**Table 2.**

*Physicochemical characterization of wastewater.*

the wastewater, the parameters of TN and TP were also evaluated. Because the wastewater exceeds the maximum permissible limits of contaminants in water, a treatment must be carried out which reduces the degree of contamination, since it has a large contribution of essential nutrients for the growth of organisms, such as nitrogen and phosphorus. These can stimulate the growth of macro and photosynthetic microorganisms in harmful quantities, which would trigger a eutrophic environment in water bodies.

On the other hand, the parameter ζ was measured because it is directly related to the ionic properties of the dissolved solids present in the wastewater.

Solid/aqueous interfaces suffer from a pH-dependent surface charge, that is, they tend to have a positive charge at acidic pH and a negative charge at basic pH. The sign and magnitude of the surface charge govern the adsorption of ionic species in solution and the physical properties of dispersions (e.g., their stability against coagulation). That is why, in the coagulation process, the suspended solids are destabilized by varying the pH of the water and this tends to zero when it approaches the isoelectric point. A simple variation of pH could be enough to stabilize or destabilize the solids that are dissolved in the water [10]. Therefore, the pH value can control both the charge density of the bio-polyelectrolyte and the surface charge of the suspended particles (**Figure 1**).

The surface charge of both coagulants and colloids in water depend on pH and their behavior having a great influence and performance in the coagulationflocculation processes, which is why ζ measurements are required to characterize the colloidal system and understand repulsion and aggregation between colloidal particles [11].

The dosing strategy was determined by measuring the ζ of both the organic matter colloids and chitosan, and also by the optimum pH value to reach the isoelectric point. The purpose of the chitosan dose is to reduce interparticle repulsion by neutralizing negatively charged particles of organic matter.

In general, the electro-neutrality zone for the chitosan-organic matter system is below pH 6 as shown in **Figure 2**. Working at this pH improves the efficiency of the coagulation-flocculation process, since chitosan achieves a higher charge density in an acid medium, therefore its concentration can be decreased.

The best clarification of the wastewater was at pH 5.9, at this pH the positive charges in the chitosan lead to an increase in the hydrodynamic diameter (Dh) due to the repulsion between the intramolecular protonated amino group and this is beneficial in the effect of dosing in turbidity removal efficiency [8]. Furthermore, at this pH, the system reaches the maximum surface contact between chitosan and organic matter in the wastewater [12].

**Figure 1.** *Ionic behavior of different polyelectrolytes at different pH values.*

*Physicochemical Insights of the Organic Matter Particles Dispersed in Wastewaters Induced… DOI: http://dx.doi.org/10.5772/intechopen.99026*

**Figure 2.**

*Effect of chitosan dosage on turbidity removal efficiency. (A) Sanguaza process; (B) flour process. BP: Bio-polyelectrolyte, TSS: Total Suspended Solids.* 

The optimal dose of chitosan was 10 ppm, thus obtaining a turbidity removal efficiency of around 97% at this dose, the surface charges of the organic matter particles were neutralized by chitosan molecules resulting in a ζ value close to zero.

Particle size influences many properties of particulate materials and is a valuable indicator of their quality and performance. Larger, spherical particles will flow more easily than small ones, but smaller particles dissolve more quickly and result in higher suspension viscosities than large particles. Smaller particle sizes and a high surface charge (ζ) typically improve the stability of the particles in solution [13–15].

For the measurement of the particle size, the dynamic light scattering technique (DLS) was used, as can be seen in **Figure 3**, as the chitosan dose is increased, the size of the particles in solution increases due to the adsorption of organic matter by the active functional groups of chitosan and in turn the decrease in the ζ. This indicates that the system is unstable and that this in turn, as the dose increases, will reach the isoelectric point, generating electroneutrality in the system. Therefore, the suspended solids by gravity and their own weight will settle.

The performance of the coagulation-flocculation process was evaluated with different parameters such as COD, COT and TSS. In addition, different doses of polymer through profiles of ζ and pH were evaluated (**Figure 4**).

Electro-neutrality occurs at ζ = − 0.3 at pH = 5.7 and required a dose of 100 ppm of chitosan. At this point, the lowest turbidity was observed in the supernatant (4 FAU) compared to the original turbidity (369 FAU) in the wastewater suspension at room temperature. Furthermore, it can be observed that the floc formation is of higher quality when the isoelectric point is reached. For the COD measurements, the potassium permanganate (KMnO4) procedure was chosen, in which a known amount of KMnO4 is added, which is assessed with a primary calcium oxalate standard. The excess KMnO4 reacts with the excess oxalate and finally, the excess oxalate is titrated

with the permanganate and this reaction was carried out at elevated temperature to accelerate the process, obtaining an efficient coagulation-flocculation process, removing a total of 93% of total COD and 100% of TSS in jar tests (**Figure 5**).

**Figure 3.** *Effect of chitosan dosage on particle size and Z potential.*

#### **Figure 4.**

ζ *and evaluation of water quality parameters as a function of chitosan dose in jar tests. (A) Sanguaza process; (B) Flour process. z: zeta potential, BP: Bio-polyelectrolyte, Chemical Oxygen Demand, TSS: Total Suspended Solids.*

**Figure 5.** *Bio-polyelectrolyte contaminant removal efficiencies.*


*Physicochemical Insights of the Organic Matter Particles Dispersed in Wastewaters Induced… DOI: http://dx.doi.org/10.5772/intechopen.99026*

**Table 3.**

*Evaluation of the quality of the wastewater treated by coagulation-flocculation process.*

The main objective of coagulation-flocculation, as it is a primary treatment in wastewater, is to eliminate the suspended solids present in the water as shown in **Table 3**. When carrying out a good dosage of polyelectrolytes, the removal efficiency can be as high as 100%. In the best dose of chitosan, the coagulationflocculation stage leads to the sedimentation of the suspended pollutants, reaching 92% and 76% removal of COD and TOC, respectively. However, the effluent has a high content of TN and TP represents a risk of eutrophication in the environment, which makes it necessary to couple the coagulation-flocculation process to a secondary treatment.
