Nutrient loading as a result of industrial discharge is a large contributor to the eutrophication of aquatic environments. Industries managing landfills are one of the largest sources for water contamination since the leachate water often contains high levels of ammonium (NH4+) and other substances that cost a lot, both environmentally and economically, to clean. Therefore, biological cleaning by microalgae has been proposed to provide efficient biofiltration of nutrients and production of a valuable resource in the form of raw material for biofuels and biomaterial. Kalmarsundsregionens renhållare (KSRR) is a landfill industry battling harmful levels of NH4+ in their leachate water released to the recipient. In parallel, the leachate water has a low phosphorus level that prevents high production in existing ponds and wetlands. Were a phosphorus source introduced, the reduction of NH4+ by microalgae could be a complement to KSRRs cleaning efforts. This study focuses on identifying which phytoplankton species are suitable to reduce NH4+ from the NH4+ rich leachate water and if a natural community is more efficient than cultured ones. Since temperature is one of the most influential abiotic factors, the impact of temperature on NH4+ reduction efficiency will also be studied. The results revealed that the autochthonous community in pond D3 in KSRRs Moskogen and the NC1 natural community from Kalmar Dämme had the highest growth rates. Community D3 showed the highest NH4+ reduction efficiency at both 8 °C and 16 °C but overall, NH4+ reduction efficiency was highest at the lower temperature. The Moskogen D3community consisted of various small green algae phytoplankton species. The strongest selective force in terms of community composition seemed to be NH4+ with interference of optimal growth conditions in the lab. Ultimately, when including the seasonal factor of algal cultivation, a broad estimate of a reduction of 2 tons NH4+ year-1 could be reached in a 1.8-2 m3 culture volume. This would make it easier to stay within the 1 ton NH4+ year-1 threshold of the last pond connected to the recipient. Therefore, with the introduction of a phosphorus source, algal biofiltration could be the solution to high NH4+ levels in wastewater from many industries such as KSRR.