Mixing Efficiency of Compost Tea Brewing Machines with Various Airlift Pump Air Jacket Structures and Air Injection Pressures

Abstract

Compost tea is an organic agriculture product that is used as a bio-fertilizer and biopesticide in modern agriculture. It is produced from compost using various brewing machines. The compost must be well mixed with water to support optimal extraction of nutrients and microorganisms. Therefore, in this study, the mixing efficiencies of brewing machines equipped with six different structured airlift pumps operating at six different air injection pressures (8, 9, 10, 12, 14, and 16 kPa) were investigated via comparative trials of the compost liquid circulation and the electrical conductivity and data analysis. Designs with total hole areas of 0.09 cm 2 achieved the highest compost liquid mass flow rates and good mixing efficiencies. In addition, air mass flow rates increased with the number of air injection holes at fixed pressures. Together, these data indicated that the best air jacket footpiece design in this study was A2, which contained eight holes with diameters of 1.2 mm. This design achieved the highest pump efficiency, mixing time, and liquid compost mass flow at most air pressures. This paper will help designers and manufacturers of this type of machinery.