Leachate Treatment Systems 101 – Landfill Training for Beginners

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All you need to know about the term “leachate treatment systems“. In this 101 style article we have set out to answer any questions beginners may have about leachate treatment systems. We have tried to cover all the basic principles and concepts using curation. Through curation we provide extracts and links to the original authority sites, for further student research.

We start by describing leachate itself, and follow on by the systems available for leachate treatment in leachate treatment plants (also known as facilities). In this use “plants” and “facilities” are closely interchangeable terms.

Leachate Definition

A leachate is any liquid that, in the course of passing through matter, extracts soluble or suspended solids, or any other component of the material through which it has passed.

Image shows leachate tanks, often used as part of leachate treatment systems. Leachate awaiting removal to a POTW.
Leachate Holding Tanks. Click image to enlarge.

Leachate is a widely used term in the environmental sciences where it has the specific meaning of a liquid that has dissolved or entrained environmentally harmful substances that may then enter the environment. It is most commonly used in the context of land-filling of putrescible or industrial waste.

In the narrow environmental context, leachate is therefore any liquid material that drains from land or stockpiled material and contains significantly elevated concentrations of undesirable material derived from the material that it has passed through.

Leachate from a landfill varies widely in composition depending on the age of the landfill and the type of waste that it contains. It usually contains both dissolved and suspended material. The generation of leachate is caused principally by precipitation percolating through waste deposited in a landfill. via en.wikipedia.org

It is a common misconception that leachate extracted from landfills holds a lot of inert particulate matter. This is seldom the case for established sites operated as Sanitary Landfills.

The Leachate Treatment System Overall

The leachate treatment system at a landfill site will include a leachate collection system to drain the leachate to where if can be extracted by pumping, or by gravity flow.

The treatment requirements for leachate from landfills can vary, depending on the discharge requirements, and the contaminants present. Leachate from sanitary landfills is generally characterized by high TDS (total dissolved solids), heavy metals, high BOD and/or COD (some very refractive), high ammonia, and color. Discharge options include discharge to a POTW or, where no access to sewer is available, discharge to ground or surface water. In the case of the latter, the treatment requirements are much greater than when discharge to a POTW is available.

In general, when discharging to a POTW, treatment requirements may include removal of heavy metals and ammonia. Further requirements may include removal of some BOD and also COD if maximum discharge limits are in place. Some discharge permits may also include color removal requirements, and occasionally, removal of some TDS, although these requirements are not typical.

In the case of ground or surface water discharge, removal of heavy metals, color, BOD/COD, ammonia and color, and also perhaps TDS will all be required. via dynatecsystems.com

A Leachate Treatment System Definition

A leachate treatment system is by definition all the infrastructure, plant, operating, monitoring, and management systems which provides the function of converting incoming leachate into a form safe for discharge off-site, while also providing for the safe and sustainable disposal of any by-products of the process.

For a leachate treatment system to function it will need to be integrated with a collection system to deliver the leachate to the treatment plant when required by the treatment facility. This is known as the leachate collection and treatment system.

Requirements of Leachate Treatment Systems for Young and Old Leachate

Image shows old leachate looks quite different than fresh often black, and always smelly young leachate.
Landfill leachate at a place called Maendy, UK, the orange froth is a vile mixture of solvents, phenols and other nasties from a dump created back in the day before such things had any regulation. – CC BY-NC-ND by richie rocket

Leachates can be classed as acetogenic or methanogenic depending on the state of degradation of the waste materials in the landfill.

Leachate from “young” acetogenic wastes is characterized by high chemical oxygen demand (COD) and biological oxygen demand (BOD) values, and by high ratios of BOD to COD.

Methanogenic leachates are derived from older landfills where extensive degradation of organic materials in the wastes has occurred.

In older leachates of this type it is categorized by lower COD values, very much lower BOD values, and lower BOD to COD ratios. via waste-management-world.com

Young and old leachate at each end of the range hold different challenges for their reliable and cost effective treatment.

How to tell young from old leachate

“Old leachate” (shown above) looks quite different to fresh (often black), and always smelly “young leachate”.

Types of Treatment Systems

Regulators of landfilling practice in various countries often say that leachate generated from their landfills is peculiar to their country and different from that in others, and that known and practiced techniques for treatment are not appropriate for their situation.

Image shows reeds as used in engineered wetland leachate treatment systems.
Click on image to enlarge – CC BY by Sustainable sanitation

Actually, this is not so. Research has shown that landfilling of domestic wastes in well engineered, large, deep landfills produces leachate of similar characteristics, regardless of climate or national income levels. via waste-management-world.com

This being so, the following treatment system types can be applied globally subject to detailed analysis of leachate quality, and volumes to be treated.

During the phases of development of any landfill one type of treatment may be appropriate initially, but later require modification as the nature of the leachate evolves over time, as the landfill matures.

Many different methods are currently in use to treat the landfill leachate. Most of these methods are adapted for wastewater treatment processing and can be divided into two main categories: biological treatments and physical/chemical treatments.

Methods of Leachate Treatment

There are many methods of leachate treatment such as:

  • Aerobic Biological Treatment such as aerated lagoons and extended activated sludge techniques.
  • Anaerobic Biological Treatment such as anaerobic lagoons, Continuous Stirred Tank (CSTR) reactors, and Upflow Anaerobic Sludge Banket Reactors (UASBRs)*.
  • Physiochemical treatment such as air stripping, pH adjustment, chemical precipitation, oxidation, and reduction.
  • Coagulation using lime, alum, ferric chloride, and land treatment.
  • Advanced techniques such as carbon adsorption (Activated Carbon Filtration), and ion exchange. via www.sciencedirect.com
  • Evaporation, which offers the possibility of complete leachate destruction with the use of landfill gas or other sources of waste heat. In hot climates evaporation will be easily achieved in ponds with nothing more than the heat of the sun, especially if done during hot dry seasons.
  • Natural systems are used as in “engineered wetlands”, and the reed Phragmites Australis is the most common plant used. The two main types of engineered wetlands are horizontal flow reed beds, and vertical flow reed beds.

* – Not applicable for methanogenic leachates which have already undergone anaerobic digestion within the landfill.

Discussion of the Above Methods

The difference between a “natural treatment” system, such as a reed bed, and a mechanised biological treatment system, such as a sequencing batch reactor, is that the former proceeds at natural rates without the use of significant amounts of energy input. Therefore, natural treatment systems are the most sustainable, once constructed.

Groundwater and leachate treatment system design should be flexible and consider the possibility of changing field conditions in the design and cost analysis of technically and economically attractive alternatives.

Very few projects will fall into the “rapid cleanup” category; therefore, long project life will most likely be required.

Due to the time value of money, rapid cleanups for finite problems may not be cost effective if expensive equipment is used for a short period unless operating costs are significantly less.

Also, operator attention may be costly, so reducing this annual expense in favor of automation may prove economically attractive. via www.sciencedirect.com

Other Leachate Management Practices which Avoid Its Production or Reduce Its Initial (Acetogenic) Strength

Installing new cover at closed Pine Lane Landfill. Reducing leachate by sealing the surface.
The best form of leachate treatment is to avoid it! Seal the surface a rapidly as possible, and don't let the rain soak in!  – CC BY-NC by MN Pollution Control Agency

Specific leachate management practices, are often adopted by landfill site managers which can significantly reduce the treatment burden.

By far the most important is the management of landfills to at all times to minimize the volume of leachate by reducing the flow/ rainfall entering the waste in the first place.

The simplest way to do this is by building each waste filling phase up quickly, to a level at which the surface can be capped in a manner which will minimize the surface area exposed to rain. A wise landfill operator will always do this. Every unit volume of leachate not created is a significant saving, and all efforts expended to this purpose are financially rewarding.

Other operational expedients such as recirculation (bioreactor landfill) and blending young and old leachate for consistent leachate plant feed quality, can hugely impact the cost of treatment.

Other Challenges Encountered by LTFs

Cold temperatures in winter can also be a challenge to designing leachate treatment facilities (LTFs) in cold climates.

Traditionally, landfill leachate has been hauled or pumped to off-site wastewater treatment facilities (POTWs) for disposal.

Disposal to off-site facilities has recently generated opposition from plant owners due to more stringent effluent discharge criteria. Regulatory requirements may also prevent POTW operators from being able to allow tankered leachate to be disposed at POTWs.

When discharged to a wastewater treatment facility, it has been reported that leachates can interfere with ultraviolet disinfection by strongly quenching UV light.

Leachate may also contain heavy metals and high ammonia concentration that may be inhibitory to the biological processes. via esemag.com

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