North America faces serious water shortages. To preserve our limited supply of source water and ensure future sustainability, industry research is focusing on source water management.
North America faces serious water shortages. To preserve our limited supply of source water and ensure future sustainability, industry research is focusing on source water management. Paul Gallagher, global director of purified water R&D at Siemens Water Technologies, shares Siemens' views on nutrient removal, pharmaceuticals and trace organics in the water supply, recycle and reuse, and land-applied biosolids, as they relate to source water management.
Orange County Water District membrane cells.
1) Nutrient removal reduces the amount and impact of nutrients and sediments in the water supply, which ultimately affect the quality of the water. In the absence of revised federal regulations, what are states doing to address nutrients in their regions?
A. Nutrient concentrations in water, whether receiving waters from a wastewater discharge or source waters for a potable system, can cause serious problems for our environment. The most populous areas of the world have the highest concentrations of waterborne nutrients, often coupled with the lowest available area for nutrient reuse without impacting source waters for potable use.
The West Basin Municipal Water District submerged membrane system.
Within the U.S., local health boards and state agencies typically regulate the amount of excess nutrients allowed within reservoirs and source waters. Local agencies often regulate the application of reclaimed water within catchment areas of public source waters. In the most populous areas within the Sunbelt, regulation of nutrients within recreational waters often drives nutrient removal treatment to the highest levels of enhanced nutrient removal for any discharge not specifically designated for irrigation purposes.
2) Which types of technology are available for nutrient removal today?
A: The lowering of nitrogen and phosphorus levels to increase the quality of the wastewater effluent – enhanced nutrient removal (ENR) – is accomplished through the use of advanced wastewater technologies. There are a wide range of solutions and technologies, depending on the specific needs of the community. It could mean an entirely new treatment facility or simply effluent polishing, or a combination of both. For instance, the Borough of Shippensburg, PA, wastewater treatment plant required a plant upgrade and will be using a biological nutrient removal process to meet new regulatory effluent discharges required under the Chesapeake Bay initiative.
Depending on the designated use of the reclaimed wastewater, nutrient removal can be biological in nature within the main plant process, or it can be achieved by polishing treatment stages on the reclaimed effluent. In the case of reclaimed water for irrigation purposes, it's desirable to have both nitrogen and phosphorus contained within the water. As a result, the application and use of such waters has to be designed carefully to ensure that the excess nutrients don't enter source water catchments to cause undesirable biological activity.
For applications that will include indirect or direct reuse of reclaimed water, excess nutrients are often reduced to the smallest practical level before reclaimed waters are mixed with source waters. Examples such as the Orange County (Calif.) Groundwater Replenishment project, the NEWater projects in Singapore, or the very recent facility for the Beijing Olympic Park.
3) There has been a lot of press lately about pharmaceuticals and other trace organic compounds in the water. What are technology providers doing for R&D in this area?
A: Along with many other companies, universities, and governmental agencies, Siemens is looking for solutions to reduce or eliminate these compounds from drinking water and wastewater. Some of the micro-constituents are very difficult to treat. The technological and practical difficulties are enormous – these problem compounds must be identified, their traces need to be monitored, their relative toxicity and effects need to be evaluated, and removal or destruction techniques need to be implemented.
Siemens Water Technologies currently has research underway in various locales to study the formation, destruction, and/or removal of critical pollutants including pharmaceutical residuals. We'll continue with such work and offer solutions to the market as technology improvements become available. While technical solutions for removal or destruction of many of these compounds are available, the incremental cost of this additional treatment is substantial. So there's a critical regulatory question of balancing the additional treatment cost against the health and environmental benefits.
4) Wastewater recycling for groundwater re-injection or indirect potable use is sometimes a difficult "sell" to American communities, although the combined market for water recycling systems in the U.S. has reached around $620 million. As a technology provider, where do you see the greatest growth and acceptance of wastewater reuse in the marketplace?
A. We see water reclamation and reuse opportunities around the world. The actual form of reuse will vary geographically, but the growth in demand for reclaimed water currently centered in Asia will probably spread as the application becomes more politically acceptable to western populations.
We anticipate that water reclamation and reuse will continue to grow, but so will desalination and alternative supplies for water. Siemens is currently involved with impressive R&D on improved desalination technology with PUB in our Singapore R&D headquarters.
Although desalination systems play an undeniable role in alleviating water needs in specific geographic regions, water reuse clearly is a preferred alternative in most communities. Reuse water is less expensive to treat and produces the same benefits as desalination, while reducing discharge to oceans and streams, providing an ecological benefit.
5) The multi-barrier treatment approach is favored over using reverse osmosis (RO) technology alone for water reuse treatment. For this reason, many manufacturers are offering a multi-barrier, integrated solution approach to the marketplace. What is your view on this?
Membrane bioreactor system tanks installed at the Beixaohe WWTP at the Beijing Olympic Park 2008.
A: Depending on the end-use of the reclaimed water, there are a wide range of technologies that will get communities to different grades of reclaimed water from irrigation to indirect potable reuse. Because RO can be the single largest capital and operating cost at a reuse plant, protecting that investment is paramount. By pretreating feedwater to RO, plants can reduce operating costs due to maintenance and energy costs.
As part of its ENR program, the city of Fruitland, Md., installed a filter as well as a sequencing batch reactor system with a control system designed to optimize biological nutrient removal.
Orange County Water District is a great example of a community that's leading the way with a multi-barrier treatment approach. OCWD, which is one of the largest reuse systems in North America, uses a combination of submerged membrane filtration as pretreatment to RO, followed by UV and hydrogen peroxide oxidation and disinfection. The water purification system provides 86 mgd of reclaimed water for agricultural, industrial and indirect potable use. The system is part of the OCWD Groundwater Replenishment project, treating secondary sewage that was previously discharged to the ocean and turning it into a new source of very high-quality water for the more than 2 million residents of Orange County.
Similarly, the West Basin Municipal Water District operates several reuse plants encompassing membrane filtration pretreatment followed by RO. The reuse water is applied for various non-potable applications including high-grade industrial process water requirements at hydrocarbon processing plants.
A further innovation is to use a membrane bioreactor (MBR) to combine the wastewater treatment and RO pretreatment steps. The MBR may also enable more flexible treatment of dissolved contaminants in the wastewater – for example more complete removal of the dissolved organic load. The Gippsland Water Factory in South Australia is an example of this process train with both municipal and industrial wastewater feeds.
6) In several areas of the country, the amount of workable farmland is shrinking. As a result, there aren't as many places to spread treated biosolids. What are some environmentally friendly alternatives to this practice?
A. Land-applied biosolids disposal and beneficial reuse continues to be a primary disposal mechanism in many areas of the U.S. and the world. However, the most populous centers of world civilization have growing limitations on available rural land area to make use of this mechanism.
Siemens has developed a wide range of solutions to improve biosolids management programs, especially for those applications that simply don't have enough land area for land-applied solutions. These solutions, such as the Cannibal solids reduction process, help communities reduce sludge. And our new, soon-to-be-released dewatering technologies, which have resulted from R&D investment, will significantly change plant operations costs, making sludge drying more economical.