Membrane bioreactor system with in-line gas micronizer

In a continuous biodegradation process using live microorganisms in an aqueous environment to oxidize dissolved or suspended organic material in a bioreaction zone wherein biomass is aerated, and a portion of said biomass is withdrawn for circulation through a membranous ultrafiltration zone from which a permeate of high quality water is continuously withdrawn, and the remaining solids-containing concentrate is recycled to said bioreaction zone, the improvement comprising,

• (a) flowing said solids-containing stream from said membranous zone into a micronizing zone comprising a microporous air diffuser element externally disposed relative to said bioreaction zone;
• (b) contacting said solids-containing stream in said micronizing zone, with an oxygen-containing gas at a pressure in the range from about 150-1000 kPa so as to microaerate said stream infusing it with a multiplicity of gas bubbles in the range from 1-1000 .mu.m in diameter, and adding the energy of said gas to the kinetic energy of said solids-containing stream so as to provide a tail-jet leaving said micronizing zone;
• and,
• (c) introducing said tail-jet with sufficient motive force to establish a desired recirculation pattern of solids in said biomass, said motive force being provided by the sum of the energies in said solids-containing stream and said gas stream.

A wastewater treatment system to be connected between a wastewater inlet and an outlet for treated effluent, comprising,

• (a) a bioreactor constructed and arranged to operate essentially continuously while maintaining a predetermined liquid level of a biomass within said bioreactor, with means for receiving wastewater containing biodegradable solids, in which bioreactor said wastewater is contacted with waste-degrading microorganisms mixed therein;
• (b) pump means for withdrawing a suspension of said solids from said bioreactor, and impelling said suspension at elevated pressure;
• (c) membrane filtration means in direct, open flow-receiving communication with said pump means, said membrane filtration means including plural membrane element means for separating said suspended solids in a concentrate stream, from water permeate which is essentially free of solids, and means to duct said permeate away from said system;
• (d) a gas micronizing means exteriorly disposed relative to said biomass, and in direct, open flow-receiving communication with said concentrate stream from the filtration means, said gas micronizing means comprising, (i) at least one tubular microporous element having upstream and downstream ends connected by a longitudinal axial bore, said element coaxially housed within a housing means for containing said gas under elevated pressure and contacting said gas with said concentrate stream (ii) inlet means for said gas, and, (iii) inlet and outlet means for said concentrate stream;
• and,
• (e) conduit means directly placing said outlet means from the micronizing means in open flow communication with said wastewater in said bioreactor, said conduit means having a tail-jet outlet means for discharging a tail-jet of mixed gas and liquid phases below the surface of said wastewater at a velocity sufficient to generate a preselected pattern of recirculation in said bioreactor while maintaining an average liquid velocity of at least 0.3 meter/sec within said bioreactor.