I. Causes of Red Worm Proliferation
The rough surfaces of tube settlers and inclined plates facilitate the accumulation of flocculated sludge, providing an ideal habitat for red worm larvae. These larvae use flocculated particles and sediment to build nests at the bottom of sedimentation tanks, feeding on algae and organic matter. After pupating into adults, they lay eggs on the tank walls. Upon hatching, some larvae settle at the bottom, while others flow into the filtration system.
Observations of sedimentation tank sludge reveal two primary causes of red worm infestation:
- Exogenous factors: Severe organic water pollution leads to eutrophication and excessive algae growth, creating favorable conditions for red worm proliferation. Large numbers of larvae may enter the water treatment system with the inflow.
- Endogenous factors: Larvae overwinter and reproduce within the infrastructure, leading to continuous generational growth at an exponential rate.
II. Red Worm Control Measures
1. Physical Methods (Auxiliary Measures)
- Spray control: Installing spray devices over sedimentation tanks disrupts egg-laying by wetting adult wings, preventing flight and mating.
- UV irradiation: Damages larval DNA and proteins, offering a simple, cost-effective solution. However, effectiveness decreases with higher turbidity.
2. Chemical Treatment (Larvicidal Agents)
Common disinfectants-liquid chlorine, chlorine dioxide, hydrogen peroxide, ozone, sodium hypochlorite, potassium permanganate, and limewater-can rapidly eliminate larvae at sufficient dosages. Among these, chlorine dioxide is particularly effective due to its strong larvicidal action, simple equipment requirements, and lack of harmful disinfection byproducts (e.g., trihalomethanes).
Practical note: Immersing sedimentation tanks in liquid chlorine (≥24 hrs) can suppress outbreaks long-term but disrupts normal plant operation. Thus, this method is recommended only during severe infestations.