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The use of natural environmentally benign agents in the treatment of drinking water is rapidly gaining interest due to their inherently renewable character and low toxicity. We show that the common Mexican cactus produces a gum-like substance, cactus mucilage, which shows excellent flocculating abilities and is an economically viable alternative for low-income communities. Cactus mucilage is a neutral mixture of approximately 55 high-molecular weight sugar residues composed basically of arabinose, galactose, rhamnose, xylose, and galacturonic acid. We show how this natural product was characterized for its use as a flocculating agent. Our results show the mucilage efficiency for reducing arsenic and particulates from drinking water as determined by light scattering, Atomic Absorption and Hydride Generation-Atomic Fluorescence Spectroscopy. Flocculation studies proved the mucilage to be a much faster flocculating agent when compared to Al2(SO4)3 with the efficiency increasing with mucilage concentration. Jar tests revealed that lower concentrations of mucilage provided the optimal effectiveness for supernatant clarity, an important factor in determining the potability of water. Initial filter results with the mucilage embedded in a silica matrix prove the feasibility of applying this technology as a method for heavy metal removal. This project provides fundamental, quantitative insights into the necessary and minimum requirements for natural flocculating agents that are innovative, environmentally benign, and cost-effective.

Flocculants are commonly used in industrial settings where solid-liquid separations are desired including industrial and municipal wastewater management and potable water production facilities. Conventional flocculants include inorganic metal salts and synthetic organic polymers. The cost, availability, and harmful effects of the non-biodegradable nature of these flocculants have led to the widespread study of natural flocculants. Current natural flocculants being studied include polysaccharides cultivated from microbial extracellular matrix products and plant based materials. In this study, the mucilage of Opuntia ficus-indica cactus was evaluated as a natural flocculant for sediments and bacteria. The O. ficus-indica cactus is also known as the nopal or prickly pear and is commonly used as a food source in Mexico and Latin America. Using simple extraction techniques non-gelling (NE) and gelling (GE) mucilage extracts were isolated from fresh cactus pads. Column tests were used to evaluate the flocculation and removal of suspended sediment and bacteria caused by mucilage addition. Throughout this work the mucilage's ability as a flocculant was evaluated by varying mucilage type and concentration, suspended contaminant type and concentration, and cation type and concentration. Many of the results are explained in terms of the morphology and chemical composition of the GE and NE mucilage extracts. The extracts consist primarily of polysaccharides and differences in physical structure between mucilage types were seen using atomic force microscopy and transition electron microscopy. A variety of suspended particles were used to evaluate the mucilage as a flocculant including kaolin, acid-washed kaolin, and bacteria. The bacteria employed in this study include Bacillus cereus, Escherichia coli HB101 K12, and fully attenuated Bacillus anthracis Sterne strain. The addition of monovalent (Na+ and K+), divalent (Ca2+ and Mg2+), and trivalent (Al3+ and Fe3+) cations was studied alone and in combination with mucilage. In cation studies Ca2+ had the most profound effect on flocculation efficiency; therefore its efficacy was further explored. Mucilage was most effective with dosages between 5 and 50 mg/L for the contaminants studied. Using these optimal concentrations, 20 to 200 L of water could be treated with only 1 g of mucilage powder. Based on the extraction method used in this work, 1 g of mucilage can be obtained from a cactus pad weighing approximately 250 g (wet weight). Mucilage remained an effective flocculant over a wide range of suspended contaminant concentrations showing that mucilage is a versatile flocculant that can be tailored for a variety of applications. Overall, this work shows that the O. ficus-indica cactus is an effective flocculant for suspended sediments and bacteria. The cactus' low cost, abundance, and current use in many areas make it an attractive alternative to traditionally used flocculants. Additionally, this work builds upon existing knowledge pertaining to natural flocculants and could offer insight into their general behaviors for water treatment applications.

Throughout the past decade an increased amount of attention has been drawn to the water contamination problems that affect the world. As a result, a variety of purification methods targeted at communities in developing countries have surfaced and, although all have contributed to the effort of improving water quality, few have been accepted and sustained for long term usage. Case studies indicate that the most beneficial methods are those which use indigenous resources, as they are both abundant and readily accepted by the communities. In an attempt to make a contribution to the search for water purification methods that can serve in both developed and developing countries, two fractions of mucilage gum, a Gelling (GE) and a Non-Gelling (NE) Extract, were obtained from the Opuntia ficus-indica cactus and tested as a flocculating agent against sediment and bacteria suspended in surrogate ion-rich waters. Diatonic ions are known to influence both cell binding and mucilage properties, causing CaCl2 to be tested as a flocculating agent alone and in conjunction with mucilage. Column tests were utilized to determine the settling rates of contaminant removal from the waters and the precipitated flocs were then evaluated. In columns employing Kaolin as a model for sediment removal, settling rates as high as 13.2 cm/min were observed using GE versus a control (suspensions with no treatment) settling at 0.5 cm/min. B. cereus tests displayed flocculation initiation up to 10 minutes faster than columns treated with calcium chloride (CaCl2) when using less than 10 ppm (GE) and 5 ppm (NE) of mucilage in addition to CaCl2. B. cereus removal rates between 95 and 98% have been observed in high concentration tests (> 108 cells/mL). Tests on E. coli flocculation differed slightly from those seen using B. cereus with control columns requiring 5 to 10 minutes longer to begin flocculation and mucilage treated columns displaying signs of flocculation much earlier. Mucilage is an ideal material for water purification and contaminant flocculation because it grows abundantly, is inexpensive and offers communities a sustainable technology.

This work seeks to fabricate, optimize, and characterize nanofibers of cactus Opuntia ficus-indica mucilage and Poly (vinyl alcohol) (PVA) by electrospinning. Mucilage is a neutral mixture of sugars produced by cactus and PVA is a non-toxic, water-soluble, synthetic polymer, which is widely used as a co-spinning agent for polymers. Mucilage was extracted from the cactus pad and prepared for electrospinning by mixing with acetic acid. Two types of PVA were used differentiating in high and low molecular weights. Concentrations of PVA were varied to find an adequate threshold for fiber formation. Changing the ratio of PVA to cactus mucilage produced fibers of different diameter and quality. The optimizations of the parameters used in the electrospinning setup were also a factor in creating quality fibers without deformity. An acceptable PVA to mucilage ratio mixture was reached for the use of the electrospinning process and consistent nanofibers were accomplished with the use of both the low and high molecular weight PVA. The fibers were observed using a Scanning Electron Microscope, Atomic Force Microscopy, and Differential Scanning Calorimetry. In this project we were able to obtain nanofiber meshes made with environmentally friendly materials with fiber diameters raging from 50nm to 7um sized. The produced nanofibers were made in the hope that it can be utilized in the future as an inexpensive, biocompatible, and biodegradable water filtration system.