Role of Internal Nutrient Storage in Duckweed Growth for Swine Wastewater Treatment

Abstract

The objective of this study was to investigate the relationship of the nutrient content of duckweed biomass to duckweed growth in swine wastewater. Batch tests of Spirodela punctata 7776, the selected strain for highest total protein production, were conducted in an environment-controlled growth chamber at 24°C and 16 h of light per day. A prolonged growth period was observed after the nutrients in the medium were exhausted, indicating that duckweed could use its stored nutrients for growth. Prediction of growth using medium concentration as an independent variable was deemed unsuitable to describe this growth. Throughout the 30-day growing period, nitrogen and phosphorus content in the biomass varied from 59.7 to 19.7 mg N /g biomass and from 14.8 to 6.8 mg P /g biomass (dry weight basis), respectively. The relationship between biomass nitrogen content and specific growth rate of Spirodela punctata 7776 was found to follow Monod-type kinetics with m max of 0.24 g N /g biomass /day and K N of 28.8 mg P /g biomass. Reduced growth rate was observed in the duckweed culture with high duckweed density (mass per unit area). Effects of the duckweed density on growth rate and nutrient uptake are modeled and discussed.

The production of duckweed as a source of biofuels

“…Additionally, the influence of geographic isolate on the performance of duckweed in swine wastewater was more significant than that at the species level. A followup study was carried out to compare the performance of S. punctata 7776, L. gibba 8678 and L. minor 8627 in the reclamation of diluted anaerobically treated swine wastewater (67,50,33,25 and 20%) in a greenhouse [19]. It was reported that the Lemna geographic isolates produced more biomass and had higher content of tissue nutrients such as nitrogen, phosphorus and potassium than S. punctata 7776.…”

“…During the same nutrient starvation period, the duckweed biomass increased by 81.4%, resulting in a 220% increase in total starch. The continuous growth of duckweed in well water is believed to be supported by the internal nutrient storage of duckweed [67]. Assuming a corn starch yield of 5.70 t ha -1 year -1 [68,69], it takes only approximately 5 months to grow duckweed to reach the same starch yield per unit area.…”

Effect of nitrogen and phosphorus deficiency on transcriptional regulation of genes encoding key enzymes of starch metabolism in duckweed ( Landoltia punctata )

“…Moreover, it grows faster and has a longer yearly production period than most other plants (Cheng and Stomp, 2009). In fact, many species of duckweed can double their biomass every 2e3 days (Chang et al, 1977), grow year-round in warm climates (Chaiprapat et al, 2005), and ultimately achieve a biomass of 0.5e1.5 metric tons/ hectare/day fresh weight or 13e38 metric tons/hectare/year dry weight (Skillicorn et al, 1993). In addition, duckweed has also been found to accumulate up to 75% of its dry weight as starch in optimal conditions (Reid and Bieleski, 1970), thereby making it an excellent feedstock for bioenergy production with ethanol yields of 6.42 Â 10 3 l ha…”

Improving Production of Bioethanol from Duckweed (Landoltia punctata) by Pectinase Pretreatment

“…It has a longer production period than most other plants, even growing year-round in some areas with a warm climate [7]. It accumulates its biomass at more rapid rates than other higher plants, including agricultural crops [8].…”