| 
|
The National Community Decentralized Wastewater Demonstration Project, an innovative demonstration project to protect groundwater, is nearing the final report phase. If successful, the demonstration project could have national implications for preventing groundwater contamination from septic systems. This project, which was approved during the Clinton administration, funded studies in Vermont; Rhode Island; and La Pine, Deschutes County, OR.
 |
| Components of the Puraflo system. |
The Oregon Department of Environmental Quality (DEQ), in partnership with Deschutes County, hoped the demonstration project would reduce nitrates from septic systems and pollution to the shallow aquifer common to the area around La Pine. In addition to field-testing the performance of various technologies for removing nitrates from septic systems, DEQ wanted to increase groundwater monitoring and modeling in the La Pine area. The modeling's task: to answer whether or not predicted groundwater contamination in La Pine would adversely affect the Deschutes and Little Deschutes rivers.
Deschutes County's community-based Regional Problem Solving Study, and a DEQ study, first recognized the problems that could be caused by a projected high population density in La Pine. The study found nitrate contamination from septic systems already occurring; preliminary predictions, based on computer modeling, indicated nitrate concentration in groundwater could exceed safe drinking water levels (10 mg/l) in 10 to 15 years. Nitrate levels higher than 10 mg/l may represent a serious health concern for infants, pregnant or nursing women, and the elderly.
"The issue of removing nitrogen came up because Deschutes County's drinking water aquifer has a shallow, very oxygenated water table, which could easily be polluted by nitrates," says project coordinator Barbara Rich. "The nitrate, NO2, is oxygenated, which means it stays and accumulates in water, and it can then move through the water table throughout the region. As there's not a lot of organic material in our soil, it drains quickly. Excess nitrogen in water can feed algae growth, and drinking water shouldn't contain high levels of nitrogen."
 |
| Backfilling the Biokreisel Rotating Biological Contractor Installation. |
 |
| Bio-Microbic's FAST wastewater treatment system. |
Although nitrogen can enter the environment from fertilizers and animal feedlots, Deschutes County's concern was residential sewage. "In our relatively rural area, residents all have septic tanks," she explains. "There are approximately 15,000 platted lots here, 5,000 to 8,000 of which are developed. Some lots have water tables two feet or less below the surface. In many areas, homeowners let their grounds remain natural, with no big lawns, so restricting nitrogen fertilizer has not been our focus. Oregon's Department of Environmental Quality did a series of monitoring/sampling events in this area, and found 'hot spots' developing. The problem was, the systems in use were not designed to remove nitrates. So, beginning in 1999, in a joint effort between the county and the state, we studied several kinds of systems to see how they took nitrates out."
The project also enjoyed federal support; USEPA funded the project, and the US Geological Survey (USGS) performed some of the work. "The county was the subcontractor for DEQ; they got proposals from different companies who designed treatment systems. Each vendor chosen then hired the installers for their sites," Rich explains. "In this small field-test program, 49 properties participated, which were chosen through an application process. Those residents chosen for the project received a new septic system." Construction for the project ranged over several seasons; groundbreaking started in late 2000, with all test sites completed by mid-2002.
"Although we weren't able to get a lot of pre-project data, water samples from each of the 49 properties, and from surrounding properties, were taken before construction began, to measure if the groundwater was affected by nitrates," Rich goes on. "Educating the homeowners was an important component. We encouraged vendors to work with homeowners, to explain the 'dos and don'ts'of the new systems. Most of these systems can handle normal use, but homeowners were cautioned to not dump a lot of grease down the drain—but that's normal for any septic system. As for enzymes or additives, most vendors do NOT want those additives put into the septic system—some can actually be harmful."
 |
| Advantex AX-20 filter installation. |
Each system was allowed to operate one or two months before water monitoring commenced to allow the systems to flush out any debris. "Ideally, there shouldn't be construction debris in the septic system, because that would effect the quality of treatment. If there's lots of sand in the area, that could clog up the drain." After that period, the systems were tested monthly for the first year. "Then, it varied; some were tested quarterly, or every other month, for the next two years. Monitoring stopped December 2004; we're working on our final report now," Rich says.
Homeowner comments will be included in the report. "During the selection process, we surveyed residents to learn about their lifestyles, and to encourage feedback about the systems installed," Rich continues. No matter which system the home received, it had the usual alarms—high water alarms, etc. If the process was having trouble, we'd hear about it when we came out to test. Homeowners were pretty up front about any problems they experienced."
Not every system was alike. "Differences varied situation to situation and system to system; units were selected by the location, physical constraints of the property, or the environmental needs of the area. Some systems offered just good sand filter replacements; for example, some used fabric, foam cubes, peat—so, when our data is compiled, we'll have good information for those who use sand filters. As for removing nitrogen, the preliminary results ranged from 30% to 95% removal," says Rich.
Controls and Creative Processes
 |
 |
 |
| The Nitrex filter is under continual development at Lombardo Assoc. and a second-generation system is being developed to reduce total N levels to below 1 ppm. |
Of the 49 sites installed, nine were control systems to be used as a basis of comparison. Control systems, which included standard tank and dispersal fields, pressurized distribution, and sand filters, were sampled at the same rate and schedule as the denitrifying systems.
Forty sites received denitrifying systems or designs, which included
- AdvanTex RX-30, a recirculating textile filter with a shallow gravel-less trench for the soil absorption field.
- AdvanTex AX-20 system in Mode 3, a recirculating trickling filter system that uses textile sheets in a pre-fabricated and pre-packed container. Both systems are produced by Orenco Systems Inc. (www.orenco.com), located in Sutherlin, OR.
-
Amphidrome system, a sequencing batch reactor for residential use, produced by FR Mahony and Assoc. Inc., of Rockland, MA (www.frmahony.com).
-
Biokreisel Rotating Biological Contractor, a bowl-shaped unit that encloses a rotating screen. The unit provides aeration, recirculation, and discharge, and is manufactured by Nordbeton North America Inc., of Lake Monroe, FL (www.nordbeton.com).
-
DYNO2 System is a vertical flow wetland in a concrete container produced by Reactor Dynamics Inc. of Forest Lake, MN (www.reactordynamics.com).
-
EnviroServer 600, manufactured by MicroSepTec Inc. of Laguna Hills, CA (www.microseptec.com), is a pre-engineered, pre-assembled single fiberglass tank system. The tank is divided into five chambers: a primary settling tank, two chambers that allow aerobic digestion of waste, a clarifier where final settling of suspended solids and clarification of the effluent takes place, and an effluent storage compartment. If desired, or required, ultraviolet light can be introduced at this point, for disinfection of the water prior to surface or sub-surface discharge.
-
FAST (Fixed Activated Sludge Treatment) Wastewater Treatment System from Bio-Microbics Inc. (www.biomicrobics.com) of Shawnee, KS, in which naturally occurring bacteria break down organic materials in the wastewater into simple byproducts like water and carbon dioxide. The unit employs a settling chamber and an aeration unit in its operation; air continuously pumped into the unit ensures the bacteria have access to enough oxygen and food. The system operates in both an attached and suspended growth fashion.
-
IDEA BESTEP, from Advanced Environmental Systems Inc. of Sparks, NV (www.aeswastewater.com), is a sequencing batch reactor contained within a single tank with the AES equipment installed in it.
-
Three innovative trench designs were designed by Wert and Associates of Bend, OR, to promote denitrification.
-
The Nayadic system, a forced-aeration treatment process in a housing based on an Imhoff cone design, was produced by Consolidated Treatment Systems Inc. of Franklin, OH (www.consolidatedtreatment.com).
-
The NiteLess System, created by On Site Wastewater Management LLC, of Cherry Hill, NJ (www.oswm.com), is a denitrifying process installed in a custom-built concrete tank. A nonrecirculating forced aeration process that adds carbon to promote denitrification.
PHOTO: MVC-006F.JPG
CAPTION: Components of the Puraflo System.
. Puraflo System, created by Bord na Mona of Greensboro, NC, (www.bnm-us.com) is a trickling filter system that uses peat in a pre-fabricated and pre-packed container.
The Nitrex Procedure
Along with 16 other technologies, the La Pine Project evaluated two Nitrex Filters. Based on more than a decade of research, this proprietary patented nitrate-reactive media converts nitrate to inert nitrogen gas (denitrification). The Nitrex reactive media—developed by Lombardo Associates Inc. (www.lombardoassociates.com) in Newton, MA—can be contained in a prefabricated tank or, for larger installations, in an engineered excavation. Gravity feeds the nitrate-contaminated wastewater through the treatment module.
For septic tank applications, an oxidative pre-treatment step (achieved with any of the existing oxidative technologies commonly used in wastewater treatment) is required to convert ammonium (NH4+) to nitrate (NO3-) before the Nitrex filter can perform the reductive denitrification step. The nitrate-free effluent from the Nitrex filter is then discharged to a conventional tile bed or receiving water body. Compared to other technologies, the Nitrex filter is passive and essentially maintenance-free, while providing almost 100% nitrate removal in a low cost, easy-to-install process. For a typical residential septic system installation (three- or four-bedroom home) the Nitrex filter will cost approximately $3,000 (plus shipping and local installation costs). For wastewater flows exceeding 2,500 gpd, a lined excavation Nitrex filter application will cost approximately $4 to $10 gpd, but no additional ongoing operational or maintenance costs are necessary.
The Nitrex filter is the only known treatment technology to provide virtually complete single-pass nitrate removal (97%+) to produce an effluent quality that meets new stringent surface water discharge criteria for ammonium and nitrate. Overall average removal rates of 97%+ for nitrate (NO3 - ) have been attained, achieving nitrate effluent quality of 0.1 mg/l, when water temperatures are above 48°F. As the reactive media is eventually consumed, the Nitrex filter typically must be replaced within 15 to 20 years.
For the La Pine National Decentralized Wastewater Demonstration Project, the Nitrex filter was chosen to be evaluated on its capability to protect groundwater from the impacts of an onsite septic system. In one single family residence, the Design Wastewater Flow was 132 gpd and the Wastewater Treatment Process flowed through a septic tank, an ISF, and a Nitrex filter, providing almost complete (94.3% average) removal of nitrate from the sand filter effluent over the three years it's been in operation.
JANIS KEATING is a frequent contributor to Forester Communications
publications.
OW
- September/October 2005
|
