NOVELTY - Photobioreactor comprises support frame, having a top and a bottom, several separate flow paths supported by the support frame, reservoir connected to the several separate flow paths, a liquid pump having an intake side and a discharge side, a gasser tube, a gas injector, gas injector including a bubble size limiter, and gasser tube, liquid pump, and gas injector being configured so that the liquid nutrient medium requires at least 30 seconds to travel from the bottom of the gasser tube to the top of the gasser tube.    USE - The photobioreactor is used for growing biomass within a liquid nutrient medium (claimed) for producing biodiesel.    ADVANTAGE - The photobioreactor prevents formation of large segregated gas volumes, maximizes surface-area-to-volume ratio for bubbles, provides bubble-through time of minute or even more and is space efficient.    DETAILED DESCRIPTION - Photobioreactor comprises (a) (i) support frame, having a top and a bottom, (ii) several separate flow paths supported by the support frame, each of the separate flow paths including several connected transparent tubes, (iii) reservoir connected to the several separate flow paths, the reservoir configured to feed the liquid nutrient medium to the separate flow paths, the reservoir being located proximate to top of the support frame, (iv) a liquid pump, having an intake side and a discharge side, the liquid pump being located proximate to bottom of the support frame, (v) intake side of the liquid pump being configured to take in the liquid nutrient medium from the separate flow paths, (vi) a gasser tube, the gasser tube being vertically oriented and having a lower portion and an upper portion, (vii) lower portion of the gasser tube being connected to the discharge side of the liquid pump, (viii) upper portion of the gasser tube being connected to the reservoir, (ix) a gas injector configured to inject a gas into the lower portion of the gasser tube, by which creating a mixture of the liquid nutrient medium and the gas in the gasser tube, (x) gas injector including a bubble size limiter configured to limit an average size of a gas bubble introduced by the gas injector into the liquid nutrient medium to below 2 mm, and (xi) gasser tube, liquid pump, and gas injector being configured so that the liquid nutrient medium requires at least 30 seconds to travel from the bottom of the gasser tube to the top of the gasser tube, or (b) (i) support frame, (ii) several hollow, transparent tubes defining a flow path through which the liquid nutrient medium circulates, the tubes being supported by the support frame, (iii) a liquid pump, (iv) intake side of the liquid pump being configured to take in the liquid nutrient medium from the several transparent tubes, (v) a gasser tube, the gasser tube being vertically oriented and having a lower portion and an upper portion, (vi) lower portion of the gasser tube, (vii) upper portion of the gasser tube being connected to the several transparent tubes, (viii) gas injector configured to inject a gas into the lower portion of the gasser tube, (ix) gas injector including a bubble size limiter, and (x) gasser tube, liquid pump, and gas injector being configured so that the liquid nutrient medium requires at least 30 seconds to travel from the bottom of the gasser tube to the top of the gasser tube.