In rural areas of the Vietnamese Mekong delta, biogas digesters are applied as a potential solution to treat waste from pig rearing. Wastewater from biogas production typically contains a high level of nutrients, which requires appropriate techniques for removal. In order to contribute to making small-scale rural pig rearing in the Vietnamese Mekong Delta more sustainable, this study examines the uptake of inorganic nitrogen by water lettuce under lab scale conditions. Two treatments, including a control (No water lettuce) and with water lettuce (8 plants # 112.6±0.5 g) were conducted in triplicate using plastic tanks (57 x 38 x 30,5 cm3). Each replicate contained 50 L of solutions (nominal concentration: 5 mgN/L NH4-N + 5 mgN/L NO3-N). The experiment was set up in a wet lab for 28 d. The environmental parameters of solution and plant weight were monitored every 7 days. The results showed that water lettuce could absorb both ammonium and nitrate, but ammonium uptake was preferential. With approximately 112 g of fresh biomass, over 28 days this biomass was approximately 4 times greater and removed at about 0.26 g nitrogen. The results highlight that water lettuce can be used to remove nutrients from biogas wastewater without aeration.
Keywords: nutrient removal, water lettuce