Population growth, especially in urban areas, combined with modern levels of social consumption, contribute for a significant increase of waste production. Among the environmental impacts resulting from the operation of landfills, the generation of leachate is certainly one of the most significant and most difficult to control. The composition of leachate is complex and varied; it contains physicochemical and biological characteristics that are aggressive to the soil, water resources, fauna and flora. The technical and operational difficulties to handle it are challenges for waste managers. There are several methods to treat leachate which are widely debated in the literature, each having advantages and disadvantages. The present paper has the objective of carrying out a bibliographical review of leachate treatment from landfills, addressing the main technologies, as well as discussing their applications, advantages, disadvantages and uncertainties. According to what was studied, the technologies that have been found to have the best practical results and, in general, reach the parameters for treated effluent provided for environmental legislations, are those that use filtering membranes. However, one of the major disadvantages of these processes is the generation of a concentrate, which is normally recirculated in the landfill itself.

Estimating leachate generation during a landfill lifespan is a key issue in reducing its potential risk. Hence, a useful tool is represented by empirical and computational models. In order to ratify the applicability of the Swiss Method, most applied tool in Brazil, and the Hydrologic Evaluation of Landfill Performance (HELP), most utilized in USA, the present article carried out a case study in the São Gonçalo Waste Treatment Center (CTR-SG), located in a humid subtropical climate. Firstly, climate data were collected with Brazil’s National Institute of Meteorology, and landfill structural and operational data were assembled with the company responsible for CTR-SG’ management, Foxx-Haztec, from 2014 to 2018. Subsequently, simulations were conducted on both tools, which indicated that: Swiss Method and HELP do not consider relevant variables for leachate prediction, such as: waste composition and moisture content, organic matter decomposition and dumping methods; thus, these techniques results vary mainly according to annual precipitation, landfill surface area and, for HELP, covering layer thickness. In addition, it was verified that the models forecasted approximately half of the actual volume of generated leachate. In this bias, despite the requirement of few and generally known parameters, these are not reliable tools for assertive prediction. Furthermore, it was found that the Swiss Method employs an imprecise variable, the compaction coefficient, which made pertinent the proposal of a new coefficient, suitable to tropical regions, which should be validated in other landfill scenarios.

The different methodologies of leachate treatment are widely debated in the literature, promoting a great discussion among the scientific and academic community on the most efficient and propitious methods. Membrane treatment processes, especially Reverse Osmosis (RO), stand out as the best solution. The RO has pollutant removal rates higher than 99%, with operational cost and complexity competitive with other technologies. Its main disadvantage is the concentrated residue generated in the process that covers about 30% of the volume of leachate entering the system. Its recirculation in the body of the landfill arises as an alternative of low destination cost. Its effectiveness is directly related to the method of recirculation along the geological, climatological, technical and operational conditions of the landfills. Although already widespread, the treatment or destination of the concentrate requires a greater technological assertion. Further research is needed on the recirculation methods of the concentrate and its medium and long-term effects on leachate, settlement and landfills after care period. It is important to make a comparative analysis of landfills with similar characteristics, one with and another without recirculation of the concentrate. Alternatives to treat the concentrate are also of great interest whether they are economically viable in real scale.