REVIEW ON LANDFILL LEACHATE TREATMENTS

CHAPTER ONE
INTRODUCTION
Various driving factors influence the waste management system in a country. Thus, identifying related obstacles are a necessary first step towards achievement of a sustainable practice. Waste management has become an issue of concern ever since humans began to build communities within a concentrated area. The greater the population density the more important is a proper waste management system. The management of solid waste demands solutions at all the levels from local to global [1]. Initially, waste management systems were implemented solely to remove food and breeding media for flies and rats, removing wastes from and near living spaces and depositing it „out of sight‟. The main objective of the disposal system was to take care of the sanitation and health of the community. However, with the development of modern civilization, simply removing waste became an insufficient solution because waste disposal dumps became major sources of regional environmental contamination due to emissions of leachate and gas into groundwater and surface water; dumps were soon recognized as unsustainable disposal practices. Therefore, various strategies have been introduced to improve the concepts of waste management [2]. Waste reduction, reutilization and recycling, the 3Rs concept, is widely practiced throughout the globe to achieve sustainable waste management. A final disposal element is still necessary since there is neither technology available to prevent all unwanted materials from the waste stream nor funds available to achieve zero waste. Therefore, sustainable landfilling is a necessary part of an efficient integrated waste management system. Sanitary landfilling is one of the most common methods for disposing Municipal Solid Waste (MSW). Modern sanitary landfills are designed, constructed, and maintained to minimize the adverse environmental impacts from the waste disposal over both the short and long terms. After landfilling, solid waste undergoes physico-chemical and biological changes. Consequently, the degradation of the organic fraction of the wastes in combination with percolating rainwater leads to the production of a dark coloured, highly polluted liquid called “leachate”. Landfill leachate is a highly contaminated liquid produced by the percolation of precipitation water through an open landfill or through the cap of a completed site. Leachates may contain enormous quantities of organic contaminants, ammonia, suspended solid, heavy metals, and inorganic salts, phenols and phosphorus. If not treated and carefully disposed the movement of leachate into the surrounding soil, ground water, or surface water, may lead to severe pollution and thus regulations concerning leachate discharge into receiving waters are becoming more and more stringent [3]. Characteristics of a landfill leachate can be represented by chemical oxygen demand (COD), biochemical oxygen demand (BOD), pH, total dissolved solid (TDS) and heavy metals. To reach environment friendly criteria for landfill leachate, these values should be carried out to an acceptable discharge limit. Hence, landfill leachate must be collected and treated. Considering that the leachate contains larger pollutant loads than raw sewage or many industrial wastes, leachate is now widely known as the significant source of contamination to groundwater and surface water. Leachates may contain enormous amounts of organic matter, ammonia-nitrogen, phosphate, sulphide, hardness acidity, alkalinity, salinity heavy metals, chlorinated organic and inorganic salts and other toxicants. The complexity of these characteristics makes the leachate more difficult to manage
PROBLEM STATEMENT
Since the first operation in 1938 at site Gladö, three landfills have been practiced. So far, the first landfill has already been capped because of its maximum capacity, and landfill II will be covered 2007 as well. Nowadays, solid waste is mostly landfilled in landfill III. Because of modern landfill design, according to latest regulations on landfilling, it can and will be utilized within a long period. The leachate water, which is produced from the landfills I and II, is collected into different ponds (L1, L2) and delivered to Stockholm Vatten AB directly for treatment. Since there are different waste categories at the municipal landfill, the generated leachates composition is quite complicated, including metals, hazardous, organic compounds etc. Besides two leachate ponds mentioned above, a brand new plant with a number of collecting ponds and a combined local leachate treatment station has been build as to store and treat the leachate water from landfill III. Through periodic environmental inspections, SRV återvinning AB found out that leachate water continuously contains high level of nitrogen, BOD and metals. Moreover, there is potential risk that the sewage treatment work pipes will be destroyed. Due to the highly pollutive nature, the treatment of landfill leachate becomes a particularly critical part in landfill management. For a long time, leachate water has been treated by Stockholm Vatten AB. However, since the leachate contains rather high levels of organic and inorganic pollutants such as ammonium, ions, heavy metals, hydrogen sulphide and some unknown toxic compounds, it should be treated before passing into the sewer or receiving water course. Moreover, the leachate is collected by a system of pipes from which leachate is pumped to leachate treatment plant. While the system only works well when new, leachate collection systems can clog up in less than ten years. Pipes become clogged by silt, the growth of micro-organisms or precipitating minerals. There is also the danger that the collection pipes will collapse as they become weakened by chemical attack. Last but not the least, the toxicity in leachate has potential adverse impact on sewage sludge. Under such unseen risk, the sludge might not be used as fertilizer in the future. As mentioned before, after 2007, there is a slight chance that Stockholm Vatten AB will accept that SRV återvinning AB directly discharge leachate water to the sewage treatment system, which contains the above-mentioned substances with such high concentrations. In the near future, the problems have to be solved by SRV återvinning itself. Indeed, the company owns treatment plant, which will be put into practice soon. But before applied, the treatment efficiency should be evaluated to check out how much nitrogen compounds, BOD and metals could be handled and decreased. Because of lacking previous experience or treatment performance data, there is no guarantee that high levels of treatment can be achieved. In such cases, methods that reflect site-specific conditions, and a full consideration of cross-media impacts should be proposed for SRV återvinning AB as to find out the preferred methods that reduce the leachate contaminants rather that simply transferring the environmental problem to another medium. To be successful in the treatment of landfill leachate, close examinations of leachate flow, leachate composition, and the variability in its compositions on a long-term basis are needed. As leachate composition varies temporally, an adopted treatment technology should reflect these changes either. In order to provide better knowledge and suggestions to decide how to solve the leachate problems, a research and development project work was started at SRV återvinning and this master thesis work has been carried out correspondingly.