Abstract: The process includes operation as follows: putting ozone generated by an ozone generator into raw water, in a normal mode, to subject the raw water to ozone treatment; injecting a flocculant into the raw water before or after the ozone treatment; filtering the raw water by a separation membrane after the ozone treatment and the injection of the flocculant; and intermittently setting cleaning mode to put a larger quantity of cleaning ozone than that in the normal mode into the raw water so as to intermittently increase the concentration of dissolved ozone, thereby cleaning the filtration membrane.

Abstract: A method of wastewater reutilization by which reusable water can be stably obtained from a wastewater. Ozone is added to a wastewater, such as water resulting from sewage treatment, in such a small amount as to result in a residual ozone concentration as measured before membrane filtration of 0.01-1.0 mg/L. Ozone is thus brought into contact with fine solids contained in the wastewater to alter the surface properties of the fine solids so that the solids are easily to coagulate. Thereafter, a coagulant, e.g., PACl, is added from a coagulant addition device (3). The fine solids are coagulated in a coagulation tank (5) or a line mixer and the resultant water is subjected to membrane filtration with an ozone-resistant separation membrane (6) such as ceramic membrane. Thus, reusable water is obtained which has a residual ozone concentration, as measured after filtration through the membrane, less than 0.5 mg/L.

Abstract: When a separation membrane (3) is washed with a chemical solution that is a sodium hypochlorite solution, which has a high concentration, diluted with membrane treated water stored in a chemical solution tank (6), an ammonic nitrogen concentration in membrane-treated water is monitored with a monitoring device (9), and a control device (8) controls a chemical solution dosing pump (7) using the concentration measured by the device (9) to adjust a dilution rate. Thereby, even when water quality of membrane-treated water varies, a sodium hypochlorite concentration in backwashing water can be retained constant, and fluctuation in the chemical washing effect can be prevented.

Abstract: The process includes operation as follows: putting ozone generated by an ozone generator into raw water, in a normal mode, to subject the raw water to ozone treatment; injecting a flocculant into the raw water before or after the ozone treatment; filtering the raw water by a separation membrane after the ozone treatment and the injection of the flocculant; and intermittently setting cleaning mode to put a larger quantity of cleaning ozone than that in the normal mode into the raw water so as to intermittently increase the concentration of dissolved ozone, thereby cleaning the filtration membrane.

Abstract: The invention provides a side stream type membrane bioreactor process which does not cause an excessive fall in the MLSS concentration in a bioreactor, does not require any additional effluent treatment facility for discharging backwash effluent, and can further ensure the stability of the membrane filtration performance of a separation membrane. According to the invention, in a side stream type membrane bioreactor process, a backwash effluent containing foulants that are generated by backwashing a separation membrane is collected in a backwash effluent tank, and subjected to ozone treatment, and the resultant is returned to a bioreactor. By this ozone treatment, the foulants close to the membrane pore size of the separation membrane are made fine or are made into a state be easily taken into activated sludge flocs. Therefore, even when the treated effluent is returned to the bioreactor, the membrane filtration performance of the separation membrane is not deteriorated.

Abstract: There is provided a process capable of inexpensively producing reclaimed water having excellent quality from wastewater without using a large amount of ozone. The process for producing reclaimed water comprises: bringing ozone into contact with raw water such as treated sewage using an ozone contact column 2 or the like to enhance coagulability of a solid matter contained in the raw water; injecting a coagulant into the raw water using a coagulant-injecting pump 6 to coagulate the solid matter; and membrane-filtering the coagulated solid matter through a separation membrane 8. A residual ozone concentration in the raw water before a separation membrane is measured by a dissolved-ozone meter 5. When deterioration of quality of the raw water results in an ozone demand exceeding capacity of an ozone generator and in the residual ozone concentration lower than a given value, an amount of the coagulant to be injected is increased.

Abstract: The invention provides a side stream type membrane bioreactor process which does not cause an excessive fall in the MLSS concentration in a bioreactor, does not require any additional effluent treatment facility for discharging backwash effluent, and can further ensure the stability of the membrane filtration performance of a separation membrane. According to the invention, in a side stream type membrane bioreactor process, a backwash effluent containing foulants that are generated by backwashing a separation membrane is collected in a backwash effluent tank, and subjected to ozone treatment, and the resultant is returned to a bioreactor. By this ozone treatment, the foulants close to the membrane pore size of the separation membrane are made fine or are made into a state be easily taken into activated sludge flocs. Therefore, even when the treated effluent is returned to the bioreactor, the membrane filtration performance of the separation membrane is not deteriorated.

Abstract: A method of wastewater reutilization by which reusable water can be stably obtained from a wastewater. Ozone is added to a wastewater, such as water resulting from sewage treatment, in such a small amount as to result in a residual ozone concentration as measured before membrane filtration of 0.01-1.0 mg/L. Ozone is thus brought into contact with fine solids contained in the wastewater to alter the surface properties of the fine solids so that the solids are easily to coagulate. Thereafter, a coagulant, e.g., PACl, is added from a coagulant addition device(3). The fine solids are coagulated in a coagulation tank(5) or a line mixer and the resultant water is subjected to membrane filtration with an ozone-resistant separation membrane(6) such as ceramic membrane. Thus, reusable water is obtained which has a residual ozone concentration, as measured after filtration through the membrane, less than 0.5 mg/L.

Abstract: A method of cleaning a membrane in a membrane separation activated-sludge process. By the method, deposits adherent to the surface of a membrane used in a membrane separation activated-sludge process can be effectively scratched off and the membrane filtration rate can be prevented from decreasing. Membrane-cleaning particles (4) in which the surface to be in contact with the water to be treated has been hydrophilized and has a surface roughness of 100-2,500 ?m are introduced into a bioreactor (1). The particles are caused to flow by the lifting effect of air bubbles ejected from an aerator (3) or by the fluidizing effect of a fluidizing means to thereby cause the particles to scratch off deposits adherent to the surface of a separation membrane element (2). In one embodiment, membrane-cleaning particles (4) which are non-porous or have closed cells are used.

Abstract: A method of cleaning a membrane in a membrane separation activated-sludge process. By the method, deposits adherent to the surface of a membrane used in a membrane separation activated-sludge process can be effectively scratched off and the membrane filtration rate can be prevented from decreasing. Membrane-cleaning particles in which the surface to be in contact with the water to be treated has been hydrophilized and has a surface roughness of 100-2,500 ?m are introduced into a bioreactor. The particles are caused to flow by the lifting effect of air bubbles ejected from an aerator or by the fluidizing effect of a fluidizing means to thereby cause the particles to scratch off deposits adherent to the surface of a separation membrane element. Membrane-cleaning particles which are non-porous or have closed cells can be used. Membrane-cleaning particles having an antibacterial ingredient can be supported on the surface or in inner parts thereof.

Abstract: When an out-of-basin type separation membrane, which is connected to a biological treatment tank through a circulation passageway for filtering tank water, is cleaned, a part or all of the backwash drainage containing the sludge peeled from the membrane surface is returned to the biological treatment tank through a backwash drain passageway or circulation passageway to maintain MLSS of the biological treatment tank constant. In the case of chemical cleaning, the sludge is peeled from the membrane surface by backwash with water, and the sludge is discharged out of the membrane module through a sludge line and then followed by chemical cleaning. Thus the need for using a large amount of a chemical solution is eliminated and the peeled sludge containing the chemical solution can be discharged out of the system as well, thereby preventing the microorganism from being damaged by the chemical solution.

Abstract: When a separation membrane (3) is washed with a chemical solution that is a sodium hypochlorite solution, which has a high concentration, diluted with membrane treated water stored in a chemical solution tank (6), an ammonic nitrogen concentration in membrane-treated water is monitored with a monitoring device (9), and a control device (8) controls a chemical solution dosing pump (7) using the concentration measured by the device (9) to adjust a dilution rate. Thereby, even when water quality of membrane-treated water varies, a sodium hypochlorite concentration in backwashing water can be retained constant, and fluctuation in the chemical washing effect can be prevented.

Abstract: Pulse back washing for applying a back pressure from the filtrate side to the raw water side of the membrane is repeated plural times for recovering a TMP during usual main back washing applied by suspending membrane filtration, when the TMP is increased when tank water extracted out of a biological treatment tank 1 is filtrated through the membrane by a cross-flow method. Pulse back washing is applied at a stage when the TMP is 80% or less of the permissible TMP to peel the deposits on the membrane surface, and the peeled deposits are returned to the biological treatment tank concomitantly with a circulating flow. Clogging substances on the separation membrane is removed in a direction opposite to the direction of pulse back washing by selecting the destination of discharge of back wash drain to be the inlet side of the separation membrane in the main back wash step.

Abstract: When an out-of-basin type separation membrane, which is connected to a biological treatment tank through a circulation passageway for filtering tank water, is cleaned, a part or all of the backwash drainage containing the sludge peeled from the membrane surface is returned to the biological treatment tank through a backwash drain passageway or circulation passageway to maintain MLSS of the biological treatment tank constant. In the case of chemical cleaning, the sludge is peeled from the membrane surface by backwash with water, and the sludge is discharged out of the membrane module through a sludge line and then followed by chemical cleaning. Thus the need for using a large amount of a chemical solution is eliminated and the peeled sludge containing the chemical solution can be discharged out of the system as well, thereby preventing the microorganism from being damaged by the chemical solution.