Introduction
Water reuse is not a new concept, as domestic wastewater has been used for irrigation and aquaculture by several civilizations. From ancient to modern times, water recycling has declined and been reborn due to population growth, development of megacities, climate change and the fact that the world’s fresh water supply is finite. Water reuse can provide alternative options for existing water supplies and can be used to enhance water reliability and resilience. Water reuse is defined as planned or unplanned. Planned water reuse refers to water systems engineered with the goal of beneficially reusing a recycled water supply. This article will focus on planned water reuse system technologies and standards developed for them to meet certain minimum performance requirements.
Technologies
Due to advancements in the water purification field, multiple processes are being used in water reuse systems. Some of those technologies include membrane biological reactor, microfiltration or ultrafiltration solutions, reverse osmosis systems, ultraviolet light disinfection, chlorine disinfection, ozone disinfection, electrodialysis reversal, thermal evaporation and crystallization systems. Membrane biological reactor technology combine reaction with separation to increase the conversion and provide high quality water. Microfiltration or ultrafiltration separate solids from liquid streams based on the particle sizes. These are typically downstream liquid filtration process. Reverse osmosis systems are used with a pre-filter in place prior to the membrane to remove organics, solids and metals so it does not damage the membrane. The process includes applying sufficient pressure against the feedwater to force it through the membrane and separate the water molecules from the other impurities. Disinfection technologies using ultraviolet light, chlorine and ozone processes are used as a post filter in water reuse application to reduce total organic carbon (TOC) and remaining organics. Electrodialysis reversal is an electrically driven membrane process in which electricity is applied to electrodes to pull naturally occurring dissolved salts through an ion exchange membrane to separate the water from the salts. Thermal evaporation and crystallization systems are the ideal solution for brine treatment and wastewater for zero liquid discharge (ZLD) desalination. Evaporation and crystallization minimize the cost of disposal and environmental impact to squeeze out the last bit of clean water.
NSF/ANSI 350
The NSF/ANSI 350 standard has been developed to establish minimum material, design, construction, performance and literature requirements for on-site residential and commercial water reuse treatment systems. The material requirements for the systems include evaluation of interior and exterior surfaces, welding, and dissimilar metals. The design and construction requirements for the system include evaluation of exposed surfaces, structural integrity, water tightness, noise, mechanical and electrical components, access ports, visual and audible alarm test, and flow design. These evaluations are included to make sure the system is durable and capable of withstanding stresses and wear along with not affecting the environment. The literature requirements include an installation manual, operation and maintenance manual, troubleshooting and repair manual, drawings of the system, system label and basic description of the system. These documents are required so the user can have access to the important information about the system installation, operation and maintenance as required. The systems are classified between two classes in the standard with Class R (single-family residential) and Class C (multifamily and commercial facilities). These classifications for the system are based on the evaluation of effluent samples collected over a six-month (26-week) testing period. The system can be evaluated for bathing-only water, laundry-only water or combined bathing and laundry water based on its design and capability to treat the water. The influent characteristics of the test water and schedule for stress tests vary based on the system design. The effluent samples are analyzed and compared to the specifications for Class R and C to establish whether it meets the minimum requirements as noted in the standard. The parameters that are measured as part of this evaluation include CBOD5 (carbonaceous biochemical oxygen demand), total suspended solids (TSS), turbidity, E. coli, pH level, storage vessel disinfection, color, odor, oily film and foam level, energy consumption and sodium adsorption ratio (SAR).
IAPMO IGC 324
IAPMO IGC 324 is another standard for water reuse systems that has been developed by IAPMO. This standard is intended for multifamily, residential and commercial use. NSF/ANSI 350 only covers greywater, where IAPMO IGC 324 covers greywater, rainwater, stormwater air conditioning condensate, cooling tower makeup, vehicle wash and other non-potable reuse applications not specifically listed, for use in subsurface and/or surface irrigation and toilet/urinal flushing applications. The standard specifies materials, physical characteristics, performance testing and markings. The general requirement in this standard includes evaluation of materials, plumbing fixtures, disinfection systems and air gap. The standard covers ultraviolet disinfection systems, ozone systems, chlorine disinfection systems and alternative disinfection systems. Additional requirements include hydrostatic test for pressurized systems and leakage test for non-pressurized systems along with overflow test, failure mode effects analysis (FMEA) and long-term monitoring. The performance testing evaluation requires bacteria challenge testing, which includes A2 fine Arizona test dust for turbidity and E. Coli for bacteria. Free available chlorine, combined chlorine, TSS, pH and total coliform are other parameters that are evaluated as part of performance testing under this standard. The standard also has different log reduction requirements based on the type of water used for testing such as greywater, stormwater or foundation drainage or rainwater. The performance testing under this standard is 12 weeks long and also has a marking and installation instruction requirement to make it easier for the user to operate the system and maintain it. This standard has a testing and certification option for systems with capabilities to treat alternate source water beyond greywater and provides a competitive advantage in the marketplace.
Testing & Certification
Many organizations can test and certify to either or both standards, including IAPMO R&T. The Uniform Plumbing Code (UPC®) and the International Plumbing Code (IPC) both mention compliance requirements for water reuse systems. Thus, compliance is required in many U.S. states and jurisdictions, and certification is a great way to prove continued compliance. Even in places where this standard is not a regulatory requirement, testing and certification provide manufacturers with important product data, assurance that the product is functioning properly and a marketing advantage.
Future
As the world’s population grows and climate change continues to affect our environment, there will inevitably be an increase in the demand for water reuse systems. It is already becoming increasingly necessary to expand the use of nonconventional water resources such as reclaimed water in water-stressed areas. The positive news is that the purification technologies are advancing at a greater rate, which will make water reuse even easier and cheaper than other feasible options. It is fair to say that more water reuse programs are going to be created in the future. There are number of benefits for reusing the water for many different purposes and those benefits would keep pushing to implement additional water reuse programs. Every drop of water that we recycle is a drop that we do not have to take from our limited water resources.
