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When to Install Reed Beds or Biological SBR Treatment

“Making a good choice whether to Install Reed Beds or Biological SBR Treatment Processes for Treating Landfill Leachate”

The question often arises for landfill operators, of whether to use a “SBR” Leachate Treatment Process, or if the cheaper alternative of a reed bed can be used.

Reed Beds or Biological SBRThe answer is that it depends entirely on the strength of the contaminants in landfill leachate.  The first choice, when enough land is available to site a reed bed, is the use of low running cost, low energy consumption, reed beds.

However, simple reed beds designed to be fed with leachate as horizontal flow type, engineered wetlands have a limited application for landfill leachate, because these traditionally laid-out reed beds can only be used for very dilute leachate from the very oldest landfill sites. These are sites which were built before the adoption of sanitary (lined) landfill practise, where the leachate is at its weakest.

An Example of reed beds used to treat a weak leachateThese landfills where reed beds alone can be used for leachate treatment are usually those landfills which are not lined nor capped, and located in temperate and wet places. This means that their leachate is substantial diluted, and old, and has been weakened by the addition of groundwater and rainwater entering the landfill. These would have been called tips or dumps in their day.

Modern “sanitary” (lined and capped) Municipal Solid Waste (MSW) Landfills invariably have a much more heavily contaminated and “fresher” (more acetogenic) leachate, and a more high-tech treatment system then becomes essential.

For many landfill operators the most successful method a leachate treatment for the past 30 years has been the biological aeration of a microbiologically active sludge, and this is followed by a anoxic phase reaction known as denitrification, where removal of total nitrogen is required.

“If a reed bed won’t do the job, an SBR, or nitrification followed by denitrification type system, is the next option to look at in most cases”, Leachate Expert, Steve Last of IPPTS Associates said.

A common feature of such process designs is that they are “sequencing reactors”, which simply means that they are run by computer controls, on a batch process system. The computer is used to automatically control the periodic feeding of leachate, aeration, chemical dosing, and discharge of each batch, etc.

Plants like this have become known as simply “SBRs” (Sequencing Batch Reactor Plants), in the leachate treatment industry.

An SBR Plant for leachate treatmentSBR Plants, usually with a denitrification stage, can be configured to:

  • discharge it directly to a river or stream, usually via a reed bed which is used as a final polishing process stage. In which case the plant will need to treat the leachate to a high quality, or
  • they may alternatively only pre-treat the leachate to remove a proportion of the contaminants, before discharging it for further treatment into a public sewer. In such cases the receiving sewage works provides the necessary additional treatment.

When to Install Reed Beds or Biological SBR Treatment – SBR Leachate Treatment Process Description

Reed Bed vs SBR Leachate treatment plant - image

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The simplest SBR landfill leachate treatment plants use the biological aeration (nitrification) process in a single tank or lagoon.

These plants work automatically to run each batch filling of leachate through its treatment cycle.

Once every predetermined time interval of from 6 hours to a day or more depending on the raw leachate strength and the discharge effluent quality needed, to satisfy the requirements of the local environmental regulating body.

More than 50 SBR landfill leachate treatment plants have been constructed to designs by Last, Robinson and Olufsen, in many countries worldwide, and original plants have been in operation for in excess of 20 years. SBR landfill leachate treatment plant technology is now thoroughly tried and tested, and a wide range of operational data on such plants while in operation, has been reported in published papers.

The design of this type of SBR is similar in principle to the activated sludge process, which until recently was the process adopted for almost all wastewater treatment works (sewage works). In an SBR, similar aerobic reactions occur. Similar microorganism do the work of “treatment” in the tanks of both systems.

But, there are important differences between sewage and leachate, and the most important difference is the far higher ammonia (ammoniacal-N) in leachate, so that is where the similarity ends.

In fact, the activated sludge process as used by designers of sewage treatment works, suffers from the problem that it becomes unstable when treating the high ammoniacal-nitrogen concentrations in full strength sanitary landfill leachates.

Perfectly well experienced sewage treatment process experts have many times come unstuck, when making attempts to modify sewage works type activated sludge treatment systems to adapt sewage works designs for use in leachate treatment.

Activated sludge wastewater processes which have been used to treat leachate cannot match the robustness of a well-designed SBR/ nitrification/ denitrification process, provided by a leachate treatment expert experienced in leachate treatment plant design.

Most people in the landfill industry say that leachate is hard to treat. But, that sentiment comes from the large number of failed leachate plants which have been designed as if leachate was somehow comparable with sewage, and in that the mis-judged use of reverse osmosis (RO) Plants can also be considered a factor.

However, use of the SBR nitrification/ denitrification process, when applied correctly, often in combination with RO and/or ultrafiltration offers a robust and as stated previously proven technique for the treatment of strong leachate from all modern sanitary landfills.

Other processes may be required depending on the local environmental regulator’s requirements for such higher quality water at the discharge point as local conditions, and national regulations, may dictate. These may include:

  • Membrane Processes
  • Dissolved Air Flotation (DAF)
  • Activated Carbon Filtration.

A stated earlier, as well, in many examples these are provided in combination with a compact reed bed which provides polishing of the effluent to a very high level of purity, and provides a process performance buffer, before the treated water enters the natural environment.

The SBR Treatment Cycle and features (in a simple nitrifying SBR) are:

Feed and fill the tank/ reactor

  • Minimise energy use through control of aeration rate and aerator run-time duration, throughout the aeration period in each cycle
  • Settle the contents by waiting for the particles to coagulate and fall to the bottom
  • Open a valve and draw-off the clean water off the top of the tank.

Secondary clarifiers for particulates removal are not needed in many cases, and therefore a compact footprint is possible.

The removal of pollutants is achieved by biological action, requiring a very minimum of chemical addition, and this is achieved through

  • Close monitoring and supply adjustment for pH control and oxygen demand adjustment
  • Robustness in operation arising from the large water volume stored in the reactor tank(s)
  • Minimising and absorbing shock leachate flow and high strength loadings;
  • Economic operation under normal low dry weather flow/ loading conditions but readily adjustable to operation at a higher flow per cycle of operation during extended wet weather periods;

The SBR process, also operates with minimal sludge generation for most leachates, so there are none of the large sludge disposal cost of some other designs.

Conclusion

So, you now should have found out when to Install Reed Beds or Biological SBR Treatment.

References:

  1. Robinson, H.D. Olufsen, J.S. and Last, S.D. (2005). Design and operation of cost-e=ective leachate treatment schemes at UK landfills: Recent case studies. Published in the CIWM Scienti%c and Technical Review, April 2005, pp 14-24 © 2005 IWM Business Services Ltd.
  2. Other Published Conference Papers:
  3. CIWM Scientific and Technical Review, April 2005, 14-24. ROBINSON H D, FARROW S, CARVILLE M S, GIBBS L, Operation of the UK’s Largest Leachate Treatment Plant 6 Years of Experience at Arpley Landfill, Roberts S J and Jones D. Paper presented to XII International Landfill Symposium Sardinia, October 2009, 10pp
  4. Robinson H.D., Farrow, S., Last, S.D. and Jones, D. (2003). Remediation of leachate problems at Arpley Landfill Site, Warrington, Cheshire, UK. Paper presented to XII International Landfill Symposium Sardinia, October 2003, 10pp, 10pp

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Download our FREE time saving calculator which is intended for use for trade effluent discharge cost assessments for England, Wales and Northern Ireland in respect of sewer discharges. The Free Trade Effluent Charges Calculator software will be useful for anyone making an industrial effluent discharge to a sewer, and who wants to know how much […]

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Software Resources

Mogden Calculator - Trade Effluent Charge Formula Calculator

We plan to add a number of leachate software applications to this page over the next few months, which our visitors can download and install, and which will provide solutions to a number of problems experienced by leachate treatment plant operators. Our first two are now available, a handy conversion calculator (see below), and (see right) our Trade Effluent Charges Calculator here.

Ammonia to Ammoniacal Nitrogen “Expressed as N” – Free Conversion Calculator

There are two methods used by analytical laboratories for expressing the quantity of ammonia in contaminated water. The first is that provided bythe majoirty of water quality analytical laboratories when reporting the quality of a polluted water. They provide a weight of ammonia as the weight of the nitrogen (elemental N), “ammoniacal- N” and that is the method  used by the Enviroment Agency UK.

However, some water quality labs report the weight of “ammonia”, (ie the whole NH4 molecule) which includes the weight of the hydrogen atoms as well as the nitrogen atoms, and landfill site operators may at times erroneously think that they are closer to their maximum permitted ammoniacal nitrgen strength for discharge, than they really are.

To help landfill operators correct for the difference between the two methods of expressing ammoniacal nitrogen values we devised the software below, which will walk you through how to calculate Ammoniacal-N (ammonia expressed in mg/l as N) concentrations (as used in UK Trade Effluent charging and dicsharge consents and environmental permits).

Get started now using our software, in three steps, as follows:

1. Simply download the zipped file below and unzip it into its own new directory location on your hard drive where you will be able to go back to it later.

2. Double click on the executable file (file extension “.exe”) called “ammonia-converter.exe”, and the software will load up and you can start to use it.

3. Follow the instructions given inside the software program.

For your free software DOWNLOAD click here >>>Ammonia to Ammoniacal-N Converter Software Package Version 1

Please give us your feedback by filling in a comment below about our Ammonia as Nitrogen (N) converter software, and if we like your suggestions we may be able to incorporate them into a later version.

Help

This is our Software Help page.

1.  Is your software safe to use?

Our software is based upon a proprietory system for compiling the executable files which has been rigorously tested on all windows systems. However, in common with all other software providers, we can never be totally certain that someone may experience a problem while using it. It is safe as far as we can reasonably ascertain, however its use is at the risk of the user, and we accepat no liability. See out Terms of Use. It has also been virus checked and found free of infection.

2. How Do I Run Your Programs?

Simply unpack the zip files into a directory somewhere on your hard drive where you will be able to return to them easily. Once all the files have been “extracted” open the extracted folder and find the file which is listed as a .exe, (executable program) (it may be in the Source-Files folder). Double click on that file to “run” it and the software will open and run, presnting you with the initial window and further instructions appear to take you through using the program.

3. How Do I Install Your Programs?

The beauty of the software we provide is that the programs run without being installed. Just run the executable (.exe) file in the unzipped directory, as described in 2. above.

4. Why Does Windows Tell Me That This Software is an “Undefined Security Risk”

Microsoft is just pointing out that running any executable file brings a risk to your computer in the event that it contained a virus infection or other pernicious code, and you should not be unduly concerned about this for our software, beyond the normal precautions computer users should always take to run up to date anti-virus /security software in the background, on their computers.

Still Need Help?

We will be adding additional Frequently Asked Questions here, in response to our users queries, as they arise.

If you still have a problem after reading this page, we suggest that you email us with your question, via our Contact page on this blog. We will assist as soon as possible.

Contact

Steve Last image

Steve Last BSc MICE CEng MCIWM

Steve Last is a self employed consultant who offers consultancy advice through his business (IPPTS Associates). (For more information on the consultancy service we offer, please go to our About page.)

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