The development of technology for nitrogen removal from swine wastewater is necessary to meet the effluent standards of nitrogen for water pollution prevention. However, because the composition of swine wastewater differs among various farms, it is necessary to select a nitrogen removal method based on the wastewater conditions present. Depending on the organic matter/nitrogen ratio in the influent wastewater in activated sludge treatment, it is necessary to select nitrification-denitrification, nitritation-denitritation, or anammox treatment strategies. In particular, the practical application of anammox treatment technology to treat wastewater with a low organic matter/nitrogen ratio is expected to be productive. Many cases of natural accumulation of anammox bacteria have been reported in full-scale activated sludge treatment facilities installed on pig farms under various conditions. It is thought that anammox can flexibly adapt to changes in the environmental conditions such as water temperature or changes in the influent composition. Additionally, stable nitrogen removal is possible by controlling the facility. This study outlines the characteristics of swine wastewater and nitrogen removal technology, with a focus on anammox treatment.

Duckweed holoboionts which consist of plant body and sympatric rhizospheric microorganisms have attracted attention as both of polluted water purifier and useful bioresource producer with easy maintenance and low energy consumption. The purification activities of duckweed system can be summarized into nutrient uptake by plants and microbial degradation in the rhizosphere. Previous research data indicate applicability of various duckweed holobionts to water treatment against wide variety of organic pollutants and inorganic nutrients. And more, duckweed plants show high biomass productivity and high protein/starch contents easily used for methane or ethanol fermentation. Some challenging studies on managing the contaminants degrading or plant growth promoting microorganisms in the duckweed holobionts showed possible enhancement of water treatment efficiency and biomass production. These facts clearly underline the potential of duckweed holobionts in the sustainable environmental treatment techniques and expected progress in the research and development for the practical use in the future.

Synthetic landfill leachate containing phenolic compounds (phenol and bisphenol A) and heavy metals (chromium (Cr) and manganese (Mn)) at 30 mg/L each were treated using column-type two-stage constructed wetland (CW) systems which were compiled with gravel and activated carbon as the substrate. Four types of CWs with and without planting common reeds and with two feeding modes (continuous and batch feeding modes) were operated for 96 d with varying hydraulic retention times (HRTs) of 5, 3, 2, and 1 d. Longer HRT (i.e., 5 d) was required for efficient removal of NH₄－N, Cr, and Mn. The removal of NH₄－N was higher in continuous-feed CWs, whereas batch-feed CWs were effective in the removal of heavy metals. Chemical oxygen demand and phenol could be removed efficiently, irrespective of vegetation, feeding mode, and HRT, which indicated the importance of substrate selection. By contrast, the adsorption onto the substrate as well as aerobic degradation by microorganisms in the presence of sufficient dissolved oxygen were likely significant on the removal of BPA. This study demonstrated the effectiveness of column-type two-stage CWs, and the distinct impact of feeding mode and HRT in the treatment of pollutants with different physical and chemical properties.