Water Treatment Biocide and Algaecide

Water Treatment Biocide and Algaecide

Water treatment biocide and algaecide is a chemical agent used to inhibit or kill microorganisms in water (such as bacteria, fungi, and algae), prevent the formation of microbial slime, and protect the safe operation of water system equipment. Its core classification, mechanism of action, typical formulas and application scenarios are as follows:

I. Core Classification and Mechanism of Action

Oxidizing Biocides

Representative products: Chlorine, sodium hypochlorite, chlorine dioxide, ozone, bromides, etc.

Mechanism of action: Destroy the cell wall and protein structure of microorganisms by releasing active oxygen or halogens to achieve rapid killing.

Characteristics: Broad-spectrum and highly efficient, but easily affected by pH and ammonia nitrogen, requiring fresh preparation before use; some products (such as chlorine) may produce harmful by-products (such as chloroform).

Non‑oxidizing Biocides

Representative products: Quaternary ammonium salts, isothiazolinone, glutaraldehyde, methylene dithiocyanate, etc.

Mechanism of action: Inhibit microbial metabolism or directly cause death through molecular intercalation or damaging cell membrane integrity.

Characteristics: Long‑lasting bacteriostasis (action cycle 7–15 days), heat‑resistant, less likely to precipitate with anionic surfactants, but may induce drug resistance.

Composite Biocides

Representative products: TH‑401 (quaternary ammonium salt + peroxide), TH‑402 (quaternary ammonium salt + isothiazolinone), etc.

Mechanism of action: Combine the advantages of oxidizing and non‑oxidizing agents to achieve both rapid and long‑lasting effects.

Characteristics: Suitable for high organic load scenarios; less likely to induce microbial resistance after long‑term use.

II. Typical Formulas and Preparation Methods

Isothiazolinone‑based Formula

Components: 5‑Chloro‑2‑methyl‑4‑isothiazolin‑3‑one (CMI) and 2‑methyl‑4‑isothiazolin‑3‑one (MI).

Function: Inhibit the growth of bacteria and algae and cause cell death by breaking the protein bonds.

Characteristics: Broad‑spectrum and highly efficient, good degradability, no residue, miscible with chlorine and most surfactants.

Quaternary Ammonium Salt‑based Formula

Components: Dodecyl dimethyl benzyl ammonium chloride (1227), tetradecyl dimethyl benzyl ammonium chloride, etc.

Function: As cationic surfactants, destroy microbial cell membranes, with functions of sterilization, slime stripping and corrosion inhibition.

Characteristics: Low toxicity, biodegradable, but produces relatively much foam, requiring strict dosage control.

Composite Formula Examples

TH‑401: Composite of quaternary ammonium salt and peroxide, suitable for industrial circulating cooling water systems such as power plants and chemical plants, dosage 100–200 mg/L.

TH‑402: Composite of quaternary ammonium salt and isothiazolinone, no drug resistance after long‑term use, suitable for oilfield water treatment.

III. Application Scenarios and Selection Strategies

Industrial Circulating Cooling Water System

Scenario characteristics: High water temperature, rapid microbial reproduction, easy formation of slime deposition.

Recommended schemes:

Oxidizing biocide: Chlorine dioxide (suitable for fertilizer plant circulating water, wide pH adaptation range).

Non‑oxidizing biocide: Isothiazolinone (broad‑spectrum and efficient, excellent slime stripping effect).

Composite biocide: TH‑401 or TH‑402 (both rapid and long‑lasting effects).

Oilfield Water Injection System

Scenario characteristics: Oily wastewater promotes the growth of sulfur bacteria, requiring special biocides.

Recommended schemes:

Glutaraldehyde: Special agent for killing sulfate‑reducing bacteria, biodegradable.

Composite product: Glutaraldehyde compounded with dodecyl dimethyl benzyl ammonium chloride (enhances penetration and improves killing effect on under‑deposit bacteria).

Swimming Pool Water Treatment

Scenario characteristics: Requires continuous bacteriostasis and clear water quality.

Recommended schemes:

Chlorine dioxide: Continuous dosing (residual chlorine 0.3–0.5 mg/L), supplemented with isothiazolinone (10 mg/L) every week.

Sodium dichloroisocyanurate: Dosed at 15–20 ppm every 2–3 days in summer, and every 3–5 days in spring and autumn.

IV. Usage Precautions

Water quality testing: Before dosing, test water indicators such as pH, COD and residual chlorine to ensure the efficacy of the agent.

Dosing method:

Initial dosing: Concentration 200–300 g/ton, for one‑off removal of moss, algae and slime.

Regular dosing: 150 g/ton every 5–7 days in summer, and once every 30 days in winter.

Safety protection: Operators must wear rubber gloves, masks, etc., to avoid contact of the agent with skin and eyes.

Environmental requirements: Select biodegradable agents to reduce environmental impact.