NOVELTY - Method (M1) for clarifying feed containing target biomolecule and several cellular debris and/or colloidal particulates by depth filtration, involves providing a depth filtration device having a porous depth filter media, providing a feed containing a target biomolecule and several cellular debris and/or colloidal particulates, contacting the depth filter media with the feed, and separating the target biomolecule from the cellular debris and the colloidal particulates in the feed.    USE - The method (M1) is useful for clarifying feed containing target biomolecule and several cellular debris and/or colloidal particulates by depth filtration. The target biomolecule is chosen from monoclonal antibodies (mAbs), polyclonal antibodies, and biotherapeutics. The feed is chosen from cell cultures, transgenic mammalian cell cultures, bacterial cell cultures, non-transgenic mammalian cell cultures, tissue cultures, microbial fermentation batches, plant extracts, biofuel, seawater cultures, freshwater cultures, wastewater cultures, treated sewage, untreated sewage, milk cultures, blood cultures, and their combinations. The method (M2) is useful for purifying target protein from sample (claimed).    ADVANTAGE - The method (M1) is performed without using primary clarification centrifugation or primary clarification tangential flow microfiltration, reliable and cost-effective, and produces target biomolecules with high purity.    DETAILED DESCRIPTION - Method (M1) for clarifying feed containing target biomolecule and several cellular debris and/or colloidal particulates by depth filtration, involves (a) providing a depth filtration device having a porous depth filter media, providing a feed containing a target biomolecule and several cellular debris and/or colloidal particulates, contacting the depth filter media with the feed, and separating the target biomolecule from the cellular debris and the colloidal particulates in the feed, or (b) providing a depth filtration device having a porous depth filter media, providing a chemical flocculant, providing a feed containing a target biomolecule and several cellular materials and/or colloidal particulates, adding the chemical flocculant to the feed, forming a chemically flocculated feed including flocculated cellular materials and/or colloidal particulates, contacting the depth filter media with the chemically flocculated feed, and separating the target biomolecule from the flocculated cellular materials and/or flocculated colloidal particulates in the feed. INDEPENDENT CLAIMS are included for the following:    (1) depth filtration device comprising a porous depth filter media having at least 2 graded layers of non-woven fibers having a total thickness of 0.3-3 cm, and the pores have a nominal pore size rating of 25 mu m or more; and    (2) method (M2) for purifying a target protein from a sample, involves (i) providing a sample comprising a target protein and one or more impurities, (ii) adding a precipitant to the sample and removing one of more impurities using a gradient density depth filter to obtain a clarified sample, (iii) subjecting the clarified sample to a bind and elute chromatography step, (iv) contacting the eluate from step (iii) with one or more virus inactivating agents using one or more in-line static mixers or one or more surge tanks, (v) subjecting the output of the virus inactivation step to a flow-through purification process using two or more matrices chosen from activated carbon, anion exchange chromatography media, cation exchange chromatography media and virus filtration membrane, and (vi) formulating the output from step (v) at desired concentration and buffer conditions, where the process is performed continuously such that at least two or more of the process steps are performed concurrently during at least portion of their duration.