| Abstract: | Two subsurface reactors of 1 m3 volume, filled with fine gravel or coarse sand, are fed with a medium similar to groundwater having a nitrate concentration of 208 mg/l. The retention time of water in the reactor is 400 d. After 30 months the reactor effluent shows a stationary behaviour of the nitrate concentration. Then, the effluent concentration is 90 or 100 mg/l nitrate. The breakthrough curves of nitrate show four pronounced sections: up to the retention time, increase of nitrate to ca. 40 mg/l, a stationary intermediate phase, a further increase of nitrate to the final stationary phase. The stationary intermediate and final phases show 1st-order reaction constants of 0.0046 d?1 and 0.0019 d?1, respectively, or half-times of 150 and 330 … 400 d, respectively. The higher reaction constants of the intermediate phase are connected with the bituminous coating of the reactors by the relatively easily degradable organic substance of which reaction is accelerated. With respect to variance analysis the annual minima and maxima of the nitrate turnover show significant differences. This is demonstrated by the temperature dependence of denitrification. |
