Treatment systems are designed to handle the specific contaminants present. Common methods often work in stages:

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  Primary Treatment: Separation and Settling. The first step is often to remove solid waste. This is frequently done using a settling tank or lagoon. Here, solids sink to the bottom to form sludge, while oils and greases float to the surface to be skimmed off. For animal manure, a solid-liquid separator (like a screw press or centrifuge) is commonly used to separate fibrous solids from the liquid effluent.

  
  


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  Secondary Treatment: Biological Processes. This stage tackles dissolved organic matter and nutrients. Anaerobic Digesters are highly effective for animal effluent, breaking down organic material in the absence of oxygen to produce biogas (a renewable energy source) and a more stable effluent. Aerobic Lagoons or Constructed Wetlands use bacteria and plants in the presence of oxygen to consume nutrients and further purify the water naturally and cost-effectively.

  
  


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  Tertiary Treatment: Polishing. This final "polishing" stage aims to remove specific remaining contaminants like excess nitrogen, phosphorus, or pathogens. Methods include nutrient recovery technologies (to capture nitrogen and phosphorus for reuse as fertilizer), sand filters, or disinfection (using UV light or chlorine).

  
  

The best system often combines several of these methods for optimal results.