Purification of agricultural waste water by pooling in an irrigation tank

点击翻译按钮获取中文摘要

In recent years, there are some experiments to purify the agricultural wastewater that includes much nutrients and suspended solids by pooling it temporally in irrigation tanks. It certainly purify the water, however, its mechanism and quantitative ability is still unidentified. The aim of this research is to makes them clear.Water quality of an irrigation tank called "Higashi-ike" that is located in Minakuchi, Shiga prefecture has been investigated during 2000-2001. The indices of water quality are phosphorus, nitrogen, chlorophyll-a, and so on. The results show that phosphorus of 11.9kg and nitrogen of 37.61kg have flowed into the irrigation tank and about 50 % and 7.5 % of them have stayed as residuals in the irrigation tank, respectively. The rate of residuals is quite high, compared with past researches. It may be mainly because the tank pools the agricultural wastewater and therefore its concentration of nutrients sometimes becomes extremely high.This result is only a case of small irrigation tank, however, the residual of nutrients may be substantial amount, when summing them of many irrigation tanks in Japan.And the effects of bio-manipulation by shells and drainage are also examined. Both have certainly enhanced the ability of purification, however, their degrees have unfortunately not become apparent through these experiments.In addition classification of irrigation tanks is exequted to grasp the characteristics of irrigation tanks in Minakuchi region. It shows that tanks in this region are classified into 4 categories.