Abstract: In order to investigate purification efficiency of the high-loading shallow underground infiltration system under the conditions of uneven influx of domestic sewage from widely scattered farm households and intermittent operation of the drainage pumps,4350 mm-tall infiltration columns were built up for an experiment to compare different loading and draining modes in effect of purifying domestic sewage with a daily hydraulic load of 12.5 12.5  cm·d^-1.The experiment was designed to have four different loading and draining modes,that is,continuous loading,intermittent loading,free draining and intermittent draining.Results show that the average NH₄⁺-N removal rates of all the columns were over 96%,and the average COD removal rates of the columns were in the range of 41.2%-67.7%.Of the four,intermittent loading and intermittent draining was the lowest in removal rate,but their drainages still met Grade Ⅱ criteria of the National Standard GB8978-1996"Integrated Standard for Drainage of Wastewater".The average TN removal rates of the columns were 17.5%-37.2%.The modes of intermittent loading and intermittent draining were the highest in TN removal rate,suggesting that to enhance nitrification/denitrification is the main way to increase N removal rate.The average TP removal rates of the four columns were in the range of 51.0%-78.0%.The columns of continuous loading and intermittent draining were the highest in TP removal rate,suggesting that to prolong stay of the wastewater in the column and to expand area of the contact surface between the wastewater and the filler are effective to increase P removal rate.the modes of intermittent loading and intermittent draining decreased COD removal rate,but were the most effective in removing N and P nutrients from wastewater.

Key words: rural wastewater, on-site treatment, subsurface infiltration system, loading and draining condition