Preliminary design of microalgal biomass harvesting module using ultrasound wave trapping principle

Photobioreactor have been a prominent way to produce biomass in case of biofuel production. One of the most important procedure in this line of production is harvesting. Nowadays, microalgae biomasses are harvested by using many methods such as flocculation, filtration, centrifugation, and the other methods. Those methods are the commonly used by many bioenergy companies to accumulate their biomass before extraction phase. This process requiring a lot of cost and times. In order to increase cost and time efficiency, examination of ultrasound wave trapping method has been done. A harvesting module was assembled as a system consisted of two piezoelectric circuit (ultrasound wave generator) in a transparent box. Data shown by generating 1.7 MHz wave for 20 minutes, turbidity of Synechococcus (coccoid cyanobacteria) biomass was decreased from 56.3 NTU to 55.6 NTU. The other data also shown decreased turbidity of mixed culture biomass from 46.5 NTU to 16.4 NTU. This results also followed by weight measurement for both biomasses. This module capable to accumulating microalgal biomass a number of 0.0138 gram for Synechococcus and 0.8544 gram for mixed culture. The difference in biomass accumulation results are caused by cell size and density. Synechococcus cell size range between 0.5-2 µm with a very low density. This phenomenon makes any kind of small-sized coccoid cyanobacteria are need more time to be accumulated. Meanwhile mixed culture of microalgae is easier to accumulated due their variety of size and density.