Table 2 presents Pearson correlation coefficient analysis results using a two tailed test at 95% significance while Figure 4(a)–(e) presents the relationship between AE and input parameters (COD, airflow rate, temperature, OUR, and OTR/KLa). COD (−0.043**) produced a negative correlation relation to AE as shown in Table 2. This was because high concentrations of organic matter causes bubble coalescence in the biological treatment process. Bubble coalescence results in large bubbles that are faster, reducing contact time between air bubbles and wastewater. The less contact time between air bubbles and wastewater results in low AE, since the oxygen molecules carried by the air bubbles will not be able to penetrate wastewater thickness caused by high organic matter (Fan et al. 2014; Durán et al. 2016; Odize et al. 2017). Odize et al. (2017) reported that AE decreased by 0.47% with an increase in colloidal/particulate COD from 5 mg/L to 20 mg/L. Fan et al. (2014) reported a decrease of 1.744% in AE when the organic content increased from 2.840 g/L to 10.498 g/L in the biological activated sludge process. This can also be justified by the relationship between COD and OTR/KLa that produced a negative correlation of - 0.579**, which indicates that when COD increases, OTR/KLa decreases. The relationship between AE and COD shown in Figure 4(a) shows high AE at low COD concentration.
Table 2

Pearson correlation coefficient (2 tailed) between aeration efficiency and the parameters of interest

Correlation
TemperatureOUROTR/KLaCODAirflow rateAE
Temperature Pearson Correlation      
OUR Pearson Correlation 0.271**     
OTR/KLPearson Correlation 0.305** 0.747**    
COD Pearson Correlation 0.123** −0.695** −0.579**   
Airflow rate Pearson Correlation 0.000 0.097** 0.229** 0.008  
AE Pearson Correlation 0.575** 0.206** 0.542** −0.043** −0.061** 
Correlation
TemperatureOUROTR/KLaCODAirflow rateAE
Temperature Pearson Correlation      
OUR Pearson Correlation 0.271**     
OTR/KLPearson Correlation 0.305** 0.747**    
COD Pearson Correlation 0.123** −0.695** −0.579**   
Airflow rate Pearson Correlation 0.000 0.097** 0.229** 0.008  
AE Pearson Correlation 0.575** 0.206** 0.542** −0.043** −0.061** 

**Correlation is significant at the 0.01 level (2-tailed).

*Correlation is significant at the 0.05 level (2-tailed).

Figure 4

Relationship between aeration efficiency and COD (a), airflow rate (b), temperature (c), OUR (d), and OTR (e).

Figure 4

Relationship between aeration efficiency and COD (a), airflow rate (b), temperature (c), OUR (d), and OTR (e).

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