Groundwater Pollution by Nitrate Nitrogen and Livestock Waste Management

The rapid growth in livestock farming since the late 1960s has resulted in problems managing excess waste excreted from livestock. A study on the water quality of groundwater, river water, and soil solution clarified that groundwater pollution by nitrate nitrogen was caused by nitrogenous compounds permeating livestock wastes under inappropriate waste management, including dumping and/or digging in. The appropriate treatment of livestock waste as compost and liquid fertilizer improved nitrate nitrogen pollution. The full-scale enforcement of "The Law Concerning the Appropriate Treatment and Promotion of Utilization of Livestock Manure" in 2004 reduced inappropriate waste management practices such as dumping and/or digging in. In 2019, all livestock farms installed comprehensive waste management facilities for composting, wastewater treatment, and other measures. However some issues remain to be resolved relating to the inappropriate operation of facilities and the existence of facilities aged over 20 years, which may cause pollution problems. In addition, elution of nitrate nitrogen from place of use digging in requires care even now. In 2021, an investigation report on livestock waste management was published by the Ministry of Agriculture, Forestry and Fisheries. Most solid livestock waste matter is converted into compost, which can be widely distributed on croplands of agricultural farms. Broiler litter is used for combustion energy. Liquid dairy cattle waste is applied on croplands. Wastewater from pig farms is purified with an activated sludge process to obtain clear water that complies with effluent standards and then is discharged into rivers and public waters. An appropriate application rate of compost on croplands is recommended to promote the recycling of organic and nitrogen resources and to control nitrate nitrogen in groundwater.