years. Many cities and regions are enduring unprecedented water restrictions and unfortunately, it looks like there is no end in sight.
Charles Fishman, investigative journalist and author of The Big Thirst: The Secret Life and Turbulent Future of Water, recently penned an op-ed in The New York Times entitled, “Don’t Waste the Drought.” As you can glean from the title, the purpose of the article was to provoke a re-imagination of the way we approach water in the U.S. If we use this year’s drought as an opportunity to think outside the box about planning and conservation practices, we ought to be better prepared when the next drought comes knocking at the door.
Not surprisingly, wastewater recycling is one of the central tenets of Fishman’s campaign. Whereas 10 years ago wastewater recycling was only feasible in a large, centralized or municipal scenario, the circumstances are different today. Technological advancements make wastewater reuse viable at a much smaller scale—even on an individual building scale.
In light of Fishman’s crusade, let’s not waste this opportunity to take a closer look at decentralized wastewater recycling as a comprehensive water conservation practice. Moreover, let’s look at what our water-strapped friends in Australia are doing to tackle drought head on.
Innovative Reuse Scheme
One Bligh Street, a new 29-story office tower overlooking Sydney Harbor, has won numerous awards for its innovative design, but below the captivating full-height atrium is an Aquacell blackwater recycling system that produces 90% of the water for the building. The system, located just off the parking garage in a maintenance room, treats approximately 26,000 gal of blackwater on site daily.
Not all of the wastewater reused at 1 Bligh Street comes from the building itself, however. Water balance calculations revealed that the building’s total waste stream would not meet thenon-potable demand for cooling tower makeup and toilet flushing, the desired reuse applications.
To avoid using municipal water to make up the difference, the development engaged in “sewer mining,” which involves tapping into a nearby city sewer main to extract raw sewage as an additional blackwater source. Sewer mining enabled the property to fulfill all of its non-potable needs with recycled water and achieve 90% conservation.
Water Recycling Technology
A modular membrane bioreactor (MBR) is the treatment technology utilized at 1 Bligh Street. Advances in modular mechanical design, membranes, instrumentation and remote monitoring via the Internet have helped improve the cost and reliability of MBR systems in recent years. Aquacell has leveraged these advances to engineer a modular treatment system for in-building or small community projects.
The MBR treatment system at 1 Bligh Street consists of mechanical screening, biological treatment and ultrafiltration with 0.04-μ membranes. Disinfection follows the MBR, using ultraviolet (UV) light and chlorine residual to provide multiple treatment barriers. The recycled water reused for cooling tower makeup also is treated with reverse osmosis (RO) to remove salts. This approach provides the building with a small-footprint system with high yields and high-quality effluent.
Fit-for-Purpose Water
The basis of the blackwater system design was drawn from the Australian Guidelines for Water Recycling’s “fit-for-purpose water” methodology. This approach involves an exposure risk calculation adopted from the World Health Organization’s (WHO) Guidelines for Drinking Water Quality. The methodology designates tolerable risk to be 10-6 disability-adjusted life years (DALYs), or one infection per 1,000,000 people per year. DALYs have been used extensively to account for illness severity by organizations such as WHO.
For this particular site, in order to reach 10-6 DALYs for protozoa, viruses and Camplyobacter, calculations determined the log reduction values (LRVs) needed to be 4.6, 6 and 4.8, respectively. Once the LRVs were established, system performance objectives and components could be determined.
In this case, a UV unit provides 1 LRV for viruses and 4 LRV for protozoa. An RO unit provides less than 1 LRV for each, and chlorine disinfection provides 4 LRV for viruses. Thus, the performance requirements for the system were achieved. Note that the LRV calculations did not receive credits for the submerged membranes. This is the current standard in Australia; however, frameworks in the U.S., such as California’s Title 22, do receive LRV credits for membrane filtration.
Preventative Risk Management
It is important to understand that a blackwater recycling scheme at the building scale does not have much in common with a conventional wastewater treatment plant, or even a larger centralized wastewater recycling plant.
While safety remains a top priority in both scenarios, economic viability is a central concern with building-scale installations. Consequently, innovation is required not only in treatment technology, but also in the fundamentals of risk management. If risk can be properly contained or eliminated as a principle of design, the system requires less attention, and operational costs are reduced.
In order to accomplish this, the water treatment industry in Australia has adopted a preventive risk management methodology borrowed from the food and beverage industry entitled “Hazard Analysis and Critical Control Points” (HACCP). HACCP has played a critical role in the proliferation of water recycling schemes throughout Australia, and global adoption of this approach is rising because it offers newfound efficiencies in the operation of treatment plants.
HACCP breaks down the treatment process into steps. At each step, the question, “What might happen, and how might it occur?” is asked.
At 1 Bligh Street, six CCPs were identified, including influent pH, turbidity, electrical conductivity across the RO, UV dosing, chlorine residual and effluent pH. For each CCP, upper and lower limits were identified. If during the course of production any one of the six CCPs reveals data outside the limits, production is halted and an alarm is sent via text message to a technician. Thus, HACCP ensures the delivery of quality water.
As a result, end-of-pipe monitoring frequency can be reduced, which reduces lab costs and directly affects the viability of the installation without sacrificing public safety. Whereas
E. coli sampling might have typically been required daily on a project like 1 Bligh Street, with HACCP real-time verification monitoring in place, regulators agreed to monthly E. coli sampling. The monthly sampling for E.coli simply serves as confirmation that the HACCP methodology is functioning properly.
The integration of HACCP into the design of the blackwater system at 1 Bligh Street is largely responsible for its viability. It is time to embrace innovative technologies and methods like HACCP that give us the ability to combat drought. Otherwise, we will look back and realize that we wasted opportunities.
