This SBIR Phase I project will improve operation of deep-bed filter biological denitrification through a number of modifications to the current process. These include (i) Replacement of air usage with compressed Nitrogen gas for bump, scour, and airlift. (ii) Elimination of nuisance biological growth on weir walls by dosing carbon right over the filter bed using Venturi eductor principles. (iii) Inclusion of alkalinity buffering rock materials in bed media.

The broader/commercial impact of the project will be more efficient treatment of municipal wastewater in order to reduce total nitrogen concentrations entering the nation's waters. A secondary benefit is reduction in the use of methanol that is currently used as a carbon source in the filtration process.

Project Report

Loss of fish populations, green algae blooms and foul odors in and around water bodies are known to be caused by high levels of nitrogen and phosphorous. Under controlled conditions, these elements are a necessity for plant growth and human existence, but in excess, they can harm the environment. One of the primary sources of excess nitrogen and phosphorus in the environment comes from the processing facilities that treat sewer and other wastewaters. These facilities use a number of technologies to remove solids, dissolved materials, phosphorous and nitrogen from the wastewater and then release the water to the environment. One of the technologies often used to reduce the nitrogen to very low levels is call a "denitrifying sand filter". These filters use natural biological processes (i.e., microorganisms) to turn nitrate into nitrogen gas. These filters can be operated with the water flowing down through the sand or water flowing up through the sand. The nitrogen gas produced in the denitrification process enters the atmosphere and combines with the nitrogen gas already present in the air we breathe (air is almost 80% nitrogen). In order to remove the nitrate, a soluble organic (i.e., carbon-containing) compound must be added in small quantities to the filter to feed the microorganisms. Unfortunately, most wastewater treatment facilities have historically used methanol for this purpose because methanol is a compound with a simple chemical structure. Methanol is produced from natural gas, and is made almost exclusively outside the United States. There are operational challenges associated with using more complex chemicals due to the manner in which the microorganisms use the chemical for growth. The objective of this SBIR project was to investigate and develop operating strategies for denitrifying sand filters that would allow for the use of more complex, but also more environmentally friendly (i.e., non-flammable) and sustainable, materials such as sugars and glycerin derived from U.S. agricultural supplies. Compressed air is typically used to periodically clean the sand and thus maintain denitrifying filters in good working order. However, the microorganisms within these filters that convert nitrate to nitrogen gas (called "denitrifiers") also consume the dissolved oxygen in the water, and must consume the oxygen first before they can remove the nitrate. While necessary for filter cleaning, the introduction of air raises dissolved oxygen levels, thereby reducing the treatment ability of the filter. This is especially pronounced when feeding more complex molecules to the microorganisms for food (such as sugars and glycerin). A reduction in pH is also often observed when feeding these complex molecules, because of higher amounts of carbon dioxide production, which does not occur when feeding methanol. Lower filter pH is known to reduce the efficiency of nitrate transformation to nitrogen gas. Finally, for down-flow filter systems, the challenges associated with evenly distributing a chemical directly above the sand bed have led to a dosing method of adding the material to the water in the feed pipe leading to the filter. This method has led to nuisance biological growth on the influent walls of the filter, which can lead to operational problems that are again more pronounced when using more complex molecules compared to methanol. Hence modifications to denitrifying sand filter operations that would (1) lower oxygen addition; (2) allow for good pH control; and (3) reduce biological grown on influent walls, would be advantageous when more complex molecules derived from renewable (i.e., non-petroleum) sources are used as food for the denitrifying microorganisms. As such, this SBIR project investigated the replacement of air with compressed nitrogen gas for filter maintenance and also investigated whether filter performance could be stabilized or improved by adding a solid pH-control material to the sand. The final task of this project centered on using eductors to evenly distribute a chemical to the top of a fixed-bed down-flow filter. The work was conducted at the laboratory-scale using small columns measuring 3 inches in diameter containing approximately 3 feet of sand. The work clearly showed that denitrifying sand filters operated using nitrogen for filter maintenance were more efficient than those using air. It was difficult to quantify this, but it appeared that the effects, if any, were less pronounced, at lower nitrate loading conditions. The work also clearly showed that filter pH values can be stabilized at approximately a neutral pH value of 7.0 by the addition of a pH-control material. For more heavily loaded filters, this ability to maintain a more stable pH close to or above 7.0 should result in increased efficiency when using complex molecules as a food source for the microbes. Finally, the work showed that a nozzle and eductor system is effective in suctioning viscous materials such as glycerin. However, additional testing on nozzle configuration and placement is required.

Project Start
Project End
Budget Start
2010-07-01
Budget End
2010-12-31
Support Year
Fiscal Year
2010
Total Cost
$149,881
Indirect Cost
Name
Environmental Operating Solutions, Inc
Department
Type
DUNS #
City
Buzzards Bay
State
MA
Country
United States
Zip Code
02532