lab: 5Title: Arsenic BiosorptionLecturer: Hassan MohammadSubject Objectives: At the end of this subject student should be

able to Understand common issues with Arsenic in drinking waters and How Biosorption can play an excellent roll in managing it.

Scientific Content: In this subject we will cover Description of

Arsenic, applications and rate of production and its sources in drinking and Biosorption: An eco-friendly alternative for Arsenic removal.

Arsenic is the chemical element that has the symbol As, atomic number 33 and atomic mass 74.92.

Arsenic is a notoriously poisonous metalloid with many allotropic forms, including a yellow and several black and grey forms.

Three metalloidal forms of arsenic, each with a different crystal structure, are found free in nature .

it is more commonly found as arsenide and in arsenate compounds.

The most common oxidation states for arsenic are −3 ( arsenides ), +3 ( arsenites ), the most organo arsenic compounds , and +5 (arsenates: the most stable inorganic arsenic oxy compounds).

Arsenic is very similar chemically to its predecessor in the Periodic Table, phosphorus.

Like phosphorus, it forms colourless, odourless, crystalline oxides As2O3 and As2O5 which are hygroscopic and readily soluble in water to form acidic solutions.

Arsenic acid (H3AsO4) Arsenous acid (H3AsO3)

The toxicity of arsenic to insects, bacteria, and fungi led to its use as a wood preservative.

In the 1950s a process of treating wood with chromated copper arsenate (also known as CCA) was invented, and for decades this treatment was the most extensive industrial use of arsenic.

Due high level of toxicity, most countries banned the use of CCA in consumer products.

The European Union and United States led this ban, beginning in 2004.

Arsenic trioxide is used in metallurgy and in glass and ceramic manufacturing.

During the Vietnam War the United States used Agent Blue (a mixture of sodium cacodylate) and dimethyl arsinic acid as one of the rainbow herbicides to deprive the Vietnamese of valuable crops.

Various agricultural insecticides, termination and poisons. For example Lead hydrogen arsenate was used well into the 20th century as an insecticide on fruit trees.

In 2005, China was the top producer of white arsenic with almost 50% world share, followed by Chile, Peru and Morocco, reports the United States Geological Survey.

The arsenic was recovered mostly during mining operations, for example the production from Peru comes mostly from copper mining and the production in China is owing to gold mining.

Arsenic contamination of groundwater has led to a massive epidemic of arsenic poisoning in Bangladesh, and neighbouring countries. Presently 42 major incidents around the world have been reported on groundwater arsenic contamination.

It is estimated that approximately 57 million people are drinking groundwater with arsenic concentrations elevated above the World Health Organization's standard .

The arsenic in the groundwater is of natural origin, and is released from the sediment into the groundwater owing to the anoxic conditions of the subsurface.

Sometimes natural erosion can introduce large quantities of arsenic into a local water source.

Arsenic is also released into the environment through the manufacturing of pesticides, the burning of fossil fuels, and cigarette smoke.

It enters water sources through the dissolution of minerals and ores, from industrial effluents, and from atmospheric deposition.

Analyzing multiple epidemiological studies on inorganic arsenic exposure suggests a small but measurable risk increase for bladder cancer at 10 parts per billion.

The Department of Health and Human Services and the Environmental Protection Agency (EPA) classified arsenic as a human carcinogen based on sufficient evidence from human data.

Arsenic trioxide causes skin and lung cancer, and may cause internal cancers such as bladder, kidney, colon, and prostate cancers.

Arsenic oxide may cause an allergic respiratory reaction.

Anyone who thinks they have been exposed to arsenic should be tested.

The most reliable means of testing for arsenic is by sending your urine to a lab.

This method is sometimes complicated by the fact that fish contains arsenic, so if you have recently eaten fish, the results may be exaggerated.

It is also possible to send hair, fingernails, or blood to a lab. These methods of testing are not as reliable for small doses, however, they are more accurate to determine long term exposure.

Techniques presently in existence for removal of arsenic from contaminated waters include:

Reverse osmosis, electro dialysis, ultra filtration, ion exchange, chemical precipitation, etc.

all these methods have disadvantages like incomplete metal removal, high reagent and energy requirements.

Mechanisms involved in biosorption can be classified

taking into account various criteria that are, based on cell metabolism, they are classified as metabolism dependent and non- metabolism dependent .

It is classified as extra cellular accumulation and cell surface sorption and intra cellular accumulation.

A successful biosorption process requires preparation of good biosorbent.

Pre-treatment and immobilization are done to increase the efficiency of the metal uptake.

The adsorbed metal is removed by desorption process and the biosorbent can be reused for further treatments.

Biomass can come from, activated sludge or fermentation waste from industries like those of food, diary and starch.

Organisms com in from their natural habitats are good sources of biomass.

Fast growing organisms that are specifically cultivated for biosorption purposes can be used as biosorbents .

Apart from the microbial sources even agricultural products such as wool, rice, straw, coconut husks, peat moss, exhausted coffee ,waste tea.

Sea weeds, yeasts, bacteria have been tested for metal biosorption with encouraging Results.

several advantages including : Cost effectiveness. High efficiency. Minimization of chemical/biological sludge. Regeneration of biosorbent. Possibility of metal recovery.

In countries, with the rush for rapid industrialdevelopment coupled with lack of awareness

about metal toxicity there is an urgent need for developing an economical and eco-friendly technology which satisfies these demands when other conventional methods fail.

www.academicjournals.org/AJB/PDF/pdf2007/.../Cernansky%20et%20al.pdf

water.usgs.gov/wrri/05grants/progress...reports/.../2005AK43B.pdf

biosorption.mcgill.ca/publication/.../187-WR'07-41(11)2473-2478,NiuAs. Pdf

www.ncbi.nlm.nih.gov/pubmed/19131161