## 1 Introduction  
Large volumes of nitrogen and phosphate pollution are released into water bodies as a result of the social economy's growth and extensive industrial and agricultural production, posing a major threat to domestic water safety and productivity [1]. Furthermore, the eutrophication of rivers due to the combined pollution of phosphorus and nitrogen can quickly put human life and the aquatic environment at even greater risk [2]. Currently, some removal technologies, including ion exchange, membrane methods, electro-dialysis, coagulation sedimentation, and biological processes, are frequently employed for the removal of phosphorus and nitrogen [3, 4, 5]. Nevertheless, the majority of these techniques are not appropriate for the large-scale advanced treatment of phosphorus and nitrogen wastewater and involve substantial operating costs. Constructed wetlands (CWs) are now a commonly accepted solution for wastewater treatment. Unlike natural ecosystems, this sustainable ecotechnology uses a more controlledsetting to remove pollutants using physical, chemical, and biological processes found in natural wetlands [6]. Wastewater remediation can be carried out more effectively, sustainably, and economically with CWs. It also has a high rate of nutrient recovery and low maintenance/operational costs in an environmentally beneficial manner [7]. The vegetation type and flow patterns within the system can be used to categorize CWs into two groups: surface flow constructed wetlands (SF CWs) and subsurface flow constructed wetlands (SSF CWs). SF CW systems are often designed with a water column above a substrate layer, which is typically soil. Gravel beds with vertical flow (VF) or horizontal subsurface flow (HSSF) are commonly used as SSF CWs. Further differentiation of emergent and submerged macrophyte wetlands is based on the kind of vegetation. Rooted emergent macrophyte systems are the most prevalent. The combination of many CW types in a single facility is referred to as a hybrid wetland system [8; 9]. CWs can manage wastewater from a variety of sources, including storm runoff, acid mine waste, municipal, agricultural, industrial, livestock, and landfill leachate [6; 10; 11; 12]. Through microbial degradation, plant uptake, substrate adsorption, filtering by the packed media, and sedimentation, CWs can remove a range of contaminants from wastewater, such as total suspended solids (TSSs), total Kjeldahl nitrogen (TKN), total phosphorus (TP), total coliforms (TCs), biochemical oxygen demand (BOD), chemical oxygen demand (COD), heavy metals, antibiotics, pesticides, textile dyes, hormones, petroleum, and explosives [11; 13]. The three key elements of these biologically designed systems are plants, microorganisms, and porous filler materials. Microorganisms are essential for the elimination of pollutants in CWs because they break down organic contaminants and convert different nutrients [14; 15]. Aquatic plants, or macrophytes, are essential to CWs since they are the main means of moving dissolved oxygen (DO) through the system. Also, macrophytes reduce eutrophication in downstream streams through the uptake of pollution and the absorption of nutrients like phosphate and nitrogen [16]. In addition to serving as a filtration and/or adsorption medium for pollutants in the water, the materials in the media (soil, sand, pebbles, and gravel) offer a vast surface area for microorganisms to adhere to, promoting the growth of macrophytes [17]. The microorganisms that create biofilms in the rhizosphere and porous media are responsible for the mechanisms that change organic matter and nutritional compounds [9; 18]. However, the removal performance of CWs is not consistent. There have been numerous issues with nitrogen and phosphorus when using CWs globally. The removal of COD, BOD, TSS, and other contaminants can be accomplished well by CWs, but the removal of nitrogen and phosphorus is comparatively less effective.