Nitrogen Removal from Landfill Leachate by Chemical and Biological Treatment: Process Comparison

Abstract

The efficiency of nitrogen removal from leachate by different chemical and biological methods was explored. The leachate was derived from Filborna landfill (NSR AB, Helsingborg, Sweden) and was characterized as an old leachate with pH = 8.0 and comparatively low concentrations of nitrogen and organic compounds (ca. 150 mg/l NH₄-N and 500 mg/l COD). Three treatment processes were tested in lab-scale experiments; combined nitrification and denitrification in a sequencing-batch reactor (SBR), one-reactor nitritation-anammox process in a moving-bed biofilm reactor (MBBR) in sequencing-batch configuration and nitrogen precipitation in the form of magnesium-ammonium-phosphate (MAP). State-of-the-art of these processes is described.

The conventional combined nitrification/denitrification process allowed 99% removal of inorganic nitrogen with 23 mg NH₄-N/(l·h) being the highest nitrification rate achieved. Aeration during nitrification step and addition of carbon source according to the stoichiometric ratio for denitrification was required, accounting for the operational costs. The nitritation-anammox process also allowed 99% removal of inorganic nitrogen with 3.7 g NH₄- N/(m²·d) being the highest process rate achieved while running the reactor at 25°C and pH 8.0. The process is advantageous in comparison with the conventional biological removal process, as oxygen consumption is lower and addition of carbon source is not required. With MAP precipitation at the optimal Mg:N:P ratio (1.2:1:1) only 78% removal of inorganic nitrogen was achieved. The precipitation process led to a significant increase of phosphorous concentrations in the effluent, while external magnesium and phosphorous sources to be added resulted in high process costs. Detailed descriptions of the processes and obtained
results are given in the article.

Comparing the three processes, conclusions are drawn that it is possible to achieve effluent nitrogen requirements (15 mg N/l) by treatment of leachate with both tested biological processes, but not with MAP precipitation. One-reactor nitritation-anammox would require the lowest operational costs, while MAP precipitation – the highest.