Long-Term Assessment of 1,4-Dioxane Uptake via Duckweed with Emphasis on Operational Parameters

Duckweed (Lemna Gibba) was successfully used for phytoremediation of wastewater containing 1,4-dioxane, which could also result in biomass with high protein and carbon content. 1,4-dioxane is not easily removed or separated from wastewater by traditional physicochemical processes such as coagulation and activated carbon adsorption because of its high solubility [1]. Three duckweed-pond continual streams (DWs) lab-scale reactors, i.e., one pond (DW1), two ponds (DW2), and three ponds (DW3), were operated at variable hydraulic retention times (HRTs) of 2, 4, and 6 days respectively that are designed to treat wastewater containing 1,4dioxane. The results showed that the removal efficiency of 1,4 dioxane, COD, TOC, and ammonia were quite high in the DW3 which had the highest removal efficiency in 1,4-dioxane and NH4-N. 1,4-Dioxane and NH4-N removal efficiencies using DW3 (i.e., 56.9 ± 25% and 87.2 ± 7.1%, respectively) were slightly higher than that obtained using DW2 (i.e., 44.8 ± 19.6% and 81.9 ± 8.6%, respectively). Further, it was noted that, at DW3, the average effluent pH decreased that range from (8.80) to (7.45, c (TDS) decreased that range from( 921.5 ± 120.6) to (837.6 ± 83.6) mg/L, and Dissolved Oxygen (DO) increased that range from (3.5 ± 1.9) to (7.5 ± 3) mg/L. Eventually, DW removed 1,4dioxane effectively from wastewater, representing an effective, low operation, eco-friendly, and maintenance costs technology.

Effect of treated sewage characteristics on duckweed biomass production and microbial communities

Duckweed biomass production in a duckweed pond fed with three differently treated sewage (i.e. sewage treated by primary sedimentation (PS); conventional activated sludge process (CAS); and downflow hanging sponge process (DHS)) was evaluated in order to assess the effects of water quality on biomass yield. Higher and stable biomass production was observed when the duckweed pond was fed with PS or DHS-effluent than with CAS-effluent, evidently due to the difference in nutrient loads. Availability of nutrients, especially phosphorus, affected the biomass production rate: higher the nutrient, faster the production. Microbial community analysis revealed that the members of Rhizobiales were likely to contribute to stable and high biomass growth. From the results of the study, a sewage treatment system consisting of a primary sedimentation followed by a duckweed pond and a tertiary treatment unit can be proposed to maximize biomass production without compromising treatment objectives. Size and operational parameters of the duckweed pond should be determined primarily based on the nutrient availability in the influent water to maximize duckweed growth.

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 m3, operating in continuous flow with an outflow of 0.12 m3/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/m2/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.

Nutrient recovery from swine waste and protein biomass production using duckweed ponds (Landoltia punctata): Southern Brazil

Brazil is one of the most important countries in pork production worldwide, ranking third. This activity has an important role in the national economic scenario. However, the fast growth of this activity has caused major environmental impacts, especially in developing countries. The large amount of nitrogen and phosphorus compounds found in pig manure has caused ecological imbalances, with eutrophication of major river basins in the producing regions. Moreover, much of the pig production in developing countries occurs on small farms, and therefore causes diffuse pollution. Therefore, duckweed pond have been successfully used in the swine waste polishing, generating further a biomass with high protein content. The present study evaluated the efficiency of two full scale duckweed ponds for the polishing of a small pig farm effluent, biomass yield and crude protein (CP) content. Duckweed pond series received the effluent from a biodigester-storage pond, with a flow rate of 1 m3/day (chemical oxygen demand rate = 186 kg/ha day) produced by 300 animals. After 1 year a great improvement of effluent quality was observed, with removal of 96% of total Kjeldahl nitrogen (TKN) and 89% of total phosphorus (TP), on average. Nitrogen removal rate is one of the highest ever found (4.4 g TKN/m2 day). Also, the dissolved oxygen rose from 0.0 to 3.0 mg/L. The two ponds produced together over 13 tons of fresh biomass (90.5% moisture), with 35% of CP content, which represents a productivity of 24 tonsCP/ha year. Due to the high rate of nutrient removal, and also the high protein biomass production, duckweed ponds revealed, under the presented conditions, a great potential for the polishing and valorization of swine waste. Nevertheless, this technology should be better exploited to improve the sustainability of small pig farms in order to minimize the impacts of this activity on the environment.