Removal of Dyes from Wastewater using Plant based Biosorbent Hydrilla Verticillata

By Dr. N. Rajamohan and Rajesh Kannan
July 2008

The Author is an Associate Professor in Chemical Engineering at the Environmental Engineering Lab, Department of Science and Technology of Annamalai University in Tamil Nadu, India. → See also:

Introduction

Hydrilla verticillata is a submerged aquatic weed that can grow upto the surface and form dense mats in all bodies of water. Dye pollutants from various industries are an important source of environmental contaminations. Most industries use dyes and pigments to color their products, which include textile, tannery, food, paper and pulp, printing, carpet, and mineral processing industries. Perhaps dyes are the serious polluters of our environment as far as color pollution is concerned. Color is a visible pollutant and the presence of even very minute amount of coloring substance makes it undesirable due to its appearance. The effluents from dye manufacturing and consuming industries are highly colored coupled with high chemical and biochemical oxygen demands (COD and BOD) and suspended solids. Discharge of such effluents imparts color to receiving streams and affects its aesthetic value. The dyes are, generally, stable to light, oxidizing agents and heat, and their presence in wastewaters offers considerable resistance to their biodegradation, and thus upsetting aquatic life. Color affects the nature of water and inhibits the sunlight penetration into the stream and reduces photosynthetic activity. Some of the dyes are carcinogenic and mutagenic. The removal of color from dye-bearing effluents is one of the major problems due to the difficulty in treating such wastewaters by conventional treatment methods. The most commonly used methods for color removal are physical or chemical processes. All these methods have different color removal capabilities, capital costs, and operating rates.

Liquid phase adsorption processes have been shown to be highly efficient for removal of dyes from industrial wastewater. Granular activated carbon (GAC) is the most-popular adsorbent, which has been used with great success. However, GAC is expensive and its regeneration and reuse makes it more costly. Sorption process becomes economic, if the sorbent is inexpensive and does not require any expensive pre-treatment. Thus, there is a continuous search for alternate low-cost sorbent material to replace high cost activated carbon for water and wastewater treatment. The use of biomaterials as low-cost sorbent for the removal of dyes from water, to our knowledge, has not been investigated.

Dyes once they contaminate the environment have permanent adverse ecological effects. Therefore, dye industry wastewater in the environment has become an area of increasing concern. With increasing environmental awareness and the toughening of governmental policies, it has become necessary to develop new environmentally friendly ways to clean up contaminants using low-cost methods and materials. Biosorption is a process that utilizes dead or living biomass to sequester toxic heavy metals and is particularly useful for the removal of contaminants from industrial effluents. Biosorption processes are particularly suitable for the treatment of wastewater containing low heavy metal ion concentrations. Adsorbent materials (biosorbents) derived from suitable biomass can be used for the effective removal and recovery of heavy metal ions from wastewater streams. Aquatic plants, both living and dead, are heavy-metal accumulators. Therefore, the application of aquatic plants to the removal of heavy metals from wastewater has gained increasing interest. Some freshwater macrophytes including Potamogeton lucens, Salvinia hergozi, Eichhornia crassipes, Myriophyllum spicatum, Cabomba sp., Ceratophyllumdemersum have been investigated for their potential in heavy-metal removal. Their mechanisms of metal removal by biosorption can be classified as extracellularaccumulation/precipitation, cell surface sorption/precipitation, and intracellular accumulation. These mechanismscan result from complexation, metal chelation, ion exchange, adsorption and microprecipitation. The biomasses of aquatic plants, algae and plant materialsare biological resources available in large quantities and can be used for the development of biosorbent materials.

Preparation of Bio Sorbent

The Hydrilla verticillata used in this study were obtained from a pond near by Department of Chemical engineering, Annamalai University, Annamalainagar, Tamilnadu, India. The collected biomaterial was extensively washed with tap water to remove soil and dust and sliced into pieces. The sliced material was dried by exposure to the sunlight for 3 days and subsequently at 80 °C for 3 h in a hot air convection oven. The dried material was milled into a powder using “domestic preethi mixie” and was allowed to pass through a + 65 to – 80 mesh opening size sieve.  For further studies the sieved powder was treated with 2.0 N HCl for 24 h. After that, the samples were filtered and rinsed with distilled water. The treated material was dried again at 80 °C for  6 h, sealed in plastic bags, and stored in desiccators for use.

Hydrilla is derived from the Latin hydro plus illa meaning something that lives in the water. Verticillata is the Latin word for whorled and refers to the leaf arrangement of this plantHydrilla is a submerged aquatic perennial. Stems typically are rooted in the substrate and branch freely.Stems nodes and fragments can develop adventitiousroots. Leaves are sessile, linear to lanceolate, four toeight at the whorl, ¼ to ¾ inches long. Leaves have toothed margins which are usually visible to thenaked eye. Roots slender, unbranched, developingovoid structures at the tips (tubers). Tubers are tough,whitish to brown-black, ¾ inches long. Male and female flowers are floating on long threadlike flowertubes. Sepals and petals are translucent, white toreddish. Male flowers detach at maturity and float onthe surface, releasing pollen. Monoecious (both maleand female flowers on the same plant) and dioecious(male and female flowers on different plants) biotypes occur in India. Fruit is narrowlycylindrical, smooth or with irregular spines, Hydrilla grows very rapidly from rootstocks, subterranean turions, vegetative buds (turions), and vegetative nodes. Only one node (whorl of leaves) is necessary for growth. In clear water the plant can grow in depths of more than 40 feet. When growing from the bottom the leaves may be up to, or more than, 6 inches apart. The leaves on the lower part of the stem may be opposite.

As the stem reaches the surface the leaves become whorled and occur much more closely together on the stem. As the stem reaches the surface extensive branching occurs, often forming dense mats. Hydrilla can spread rapidly and will replace native vegetation. Pollination occurs above the surface of the water. The pollen is dispersed aerially and must land dry on the stigma. Hydrilla is a submersed, freshwater perennial herb, generally rooted on the bottom in depths of greater to 20 feet where water clarity is good.  It is found in lakes, rivers, reservoirs, ponds, and ditches.  It tends to form monospecific stands that can cover hundreds of acres.

Sorbent Activation Methods

To improve the sorbent efficiency sorbent can be activated by following two methods

References

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