CO2 Removal in Column Aerator

Abstract

Carbon dioxide (CO2) removal has been an important water treatment stage in recirculating aquaculture system (RAS) because of the intensive fish load in land-based fish farm. Higher levels of CO2 12 mg/L were reported to influence optimal fish growth and welfare, as well as resulting in nephrocalcinosis. Different CO2 stripping methods including chemical, physical, and biological technologies, were used in many fields. This thesis has been conducted with considerations regarding lower energy cost, easy principle and satisfactory performance, optimizing column aerator performance by changing its influencing parameters. The column diameter was 9.8 cm, distribution plate diameter as 5.6 cm, 2.5 cm diameter pall-rings with specific surface area of 209 m2/m3 media used for packing. The column aerator was tested with height effect, packing type effect, 3 different hydraulic loads (0.095 L/min/cm2, 0.185 L/min/cm2 and 0.371 L/min/cm2) with co and counter-current air flow of 6 different corresponding gas liquid ratios (G/L) (Open, 5:1, 10:1, 20:1, 30:1, 40:1 ) in 120 cm and 60 cm column, reduced inlet CO2 concentration 15 mg/L with 0.185 L/min/cm2 hydraulic load in 120 cm and 60 cm column, salinity with 3.5 ppt and 35 ppt of saline water and artificial sea water. Experimental water was made by diffusing commercial sparkling water (Taffel) in tab water, while saline water was made by adding sea salt to tab water and sea water added extra bicarbonate saline water to increase the alkalinity. Water temperature was near 15 ℃ and CO2 were measured three repetition in each sample, alkalinity and pH were tested meanwhile. Results showed that the higher G/L was better for CO2 stripping. Column height is very important, but in this scale 120 cm column was the best. Packing type had smaller effect. Co and counter-current air flow did not have significant different effect. Hydraulic load with 0.185 L/min/cm2 was better than others. Sea water is more difficult to remove CO2 than in fresh and saline water, that is mainly caused by higher alkalinity in the sea water. Reduced CO2 level of 15 mg/L did not result in large difference from inlet concentration with 20 mg/L. The tests were only conducted in one specific column; Therefore, further tests with different scale is required.