Investigating COD and Nitrate-Nitrogen Flow and Distribution Variations in the MUCT Process Using ORP as a Control Parameter

Xiaoyu Zhang; Xiaoling Wang; Weihao Feng; Xueqi Li; Hai Lu

doi:10.1021/acsomega.9b04016

Investigating COD and Nitrate-Nitrogen Flow and Distribution Variations in the MUCT Process Using ORP as a Control Parameter

ACS Omega. 2020 Feb 28;5(9):4576-4587. doi: 10.1021/acsomega.9b04016. eCollection 2020 Mar 10.

Authors

Xiaoyu Zhang^{1

2}, Xiaoling Wang^{1

2}, Weihao Feng^{1

2}, Xueqi Li^{1

2}, Hai Lu³

Affiliations

¹ Key Laboratory of Songliao Aquatic Environment, Ministry of Education, Jilin Jianzhu University, Changchun City 130118, Jilin Province, The People's Republic of China.
² School of Municipal and Environmental Engineering, Jilin Jianzhu University, Changchun City 113118, Jilin Province, The People's Republic of China.
³ College of Civil Engineering and Architecture, Changchun Sci-Tech University, Changchun City 130600, Jilin Province, The People's Republic of China.

Abstract

This study aimed to reveal the flow and distribution lows of chemical oxygen demand (COD) and nitrate-nitrogen under different main anoxic stage oxidation-reduction potential (ORP_an) conditions based on the analysis of material balance in each reaction stage of the modified university of cape town (MUCT) process, combined with the biochemical reaction principles of activated sludge. The rule of the carbon source saving effect was also clarified. The study adopted the programmable logic controller automatic control system and the feedback control structure using the inner circulation flow of nitrate as the controlled variable. The ORP_an setting values of control parameters were -140, -125, -110, -95, -70, and -60 mV, respectively. The results showed that when the ORP_an setting value was -95 mV, COD distribution ratios of phosphorus-accumulating bacteria reached the highest in the anaerobic stage and preanoxic stage, with the values of 51.74 and 7.70%, respectively. The COD was distributed between heterotrophic bacteria and denitrifying bacteria in the main anoxic stage, and the distribution ratios were 4.40 and 7.19%, respectively, when the ORP_an setting value was -95 mV. The study also showed the distribution of nitrate-nitrogen between denitrifying bacteria and denitrifying phosphorus-accumulating bacteria in the main anoxic stage, and when ORP_an increased from -140 to -60 mV, the distribution ratios of denitrifying phosphate-accumulating bacteria increased from 76.46 to 86.32%. When there was no denitrification and phosphorus absorption, the acetic acid dosage increased from 20.33 g/d at -140 mV to 24.76 g/d at -95 mV, and the carbon source saving rate increased from 23.19 to 26.56% under similar conditions. Therefore, in the MUCT process, the regulation of ORP_an changed the material flow direction and mass quality distribution of COD and nitrate nitrogen. When ORP_an set value was -95 mV, COD and nitrate-nitrogen got the best distribution and the carbon source saving effect was the most significant.