Influence of Top Clearance Height in Airlift Reactor on the Aerobic Granular Formation

Abstract

Conventional active sludge is the technology that is usedcommonly in wastewater treatment. However, this technology has thedisadvantage, its relatively low settling speed causing a large landrequirement. One technology that can be used to overcome this deficiencyis aerobic granular. In this study aerobic granular is formed in acontinuous flow system of airlift reactor with a 12 (twelve) hourshydraulic retention time. Aeration is carried out for 24 hours at a rate of 2liters per minute (lpm). The height variation of top clearance (ht) is usedto determine its effect on the aerobic granular formation. The ht variationused is 15 cm, 20 cm, and 30 cm. The height of top clearance at the airliftreactor affects the circulation and superficial gas velocity which thenaffect the hydrodynamic shear force. The larger the hydrodynamic shearforce, the better the granular quality will be. The granular quality isdetermined based on physical characteristics including Sludge VolumeIndex (SVI), sludge density index (SDI), settling velocity, size, and aspectratio. The result shows that the height of top clearance affects the granularquality that formed. However, the effect is not linear. The non-linearity ofthe relationship between the top clearance height and granular formationcan be due to the sizeable superficial gas velocity and biomass washout. The ht variation that provides the best granular quality is achieved at 15cm, followed by 30 cm, and finally 20 cm. The ht variation of 15 cmreaches an optimum result with the value of SVI is 50 ml/g, settlingvelocity 39,4 m/hour, SDI 2.02 g/ml, size 3.5 mm, the aspect ratio of 0.86, and organic removal efficiency reaches 87.2%.