Recovery of water from cacti for use in small farming communities

摘要

In this study, an extensive investigation was conducted to determine if declared weeds could be used as a source of water for agricultural practices in dry areas. The objective of this study was to determine if declared weeds could successfully be used as a source of water for agricultural practices in dry areas by extracting the water by means of mechanical and chemical methods. The?Cereus jamacura?cactus, also known as Queen of the Night, with a moisture content of 91 wt%, was selected for this study. Both mechanical and chemical extraction methods were used to determine the maximum water yield possible. Juicing, pressing with a hydraulic cold press and pressing with rollers were used as mechanical methods to extract water from the cacti and water yields of 7.0, 4.9 and 2.9 wt% were obtained respectively. The chemical extraction processes entailed the pulping of the cacti and the filtering off of the water. The effect of pectinase, cellulase and a surfactant at a fixed dosage on the amount of water extracted (mass of water per mass of cacti used) was investigated. The quality of the water was also determined. Temperature (30 to 50°C) and pH (2.5 to 6.5) were varied to find the optimum extraction conditions. The highest water yield (55 wt% of total cacti mass) was obtained using pectinase enzymes at a temperature of 40°C and a pH of 3.5 and cellulose enzymes at a temperature of 35°C and a pH of 5.5. This relates to a yield of 550 L of water per ton of cacti, making chemical water extraction a viable option if compared to the pollution created by the annual burning of the cacti. It was concluded from this study that the water that was extracted from theC. jamacaru?cacti would not be suitable for either domestic or industrial application due to the high levels of potassium (up to 2,650 ppm), phosphates (up to 2,200 ppm), sulphates (up to 3,800 ppm) and nitrates (up to 670 ppm) in the water. The high concentration of phosphates and nitrates, however, makes the extracted water an excellent fertiliser for crops requiring high nitrate and phosphate dosages. Small community farmers could thus benefit by using cacti as a source of water for small scale biofuels production plants while also obtaining an excellent additional fertiliser for crop cultivation.