For the selection of water treatment equipment in regions with a high incidence of kidney stones, the core principle is: on the basis of ensuring drinking water safety, appropriately reduce the content of calcium and magnesium ions (hardness) in water while avoiding the excessive removal of all minerals. The specific selection requires comprehensive decision-making based on factors such as local water quality test results, water consumption scale, and economic budget. A complete water quality test must be conducted before formulating a water treatment plan, including at least the following indicators:

• Total Hardness (calculated as CaCO₃): To determine whether softening treatment is required

• Concentrations of Calcium and Magnesium Ions: To identify the main hardness-causing components

• TDS (Total Dissolved Solids): To understand the total amount of minerals

• Other Indicators: pH value, sulfate, chloride, etc.

A comprehensive analysis of the customer's water quality report shows that the water contains a certain amount of salt. Combined with the customer's need to address the high prevalence of kidney stones among local residents and develop a functional drinking water product that can prevent and alleviate kidney stones, we first need to clarify the main causes of the frequent occurrence of kidney stones. An analysis based on the local climatic environment and living habits in Yemen is as follows:

1. High Sweat Metabolism: Yemen has a tropical desert climate with high temperatures and little rainfall all year round, and the temperature often exceeds 40℃. The human body sweats heavily through the skin, leading to urine concentration, increased concentrations of crystals such as calcium, oxalic acid, and uric acid, which easily precipitate to form stones.

2. Insufficient Water Intake: Water resources are scarce and unevenly distributed. Drinking water supply is inadequate in many areas (especially rural areas), and residents' daily water intake is far below the safety standard of 1500-2000 milliliters, resulting in long-term high urine concentration.

3. Hard Drinking Water Quality: Drinking water in some areas has high hardness (high content of calcium and magnesium ions). Long-term consumption will increase the risk of calcium salt deposition in urine and promote stone formation.

4. Impact of High Animal Protein Intake on Metabolism: The diet in some areas of Yemen is dominated by animal protein (such as red meat and offal). Excessive intake will lead to increased excretion of calcium and uric acid in urine, inducing calcium oxalate and uric acid stones; at the same time, acidic metabolites produced by a high-protein diet will lower the urine pH value, further promoting crystal precipitation.

5. Impact of High-Salt Dietary Habits on Metabolism: Traditional diets have a high salt content. High sodium will reduce the reabsorption of calcium by renal tubules, increase urinary calcium excretion, and reduce the concentration of citrate (a substance that inhibits stone formation) in urine, doubling the risk of stones.

6. Low Intake of Vegetables and Fruits: Insufficient intake of vegetables and fruits leads to a lack of dietary fiber, reducing the intestinal tract's ability to regulate the absorption of calcium and oxalic acid; in addition, inadequate intake of fruits and vegetables will reduce water and citrate intake, which is not conducive to stone prevention.

Among the above factors, climate is an unchangeable factor by human effort, and food is related to complex dietary habits that are difficult for us to control. However, drinking water is our professional field and something we can manage well. We can solve or prevent kidney stones to a certain extent through water treatment technology.

We have basically clarified the process route direction for this water treatment system, with the main directions as follows:

1. Reduce the salt and hardness in drinking water, decrease the human body's intake of hardness and salt through drinking water, and reduce the renal burden of human metabolism.

2. Add potassium mineral, which has the effect of preventing and alleviating kidney stones, to the water with reduced salt and hardness, so that the drinking water can be more beneficial to health, and kidney stones can be prevented and alleviated to a certain extent through drinking water.

For this water treatment direction, we can rely on nanofiltration (NF) equipment and reverse osmosis (RO) equipment to meet the customer's demand for producing potassium mineralized water.

The water filtered by these two sets of equipment (32t/h RO Potassium Mineralization System vs 32t/h NF Potassium Mineralization Device) differs in water quality components, mineral retention, and water production characteristics. The core difference lies in the variation of desalination rate and mineral interception effect caused by the different membrane separation principles of reverse osmosis (RO) and nanofiltration (NF).

Comparison of Produced Water Quality Between the Two Systems

Difference Analysis

1. Fundamental Difference in Desalination Degree

• Reverse Osmosis System: Adopts RO membranes (pore size 0.1-1 nm) driven by high pressure (110-meter head), with an extremely high rejection rate (>98%) for almost all ions (including monovalent and divalent ions). The produced water is close to pure water with extremely low TDS.

• Nanofiltration System: Adopts NF membranes (pore size 1-2 nm) with lower operating pressure (95-meter head). It has a high rejection rate (>90%) for divalent ions but only 20%-80% for monovalent ions (such as K⁺, Na⁺, Cl⁻), so the produced water retains some minerals.

2. Difference in Potassium Supplement Methods

Although both systems are equipped with a "potassium mineralization device":

• RO System: Almost all potassium ions in raw water are removed, and the potassium content in produced water is nearly zero. Therefore, potassium must be fully added via the mineralization device.

• NF System: Some potassium ions (monovalent ions) in raw water may pass through the membrane into the produced water. The actual potassium content in produced water = retained part from raw water + supplementary amount from the mineralization device.

3. Taste and Stability of Produced Water

• RO Produced Water: Tastes "soft" and slightly sweet.

• NF Produced Water: Retains some minerals and tastes closer to natural water.

4. Equipment Cost and Operating Cost

• RO System: Higher operating pressure (110 meters vs. 95 meters for NF), resulting in 15%-20% higher energy consumption of the high-pressure pump and higher power consumption overall.

• NF System: Lower operating pressure, relatively lower energy consumption, and may require less scale inhibitor.

In addition, the RO membrane is actually a very dense desalination layer. Salt ions are dense, so both beneficial and harmful substances can be removed, producing pure water. Although NF technology is also based on RO, it adopts "selective" filtration. With a pore size of 1 nanometer, it not only can completely filter out harmful substances such as bacteria, colloids, and heavy metals from water but also retain beneficial minerals in water. NF is more technically difficult to implement, which is why the NF system is more expensive.

The produced water of the two systems differs significantly in mineral content, desalination degree, taste, energy consumption, etc. The specific selection needs to be comprehensively evaluated based on factors such as the final water quality requirements, raw water quality, and operating costs.

The core difference between the two treatment systems lies in the different membrane separation technologies of RO and NF membranes:

The working principle of the NF membrane is based on the synergistic effect of the sieving effect and Donnan effect, realizing the separation of ions with different valences and substances with molecular weights ranging from 200 to 1000 Da.

Core Separation Mechanisms

1. Sieving Effect (Pore Size Sieving): The pore size of the NF membrane is usually between 1-2 nanometers, between that of the RO membrane (0.1-1 nm) and the ultrafiltration (UF) membrane (2-100 nm). When the solution passes through the membrane, substances with molecular weights larger than the membrane's molecular weight cutoff (such as multivalent ions, organics, colloids, etc.) are retained, while water molecules and small-molecule substances (such as monovalent ions) pass through. This physical sieving effect is mainly for neutral molecules and uncharged particles.

2. Donnan Effect (Charge Repulsion): The surface of the NF membrane is usually negatively charged (through modification). When a solution containing ions passes through, the membrane surface generates electrostatic repulsion with ions of the same charge (such as Cl⁻, SO₄²⁻), making the rejection rate of high-valent anions (such as SO₄²⁻) much higher than that of monovalent anions (such as Cl⁻). At the same time, to maintain electrical neutrality, some counterions (such as Na⁺) are also retained. This charge effect enables the NF membrane to have a rejection rate of over 90% for divalent and multivalent ions, while only 20%-80% for monovalent ions.

3. Solution-Diffusion Mechanism: For some small-molecule organics, there is also a solution-diffusion effect: the solute dissolves on the membrane surface and then diffuses through the membrane driven by the concentration gradient.

Actual Separation Process

Driven by pressure (operating pressure usually 0.5-2.0 MPa), water molecules and some small-molecule substances in the raw water pass through the membrane to become produced water, while the retained substances are concentrated on the membrane surface and discharged with the concentrated water. The NF membrane has a high rejection rate for divalent salts (such as CaSO₄, MgSO₄) and a low rejection rate for monovalent salts, so it is particularly suitable for application scenarios such as water softening, organic matter removal, decolorization, and partial desalination.

The working principle of the RO membrane is selective permeation. Driven by pressure higher than the osmotic pressure of the solution, water molecules pass through the semipermeable membrane, while soluble salts, organics, bacteria, viruses, and other impurities are retained, realizing the separation of water and solutes.

Core Separation Mechanisms

1. Solution-Diffusion:

• Dissolution: Water molecules and solute molecules are adsorbed and dissolved on the membrane surface.

• Diffusion: Driven by the concentration gradient or pressure gradient, water molecules preferentially diffuse through the membrane pores.

• Desorption: Water molecules desorb on the other side of the membrane.

• Due to the small size (about 0.3 nm) and high polarity of water molecules, their solubility and diffusion rate in the membrane material are much higher than those of other solute molecules, so they can pass through the membrane preferentially, while most ions, organics, etc., are retained.

2. Pore Size Sieving Effect: The pore size of the RO membrane is usually between 0.1-1 nanometer, much smaller than the hydrated ion radius (such as the hydrated radius of Na⁺ is about 0.36 nm, and that of Cl⁻ is about 0.33 nm). Under high pressure, water molecules (about 0.3 nm) can squeeze through the membrane pores, while hydrated ions, organic molecules, colloids, etc., are physically blocked because their sizes are larger than the membrane pores.

3. Charge Repulsion Effect: The surface of some RO membranes is negatively charged, generating electrostatic repulsion for anions (such as Cl⁻, SO₄²⁻) and enhancing the retention effect. However, this effect is relatively weak in RO, and the main separation mechanisms are still physical sieving and solution-diffusion.

Operating Pressure

Must be higher than the osmotic pressure of the solution (about 2.5-3.0 MPa for seawater, about 1.0-1.5 MPa for brackish water). Usually, the operating pressure of the RO system is 1.0-8.0 MPa. Pressure provides the driving force for water molecules to pass through the membrane and overcomes the osmotic pressure difference.

Membrane Material Characteristics

Polyamide composite membranes are currently the mainstream, with high desalination rate, high flux, and pollution resistance. The hydrophilicity, pore size distribution, and charge characteristics of the membrane surface jointly determine the separation performance.

Actual Separation Process

Driven by the high-pressure pump, raw water flows through the membrane surface at a certain flow rate. Water molecules pass through the membrane to become produced water (pure water), while the retained solutes are concentrated on the membrane surface and discharged with the concentrated water. The RO membrane has a rejection rate of 98%-99.5% for monovalent ions (Na⁺, Cl⁻), >99% for divalent ions (Ca²⁺, SO₄²⁻), and almost completely removes organics, bacteria, viruses, etc.

The two sets of configurations adopt different membrane separation technologies, so there are some design differences in configuration and quantity: the RO system uses 36 pieces of 8040 membrane elements (6 membrane housings, 6 elements per housing), and the NF system uses 30 pieces of 8040 membrane elements (5 membrane housings, 6 elements per housing). The difference in the number of membranes also reflects the different designs of flux and recovery rate between the two types of membranes.

Detailed Technical Explanation

I. The Difference in Membrane Flux is the Fundamental Reason

Membrane flux (water production per unit membrane area per unit time, unit: L/m²·h) is the core parameter of membrane system design:

• RO Membrane: The standard design flux is relatively low, usually 15-25 L/m²·h (affected by water quality and pollution tendency).

• NF Membrane: The design flux is relatively high, usually 20-35 L/m²·h (due to larger pore size and lower operating pressure).

In this water treatment equipment case, the customer requires a water production capacity of 32t/h (32 m³/h):

In the actual configuration, the RO system uses 36 membranes (6 housings × 6 elements), and the NF system uses 30 membranes (5 housings × 6 elements). This design difference is to match the different water production fluxes and system recovery rate requirements of the two types of membranes, ensuring that both systems can achieve a water production capacity of 32t/h while maintaining reasonable operating parameters. It is precisely based on this engineering design for flux differences—RO membranes require more membrane area to achieve the same water production.

II. Design Balance of System Recovery Rate

Recovery rate (produced water volume/feed water volume) affects the pollution rate of the membrane surface and operating pressure:

• Excessively high recovery rate of a single membrane → reduced flow rate on the membrane surface → easy deposition of pollutants → increased scaling risk.

• Excessively low recovery rate of a single membrane → large discharge of concentrated water → waste of water resources.

For 8040 membrane elements, the design recovery rate of a single membrane is usually 8%-15%. To achieve the total system recovery rate (such as 75%), multiple membranes need to be connected in series or parallel.

Design logic of recovery rate for the two systems:

• RO System: 36 membranes (6 membrane housings in series, 6 elements in parallel per housing) can be designed with a higher system recovery rate (such as 75%-80%). Because the RO membrane intercepts pollutants more thoroughly, more membrane area is needed to disperse the pollution load.

• NF System: 30 membranes (5 membrane housings in series) have a slightly lower system recovery rate (such as 70%-75%). Because the NF membrane has a low rejection rate for monovalent ions, the scaling tendency on the concentrated water side is relatively small.

III. Relationship Between the Number of Membrane Housings and Operating Pressure

The number of series-connected membrane housings directly affects:

• System operating pressure: The more series stages, the lower the feed water pressure of the terminal membrane housing (accumulation of pressure loss).

• Concentration on the concentrated water side: The concentration of concentrated water in the final membrane housing is the highest, with the greatest scaling risk.

RO System: 6 membrane housings in series:

• Requires higher initial feed water pressure (110-meter head vs. 95 meters for NF).

• The concentration of concentrated water in the final membrane housing is higher, requiring stricter scale inhibition control.

• But a higher system recovery rate can be achieved.

The NF system has 5 membrane housings in series, with relatively lower operating pressure and lower scaling risk on the concentrated water side.

IV. Practical Considerations for Engineering Design

This configuration difference also reflects the following engineering optimizations:

• Standardized Selection: 8040 membrane elements are industrial standard specifications, and membrane housings are usually configured with 6 elements per housing for easy procurement and maintenance.

• Spatial Layout: The rack lengths of 6 housings and 5 housings are different, affecting the equipment floor space.

• Operating Energy Consumption: The high-pressure pump head of the RO system is 110 meters (about 1.1 MPa), and that of the NF system is 95 meters (about 0.95 MPa), with an energy consumption difference of about 15%.

Difference in membrane flux (RO membrane has low flux, NF membrane has high flux) → different membrane areas required to achieve the same water production (RO requires more membranes) → different configurations of the number of membrane elements → different series stages of membrane housings → corresponding adjustments in operating parameters such as system recovery rate, operating pressure, and energy consumption → ultimately ensuring that both systems can stably produce 32t/h of water under their respective optimal operating conditions.

This design difference is a typical embodiment of "on-demand configuration" in membrane separation engineering, rather than a simple increase or decrease in quantity.

Through the above detailed case in Yemen, the analysis of the reasons for the customer's customized water treatment equipment and the detailed equipment configuration analysis by engineers, both RO and NF equipment can meet the production of potassium mineralized water, a functional drinking water product for preventing and alleviating kidney stones. The specific selection needs to be comprehensively evaluated based on factors such as the customer's budget, final water quality requirements, raw water quality, and operating costs. The Amanda & UMEK team is a professional one-stop comprehensive water treatment service provider, capable of providing customers with targeted project design and engineering support. The team will conduct rigorous technical analysis based on the local water quality data, specific water needs, and target uses provided by the customer. Engineers will design technical solutions that meet the customer's budget and accurately meet their water quality requirements, covering water treatment equipment solutions for various industries such as direct drinking water RO equipment, containerized water purification systems, marine seawater desalination for fishing boats, barreled and bottled water filling lines, pharmaceutical pure water and water for injection preparation, food and beverage production, boiler feed water, electronic high-purity water, and automatic water softening systems.

Contact Information

Tel: +8619331305749

Email: sales@cnumek.com / sales@amandawatertech.com

Website: www.amandawatertech.com / www.cnumek.com