Wastewater with low pollution concentrations are common in cities of the developing countries also in Vietnam because sewer network for wastewater is not yet construction that rely on combined sewer network. The results of the decomposition of organic matter partly in combined sewer network significantly reduced levels of BOD, while reducing nitrogen only a small part. The imbalance of BOD, nitrogen ratio is a challenge for treatment of wastewater - especially to ensure the nitrogen meets requirements.
