Recovery cleans on MEMPAC systems with Membranes

Recovery cleans on MEMPAC systems with Membranes


Overview of automated CIP’s and Recovery Cleans:

The typical membrane cleaners used on MEMPAC systems are Sodium Hypochlorite to remove organics, and citric acid to remove inorganics (hardness).  Sodium hypochlorite is used at a higher frequency, as organics can grow on the membrane fibers and reduce permeability if not kept in check.

The MEMPAC performs automated CIP’s (sometimes called Maintenance cleans) which can be scheduled and/or initiated via the SCADA on the system.  The operator can choose the dates and times when an automated CIP occurs.  The process typically lasts one hour, and during this time, the membrane train is not available to produce filtrate. IMPORTANT: the operator should not schedule cleans to occur at the same time on different membrane trains.

A Recovery Clean is a manual process which is done less often and at a higher chemical concentration.  Optimizing CIP’s (Maintenance cleans) will reduce the frequency of Recovery cleans.

The following table is a recommendation for cleaning frequency for ZeeWeed membranes (courtesy Veolia).  Confirm which type of membranes are installed in your system in the vendor data section to ensure your cleaning strategy aligns.

Coagulant Addition in Influent

Effluent (Permeate) Alkalinity (mg/L)

Maintenance Cleaning (number per week)

Typical Duration (h)

Recovery Cleaning (number per year)

Typical Duration (h)

Sodium Hypochlorite 200 mg/L

Citric Acid 2000 mg/L

Sodium Hypochlorite 1000 mg/L

Citric Acid 2000 mg/L

No

< 70

2

0

1–1.5

2–4

1–2

10

No

> 70

2

1

1–1.5

2–4

1–2

10

Yes

< 70

2

1

1–1.5

2–4

1–2

10

Yes

> 70

2

1

1–1.5

2–4

1–2

10

IMPORTANT:
the two chemicals must never be used at the same time or otherwise come into contact with each other.  If cleans with each chemical are performed in succession, ensure all common lines, tankage, components are fully flushed beforehand.

Steps for performing a manual Recovery Clean:

Items required for each cleaning on each membrane tank:

l 
Access to clean water and hoses, and enough flow to fill your membrane tank in about 1-2 hours to protect the membranes from drying out.

l 
Access to a submersible pump or external pump to drain down the membrane tank if hydraulic profile does not allow for gravity draining.

l 
Required gallons of standard 12% sodium hypochlorite per membrane tank

l 
Required gallons of 50% citric acid per membrane tank

l 
PPE (Personal Protective Equipment)

The following table is an example cleaning process from the membrane vendor and with additional details for Cloacina systems.  There are several methods to perform this process, so speak to Cloacina if your site has specific needs to address.

Step

Process

1

For the membrane chamber to be cleaned, stop permeation and continue FAS and aeration for an hour to assist with removing solids from the membranes.

2

Turn off the isolation valve on the FAS line (remember to open this back up after the clean) and turn off membrane aeration.

3

Open membrane drain valve if hydraulics allow for draining of the mixed liquor into tankage such as an upstream lift station, equalization, or the bioreactor (via the RAS chamber is often convenient).  

If this is not possible, attach a gas or electric pump to the drain line to allow for pressurized flow to one of the locations noted above.

Sample portable pump: https://www.harborfreight.com/2-in-212cc-gasoline-engine-semi-trash-water-pump-158-gpm-63405.html?hftm_sc=171&utm_source=google

Another option which requires more caution is to place a submersible pump in the corner of the membrane chamber (ensuring the membranes aren’t touched by the pump or the hose/power wire at any time).

Begin draining the tank.

4

Use a clean water hose to wash down the cassette fibers as the tank is being drained. For water pressure, test by holding the hose horizontally 3 feet above the ground, and the water should land 3 feet away.  Then use this to wash down any accumulated solids and treat the fibers gently

5

Once the tank is drained and as much of the solids as possible have been pumped away, fill the tank with clean water, while ensuring the hose and flow aren’t touching the membranes. 

Use another line with a water sprinkler on top of the tank to keep the membranes moist, if necessary, due to environmental conditions.

6

Aerate the tank for another hour

7

If the membrane fibers are still surrounded by solids, you may need to aerate and drain/refill again. (Steps 3 to 6)

8

Once all the membrane fibers are fully submerged with clean water, add the hypochlorite or citric acid (only one chemical type clean to be done at a time) into the side of the tank (avoid hitting the membranes).

9

Allow membranes to soak in residual chemical concentration for 6-16 hours. Membranes should be aerated for 20 seconds every 30 minutes for mixing during soak if possible.

10

Drain the cleaning solution to the sludge holding tank.

11

Open the FAS line valve and return the train to normal operation.

The same procedure can then be repeated, though with citric acid instead of hypochlorite.

It is extremely important that the cleans do not happen at the same time and the different chemicals never touch each other, as poisonous gas can be released.

The following table will provide details on how much chemical is required per membrane tank for each clean.

System

Tank Length (Feet)

Tank Width (Feet)

Tank cleaning volume
(US Gallons)

Volume of 12% Sodium Hypochlorite stock solution to use if performing an organics clean
(US Gallons)

Volume of 50% Citric Acid stock solution to use if performing an inorganics clean
(US Gallons)

MEMPAC-M

7

8

3,710

31

12.2

MEMPAC-R

7

3.9

1,523

12.7

5

MEMPAC-Mini

3

3

539

4.5

1.8

MEMPAC-H

7

8

3,710

31

12.2

MEMPAC-X

4

5

1,198

10

3.9

MEMPAC-I

6

4

1,437

12

4.7
If preferred, Cloacina can provide cleaning services for your facility.

Note: Membrane vendors recommend an inspection of membranes on an annual basis, which should occur after a Recovery Clean. 




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