Wastewater Treatment Ponds

        Sewage treatment is primarily intended to remove potentially harmful micro-organisms, eliminate odors, and improve water quality by reducing organic matter and nutrient content. Ponds can be an inexpensive and efficient way of

Fig. 13. Water treatment pond at Okehocking Preserve, Willistown Township. Aeration is needed to enhance microbial breakdown of organic molecules in the water. Note the abundance of duckweed, thriving on the rich nutrient supply.

achieving these objectives, and considerable research has therefore been directed toward the use of wastewater treatment ponds as secondary polishers of sewage effluent.
        About a third of wastewater treatment plants in the United States currently use some form of pond system. Most are clearly not intended as habitat amenities, and often have a very “industrial appearance”, with rectangular, cement basins and high fences. It is nonetheless possible to design treatment ponds that add aesthetic value to their surroundings, as shown by the treatment facility at Okehocking Preserve (Fig. 13).
        The nutrient removal efficiency of wastewater treatment ponds is often quite high, but depends on size and shape (especially depth), aeration, and the composition of the algal and plant communities (Crites et al. 2005). Duckweeds are an effective means of nutrient removal from the water column, and are intentionally grown in some wastewater systems (Körner et al. 2003).