Enhancing nitrate removal from wastewater by integrating heterotrophic and autotrophic denitrification coupled manganese oxidation process (IHAD-MnO): Internal carbon utilization performance.

Due to cause the deterioration of water quality and can produce toxic nitrite, the nitrate constituted of great threatens to human health and eco-systematic safety. Among most well-known biotechnology to remove nitrate, the integrated heterotrophic and autotrophic denitrification (IHAD) process is promising, especially for the organic-limited polluted water. In this work, the IHAD coupled manganese oxidation (IHAD-MnO) process was developed by using Pseudomonas sp. SZF15 (Gram negative strain, and rod-shaped morphology with 2.3 μm in length) in the glass serum bottles. It was found that limited organic content could accelerate nitrate removal rate, and manganese oxidation efficiency can reach up to 60.08%. To further explain carbon conversion characteristics of the process, pure heterotrophic condition assays were conducted, the results confirmed that inorganic carbon will be generated by organic carbon metabolism in heterotrophic condition, the maximum accumulation content of inorganic carbon was 142.21 mg/L (when the initial organic carbon level was 293 mg-C/L). Subsequently, since the consumption of organic carbon, biogenic inorganic carbon can be further utilized by microorganisms to support autotrophic denitrification (AuDN). Besides, X-ray photoelectron spectroscopy (XPS) was employed to analyze precipitation products produced from the process. The magnified Mn 2p spectra results showed that a typical characteristic peak of manganese dioxide was observed with the intense peak at 641.8 eV and a satellite peak at 653.7 eV, respectively. This showed that Mn(II) was oxidized to manganese dioxide by the process, which may be a functional material with adsorption properties. The process posed a highly efficient and cost effective solution with less carbon consumption and less greenhouse gas emission for sustainable water treatment technologies.