Online Control of Lemna minor L. Phytoremediation: Using pH to Minimize the Nitrogen Outlet Concentration

Abstract

Phytoremediation technologies are employed worldwide to remove nutrient pollutants from agricultural and industrial wastewater. Unlike in algae-based nutrient removal, control methodologies for plant-based remediation have not been standardized. Control systems that guarantee consistently low outlet concentrations of nitrogen and phosphorous often use expensive analytical instruments and are therefore rarely viable. In this study, pH measurement was used as the sole input to control the nitrate outlet concentration in a continuously operated Lemna minor (lesser duckweed) phytoremediation tank. When grown in 20 L batches of modified Hoagland’s solution, it was found that a constant ratio exists between the amount of nitrate removed and the amount of acid dosed (required for pH control), which was equal to 1.25 mol N·(mol H+)−1. The nitrate uptake rates were determined by standard spetrophotometric method. At critically low nitrate concentrations, this ratio reduced slightly to 1.08 mol N·(mol H+)−1. Assuming a constant nitrogen content, the biomass growth rate could be predicted based on the acid dosing rate. A proportional-integral controller was used to maintain pH on 6.5 in a semi-continuously operated tank covered by L. minor. A nitrogen control strategy was developed which exploited this relationship between nitrate uptake and dosing and successfully removed upwards of 80% of the fed nitrogen from synthetic wastewater while a constant biomass layer was maintained. This study presents a clear illustration of how advanced chemical engineering control principles can be applied in phytoremediation processes.

Plant Effectiveness of Acorus calamus, Pistia stratiotes, Azolla pinnata as Hyperaccumulator Candidate of Phytoremediation Agent for Copper (Cu) Absorption

“…The plant condition that has a high water temperature and pH, is characterized by the physical condition of the plants, which turn yellow, wither, and begin to fall off. The higher the absorption of Cu levels by aquatic plants, the higher of pH water (Sigcau et al, 2022). According to metal toxicity, plant roots, particularly those of the Acorus calamus plant, have absorbed or bound Cu, which is what has caused the decrease in the pH level.…”

Phytoremediation of Pollutants: Applicability and Future Perspective

“…However, the use and development of continuous systems are crucial to the implementation of large-scale phytoremediation. The study by Sigcau et al [9] focused on optimizing a continuous phytoremediative water treatment system involving the aquatic macrophyte Lemna minor in the removal of nitrogen (N). In detail, the purpose of the study was the online control of pH in the discharge water to use this parameter as the sole input variable of the system for the prediction of N removal.…”