**Author details**

**Figure 3.** ζ = f (chitosan dose) in coagulation-flocculation tests from recycled cellulose and paper wastewater.

at this pH by pure electrostatic interaction ensures its reaction.

chitosan has a value of BOD5 = 150 mg O<sup>2</sup>

and hardness = 250 mg CaCO<sup>3</sup>

**4. Conclusions**

134 Wastewater and Water Quality

**Figure 2** shows the variation of zeta potential with respect to the pH of the wastewater and chitosan. The zeta potential value of the wastewater shows that the suspended particles have a negative surface charge density at pH 5–9. The ζ = f (pH) profile shows that at pH = 4.0 and pH > 10.0, the wastewater has two isoelectric points (ζ = 0). The stability of the particles to remain suspended is due to the value of the negative zeta potential (ζ = −25.5 mV). In order to destabilize the dispersion of cellulose fiber particles, the addition of a cationic coagulantflocculant agent that allows the neutralization of the negative surface charge is necessary. The wastewater at pH 5.4 has a ζ = −25.5 mV and the chitosan ζ = 15.0 mV, the dosage of chitosan

In **Figure 3**, it is shown that the zeta potential value of the wastewater from cellulose and paper industry increases linearly as the dose of chitosan increases (ζ = −25.5 mV to ζ = −5.1 mV), reaching the isoelectric point at a dose of 10 mg/L chitosan. The water treated at pH 5.4 with

The wastewater generated by industries is becoming more complex and difficult to treat to restore its quality and reuse it. The coagulation-flocculation process has become one of the

istics can be discharged into the municipal sewer system or reused as process water.

/L, turbidity = 5 FAU, TSS = 2 mg/L, COD = 200 mg/L

/L, and the treated water with these physicochemical character-

Eduardo A. López-Maldonado1 \* and Mercedes T. Oropeza-Guzmán<sup>2</sup>

\*Address all correspondence to: elopez92@uabc.edu.mx

1 Faculty of Chemical Sciences and Engineering, Autonomous University of Baja California, Tijuana, Mexico

2 Graduate and Research, Center of the Technical Institute of Tijuana, Tijuana, México
