NOVELTY - Harvesting or separating one or more biological cells from an aqueous feed or stream, comprises: providing the aqueous feed or stream comprising the biological cells in a tank or a vessel; precipitating one or more solids in the aqueous feed or stream, where the biological cells are associated with the precipitated solids; allowing the precipitated solids to settle to a bottom portion of the tank or the vessel; separating an aqueous supernatant from the settled solid precipitate; and acidifying the settled solid precipitate.    USE - The method is useful for harvesting or separating one or more biological cells from an aqueous feed or stream for producing a biodiesel, a fatty acid methyl ester, a biofuel and/or their modifications from a microalgal cell culture, where the biological cells comprise algal cells, bacterial cells and/or viral cells, the algal cells comprise microalgae including a class comprising Bacillariophyceae, Eustigmatophyceae or Chrysophyceae, the microalgal genera are Nannochloropsis, Chlorella, Dunaliella, Scenedesmus, Selenastrum, Oscillatoria, Phormidium, Spirulina, Amphora or Ochromonas, and the microalgal species are e.g. Achnanthes orientalis, Agmenellum spp., Amphiprora hyaline, Amphora coffeiformis, Amphora coffeiformis var. linea, Amphora coffeiformis var. punctata, Amphora coffeiformis var. taylori, Amphora coffeiformis var. tennis, Amphora delicatissima, Amphora delicatissima var. capitata, Amphora sp., Anabaena, Ankistrodesmus, Ankistrodesmusfalcatus, Boekelovia hooglandii, Borodinella sp., Botryococcus braunii, Botryococcus sudeticus, Bracteacoccus minor, Bracteococcus medionucleatus, Carteria, Chaetoceros gracilis, Chaetoceros muelleri, Chaetoceros muelleri var. subsalsum, Chaetoceros sp., Chlamydomas perigranulata, Chlorella anitrata, Chlorella antarctica, Chlorella aureoviridis, Chlorella candida, Chlorella capsulate, Chlorella desiccate, Chlorella ellipsoidea, Chlorella emersonii, Chlorella fusca, Chlorella fusca var. vacuolate, Chlorella protothecoides var. Acidicola or Chlorella regularis, and the aqueous feed or stream comprises saltwater, brackish water, fresh water and/or treated wastewater (all claimed).    ADVANTAGE - The method: allows continuous harvesting of algae from a variety of source waters; does not add contaminants that can limit the downstream usage possibilities for the algae concentrate produced; and is cost effective, scalable, and generates useful effluent water and algae concentrate as products.    DETAILED DESCRIPTION - Harvesting or separating one or more biological cells from an aqueous feed or stream, comprises: either (a) providing the aqueous feed or stream comprising the biological cells in a tank or a vessel, (b) precipitating one or more solids in the aqueous feed or stream, where the biological cells are associated with the precipitated solids, (c) allowing the precipitated solids to settle to a bottom portion of the tank or the vessel, (d) separating an aqueous supernatant from the settled solid precipitate, and (e) acidifying the settled solid precipitate, where the acidification results in a separation or a release of the biological cells from the solid precipitate to form a concentrated slurry comprising the biological cells; or (a1) the step (a) as above per se, (b1) raising a pH of the aqueous feed or stream by addition of a base, (c1) the step (b)-(d) as above per se, and (d1) contacting the settled solid precipitate with carbon dioxide or other acid to acidify the solid precipitate. INDEPENDENT CLAIMS are included for:    (1) the microalgal cells harvested by the method; and    (2) an apparatus for producing a biodiesel, a fatty acid methyl ester, a biofuel and/or their modifications from a microalgal cell culture, comprising an algal growth tank or a cultivation tank comprising the aqueous feed or stream for growing the algal species in presence of water and other growth factors comprising nutrients, minerals, carbon dioxide, air or light, a harvesting tank for separating or harvesting the microalgal cell culture from the aqueous feed or stream, where the method of harvesting or separating the microalgal cell culture comprises the step (b1)-(d1) as above per se, and a processing unit for processing the concentrated slurry of the microalgal cells comprising one or more lysing units to electromechanically lyse the microalgal cell culture by application of an electromagnetic field, where the lysis results in a release of one or more cellular components comprising oils, neutral lipids, proteins, triglycerides, sugars and/or their modifications from the algal cells, one or more separations unit to separate the released oils and lipids from the medium resulting in a generation of a residual biomass, a reaction vessel for converting the separated algal lipids, triglycerides to the biodiesel, fatty acid methyl ester, biofuel and/or their modifications by a transesterification reaction, one or more optional pumping equipment, heat exchangers, distilling equipment, reboilers, condensors and/or their modifications, one or more power supply units to provide electricity to run the dewatering, lysing, and separations units and to remotely operate the unit, and one or more control panels to operate and monitor the performance of the dewatering, lysing, and separations units.