NOVELTY - Sewage disposal carbon emission reduction airlift circulation microalgae autotrophic-heterotrophic coupling photobioreactor having a shape of a long trapezoid, comprises microalgae heterotrophic area, air-liquid separating chamber, microalgae autotrophic area, bottom backflow area, and liquid discharge area. The microalgae heterotrophic area is a cube structure comprising material charge pipe, air diffusing device, algae liquid lifting area, and heat exchange pipe.    USE - Sewage disposal carbon emission reduction airlift circulation microalgae autotrophic-heterotrophic coupling photobioreactor.    ADVANTAGE - The carbon dioxide supply device and air lifting device are arranged separately; and air is distributed by a piece of panel ultrafiltration membrane cloth, so that the mass transfer and utilization efficiency of carbon dioxide are improved. The air lifting device only satisfies the requirement for lifting of algae liquid and annular flowing, via the coupling of photoautotrophic and heterotrophic of algae, so that the characteristic of microalgae for utilizing different carbon sources is exerted. Thus, problem of sealed pipeline that makes the photobioreactor to hardly release oxygen and the inhibition of dissolved oxygen are decreased. The transverse mixing of algae liquid in the photoautotrophic area is enhanced. The adverse effect resulting from the mutual shading between cells is lowered. Thus, the natural sunlight can be completely used to decrease the culture cost; and illumination utilization efficiency of photobioreactor is improved. The photobioreactor has high carbon fixation efficiency, high culture concentration of microalgae, stable system operation, easy amplification of reactor, simple processing, convenient operation, and low operation and maintenance cost. It is suitable for low-cost and efficient culture of microalgae at large scale.    DETAILED DESCRIPTION - Sewage disposal carbon emission reduction airlift circulation microalgae autotrophic-heterotrophic coupling photobioreactor having a shape of a long trapezoid, comprises microalgae heterotrophic area, air-liquid separating chamber, microalgae autotrophic area, bottom backflow area, and liquid discharge area. The microalgae heterotrophic area is a cube structure comprising material charge pipe, air diffusing device, algae liquid lifting area, and heat exchange pipe. The material charge pipe is located on the middle lower part of side face of microalgae heterotrophic area. The air diffusing device is located on the bottom part of microalgae heterotrophic area. The air diffusing device is connected with the air inlet pipe and a flow rate control valve. The algae liquid lifting area is located on the middle upper part of microalgae heterotrophic area. The heat exchange pipe is located at the middle part of algae liquid lifting area. The top part of microalgae heterotrophic area is connected with the air-liquid separating chamber. The bottom part of microalgae heterotrophic area is connected with the bottom backflow area. The air-liquid separating chamber is a square structure, which is symmetrical from left to right. It is internally provided with distribution overflow weir, outlet liquid overflow weir, exhaust pipe, and sample observing hole. The outlet liquid overflow weir is vertically arranged on 1 side of distribution overflow weir. It has a height, which is higher than the distribution overflow weir. The other side of outlet liquid overflow weir is a liquid discharge area. The bottom part of liquid discharge area is provided with a liquid discharge pipe. The top part of liquid discharge area is connected with the exhaust pipe; and the sample observing hole is mounted on the top part of air-liquid separating chamber. The microalgae autotrophic area is in the shape of inclined cube, and comprises phototropic plate, backlight plate, photoreaction area, and carbon dioxide (CO2) supply device. The phototropic plate is located on 2 side exteriors of microalgae autotrophic area and separately mounted with the horizontal plane at an inclined angle. The upper end of phototropic plate is connected with the air-liquid separating chamber. The lower end of phototropic plate is connected with the bottom backflow area. The backlight plate is located on 2 side interiors of microalgae autotrophic area. The area between the phototropic plate and backlight plate is a photoreaction area. The CO2 supply device is embedded into the middle part of backlight plate. One side of CO2 supply device is connected with CO2 supply pipe and flow rate control valve. The distribution overflow weir is mounted between the microalgae autotrophic area and microalgae heterotrophic area.