🔬 Seaweed Processing Technologies: Extracting Active Ingredients

Over half a century of development has yielded diverse technologies to extract and isolate active compounds from seaweed. Those widely used in seaweed fertilizer production include: water extraction, acid/alkali extraction (with acids like formic acid, acetic acid, sulfuric acid; or alkalis like NaOH, KOH, carbonates), low-temperature processing, high-pressure cell disruption, and enzymatic hydrolysis.

💧 1. Water Extraction

Preprocessing: Raw seaweed is first rinsed with fresh water to remove sand, stones, and debris. It is then chopped and dried in an oven at <80°C (to prevent active ingredient degradation).
Particle Sizing: Coarser granules (1–4mm) are used for agricultural biostimulants; finer particles for feed formulations.
Extraction Process: Water-soluble components are extracted under normal pressure (no acids/alkalis). Solids content is concentrated to 15–20% via evaporation.
Stabilization: Food-grade preservatives (e.g., acetic acid, sodium carbonate) maintain product stability.

🧪 2. Acid & Alkali Extraction

Acid Pretreatment:
Sulfuric acid (40–50°C for 30min) removes phenolic compounds and enhances polymer degradation, improving subsequent alkali extraction efficiency and product quality.

Acid Treatment:
Seaweed treated with 0.1–0.2mol/L sulfuric acid or HCl becomes more fluid (vs. untreated) and takes on a green hue, aiding separation via drum screening.

Alkali Extraction:
Ground seaweed slurries are heated in water; K₂CO₃ is added in pressure reactors (275–827kPa, <100°C) to break polysaccharide chains into low-molecular-weight substances.
Post-alkali extraction, solutions are neutralized with H₃PO₄ or citric acid (C₆H₈O₇).

⚗️ Alkali-Driven Reactions & Byproducts

Alkali treatment triggers degradation, recombination, and condensation reactions, producing compounds not naturally present in seaweed:

Polysaccharide Breakdown: Brown algae polymers (alginate, fucoidan, laminarin) are degraded into low-molecular-weight oligosaccharides and monosaccharides under alkali catalysis.

Carboxylic Acid Formation: Studies on alginate hydrolysis show 0.1–0.5mol NaOH (95–135°C) produces:

Monocarboxylic acids (lactic, formic, acetic) accounting for 9.8–14.2% of initial alginate mass.
Dicarboxylic acids (saccharic acid, pentacarboxylic acid, malic acid, etc.) making up 17.3–42.2% of initial mass.
Total conversion: 27–56% of alginate becomes carboxylic acids, some of which actively promote plant growth.

❄️ 3.  Low-Temperature Processing

Wild seaweed collected from coasts is first transferred to cold storage for rapid freezing, then pulverized into a suspension (10μm particle size) using liquid nitrogen.  This green-brown micro-pulverized suspension undergoes acidification to preserve bioactivity, resulting in a final product with pH <5.  The extract is viscous, stable at room temperature, and dilutable for use.
Key components include chlorophyll, alginate, laminarin, mannitol, fucoidan (total solids: 15–20%), plus growth regulators (auxins, cytokinins, gibberellins, betaines), amino acids, minerals (S, Mg, B, Ca, Co, Fe, etc.), antioxidants, and vitamins.  Unlike chemically processed fertilizers, this method avoids organic solvents, acids, or alkalis—preserving active substances intact.

💥 4.  High-Pressure Cell Disruption

This technology uses no heat or chemicals.  Seaweed biomass is rinsed with fresh water, frozen at -25°C, then crushed into fine particles.  After homogenization (6–10μm emulsion), the mixture is injected into a low-pressure chamber under high pressure.  Rapid pressure drop triggers cell wall rupture via internal energy release, releasing cytoplasmic contents.
Filtration recovers water-soluble fractions rich in natural actives.  Additives can be blended later for tailored applications.  South Africa’s Kelpak used this frozen cell disruption method in 1983, producing seaweed fertilizers from local Ecklonia maxima.

🔬 5.  Enzymatic Hydrolysis

A biodegrading process using specific enzymes, this method retains more active ingredients, enhancing fertilizer efficacy.  In recent years, it has replaced traditional chemical/physical extraction.
Key to Success: Enzyme selection via gene screening, optimized protein expression, and enzyme refinement through protein engineering for industrial use.
Process: Seaweed is crushed in workshops, then fermented with selected enzymes to produce the final fertilizer.
Benefits: High bioactivity, eco-friendliness, and efficiency.  It avoids harsh chemicals/high temperatures (flaws of chemical extraction) and breaks down large molecules (a limitation of physical methods), making nutrients more accessible to crops.