| River waters in China have dual contamination by nutrients and recalcitrant organic compounds. In principle, the organic compounds could be used to drive denitrification of nitrate, if the recalcitrant organics could be made bioavailable and regarded as the carbon for denitrification. Thus the problem on eutrophication and low TN removal of denitrification can be solved effectively. This study investigated the potential to make the recalcitrant organics bioavailable through photocatalysis. Batch denitrification tests demonstrated that dual-contaminated river water was short of available electron donor, which resulted in low total nitrogen (TN) removal by denitrification. However, the denitrification rate was increased significantly by added glucose or by making the organic material of the river water more bioavailable through photocatalysis. TN removal increased fourfold with photocatalysis for 15 minutes, and this gave the same effect as adding 92 mg/L of glucose. During the photocatalysis experiments, the COD increased because photocatalysis transformed organic molecules from those that are resistant to dichromate oxidation in the COD test to those that can be oxidized by dichromate. This phenomenon was verified by photocatalysis of pyridine. While these finding points to the potential for N removal via denitrification after photocatalysis, they also suggest that the rivers in China may be far more polluted than indicated by COD assays.According to the research on surface water, it was found that pyridine, one of bio-recalcitrant compounds, was treated with photocatalysis to cause destruction of its molecular structure. It could not be oxidized by potassium dichromate until photocatalysis, which was proved by COD increasing with photocatalytic time increasing. Pyridine was taken as organic carbon source to reduce nitrate in denitrification, and experimental results indicated that nitrate removal percentage with photocatalysis was increased as 4.2 times as that without photocatalysis. When pyridine was treated with photocatalysis and used as organic carbon source for denitrification of 30 min, the nitrate removal percentage was equivalent to the same effect by adding 150 mg/L of glucose as carbon source, which suggested that biodegradability of pyridine was improved after photocatalysis, which could realize pyridine and nitrate removal at the same time. |
