## 1 Introduction
A schematic illustration of the CLC process is shown in Figure 1. The CLC system is composed of two interconnected fluidized bed reactors, i.e., the air reactor and fuel reactor. Biomass fuel is transported into the fuel reactor and pyrolyzed and then gasified by a gasification agent. The gasification products would react with the lattice oxygen from the OC to realize completed combustion. The reacted or reduced OC is then transported to the air reactor, where it is oxidized by air to the initial state and then starts a new cycle in the fuel reactor. The circulating OC particles process remarkable catalytic properties, which can realize catalytic reaction and tar cracking, which is the biggest problem for biomass fuel disposal [19; 20; 21; 22; 23]. In addition, due to the complete elimination of airborne N\({}_{2}\) and lower reaction of temperature (about 800-1100 \({}^{\circ}\)C) in the fuel reactor, the produced NO\({}_{\text{x}}\) emission from the CLC of briquete cyanobacteria is decreased greatly [24]. Besides, CLC has the potential to effectively recover phosphorus from organic wastes [25]. In the CLC process, the reduction condition in the fuel reactor would result in the potential production of water-soluble phosphate. Water-soluble phosphate is favorable as an agricultural fertilizer. Cyanobacteria contain a high content of phosphorus and represent an important secondary phosphorus source. Therefore, CLC is indicated to be an innovative cyanobacteria treatment technology with low NO\({}_{\text{x}}\) emission and the potential to recover phosphorus. Various biomass particles have been studied in the CLC process [26; 27; 28; 29]. These biomass fuels are all lignocellulosic biomass, which mainly includes hemicellulose, cellulose and lignin. The main components of cyanobacteria are extract, such as fat, wax or resin. The structure is totally different from the lignocellulosic biomass. So far, there are no academic reports about briquette cyanobacteria as fuel in CLC. The combination of CLC and biomass densification technology is thought to be a promising cyanobacteria utilization selection, where the energy density of briquette cyanobacteria is evidently increased, and tar cracking, NOx emission reduction and phosphorus recovery may be realized. In the CLC of briquette cyanobacteria, the selection of an OC material is vital. Many metal oxides have been investigated as an OC for the CLC of biomass [30; 31; 32; 33], while catalyzed cracking of tar could happen due to the presence of hematite. The active metallic Fe can mediate C-H and C-C bond cleavage, and the produced tar can be catalyzed cracking to small-molecular-weight gases by iron oxide [34]. The present work aims to investigate the characteristics of briquette cyanobacteria as a fuel in the process of CLC with hematite as an OC. First of all, the cyanobacteria powder is selected as raw material to extrude and pelletize to briquette cyanobacteria by a single briquetting unit device. Through the apparent measurement, the mechanical strength of briquette cyanobacteria samples is analyzed by varying the moisture content and compressive load. Besides, the thermochemical transformation process of briquette cyanobacteria is divided into three stages: drying (first break), devolatilization (second break) and char burnout (third break). The mechanical strength of briquette cyanobacteria after drying and devolatilization is analyzed by a thermogravimetric analysis reactor (TGA), and the combustion characteristics in the CLC process with hematite as an OC are analyzed in a single fluidized bed. The NOx release rule in CLC is also compared to that in the conventional combustion process. At last, 10 redox cycle experiments were conducted to investigate the reactivity stability, the morphological feature of hematite OC and phosphorus recovery possibility in the CLC of briquette cyanobacteria.