the vat 6 as the belt 13 emerges from the vat 6 above the surface 8 and is entrained around the recovery drum 14 and especially as it passes over the receiving chamber 16 the then adjacent dunaliella with the necessarily accompanying spirulina are drawn off together with some of the entrained liquid medium to the receiving chamber 16 from which they flow or are transported to an appropriate discharge the belt after leaving the receiving chamber 16 and being more or less devoid of both algae spirulina and dunaliella then travels back toward its point of beginning for recycling as an alternate or an addition the belt just after rounding the roller 18 can be provided with a precoat of spirulina from a source 34 this feeds through a duct 36 onto the belt surface while the set of sprays 31 is preferred it is sometimes helpful to utilize a precoat in air from a source such as the duct 36 leading from the tank 34 this apparatus works appropriately to utilize a relatively large filamentous preferably spirally or helically configured alga as a filter aid or medium or as part of a way of separating a much smaller generally flexible alga such as dunaliella from its carrier liquid the product is somewhat an admixture of both dunaliella and spirulina but since the two algae are generally suitable for the same purposes the fact of admixture is not detrimental the method involved includes providing on a suitable filtering substrate a first coating.