# A Simple Analysis Method of Specific Anammox Activity Using a Respirometer
###### Abstract  
Anaerobic ammonium oxidation (anammox) is a biological nitrogen removal process with attractive prospects, such as no carbon addition, less aeration, lower greenhouse gas generation, and lower sludge production. However, it is difficult to maintain a stable anammox process since the anammox bacteria have a slow growth rate and high sensitivity to many factors. Therefore, it is very important to analyze and maintain the anammox activity as a process indicator for its successful operation. The conventional method for measuring the concentration of nitrogen compounds, such as ammonium, nitrite, or nitrogen gas is inconvenient during the reaction time for specific anammox activity (SAA) analysis, which can result in an inaccurately determined SAA due to the substrate loss and temperature change. In this study, a respirometer was utilized to analyze the SAA. The SAA values from a respirometer (rSAA) showed a similar pattern to the SAA values (mSAA) from the conventional method. All of the SAA analyses showed the highest value at 35 \({}^{\circ}\)C with a granule size of <1 mm. Statistical analysis showed no significant differences regardless of the analysis method, since the \(p\)-values for the \(t\)-test and Wilcoxon rank-sum test were >0.05. Therefore, the respirometer can be used as a simple and efficient tool for SAA analysis. Moreover, the operating maintenance and management of the anammox process can be improved due to the simple SAA analysis in the field.  
anammox; granule; respirometer; SAA analysis; statistical analysis +
Footnote †: journal: Applied sciences  
0000-0002-22000-2000-2000-20000-20000-2000-20000-20000-20000-20000-20000-20000-20000-20000-20000-20000-20000-20000-20000-20000-20000-20000-20000-20000-200000-20000-2000  
time for the SAA analysis, which can result in an inaccurately determined SAA due to the substrate loss and temperature change.  
\[\text{NH}_{4}{}^{+}+1.32\text{NO}_{2}{}^{-}+0.066\text{HCO}_{3}{}^{-}+0.13\text{H} ^{+}\to 1.02\text{N}_{2}+0.26\text{NO}_{3}{}^{-}+0.066\text{CH}_{2}\text{O}_{0.5} \text{N}_{0.15}+2.03\text{H}_{2}\text{O} \tag{1}\]  
The respirometer is a device that analyzes the microbial activity simply and rapidly by in situ measurements of the gas consumed or produced from the respiration of microbes [8]. Numerous studies have made use of respirometers to evaluate the activity of iron-and sulfide-oxidizing bacteria [9; 10], sulfur-oxidizing bacteria [11], thermophilic bioleaching archaea [12], hydrogen-producing bacteria [13], soil bacteria [14], activated sludge [15; 16], anaerobic sludge [17], marine bacteria [18], and sediment [19]. These results can be used for wastewater treatment operation and management [20]. In addition, SAA can be measured using a respirometer since anammox bacteria produce nitrogen gas from ammonium and nitrite. However, to the best of our knowledge, there are little reports of SAA analysis using a respirometer.  
This study evaluated a simple method for the determination of SAA using a respirometer and applied it to investigate the effects of granule size and temperature on the SAA. These results were compared with the SAA results of conventional analysis methods, providing readers with comprehensive and useful reference information for SAA analysis using a respirometer.