Excess nitrogen and phosphorus runoff from farm fertilizers, sewage, and industrial pollutants can adversely affect plant and animal growth, as well as human development.  As a result, nutrient pollution has become of increasing concern in recent years, with government agencies, public utilities, private industries, equipment manufacturers, community leaders, and other stakeholders taking interest – and action.   
 
Nutrient removal from wastewater and nutrients’ effects on the ecosystem topped the issues discussed at the Water Environment Federation (WEF)’s first “Nutrient Removal” specialty conference in 2007, which was attended by more than 500 stakeholders.  During his keynote presentation, U.S. EPA Assistant Administrator for Water Benjamin H. Grumbles encouraged attendees to be watershed advocates, citing nutrient excess as the third largest cause of impairment in watersheds.  The “dead zone” in the Northern Gulf of Mexico is a prime example of nutrient-related impairment. 

A “dead zone,” or “hypoxia,” is an area where oxygen levels fall below 2 ppm.  The lack of oxygen suffocates almost all marine life.  Studies have shown that as little as 1 lb of phosphorus can cause 500 lbs of algae.  And algae, as it dies off, consumes oxygen.  In 2007, the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force measured the Northern Gulf of Mexico hypoxic zone at 7,900 sq mi, which is comparable in size to Massachusetts.  At times, the zone can extend up to 80 miles offshore and stretch from the mouth of the Mississippi River westward to Texas coastal waters.  Researchers forecast that this year, the Gulf of Mexico’s dead zone could extend more than 10,000 sq mi.  This is the second largest of at least 169 known hypoxic zones located around the world.
 
The Gulf’s dead zone is caused, in part, by excess nutrients that originate from productive farms and industries in Middle American cities.  It is also worsened by the stratification of the water column, which results from warmer, low salinity surface waters that isolate the organic-rich bottom waters from the surface and prevent oxygen exchange with the atmosphere.  In addition to helping identify sources of the nutrient loads flowing into the Gulf of Mexico, the Gulf Hypoxia Action Plan 2008 updates the critical needs, nitrogen load, and environmental progress in the major sub-basins including the Upper Mississippi, Missouri/Platte, Ohio/Tennessee, Arkansas/Red, and Lower Mississippi.  
   
Similarly, researchers at the University of Minnesota discovered in 2007 that nitrate levels in Lake Superior are slowly climbing.  The lake contains approximately 10% of the Earth’s fresh water supply.  Because the underlying causes for the increase are not fully understood, scientists cannot accurately predict when the water will become unhealthy to drink.  Nitrate levels in Lake Superior have increased about five-fold since the earliest measurements in 1906.  Too much nitrate can reduce oxygen levels in blood, putting infants, children, and adults with lung or cardiovascular disease at increased health risk. Long-term consumption of excess nitrates may also cause cancer.

The Chesapeake Bay Agreement

Since no new federal regulations on nutrient removal are being promulgated, some regions of the country have implemented their own nutrient discharge regulations to reduce the levels of nitrogen and phosphorus discharged from wastewater treatment facilities (WWTFs).  For instance, under the 1983 Chesapeake Bay Agreement, Maryland, Virginia, Pennsylvania, and the District of Columbia successfully reduced their nitrogen and phosphorus loads from point sources at 66 targeted treatment plants by 16.9 million lb/yr (or 52%) and 1.7 million lb/yr (or 63%), respectively, compared to 1985 levels.  Through the Chesapeake Bay Initiative and the 2000 Chesapeake Bay Agreement, proposed legislation will require all new treatment facilities and other existing point source dischargers in these states and district to comply with even stricter nutrient removal levels by 2010.

Most of the treatment facilities in these areas have already installed biological nutrient removal (BNR) technologies, to help reduce nutrient pollution.  Some, like the Aberdeen (Md.) Proving Grounds WWTP on the western shore of the Chesapeake Bay, have even used more advanced wastewater technologies, commonly referred to as enhanced nutrient removal (ENR).  These ENR technologies can reduce total nitrogen (TN) down to 3 mg/L or less and total phosphorus (TP) to 0.3 mg/L or less.  Aberdeen’s ENR technology choice for its 1-MGD plant consists of a continuous backwash filter that has reduced its TN discharge from 7 mg/L to 3 mg/L.  Aberdeen is one of the most diverse testing facilities of the U.S. Department of Defense. 

Likewise, the King George County WWTP in Dahlgren, Va., needed to optimize its TN and TP removal to meet annual nutrient poundage caps allocated to “significant discharger” WWTPs by the Chesapeake Bay nutrient regulations.  The plant is currently treating 0.25 MGD but is designed for 1 MGD.  Its nutrient discharge poundage allocation translates to 12 mg/L TN and 0.3 mg/L TP in the plant effluent at current flow.  In 2007, Siemens helped create a BNR process optimization program for the Dahlgren plant that, after only one month, had reduced effluent TN from 12 mg/L to less than 4 mg/L.  Advanced controls resulted in improved process performance and greatly reduced operating costs.  In fact, power usage for aeration was reduced by about a quarter, and chemical costs for phosphorus precipitation and supplemental alkalinity were cut in half. 

The Hampton Roads Sanitation District’s existing 25,000 GPD extended aeration plant in Virginia Beach, Va., was only used to collect wastewater, with hauling costs of approximately $1,500 daily ($550,000 annually).  A new residential development required the King William plant to quadruple its capacity to 100,000 GPD – in only nine months’ time!  And, as the plant discharges into the Chesapeake Bay, it had to adhere to stringent nitrogen (3.0 mg/L) and phosphorus (0.3 mg/L) removal limits.  The plant installed two Siemens membrane bioreactor packaged systems, each rated for 50,000 GPD.  The custom-designed systems include a five-stage biological process that meets the demands of low loading and flow.  Low loading is a serious process issue when there are very low TN requirements as there are in the Chesapeake Bay area.   The plant started by using a conventional anoxic/aerobic/anoxic combination.  Later, when flow and loading are closer to design, the process will switch to simultaneous nitrification and denitrification using an aerated anoxic process to reduce overall process energy requirements.  
 
Other Plans and Initiatives

In addition to working with the Chesapeake Bay region, the U.S. EPA is working with each state to develop water quality criteria and implement pollution control practices to reduce the amount and impact of nutrients and sediments in the nation’s waters.  In 2006, the agency issued the National Stream Report that surveyed the biological condition of small streams throughout the U.S.  It will be used for future monitoring of streams.  Similar reports will be issued for coastal waters, lakes, large rivers and wetlands.
 
Additionally, the EPA has created a national nutrient criteria strategy that will require states to adopt numeric nutrient standards.  As a result, many U.S. utilities will need to achieve effluent nitrogen and phosphorus concentrations that challenge current technical capabilities.  To address these and similar issues, earlier this year the Water Environment Research Foundation (WERF) formed a team for its comprehensive five-year nutrient removal program.  More than 30 wastewater utilities, universities, consultants, and water organizations in the U.S and abroad have expressed interest in participating, with many more expected to join this WERF-led initiative.   

As part of this challenge, WERF intends to develop the science, application tools and practices associated with such issues as nutrient characterization and bio-availability in aquatic environments; selection of sustainable, cost-effective processes to meet nutrient limits in WWTFs; and demonstration of new nutrient removal technologies and practices as well as improvements to existing ones.  One of the goals of this initiative is to reduce capital, operating, and maintenance costs for nutrient removal at WWTFs by at least 10%.

Research projects identified as top-priority include refractory dissolved organic carbon, carbon augmentation alternative sources, and phosphorus speciation and particle characterization.  The stakeholders will be able to impart their experience and knowledge, share data and reports from experiences, and contribute funding through WERF’s targeted collaborative research program. 

Conclusion

Nutrient removal is one of the most pressing water quality challenges currently facing many utilities, not just in North America but all over the world.  The various stakeholders on this issue, such as regulators, industrial dischargers, environmentalists, and water and wastewater utilities must work together to do a better job of reducing nutrients.  Several special interest associations, government agencies, and technology manufacturers have already stepped up to the challenge. 

Advanced wastewater technologies, such as ENR, can help utilities meet increasingly stringent nitrogen and phosphorus discharge limits.  These advanced ENR technologies can be more economical to operate and can easily adapt to existing facilities.  Perhaps more importantly, such technologies also make significant progress toward restoring and protecting our waterways to protect public health and aquatic life. 

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