Pushing Water Reuse to The Extremes
Large-scale water-reuse treatment plants have had a sustainable impact in populated areas where the volume of water to be treated and reused in a concentrated area makes them practical. Today, the flat-sheet membrane aerated biofilm reactor (MABR) technology that is delivering high-quality wastewater treatment to remote locations is poised to realize the promise of sustainable water reuse in those same locations.
The Value Of A Circular Economy For Water Use
According to an in-depth report from a major international banking and financial services group, a shift to a circular economy for global water use could help save more than 400 billion cubic meters of water per year. For a deeper appreciation of what that means, follow the link at the bottom of this webpage to the full 2017 ING report on circular economy solutions to water shortages.
Cost-Efficient Water Treatment For Limited-Resource Applications
While the potential for water savings is immense, the logistics of bringing it to fruition need to be practical in today’s water use environments. Field-proven applications of flat-sheet MABR technology have demonstrated exceptional value for decentralized wastewater treatment and reuse installations. In some cases, the entire MABR process can be delivered in a containerized package that enables complete setup and operation with minimal site preparation (Figure 1).
Figure 1. This self-contained WWTP features eight flat-sheet, spirally wound MABR reactors plus secondary clarification and tertiary filtering and disinfection in a 53,000 GPD (200 m /d) wastewater treatment plant. The remote location is designed to serve highway service stations and provide high-quality water effluent allowing safe discharge into the environment, or water reuse for irrigation, with additional nutrients removal.
This technology holds promise for locations that are simply too isolated to make a large investment in centralized wastewater collection and redistribution infrastructure worthwhile. MABR’s unique attributes collectively provide a viable cost-effective foundation for meeting the stringent requirements of water reuse applications with minimal OPEX costs. These attributes include:
Simultaneous nitrification-denitrification in a compact footprint, with routine biological nutrient removal (BNR) of nitrogen down to 10 mg/L and enhanced nutrient removal down to 3.0 mg/L.
The ability to achieve up to 90 percent biological reduction of phosphorus levels without adding chemicals and to achieve levels down to 0.3 mg/L with only moderate chemical use.
Low-volume, low-pressure air use that reduces aeration energy costs by as much as 90 percent, as compared to typical conventional activated sludge (CAS) systems.
Achieving Multiple Levels Of Water Reuse, Cost-Effectively
One of the most demanding aspects of water reuse from MABR systems (Figure 2) is the consideration of nutrient reduction and the need for tertiary treatment, based on the intended application for the effluent. Each level of application comes with its own unique requirements and solutions.
Figure 2. The key to cost-efficient performance in flat-sheet, spirally wound MABR is the low volume/ low-pressure air that permeates through the membrane to support an aerobic nitrifying biofilm. Simultaneous nitrification/denitrification takes place within the same reactor chamber, with phosphorus reduction achieved as part of the biological process.
- Agricultural Reuse. Treated wastewater being used for irrigation will have special standards based on the crop. Some of those applications can actually benefit from leaving controlled amounts of nutrients in the recycled water, depending on the specialized standards for the specific crop. Even though the effluent is chlorinated, pathogen-free, and contains very low carbon, biochemical oxygen demand (BOD), and chemical oxygen demand (COD), naturally occurring nutrients in the effluent can help to reduce fertilizer costs for those crops.
- Industrial Reuse. With appropriate tertiary treatment solutions, MABR-treated wastewater can satisfy even the most stringent demands of industrial users — for process water and even ultrapure water required to support their production requirements.
- Potable Water Reuse. The first MABR containerized wastewater treatment pilot plant to meet California Title 22, Chapter 3 Water Recycling Criteria for indirect potable reuse in subsurface aquifer-recharging applications was installed in 2018 at the William and Cloy Codiga Resource Recovery Center in Palo Alto, CA. Today it is operating in an extended testing stage, following published findings in February 2019 proving the unit’s ability to reliably exceed California Title 22. The unit is now being tested for its ability to exceed Biological Nutrients Removal standards to meet requirements in Maryland and the Chesapeake Bay area. This additional testing is anticipated to be concluded by May 2019.
Gaining A Better Understanding Of Water Reuse
As water scarcity issues increase and water recycling for potable water use becomes more attractive, more communities and utilities will look for viable solutions to their water needs. A good starting point is this U.S. EPA Compendium, which cites five overall treatment objectives for potable reuse applications:
- Removal of suspended solids.
- Reducing concentrations of dissolved chemicals.
- Disinfection and removal of trace organic compounds.
- Stabilization with lime, calcium chloride, or sodium hydroxide to reintroduce minerals lost due to reverse osmosis (RO) or nanofiltration (NF).
- Removal of noticeable aesthetics compounds (i.e., taste, odor, and color) above the secondary maximum contaminant level (MCL). It also cites a range of advanced wastewater treatment facility (AWTF) options for tertiary treatment processes that can be added to flat-sheet MABR treatment plants for direct or indirect potable reuse applications. These processes include, but are not limited to:
- Ultrafiltration (UF) for removing suspended solids, taste and odor compounds, endotoxins, bacteria, viruses, and other pathogens.
- Reverse osmosis (RO) for reducing the concentration of dissolved chemicals, as well as taste and odor compounds.
- Ozonation, UV disinfection, and advanced oxidation for disinfection and removal of trace organic compounds.
- Biologically activated carbon (BAC) for aesthetics of taste, odor, and color control.
A Final Note On Nutrients In Water Reuse
Successful water reuses, worldwide, tend to demonstrate strong control over nutrient levels.
When using UF and RO tertiary treatments in water reuse applications, it is important to achieve appropriate nitrogen and phosphorus reduction to protect filtration media and membranes against premature failure due to fouling. Flat-sheet MABR technology’s ability to deliver significant reductions in the total nitrogen (TN) levels of treatment plant effluent helps to reduce the risk and severity of such potential fouling in tertiary treatment units (Figure 3).
Figure 3. With the ability to assemble diverse self-sufficient configurations of MABR reactors,
secondary clarifiers, and a variety of tertiary treatment options, compact MABR systems can
satisfy a range of water reuse applications in small, decentralized locations.