Proceedings

Duckweed ponds have been recognized as a low coast and efficient technology to provide nutrient removal from wastewater and also a valuable biomass production. The community of microorganism that growing under duckweed shelter can play an important role on treatment processes. Therefore the present study aimed to assess the dynamic of zooplankton and microbial community in duckweed ponds applied for domestic wastewater treatment under real (open field) conditions. A pilot system comprised by two duckweed ponds in series (DP1 and DP2), with 10m2 each, received loads of wastewater from a residential condominium through a flow rate of 200L.day-1. Thus, the system was monitored during 314 days by samples collected and analysed weekly. Also the zooplankton organisms present in rhizosphere and water column were identified and quantified. DNA sequencing (rRNA 16S V3/V4 region amplification) was performed in order to obtain a profile of bacterial communities. 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 (cladocerans and ostracodes) was observed in DP1 reaching 4,700 org.100mL-1 and rotifers (over than 32,000 org.100mL-1) in DP2, that could be related to the low suspended solids concentration (<30mg.L-1) and turbidity (< 10 NTU) along the experiment. The bacterial community showed a strong heterogeneity between samples collected along seasons. In spite of high nitrogen removal, nitrifying bacteria was found in low quantity representing less than 1% of relative frequency for both ponds. Through these findings is possible to realise that the understanding of ecology could help to enhance the operation and designs of duckweed ponds.