Physical-chemical treatment and disinfection of a landfill leachate

Water, flowing through beds of refuse in a sanitary landfill, will leach organic and inorganic substances from the fill. These leached substances may be a source of pollution for receiving surface or ground waters. The leachate, before it is diluted by the receiving water, can usually be classed as a very strong waste water; that is, the levels of the waste water parameters COD, Suspended Solids, low dissolved oxygen and turbidity are many times those found in normal, municipal waste water. Added to these foregoing parameters are possible high levels of toxic chemicals and metals. It is now generally recognized that the leachate from refuse landfills should be controlled, and in some recently designed landfills, leachate collection is incorporated into the overall design. Toxic chemicals and metals are not adequately removed from waste waters by the standard biological sewage treatment processes; thus, the collected landfill leachate often requires pretreatment before it can be discharged to a municipal sewer system. If it is to be discharged to a natural receiving water, it requires more complete treatment. It was the purpose of this research to attempt to develop a physical-chemical treatment system for landfill leachate, such that the effluent might be safely discharged to a biological treatment plant or a natural receiving water. To deal with the extremely large number of possible chemical reagents, and to a lesser extent, physical methods available-, it was first necessary to select a number of primary candidates from prior information and theory available in the literature; secondly, it was advantageous to use a statistically designed experimental programme for screening those candidates chosen. In the screening process, no changes in the physical parameters screened, such as duration and speed of mixing or duration of settling, were found to be significant, if normal minimum times and usual speeds were used. Four chemical reagents, lime, ozone, ferric sulfate, and alum were indicated as having a potentially significant effect on the leachate-contained Total Solids (TS), Total Carbon (TC), Turbidity (Turb), Cadmium (Cd), Copper (Cu), Iron (Fe), Zinc (Zn), Potassium (K), Calcium (Ca), Sodium (Na), Phosphorus and the acid-base relationship as expressed by the term pH. The follow-up experiments determined that only two of the above four reagents were significantly effective in removal of the afore-named pollutants, as well as Manganese (Mn), Lead (Pb), Colour, Chemical Oxygen Demand (COD), the components of Total Carbon (TC) Total Inorganic Carbon (TIC) and Total Organic Carbon (TOC), and the components of Total Solids (TS)—Suspended Solids (SS) and Dissolved Solids (DS). All of the multivalent metals, except Calcium, were significantly removed from this wastewater by pH adjustment with lime, with additional minor removals by oxidation with ozone. Dissolved organic materials were not removed by pH adjustment and only removed in approximate stoichiometric amounts by reaction with ozone. In these experiments, the polymers tested were not effective in the removal of the named pollutants. Ozone is indicated to be an effective disinfectant, but highly sensitive to the COD of the leachate. An ozone-COD ratio, which determines the quantity of applied ozone necessary for the oxidation of some of the dissolved metals and for disinfection, as a function of the contained COD, is proposed for this leachate. The possibility of the application of this ozone-COD ratio is put forth, subject to further investigation.Applied Science, Faculty ofCivil Engineering, Department ofGraduat