How to choose suitable filter element for environmental protection water treatment project?

The core of selecting the filter element of environmental protection water treatment project is to determine the water quality and target first, then match the accuracy/material/flow/working condition, and finally make the combination and verification to ensure that it meets the standard stably, economically and reliably.

First, define the core requirements (selection starting point)

1. Water quality and pollutant analysis

Particles/suspended solids: sediment, rust, colloid, microorganism (bacteria/virus) and algae.

Soluble pollutants: residual chlorine, organic matter, heavy metals, hardness, salts, acids, bases and oils.

Key indicators: turbidity, SS, COD, pH, temperature, pressure, flow rate, salt content and microbial indicators.

Step 2 deal with the target and the scene

Pretreatment: protect the back-end membrane/pump/heat exchanger to reduce turbidity and large particles (such as pre-RO security filtration).

Deep purification: sterilization, virus removal, heavy metal removal and salt removal (ultrapure water/drinking water/medicine/electronics).

Reuse/discharge up to standard: meet GB 18918, GB 5749, GMP, electronic grade water and other standards.

Special working conditions: high temperature, high pressure, strong corrosion, high viscosity, high impurity and aseptic requirements.

II. Filter element types and applicable scenarios (classified by precision/material)

1. Coarse filtration (1–100μ m, pretreatment is preferred)

PP meltblown filter element (1–50μ m)

Material: polypropylene (PP)

Features: low cost, medium pollution capacity, acid and alkali resistance, disposable.

Application: municipal/industrial water pretreatment, RO/UF pre-treatment, circulating water, removing sediment rust.

PP folding filter element (0.1–10μ m)

Features: higher precision, larger flow rate, lower pressure and larger pollution capacity.

Application: precision pretreatment, RO security filtration (commonly 0.45 μm), food/electronic grade water.

Metal sintered filter element (stainless steel/titanium, 1–50μ m)

Features: high temperature resistance (≤400℃), high pressure, corrosion resistance, cleanable and reusable.

Application: High temperature steam, strong acid and alkali, high solid content, backwashable system.

2. Adsorption filtration (removing color/odor/residual chlorine/organic matter)

Activated carbon filter element (granular/compressed/silver loaded)

Function: Adsorption of residual chlorine, odor, pesticides, small molecular organic matter; Silver loading can inhibit bacteria

Application: drinking water, RO post-treatment to improve taste, decolorization and deodorization of chemical/printing and dyeing wastewater.

Resin filter element (cation/anion/mixed bed)

Function: ion exchange, removing hardness, heavy metals, salts and ultra-pure water polishing.

Application: softened water, pure water/ultrapure water terminal, electronic/medical ultrapure water (18.2 MΩ・cm).

3. High precision/membrane filtration (0.0001–0.1μ m, deep purification)

Ultrafiltration (UF) (0.01–0.1μ m, PVDF/PAN)

Function: intercept bacteria, colloid and macromolecular organic matter, and retain minerals.

Application: municipal clean water, food and beverage, reclaimed water reuse and slightly polluted water.

Nanofiltration (NF)(0.001 μm)

Function: Selective desalting, removing heavy metals/hardness and retaining some minerals.

Application: Softening of drinking water, mineral water and high hardness water.

Reverse osmosis (RO)(0.0001 μm, polyamide)

Function: Desalination rate is 97%-99%, and almost all impurities (heavy metals/viruses/salts) are removed.

Application: pure water/ultra-pure water, seawater desalination, medical/electronic/chemical high-pure water.

PTFE folding filter element (0.1–0.22 μ m)

Features: strong acid and alkali resistance, high temperature resistance, steam sterilization and sterilization grade (0.22 μm)

Application: terminal filtration of medical sterile water, electronic ultrapure water and highly corrosive liquid.

Ceramic filter element (0.1–10μ m, diatomite/alumina)

Features: Repeated brushing, acid and alkali resistance and long service life (1-5 years).

Application: rural well water, small flow in laboratory, and manual maintenance scene.

Three, the selection of five key parameters (must be calculated and core)

1. Filtering accuracy (core matching)

Principle: Enough is enough, not blindly seeking high; The higher the accuracy, the greater the resistance, the higher the cost and the shorter the service life.

Reference:

Coarse filtration: 10–50μ m (sediment/rust)

Precision pretreatment: 1–5 μ m (colloid/small particles)

RO security: 0.45 μm

Sterilization/Asepticism: 0.22 μm(PTFE/nylon)

Ultra-pure water terminal: 0.05–0.1μ m (PTFE/polyethersulfone)

2. Traffic matching (avoiding bottlenecks)

Formula: rated flow of filter element ≥ actual flow × 1.2 (20% margin reserved)

Selection:

Small flow (≤ 30 m/h): 20-inch filter element.

High-flow (30–110m/h): 40/60-inch high-flow filter element (single branch and multiple branches, saving space)

Differential pressure control: the initial differential pressure is 0.05–0.15mpa, and the terminal is ≤0.3 MPa (overpressure is easy to break the membrane/cut off).

3. Material compatibility (anti-corrosion/dissolution)

Neutral water/normal temperature: PP, PES, nylon

Strong acid/alkali/high temperature: PTFE, 316L stainless steel, titanium alloy.

Food/medicine: FDA food grade, non-adhesive, steam sterilization.

Prohibited: material reacts with medium, dissolves impurities, and causes secondary pollution.

4. Working conditions (temperature/pressure/life)

Temperature: PP≤60℃, PTFE≤120℃, metal ≤400℃

Pressure: fiber filter element ≤0.6 MPa, metal filter element ≤10 MPa.

Life: PP 3–6 months, activated carbon 6–12 months, UF/RO 1–3 years, ceramics 1–5 years.

Maintenance: washable (metal/ceramic) vs disposable (PP/PTFE)

5. Pollution capacity and cost (long-term economy)

High impurity water quality: priority is given to large pollution capacity and deep filtration (PP melt blowing/folding)

Combination strategy: coarse filtration+fine filtration+adsorption/membrane, and staged interception to prolong the life of the main filter element.

Total cost: purchase+replacement+energy consumption+maintenance, not just unit price.

Fourth, the actual steps of engineering selection (can be directly applied)

Water quality detection: measure turbidity, SS, pH, temperature, hardness, COD, microorganism and salt content.

Determine the target: pretreatment/advanced purification/reuse/reaching the standard, and define the effluent standard.

Accuracy grading: Select the accuracy (coarse/fine/membrane) according to the size of pollutants.

Material matching: select compatible materials according to pH, temperature and corrosiveness.

Flow accounting: Select the specifications and quantity of filter elements according to the maximum flow ×1.2.

Combination scheme:

Conventional: PP melt blowing (5 μm)+ activated carbon+PP folding (0.45 μm)+ RO.

Ultra-pure water: RO+mixed bed resin+PTFE(0.22 μm)

Sterility of medicine: multi-stage folding+PTFE(0.22 μm)+ steam sterilization.

Verification and optimization: small test/pilot test, pressure difference, service life and effluent quality, adjustment and combination.

V. Common misunderstandings and pit avoidance

Only look at the accuracy but not the flow: the accuracy is enough but the flow is insufficient, and the system is paralyzed.

Incompatible materials: PP used in strong acid, resulting in dissolution/damage.

No pre-filtration: directly use high-precision filter element, which can quickly block and have a very short service life.

Ignore pressure difference: too high pressure difference increases energy consumption and damages membrane elements.

Must do: pre-filtration protection+graded filtration+regular replacement/cleaning.