Sustainable treatment for low ammonia nitrogen sewage wastewater in cold climates: natural polymer gel–organic synthetic polymer embedded anammox bacteria immobilized pellets†

The sewage denitrification process is concerned mainly with the treatment of industrial water with high NH₄⁺–N (>500 mg N L⁻¹). In this work, the denitrification effect of hybrid carrier (a natural polymer gel and an organic synthetic polymer)-embedded anammox bacteria pellets to treat NH₄⁺–N urban sewage wastewater at low temperature through batch and continuous tests was studied. After 99 days of operation in a UASB reactor, the rapid start-up of anammox was realized. The TN volumetric load grew gradually as the influent substrate concentration increased. The final influent water had an NH₄⁺–N load of 300 mg L⁻¹, an HRT of 5 h, a temperature of 32 °C, and NH₄⁺–N and nitrite nitrogen removal efficiencies above 85%. Batch tests for polyvinyl alcohol, polyvinyl alcohol–sodium alginate and polyvinyl alcohol–sodium bicarbonate pellets were performed. The optimized pellets performed exceptionally well in terms of mass transfer, elasticity, and mechanical strength. Embedded carrier materials are enhanced by added sodium alginate, silica powder, CaCO₃ powder and iron powder. A device containing embedded anammox bacteria pellets (EABP) was more resistant to low-temperature stress throughout the process of gradually cooling and lowering NH₄⁺–N than a device containing mature free sludge. In the analysis and strengthening test of EABP at 15 °C, NH₄⁺–N removal increased from 59% to 99%. At an HRT of 10 h, the increase in rate reached 67.8%. Compared to unembedded anammox bacteria pellets, the PS/PN of embedded pellets was lower, and the sludge activity and settleability were improved. Increasing HRT improved the ability of the embedded bacteria to withstand low temperatures, stimulating bacterial strains to produce more EPS. This study can be used to build a test to simulate future engineering applications in protecting the freshwater environment from the potential deleterious effects of pollutants from untreated sewage wastewater under low-temperature conditions and ammonium concentrations.