# The Effect of Retention Time and Seasonal Variation on the Characterization of Phyto-Remediated Aquaculture Wastewater in a Constructed Wetland

## TL;DR

This study shows that using Phragmites karka and Typha latifolia in constructed wetlands can effectively treat aquaculture wastewater, with removal efficiency influenced by retention time and seasons.

## Contribution

The study introduces a phytoremediation strategy using specific macrophytes in constructed wetlands for aquaculture wastewater treatment in water-scarce regions.

## Key findings

- Phragmites karka and Typha latifolia significantly removed heavy metals and nutrients from aquaculture wastewater.
- Removal efficiency increased with longer hydraulic retention times, reaching up to 100% for most heavy metals at 21 days.
- Seasonal variations and plant type had significant effects on the wetland's treatment performance.

## Abstract

This study investigates the effectiveness and efficiency of macrophyte plants (Phragmites karka and Typha latifolia in removing heavy metals and some nutrients from aquaculture wastewater in a constructed wetland. Raw and treated wastewater from constructed wetlands were collected and analyzed using standard laboratory procedures for the determination of physicochemical properties and heavy metals. The performance of the wetland was assessed based on the type of plant, retention time, and season. The results revealed a significant impact of plant type, retention time, and season on the removal of nutrients and heavy metals, when compared to the raw wastewater’s physicochemical and heavy metal values. These findings suggest the need to adopt a phytoremediation strategy using Phragmites karka and Typha latifolia to promote the reuse of aquaculture wastewater for further agricultural purposes in areas where water is limited.

The insufficient availability of safe water has emerged as a prevalent issue severely impacting public health in developing nations. Moreover, studies reporting the efficacy of treatment plants (TPs)—specifically Phragmites karka and Typha latifolia—in removing toxic elements in aquaculture wastewater are scanty. Therefore, this study is aimed at investigating the effects of hydraulic retention time (HRT), seasonal variations, and TPs on the removal efficiency of pollutants from a vertical subsurface flow constructed wetland (VSSF-CW) in Nigeria. The experiments spanned three seasons (November–December–January—NDJ; March–April–May—MAM; and July–August–September—JAS) of the year, with samples collected from the CW at 7 day intervals for analysis. The aquaculture wastewater was analyzed in the laboratory to determine its chemical and toxic compositions before and after the introduction of treatment plants. Three-way ANOVA was used to analyze the main and interactive effects between HRT, seasons, and TPs on the physicochemical properties of the CW’s effluents. The removal efficiency was determined to evaluate the performance of the constructed wetland in comparison to the treatment plants. Results showed that these constructed wetlands effectively removed contaminants, with significant differences (p < 0.05) mostly observed in the effects of treatment plant types and seasons on the chemical and heavy metal concentrations. This was further confirmed by the main effects of HRT, seasons, and treatment plant choice, which significantly (p < 0.05) influenced treatment efficiency. Removal efficiencies increased with longer HRTs, reaching peak removal efficiencies of approximately 69, 67, and 61% for Na, K, and Ca, respectively. The BOD and COD reached 85 and 90% removal efficiency, while removal efficiency of 100% was achieved for most heavy metals at 21 day retention time. In summary, the study found that TPs (Phragmites karka and Typha latifolia), HRT, and seasonal variation are important for treating integrated poultry and aquaculture wastewater in a VSSF CWs.