US 5,254,253 AGranted

Modular shipboard membrane bioreactor system for combined wastewater streams

AssigneeZenon Environmental Inc.

InventorHenry Behmann

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Abstract

Raw sewage ("black water" from toilets), wastewater from showers, sinks, kitchen facilities ("grey water") and oily water from the bilge of a host vessel ("oily water"), in combination, unexpectedly provide the essential nutrients for a live mass of mixed microorganisms which are peculiarly well-adapted to ingest the nutrients. To facilitate availability of oxygen to the microorganisms so as to provide growth of the microorganisms, and also, to allow them destroy to themselves, excess oxygen is discharged, in a combination of microbubbles and macrobubbles, into a membrane bioreactor ("MBR"). The mixture of bubbles is preferably generated with coarse (>2 mm) and fine (<20 .mu.m) bubble diffusers. An auxiliary stream, whether alone, or a recirculating stream into which air is drawn, may provide the coarse bubbles. The air is entrained, in a jet aerator or eductor, in a recirculating loop of activated sludge taken from the MBR. Another portion of the contents of the MBR is pumped to a semipermeable membrane which provides water (permeate) of excellent quality. The remaining concentrate is led to a gas micronizing means which produces a tail-jet of microaerated concentrate. The tail-jet is returned to the MBR to provide kinetic energy for maintaining a high velocity of liquid flow in the MBR. A portion of the concentrate is disposed of. Preferably the liquid waste to be treated on-board does not substantially exceed about 21 meters.sup.3 /day.

Claims20

Dependent claims

A process for treating organic liquid waste generated on-board a host marine vessel, utilizing a membrane-bioreactor system, said process comprising,

(a) feeding an aqueous suspension of said liquid waste comprising black water, grey water, and oily water to a bioreaction zone containing live microorganisms adapted to digest said liquid waste;
(b) flowing activated sludge withdrawn from said bioreaction zone, to a membrane filtration zone at a velocity and pressure sufficient to maintain a predetermined membrane flux in said zone, at which flux essentially no solids are retained on the surface of said membrane having a predetermined molecular cut-off which will permit passage of only molecules smaller than 500,000 Daltons;
(c) separating water which is essentially solids-free, as a permeate, from a solids-containing concentrate, and removing the permeate from said membrane filtration zone;
(d) flowing said concentrate from said membrane filtration zone into a gas micronizing zone comprising a microporous air diffuser element without introducing additional energy into said concentrate until it is introduced into said micronizing zone;
(e) introducing said concentrate axially into said micronizing zone, while discharging into said zone a gas containing at least about 20% oxygen under pressure in the range from about 150 kPa to about 1000 kPa so as to incorporate micronized gas bubbles having an average diameter in the range from about 1 .mu.m to about 1000 .mu.m into said concentrate, forming a microaerated concentrate having separate gas and liquid phases;
(f) directly flowing a continuous stream of the microaerated concentrate from said micronizing zone into said bioreaction zone without introducing any additional energy into the microaerated concentrate after it leaves said micronizing zone;
(g) introducing a first tail-jet of said microaerated concentrate below the surface of liquid in the reactor to establish a recycle loop in said bioreaction zone;
(h) flowing an auxiliary stream of air in the form of coarse bubbles greater than about 2 mm in diameter, with enough energy to maintain a desirable recirculation pattern in said reaction zone;
and, at the same time, directing said first tail-jet into said bioreaction zone so as to maintain an average liquid velocity of at least 03. meter/sec within said bioreaction zone while also maintaining said recirculation pattern therein;
whereby an adequate hydraulic retention time, based on flow of said liquid waste, and solids retention time is obtained to retain soluble organics greater than said molecular weight cut-off in said reaction zone for a period at least 10 times longer than the hydraulic retention time based on liquid waste flow.

7 more elements

A treatment system for liquid waste generated aboard a host marine vessel, said system to be connected between an inlet for said liquid waste, and, an outlet for treated effluent, comprising,

(a) a bioreactor constructed and arranged to operate essentially continuously while maintaining a predetermined level of activated sludge within said bioreactor, with means for receiving said liquid waste to be contacted with waste-degrading microorganisms agglomerated as solids mixed in said waste, said bioreactor preferably being no higher than it is wide;
(b) pump means for withdrawing a suspension of said solids from said bioreactor, and pumping said suspension at elevated pressure through a discharge line;
(c) membrane filtration means in fluid 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 bioreactor and in direct open-flow communication with said concentrate stream from said filtration means, in fluid communication with said filtration means;
(e) auxiliary aeration means providing motive force with relatively coarse bubbles greater than about 2 mm in diameter introduced below the surface of said bioreactor to establish a recirculation pattern;
said gas micronizing means comprising, (i) a tubular microporous body coaxially housed in a housing means for containing 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 the concentrate stream to be flowed through the gas micronizing means;
control means on inlet means to modulate the flow of oxygen to said gas micronizing means, in an amount proportional to the residual dissolved oxygen ("DO") concentration;
and,
conduit means directly placing said outlet means from said micronizing means in open fluid 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;
said aerator means comprising a macroporous element through which air is flowed at a velocity sufficient to generate a chosen pattern of recirculation in said bioreactor while maintaining a liquid velocity of at least 0.3 meter/sec within said bioreactor.

9 more elements

In a continuous biodegradation process carried out in a marine host vessel, said 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 filtration zone from which a permeate of high quality water is continuously withdrawn, and the remaining solids-containing concentrate is recycled to said bioreaction zone;

said solids-containing concentrate is flowed into a micronizing zone comprising a microporous diffuser element externally disposed relative to said bioreaction zone, said solids-containing concentrate in said micronizing zone is contacted with an oxygen-containing gas at a pressure in the range from about 150-1000 kPa so as to microaerate said concentrate 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, said tail-jet is introduced 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;
the improvement comprising,
(a) combining black water, grey water, and oily water generated on board said host vessel into a liquid waste stream;
and,
(b) flowing an auxiliary stream of air in the form of coarse bubbles greater than about 2 mm in diameter with enough energy to maintain a desirable recirculation pattern in said reaction zone;
whereby activated sludge solids are separated only after flowing said biomass through said membranous filtration zone.

4 more elements

Dependencies are inferred from the claim text.

Facts

Application: 07/934,879Filed 21 Aug 1992 · continuation in part
Priority: 19 Nov 1991
Granted: 19 Oct 1993
Term ends: Not estimatedThe source records don’t support an estimate.

Classification27 codes

C02F 3/1284
Provisions for mixing or aeration of the mixed liquor: mixing devices
B01F 23/23123
Diffusers: consisting of rigid porous or perforated material
B01F 23/2373
Characterised by the physical or chemical properties of gases or vapours introduced in the liquid media: for obtaining fine bubbles, i.e. bubbles…
B01F 25/313
In conduits or tubes through which the main component flows: wherein additional components are introduced in the centre of the conduit