Membrane Processes – Reverse Osmosis and Nanofiltration

EXPERIENCE, EXPERTISE, and BENEFITS of DESALINATION

WATER TREATMENT USING MEMBRANE PROCESSES (RO, NF)

Raw water, sourced from surface or groundwater with low, medium, or high salt content, is, in most cases, not directly suitable for use as drinking water – especially seawater – and rarely suitable for industrial use.

The goal of water treatment using reverse osmosis membrane processes and the application of the latest technologies in pretreatment is to produce safe and fresh drinking water. Simultaneously, it aims to meet the industrial requirements for providing adequate water quality.

To desalinate surface or well water (e.g., seawater, brackish water, or slightly saline water) using membrane processes, sufficient pretreatment must be applied according to membrane requirements.

Pretreatment and preprocessing before a reverse osmosis system (RO) are essential in most cases and protect the membranes from unwanted operational failures. Factors that can negatively impact membrane permeability include:

• Unsettled and dissolved organic and inorganic substances such as sand particles, clay-like substances, suspended solids, colloids, and other inorganic substances.
• Microorganisms (viruses, bacteria, protozoa, microalgae, lichens, fungi, etc.).
• Other putrescible organic and inorganic substances.
• Dissolved gases.
• Deposits of any kind and influences of impurities from municipal or industrial wastewater, etc.

For the effectiveness of pretreatment and the trouble-free operation of the overall RO system, especially in larger and industrial-scale plants with fluctuating raw water qualities, the use of a pilot or test plant is recommended. This plant, deployed on-site with several months of operation, aims to provide reliable data as a basis for designing and optimizing the large-scale plant.

Preventing contamination on the membrane surface leads to a significant increase in the efficiency of the system, resulting in enhanced productivity. Consequently, it leads to a significant reduction in operating costs, including energy, chemicals, personnel, and service costs, as well as an extension of the overall system's lifespan.

AMV offers systems that include all necessary treatment steps to meet technical, commercial, and environmental requirements and ensure the desired water quality specified by the customer.

AMV REVERSE OSMOSIS SYSTEMS (RO)

AMV combines technological progress with economic consideration in its desalination systems for the production of clean and impeccable drinking and utility water for cities and municipalities, as well as utility water for various industrial sectors. The following treatment steps are employed to achieve the above goals:

• Pretreatment involving disinfection, microfiltration (MF), ultrafiltration (UF), dissolved air flotation (DAF), conventional pretreatment such as coagulation (destabilization and transport process), flocculation, sedimentation, filtration, softening, and chemical pretreatment in the feed to the RO.

• Main process step: includes microfiltration, RO feed pumps combined with various energy recovery methods (mainly for seawater plants), single or multistage RO systems equipped with highly efficient, energy-saving membranes, including a membrane cleaning unit (CIP).

• Post-treatment such as re-mineralization, pH adjustment, and disinfection using various disinfection methods, as well as treating the resulting concentrate (retentate).

AMV provides its CUSTOMERS with the following advantages:

• International experience (35 years in RO system construction).
• Highly efficient RO systems with increased production while reducing the feedwater volume.
• Standard RO systems.
• Customized solutions for RO systems.
• A wide range of pretreatment processes.
• Supply of individual components.
• Cost-effective solutions.
• Technically/commercially optimized solutions for complete systems as well as individual designs.
• Support for involved construction companies through design specifications (construction drawings, etc.).
• Collaboration with internationally recognized companies and partners.
• Flexible and competent problem-solving in various processes.
• Competence, reliability, and adherence to deadlines.
• Highly qualified personnel for overseeing installation.
• Professional training for operator personnel.
• Expert supervision for commissioning.
• Customer service.
• Project management.

Our engineers provide the planning of reverse osmosis systems in conjunction with the corresponding pretreatment stages to ensure the required water quality for our customers, taking into account technical and economic goals.

AMV Scope of Supply

Complete reverse osmosis systems are categorized into the following groups:

• Raw water extraction (option).
• Pretreatment.
• Chemical pretreatment.
• Main process - membrane process.
• Post-treatment.
• Removal of by-products.
• Advanced treatment for higher water quality requirements, such as pure and ultrapure water for industrial applications.

a- Raw water extraction (option)

The water extraction systems that supply raw water to the corresponding treatment steps can be divided as follows:

• Open extraction, e.g., seawater directly at the coast.
• Coastal wells.
• Deep wells.
• Shallow wells.
• River water extraction.
• Dam or water canal extraction.

A careful selection of the raw water extraction point can positively support the process.

b- Pretreatment

Depending on the respective raw water qualities (chemical/physical/biological), the following treatment steps can be combined accordingly or used as individual cleaning stages:

• Grate systems – for the removal of coarse substances.
• Sieve systems – e.g., microscreens for the removal of finely suspended substances.
• Sand trap stage – removal of mineral, sedimentable substances.
• Pre-disinfection (sterilization) – ozone systems, UV systems, or calcium or sodium hypochlorite dosing stations (also for shock disinfection).
• pH/ORP value adjustment.
• Aeration/oxidation (of iron and manganese compounds, removal of unwanted odors and tastes, dissolved gases, etc.).
• Pre-settling tank – removal of turbidity > 100 NTU.
• Dissolved air flotation (DAF), e.g., for the removal of algae and hard-to-settle substances.
• Precipitation, coagulation, flocculation, and sedimentation (conventional or via lamellar separators).
• Filtration through granular filter media (SMF, DMF, MBF, GSF (glauconite)).
• Filtration through powdery media (diatomaceous earth, diatom pellets).
• Activated carbon filtration, adsorption (GACF, PACF, BACF).
• Ultrafiltration (UF) – an important alternative to conventional pretreatment for an RO.
• Microfiltration (MF).
• Softening using various technologies.
• Ion exchange processes (mainly for industrial applications).
• Alkalinity adjustment.

c-  Chemical pretreatment

To avoid deposits of sparingly soluble salts and also due to the presence of free chlorine and other oxidizing agents on the membrane surface, a chemical pretreatment must be carried out in almost all cases:

• pH adjustment before RO.
• Dechlorination when using oxidizing agents like chlorine.
• Dosing of scale inhibitors (anti-scalants).

d- Main process – RO- or NF-process

The central membrane process with a pre-filtration (MF) removes dissolved salts, thus reducing the total salt content in the permeate to a desired level. The steps include:

• Micro (candle) filtration (MF).
• High-pressure or RO/NF feed pumps.
• Energy recovery (ER).
• Nanofiltration systems (NF) or
• Reverse osmosis systems (RO). Depending on the application and requirements, a variety of membrane types are available, selectively chosen by us for the desired result.
• Membrane cleaning (CIP): If unexpected contaminations (scaling, fouling, oxidation) affect the membrane surface during operation, this usually indicates inadequate pretreatment, leading to a deterioration in performance. A carefully selected combination of cleaning chemicals helps restore the membranes to their efficiency.

e- Post treatment

Post-treatment aims to bring the permeate and retentate of the RO to the desired final quality. This includes, among other steps:

• pH/ORP value adjustment, neutralization for permeate and concentrate.
• Re-mineralization.
• Disinfection using various methods such as chlorination, UV disinfection, or ozone treatment is successfully employed.
• Processing of residues.

The above-mentioned treatment sections (b-) and (c-) are an excerpt from the most common but also the latest treatment methods for pretreating raw waters. Due to the multitude of possible impurities in raw water entering the RO system and considering physical conditions such as temperature, fluctuations in raw water supply, etc., most treatment steps must be individually planned by combining the above steps. Only this approach, in conjunction with a qualified water analysis and, in some cases, the recommended use of a pilot plant, ensures an optimally functioning system.

f- Removal of Disinfection By-Products (DBP) in the case of chlorine disinfection

Care should be taken to ensure that the permissible limits of disinfection by-products are not exceeded.

g- Advanced treatment for higher water quality requirements, such as pure and ultrapure water

AMV offers ion exchange systems for the further treatment of the permeate to produce pure or ultrapure water. Other applications include waters that, through the selective removal of unwanted water constituents, achieve the required water quality. Primarily, our systems are used in the industry. Our cation and anion exchangers are used separately or in combination, ranging from regular softening to the removal of all dissolved substances down to a conductivity of 0.05 µS/cm.

We only use resins from production facilities that are qualitatively at the highest level.

 

RO - SYSTEM PLANNING

AMV RO systems are fundamentally planned based on available or prescribed European environmental standards.

The RO systems remove dissolved salts and organic substances to the highest extent. Impurities harmful to RO membranes, such as suspended solids, turbidity, and other contaminants in the available raw water extraction, are reduced by pretreatment to achieve water quality corresponding to WHO guidelines for drinking water and qualities for other applications.

All components chosen by us meet the highest quality and lifespan standards, are tested and certified, and fulfill – if required – local regulations and provisions. The selected materials are carefully matched to the usage in each application, with various media in dosing stations, pump systems, piping, fittings, etc.

PLANT SIZE

Seawater desalination plants are available for the following capacities:

• From 500 m³/d to 10.000 m³/d

In special cases, also for lower/higher capacities.

Brackish water desalination plants are available for the following capacities:

• From 500 m³/d to 25.000 m³/d.

REQUIRED INFORMATION FOR PLANT PLANNING

In order to plan a facility that meets the specified requirements, appropriate raw water analysis, as well as other general information, is necessary. For this purpose, upon request, AMV provides a corresponding questionnaire.

The minimum data requirements for design are:

• The raw water extraction point/source and the corresponding physical, chemical, and biological water analysis, at least the total salt content and the SD index.
• Average water demand during dry and rainy seasons.
• Desired/required plant capacity [m³/d].
• Average and maximum turbidity.
• Average and maximum suspended solids content.
• Desired quality of treated water or standards for treated water quality (if deviating from EU or WHO standards).
• Disposal or treatment of wastewater such as backwash water, retentate, etc.

PLANT EXECUTION

AMV RO systems, whether stationary, containerized, or compact, are individually adapted to the environmental conditions in the respective countries based on specific requirements. This is done primarily in terms of material selection and customer-specific needs.

PLANT OPERATION

AMV RO systems are primarily designed for user-friendly operation. Attention is also given, if necessary, to deployments in remote areas.

After commissioning, operation, depending on the plant size, will be ensured by an experienced plant operator and a group of technicians, as well as trained specialists.

During the commissioning phase, the qualified and experienced operator personnel will be theoretically and practically trained on the specific system by our specialists (Learning by Doing!

TREATED WATER QUALITY AND USE

The treated water is used either as drinking water (in accordance with WHO guidelines) or, in the industry, based on its specific requirements.

Process wastewater such as backwash water can usually be discharged into the sewer when using food-grade chemicals.

The retentate can be returned to the raw water source (in the case of seawater extraction) with additional treatment.