Based on synthesizing a lot of home and abroad researches, the paper expounded the research status of infiltration media, filtration bed thickness, hydraulic loading cycle, wet/dry ratio, oxygen restoration, removal mechanism, system blocking, and engineering application in the constructed rapid infiltration system and the progress in improving and strengthening the CRI system. In addition, the research direction and development prospect were discussed.
Carbon source used as electron donors is critical to heterotrophic denitrification. Addition of external carbon source is necessary when internal organics are deficient. A review was conducted on the use of external carbon source in denitrification. Traditional carbon sources such as methanol and ethanol, alternative carbon sources such as cellulose-rich materials, biodegradable polymers and primary sludge are included in external carbon sources. Present situation and problems of its biodegradability and effects in denitrification are summarized. Focus in external carbon source includes further study on the biodegradation mechanism of the media, slow release performance and nitrate removal rate of available carbon source and continuous research on new kinds of substrates. Recommendations on further study of carbon source are put forward.
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