# Enzymatic Activity in the Anaerobic Co-Digestion of Cavitated Coffee Waste and Sewage Sludge
## 3 Results
### Coefficients of Correlations Between Parameters  
Figure 7 shows the correlation analyses between the enzymatic activity, content of macro- and micro-elements and methane, biogas/methane yield and physico-chemical properties of the feedstock (A) and digestate (B) for each variant. The correlation analyses in the feedstock showed a positive relationship between the PR activity and the Na, K and Ca concentrations (r = 0.88, r = 0.61, r = 0.77, respectively), \(\beta\)-Glu activity and Ni, Cd and Pb concentrations (r = 0.57, r = 0.74, r = 0.75, respectively), and the PAL and URE activity and Na (r = 0.72, r = 0.63, respectively), Mg (r = 0.74, r = 0.69, respectively), K (r = 0.91, r = 0.88, respectively), Ca (r = 0.83, r = 0.77, respectively) and Mn concentrations (r = 0.75,  
Figure 6: The influence of CW and HDC on the enzymatic activity in the feedstock and digestate. The results are presented as mean \(\pm\) SE. Different letters above the error bars indicate statistically significant differences evaluated by [PERSON]’s test at \(p\) < 0.05.  
r = 0.77, respectively), according to \(p\leq 0.05\). In comparison, a negative correlation was observed for the \(\beta\)-Glu activity and Na concentrations (r = \(-0.63\)), PAC activity and P, Fe, Mn and Ni concentrations (r = \(-0.52\), r = \(-0.53\), r = \(-0.59\), r = \(-0.51\), respectively), and the PR activity and the P and Cd concentrations (r = \(-0.72\), r = \(0.76\), respectively).  
Moreover, digestate showed a positive correlation between the PR and URE activity and Na concentration (r = 0.69, r = 0.51, respectively) and K concentration (r = 0.85, r = 0.84, respectively), the \(\beta\)-Glu activity and the Na, P, K, Ca, Fe, Cu, Zn, Mn, Ni, Cd and Cr concentrations (r = 0.83, r = 0.74, r = 0.75, r = 0.58, r = 0.62, r = 0.60, r = 0.67, r = 0.79, r = 0.59, r = 0.67, r = 0.62, r = 0.67, respectively) at \(p\leq 0.05\) (Figure 6). The analyses of the correlations in the digestate showed that the strongest negative correlation was between the PAC activity and the Mg, P, Ca, Fe, Cu, Zn, Mn, Ni, Cd, Cr, Pb and Hg concentrations (r = \(-0.84\), r = \(-0.84\), r = \(-0.92\), r = \(-0.93\), r = \(-0.90\), r = \(-0.82\), r = \(-0.92\), r = \(-0.91\), r = \(-0.90\), r = \(-0.88\), r = \(-0.90\), r = \(-0.89\), respectively) at \(p\leq 0.05\). In addition, a negative correlation was observed between the PAL activity and Ca, Fe, Cu, Mn, Ni, Cd, Cr, Pb and Hg concentrations (r = \(-0.52\), r = \(-0.55\), r = \(-0.53\), r = \(-0.52\), r = \(-0.61\), r = \(-0.78\), r = \(-0.61\), r = \(-0.54\), r = \(-0.57\), respectively), URE activity and Pb and Hg (r = \(-0.55\), r = \(-0.54\), respectively).  
The results indicated that the relationship between the \(\beta\)-Glu activity and biogas yield showed the strongest positive correlation (r = 0.98 at \(p\leq 0.05\)). At the same time, a positive correlation was also observed between the PAC, PAL, URE and PR activity and methane yield (r = 0.72, r = 0.59, r = 0.86, r = 0.77, respectively) and methane content (r = 0.78, r = 0.55, r = 0.85, r = 0.76, respectively), according to \(p\leq 0.05\) (Figure 7).