# Optimized Analytical-Numerical Procedure for Ultrasonic Sludge Treatment for Agricultural Use
## 10 Experimental Activity: Some Survey Results  
### On the Sonication Process  
It is evident, as shown in Figure 13, that high electric currents rapidly stabilize the average particle size, exhibiting a marked decrease of up to 55% in particle size at 1.6 W (corresponding to a 60% amplification of the current), between the 20 th and 25 th minutes of the sonication treatment. However, the reduction is not pronounced by halving the power (corresponding to an amplification of 40% of the current), standing at 49% in the same time interval. By further reducing the power (0.3 W), the size reduction is around 52% with but between the 30 th and 45 th minutes (corresponding to current amplification of 20%). As for the \(\zeta\) potential decreases if the negative surface charge does likewise, providing a clear indication of the stability of the colloids present. As highlighted in Table 5, starting from \(\zeta=-11.8\) mV, belonging to the usual range from \(-10\) mV to \(-30\) mV, it showed, after sonication pretreatment, a slight fluctuation with a negative trend as the percentage of applied electric current increased. Since the particles tend to repel each other electrostatically in these cases, it is necessary to add flocculating chemical agents.  
Figure 12: Distribution of sludge structure during ultrasonic treatment. A gradual disintegration of the agglomerates and a reduction in viscosity are observed, indicative of the cavitational effect induced by sonification, which facilitates the breaking of the particles and the release of intracellular and extracellular materials.  
Figure 13: Particle size distribution over time at different amplifications.  
Then, as is well known [68], the addition of Ca\({}^{2+}\) and Mg\({}^{2+}\) contributes significantly to the flocculation process by neutralizing surface negative charges, as well as by creating ionic bridges between negatively charged particles or between functional groups in the polymer flocculants and the sludge particles by increasing [Ca\({}^{2+}\)] and [Mg\({}^{2+}\)] reduces the electric double layer of the particles by decreasing electrostatic repulsion, increasing the attractive van der Waals forces that promote aggregation. However, [Ca\({}^{2+}\)] and [Mg\({}^{2+}\)] must be carefully controlled to avoid excess cations that cause very dense or unstable floccules settling rapidly or difficult to separate.  
Dispersion agents (non-superactive polymers or highly active substances) added to sludge also prevent sedimentation by defalloculating solids by reducing their viscosity and increasing the amount of dispersible powder material.  
To achieve a stable dispersion (\(\zeta\) potential greater than +30 mV or less than \(-\)30 mV), we used the combined effect of Silcosperse HLD5 at 3% \(v/v\), silicon-free high-performance for water-based pigmented systems (total solids: 49.0-51.0%; active agent: 39.0-41.0%; pH: 7.0-9.0, with the ultrasound treatment (Table 6).  
The results confirmed that the above combination of treatments produces stable dispersion by improving the interaction between US and sludge. The additive allows the sludge to become conductive. Since the additive allows the sludge to become conductive, as its concentration increases, conductivity increases.  
The effectiveness of sludge disintegration and solubilization was monitored by observing COD trends in the sludge supernatant.