NOVELTY - Biodegradation of wastewater containing nitrogen-containing heterocyclic compounds, comprises (1) adding nitrogen or its oxide or sulfur or its oxide to nitrogen-containing heterocyclic compounds combined wastewater collected into a pool, (2) passing the wastewater to upflow biological aerated filter pool through a pump, (3) setting up online water quality monitoring system on a top of the upflow biological aerated filter, (4) maintaining the degradation time for 5-25 hours, and (5) collecting the treated water in a top of a weir pool.    USE - The method is useful for the biodegradation of wastewater containing nitrogen-containing heterocyclic compounds such as pyridine, indole or quinoline and its derivative (all claimed) into carbon dioxide and water.    ADVANTAGE - The method ensures complete biodegradation of wastewater into carbon dioxide and water.    DETAILED DESCRIPTION - Biodegradation of wastewater containing nitrogen-containing heterocyclic compounds, comprises (1) adding nitrogen or its oxide or sulfur or its oxide to nitrogen-containing heterocyclic compounds combined wastewater collected into a pool, where ratio of chemical oxygen demand (COD)/nitrogen oxide is 5-10:1, and ratio of COD/sulfate ion (SO42-) is 8-15:1, (2) passing the wastewater to upflow biological aerated filter pool through a pump, where the filter pool comprises 5-50 mm filter material, and a lower part of the upflow biological aerated filter is provided with perforated microaeration tube having an external air compressor for oxygen, (3) setting up online water quality monitoring system on a top of the upflow biological aerated filter, where the monitoring system comprises a signal output display connected to a pH sensor for controlling pH to 7-7.5, a sensor for controlling dissolved oxygen concentration to 0.05 to 0.3 mg/l and a sensor for controlling a redox potential to -150 mV to 50 mV, (4) maintaining the degradation time for 5-25 hours, and (5) collecting the treated water in a top of a weir pool.