Reuse, Reclaim, Recycle
Membrane bioreactor technology is helping treatment facilities find usable water in some unlikely places
Water reuse has gone from being a positive environmental alternative to a growing necessity. Reusing wastewater saves money and the environment, but it can be expensive to pipe treated water through miles of distribution lines from a centralized reclamation facility to where it is needed.
The ability to economically and safely treat wastewater remotely for reuse provides a new, reliable, drought-proof supply of water that can benefit communities by reducing the reliance on over-stressed existing supplies and infrastructure, increasing availability of potable water, and improving the environment by decreasing discharges of wastewater to oceans, lakes, rivers, streams, and creeks.
That is just one of the reasons why satellite treatment plants are gaining popularity in wastewater reclamation treatment. The plants provide an alternate means of recycling and reusing water. They also save public works time and money and cause minimal infrastructure disruptions within communities.
Also called "sewer mining," this treatment method uses high-tech membrane bioreactor (MBR) units to tap into wastewater distribution lines close to where reclaimed water is needed. This localized installation eliminates the high costs of piping reclaimed water from a central treatment plant. Several units may be installed, depending on customer demands. The MBR units treat the water onsite for reuse and it is piped to an area close to where it is needed.
How MBRs Work
The MBR system uses an aerobic biological process and an integrated, immersed membrane-filtration system to produce high-quality effluent that meets the most stringent state reuse standards. The system captures minute particles, bacteria, and viruses as water passes through the membranes. Solids from the biological process are removed and returned to the sewer system where they are routed to the main wastewater treatment plant to undergo further treatment.
The biological process and membrane operating systems are located in separate tanks to optimize performance of the overall process and to simplify operation and maintenance. This form of filtration also eliminates the need for clarifiers and other peripheral equipment, process control, and maintenance normally associated with a conventional clarification process -- considerably reducing the overall footprint.
Replacing clarifiers with microfilters allows the biological process to be designed and operated as a high-rate wastewater treatment process. The system can provide advanced nitrogen and phosphorus removal to meet the most stringent effluent requirements. By reducing the biological volume requirements and the maintenance-intensive clarifier technology, the footprint can be reduced to less than 50 percent of a conventional biological process.
Advancements in membrane filtration have fostered a new generation of compact MBR systems. These systems offer cost-effective water and wastewater treatment solutions to small communities, municipalities, developers, and industrial clients that require high-quality treatment with a small footprint, minimal installation costs, and reliable performance.
The MBR packaged plant is a robust wastewater treatment process with inherent features designed to reduce maintenance and provide reliable and efficient wastewater treatment for small-scale applications. Operation of the treatment process is easily automated and can be controlled with a microprocessor while delivering remote access for monitoring. The highly automated design helps operators meet the demands of stringent environmental requirements -- even at remote locations.
Benefits of Localized Treatment
In addition to benefiting from recycled water, public works that employ sewer mining enjoy several other advantages. First, they can postpone expansion of existing treatment facilities by relieving some of the load sent to the local wastewater treatment plant. They can also avoid the costs associated with installing reclaimed water piping and the resulting infrastructure disruptions. Because the satellite plant is a side stream to the main treatment plant, it does not need standby or redundant back-up equipment, occupies less space than a conventional treatment plant, and requires minimal operator attendance -- all of which further reduce costs.
If one of the satellite plants needs to be taken offline, untreated water simply bypasses the MBR unit and flows directly to the main wastewater treatment plant downstream where it is treated. Such a shutdown would only affect customers serviced by that particular plant, as opposed to all reclamation customers in the area.
Water recycled by the MBR system is used for landscape irrigation, groundwater replenishment, cooling tower feedwater, or other non-potable uses. And because wasted sludge from the MBR is treated at a centralized facility, odors are not usually an issue.
One Technology, Many Applications
Designed for wastewater applications from 25,000 gallons per day (gpd) to 100,000 gpd, this separation solution is ideally suited for a wide range of municipal and industrial wastewater applications, including:
- Residential development projects: single dwelling, housing cluster or subdivision;
- Commercial development projects;
- Remote installations;
- Emergency response wastewater treatment applications;
- Military bases and rapid infrastructure deployment;
- Sports facilities;
- Shopping centers; and
- Office parks.
Some municipalities have already taken advantage of the benefits of satellite treatment. For example, the Hawks Prairie Reclaimed Water Satellite Plant in Olympia, Wash., which reclaims wastewater from four separate communities, expects to save its 78,000 customers hundreds of millions of gallons of drinking water annually.
The Hawks Prairie satellite plant is the first of three planned reclaimed water satellites that are part of the community's 20-year wastewater resource management plan. In March 2005, Washington State Governor, Christine Gregoire, asked the state legislature for $12 million to address drought-related issues in the state, citing the economic impact of drought conditions1. The state is currently under a drought and wildfire emergency -- reiterating the importance of strong water-management programs.
The Hawks Prairie location was chosen first because it has several potential users of the reclaimed water for irrigation, commercial, and institutional purposes. A portion of the treated wastewater is used for groundwater recharge, where the treated water filters through the ground to replenish groundwater supplies.
The Hawks Prairie project includes a reclaimed water plant, a series of constructed wetlands ponds, eight acres of groundwater recharge basins, and three miles of distribution pipelines. Most of the treatment process occurs in underground tanks, covered with above-ground roofs featuring water efficient plants and grasses1. Membrane bioreactor technology was chosen for its reliability to produce quality reuse water and its ability to be integrated into remote sites.
Currently, the plant treats 2 million gallons per day (mgd) of wastewater, and over time the plant will be expanded to handle up to 5 mgd. The reclaimed water meets Washington's "Class A" reclaimed water standards, which is the highest quality of water as defined by the Washington State Departments of Health and Ecology. It is suitable for irrigation, commercial, and industrial uses, and a variety of other environmentally beneficial uses.2
As part of the plan, each satellite plant will intercept existing regional sewer lines and extract municipal wastewater for local use. At the Hawks Prairie site, the clean water will travel three miles through a pipeline from the plant to the ponds and recharge site. Along the way, some of the water will be drawn off for irrigation or other beneficial uses.2
Located in the heart of Florida near Orlando, the city of Kissimmee is the new home to a 50,000-gpd MBR satellite treatment facility. In a region where water reuse is commonplace and necessary, the challenges of existing infrastructure, ever-growing populations, and drought stress the existing water supply. Personnel at the city of Kissimmee are hoping to learn from the new MBR demonstration facility operating at one of the city's water treatment plants.
The full-scale MBR demonstration facility has illustrated the viability of satellite treatment and sewer mining applications for the city through research and operating data. The plant has demonstrated that advanced treatment with MBR technology is a practical and reliable means of providing remote reclamation of wastewater. Minimal attention is required to operate the plant, and the reclaimed water's quality was excellent.
Even though the city already reclaims more than 3 million gallons of water for irrigation each day, it has a long-term, growing need for advanced wastewater treatment and reclaimed wastewater.
The Proof Is In the Numbers
On average, sewer mining satellite treatment plants can treat between 25,000 gpd and 100,000 gpd. Although conventional, centralized plants are usually capable of treating greater amounts, hundreds of thousands of gallons of water are often lost each day within the distribution lines due to aging infrastructures.
Capital costs for a satellite treatment plant are higher than costs for a conventional plant because of their smaller scale. However, distribution system capital costs are avoided, or significantly reduced, with satellite plants. Additionally, as these plants are automated, they have considerably lower operating and maintenance costs than do centralized plants.
More and more developers are using satellite plant designs to integrate reuse for irrigation into planned communities. Small satellite plants are relatively easily integrated in planned communities around golf courses and recreation facilities. Also based on the exceptionally high quality effluent, this technology is well received by most state regulators, thereby expediting the approval process. In addition, the satellite plant can take the load off the main treatment facility, delaying costly expansions and permitting.
Robert W. McIlvaine of the McIlvaine Company predicts costs will continue to decrease as further advancements in membrane technologies are made.
Increased MBR Usage
The growing trend in MBR usage is still too new to track effectively. But Robert W. McIlvaine of the McIlvaine Company (www.mcilvainecompany.com), an environmental market research firm, has noticed a 30-percent to 40-percent increase in MBR sales over the past few years. Within that number, MBR usage for wastewater treatment has increased by 60 percent. Of those wastewater units, how many have been installed in satellite treatment plants still remain to be seen.
McIlvaine projects that, by 2007, the total installed base of membrane wastewater reclamation systems will increase in the United States to 786 million gallons per day (mgd) and in the world, to 1,855 mgd. In 2007, system sales for wastewater reclamation sales will be $262 million in the United States and $605 million worldwide.
This article originally appeared in the 11/01/2005 issue of Environmental Protection.