Ecology of duckweed ponds used for nutrient recovery from wastewater

Abstract

The microorganism community that grows under duckweed shelter can play an important role on treatment processes. Therefore, the present study aimed to assess the zooplankton dynamic and microbial community in duckweed ponds (DPs) applied for domestic wastewater treatment under open field conditions. A pilot system comprised of two DPs in series (DP1 and DP2), with 10 m each, received domestic wastewater through a flow rate of 200 L·day. Thus, the system was monitored during 314 days through samples collected and analysed weekly. Also, the zooplankton organisms were identified and quantified. DNA sequencing was performed in order to identify the bacterial populations. The findings showed a high efficiency of nutrient removal with 93% and 91% of total phosphorus and total nitrogen, respectively. A high density of microcrustaceans was observed in DP1 reaching 4,700 org.100 mL and rotifers (over than 32,000 org.100 mL) in DP2, that could be related to the low suspended solids concentration (<30 mg·L) and turbidity (<10 NTU). The bacterial community showed a strong heterogeneity between samples collected along the seasons. Through these findings, it is possible to realise that the understanding of ecology could help to enhance the operation and designs of DPs.

Duckweed systems for eutrophic water purification through converting wastewater nutrients to high-starch biomass: comparative evaluation of three different genera (Spirodela polyrhiza, Lemna minor and Landoltia punctata) in monoculture or polyculture

“…6 Duckweed uptake, which was far beyond microbial contribution, was the main way to N removal in duckweed system. 20 In the rst 10 days, the TN concentration in the S. polyrhiza K1-based system decreased below 1.5 mg L À1 (corresponded to the standard of Grade IV which is mainly applicable to the water areas for industrial use according to CSWEQS), while TN concentrations of L. minor K2, L. punctata K3 and the polyculture duckweed were all over 1.5 mg L À1 (Table 2). Then TN concentration gradually declined to below 1.0 mg L À1 at the end of the experiment, with the highest TN removal efficiency of 98.8% for S. polyrhiza K1, 98.5% for L. minor K2 and 95.6% for L. punctata K3 and 99.1% for the polyculture, respectively (Fig.…”

“…As evidenced by previous studies, microbial nitrication and denitrication occurred in duckweed system. 20,45 For instance, Teles et al found that 40 genera of bacteria exhibited high abundance in duckweed system, including functional groups as nitrifying bacteria (Nitrospira and Nitrosomonas) and denitrifying bacteria (Rhodopseudomonas). 20 However, unlike activated sludge system, microbial nitrication/denitrication was the predominant route of N removal.…”

“…20,45 For instance, Teles et al found that 40 genera of bacteria exhibited high abundance in duckweed system, including functional groups as nitrifying bacteria (Nitrospira and Nitrosomonas) and denitrifying bacteria (Rhodopseudomonas). 20 However, unlike activated sludge system, microbial nitrication/denitrication was the predominant route of N removal. 6 Duckweed uptake, which was far beyond microbial contribution, was the main way to N removal in duckweed system.…”

“…Due to this ability, duckweed has already been used for the treatment of domestic, industrial, and swine wastewaters. [18][19][20][21][22] In addition, the duckweed system can effectively accumulate high content of starch. The starch content of 64.9% (dry weight) can be achieved in duckweed during nutrients starvation.…”

Toxicological Evaluation of Biological and Electrochemical Treatments of Coal Mine-impacted Water (MIW) on Duckweed Landoltia Punctata

“…In the present study, since a slight stimulus in the growth of plants exposed to the effluent from the elC treatment was observed, a sufficient removal of metal ions ceasing to be toxic and behaviour like nutrients can be inferred. As macrophytes need nutrients for their development (Teles et al 2017), the results suggest that the treated effluent may have a nutrient function for the duckweed.…”