# Enhanced Phosphorus Removal from Wastewater Using RSPRC and a Novel Reactor
## 1 Introduction  
Phosphorus (P) usually originates from human and animal wastes, household detergents, food-processing effluents, commercial fertilizers, and agricultural land runoffs. Phosphorus is a major nutrient for biomass growth [1; 2; 3]. However, excessive concentrations of P in water bodies such as lakes, lagoons or rivers cause an abnormal growth of algae and aquatic plants resulting in the degradation of the water quality [4; 5]. The State Environmental Protection Administration of China has recommended that total P should not exceed 0.5 mg/L according to the class A demands of discharge standard of pollutants for municipal wastewater treatment plants (GB18918-2002). The European Union (EU) maintains that the cut-off for total P concentration between risk and no risk of eutrophication in lakes is \(<\)10 ug/L to \(>\)100 ug/L, and for rivers, while total P concentrations below 0.01-0.07 ug/L are considered ideal. Therefore, the enhanced removal of phosphorus is a current trend. At present, removal methods of phosphorus from wastewater can be roughly divided into chemical precipitation [6], advanced biological treatment [7; 8] and adsorption [9; 10]. The biological phosphorus removal process is complicated and easily affected by the environment, which means that the effluent phosphorus concentration stability is poor [11]. Although the chemical removal method has a good effluent effect, most phosphorus removal agents used are industrial products such as lime, aluminum salt, iron salt, ferrous salt and magnesium salt, which lead to high phosphorus removal costs and a large amount of sludge. Thus, chemical precipitation has not been widely applied in practice [12]. Compared with other kinds of phosphorus removal methods, adsorption has the advantages of easy operation, simple process, reliable operation, high efficiency, low consumption, etc. [13]. Therefore, it has broad application prospects.  
Studies over the past two decades have provided significant information on the profound phosphorus removal performance of steel slag and fly ash. However, there is clearly a lack of research related to the phosphorus removal performance of activated clay. Although extensive research has been carried out on steel slag and fly ash, there has been little research on combining active clay, steel slag and fly ash to remove phosphorus. Most studies in the field of phosphorus adsorption have only focused on the adsorbents. So far, very little attention has been paid to the role of reactors used for adsorption reactions. Currently, high efficiency phosphorus removal material with strong adsorption capacity, certain strength and chemical stability, low water flow resistance and low cost should be developed urgently and applied to the phosphorus removal process of various wastewaters to ensure the phosphorus removal effect on the wastewater and recover the phosphorus [14]. In addition, the development of a reactor that is easy to operate, has a large capacity for water treatment and can guarantee an excellent adsorption effect for a long period of time is also one of the hot topics in recent years.  
Therefore, the prepared RSPRC was used as the adsorbent and a concentric circular diversion wall adsorption reactor was developed as the adsorption device. The main objectives of the current work are as follows: (1) assess the decolorization and dephosphorylation performance of activated clay at different ratios to determine the optimum ratio of raw materials for preparing RSPRC. (2) Investigate the phosphorus removal characteristics of RSPRC. (3) Investigate the effect of RSPRC dosage on the phosphorus removal efficiency of the reactor. (4) Investigate the effect of RSPRC distribution on phosphorus removal efficiency to optimize the placement of RSPRC for adsorption reactors. Moreover, (5) investigate the effect of hydraulic retention time (HRT) in the reactor on the phosphorus removal efficiency.