According to the U.S. EPA 2002 Onsite Wastewater Treatment Systems Manual, approximately 26 million homes, businesses and recreational facilities in the United States use onsite wastewater treatment and disposal systems (OWTD) (also called septic systems). Numerous studies have found correlations between OWTDs and elevated NO₃ levels in drinking water. The U.S. EPA has reported that nitrates (NO₃) were the contaminant that most frequently exceeded federal drinking water standards among organic and inorganic contaminants in public water systems (USEPA, 2005).

 

Conventional septic tanks remove only 1-3 percent of total nitrogen (N) before effluent is released into the environment. Almost all current N removal technologies on the market rely on organic compound digestion as a precursor to N removal. The current technologies rely on long hydraulic retention times, hydraulic circulation, and the high amounts of aeration for any N removal through nitrification and denitrification. These pre-packaged systems generally entail a treatment train of multiple tanks coupled with recirculation pumps, aerators or large amounts of treatment media. There is a large potential market for cost effective N removal system that the typical household could afford. Current technologies have been limited by high costs due to the required installation of new and multiple tanks. Several states are currently mandating the N removal technologies be utilized in new septic systems in certain areas.

 

Enviro Utilities, Inc. (EU) a wastewater treatment system design company has collaborated with Ion Power, Inc., which specializes in ion selective membranes and electro-chemical technologies to design a unique device to remove N from within existing septic tanks. The device uses a combination of electrolytic chemistry, chemical species separation and biological transformations.

 

The Innovation:  An Insertable Electrolytic Nitrogen Removal Device

 

The innovation of the EU device is that it is small enough to be inserted into existing septic tanks and remove N from wastewater without the need for organic compound digestion. Almost all current treatment technologies on the market rely on organic compound digestion as a precursor of N removal. Nitrogen removal in the EU system is conducted by isolating ammonium (NH₄⁺) from the waste stream into a compact nitrifying through a cation selective membrane and electrode system. The N is ultimately converted to dinitrogen gas (N₂) and released to the atmosphere. All of these processes will occur within the existing septic tank.

 

Project Objective 1:  Test Device Configuration

 

One key to the success of the device is that it is small enough to fit into an existing septic tank. For that purpose, several configurations of the anode, membrane and cathode placement and size of the device will be evaluated. Several unknown design questions will be addressed in bench scale reactors.

 

Project Objective 2:  Measure the N Removal Efficiency and the Microbial Environment

Several configurations will be tested for their ability to isolate NH₄⁺ and remove N from a synthetic domestic wastewater system. The N removal efficiency will be determined by direct measurements of the reactor influent and effluent NH₄⁺ and NO₃ concentrations. Denitrification efficiency will also be directly measured. The water chemistry within the device and its effects on the nitrosomonas nitrifying microbial population will be evaluated. Water chemistry parameters within the reactors to be evaluated include: alkalinity, carbon dioxide (CO₂) content and oxygen (O₂) content.

 

Commercial Application

 

This technology would create a new class on onsite wastewater pretreatment units that benefit rural development. Current technology focuses on organic compound digestion prior to N removal through extended aeration or fixed film digestion. These existing technologies usually require the installation of new multiple tanks and pumps at major costs and disruptions for the typical homeowner. The EU system can upgrade existing conventional septic tanks with an N removal component. An affordable insert the may remove 70-80 percent or more of the N in conventional septic systems should gain the interest of environmental health officials and environmentalists worldwide. Some states are now mandating N removal in certain septic systems creating a market demand. The high cost of existing technologies has limited the use of N removal systems in rural developments. This consequently has degraded drinking and surface water quality. The cost saving created by eliminating organic digestion would create affordability for the typical owner of a standard septic tank. Successful configurations of the EU system evaluated in Phase I can be developed into full scale prototypes for Phase II testing.

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