Use of a duckweed pond for the domestic wastewater polishing in Ilha Solteira, SP, Brazil

Purpose - The purpose of this paper is to evaluate the efficiency of a duckweed pond in the polishing of a stabilization pond effluent, as well as quantify its biomass production. Once an adequate destination is given to the produced biomass, the wastewater treatment plant can work in a sustainable and integrated way. Design/methodology/approach - The duckweed pond consisted of a tank with volume 0.44 m(3), operating in continuous flow with an outflow of 0.12 m(3)/day and hydraulic retention time of 3.8 days. Effluent samples were collected before and after the treatment, with analyzes made: daily-pH, dissolved oxygen and temperature; twice a week - total nitrogen (TN), total phosphorus (TP) and chemical oxygen demand (COD); and weekly - total solids (TS) and Biochemical Oxygen Demand (BOD5). The duckweeds were collected each for seven days for its production quantification. Findings - The highest efficiency of TN, TP, COD, BOD5 and TS removal were of 74.67, 66.18, 88.12, 91.14 and 48.9 percent, respectively. The highest biomass production rate was 10.33 g/m(2)/day in dry mass. Research limitations/implications - There was great variation in biomass production, which may be related to the stabilization pond effluent conditions. The evaluation of the effluent composition, which will be treated with duckweeds, is recommended. Practical implications - The evaluated treatment system obtained positive results for the reduction in the analyzed variables concentration, being an efficient technology and with operational simplicity for the domestic effluent polishing. Originality/value - The motivation of this work was to bring a simple system of treatment and to give value to a domestic wastewater treatment system in a way that, at the same time the effluent polluter level is reduced and it is also possible to produce biomass during the treatment process.