With the global aquaculture industry moving toward intensification and high-density production, the accumulation of organic waste and nutrients in water has become increasingly problematic. Continuous increases in biological load lead to water quality deterioration, threaten aquatic organism health, and limit production efficiency. Traditional water treatment technologies often struggle to address these challenges alone. However, the combined system of microscreen filters and Moving Bed Biofilm Reactors (MBBR) has emerged as an efficient solution for modern aquaculture water treatment. This article explores the technical principles of this integrated system, the advantages of its self-cleaning function, and the synergistic mechanisms with MBBR.
Microscreen Filter Technology and Its Application in Aquaculture
Basic Working Principle of Microscreen Filters
A microscreen filter is a mechanical filtration device that uses a fine-pore mesh (typically 20–200 microns) for physical screening. In aquaculture systems, the microscreen filter achieves solid-liquid separation through the following process:
Inflow and Pre-Filtration: Aquaculture water enters the filter through an inlet, where coarse screens remove larger particles.
Fine Filtration: Water passes through a rotating microporous drum, trapping suspended solids (SS) on the inner surface.
Self-Cleaning Process: Accumulated solids are removed via high-pressure backwashing or a scraper system.
Clean Water Discharge: Filtered water exits through the mesh into the outlet system.
Key Roles of Microscreen Filters in Aquaculture
Solid Waste Removal: Effectively removes 50–95% of total suspended solids (TSS), significantly reducing turbidity.
Organic Load Control: Captures uneaten feed (5–25% of input) and feces (15–30% of input).
Pathogen Reduction: Removes 30–70% of free-floating pathogenic microorganisms.
Dissolved Oxygen Improvement: Reduces chemical oxygen demand (COD) by 10–40%, enhancing dissolved oxygen levels.
Downstream Treatment Protection: Prepares water for biological treatment (MBBR) by preventing biofilm clogging.
Technical Parameters and Selection Considerations
|
Parameter |
Typical Range |
Influencing Factors |
|
Mesh Pore Size |
20–200 μm |
Aquaculture type, solid properties |
|
Treatment Capacity |
5–500 m³/h |
System scale, investment cost |
|
Head Loss |
0.1–0.5 m |
Mesh cleanliness, design |
|
Power Consumption |
0.5–5 kW |
Equipment size, cleaning frequency |
|
Removal Efficiency |
60–95% |
Pore size, solid characteristics |
Selection should consider stocking density (kg/m³), feeding rate (% body weight/day), and waste generation rates.
MBBR Technology in Aquaculture
Basic Principles and Design
MBBR uses suspended biofilm carriers to remove pollutants:
Carrier Properties:
Material: HDPE
Shape: Cylindrical, cross-shaped, porous spherical
Surface area: 300–1,200 m²/m³
Fill ratio: 25–70% (optimal 35–40%).
Biofilm Formation:
Colonization time: 2–6 weeks (temperature-dependent).
Biofilm thickness: 50–300 µm (ideal 100–200 µm).
Microbial composition: Nitrifiers, denitrifiers, heterotrophs.
Pollutant Removal Mechanisms
Ammonia Oxidation:
Nitrification rate: 0.5–4 g NH₄⁺-N/m²·day (20–30°C).
Temperature effect (Q₁₀ = 1.5–2.5).
Organic Degradation:
COD removal: 60–90%; BOD₅ removal: 70–95%.
Partial Denitrification:
Simultaneous nitrification-denitrification (SND): 15–40%.
Optimized Operational Parameters
|
Parameter |
Range |
Recommendation |
|
Dissolved Oxygen |
3–6 mg/L |
>2 mg/L for nitrification |
|
pH |
6.5–8.5 |
Optimal 7.0–8.0 |
|
Temperature |
15–30°C |
Efficiency drops below 10°C |
|
Hydraulic Retention Time |
2–6 h |
Adjust based on load |
|
Carrier Fill Ratio |
40–60% |
Ensure proper fluidization |
Synergistic Advantages of Drum filter-MBBR Combined Systems
Technical Complementarity
Pollutant Load Distribution:
Microscreen removes 60–90% particulate organics.
MBBR treats dissolved pollutants (ammonia, soluble organics).
Total nitrogen removal: 50–80% (vs. 30–50% for MBBR alone).
Biofilm Protection:
Microscreen reduces carrier abrasion.
Prevents biofilm smothering (+30% activity).
Oxygen Transfer Efficiency: Pre-filtration lowers COD (20–40%), saving oxygen for nitrification (+25–50% efficiency).
System Design and Performance
Typical Process Flow:
Aquaculture effluent → Microscreen (SS removal) → MBBR (bio-treatment) → Disinfection/Temperature adjustment → Return to tanks.
Key Design Considerations:
Flow matching: Microscreen capacity ≥ MBBR design flow.
Hydraulic linkage: Avoid abrupt pressure changes affecting carriers.
Sludge handling: Microscreen waste (80–90% moisture) requires further treatment.
Emergency bypass: Allows microscreen bypass if needed.
Performance Comparison (Carp-Crucian System):
|
Parameter |
MBBR Alone |
Drum filter+MBBR |
Improvement |
|
Ammonia Removal |
68% |
89% |
+21% |
|
COD Removal |
76% |
93% |
+17% |
|
Energy Use (kWh/kg feed) |
1.2 |
0.9 |
-25% |
|
Cleaning Frequency |
2x/week |
1x/month |
-87% |
|
Fish Growth Rate |
1.8%/day |
2.3%/day |
+28% |
Economic and Environmental Benefits
Cost Savings: 30–50% longer carrier lifespan.15–30% lower aeration energy.40–60% reduced labor costs.
Production Gains:
20–50% higher stocking density.
Feed conversion ratio (FCR) reduced by 0.1–0.3.
30–70% fewer disease outbreaks.
Sustainability:
30–60% less wastewater discharge.40–70% lower nitrogen emissions.
50–80% less sludge vs. activated sludge systems.
Conclusion
The Drum filter-MBBR combined system represents a cutting-edge solution for modern aquaculture water treatment. By integrating self-cleaning mechanical filtration with efficient biological processing, it addresses the challenges of high-density farming while reducing operational costs and enhancing productivity. Future advancements in smart controls, materials, and modular designs will further optimize this technology, supporting sustainable aquaculture development worldwide.