Piggery wastewater treatment by Acinetobacter sp. TX5 immobilized with spent mushroom substrate in a fixed-bed reactor

Highlights: • Spent Hypsizygus marmoreus substrate (SHMS) was used to immobilize TX5 cells. • SHMS-immobilized beads were comparable to those immobilized with activated carbon. • SHMS-immobilized TX5 could adapt rapidly to the appropriately diluted RPW. • Nitrogen removal in TX5 was clarified by isotope analysis and enzyme purification. Acinetobacter sp. TX5 immobilized with spent Hypsizygus marmoreus substrate (SHMS) was used to treat the raw piggery wastewater (RPW). In batch experiments, NH₄⁺-N in the diluted RPW decreased from initial 34.95 mg/L to 3.83 mg/L at 8 h with the removal efficiency (RE) being 89%, and the beads immobilized with SHMS were comparable to those immobilized with activated carbon. In continuous experiments, the RE ranged from 74% to 95% for NH₄⁺-N, from 73% to 93% for TN and from 54% to 82% for COD when the RPW was treated in a fixed-bed reactor packed with SHMS-immobilized TX5. The isotope analysis and enzyme purification indicated simultaneous nitrification and denitrification existing in TX5. This is the first time that spent mushroom substrates have been used to immobilize Acinetobacter species to treat the real RPW and a denitrifying nitrite reductase (dNiR) has been purified to make the nitrogen removal pathway in this species clearer.