Nitrate and phosphate removal in sulphur-coral stone autotrophic denitrification packed-bed reactors

The removal effect on nitrate and phosphate of a sulphur-based autotrophic denitrifying bioreactor in composite packing of sulphur with coral stone were investigated on a pilot scale. The results showed that the optimal influent loading rate of the bioreactor (the ratio of sulphur volume to coral stone volume was 1:1) was in the range of 0.080-0.244 kg N[O.sub.3.sup.-]-N/([m.sup.3]xd) when the water temperature was 29 ± 1 °C. In this range, the removal efficiency of nitrates was higher than 95% and no nitrite accumulation occurred in the effluent. The maximum nitrate volumetric removal rate of 0.594 kg N[O.sub.3.sup.-]-N/([m.sup.3]xd) was achieved at an influent loading rate of 0.716 kg N[O.sub.3.sup.-]-N/([m.sup.3]xd) with obvious nitrite accumulation in the effluent. Along with the autotrophic denitrifying reaction, an influent loading rate between 0.070-0.210 kg P[O.sub.4.sup.3-]-P/ ([m.sup.3]xd) achieved the removal efficiency and volumetric removal rate of phosphates were 50.5%-89.2% and 0.045- 0.179 kg P[O.sub.3.sup.-]-P/([m.sup.3]xd), respectively. The phosphates related to the resistance ability of the bioreactor (the ratio of sulphur volume to coral stone volume was 1:1) was stronger than that of bioreactors (the ratio of sulphur volume to coral stone volume was 1:2 and 1:4).