Chemical cleaning backwash for normally immersed membranes
First Claim
1. A method for cleaning one or more membranes normally immersed in a water containing solids in a tank and used to produce a permeate comprising:
- performing cleaning events having the steps of;
(a) stopping permeation;
(b) flowing a selected concentration of a chemical cleaner through the membranes in a direction opposite to the direction in which permeate passes through the membranes, while the membranes remain immersed in the water containing solids, in repeated pulses followed by waiting periods, the repeated pulses and waiting periods in a cleaning event cumulatively having a selected duration; and
, (c) resuming permeation;
wherein the membranes are not agitated while the chemical cleaner is flowed through the membranes.
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Accused Products
Abstract
A method of chemically cleaning normally immersed suction driven filtering membranes involves backwashing a chemical cleaner through the membranes while the tank is empty in repeated pulses in which the chemical cleaner is pumped to the membranes separated by waiting periods in which chemical cleaner is not pumped to the membranes. The duration and frequency of the pulses is preferably chosen to provide an appropriate contact time of the chemical, preferably without allowing the membranes to dry between pulses and without using excessive amounts of chemical. In other aspects, such membranes preferably used for filtering water to produce potable water in a batch process are backwashed with a chemical cleaner substantially at the same time as the tank is being drained. The chemical cleaner is optionally supplied in pulses. In other aspects, chemical cleaner backwashes are started before the membranes foul significantly and are repeated at least once per week to reduce the rate of decline in the permeability of the membranes so that intensive recovery cleaning is required less frequently. When performed in situ, each cleaning event comprises (a) stopping permeation and any agitation of the membranes, (b) backwashing the membranes with a chemical cleaner in repeated pulses and (c) resuming agitation, if any, and permeation. The pulses last for between 10 seconds and 100 seconds and there is a time between pulses between 50 seconds and 6 minutes. Each cleaning event typically involves between 5 and 20 pulses.
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Citations
30 Claims
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1. A method for cleaning one or more membranes normally immersed in a water containing solids in a tank and used to produce a permeate comprising:
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performing cleaning events having the steps of;
(a) stopping permeation;
(b) flowing a selected concentration of a chemical cleaner through the membranes in a direction opposite to the direction in which permeate passes through the membranes, while the membranes remain immersed in the water containing solids, in repeated pulses followed by waiting periods, the repeated pulses and waiting periods in a cleaning event cumulatively having a selected duration; and
,(c) resuming permeation;
wherein the membranes are not agitated while the chemical cleaner is flowed through the membranes. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method for cleaning one or more membranes immersed in water rich in solids and used to permeate a water lean in solids wherein each cleaning event comprises the steps of:
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(a) stopping permeation and agitation of the water containing solids;
(b) flowing a chemical cleaner through the membranes in a direction opposite to the direction in which permeate passes through the membrane;
(c) resuming permeation; and
,(d) resuming agitation, and wherein permeate collected before resuming agitation is wasted or recycled to the water containing solids and wherein the membranes and the membranes remain immersed during steps (a), (b), (c) and (d).
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16. A method for cleaning one or more filtering membranes normally immersed in tank water containing solids in a tank and used to produce a permeate in one or more cleaning events, each cleaning event comprising the steps of:
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(a) stopping permeation;
(b) draining the tank water from the tank to below the level of the membranes; and
,(c) flowing a chemical cleaner in pulses through the membranes in a direction opposite to the direction in which water lean in solids normally permeates through the membranes; and
,(d) refilling the tank, wherein, (e) the cleaning events are performed at least once a week; and
,(f) the product of the concentration of the chemical cleaner expressed as an equivalent concentration of NaOCl in cleaning efficacy and the duration of all cleaning events in a week is between 2,000 minutes*mg/L and 20,000 minutes*mg/L. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25)
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26. A process for filtering water containing solids with membranes in a tank comprising the steps of:
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a) filling the tank with a feed water to be filtered to immerse the membranes;
b) creating a transmembrane pressure between a permeate side and a retentate side of the membranes, the retentate side of the membranes being in contact with the water in the tank, the permeate side being fluidly connected to a filtered permeate outlet, to generate a filtered permeate at the permeate outlet;
c) aerating the membranes to dislodge solids from the membranes;
d) backwashing the membranes;
e) draining the tank; and
,f) performing the steps above in repeated cycles wherein the steps of backwashing the membranes and draining the tank may be performed either before the other or partially or substantially simultaneously and the step of backwashing the membranes in the repeated cycles periodically involves backwashing with a cleaning chemical having a selected concentration for a selected duration. - View Dependent Claims (27, 28, 29, 30)
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Specification