From The Septic System Owner's Manual
What’s New In This Edition of the Book?
Following are some of the components and systems not covered in the first edition of this book six years ago. For one thing, new technology at the septic tank end of the system has proven to dramatically reduce solids loading on the drainfield, helping maintain healthy conditions in the soil. Aerobic treatment units, which can reduce the BOD (biological oxygen demand) in the septic tank effluent by over 90 percent, greatly reduce the load on the soil of the drainfield. Following are just a few advanced systems.
Cleaning up effluent: These are excellent for communities on bays, lakes, or rivers who are facing septic system upgrade requirements. Trickling biofilters are used in place of sand filters (and are much smaller) and are especially effective in nitrogen removal. They work by dripping effluent over a medium, which constitutes a large surface area where bacteria digest and purify wastes.
Maintenance must be performed regularly with these units, and many health departments require that a homeowner have a maintenance contract with a qualified inspection service. We list four different systems below. There are many other makes of trickling biofilters.
Advantex® Treatment System
The Advantex® System features a small (7 1/2' x 3' x 2 1/2') fiberglass basin (it is small enough to fit under a deck) filled with a highly absorbent textile material that receives effluent from the septic tank. Bacteria on the geotextile fabric digest solids and produce a clear, odorless effluent that exceeds Secondary Treatment Standards. It can be monitored via telemetry by a remote monitoring system that will alert the homeowner to problems. It is produced by Orenco of Oregon.
Aerocell Treatment System
This system consists of several modular units that are configured according to specific site requirements, typically 4 to 6 modules for a 3- to 4-bedroom house, respectively. Effluent is sprayed over the surface of open-cell foam media and collected in the bottom of the modules for return to the septic tank for denitrification. The units are lightweight and can be moved by one person. Modular systems such as this offer flexibility of installation. Maintenance consists of regular inspection and cleaning of the spray nozzle, control panel, and pumps.
Puraflo® Peat Biofilter
The Puraflo® is a modular pre-engineered biofiltration system that uses natural peat fiber as a biofiltering media. Primarily used in a single-pass mode, the processes occurring are filtration, absorption, adsorption, ion exchange, and microbial assimilation. The system significantly reduces biological oxygen demand (BOD) and total suspended solids. Ammonia and pathogens are reduced. These systems can be used in critical resource areas and used with shallow pressurized drainfields.
This system was developed in Ontario for treatment of domestic wastewater and has been used for wastewater treatment at small towns, resorts, and food processing facilities. It has been used in cold climates and on sites where water is reused onsite. The medium used is a lightweight open-cell foam which has a high surface area and is resistant to clogging. Settled wastewater is sprayed on the surface of the biofilter. The Waterloo® unit can be placed above or below ground according to site conditions and can be used in single-pass or multi-pass modes.
These systems include pump vaults that filter and physically trap solids, either from a septic tank or a dosing tank, before they get to the disposal field. Water inside the septic tank (or pump vault) must pass through a screen before entering the disposal field. Screens come in a variety of mesh sizes. This is an inexpensive way to significantly improve effluent quality and thereby decrease solids accumulation in drainfields. (For drawings of two types of filters, both inside septic tanks, see p. 9.) Maintenance is important, since solids accumulate on the filtering screen and will eventually block it. Alarms can be installed to alert the homeowner when water level in the septic tank is rising and that the filter therefore needs cleaning. The filters are placed either within the tank or in a separate tank (pump vault).
This unit is manufactured by Orenco Systems, Inc. It is designed to be used in both new systems and retrofit applications and comes with filters with various size openings, and in diameters of 4, 8, 12, and 15 inches. See:
See p. 175.
Zabel Effluent Filters
Bio-Kinetic Effluent Filters
These go in a pump vault adjacent to the septic tank. They equalize flow and are rated for flow rates of up to 2,000 gallons per day.
Drip Irrigation Systems
Recycling water for the garden: Properly designed, drip irrigation systems are the most environmentally friendly drainfields, minimizing site impact and reusing water. Drip dispersal is useful in a number of soil conditions as it discharges into the shallow horizons where there is good percolative capacity, root uptake of water and nitrogen, more microbes, and high soil content. Treated and filtered wastewater is distributed directly into the soil slowly and uniformly from a network of narrow pipes. Wastewater is pumped through the drip lines under pressure and drips slowly from evenly spaced “emitters.” There is minimal site disturbance due to the flexible tubing that can be placed around trees and shrubs. Drip systems must be carefully designed to follow the contours of the site as well as to avoid problems with drainback and freezing in the wintertime.
It’s very important that the effluent be clean to avoid clogging of the emitter orifices. Some drip systems are designed for use with screened septic tank effluent. Wastewater is collected in a sump and pumped through the drip tubing. Anti-siphon valves are placed at high points in the drip irrigation network to prevent backflow of soil particles into the emitters. A recent improvement in drip systems is recirculating the drip lines back through the system, which helps avoid clogging. For obtaining the National Small Flows Clearinghouse paper (#SFPLNL16) “Spray and Drip Irrigation for Wastewater Reuse and Disposal,” see:
Following are a few drip irrigation systems:
Geoflow, Inc., is a large manufacturer of drip irrigation systems. Their drip systems include large orifices to prevent clogging. They also utilize what they call Root Guard technology, which releases an herbicide called Treflan® into the soil immediately surrounding the drip emitter to prevent root growth from entering the emitter. You certainly wouldn’t want such a system near vegetables. The idea of using an herbicide in your garden seems questionable.
This drip irrigation system has pressure-compensating emitters and a self-flushing feature to minimize clogging.
These designs utilize Bioline (see above) and automatic backwashing disk filters.
Shallow Leachfield Systems
It is estimated that there are now over 750,000 shallow drainfields in North America, with more being installed each year. They can be installed with a shovel, requiring no heavy equipment, and there is no gravel. Most important, effluent is distributed in the top 16 inches of soil, where over 98% of soil life exists; very real purification takes place in this environment, as opposed to 23 feet down in a typical gravel-filled drainfield. In addition to the very popular Infiltrator® shallow drainfield chambers (see p. 23), here are other manufacturers of chamber systems or pipe intended for shallow drainfields:
Cultec Contactor and Recharger
A variety of leaching chamber sizes
Corrugated 12" diameter drainage pipe wrapped with polypropylene mat and fabric.
Chamber systems and corrugated drainage pipe wrapped with filter fabric.
Restoring Failed Drainfields
If your drainfield has failed, or is showing signs of failure, first read pages 5861, where partially failed and completely failed drainfields are described. Also, a helpful paper on the subject is “Drainfield Rehabilitation,” the Winter 2005, Vol. 16, No. 1 issue of Pipeline from National Environmental Services Center:
Following are two systems for drainfield rehabilitation that we have discovered since the first edition of this book:
The Pirana/Sludgehammer System
This consists of an “aerobic bacteria generation system,” a unit mounted on the bottom of the tank near the inlet, and a 40-watt air pump at the top of the tank that aerates septic effluent. A special blend of microbes is introduced into the system which helps digest wastes in the tank. The microbes also travel into the drainfield, where they are said to digest the biomat and provide for freer distribution of effluent in the soil. Tests of the system at the University of California at Davis and approvals for remediation use by the Massachusetts Department of Environmental Protection show the Pirana’s ability to rejuvenate otherwise failed drainfields. See:
White Knight Microbial Innoculator/Generator
This unit consists of a high-density polyethylene cylinder, which is installed within the septic tank, continuously inoculating the tank with non-pathogenic bacterial cultures. An air pump provides fine bubble aeration and circulation within the system, bringing the bacteria into contact with fixed film substrate and suspended organic compounds in the tank. The bacteria digest organic wastes in the septic tank and in the drainfield.
Wetlands provide a low-cost method of purifying effluent. They are typically used by municipalities, but there are a growing number of small scale wetlands being used for individual homes, providing final treatment of effluent where subsurface disposal methods cannot be used. The town of Arcata, California utilizes a freshwater wetlands marsh to treat the town’s wastewater, and it is often studied and referred to as a working example of ecologically sensitive wastewater treatment.
Different Wetlands Designs
There are two basic types of wetlands design:
- Free-water surface wetlands. These are shallow, open ponds with plants (such as cattails) rooted in the pond bottom and a free water surface open to the air.
- Subsurface flow wetlands. These are shallow beds filled with gravel or sand in which plants are rooted. The top layer is earth, and water flows through the gravel or sand media several inches below the surface. You can walk on these.
Note: Transporting effluent directly from the septic tank to free-water surface ponds seems risky, since insects and animals have access and could transmit pathogens. A subsurface-type setup would seem safer. Free-water surface wetlands are generally not allowed for single family homes.
How Do They Work?
Effluent is piped from the septic tank into a man-made marsh rather than a drainfield. The marsh is sometimes lined with plastic or concrete. Water flows into another perforated pipe at the other end of the marsh and into an outlet tank, where a pipe controls the flow and keeps the effluent from surfacing in the marsh. Overflow from the tank goes through another pipe to a small pond where the water is “polished” by algae before evaporating or soaking into the ground (or being transported to a drainfield).
In cold climates, the reeds growing in the marsh die back in the winter. They form a thick blanket which insulates the marsh so that the roots continue to grow all year.
Purification by Plants
One interesting quality of wetlands is the ability of plants to assist in the cleanup of pollutants. Although the plants themselves take up very few of the pollutants, they provide oxygen to the bacteria aerobic microbes that grow on root surfaces that do most of the work. Anaerobic bacteria, which don’t require oxygen, then finish the job. For example, dangerous nitrites are converted into nitrate, which is essentially plant fertilizer. It is also said that wetlands can clean up many hazardous chemicals that would not be filtered out in a regular septic system. For case examples of small community wetlands construction, see Natural Systems International at http://www.natsys-inc.com/. For an article on home-sized wetlands titled: “Build Your Own Constructed Wetland” from the National Small Flows Journal, see:
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