Chedly Tizaoui
Swansea University
How to treat landfill leachates?
The challenge
Landfill leachates result from the percolation of water through the solid wastes that have been disposed of in landfills. Such leachates are made of cocktails of a variety of toxic organic and inorganic substances. Their disposal in the environment is not permitted hence they require treatment before discharge into a receiving water. Due to the toxic nature of the leachates, their treatment with conventional biological systems is not effective which requires the use of other treatment technologies.
The solution
The treatment of landfill leachates is an important aspect of sustainable wastewater management to protect current and future generations’ health and environment. Although there are many potential wastewater treatment techniques, options for the treatment of leachates are generally limited due to their toxic nature and composition. In this research ozone-based advanced oxidation treatment techniques were studied and were found effective to treat a complex landfill leachate. The treatment systems used ozone combined with solid catalysts including activated carbon, expanded perlite, and titanium dioxide and ozone combined with hydrogen peroxide. It is well established that ozone is an effective oxidant and disinfectant that has long been applied in drinking water treatment as early as in the first decade of the 20th century and the technology has also been applied in wastewater treatment.
In the ozone systems studied in this research, hydroxyl radicals (•OH), which possess high oxidation potential, are generated due to the use of catalysts and hydrogen peroxide. The studied leachate was non-biodegradable with a biodegradability ratio, BOD5/COD, of 0.1. Ozone alone was found to remove about 20% of the COD and increase the biodegradability to less than 0.2. By adding the solid catalysts or hydrogen peroxide to the ozonation systems, treatment of the leachate was improved significantly with almost 50% COD removal and enhancement of biodegradability to 0.34 and to 0.7 when expanded perlite and hydrogen peroxide were used respectively. Colour removals of about 95% were also achieved. The results obtained suggest the use of a hybrid AOP/biological system for an effective treatment of the landfill leachate.
Resulting benefits
The research has helped to assess different technologies for treating landfill leachates. Clearly traditional biological treatment systems were not effective to treat the leachate studied here but the use of an ozone-based AOP rendered this complex wastewater biodegradable and hence can be treated further in a biological process.
Future directions
Finding a suitable treatment process is an important aspect of leachate management. Further research using hybrid AOP/biological treatment systems at pilot scale should provide robust technical and cost data to support the design and operation of advanced treatment strategies for a given leachate in the UK. Such information will inform stakeholders and support decisions.
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