The use of algae and duckweed for wastewater treatment (Shi et al., 2010)

Estrogen is a female hormone that many people take in the form of medication. However, the human body never fully uses any medication and some of it passes through the body and is excreted. This estrogen, not used by humans, is carried in the waste stream to wastewater treatment plants. Unfortunately, most wastewater treatment plats have no way of removing. Without treatment, the estrogen flows through the plat, into streams or lakes where it is consumed by fish, frogs, and other amphibians. The animals that consume this estrogen are, not surprisingly affected by it; over time, these communities of fish and amphibians become more feminine—either by having higher percentages of females in the communities or by having feminine characteristics develop in males (this can occur to the extent of producing androgenous individuals).

A study conducted by Shi et al. was published in March of this year in Environmental Science and Pollution Research; they examined the fate of endocrine disrupting compounds (EDCs) in algae and duckweed wastewater treatment ponds (Shi et al., 2010). The EDCs 17α-ethinylestradiol (a synthetic estrogen compound), estrone (a naturally occurring estrogen form), and 17 β-estradiol (also naturally occurring) are commonly found in domestic sewage and were hence chosen for Shi et al.’s study (Shi et al., 2010). They used a species of Lemna duckweed (Shi et al., 2010). Several species of algae were used for the study including the following species: Anabaena cylindrical, Chlorococcus sp., Spirulina platensis, Chlorella sp., Scenedesmus quadricauda, and another Anaebena variant (Shi et al., 2010).

They conducted continuous-flow studies and batch tests (Shi et al., 2010). The batch test was carried out for 6 days; this time period, they found that algae or duckweed greatly helped with the removal of estrogens (Shi et al., 2010). The duckweed removed a higher percentage of estrogens than did the algae, but both were effective (Shi et al., 2010). Similar results were observed in the continuous-flow model. The continuous-flow system consisted of an initial pond and then two following tanks (Shi et al., 2010). The first pond was the most effective of these three: the duckweed first pond removed 85.4% of estrogens and the algae pond removed 76.8% (Shi et al., 2010). The following tanks removed 7.1 and 8.9 % for algae and duckweed respectively (Shi et al., 2010). Hence, the continuous-flow algae system removed a total of 83.9% of estrogens and the continuous-flow duckweed system removed 95.4% (Shi et al., 2010).

Some of the genera of algae studied here are also being studied by biofuel researchers. This system of wastewater treatment could be coupled with a biofuel production system.

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