In the battlefield of aquaculture, solid particulate matter is the number one "invisible killer"! They not only make the water murky like mud soup, but also cause a sharp drop in dissolved oxygen, a proliferation of pathogenic bacteria, and even illness and death of fish and shrimp.
Today, we will use practical experience and solid data to reveal how factory-based recirculating water aquaculture can "catch all" solid particles in one go!
I. What is solid particulate matter?
In aquaculture, 90% of solid waste comes from feed, mainly including:
Leftover bait (25% of the feed fed will be converted into suspended matter)
Fish manure (settleable and non-settleable particles)
Biological flocs (dead bacteria, mucus, etc.)
External pollutants (such as sediment and algal remains brought in by rainwater erosion, commonly found in external pond aquaculture)
These particles can be classified according to their sedimentation characteristics as:
Settleable particles (>100μm) : Such as large pieces of fish manure and feed residues. These particles settle relatively quickly in water and can be removed in part through simple sedimentation methods.
Suspended particles (<100μm) : The main source is fish feces, which remain suspended in water for a long time and are rather difficult to handle.
What are the hazards of solid particulate matter?
If these "garbage" are not cleared away, the consequences will be very serious:
The impact on water quality
Water turbidity: Transparency drops sharply from 30-50cm to below 10cm, affecting light.
Oxygen consumption surges: The decomposition of organic particles consumes a large amount of oxygen, causing a sharp increase in BOD/COD ratio and oxygen deficiency in fish.
2. Damage to fish
Gill blockage: Suspended particles adhere to the gills of fish, hindering breathing and causing slow growth.
Disease breeding: Particulate matter carries bacteria and parasites, increasing the risk of fish infection.
Iii. How to Measure Solid Particulate Matter? What is the international standard?
In the aquaculture industry, TSS (Total suspended Solids) is commonly used to measure the concentration of particulate matter, and the standards vary from country to country:
Eu: TSS <15mg/L
The United States: TSS 8-12mg/L
China: SS (suspended solids) <10mg/L (for precious varieties such as salmon, the requirement is <5mg/L).
Iv. Solid Particle Removal Process
Factory-based recirculating water aquaculture adopts a three-stage purification process of "pretreatment → coarse filtration → fine treatment", which intercepts particulate matter layer by layer like a sieve.
1. Pretreatment: Intercept "big guys" (>100μm)
Fish toilet: An "automatic sewage suction device" at the bottom of the fish pond, capable of collecting 85% of feces and leftover feed.
Vertical flow sedimentation tank: It utilizes gravity sedimentation to remove 50%-70% of large particles.
Dual drainage system: combined with bottom drainage and side drainage to prevent secondary particle breakage.
2. Coarse filtration: Screen out "medium residues" (30-100μm)
Drum type microfilter: Like a drum washing machine, it uses a microporous filter screen to intercept 30%-50% of suspended particles.
3. Fine processing: Eliminate "micron-level assassins" (<30μm)
Protein separator: It utilizes the surface of bubbles in water to adsorb various granular dirt and soluble organic matter mixed in the water.