Waste sent to MSW landfills is subjected, prior to or at the same landfill, a compaction process that generates liquid drainage containing hazardous pollutants.
The composition of such drainage can vary depending on the compacted waste and weather conditions. This waste should be subjected to a purification treatment before being discharged into the general collector.
In the majority of instances, the most appropriate technology is thermal dehydration by vacuum evaporation. On the one hand, this allows us to obtain a solid rejection that can be compacted with the rest of the MSW in addition to a very high percentage of clean water that can be discharged or reutilized for washing.
Vacuum evaporators have also proved to be a very suitable technology for the treatment of leachate. They obtain a much higher percentage of distillate. In addition, vacuum evaporators achieve a much cleaner distillate than other technologies such as biological treatment or reverse osmosis.
Sergio Tuset is the CEO of Condorchem Envitech, with over 20 years’ experience in management of industrial companies.
Specially focused on environmental projects for customers, recognized specialist in conceptual engineering applied in wastewater, liquid &solid wastes treatment and air pollution treatment.
Steve Bleaning August 2, 2012 at 10:23 am
Vacuum evaporation (called low pressure evaporation) was offered by one equipment manufacturer in the United Kingdom for leachate management from around 1990 for about 10 years. I don’t think that the product is still offered for this purpose any more though. The problem is that it is just a concentration method, and the remaining leachate concentrate still needs to be disposed of, and it is a hazardous waste with all those heavy metals etc present, now in concentrated form. That in my view is what prevented the uptake of this technology in the UK because hazardous waste disposal costs are so high. Instead, biological treatment (much as would occur in a seage treatment works, but done more efficiently) has been much more successful with many hudreds operating around the world. Thanks.
Condorchem August 6, 2012 at 5:03 pm
We agree that biological treatment (with nitrification-denitrification) has been successful for leachate treatment, usually is the most installed system for this purpose. Biological system can remove BOD/COD and TN as well, but when high salinity content in leachate biological must be followed by membrane equipment (usually UF+RO), RO permeate achieve the permitting discharge limits but brine reject are very expensive to disposal, then vacuum evaporation can be used also to reduce amount to liquid disposal.
In the other hand we have observed that when old landfill the leachate reduce the amount of BOD instead COD is the same, sometimes the ratio COD/BOD are smaller to 10. COD practically isn’t reduced (named refractory COD) and conventional activated carbon filters can’t adsorbs this organic matter. Values of treated COD usually are about 220-300 mg/l when limit to discharge is 120 mg/l.
Only vacuum evaporation process can be expensive for energy consumption but MVR have a reduced energy consumption, also when thermal energy are available from biogas combustion) can be cheapest. Use the evaporation equipment needs a appropriate pretreatment to avoid scale, distillate need post treatment with stripping and scrubbing columns to strip ammonia and fixed then with sulfuric acid to produce ammonia sulfate. Liquid concentrate need to be reduced or stabilized, we are using 2 procedures:
a) Maximal reduction with super concentration by special vacuum evaporation equipment to produce sludge packaged in super sack to be disposed in special hazardous household. This disposal is less expensive than hazardous liquid waste and volume has been reduced to maximum.
b) Concentrated liquid brine and organics from evaporation can be mixed with lime or cement (1:1), liquid will be stabilized and lixiviate test result could be not toxic and harmful, then can be disposed in the same landfill in dedicated cells.
Several evaporation equipment installed for the pioneers during last of 90’s or beginning of next decade have been retired for failure function (heavy scaling: low production and duty maintenance materials corrosion, etc.) now we know better “how” and “when” can be named BAT for landfill leachate treatment. We know several applications working together with biological process, membranes and physic chemical equipment.
In our point of view only the thermal separation (evaporation) can produce leachate treatment when are necessary remove COD/BOD/AOX/NTK/Heavy metals/TDS/chlorides/sulfates/etc. Evaporation like a mechanical system is not sensible to abrupt change in pollutants concentration in feed leachate produced in seasonal period (dry or rain) like other P/C or biological systems.
Finally, which is the best system to appropriated landfill leachate treatment?. It depends, for each case and working conditions, sometimes could be better biological, sometimes membrane separation and why not? also vacuum evaporation or all process together.
We’d like to have your feedback about this interesting technical discussion and we appreciate your time for request.
Evaporator manufacturers October 23, 2012 at 1:37 pm
There is also a type of shell and tube chiller where the water runs through the tubes and the refrigerant flows over the outside of the tubes within a closed shell. This is known as a flooded type. However, this arrangement is not as common as the dry type of construction.
RENE PERRIN August 25, 2014 at 10:22 am
Evaporation remains the solution that allows the minimum discharge of pollutants to the environment
Contrary to what has been said by Condorchem, if any heavy metal in a biological treatment, these metals remain in the sludge. In an evaporator these metals are also concentrated in the sludge. Where is the difference?
Biogas production also allows powering evaporators, which limits the energy cost, it is also possible to evaporate the condensates to atmosphere which prevents any aqueous pllutants discharge. The concentrated sludge can be stored in the landfill which avoids any transport and any costly destruction in an external treatment facility for hazardous waste.