Physiological and biochemical responses of Phragmites australis correlate with water quality in lagoon wastewater treatment system. Journal Environmental Technology and Innovation

Abstract

Natural wastewater lagooning is an energy-efficient process, and its effectiveness is significantly influenced by the selection of plant species, whose capacity to purify water is affected by various environmental parameters. This study aimed to establish the correlation between the physiological and biochemical responses of a purifying plant, Phragmites australis, and the water quality index (WQI) of water in a lagoon treatment plant across four seasons. A comparison was made with control water and plants from the Wadi (ephemeral riverbed that contains water only when rain occurs). Several physicochemical parameters were measured before and after the wastewater treatment. The analyses of the plant focused on the carbohydrate and proline content in its roots, stems, and leaves. The physicochemical analysis of the water revealed very high levels of chemical oxygen demand (COD), biochemical oxygen demand (BOD5), volatile suspended solids (VSS), and total suspended solids (TSS) in the raw wastewater (RWW). These levels subsequently decreased in the treated water (TWW), contrasting with the control water (Wadi), which exhibited very low levels. In this context, RWW had a WQI of 284.3 ± 40.5, which was highly correlated with the tested parameters, indicating a water quality classification ranging from unsuitable to questionable for irrigation use. In contrast, TWW had a WQI of 172 ± 33.2, reflecting a classification from Doubtful to Permissible, while the control water displayed excellent quality with a WQI of 14.7 ± 2.2. The concentrations observed in TWW were as follows: COD (192.5 ± 58.1 mg/L), BOD5 (6 ± 38 mg/L), VSS (45.8 ± 16.8 mg/L), and TSS (101.6 ± 27 mg/L). A high concentration of NH4+ ions was noted compared to NO2– and NO3–, which had an insignificant effect. The values of electrical conductivity (EC) were notably high but did not show a significant difference between the water types. The effect of WQI for the three types of water (RWW, TWW, and control) on proline accumulation in the two plant organs (leaves and roots) showed no significant effect, unlike in the stems. However, the variation of this osmoticum was significantly affected by seasonal changes. The highest proline concentrations were recorded during the autumn season in all three organs studied, with values ranging from a minimum of 0.5 µg/g dry matter (DM) to 2 µg/g DM. A similar trend was observed for carbohydrates, with the highest concentrations also noted in the autumn season across all water types and plant organs. The observed values for carbohydrates ranged between a minimum of 0.5 µg/g DM and 1.5 µg/g DM. The results indicated a significantly higher accumulation of proline and carbohydrates in the roots, stems, and leaves during the autumn season. The concentrations recorded in these organs were 1.6 ± 0.2 µg/g DM, 1.6 ± 0.1 µg/g DM, and 1.8 ± 0.04 µg/g DM, respectively. These levels were higher in the control plants compared to those at the treatment station, with the exception of carbohydrates in the stems.

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