Biofouling of Reverse Osmosis Membranes in a Petrochemical Complex: Possibility of Anti-Microbial Coating Based on Initial Experimental Results: A Case Study
Subject Areas : Biotechnological Journal of Environmental Microbiology
Kiana Alasvand
1
(Poya sanat Arya Company, Tehran, Iran )
Keywords: Biofilm, Biofouling, Biodeterioration, Reverse osmosis (RO)-Antimicrobial coating, Temenos,
Abstract :
AbstractIn this root cause analysis, biofouling of membranes in the reverse osmosis (RO) unit of a Petrochemical Complex is studied. The overall cause of getting biofouling was found to be inappropriate water treatment of Pre-RO systems. More specifically, the undertreatment of water by sand filters, pressurized filters, and cartridges caused increased microbial contamination on RO membranes, leading to biofouling. Biodegradation of polymers is a mechanism by which the act of microorganisms will cause loss of mechanical integrity in such materials. It is important to understand the mechanism and look for ways by which such a mechanism can be controlled. The following were advised to control biofouling in the RO system of this Petrochemical complex 1. Chemical washing of sand filters as pressurized filters as well as RO membranes, 2. Application of UV or removal of chemical chlorination and installation of non-oxidizing biocides after chlorination,3. Replacement of Phosphorus-containing anticalins instead of non-phosphorus sealants,4. Application of superhydrophobic anti-microbial coatings on membranes
INTERNATIONAL CONFERENCE ON MATERIALS corrosion, heat treatment, testing and tribology, 2021
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رسوب زیستی (بیو فولینگ) غشاهای اسمز معکوس در یک مجتمع پتروشیمی:
امکان اعمال پوشش ضد میکروبی بر اساس نتایج تجربی اولیه-بررسی موردی
دکتر رضا جواهردشتی،دکتر کیانا علسوند، دکتر آرزو عصاریان
چکیده:
در این تحلیل علت ریشه ایRoot Cause Analysis))، رسوب زیستی غشاها در واحد اسمز معکوس (RO) یک مجتمع پتروشیمی مورد بررسی قرار می گیرد. علت کلی رسوب زیستی، تصفیه نامناسب آب سیستم‌های Pre-RO بود. به طور خاص تر، تصفیه آب توسط فیلترهای شنی، فیلترهای تحت فشار و کارتریج باعث افزایش آلودگی میکروبی در غشاهای RO و در نتیجه منجر به رسوب زیستی می شود. تجزیه بیولوژیکی پلیمرها مکانیسمی است که توسط آن عمل میکروارگانیسم ها باعث از بین رفتن یکپارچگی مکانیکی این مواد می شود. درک مکانیسم و جستجوی راه‌هایی برای کنترل چنین مکانیزمی بسیار مهم است. موارد زیر جهت کنترل رسوب زیستی در سیستم RO این مجتمع پتروشیمی توصیه شد:
1. شستشوی شیمیایی فیلترهای شنی به عنوان فیلترهای تحت فشار و همچنین غشاهای RO،
2. استفاده از اشعه ماوراء بنفش یا به طور متناوب، حذف کلرزنی شیمیایی و نصب بیوسیدهای غیر اکسید کننده پس از کلر.
3. جایگزینی آنتیکالین های حاوی فسفر به جای سیلانت های غیر فسفری،
4. اعمال پوشش های ضد میکروبی فوق آبگریز(superhydrophobic) بر روی غشاها.
کلمات کلیدی: تخریب زیستی - رسوب زیستی - اسمز معکوس (RO) - پوشش ضد میکروبی- بیوفیلم- Temenos.
Biofoulingiofouling of Revrse Osmosis membranes In a Petrochemical COMPLEX: POSSIBILITY of anti-microbial coating based on initial experimental results-A Case study
Reza Javaherdashti1,Arezoo Assarian1,Kiana Alasvand2
Abstract
In this root cause analysis, biofouling of membranes in the reverse osmosis (RO) unit of a Petrochemical Complex are studied. The overall cause of getting biofouling was found to be inappropriate water treatment of Pre-RO systems. More specifically, undertreatment of water by sand filters, pressuresrised filters and cartridges caused increase in microbial contamination on RO membranes and therefore leading into biofouling. Biodegradation of polymers is a mechanism by which the act of microorganisms will cause loss of mechanical integrity in such materials. It is important to understand the mechanism and look for ways by which such mechanism can be controlled. The following were advised to control biofouling in RO system of this Petrochemical complex.
1. Chemical washing of sand filters as pressurised filters as well as RO membranes,
2. Application of UV or alternatively, removal of chemical chlorination and installation of non-oxidising biocides after chlorination,
3. Replacement of Phosphorus-containing anticalins instead of non-phosphorus sealants,
4. Application of superhydrophobic anti-microbial coatings on membranes.
Keywords: Biodeterioration-Biofouling- Reverse osmosis (RO)-Antimicrobial coating, biofilm, Temenos.
Introduction
Reverse Osmosis (RO) is a method by which the water needed by industrial units is refined. By application of pressure on the water to pass it through semi-permeable spiral-shaped membranes, about 99% of the salts in the water are separated from it physically. RO is a routine process applied in industry and some of its advantages are low energy consumption, high efficiency and high rate of recyclying purified water from contaminated waters. On the hand, however, one of their serious drawbacks is that they are very suitable environmnets to allow “fouling”.
Four main types of foulings common in RO systems are:
1. Organic debris fouling
2. Non-organic debris fouling (trap of colloids and other particles)
3. Crystal fouling (slits)
4. Biofouling
A case of biofouling of RO memberans in a Petrochemical complex has been root cause analysed. More RO systems are composed of two phases:
Phase 1 (Pre-treatment): In this phase, via filteration and goacoliation of the feed water, solid and sustained particles in the feed water are separated. As a common practice, multi-media filters are used to pick up particles between 5 to 20 microns. Cartridge filters, on the other hand, separate more than 10 microns colloids and microoragnisms. Chemical treatment (such as Chlorisationor application of biocides) is also done at this phase.
Phase 2: The focus in this phase is the RO’s semi-permeable membranes. In this phase, the water is passed through the memberanes with high pressure. Each bundle contains about 30 polyamid spiral membrane folios. Each folio is made up two memebranes with a permeate spce in between. To make a unit of RO memberane, membranes with a feed spscer in between are wrapped around eachother. Upon purification, the feed water enters via feed canals and leaves as brine (10-20% of the feed water leaves the system as brine).
The cardinal elements of the water purification circuit can be shown in Figure 1. However, it is important to understand biofilm formation mechanism (in water containing environment) and, even most importantly, why biofilm is a wrong name for a correct concept and what can be suggested instead.
Figure 1: Main elements of water purification circuit where filters and RO unit and their role in whole circuit.
Biofouling happens when biofilm is formed on the memberanes. The biofilm thus formed can have a lot of adverse effects perhaps the most important of which will be reducingthe Feasibility of the treatment. Figure 2 shows the examples of biofilms formed on the memberanes:
Figure 2: (Clockwise) Example of the biofilm formed on the membernes from different angles.
1. Biofilm Formation dynamism:
Biofilm is actually a process of contnous construction-decosnstraction that contuse till an external factor (chemical , such as application of biocides; mechanical-physical, such as scrubbing/pigging) destroys its survival. One very important point here is that “Biofilm” is a wrong name for a right mechanim, because a biofilm is neither completely made up of biological material nor it has a film structure, the best alternative term we have proposed is “Temenos” [1]. In this paper, from now on, instead of technically wrong term of “Biofilm”, we will be using the term “Temenos”.
Figure 3 shows various steps involved in Temenos formation:
Figure 3: Six steps involved in biofilm formation [2]
Temenos can be leading into pitting most probably by creating electrochemical cells such as but not limited to differential aeration cells via mechanisms shown in Figure 4:
Figure 4: Schematic presentation of establishing differential aeration cells and differential concentration cells leading into pitting in the vicinity of Temenos [3]. These corrosion mechanisms may act as eithet “series” or “parallel” corrosion processes geometries, details of which have been discussed in detail elsewhere [4,5].
2. MIC prevention and control methods:
Out of five main measures by which MIC can be addressed and rectified, that is to say, physical measures (e.g., Coating), chemical measures (biocides), electrical measures (cathodic protection), mechanical measures (pigging) and materials selection/design mesures, the two important methods applicable to surfaces on which Temenos is highly likely to occu, such as Ro memberanes, are:
a) Chemical treatment by using biocides
b) Application of antimicrobial coating
The classification of biocides and the pros and cons of each class have been addressed elsewhere [6].
2.1. Anti-microbial Coating:
The main mechanism by which microbial corrosion is facilitated is the formation of biofilms (more correctly Temenos) because these structures constitute diffusion barriers beneath which electrochemical cells are stablished. These cells such as but not limited to differential aeration cells serve to create spots with different local oxygen partial pressures leading into anode & cathode formation thus pitting corrosion. While there are various methods to treat biofilms such as use of biocides that is applicable on already - formed biofilms, the antimicrobial coating formulated by Eninco Engineering BV group prevents biofilms formation in the first place.
MIC is a serious issue in many industries such as ship hulls, ballast tanks, piers and jetties, pipelines, water and wastewater facilities, power plants equipment and assets such as the condensers, hot - box and boiler fit pumps as well as wet type cooling towers, upstream and downstream, oil and gas, offshore and onshore industries as well as under ground metallic fire water systems. Therefore, the coating can be applicable on all metallic parts made up of carbon steel and therefore reduce MIC very efficiently.
There are five methods by which MIC can be controlled: material selection, cathodic protection, use of biocides, use of coatings and mechanical removal of biofilms (e.g., by applying PIGs).
The main disadvantages of the above methods are:
1- material selection is always too costly,
2- cathodic protection is not effective all the time,
3- use of biocides even so-called “green biocides” is introducing synthetic compounds into the nature,
4- currently coating in use do not apply smart technology as we have proposed and therefore may not be reliable,
5- mechanical removal does not always remove all the biofilms thus re-growth may occur.
This coating is formulated based on nano silver phosphate, nano silica and copper II oxide in the resin network and co-reactant. The nanoparticles are touch and heat-sensitive agents.
The method which is used to keep nanoparticles in the film coating is the encapsulation of active ingredients. By this method, the incompatibility between different particles will prevented. For producing microcapsules will be used the interfacial cross-linking method by adding an active ingredient to an aqueous solution of the cross-linkable polymer.
Based on our experimentations we have confirmed that there are some important properties of this coating such as:
• long time durability (no water - uptake happened after > 10,000 hours (ten thousand hours)
• needs a very thin layer of film coating (less than 200 microns)
• it is not toxic (very low VOC%)
• easy method of application (applicable by conventional methods such as brush, rollers, and spraying)
• biofilm prevention efficiency up to 99.99%
• cost-effective (compared with the conventional prevention methods)
• protecting environment (due to not using biocidal chemicals and very low VOC %
• the adhesion of the coating in interface is extremely high (5 B, ASTM D 3359)
• the surface is completely hydrophobic
• this coating is the total resistance to mechanical and chemical defects
• Transparent film layer
• Fast drying time (less than 30 min.)
• Polyaspartic-acrylic based solvent
Theoretical study on the possibility of using self healing principals in creating structures containing corrosion inhibitors and biofilm prevention agents started in 2010 by Dr. R. Javaherdashti as a possible way to control and prevent corrosion. However, in 2019 Dr. A. Assarian became successful in taking first experimental and practical steps to complete laboratory phase of anti-microbial coatings based on in-situ interfacial polymerization.
Nanocoating creates a compatible network of molecules on a surface. Nanocoatings are the nanoscale thin film that is applied to surfaces to crate higher corrosion protection, better antifouling, and anti-microbial properties, excellent thermal shock, heat and radiation resistant, self-cleaning or self-healing, water resistant and improvement properties. Figure 5 schematically represents the model used in manufacturing this antimicrobial coating:
Figure 5: Schematic summery of the mechanizes by which anti-microbial coating works
The following applications are some top applications of nanocoatings which are mostly used.
ü Anti-corrosive coatings
ü Waterproof and non-stick coatings
ü Anti-microbial coatings
ü Thermal barrier coatings
ü Anti-abrasion coatings
ü Self-healing coatings
ü Anti-reflection coatings
ü Anti-graffiti coatings
Non-stick coatings have the same properties such as waterproof coating but, they are able to repel oil, dirt, water and almost any liquid. It is magnificent subject in food packaging industries because they have many problems to design a package of some food products for example mayonnaise and ketchup sauce. Because these products sticking on the package and could not come out smoothly so, the last portion of these products remains in the bottles and the costumer has to throw away the remaining portions [7,8]
Figure 6: Hydrophobic contact angle in comparison with hydrophilic [9]
Anti-microbial coating prevents and reduce of growing microorganisms on surfaces. Application of these coatings is so important in public places, healthcare industries, and public transports as well as in kitchens, air conditioning, sanitary facilities, food packaging and pharmaceutical industries for reducing the risk of infectious diseases [10].
On the other hand, nano-silica is an excellent additive that can alter the functionality of other particles or fillers, increase hydrophobic or oleophobic coating characteristics, modify rheology and thixotropy and increase adhesion.
The method used to produce nanocapsules is interfacial cross-linking, as schematically shown in Figure 7:
Figure 7: Mechanism of microcapsule formation by interfacial cross-linking [11]
Fouling RO memberanes include not only Temenos formation but also the so-called “protobiofilms”. The following describes these issue very briefly, more details have been given elsewhere [7]; there are also Transparent Exopolymer Particles (TEP) that act as a hub for floang bacterial colonies to which, on the average,5 -20% of floating bacteria in the water are attached. TEPs with higher percentage of attached bacteria are referred to as “Proto-biofilms”. While Temenoses are established bacterial colonies, prot-biofilms are floating bacterial colonies.
Temenos which are mainly made up of the Extracellular Polymeric Substances -EPS) along with TEP can have several adverse effects on the RO memberanes mainly:
1. Interuption by EPS and TEP with salts disposal from water thus increasing hydraulic resistance and decreasing the effecicncy of the RO memberane,
2. Increased need for chemical washing of membranes.
3. Decrease of useful life of the assets and increased need for replacement of intensively fouled membranes.
4. Decrease in production of water due to long out-of -service periods that are also caused by chemical treartment of memberanes and downtime imposed by memberanes replacement.
It is a known practice that while it is almost impossible to prevent Temenos formation on meberanes due to contnous contact between membranes and water, by carrying out a root cause analysis and application of suitable MIC management, Temenos formation can be controlled to a high extent.
The ways by which biofouling is handled in this Pterochemical complex are as follows:
1. Adding Sodium hypochlorite as biocide,
2. Addition of Ferric chloride as coagulant
3. Adding Anionic polymers for foloculation
4. Adding sodium hydroxide and sulphuric acid to regulate pH
5. Adding anti-scalant (Flocon 260®) that contains derivatives of Phophoric acid and Carboxylic acid.
6. To dichlorination, addition of sodium meta bisulphite
7. Addition of hot water to the RO system to regulate temperature.
In this paper, we briefly discuss our approach towards the biofouling issue at a Petrochemical complex and the solutions we made that, based on the client’s report, worked well for them.
3. Research Approach methodology:
Using a strile spatula, a thin layer of microbial film developed on an out-of -service fouled memberane was taken and sent to the laboratory to extract the DNA using MMM (Molecular Microbiology Metods). Based on stages shown in Figure 1, characterisation of the bacteria studied at each stage are shown in Table 1>The results of MMM are shown in Figure 2.As shown in the Figure, both mkcrobial order and microbial classes are shown.
Having such information is a must to allow us to characterise the microorganisms involved and the way chemically they must be treated.
Table 1: Microbial characterisation table at eachprocess stage shown in Figure 1
Stage | Bacteria Count (cfu/ml)* 105 | Typeof bacteria | Contamination assessment |
1 | 150 | Anaerobic (Facultative) | Dangrous |
2 | 0.24 | Anaerobic (Facultative) | Mean |
3 | 11 | Anaerobic (Facultative & strict) | Dangerous |
4 | 75 | Strict Aerobic | Dangerous |
5 | 43 | Strict Aerobic | Dangerous |
6 | 93 | Strict Aerobic | Dangerous |
7 | 0.46 | Facultative Anaerobic | Mean |
8 | 0 | - | Safe |
Cooling Towers | 460 | Stric Aerobic | Dangerous |
Tank A | 210 | Facultative Anaerobic | Dangerous |
Tank B | 0 | - | Safe |
Tanks C | 93 | Facultative Anaerobic | Dangerous |
As it appears from Table 1, while by addition of bleach to the water coming from Raw water tank, (Figure 1),at all stages involving sand filters, pressurised filters as well as cartridge filters and mebranes instead of decreasing the planktonic bacteria numbers, it shows increase. This is an indication of poor MIC corrosion managemenrt.In addition, while water samples from exit waters from raw water tank and clarifier tank contain facultative anaerobic bacteria, the samples from sand filters contain both facultative anaerobic and strict aerobic bacteria. Bacteria observed in waters from both pressurised filters and filkter cartridges contain strict aerobic bacteria.All these indicate that the possible source of the problem is sand filters because they not only show no effect in decreasing risk level, but also they act as food source for the bacteria . However, from a health point of view, the most significant issue is appearing of Legionella in the Temenos: these bacteria have very dangerous impacts on human health (that can be leading into death) and are mostly developed in the Temenos developed in cooling towers
Figure 2: Figure 2: Distribution of microbial species in the Temenos sample taken from an out-of-order memberane due to extensive biofouling, (up)as per microbial class and (below) as per microbial orders.
3. Advised countermeasures:
The solutions were proposed as per important elemenst of the process circuit as follows:
3.1. Sand filter and pressurised filters:
To rectify MIC issue in these filters, it was advised to back wash these filters with highly oxygenated water, acid, or high dosages of ozone. To make sure if the advised solutions is working as expected, it is necessary to carry out bacterial counts using suitable kits.
3.2. Chlorination issues:
What we recommended instead of adding metabisulphite or even active carbon, was the three following alternatives:
3.2.1. Application of UV (Ultraviolet radioation). UV has an efficiency of 99.999% in reduction of viable bacterial numbers [8].
3.2.2. Installation of nanofilters before RO membranes.While the nanofilters are very efficient in physical reducing of bacteria, a serious drawback of them is very high amount and rate of biofouling.
3.2.3. addition of non-oxidising biocides such as DBNPA (2,2-dibromo-3- nitrilopropionamide) after cartridge filters. These biocides have no destructive effects on the structure of the RO membranes.
3.3. Antiscalant issues:
The antiscalant added after chlorination contain phsopahte derivatives. Phosphate is a necessary nutrient for bacteria. It was recoomended to replace non-phosphate antiscallants instead of currently in-use antiscallant chemicals.
3.4. membranes backwash regime:
The obtained results for the Temenos characterisation and bacterial scattering patterns showed that they are mainly made up of proteins and lipids. To address the formed Temenos on these membranes, it was advised to wash them using a basic solution containing a surfactant (1% sodium hydroxide, 0.03% sodium dodecile sulphate (SDS) with a pH of 11.5 at a temperature equalt to 30oC) that can absorbe both lipids and proteins. The pH and temperature must be highly observed to be within the recommended range. Recycling of the surfactnats was advised for 1 hour.
In addition to the above, it is also possible to use and apply anti-microbial coatings. These coatings do not allow temenos to be formed on the surcases, including RO membranes.
Conclusions:
1. A case study in a Petrochemical complex was studies. This Petrochemical complex is one of the biggest complexes in the region and the problem encountered is typical to almost all of such industrial complexes,
2. The case studied proved that it was microbial contamination of the RO components (the memberanes) with a high likelihood and tendency to be leading into microbial corrosion/deterioration.
3. Some suggestions that worked for the problem were:
3.1. Chemical washing of sand filters as pressurised filters as well as RO membranes,
3.2. Application of UV or alternatively, removal of chemical chlorination and installation of non-oxidising biocides after chlorination,
3.3. Replacement of Phosphorus-containing anticalins instead of non-phosphorus sealants
4. In addition to the above, as use of coating is also a proved way to address corrosion and particularly MIC/MID, we also propose application of superhydrophobic anti-microbial coatings on membranes. These new generation of smart coatings can be used against any case that would be leading to creating conditions favourable for biodterioration and microbial corrosion.
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References:
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[11] Pharmaceutics 2011, 3, 793-829; doi:10.3390/pharmaceutics3040793
[1] Eninco Engineering B.V., Aquamrijnstraat 118, 7554 NT, Hengelo, The Netherlands.
[2] Pooyesh Sanat Arya Co., Tehran, Iran.
Corresponding Author: javaherdashti@mic-corrosion.com