Modeling duckweed growth in wastewater treatment systems Livestock Research for Rural Development 17 (6) 2005 Guidelines to authors LRRD News Citation of this paper Modeling duckweed growth in wastewater treatment systems (original) (raw)
Polish Journal of Ecology
The Monod model describes the relationship between growth rate and ambient nutrient concentration, the Droop model focuses on internal nutrient resources as the driving factor. Both were applied mainly to explain phytoplankton dynamics in lakes or in experimental cultures. Our test plants were two species of duckweeds-Lemna minor L. and Spirodela polyrhiza (L.) Schleiden sampled from 18 natural stands situated in 6 different water bodies. Plants were grown outdoor in original lake water or in mineral media of varying N and P concentrations (0-21 mg N-NO 3 L-1 and 0-1853 μg P-PO 4 L-1 for L.minor and 0-4.2 mg N-NO 3 L-1 and 0-371 μg P-PO 4 L-1 for S. polyrhiza). Moreover, we analysed concentrations of mineral forms of N and P in lake water and tissue nutrient concentrations in plants. Tissue N of both plants was significantly correlated with ambient inorganic nitrogen sources, no such relationship was observed for tissue P. The growth rate of both plants measured under experimental outdoor conditions was better explained by tissue N and P variability (the Droop model) than by the external nutrient availability (the Monod model). The latter also failed to fit the growth rate of both plants in artificial mineral media with a decreasing gradient of N and P concentrations. The plants grew at the expense of internal N and P resources which remarkably declined during 9-day long experiments. Calculated minimum tissue contents (11.19 1.11 mg N g-1 and 0.97 0.07 mg P g-1 in L. minor and 6.10 1.85 mg N and 1.25 0.37 mg P g-1 in S. polyrhiza) show that the latter species would be a superior competitor under N limiting conditions and the former-under P limitation. We confront obtained results with literature data on N uptake kinetics and postulate that the luxury consumption of nutrients and plant growth dependent mainly on internal N and P resources might be an adaptation of duckweeds to varying habitat conditions typical of astatic water bodies.
Role of Internal Nutrient Storage in Duckweed Growth for Swine Wastewater Treatment
Transactions of the ASAE, 2005
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.
2021 ASABE Annual International Virtual Meeting, July 12-16, 2021, 2021
Sustainable management of leachate produced from the dumpsite is one of the major concerns in developing countries Aquatic plants such as duckweed have the potential to remove pollutants from wastewater which can also be cost-effective and feasible options for leachate treatment. Therefore, the objective of our present study was to examine the growth and nutrient removal efficiency of duckweed (Lemna minor) on leachate. Three tests were performed each by growing lemna minor on synthetic leachate under controlled conditions and on dumpsite leachate under natural conditions. During each test, duckweed was grown in 300 ml plastic containers with a surface area of 25.8 cm 2. About 60 mg of fresh mass of duckweed was grown on 250 ml leachate at an internal depth of 9.5 cm. Results revealed that, in comparison to synthetic leachate, duckweed removed Chemical Oxygen Demand (COD), nitrogen (N), and phosphorous (P) more efficiently from dumpsite leachate under natural climatic conditions. However, the amounts of N and P absorbed into duckweed body mass were about 16% and 35% respectively more at synthetic leachate under controlled conditions. Maximum growth rate of duckweed (7.03 g m-2 day-1) was also observed for synthetic leachate in comparison to the growth rate of 4.87 g m-2 day-1 at dumpsite leachate. Results of this study provide a useful interpretation of duckweed growth and nutrient removal dynamics from leachate under natural and laboratory conditions.
Duckweed culture for wastewater renovation and biomass production
Agricultural Water Management, 1994
Outdoor experiments were conducted in shallow mini-ponds (20 and 30 cm deep) for evaluating the performance of the duckweed species Lemna gibba as a purifier of domestic wastewater. It was found that under adequate operational conditions, the quality of secondary effluents meets irrigation reuse criteria. The annual yield (dry matter) of duckweed, harvested two to three times a week, is about 55 ton/ha, with a protein content of 30%. Hence, by cultivating duckweeds the ammonia in ponds for domestic wastewater treatment is converted into valuable protein rich biomass which subsequently can be used for animal feed or agricultural fertilization. The economic benefit of the additional by-product of the biomass reduces wastewater expenditures in the range of 0.020 to US$0.050 per each treated m 3 of wastewater.
Central Asian Journal of Water Research (CAJWR), 2024
Aquatic plants, including duckweed (Lemna minor), are increasingly utilized in sewage and wastewater treatment to improve pollution parameters and organic matter removal. This study aimed to investigate the impacts and efficacy of duckweed in secondary clarifier tanks in a conventional biological treatment facility. The performance of four secondary clarifiers with and without duckweed was compared based on water quality effluent and settling characteristics. As per the experiment results, the secondary clarifier tank with duckweed demonstrated higher removal efficiency for chemical oxygen demand (COD), biological oxygen demand (BOD5), ammonium, phosphate, total nitrogen (TN), and total phosphorus (TP)-of 70%, 75%, 72%, 82%, 67%, and 96%, respectively, compared to the tank without duckweed. The concentration of suspended solids in the effluent and sludge volume index (SVI) values were similar in both settings. The research findings suggest that duckweed can contribute to the treatment efficiency of conventional biological treatment plants, thus reducing the need for tertiary nutrient removal. Additionally, the cost-effectiveness of treatment with duckweed and its reuse as fertilizer and animal fodder make it a valuable resource. The optimal temperature for duck-weed growth is approx. +26°C, and it is influenced by sunlight and temperature more than nutrient concentrations .
Duckweed Lemna gibba has been listed as a promising plant for wastewater treatment and energy biomass production. This study aims to study the efficacy of L. gibba based bioreactor in removal of wastewater pollutants loads and energy-rich biomass harvesting under different plant biomass density loads. A total of four density loads: 20% (T1), 40% (T2), 60% (T3), and 80% (T4) of inoculants biomass were used to construct duckweed reactors and changes in wastewater (WW) and duckweed biomass characteristics (growth rate, biochemical composition etc.) were recorded for 21 days. The nutrient load in WW reduced significantly: NO32N (83-89%), SO 4 2-30 (85-86%) and total phosphorus (TP) (67-72%) at the end in all experimental set-ups. The reactor with 20% inoculation density showed the maximum WW nutrient removal. The weed biomass yield showed the direct relationship with inoculation density in all experimental set-ups. The yield (dry weight basis) of carbohydrate, starch and protein was: 1.39-1.77 g m 22 day 21 , 1.10-1.20 g m 22 day 21 , and 1.9-2.24 g m 22 day 21 , respectively in different set-ups. The high yield of starch under optimized density load suggests the utility of harvested biomass for bioethanol production. Results thus, suggested that inoculation density directly plays an important role in performance of duckweed reactors in terms of WW treatment and energy biomass synthesis.
Distribution and Bioresource Potential of Duckweed (Lemna minor L.) in Maiduguri, Nigeria
UMYU Scientifica, 2023
All members of the Lemnaceae family are tiny, free-floating freshwater plants with global distributions; they are the most morphologically reduced higher plant species (Cheng and Stormp, 2009). Duckweed has lately attracted the attention of scientists and governments as a new feedstock with a high biomass production rate for bioenergy production . Duckweed (Lemna minor) has long been used to remediate municipal wastewater by recovering harmful nutrients through its growth, the nutrients needed to generate vast quantities of duckweed might be found in wastewater from livestock agriculture and towns . Duckweed can reclaim contaminated streams and transform wastewater into high-quality animal feed, given its efficient nutrient uptake and inclination to accumulate high protein levels . Particularly for the treatment of industrial and agricultural effluents, duckweed was incredibly successful at removing organic pollutants from aquatic ecosystems . Humans can use duckweed as safe alternatives to conventional food and energy sources because of their distinctive physiological adaptations to their growth environments .
Water Research, 1998
ÐTo arrive at detailed nutrient balances for duckweed-covered wastewater treatment systems, ®ve laboratory-scale experiments were carried out in shallow (3.3 cm), 1 l batch systems to assess separately the contributions of duckweed itself, attached and suspended bacteria as well as algae to N-and P-removal in domestic wastewater. Depending on the initial concentrations, our duckweed-covered systems removed 120±590 mg N m À2 d À1 (73±97% of the initial Kjeldahl-nitrogen) and 14±74 mg P m À2 d À1 (63±99% of the initial total phosphorus) in 3 days. Duckweed (Lemna gibba L.) itself was directly responsible for 30±47% of the total N-loss by uptake of ammonium and, probably dependent on the initial P-concentrations, for up to 52% of the total P-loss. The indirect contribution of duckweed to the total nutrient removal was also considerable and included the uptake (and adsorption) of ammonium and ortho-phosphate by algae and bacteria in the attached bio®lm and the removal of N through nitri®cation/denitri®cation by bacteria attached to the duckweed. Together these accounted for 35±46 and 31±71% of the total N-and P-loss, respectively. Therefore, approximately 3 4 of the total N-and P-loss could be attributed to the duckweed mat. The remaining quarter is due to non-duckweed related components: uptake and nitri®cation/denitri®cation by algae and bacteria attached to the walls and the sediment of the system (including sedimentation). Other processes, like NH 3-volatilisation, N-®xation and nutrient uptake as well as nitri®cation/denitri®cation by suspended microorganisms did not in¯uence the N-and P-balance of our systems, but could become important with increasing water depths and retention times.
Bioresource technology, 2018
To assess the potential of duckweeds as agents for nitrogen removal and biofuel feedstocks, Spirodela polyrhiza, Lemna minor, Lemna gibba, and Landoltia punctata were cultured in effluents of municipal wastewater, swine wastewater, or anaerobic digestion for 4 days. Total dissolved inorganic nitrogen (T-DIN) of 20-50 mg/L in effluents was effectively removed by inoculating with 0.3-1.0 g/L duckweeds. S. polyrhiza showed the highest nitrogen removal (2.0-10.8 mg T-DIN/L/day) and biomass production (52.6-70.3 mg d.w./L/day) rates in all the three effluents. Ethanol and methane were produced from duckweed biomass grown in each effluent. S. polyrhiza and L. punctata biomass showed higher ethanol (0.168-0.191, 0.166-0.172 and 0.174-0.191 g-ethanol/g-biomass, respectively) and methane (340-413 and 343-408 NL CH/kg VS, respectively) production potentials than the others, which is related to their higher carbon and starch contents and calorific values.