## 1 Introduction  
The intensification of global food production has led to renewed interest in fertilizer development that has better application efficiency in order to achieve long-term food security. Phosphate is an essential nutrient and a non-substitutable constituent of agricultural fertilizers, and non-renewable phosphate rock, the world's major resource for phosphate fertilizer production, is becoming progressively depleted. Furthermore, phosphate overloads in aquatic environments can promote the excessive production of photosynthetic aquatic microorganisms and eventually contribute to undesirable eutrophication. Therefore, phosphate recovery from secondary sources, particularly in wastewater, is a desirable alternative for achieving sustainable phosphate supplies and simultaneously reducing detrimental environmental impacts. Adsorption is a well-established technology for rapid, highly efficient, uncomplicated phosphate removal and recovery from phosphate-contaminated water. However, the major challenge of this technique is to design environmentally friendly, low-cost, and high-capacity adsorbents that enable an economical and simple pathway for phosphate recovery [1]. A successful attempt was made in a previous study conducted by the present authors, whereby the development of waste materials as an innovative phosphate adsorbent with rice straw-derived biochar was functionalized with layered double hydroxides(BC-LDHs). The composite demonstrated cost effectiveness and a sustainable solution for phosphate control [2]. As well as playing a role in phosphate remediation, BC-LDHs have the potential to be directly reutilized as a source of phosphate after a period of use as an adsorbent, contributing to improved phosphate recovery from contaminated water for agricultural reuse. Biochar is an organic carbon-rich material obtained from the pyrolysis of biomass under high-temperature and low-oxygen conditions [3]. The resultant biochar has a large specific surface area, a porous microstructure, and abundant surface functional groups [4]. Moreover, biochar usually contains high concentrations of bioavailable nutrients, such as carbon, nitrogen, hydrogen, and some trace elements, including potassium, calcium, sodium, and magnesium [5]. These remarkable properties of biochar have been identified as the main reasons for improved soil properties and crop productivity [3; 6; 7]. According to [PERSON] et al. [8], the positive effect of wood-derived biochar on the water retention capacity of soil, which in turn promoted root growth during the initial growth stage, greatly contributed to high tomato biomass and yield production. In vegetable studies, [PERSON] and [PERSON] [9] reported that biochar produced from horse manure and dried grass could be a suitable replacement or alternative to inorganic fertilizers. In addition, layered double hydroxides (LDHs), a class of layered compounds, have attracted considerable attention for agricultural applications. The structure of LDHs consists of positively charged mixed metal hydroxide sheets, which are balanced by the intercalation of anions in the hydrated interlayer regions. The general chemical formula of LDHs is denoted as [M\({}^{2+}\)1\({}_{-}\)xM\({}^{3+}\)x(OH)2]\({}^{+}\)(A\({}^{n-}\))\({}_{x/n}\).mH\({}_{2}\)O, where M\({}^{2+}\) and M\({}^{3+}\) represent the divalent and trivalent cations, respectively, A\({}^{n-}\) is the anion in the interlayer for charge compensation, and x is equal to the molar ratio of M\({}^{3+}\)/(M\({}^{2+}\)+M\({}^{3+}\)) [10]. LDHs have recently become popular for treating anionic pollutants because of their strong positive surface charge and exchangeable interlayer anions [11]. Alternatively, some studies have indicated that LDHs have been used as agrochemicals or fertilizers because of their potential to control herbicide and nutrient losses [12; 13; 14].