Manure-free piggery wastewater is low in COD but high in concentration with a COD-to-TN (C/N) ratio less than 1. In order to removal nitrogen from the wastewater efficaciously

a wood-packed-bed A/O process with four compartments was constructed and its performance in pollutant removal was evaluated

especially the denitrification. The reactor was operated at HRT 18.7 h and 32℃ with an internal recycle ratio of 200% and DO 1.5 mg·L-1 in the last compartment. The treatment process was started up with diluted raw wastewater in which COD/TN ratio was regulated to about 3.9. When the process performed steady

the dilution rate of the raw wastewater was decreased stage by stage

synchronizing with C/N ratio. When the process was steady in the last stage even feeding the raw wastewater with a high of about 307.7 mg·L-1 and a COD/TN ratio as low as 0.47

the removal of COD

and TN was averaged out about 66.5%

93.6% and 89.0%

respectively. A load removal of TN above 0.22 kg·m-3·d-1 was obtained. The four compartments had illustrated difference in pollutant removal with a total COD removal of about 78.3% in the front three anaerobic compartments and a TN removal of about 73.1% in the last aerobic compartment. TN removal in the reactor was mainly attributed to the shortcut nitrification-denitrification process with the packed wood as the internal carbon source.