The Salcor Model 3G ultraviolet disinfection unit (patents issued and pending) was specifically designed for disinfecting the effluent from small aerobic treatment plants. It is able to reduce fecal coliform bacteria levels well below the most stringent US treatment standards, even when the upstream treatment plant is operating in a mild upset condition.

Most small aerobic treatment plants are installed so that their discharge piping is below grade. The 3G disinfection chamber directly couples to the aerobic plant discharge pipe and is permanently installed below grade.


Figure 1 (above) shows the 3G unit design, which is made up of several sub-assemblies housed in a disinfection chamber. The chamber is made of UV resistant plastic and is permanently installed below grade.

The ultraviolet light source for disinfection is mounted in a sub-assembly which can be inserted or removed through the top of the riser pipe for periodic servicing. The light source is mounted in the center of an anodized aluminum frame which divides the disinfection chamber in half. The frame seals against the inner surface of the disinfection chamber to prevent flow bypass.

When fully inserted, the disinfection sub-assembly is properly located by two pins mounted near the top of the disinfection chamber. It causes the wastewater entering one side of the unit to flow vertically downward, to make a 180 degree turn, and then to flow vertically upward and out the other side of the unit. This well-defined flow path is designed to give the proper fluid exposure time and no short circuiting.
Figure 2 of Salcor Ultraviolet Disinfection Unit The ultraviolet light source is surrounded by a clear fused quartz tube to control lamp surface temperature. A clear Teflon film covers the quartz tube to minimize surface fouling. This design feature incorporates the beneficial attributes of both quartz and Teflon.

When the disinfection chamber is filled with water, the ultraviolet light source can operate continuously, whether or not water is flowing. Continuous operation within a lamp surface temperature range of 105°-120° Fahrenheit provides optimum ultraviolet light output and long lamp lifetime. The Model 3G alarm relay circuit triggers an external alarm to warn the user when the UV lamp is not properly operating. Electronic components in the circuit sense changes in the UV lamp which correlate with the germicidal ultraviolet output. A normally closed relay actuates electrical current in an alarm circuit upon failure, or incipient failure of the UV lamp.

The alarm relay circuit has been designed to be compatible with a wide variety of alarms used on upstream aerobic treatment plants, and is capable of operation in the normally closed or normally open modes. The disinfection sub-assembly is water tight throughout its length, which extends above grade. This protects the electrical connections against a fluid backup which could cause the wastewater effluent level to rise to the maximum height of the upstream treatment plant.

Electrical components form another sub-assembly. A NEMA 4X electrical junction box houses the alarm board, and terminal blocks for electrical connections. The ballast and lamp power cable are pre-connected. A green LED indicator, located on the outside of the electrical junction box, glows when the UV lamp is producing ultraviolet germicidal light at a safe level. It ceases to glow when the light output falls below a safe level.

Installation & Operation

The 3G unit operates on 120 volt AC power (50 or 60 hertz). It draws 0.25 amps and consumes 30 watts. The unit is easily installed (usually in less than 30 minutes) and operates with minimum attention. Because of the anti-fouling properties of Teflon, periodic cleaning is virtually eliminated. Annual inspection and cleaning is recommended and the UV lamp is replaced every two years. Electrical energy use is 0.7 kilowatt – hour per day.



Maximum flow through the unit is rated at 3 gpm (4320gpd) with the following effluent conditions:
    Suspended Solids – less than 30 mg/liter.
    BOD (5 days) – less than 30 mg/liter.

If suspended solids and BOD are each less than 10 mg/liter, maximum flow rating is increased to 6gpm (8640gpd). Under the above conditions, the fecal coliform reduction by the Salcor 3G unit exceeds 3-logs, or 99.9%, at the end of UV lamp life (two years of continuous operation).

Aerobic treatment plants for individual homes are typically sized for 400-1500 gpd. They are designed to produce effluent of the following quality:
    Suspended Solids – less than 10 mg/liter.
    BOD (5 days) – less than 10 mg/liter.

Fecal coliform counts in the home aerobic treatment effluent typically range from 2000 – 80,000 per 100 ml. The Model 3G ultraviolet unit is well over designed to disinfect the effluent from home aerobic treatment units. There are no adverse effects from over exposing the effluent to germicidal ultraviolet light, because ultraviolet disinfection does not form byproducts in contrast to chlorination and other chemical disinfection methods.

Third Party Testing Validation:
Sixteen modified NSF Standard 40 tests have been initiated with combinations of aerobic treatment units plus 3G UV units. These tests are necessary to meet Washington State 2007 regulations. Each test is six months long and data include fecal coliform reduction in addition to the usual items. Seven of the tests have been successfully completed and the other nine are in progress. Other third party tests include:

  • University of Rhode Island – 6 years, annual maintenance, lamp change every two years, geometric mean fecal coliform count44 per 100 ml.
  • NSF, Waco TX – 6 months, no maintenance, geometric mean fecal coliform count much less than Washington state standard at 200 per 100 ml.
  • Orenco, Sutherlin OR – 6 months, no maintenance, geometric mean fecal coliform count under 5 per 100 ml.
  • Poway, CA – 10 months, no maintenance, geometric mean fecal coliform count less than 10 per 100 ml.


The Salcor 3G ultraviolet unit is easily installed (usually in less than 30 minutes) and operates unattended. In contrast to chlorination, the UV unit does not cause byproduct formation.
Because of the anti-fouling properties of Teflon, periodic cleaning is virtually eliminated. Annual service is required for UV lamp replacement.

Costs & Delivery

Suggested retail price for the Salcor Model 3G is $900.00 F.O.B. Fallbrook, California. Please contact our office for the most current tradesman pricing. Units are stocked at the factory and can usually be shipped within one week after an order is received.

Cluster/Multiple Residence Potential

Several Model 3G units may be connected in series and/or parallel to achieve a higher flow capacity. Salcor, Inc. also manufactures larger wastewater disinfection units with capacities up to 16 million gpd.


The Model 3G was introduced to the Salcor product line in the spring of 1997. To date over 10,000 units have been installed throughout the United States and Canada.