(US5204001-A)      The fluid is pretreated in a zone of vol. large enough to equalise variation in flow rate and adapted to remove settlable solids and skimmable free oil, finely divided solids injurous to membranes are removed, the liq. fed to a bioreactor with hydraulic retention time of 24 hours and aerated in presence of organisms in suspension in the reactor at a solids retention time of 30 days.    The suspension from the reactor is passed through a membrane zone with rate so solids are not retained on the membrane surface with permeate flow greater than the feed. Permeate is flowed with concentrate to the bioreactor.    USE -   Used for continuously biodegrading biochemically oxidisable material of solids-contg. mix of easy and difficult to degrade waste fluid in a waste water stream from a metal-working plant    (US5401400-A)      A water-water treatment system for a metal-working plant has a buffer vessel in which free oil is skimmed off, and which receives a variable flow and delivers a constant flow to a filter removing solids larger than 106 mum. Filtrate passes to a bioreactor holding a constant-vol. reaction mass and with an aerator.    A pump withdraws biomass suspension at constant rate and passes at 25-150 psig to a membrane filter with multiple membrane elements and pore size 0.01-0.1 mum. The concentrate stream and a small part of the permeate are returned to the bioreactor.    USE/ADVANTAGE -   E.g. for an automobile mfg. plant. Long and more efficient operating life is permitted with a smaller reactor.    (EP560980-B1)      Continuous biodegradation of biochemically oxidisable material comprising a solids-contg. mixt. of easy and difficult-to-degrade waste fluids in a waste water stream from a metal-working plant, comprises (a) providing a pretreatment zone for the waste water, (b) removing finely divided solids injurious to membranes, from the skimmed waste water to provide a solids-depleted waste-water feed, (c) feeding this waste water feed at an constant rate of flow to a bio-reaction zone, (d) aerating the material in the presence of live microorganisms capable of degrading the materials, (e) flowing suspension through membranous filtration zone at a velocity and pressure sufficient to maintain a predetermined membrane flux in the filtration zone, (f) sepg. permeate from a concentrate contg. the solids, (g) flowing the concentric from the membranous filtration zone into the bio-reaction zone as a concentric recycle, (h) removing an effluent of acceptable quality, (i) flowing excess permeate over that removed as effluent, back to the bio-reaction zone, and (j) periodically removing a minor proportion by vol. of the concentrate recycle to modulate the solids content in the bio-reaction zone.    USE -   For treating mixts. of natural hydrocarbons and synthetic metal-working fluids, fats, oils and greases and synthetic organic and organometallic cpds. in waste water