**2. Selection of plants with the potential to produce biopolymers for coagulation and water flocculation**

chlorine gas on heated iron [2]; and a reagent used in recent years is the aluminum polychloride obtained by the reaction of aluminum with hydrochloric acid in aqueous solution [1].

The reactions associated with the coagulants are determined by some parameters such as the pH, the temperature of the water, and the concentrations of the solids that are going to be complexed to form flocs that can be separated by density difference inside the mixture. When the flocs are separated from the mixture, sludge is generated that must be thickened and then disposed of, within a waste management plan; these residues will have a high concentration of aluminum and iron, respectively, according to the type of coagulant used, whether it be aluminum sulfate, aluminum polychloride, or ferric chloride. The final disposal of these sludges is usually difficult, because of the load of aluminum or iron as they are considered toxic

These disposal problems of the sludge, which generally has a high concentration of organic matter, generate environmental impacts when they are discharged into soils or bodies of water, changing the natural microbiota and affecting the species that have contact with high concentrations of aluminum and iron. To overcome this difficulty, different products of vegetable origin have been studied, which have properties similar to those of aluminum or iron compounds, generate coagulation and flocculation, but with organic compounds, are part of the natural components of plants come, as is the case of *Melocactus* sp., *Opuntia dillenii*, *Stenocereus griseus*, *Cereus forbesii*, *Aloe arborescens*, *Aloe vera*, and Kabuli chickpea (*Cicer arietinum* L.). These plants have shown an activity for the flocculation of substances with small particle size, below 0.2 mm, which generally cannot be separated by natural

The sludge derived from the coagulation and flocculation processes with plant extracts has a completely organic composition, which means that they can be digested by microorganisms and transformed into carbon, nitrogen, and phosphorus substances that can be incorporated into the corresponding biogeochemical cycles, with absence of toxic metals for the soil [4], or with safe concentrations for this vital resource. This technological alternative transforms water treatment into a less aggressive process with the environment, taking into account that most of the waste generated in drinking water and domestic waste

The extraction systems of plant biopolymers have different methodologies, which are easy to apply, proven, and are part of already standardized unit operations. Taking into account that different parts are harvested from each plant, we must understand that for most of the plants, their use is of the majority of the biomass, whereas when we speak of Kabuli chickpea (*Cicer arietinum* L), we are using only their seed, which diminishes its use, taking into account the weight ratio of the plant and the mass used for the preparation of

The operations developed to determine the efficiency of each plant extract in the coagulation and flocculation are defined within the established for jar tests and some of them have Z potential measurements (measure of the magnitude of the repulsion or attraction between

for the soil in high concentrations[3].

370 Desalination and Water Treatment

sedimentation [3].

treatment is sludge.

the coagulant.

the particles).

Plants with the capacity to generate biopolymers with coagulant and flocculant uses have been under study during the last decades, especially *Moringa oleifera*, *Opuntia* spp., *Cicer arietinum* [5], and others that have demonstrated coagulant capacity, as part of the traditional empirical knowledge of indigenous communities [6].

**Figure 1.** *Stenocereus griseus*. Source: http://cactiguide.com/cactus/?genus=Stenocereus&species=griseus.

**Figure 2.** Cereus forbesii. Source: http://www.kakteensammlungholzheu.de/en/cereus\_forbesii.html.

**Figure 3.** *Aloe arborescens*.

The selected plants took a part of those referenced and others of those present in semiarid regions in Colombia, such as La Guajira in northern Colombia and the banks of the Chicamocha River, in the northeastern region. The species not studied are *Stenocereus griseus* (**Figure 1**), *Cereus forbesii* (**Figure 2**), *Aloe arborescens*, and *Aloe vera*; and one already studied is the Kabuli chickpea (*Cicer arietinum* L.) [6].

In the case of *Opuntia* sp., they are used to be present in the Colombian regions already named and sufficiently studied, in the same way *Aloe vera* and *Aloe arborescens* were selected (**Figure 3**). Kabuli chickpea (*Cicer arietinum*) is reviewed with studies already elaborated by other authors [7]. It should be noted that some species of *Opuntia* spp. are used as part of the animal and human diet in communities of northeastern Colombia, in semidesert areas [8].

To have a better selection, we reviewed the massive presence of these plants and that they were not part of the list of plants in danger of extinction, to be able to access their manipulation.
