Shipboard wastewater treatment system

A method for treating wastewater in an onboard ship sewage treatment system having controlled suspended solids, the method comprising the steps of:

• (a) collecting wastewater in a collection tank;
• (b) transferring said wastewater to a bioreactor to oxidize organic material contained in said wastewater by adding oxygen or oxygen-enriched air thereto;
• (c) operating said bioreactor to provide a mixed liquor having a solids concentration of at least 5 g/l;
• (d) continuously increasing said solids concentration in said mixed liquor in said bioreactor to not greater than 25 g/l;
• (e) when the solids concentration in said mixed liquor reaches at least 15 g/l, removing about ½ to about ¾ of the volume of said mixed liquor from said bioreactor to provide a residual mixed liquor;
• (f) thereafter adding wastewater to said bioreactor to decrease said solids concentration of residual mixed liquor to not less than 5 g/l;
• (g) then further operating said bioreactor to increase said solids content again;
• (h) providing a hollow fiber membrane module container in liquid communication with said bioreactor;
• (i) disposing a hollow fiber membrane module substantially horizontally in said membrane container;
• (j) locating a gas dispersing means in said container beneath said hollow fiber membrane for gas sweeping said hollow fibers with air;
• (k) directing a flow of mixed liquor from said bioreactor to said container to cover said membranes to avoid substantial exposure of said hollow fibers membrane during motion of said ship;
• (l) returning concentrate from said hollow fiber membrane container to said bioreactor;
• and
• (m) removing purified water from said mixed liquor through said hollow fiber membranes as permeate to provide treated effluent.

An onboard ship sewage treatment system for treating wastewater, the system having controlled suspended solids, the system comprised of:

• (a) a collection tank for collecting wastewater;
• (b) a bioreactor in liquid communication with said collection tank for receiving wastewater, said bioreactor designed to oxidize organic material contained in said wastewater by adding oxygen-containing gas thereto, said bioreactor designed:
• (i) to be operated at a mixed liquor having a solids concentration of at least 5 g/l;
• (ii) to continuously increase said solids concentration in said mixed liquor in said bioreactor to not greater than 30 g/l;
• (iii) for removing a portion of the mixed liquor from said bioreactor when the solids concentration in said mixed liquor reaches at least 15 g/l;
• (iv) to decrease said solids concentration of remaining mixed liquor to not less than 5 g/l by adding wastewater thereto;
• and
• (v) for further operating said bioreactor to increase said solids content again;
• (c) a hollow fiber membrane module container in liquid communication with said bioreactor;
• (d) a fiber membrane module disposed substantially horizontally in said membrane container;
• (e) a gas dispersing means located in said container beneath said hollow fiber membrane module designed for sweeping said hollow fibers with gas, said container designed to receive mixed liquor from said bioreactor to a level which covers said membranes to avoid substantial exposure of said hollow fibers membrane during motion of said ship;
• (f) a concentrate return line for returning concentrate from said hollow fiber membrane container to said bioreactor;
• and
• (g) means for producing a reduced pressure on the inside of said hollow fiber membranes for removing purified water from said mixed liquor through said hollow fiber membranes as permeate to provide treated effluent.

A method for treating wastewater in an onboard ship treatment system having controlled suspended solids, the method comprising the steps of:

• (a) providing said wastewater in a bioreactor to oxidize organic material contained in said wastewater by adding oxygen-containing gas thereto;
• (b) operating said bioreactor to provide a mixed liquor having a solids concentration of at least 5 g/l, the bioreactor capable of being operated by increasing said solids concentration in said mixed liquor in said bioreactor to not greater than 30 g/l;
• (c) when the solids concentration in said mixed liquor reaches at least 15 g/l, removing a portion of the mixed liquor from said bioreactor;
• (d) thereafter adding wastewater to said bioreactor to decrease said solids concentration of remaining mixed liquor to not less than 5 g/l;
• (e) then further operating said bioreactor;
• (f) monitoring the dissolved oxygen (DO) content of said mixed liquor to provide a DO measurement;
• (g) relaying said DO measurement to a logic controller;
• (h) in said logic controller, comparing said DO measurement to previous DO measurements to provide a comparison;
• (i) in response to said comparison, maintaining or changing feed rate of said oxygen-containing gas to said mixed liquor to accommodate changes in organic flow rate to said bioreactor;
• (j) providing a hollow fiber membrane module container in liquid communication with said bioreactor;
• (k) disposing a hollow fiber membrane module in said membrane container;
• (l) locating a gas dispersing means in said container for sweeping said hollow fibers with gas;
• (m) directing a flow of mixed liquor from said bioreactor to said container to cover said membranes to avoid substantial exposure of said hollow fibers membrane during motion of said ship;
• (n) returning concentrate from said hollow fiber membrane container to said bioreactor;
• and
• (o) removing purified water from said mixed liquor through said hollow fiber membranes as permeate to provide treated effluent.

A method for treating wastewater in an onboard ship treatment system having controlled suspended solids, the method comprising the steps of:

• (a) providing wastewater in a bioreactor to oxidize organic material contained in said wastewater by adding oxygen-containing gas thereto;
• (b) operating said bioreactor to provide a mixed liquor having a solids concentration of at least 5 g/l;
• (c) permitting said solids concentration in said mixed liquor in said bioreactor to increase during said operating to not greater than 25 g/l;
• (d) when the solids concentration in said mixed liquor reaches at least 15 g/l, removing about ½ to about ¾ of the volume of said mixed liquor from said bioreactor to provide a residual mixed liquor;
• (e) thereafter adding wastewater to said bioreactor to decrease said solids concentration of residual mixed liquor to not less than 5 g/l;
• (f) then further operating said bioreactor to increase said solids content again;
• (g) monitoring the dissolved oxygen (DO) content of said mixed liquor to provide a DO measurement;
• (h) relaying said DO measurement to a logic controller;
• (i) in said logic controller, comparing said DO measurement to previous DO measurements to provide a comparison;
• (j) in response to said comparison, maintaining or changing feed rate of said oxygen-containing gas to said mixed liquor to accommodate changes in organic flow rate to said bioreactor;
• (k) providing a hollow fiber membrane module container in liquid communication with said bioreactor;
• (l) disposing a hollow fiber membrane module substantially horizontally in said membrane container;
• (m) locating a gas dispersing means in said container beneath said hollow fiber membrane for sweeping said hollow fibers with gas;
• (n) directing a flow of mixed liquor from said bioreactor to said container to cover said membranes to avoid substantial exposure of said hollow fibers membrane during motion of said ship;
• (o) returning concentrate from said hollow fiber membrane container to said bioreactor;
• and
• (p) removing purified water from said mixed liquor through said hollow fiber membranes as permeate to provide treated effluent.

A method for treating wastewater in an onboard ship treatment system wherein mixed liquor having high solids content generated in the system is discharged periodically, the method comprising the steps of:

• (a) introducing wastewater to a bioreactor to oxidize organic material contained in said wastewater by adding oxygen-containing gas thereto;
• (b) operating said bioreactor to provide a mixed liquor having a solids concentration of at least 5 g/l and to increase said solids concentration in said mixed liquor to not greater than 25 g/l;
• (c) when the solids concentration in said mixed liquor reaches at least 15 g/l, removing a portion of the mixed liquor from said bioreactor and adding wastewater to said bioreactor to obtain a solids concentration of not less than 5 g/l;
• (d) monitoring the dissolved oxygen (DO) content of said mixed liquor to provide a DO measurement;
• (e) relaying said DO measurement to a logic controller;
• (f) in said logic controller, comparing said DO measurement to previous DO measurements to provide a comparison;
• (g) in response to said comparison, maintaining or changing feed rate of said oxygen-containing gas to said mixed liquor to accommodate changes in organic flow rate to said bioreactor;
• (h) providing a hollow fiber membrane module container in liquid communication with said bioreactor, said container having:
• (i) a hollow fiber membrane module disposed therein;
• and
• (ii) gas dispersing means in said container for sweeping said hollow fibers with gas;
• (i) directing a flow of mixed liquor from said bioreactor to said container to maintain said container sufficiently full to avoid substantial exposure of said hollow fiber membranes during ocean motion of said ship;
• (j) returning concentrate from said hollow fiber membrane container to said bioreactor;
• and
• (kl) removing purified water from said mixed liquor through said hollow fiber membranes as permeate to provide treated effluent.

A method for treating wastewater in an onboard ship treatment system wherein mixed liquor having high solids content generated in the system is discharged periodically, the method comprising the steps of:

• (a) providing wastewater to a bioreactor to oxidize organic material contained in said wastewater by adding oxygen-containing gas thereto;
• (b) operating said bioreactor to provide a mixed liquor having a solids concentration of at least 5 g/l and not greater than 25 g/l;
• (c) monitoring the dissolved oxygen (DO) content of said mixed liquor to provide a DO measurement;
• (d) relaying said DO measurement to a logic controller;
• (e) in said logic controller, comparing said DO measurement to previous DO measurements to provide a comparison;
• (f) in response to said comparison, maintaining or changing feed rate of said oxygen-containing gas to said mixed liquor to accommodate changes in organic flow rate to said bioreactor;
• (g) providing a hollow fiber membrane module container in liquid communication with said bioreactor, said container having:
• (i) a hollow fiber membrane module disposed therein;
• and
• (ii) gas dispersing means in said container disposed for sweeping said hollow fibers with gas;
• (h) directing a flow of mixed liquor from said bioreactor to said container to maintain said container sufficiently full to avoid substantial exposure of said hollow fibers membrane during ocean motion of said ship;
• (i) returning concentrate and mixed liquor from said hollow fiber membrane container to said bioreactor;
• and
• (j) removing purified water from said mixed liquor through said hollow fiber membranes as permeate to provide treated effluent.