Understanding Decentralized Wastewater Treatment

The most commonly used method of wastewater management in urban areas is known as the centralized model. This is where domestic and industrial wastewater is transported from various buildings via sewer lines and deposited at a central collection facility for treatment at a municipal level. Rapid urbanization and poor maintenance has shown us the flaws in this system with many areas suffering from frequent sewer flooding, blockages and pollution of water sources due to an overwhelmed system. Over the years, communities and organizations around the world have sought out ways of restructuring this model to better serve our ever growing populations; this came to be known as the decentralized model of wastewater management.

Centralized Model of Wastewater Management

The decentralized model of wastewater management collects, treats, and then discharges water to the subsurface at (or close to) the point of origin. This is in comparison to the centralized model which collects wastewater from multiple sources and transfers it via pipes to a single collection facility to be treated and discharged.

An important distinguishing factor of decentralized wastewater management is the potential for the treated wastewater to be reused close to the treatment sites. The type of reuse varies from irrigation of low-value crops and lawn areas to toilet flushing and washing of public spaces. With currently available technology, the capability exists to treat thousands of liters of wastewater produced daily. These new innovative solutions have been adopted in developing countries where the sewer infrastructure is absent or limited in scope and have led to great developments at individual and community level.

Common types of decentralized wastewater solutions include:  Septic tanks, Waste stabilization ponds and onsite wastewater treatment systems.

Of these solutions, the most commonly found in Kenyan urban areas is a regular septic tank which is used to store all the wastewater for a building or area which is then pumped, transported or discharged into the underground. The water is however not treated and the quality of tanks varies widely therefore durability is not a guarantee which often leads to leakages and costly replacements.

A more efficient system is an onsite wastewater treatment plant that is installed underground and treats all incoming wastewater which can then be reused above ground for irrigation, toilet flushing or washing of common areas. This system removes the need for a municipal sewer connection while reducing water usage as well as costs associated with pumping and replacing septic tanks.


Benefits of onsite wastewater treatment plants

  • Cost-effective and economical over the long term
  • Modern technology reduces operation and maintenance costs
  • Re-use of water makes the solution green and sustainable
  • Uses minimal energy and land therefore unlocking property value


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