Step 4: Disposal

STEP 1 Service Level

STEP 2 Collection

STEP 3 Transport

STEP 4 Disposal

STEP 5 Fecal Sludge

Choose the Final Wastewater Disposal / Reuse Option

Where on-site infiltration and disposal of wastewater is inappropriate, you will have to consider off-site treatment and disposal options. There are three broad options for wastewater disposal:
 
  1. Discharge to a natural or artificial watercourse or water body.
  2. Use in agriculture e.g. to irrigate crops. Attention to should be paid to the kind of crops irrigated and the method of irrigation. WHO and others have developed guidelines for reuse of wastewater for various purposes, see selected publications.
  3. Discharge to treatment ponds or wetlands, used for aquaculture or treatment before further discharge (ponds, lagoons, constructed wetlands), see selected publications.

The first is probably the most common, although crop irrigation using wastewater (generally untreated) is common in many countries. The use of wastewater for aquaculture is less common although there are some well known examples, for instance the East Kolkata Wetlands in India.

Key points to consider when assessing wastewater disposal/reuse options include:
  • The strength of wastewater: Sewage will normally require treatment before it can be safely discharged to the environment or used for irrigation or aquaculture.
  • Existing disposal/reuse arrangements: If wastewater is already being used in agriculture or aquaculture, there will normally be a strong case for continuing with and improving the practice. In such cases, the focus should be on providing some form of treatment and/or better management  to reduce health risks.
  • Land availability: Treatment of sewage to the quality needed for unrestricted irrigation may require a long retention period to remove worm eggs.
  • The degree of treatment required: will depend to some extent on the way in which wastewater is applied. Drip irrigation has much lower health risks than spray irrigation but requires that solids have been removed from the irrigation water so that pipe openings are not blocked. The choices here may therefore relate to the combination of treatment and other measures applied to protect health and the environment.