I. Common Types of Microbial Sludge:
1. Municipal Waste Sludge: The most readily available municipal waste sludge comes from the secondary sedimentation tanks of urban wastewater treatment plants. It is the most widely used basic microbial sludge, with high microbial diversity and adaptability to most low-concentration organic wastewaters.
Key Parameters:
Color: Yellowish-brown to dark brown (normal activated sludge color; black indicates oxygen deficiency, gray may indicate sludge aging)
Moisture Content: 95%~99% (must be controlled during transportation; too low a moisture content can easily lead to microbial inactivation)
MLSS (Mixed Liquor Suspended Solids): 2000~4000 mg/L (directly related to reactor degradation capacity)
SV30 (30-minute settling ratio): 15%~30% (above 30% requires caution regarding sludge bulking risk)
Advantages: Widely available, low cost, can be put into basic aerobic treatment processes without prior acclimatization.
2. Industrial acclimatized sludge: For industrial wastewater with high salinity, high COD, and containing recalcitrant pollutants (such as phenols, benzene, and heavy metals), ordinary municipal sludge is difficult to adapt and requires specialized sludge acclimatized to similar industrial wastewater systems.
Key Parameters:
Color: Varies depending on the substrate, mostly dark brown or blackish-brown. Sludge containing specific pollutants (such as dye wastewater) may have light red or light blue hues.
Shock Resistance: Adaptable to COD load fluctuations within ±30%; high-salinity wastewater acclimated sludge with a salinity tolerance ≥5%.
Sludge Retention Time (SRT): 5~20 days (extends to 15~20 days for recalcitrant pollutants).
Dehydrogenase Activity: ≥10 mg/(L・h) (higher activity indicates faster pollutant degradation).
Advantages: Highly targeted, quickly adapts to industrial wastewater quality, avoiding bacterial incompatibility.
3. Traditional Anaerobic Granular Sludge: The "high-efficiency core" of anaerobic processes, often used in UASB, EGSB, and other anaerobic reactors. It is granular, internally encapsulating methanogenic bacteria and other anaerobic microorganisms, suitable for the methanation treatment of high-concentration organic wastewater (such as food and papermaking wastewater).
Key parameters:
Color: Brownish-black to dark black (smooth particle surface and uniform color indicate good activity)
Particle size: 0.5~3 mm (larger particle size indicates better settling performance and stability)
VSS/MLSS (Volatile Suspended Solids Ratio): 0.6~0.8 (higher ratio indicates higher microbial content)
Methanogenic activity: ≥0.2 m³CH₄/(kgVSS・d) (determines methane yield and organic load handling capacity)
Density: 1.02~1.05 g/cm³ (ensures suspension within the reactor to prevent loss with effluent)
4. Anaerobic Ammonia Oxidation Granular Sludge: A "New Energy-Saving Force" in Nitrogen Removal Technology. Specifically designed for high-ammonia-nitrogen, low-COD wastewater (such as livestock wastewater and landfill leachate), it directly converts ammonia nitrogen and nitrite nitrogen into nitrogen gas using anaerobic ammonia-oxidizing bacteria. No additional carbon source is required, and energy consumption is only 1/10 of traditional nitrogen removal processes.
Key Parameters:
Color: Bright red to reddish-brown (due to the presence of cytochromes in anaerobic ammonia-oxidizing bacteria, brighter color indicates higher activity)
Particle Size: 1~4 mm (larger and more densely structured than traditional anaerobic granular sludge)
Ammonia Oxidation Rate: 0.3~1.2 kgNH₄⁺-N/(kgVSS・d) (key indicator of nitrogen removal efficiency)
Nitrogen Tolerance Concentration: ≤500 mg/L (exceeding this threshold will inhibit bacterial activity)
Temperature Adaptation Range: 30~35℃ (optimal activity under mesophilic conditions; fluctuations should be controlled within ±2℃)
Advantages: High nitrogen removal efficiency, low energy consumption, no secondary pollution; represents the mainstream direction of low-carbon wastewater treatment.
5. Specialized Functional Sludge: Specialized sludge designed to precisely address single pollution problems and treat specific pollutants.
Common types and core parameters are as follows:
Nitrifying Sludge: Yellowish-brown in color, nitrification rate 0.5~2.0 kgNH₄⁺-N/(kgVSS・d), requires DO≥2 mg/L, pH 7.5~8.5
Denitrifying Sludge: Mostly dark brown in color, denitrification rate 0.8~3.0 kgNO₃⁻-N/(kgVSS・d), requires sufficient carbon source (C/N≥5)
Phosphorus Removal Sludge: Yellowish-brown to brownish-yellow in color, polyphosphate-accumulating bacteria content ≥20%, sludge age controlled at 8~12 days, requires an alternating aerobic-anaerobic environment.
II. Sludge Selection & Key Application Considerations for Matching Process Scenarios:
For aerobic processes, select municipal waste/industrial acclimated sludge; for anaerobic processes, select traditional anaerobic granular sludge; for high ammonia nitrogen and low COD wastewater, directly use anaerobic ammonia oxidation granular sludge.
Color-Assisted Activity Assessment: Color can quickly and initially assess sludge status. For example, fading color in anaerobic ammonia oxidation sludge may indicate decreased activity; blackening of municipal sludge requires investigation of oxygen deficiency.
Adaptation in Advance: When using municipal sludge for industrial wastewater, the concentration of target pollutants should be gradually increased, with an acclimation period of 7-15 days.
Strict Control of Operating Parameters: Anaerobic sludge is sensitive to temperature and pH fluctuations and requires real-time monitoring; aerobic sludge requires sufficient dissolved oxygen to avoid decreased activity due to oxygen deficiency.
Regular Monitoring and Maintenance: Weekly monitoring of MLSS, SV30, microbial activity, and color changes is necessary. Timely sludge removal or replenishment is crucial to prevent microbial loss.