Passive Treatment Systems

Passive water treatment systems are systems that do not require the ongoing addition of chemical reagents to conduct treatment. As a result these systems:

  • Have low running and maintenance costs
  • Are long term treatment options
  • Require minimal supervision

These systems rely on installed chemical and biological process for treatment and their use and effectiveness is therefore restricted. As a consequence they should not be considered a walk away solution. However if used appropriately they can have a positive effect on water quality for a minimal cost.

They are ideally suited to the treatment of water with low acid, pollutant and suspended particle loads. An understanding of the inflow water chemistry is required to correctly design and scale the system to achieve the desired final water quality. Incorrectly scaled systems can result in poor effluent water quality or very limited treatment system life expectancy due to precipitates and armouring of installed reactive materials (eg. limestone).

Passive Treatment Systems include:

  • Oxic limestone drains (OLD)
  • Anoxic limestone drains (ALD)
  • Limestone diversion wells (LDW)
  • Reducing and Alkalinity Producing Systems (RAPS)
  • Successive Alkalinity Producing Systems (SAPS)
  • Alkalinity Ponds
  • Pyrolusite Limestone Beds (PLB)
  • Aerobic / Anaerobic Wetlands
  • Vertical Flow Wetlands (VFW)
  • Permeable Reactive Barriers (PRB)
  • Slag Leach Beds (SLB)
  • Microbial Reactor Systems (MRS)
  • Alkalinity Producing Covers

Passive treatment systems can be used for:

  • Stormwater runoff
  • Long term treatment of low acid, pollutant and sediment load run-off
  • Landfill leachate treatment
  • As a final polishing step for effluent from a fixed plant (active) treatment system
  • Turbidity reduction
  • Phosphate, Nitrate and Ammonia Reduction and Control
  • Treatment of some types of acid drainage seepage

Earth Systems expertise in water chemistry and understanding of passive treatment systems means we can design, scale and implement appropriate low-cost passive water treatment systems for long term applications.

Contact us for more information on the suitability of Passive Treatment Water Systems for your particular application.


The following relevant publication demonstrates Earth Systems’ expertise in passive water treatment systems:

A Summary of Passive and Active Treatment Technologies for Acid and Metalliferous Drainage (2006)

This paper focuses on the various passive and active treatment alternatives, examining their strengths, weaknesses and suitability for particular applications. The paper provides a starting point for selecting an appropriate technology to meet specific treatment requirements and goals.










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