PROJECT DESCRIPTION
BACKGROUND
The Soneville company manages the sanitary landfill of Belderbusch in the municipality of Montzen-Plombières, located in the German-speaking part of Belgium. It has been operated since 1974 and entered its aftercare phase in 1998, when the available capacity was filled. This aftercare entails treating the leachates (rainwater percolating through the deposits) for a period of 10 years. The sanitary landfill of Montzen-Plombières is divided into two parts. From the older part flows a weakly-loaded leachate. Soneville treats this leachate directly on site before allowing it to flow into the nearby receiving waters. Installed since 1985, this simple plant is composed of biological treatment (a 8000 m3 aerated lagoon) followed by physico-chemical treatment (ammonia stripping and coagulation flocculation processes), that treats the effluent with satisfactory results and in conformity with the sector-based effluent quality standards. The leachate emitted by the newer part of the site is highly loaded and the existing plant's capacity is not large enough to treat it. To maintain the quality of the receiving waters, the Soneville company was forced to transport by road those highly loaded leachates to a rather distant municipal wastewater treatment plant. This practice was not very efficient from environmental and economical points of view but continued for many years. However, the local authorities no longer authorise this practice. Consequently, an efficient and, if possible, low-cost treatment plant had to be designed and built on the site to treat the leachates.
OBJECTIVES
The leachates from the two parts of the landfill may be considered to be "stabilised". As with any old leachates from sanitary landfills, the main pollutants are ammonium (NH4+) and non-biodegradable organic matter (Chemical Oxygen Demand – COD – non-biodegradable). There is also some biodegradable organic matter (Biochemical Oxygen Demand – BOD), the proportion of which decreases as the age of the landfill increases. Before reaching the receiving waters the effluents must meet the following effluent quality standards: Ammonium< 50 mgN/l; COD < 300 mgO2/l; BOD5 < 50 mgO2/l. The project’s aims are : to test and validate in the laboratory as well as at half full-scale (on site) a set of new and innovative treatment methods focusing on one or more of the main pollutants; to analyse the methods’ treatment costs and environmental benefits; and using the above results, to design and install the treatment plant with the best treatment costs/environmental benefits ratio. In addition to eliminating pollutants subject to the sector-based effluent quality standards, the plant should also as much as possible, eliminate the total nitrogen content, and thus nitrates.
RESULTS
Treatment of the highly loaded leachate requires a combination of various specific techniques related to one or more target pollutants. Nitrogen and biodegradable organic matter are preferably eliminated by biological reactors. Ammonium, here the more toxic nitrogen form, can be transformed into nitrates by bacteria during what is termed nitrification, a process that requires oxygen and inorganic carbon (CO2, bicarbonate). If further treatment is desired the nitrates may be taken up by vegetation or transformed into molecular nitrogen by bacteria able to perform denitrification. This process may occur when biodegradable organic matter is present and oxygen absent. The treatment of non-biodegradable organic matter is based on physico-chemical processes. For every pollutant, various methods were tested at laboratory as well as at half full-scale. Ammonium and biodegradable organic matter: Infiltration-percolation, Membrane bioreactor Nitrates: Epuvalisation, Membrane bioreactor Non-biodegradable organic matter: Activated carbon absorption, Ozone oxidation Biogas utilisation The Montzen-Plombieres landfill is now in a methanogeneous stage and generates, like many other old sanitary landfills, a biogas composed mainly of methane, a potentially valuable energy source. It was decided to use the biogas to produce electricity. Infiltration-percolation process The infiltration-percolation process is already a very old biological treatment system. The project has made various improvements in the basic concept, especially: the sand has been replaced by a natural material derived from sea algae that promotes optimal growth of the nitrifying bacteria. The bacteria require large amounts of oxygen. This oxygen demand is satisfied by means of a ventilating system that runs for only about one hour per day. Epuvalisation Epuvalisation is a technique consisting of plant-filled channels through which the wastewater flows. The plants’ roots take the pollutants - particularly the nitrates (a previous nitrification is therefore necessary) and phosphates for the plants’ growth - out of the wastewater. The roots are also covered by an abundant microbial flora that takes part in the wastewater treatment. During the project, the system showed its limits for the treatment of wastewater with high salt loads or low phosphate concentrations. The removal rates observed in the present case were insufficient to justify a full-scale plant for complete nitrogen treatment. However the Life project has shown that the epuvalisation system could be adapted to highly loaded and saline leachates by means of complementary research related to plant selection. Membrane technology This recent and still fast-developing technique combines biological treatment and membrane (polymeric hollow fibre’s) filtration. Wastewater is filtered directly by membranes immersed in a leachates/purification bacteria mixture. This makes it possible to confine the bacteria in the reactor and to have a high treatment capacity in a small volume. The technique yields a clarified water without suspended solids. The synergy between the aerated (nitrification) and anoxic (denitrification) tanks allows complete nitrogen removal (ammonium and nitrates). Given the leachate’s low biodegradable organic content, an exogenous carbon source (usually methanol or acetic acid) had to be added to achieve complete denitrification. The removal of the non-biodegradable organic matter The leachate contains high concentrations of non-biodegradable organic matter, principally stabilised compounds such as humic or fulvic acids, giving a dark brown colour to the leachate. Two techniques were tested in laboratory and half full-scale for removing these compounds from the highly loaded leachate of Montzen, namely: activated carbon adsorption; ozone oxidation to destroy the molecules completely or cleave them into smaller biodegradable molecules. The ozone oxidation was rapidly abandoned, as the oxidation reactions with the leachate were very slow and ozone consuming. The COD abatement standard was reached with difficulty and, moreover, necessitated high energy costs. In conclusion, the treatment plant makes it possible to meet the sector-based effluent quality standards and to perform complete removal of nitrogen from the highly loaded leachate. Moreover, the treatment of the weakly loaded leachate is occasionally improved permitting all of the landfill effluents to constantly meet the quality standards. The biological unit removes 50% of the non-biodegradable organic compounds, exceeding the expected performances and those obtained during the pilot study (15% removal). Important savings are therefore made with the activated carbon treatment. Another important saving is made on chemical costs, particularly the exogenous carbon source necessary for denitrification (the leachates of Montzen do not contain enough biodegradable organic matter). A subsidiary of Watco group (Oléa) has at its disposal a by-product of antifreeze (ethylene glycol) that is difficult to recycle. Tests showed that adding this by-product to the leachates boosted denitrification to excellent performance levels that exceeded that obtained with commonly used chemicals (40% increase in biological activity compared with methanol). Moreover, this utilisation increases the value of and ensures an excellent outlet for this by-product. The addition of antifreeze is controlled by on-line measurement of the nitrate concentration in the reactor (control of the dosage and the biological processes). The treatment cost is between 15 and 17 Euros (depending on the heating) per cubic meter of highly loaded leachate (40% lower than the maximal expected cost). Unfortunally, the web site for this project is not operating, but a very detailed “Layman report” is attached to this summary.
