## 4 Discussion
### Biogas Production and Coagulant Assessment to Enhance Treatment Processes
This could be due to higher volumes of sewage, changes in the composition of the sewage, or the need to improve treatment efficiency. The slight improvement in treatment efficiency indicated by the higher polyaluminium chloride consumption per kg of the EE load means that despite using more coagulant, the process was better at reducing contaminants in the sewage (Table A3). Coagulants like polyaluminium chloride (PAC) are used to aggregate and remove particles, improving water clarity and quality [49]. In acidic conditions, charge neutralization was the main mechanism, while in alkaline conditions, both charge neutralization and sweep coagulation worked effectively. Optimal performance was achieved within a pH range of 7.0 to 10.0. Regular monitoring and adjustments ensured high coagulation efficiency. There were no correlation values provided for polyaluminium chloride consumption alone (Table 5). The volume of discharged sludge showed a moderate positive correlation with coagulant consumption ([PERSON]'s Rho = 0.488, \(p\)-value = 0.026, [PERSON]'s \(z\) = 0.534, \(SE\) = 0.238), indicating that as the volume of discharged sludge increased, the consumption of polyaluminium chloride tended to increase. The ether extract load exhibited a moderate negative correlation with coagulant consumption ([PERSON]'s Rho = \(-\)0.443, \(p\)-value = 0.046, [PERSON]'s \(z\) = \(-\)0.476, \(SE\) = 0.237) and a strong negative correlation with the volume of discharged sludge ([PERSON]'s Rho = \(-\)0.614, \(p\)-value = 0.004, [PERSON]'s \(z\) = \(-\)0.716, \(SE\) = 0.241), indicating that higher ether extract loads corresponded to lower polyaluminium chloride consumption and lower volumes of discharged sludge. For Polystabil KWS, both correlations were statistically significant (Table 5). Polystabil KWS consumption displayed a strong negative correlation with the volume of discharged sludge ([PERSON]'s Rho = \(-\)0.569, \(p\)-value = 0.008, [PERSON]'s \(z\) = \(-\)0.646, \(SE\) = 0.240), meaning that as Polystabil KWS consumption increased, the volume of discharged sludge tended to decrease. This correlation was statistically significant. However, the correlations with polyaluminium chloride consumption ([PERSON]'s Rho = \(-\)0.388, \(p\)-value = 0.083, [PERSON]'s \(z\) = \(-\)0.410, \(SE\) = 0.236) and the ether extract load ([PERSON]'s Rho = 0.260, \(p\)-value = 0.254, [PERSON]'s \(z\) = 0.266, \(SE\) = 0.234) were not statistically significant, indicating weak or no significant associations. Phenol can be removed from sodium sulfate sewage using a ternary extractant (20% tributylphosphate (TBP), 20% diethyl carbonate (DEC), 60% cyclohexane), achieving 99.79% extraction efficiency. Stripping phenol with 1 mol/L sodium hydroxide (NaOH) solution reaches 96.29% efficiency [50]. The overall process allows up to 99.78% phenol recovery through two-stage extraction and back-extraction. A higher ether extract load correlates with a higher volume of discharged sludge. Coagulant consumption affects this relationship, with higher consumption leading to more substantial discharged sludge volume increases. This helps optimize sludge treatment by adjusting coagulant dosage. The flexplot in Figure 7 shows that a higher EE load generally means more discharged sludge, and this relationship is further influenced by the amount of coagulant used in the treatment process. As presented by [PERSON] et al. [51], coagulants were used to remove reactive dyes from sewage due to their effectiveness in improving purification efficiency. Traditional lab tests were labour-intensive and less realistic, leading to the development of an automated lab flow system. This approach optimized coagulation, achieving up to 95% colour removal with aluminium coagulants, making the process more efficient and practical. The results in Table A4 show that in Year I, the volume of discharged sludge increased compared to Year H. Despite this increase, the average monthly Polystabil KWS consumption decreased, as did the Polystabil KWS consumption per m\({}^{3}\) of discharged sludge.