Plant extract in a model suspension
Coagulation destabilizes a suspension of fine particles, while flocculation combines them into larger aggregates that settle more easily. Choque-Quispe and coauthors compared preparations from Neoraimondia arequipensis, Echinopsis pachanoi and a cactus reported as Opuntia ficus. Material came from the Santa Rosa area in Talavera district in Peru, at 3000 m elevation. The collection location of experimental material does not define the species' natural range.[Choque-Quispe et al. 2020, pp. 90–91]
Stems were stripped of spines and blended with water. Filtered juice was mixed with 96% ethanol at a ratio of 1:2. The precipitated material was washed, dried and ground. The study concerned this prepared extract. The structures of individual polymers and their contributions to the particle-aggregation mechanism were not determined.[Choque-Quispe et al. 2020, p. 91]
A model suspension was prepared from kaolin and water. Flocculating activity was assessed optically after addition of extract solution and an iron(III) solution, followed by 15 seconds of mixing and five minutes of settling. Absorbance was measured at 550 nm. Initial and final turbidity and the physicochemical properties of water were determined separately. This arrangement compares preparations in a precisely defined laboratory medium.[Choque-Quispe et al. 2020, pp. 91–92]
Three Neoraimondia solution concentrations
For N. arequipensis, extract solutions labelled 1%, 2% and 3% were compared. These concentrations describe the solution of the preparation added. The final dry-extract content in the whole sample also depends on the volume of this solution and the volume of water. The authors reported means and standard deviations without clearly specifying the number of replicates for these results.[Choque-Quispe et al. 2020, pp. 91–92, Table 1]
| Extract solution | Turbidity removal | Flocculation index | pH | BOD, mg O₂/l |
|---|---|---|---|---|
| 1% | 92,64 ± 0,33% | 28,41 ± 0,94 | 6,75 ± 0,03 | 3,08 ± 0,02 |
| 2% | 92,79 ± 0,18% | 30,36 ± 0,11 | 6,93 ± 0,04 | 3,32 ± 0,02 |
| 3% | 92,78 ± 0,09% | 30,38 ± 0,11 | 7,02 ± 0,01 | 3,34 ± 0,03 |
Turbidity-removal results for all three concentrations had the same letter in Tukey's test at a 5% significance level. Increasing concentration from 1% to 3% therefore produced no statistically demonstrated increase in turbidity removal. The flocculation index increased between 1% and 2%, while the 2% and 3% treatments also belonged to the same statistical group. The two measures describe different aspects of the suspension's response.[Choque-Quispe et al. 2020, p. 92, Table 1]
Turbidity and oxygen demand
Biological oxygen demand, BOD, describes the amount of oxygen consumed by biological decomposition of substances present in a sample. In the initial water it was 0,57 mg O₂/l. After addition of the N. arequipensis preparation, values rose to about 3,08–3,34 mg O₂/l. Removal of mineral suspension particles was thus accompanied by an increase in this measure of water loading. A large reduction in turbidity alone is insufficient to describe the entire treatment outcome.[Choque-Quispe et al. 2020, pp. 92–94, Table 1]
In the experiment, water pH increased with the concentration of the preparation. Initially it was 6,61, and after application of N. arequipensis solutions it ranged from 6,75 to 7,02. Tracking pH and BOD together shows that the added material affects more parameters than visible water clarity.[Choque-Quispe et al. 2020, p. 92, Table 1]
Predicted optimisation and the measured result
The authors fitted regression equations and used Solver to select a dose subject to constraints on water parameters. For N. arequipensis, the optimization table gives predicted turbidity removal of 92,419% at a dose described as 0,246% of a one-percent solution. This solution comes from the model, rather than a separately described trial confirming that dose. The predicted pH of 6,558 is also below the minimum constraint of 6,6 entered in the same table.[Choque-Quispe et al. 2020, pp. 92–93, Tables 2–3]
The study documents the usefulness of the extract for aggregating kaolin particles under model conditions. It does not cover efficacy against microorganisms or assessment of extract residues in relation to drinking-water quality. The documented result of this study is turbidity reduction together with measured changes in physicochemical parameters.[Choque-Quispe et al. 2020, pp. 91–94]
Optimization of the flocculating capacity of natural coagulants in water treatment
Choque-Quispe D., Ligarda-Samanez C. A., Ramos-Pacheco B. S., Solano-Reynoso A. M., Choque-Quispe Y., Peralta-Guevara D. E., Quispe-Quispe Y., Optimization of the flocculating capacity of natural coagulants in water treatment, DYNA, 2020, 87(212):90-95, doi: 10.15446/dyna.v87n212.80467
Extracts from three cacti were compared in a model kaolin suspension. The paper reports turbidity, flocculation index, pH, conductivity and biological oxygen demand, and regression predictions for selected doses.