EFFECT OF NITROGEN AND PHOSPHORUS CONCENTRATIONS ON THE TREATMENT EFFICIENCY OF BIOGAS EFFLUENT OF GIANT SALVINIA (Salvinia molesta)
Abstract
The study was conducted to determine the potential of giant salvinia (Salvinia molesta) for treating biogas effluent. The experiment was conduted in a nethouse with 6 treatments, which were the dilution ratio of biogas effluent (NT) from pig farms with river water (NS), including of 5% NT + 95% NS (NT1), 10% NT + 90% NS (NT2), 20% NT + 80% NS (NT3), 30% NT + 70% NS (NT4), 40% NT + 60% NS (NT5) and 50% NT + 50% NS (NT6). The treatments were arranged in a completely randomized design with 3 replications. A plant weight of 158 g/tank (equivalent to 158 g for 0.15 m2 of treatment area) was applied to treat wastewater with each tank volume of 35 L (25 cm). The hydraulic retention time in the system was set for 15 days and water samples were collected at each every 5 days. After 15 days of operation, the treated water quality parameters including pH, COD and TP were all within the allowable limits according to QCVN 62:2025/BTNMT (column B). The COD removal efficiency of the treatments NT1, NT2, NT3, NT4, NT5, NT6 were 77.2; 72.1; 79.4; 75.6; 82.8; 72.5%, respectively. Similarly, the total inorganic nitrogen (TIN) removal efficiency were 98.1; 98.4; 98.8; 99.0; 99.1; 98.6% and TP was removed with the respective efficiencies of 96.5; 86.6; 98.3; 96.3; 98.1; 90.3%. In which, the NT3, NT4, NT5 treatments simultaneously provided the highest COD, TIN, TP removal efficiency. This shows that the inlet concentrations of about 216.0 - 248.0 mg COD/L, 13.9 - 29.7 mg TIN/L, 5.2 - 8.3 mg TP/L of NT3, NT4, NT5 treatments are optimal for the absorption activity of giant salvinia as well as symbiotic microbial processes, helping the system operate stably and achieve outstanding treatment efficiency. Giant Salvinia fresh weight was increased 2.08 - 2.18 times after 15 days and the dilution ratios did not affect the plant growth. Using giant salvinia for wastewater treatment is an effective, low-cost biological solution, easy to apply for households in the Mekong delta in the VACB model.
