ALTERNATIVE WASTEWATER TREATMENT SYSTEMS

Alternative wastewater treatment systems serve as an option for the sewage treatment systems described previously. They may be required because one of the systems described earlier cannot be used or because they are too costly (e.g., the geological conditions are not suitable). These systems don’t use water to treat or transport human body wastes. If appropriately designed, they conserve water and avoid disposal of effluent and pollutants into waterways and the general environment.

Privy/Latrine

One of the oldest and most basic methods of waste disposal is the pit privy or latrine, a pit dug below an outhouse structure that collects human body wastes. Liquid wastes seep into the soil and percolate through the soil. Solid wastes remain and partially decompose so the pit becomes full over several years, depending on size and the number of users.

When the wastes in the pit reach a certain depth from the ground surface, the pit is cleaned out or the outhouse is moved to another location and the pit is covered with earth. Cleaning the pit is an unpleasant job and may result in exposure to fresh fecal material.

In long-term installations, a good arrangement is to plan for at least two pits. When the first pit is full, the outhouse structure is moved to the second pit and the first or is covered with earth and allowed to compost. When the second pit is full, the first pit is cleaned out and the slab and the outhouse structure aremoved back over the first pit. The second pit is covered and allowed to compost.

If soil conditions are suitable and no other system is available, a privy can be a safe method of waste disposal. It is, however, inconvenient for users and often produces offensive odors. Important considerations are that the pit be designed so it won’t pollute groundwater or permit access by insects or rodents. If wells or other supplies of water are nearby, there is a risk of contamination. As a result, a privy may not be an approved alternative waste treatment system. This system should only be used for the disposal of human body waste in extremely remote locations or in undeveloped areas. In some cases, how ever, health authorities in undeveloped countries allow such installations; as a result, it’s discussed.

Composting Toilets

A composting toilet is a self-contained waste treatment system that uses natural biological decomposition to convert toilet wastes into water vapor, carbon dioxide, and a stable compost like end product. It consists of a toilet seat and cover over a riser that connects to a compartment or vault that receives, holds, and converts human toilet wastes and other composting materials. It’s essentially an "in-house" outhouse. A venting system that extends up through the roof prevents sewer gases from entering the building.

The decomposition process in a composting toilet is achieved by aerobic (oxygen-using) bacteria and fungi. The complex population of microorganisms in the composting material makes conditions unfavorable for the growth of disease causing organisms that can be present in human waste. Pathogenic organisms die off or are consumed by the composting organisms as long as the composting process is proceeding normally and has adequate time to work.

To produce a thoroughly decomposed compost product, three conditions are necessary:

1. Microorganisms that decompose the waste need oxygen to flourish, so the process must remain aerobic. Aerobic conditions are sustained by mixing the pile and by con trolling moisture.

2. The compost must be maintained at the correct moisture content. If the compost becomes too dry, decomposition won’t occur. If the compost is too wet, it won’t remain aerobic and decomposition will cease. Humans excrete a much higher volume of liquid than solid each day. This excess liquid must be managed to ensure the composting waste does not become too wet. Excess liquid is managed either by evaporating it off using exhaust fans and heater units inside the compost chamber or by collecting it at the bottom of the unit where it must be disposed of in an acceptable manner.

3. Temperatures must be maintained above 60°F for composting to proceed effectively. At lower temperatures bacterial activity is inhibited and the composting process slows.

There are two types of composting toilets available for buildings.

IMG 10 A self-contained composting toilet.

Bi-Level Composting Toilet

Bi-level composting toilets are relatively large, two-story, watertight containers equipped with a chute that connects the toilet receptacle to the composting unit located in the basement. The bottom of the composting unit often has an inclined floor where solid wastes decompose and slide to the lower end as new waste enters at the upper end. Excess liquid is drained to the lowest part of the tank, where it’s either evaporated or collected and removed. Compared to self-contained composting toilets (described below), bi-level composting toilets have a large compost volume and long retention time.

Thus, the composting process is more stable than in smaller units, is better able to cope with peak loads, and can withstand intermittent or seasonal use. This type of composting toilet is similar to an in-house outhouse. In most units, a power vent removes excess gases and discharges them outdoors. Compost generally needs to be emptied every few years. The best known bi-level composting toilet is the Clivus Multrum.

(See IMG10.) Self-Contained Composting Toilet

The second type of composting toilet is a smaller unit in which the toilet receptacle and composting tank comprise a single self-contained unit located on the bathroom floor. These units have traditionally been installed for intermittent use such as in vacation homes. They are similar in design to a port-a-potty.

These units are marketed by BioLet USA, Inc. (the "BioLet"), Sun-Mar Corp. (the "Sun-Mar"), and SanCor Industries Ltd. (the "Envirolet").

Incinerating Toilet

Incinerating toilets are self-contained waterless systems that don’t require being hooked up to a sewer system or an in ground septic system (except to dispose of gray water). They rely on electric power or natural or propane gas to incinerate human waste to sterile clean ash. When properly installed, these systems are simple to use, safe, clean, and relatively easy to maintain.

These waterless systems look much like a standard house hold water closet. Between the gas and electric incinerating toilets, there are some mechanical and operational differences, but the overall treatment processes work the same. Both systems accept human waste, both solid and liquid, into a burn chamber. The burn chamber reaches temperatures of 970° to 1400°F (520° to 760°C) and reduces human waste into clean sterile ash.

Holding Tanks

Holding tanks are used for wastewater disposal when soil, slope, lot size, groundwater, or other features on the site render all other tank/drainage field solutions impossible to achieve.

They are used as a method of last resort in vacation homes or other short-term use facilities. Holding tanks are rarely used in facilities that generate wastewater on a daily basis.

Holding tanks are typically sized to hold seven days of wastewater flow. When the tank has been filled to within 75% of its capacity, a visual and audible alarm is automatically triggered, which alerts the user that the tank must be promptly pumped. Because holding tanks might have to be pumped on a regular basis, they can be costly to maintain.

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