2.1. Wastewater and Microalgae species
The microalgae selected in this study was Microcystis sp ..
The effluent from anaerobic fermentation tank of a pig factory in
Fengxian District, Shanghai was used as the culture substrate. Under the
microscope, the main characteristics of Microcystis sp.cultured in wastewater were chlorophyll-a (Chla) of 2533
mg/m3, and the density of algae was about
2×109 cells/mL. The size of algal cells was
10~400 μm, and they were clumped.
2.2 The device of microbubble air flotation test
The microbubble air flotation
equipment is composed of microbubble generating device and air floating
column. Among them, the microbubble generation device is composed of
gas-liquid mixing pump (Nikuni, 20 FPD04Z, flow rate: 0.9
m3/h), the water inlet tank (plexiglas, length × width
× height =200×200×500 mm3, thickness =5 mm) and the
dissolved gas tank (stainless steel cylindrical tank, diameter =110 mm,
height =810 mm,). The air floating column (length × width × height
=100×30×500 mm3) is made of plexiglas with the
thickness of 3 mm. It has good light transmittance and is convenient for
dynamic observation of microbubbles. Each part of the test device is
connected by PVC pipe (φ=25mm), and the pressure reducing valve is
installed between the microbubble generation device and the air floating
column. The design of flexible pipe joint is adopted among the above
three parts, and the distance between the pressure reducing valve and
the air floating column is adjusted by changing the length of the
release pipe. The whole test device is also equipped with pressure
gauge, gas gauge and flowmeter, which show the dissolved air pressure,
inlet air flow rate and inlet water flow rate, respectively. The flow
chart of the test device is shown in Figure 1, with the red arrow
indicating the flow direction.