Soil Bed Reactor

The term SBR was originally coined circa 1990 by Dr. Heinrich Bohn at the University of Arizona in his research supporting Biosphere 2. The research involved the scrubbing of trace atmospheric organic contaminants using biological "reactors", consisting of a living soil to support plants. In Bohn's original conceptualization, air is moved through the soil where contaminants are either

  • passively adsorbed onto the surface of soil particles,
  • chemically transformed in the soil to usable compounds that are taken up by the plants or microbes, or the
  • compounds are directly used by the microbes as a metabolic energy source and converted to CO2 and water. 

In practice, transport of contaminants is not just carried out via air movement through the soil, but also by water movement. In fact, this is predominant mechanism (perhaps contrary to the conceptualization of Dr. Bohn), so at CELSS, the term SBR has been widened to apply to both aerobic and anaerobic applications and is used on this site in the generic sense of the soil layers of an ecosystem where chemical processing takes place, and used to treat water (primarily grey water) as well as air. 

In all of these techniques, the soil acts as a physical filter to suspended particulates, as well as a bacterial substrate. In some cases, the chemistry of the soil itself reacts with contaminants in the flow media or catalyze a non biological reaction. However, the predominant mechanism is biological conversion leveraging primarily bacterial species, in some cases other microorganisms (arthropod, fungi, nematode, etc.). In essence, an SBR acts in a CELSS much the way a grow bed acts in an aquaponics system.


Leach Field 

Those with septic systems are already familiar with this, as it is typically used in conjunction with a black water septic tank. A smaller scale system can also be built into a water proofed plywood box or a ferro-cement tank with layers as follows (top to bottom):

  1. Infiltrator/Mulch layer
  2. Humus
  3. Sand
  4. Gravel
  5. Stone/Clean water drain

Water flows in intermittently (in a flood/drain cycle) through the infiltrator and out through the drain. Plants can be grown in the humus layer. Root vegetables are not advised, if human wastes are present in the inflow.



Slow Sand Filtration

Slow sand filters (SSF) are one of the the oldest water filtration methods, and provide fairly clean outflow. They utilize an anaerobic biofilter method, and require a constant inflow/outflow. As such, they require a pre-buffer or overflow valve.
SSF require surface area and volume of filter media proportionate to desired flow rate. Water with high turbidity levels can quickly clog the fine sand in these filters, so a particulate removal method such as a vortex filter is advised. SSF differs from the constructed leach field described above in that all the layers are kept wet which permits the growth of a biological scum layer (called a schmutzdecke) at the top. Waters with a very low nutrient content may impair turbidity removal since some nutrients must be present that promote biological ecosystem growth within the filter bed. 

Cleaning is traditionally done by use of a mechanical scraper, used once the bed has been dried out or by wet harrowing, where the sand is scraped while still under water, and the water used for cleaning is drained to waste.

Constructed Wetlands

The constructed wetland lends itself well to integrations with aquaponics. The system is constructed much as a flow through media (gravel) bed with marsh plants (cattails, etc). Vertical baffles are used to maximize water path length through the bed. The water entering the constructed wetland can be mixed with ammoniated fish tank water for nutrients and can return to the fish tank or used for follow on irrigation of food crops.         


Wicking Bed

A wicking bed is constructed similar to a leach box, except that water is introduced into the bottom and allowed to wick up into the soil via capillary action to feed the plants growing in the top. This method conserves water, since water surface is not exposed to air as much as in the other techniques, so evaporation is reduced. However, since water is primarily transported through the system via transpiration, this method is less efficient at cleaning water (which must be reclaimed from the atmosphere rather than a drain).

Created by admin. Last Modification: Wednesday 30 of March, 2016 08:39:17 CDT by admin.