Biologically & Biochemically Complex Ponds

Empowering People and Communities: Design-and-Construction Simplicity, Energy Efficiency, Ease of Operation, and Low Cost

Refer to Chapter 4 of the book

In rural areas and remote regions, particularly those in the developing world, ponds are most common because of their ease of operation, energy efficiency, and low cost. Researchers generally recognize that four major biological and biochemical processes occur simultaneously but at different zones in wastewater ponds (Thirumurthi, 1991):
(1) Microbial aerobic biodegradation and biotransformation
(2) Microbial anaerobic biodegradation and biotransformation
(3) Photosynthesis
(4) Sedimentation

But reactions and processes besides these four occur also in ponds:
(5) Predation on bacteria and other microorganisms by rotifers and zooplankton
(6) Fermentation of settled solids and sludges at pond bottom (in which biogas, comprising 65% methane, is generated)
(7) pH shifts in pond water
(8) Algae exuding algal toxins that eliminate pathogenic microorganisms (such as fecal coliforms)
(9) Other biochemical, biological, and physical processes not discussed here

In short, ponds are a way of simulating nature's processes of treating wastes.

Although waste-stabilization ponds and other types of pond systems are now a well-established approach to biological wastewater treatment, they have been criticized as a "low-tech" and "old-fashion" method of wastewater treatment, which requires large parcels of land and should be used when no other sewage-treatment alternatives are available (Pearson, 1996). What the critics of pond systems do not fully consider and appreciate is that this appropriate technology is flexible (i.e., it can be combined with other treatment units such as constructed wetlands and sand filters in an integrated wastewater-treatment system); simple and inexpensive to design, construct, operate, and maintain; and environmentally sustainable because no fossil fuels and chemicals are required for effective wastewater treatment.

In essence, pond systems offer small, rural, and remote communities a great measure of self-reliance and self-sufficiency, which they cannot obtain by using conventional treatment technologies (such as those systems described in Chapter 2 and 3 of this book). An example of vulnerability of conventional technologies is seen in mid-August 2003, when a massive power outage cripped electrical grids in northeastern United States and southeastern Canada. Sewage-treatment plants failed, and billions of gallons of sewage spilled into rivers, lakes, and ocean from Michigan to New York.

Photograph: An unaerated macrophyte-planted maturation pond in southern California. This pond is located on campus of Cal Poly Pomona. (Photo by Jo-Shing Yang).