Comparative Performance Studies of Water Lettuce, Duckweed, and Algal-Based Stabilization Ponds Using Low-Strength Sewage

Abstract

A bench-scale continuous-flow wastewater treatment system comprising three parallel lines using duckweed (Spirodela polyrhiza), water lettuce (Pistia stratiotes), and algae (natural colonization) as treatment agents was set up to determine environmental conditions, fecal coliform profiles and general treatment performance. Each line consisted of four ponds connected in series fed by diluted sewage. Influent and effluent parameters measured included environmental conditions, turbidity, biochemical oxygen demand (BOD), chemical oxygen demand (COD), nitrate, nitrite, ammonia, total phosphorus, fecal coliforms, mosquito larvae, and sludge accumulations. Environmental conditions and fecal coliforms profiles were determined in the sediments (0.63 m), suspensions (0.35 m), and surfaces (0.1 m) of each pond. Acidic conditions were observed in the pistia ponds, neutral conditions in duckweed ponds, and alkaline conditions in algal ponds. Fecal coliforms log removals of 6, 4, and 3 were observed in algal, duckweed, and pistia ponds, respectively, in the final effluents, with die-off rates per pond of 2.7, 2.0, and 1.6. Sedimentation accounted for over 99% fecal coliform removal in most of the algal and pistia ponds. BOD removal was highest in the duckweed system, followed by pistia and algae at 95%, 93%, and 25%, respectively. COD removals were 65% and 59%, respectively, for duckweed and pistia, while COD increased in algal ponds by 56%. Nitrate removals were 72%, 70%, and 36%, respectively for duckweed, pistia, and algal ponds. Total phosphorus removals were 33% and 9% for pistia and duckweed systems, while an increase of 19% was observed in the algal treatment system. Ammonia removals were 95% in both pistia and duckweed and 93% in algal systems. Removals of total dissolved solids (TDS) were 70% for pistia, 15% for duckweed, and 9% for algae. Mosquito populations of 11,175/m(2), 3516/m(2), and 96/m(2) were counted in pistia, algal, and duckweed ponds, respectively. Low turbidity and low sludge accumulation characterized the macrophyte ponds. Performance in the removal of fecal coliforms in the algal-based treatment system and organic load removal in both macrophytes and algal-based treatment systems met the Ghana Environmental Protection Agency guideline values.

Use of Barley for the Purification of Aquaculture Wastewater in a Hydroponics System

“…When anions are taken up more rapidly than cations, the roots release bicarbonate and hydroxyl ions into solution and the pH of the medium rises. Another explanation for the fluctuation in pH is the consumption of carbon dioxide (CO 2 ) during algal photosynthesis and the production of CO 2 during organic matter decomposition [34,55,56] . According to Lawson [2] and Meade [36] , the pH of waters used for the culture of fish and shellfish should range from 6.5 to 8.0.…”

Comparison of microbiological parameters in experimental and conventional recirculation aquaculture systems

“…The fecal bacteria could be removed from water attaching to floating aquatic macrophytes [16]. Awuah et al [17] studied duckweed and algal pond system and established that macrophytes pond systems performed better in the removal of coliforms. The numbers of Enterobacteriaceae colony forming units per milliliter of water average varied from 5.13x10 3 to 6.27x10 3 respectively in the control and experimental system ( Table 1).…”

On-farm treatment options for wastewater, greywater and fecal sludge with special reference to West Africa

“…Given the large amount of literature available on constructed wetlands, we like to refer to (a) Hoffmann et al (2011) for the recent technology review of constructed wetlands; (b) Rose (1999) for wetland applications in urban farming; and (c) Ludwig (2009) for small-scale and household-based greywater treatment, including constructed wetlands. In West Africa, the use of pond systems with duckweed or water lettuce has been reported, for example, from Senegal, Burkina Faso, Ghana and Niger (Rose 1999;Awuah et al 2004;Koné et al 2002;Quayle 2012). In Kumasi, constructed wetlands as well as macrophyte-based treatment systems have been studied, for example, by Awuah et al (2004) and Niyonzima (2007).…”

“…In West Africa, the use of pond systems with duckweed or water lettuce has been reported, for example, from Senegal, Burkina Faso, Ghana and Niger (Rose 1999;Awuah et al 2004;Koné et al 2002;Quayle 2012). In Kumasi, constructed wetlands as well as macrophyte-based treatment systems have been studied, for example, by Awuah et al (2004) and Niyonzima (2007). Awuah et al (2004) reported achieving a fecal coliform removal of 6, 4 and 3 log units for algae ponds, duckweed ponds and water lettuce, respectively.…”

“…In Kumasi, constructed wetlands as well as macrophyte-based treatment systems have been studied, for example, by Awuah et al (2004) and Niyonzima (2007). Awuah et al (2004) reported achieving a fecal coliform removal of 6, 4 and 3 log units for algae ponds, duckweed ponds and water lettuce, respectively. Algae ponds performed better as they offered more exposure to sunlight.…”