Determination of design loading rates for simultaneous anaerobic oxidation/partial nitrification–denitrification process and application in treating dairy industry effluent

Organic carbon and nitrogen removal from highly polluted streams by using a simultaneous anaerobic oxidation/partial nitrification–denitrification (SAO/PND) system are investigated. Design loading rates of the chemical oxygen demand (COD) and total inorganic nitrogen (TIN) in this new developed process are recommended as 11.80 g COD L-1 d-1 and 0.63 g TIN L-1 d-1. The results showed 97% COD and 92% TIN removal efficiencies. High performance of the system was achieved in treating real dairy wastewater as well, and the effluent complied with international discharge standards into inland surface waters. Organic carbon was removed through anaerobic oxidation, assimilation, P–uptake by polyphosphate accumulating organisms (PAOs) and denitrifying PAOs (DPAOs), aerobic heterotrophs, and denitrification by DPAOs and denitrifying ordinary heterotrophic organisms (OHOs). Nitrogen removal mechanisms were assimilation, partial nitrification–denitrification, anaerobic ammonium oxidation (anammox), and small portion uncharacterized processes. The SAO/PND system is found as an efficient, innovative, cost–effective, energy efficient, and small footprint process with less intensive operation and maintenance requirements. This system has been verified as a robust treatment method, and will yield new insights into the design of treating highly polluted streams in the future.