THE REMOVAL OF HEAVY METALS BYMICROORGANISMS: BIOREMEDIATION AT WORK A Review Paper submitted by MARGARET DE GUZMAN As fulfillment for the requirement in EDSC 350 (Advance Topics in Biology for Teachers)
WASTEWATER TREATMENTA polluted creek covered with trash in Manila,Philippines on 01 March 2009. The Department ofEnvironment and Natural Resources reported in 2008that the Philippines hosts 50 major polluted rivers,with a majority of pollutants coming from domesticwaste
SOURCES OF HEAVY METALS IN OUR HOMES HEAVY METAL SOURCES & HOW THEY AFFECT US
HEAVY METALS• chemical elements with a specific gravity that is at least 5 times the specific gravity of water. The specific gravity of water is 1 at 4°C (39°F).• Some well-known toxic metallic elements with a specific gravity that is 5 or more times that of water are arsenic, 5.7; cadmium, 8.65; iron, 7.9; lead, 11.34; and mercury, 13.546 (Lide 1992).
The main threats to human health fromheavy metals are associated withexposure to lead, cadmium, mercuryand arsenic (Järup 2003).Causes and toxicity of heavy metalcontaminants
HEAVY METAL TOXICITY IS ONE OF THE MAJOR CURRENT ENVIRONMENT HEALTHPROBLEMS AND IS POTENTIALLY DANGEROUS BECAUSE OF BIO-ACCUMULATIONTHROUGH THE FOOD CHAIN (ASCHNER 2002) http://www.csuwai.ws/heavymetal/images/ metal_contamination3.jpg
BIOACCUMULATION AND BIOMAGNIFICATION http://www.organicera.com.au/Organics/Bio Magnification/tabid/955/Default.aspx
EFFECTS OF LEAD POISONING http://trytostayhealthy.blogspot.com/2011/0 4/lead-poisoning.html http://healthandenergy.com/air_pollution_h ealth_effects.htm
HAZARDS OF CADMIUM http://www.bnl.gov/today/story.asp?ITEM_ NO=2527
CONVENTIONAL TECHNOLOGIES USED FOR THEREMOVAL OF HEAVY METAL IONS Disadvantages1. Electro-winning 1. Incomplete metal removal2. Ion exchange 2. High energy and reagent requirements3. Lime precipitation 3. Generation of toxic sludge or waste products4. Reverse osmosis5. Electro-dialysis6. Ultra-filtration7. Phytoremediation
THE POTENTIAL OF MICROORGANISMS TOREMOVE HEAVY METALS IN CONTAMINATED SITES BIOREMEDIATION
Bioremediation• Introduction of microbesinto the environment to Cadmium binding ability of therestore stability or toclean up toxic pollutants blue-green alga Hapalosiphon• oil spills, heavy metals, welwitschii Nägel underpesticides, chemicalwastes, solid wastedisposal (man-made controlled conditionsplastics and paperproducts)• water and sewagetreatment; reclamationof polluted water Bi 120 Introduction to Microbiology (mlcdg 2010)
BIOREMEDIATION• a process that uses naturally Kinds of bioremediation occurring or genetically 1. Composting engineered microorganisms such as yeasts, fungi and bacteria to 2. Bioaugmentation -introduction of a transform harmful substances group of natural microbial strain or a genetically engineered variant so as to into less or nontoxic compounds. achieve bioremediation. 3. Phytoremediation• microorganisms break down a variety of organic compounds in nature to obtain nutrients, carbon, and energy for growth and survival.
ADVANTAGES AND DISADVANTAGES OF BIOREMEDIATION Advantages Disadvantages 1. Eco-friendly, cost-effective, 1. Takes longer compared to natural method other remedial methods 2. Al technology targeted to remove heavy metals, 2. The techniques are not yet radionuclides, xenobiotic refined for sites with mixtures compounds, organic wastes, of contaminants. pesticides, etc. using biological means 3. More research is needed to 3. Used in in-situ conditions perfect this technology.
BIOREMEDIATION HOLDS ENORMOUS PROMISE FOR THE FUTURE(CLEAN UP AND PROTECTION OF THE ENVIRONMENT
MICROORGANISMS FOR BIOREMEDIATION FungiBacteria Algae • Unicellular: yeasts/molds• Single celled, with • Unicellular/mul various shapes • Multicellular: mushrooms ticellular• Cellular but have no • Photosynthetic • Saprophytes nucleus (prokaryote) • Widely distributed • Widely distributed• Autotroph/chemotroph• Stationary/motile
MICROORGANISMS THAT CAN TAKE UP AND ACCUMULATE HEAVY METALS1. bacteria: Sedum alfredii Hance (Xiong et al. 2008), Stenotrophomonasmaltophilia (Parungao et al. 2007), Bacillus circulans strain EB1 (Yilmaz and Ensari 2005), and Corynebacterium glutamicum (Choi and Yun 2004)2. blue-green algae: Nostoc calcicola (Pant 2000), Synechococcus aquatilis (Reynaud) strain SY 101 (Vallarta, et al. 1998), and Anacystis nidulans (Singh 1985): and3. microalgae: Tetraselmis suecica (Perez-Rama et al. 2002) and Chlorella vulgaris (Carr et al. 1998);
HOW DO THEY DO IT?1. The role of cellular structure, storage polysaccharides, cell wall and extracellular polysaccharides is evaluated in terms of their potential for metal sequestration.2. Binding mechanisms, including the key functional groups involved and the ion-exchange process. Quantification of metal-biomass interactions is fundamental to the evaluation of potential implementation strategies, hence sorption isotherms, ion-exchange constants, as well as models used to characterize algal biosorption . The sorption behavior (i.e., capacity, affinity) of brown algae with various heavy metals is summarized and their relative performance is evaluated
BIOSORPTION• Biosorption technology is based on extensive research work which resulted in the discovery of potent metal-binding biomass types.• This technology is capable of effectively and economically removing heavy metals from industrial aqueous solutions and wastewaters.• The metals of sufficiently high values can be recovered and resold.• These unique biosorbent materials are derived from specific types of microbial biomass by a simple process which makes them applicable in large-scale sorption processes.
DIRECTIONS OF RESEARCH• The bioremediation technology most suitable for a specific site is determined by several factors, such as site conditions, indigenous microorganism population, and the type, quantity, and toxicity of contaminant chemicals present.• Some treatment technologies involve the addition of nutrients to stimulate or accelerate the activity of indigenous microbes.• Optimizing environmental conditions enhance the growth of microorganisms and increase microbial population resulting in improved degradation of hazardous substances.• However, if the biological activity needed to degrade a particular contaminant is not present at the site, suitable microbes from other locations, called exogenous microorganisms, can be introduced and nurtured.• Other technologies being demonstrated are phytoremediation, or the use of plants to clean up contaminated soils and ground water, and fungal remediation, which employs white-rot fungus to degrade contaminants.