In a research project completed on behalf of the UK Environment Agency data was collected data and leachates were sampled from EU landfills that had received imports of MSOR (Mechanically Sorted Organic Refuse) and Mechanical Biological Treatment (MBT) wastes, several years ago. The results of the sampling exercise were analysed for, the presence of trace […]
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There are three very important leachate indicator parameters which are used as indicators to identify leachate contamination in any water sample analysed in a water quality laboratory. These three parameters can give an initial guide to anyone investigating what appears to be pollution occurring in the vicinity of a landfill, as to whether the source […]
The Reverse Osmosis process is unique, it alone consistently removes salts (salinity) from leachate, apart from prohibitively energy expensive, physical evaporative methods, so it is an obvious candidate for leachate treatment.
First of all when asked the question, “How Do You Treat Leachate?”, we would like to make a distinction between true treatment which involves converting environmentally damaging substances to less, or non-toxic, ones, and simply concentrating the contaminants from the water in leachate to give a volume reduction. In the water industry both are known as […]
If you have a problem with a substance found in leachate, we are here to help you! Our fact files, which are based on publicly published UK government research, are unique. You can save huge amounts of time hunting down this information which is otherwise spread very widely in published papers in libraries and on research databases, and is only partially accessible from the web.
What Are Trace Contaminants?
Landfill leachate invariably contains a host of different substances in addition to the major substances present (COD, BOD, Suspended solids, Metals in solution, Salinity, Ammoniacal nitrogen etc), which although only dissolved in tiny quantities (parts per million (ppm) and parts per billion (ppb)) still may represent a potential hazard to the environment and public health due to their extreme toxicity. To make a distinction between much higher concentrations of the main contaminants which are present in parts per thousand and more, and these lower concentration but much more toxic substances, the term “Trace Contaminants” is applied.
National and international standards have been set for the maximum permissible concentrations of many of these toxic (or “dangerous”) substances in drinking water, and under the EU Groundwater Directive no such substances are in principle permitted to be discharged to groundwater. In the UK these substances are often described as List 1 Substances, however since the creation of that list many more substances and species of contaminants have beeen identified which can now be analysed, and routinely reported upon within the description of “Dangerous Substances” as now applied by the environment Agency (EA).
How Does a Person Tasked With Deciding Whether a Leachate Contains Significant Quantities of Trace Contaminants Find Out About Them?
The first step is to analyse for them. Contact your water quality analytical laboratory and request a list of the subtsances they analyse when asked to complete what are variously called “List1”, “Dangerous Substances”, “or Comprehensive Prescribed List” analysis reports. Before you head off to the landfill to collect the necessary samples you will also need to await a package of special bottles which te analytical laboratory staff will prepare and send to you. Some of the se bottles wil include fixitive chemicals designed to prevent decay of some substances while en-route to the analytical test laboratory.
OK. So the Analytical Report Showed Some Dangerous Chemicals to be Present at Trace Concentrations. Does it matter? What Now?
Most leachates, especially those from older landfills, will show the presence of some of these chemicals. The next step is to decide whether they present a real hazard when the discharge route is taken into account. To do that we are writing and publishing a series of Leachate Contaminant Fact Files, each one of which will discuss the nature of a hazardous substance, or species of substances, and identify research papers written on the contaminant, to assit the reader in deciding whether the presence of the substance is significant and assist them in the decision either to treat the leachate to remove the susbtance, or to make a scientifically based case to the regulatory body or waste water treatment plant operator that negligable risk exists from the dangerous chemical at the concentration seen during water quality analysis.
Our first Leachate Contaminant Fact Files are Now Available. For more information, and purchase for immediate download, please click on the linked text below:
Rain falling on the top of the landfill is the main contributor to the generation of leachate, and is by far the largest contributor for modern sanitary landfills which do not accept liquid waste. In old unlined and un-engineered landfills, some leachate is produced from groundwater entering the waste. Some, additional leachate volume is produced during waste decomposition, and some additional surface water will sometimes run onto waste from its surroundings.
The decomposition of carbonaceous material produces some additional water, and a wide range of other materials including methane, carbon dioxide and a complex mixture of organic acids, aldehydes, alcohols and simple sugars, which dissolve in the leachate cocktail.
The precipitation percolates through the waste and takes in dissolved and suspended components from the biodegrading waste, through physical and chemical reactions.
Most landfills are designed to minimise the amount of leachate they create during their lifetimes. However, there are good scientific reasons to suggest that it would be better to flush all landfills out and to do this, would produce more leachate, faster. Landfills where the latter philosophy is adopted, are called, “bio-reactor” landfills. In Europe, bioreactor landfills are effectively prohibited by EU directives, leading them to be called “dry tombs” by some, due to their rapid capping, and minimised leachate production.
The environmental risks of leachate generation arise from it escaping into the environment around landfills, particularly to watercourses and groundwater. These risks can be mitigated by properly designed and engineered landfill sites. Such sites are those that are constructed on geologically impermeable materials or sites that use impermeable liners made of geotextiles or engineered clay . The use of linings is now mandatory within both the United States and the European Union, except where the waste closely controlled and genuinely inert.
Most toxic and difficult materials are now specifically excluded from landfill. However, despite much stricter statutory controls the leachates from modern sites are currently stronger than ever. They also contain a huge range of contaminants. In fact, anything soluble in the waste disposed will enter the leachate. Within the lists of substaces present in leachate are very low concentrations of “trace contaminants” which can have quite strongly contaminating effects. These are nowadays most often derived from materials in household and domestic retail products which enter the waste stream perfectly legally.
Unfortunately, the leachate draining from most landfills will continue to reflect the contaminants of past years, when regulatory controls were less.
These substances in include extremely low concentrations of heavy metals (for example from batteries), herbicides and pesticides (as used in gardens), etc. However, leachate is becoming less contaminated with difficult substances as time goes forward, and public awareness, recycling and increased statutory control over these substances, throughout the industrialized world is making leachate less harmful in this respect.
“Leachate has a very high ammoniacal nitrogen concentration”
The concern about environmental damage from waste leachate, largely arises from its high organic contaminant concentrations and much higher ammoniacal nitrogen than commonly found in any other organic effluent. Pathogenic microorganisms and toxic substances that might be present in it have in the past been described as the most important. However, pathogenic organism counts reduce rapidly with time in the landfill, so this only applies to the youngest leachate and leachate is seldom removed from the landfill in this condition.
One of the most comprehensive scientific studies yet undertaken worldwide on leachate, was published by the United Kingdom, DOE., in 1995. It is titled: “A review of the composition of leachate from domestic wastes in landfill sites”; Department of Environment Research Report No. CWM 07294, and still provides much essential data on the range of contaminands present in Municipal Solid Waste, and Commercial and Industrial Waste landfill leachate.