CONDICIONES DE INSTALACION 1. GENERALIDADES

Waste water contains floating, suspended, and colloidal organic matter, dissolved ions with a wide range of microorganisms and bacteria as well as miscellaneous grit, trash, grease and other chemicals.

Pesticides: DDt, herbicides, paraquat, fungicides

Dioxins: formed when organochlorine compounds are not incinerated at high enough temperatures. Very toxic and can accumulate in the liver

Polychlorobiphenyls (PCBs): used in transformers and capacitors. Persists in the environment and can accumulate in the liver, also carcinogenic

112 Nitrates: from fertilisers or acid rain. they are toxic at high levels, especially to babies because they have less stomach acid than adults, can cause blue baby syndrome

Heavy metals: Cadmium (Cd) (from recharageable batteries), Mercury (Hg) (from batteries), Copper (Cu) (from household plumbing), Lead (Pb)

[edit] E.6.2 Outline primary, secondary, and tertiary stages of waste water treatment, and state the substance that is removed during each stage.

[edit] Primary Treatment: the removal of large solids

Primary treatment removes 60% of the solid material and a third of the BOD waste in the water.

However, afterwards the water will still not be safe to drink.

Primary treatment involves running water through the below mechanisms in order:

1. Bar screens: these remove large objects and debris from the surface of the water and remove floating solids.

2. Settling tanks: these are used to settle out sand, grit, and small objects from the water (as they sink to the bottom); these particles are then sent to landfills.

3. Sedimentation tanks: Alum (Ca(OH)2 and Al2(SO4)3) precipitates out and carry with them solid suspended particles (this process is called flocculation)

[edit] Secondary Treatment: the removal of organic materials using microbes

 Activated sludge process:

o Air is bubbled into sewage which has been mixed with bacteria-laden sludge.

o Aerobic bacteria oxidize organic material in the sewage.

o Water-containing decomposed suspended particles are passed through the sedimentation tanks where the activated sludge is collected.

o Some of the sludge is recycled, and some is sent to landfills.

o This removes 90% of organic oxygen-demanding waste, 50% of nitrogen, and 30% of phosphates

 Effluent is then treated with chlorine or ozone to kill pathogenic bacteria before releasing the water to lakes or rivers

 Other methods include a carbon bed to remove the remaining organics, ion exchange which removes many soluble ions, reverse osmosis and electrodialysis.

[edit] Tertiary Treatment: the removal of remaining organics, nutrients and toxic heavy metal ions

 Heavy metal ions and phosphates are removed by precipitation, for example, nickel:

113 Ni2+(aq) + OH−(aq) → Ni(OH)2 (s)

 Aluminum sulfate and phosphates are removed by precipitation:

Al3+(aq) + PO3−4 (aq) → AlPO_{4 (s)} Al3+(aq) + SO2−4 (aq) → Al₂(SO₄)_{3 (s)}

 Aluminum sulfate and calcium oxide can be used to remove phosphates:

3CaO_(aq) + 2PO3−4 (aq) + 3H₂O → Ca3(PO₄)_{2 (s)} + 6OH−(aq)

 Heavy metals will precipitate in the presence of hydroxide:

Cr3+(aq) + 3OH−(aq) → Cr(OH)3 (s)

 Nitrates are more difficult to remove by precipitation because they’re quite soluble, however, there are some ways to remove them:

o Anaerobic denitrifying bacteria can reduce nitrates into nitrogen 2NO2−3 (aq) → N2 (g) + 3O2 (g)

 Another method is to pass them into algae ponds where algae uses nitrate as a nutrient

[edit] E.6.3 Evaluate the process to obtain fresh water from sea water using multi-stage distillation and reverse osmosis.

There are also a few other treatments, such as distillation. In distillation, sea water is pumped into a reservoir, at which point it is heated. The pure water which evaporates condenses on the cool water being pumped in, leaving a salty brine, which is then pumped out.

Another method used is the reverse osmosis system. In this type of system, there is a

semi-permeable membrane which the water is pumped through, thereby being the opposite of a normal osmosis system (in which water would flow from low concentration to high concentration).

[edit] E7 Soil

[edit] E.7.1 Discuss salinization, nutrient depletion and soil pollution as causes of soil degradation.

Soil is a complex mixture of inorganic and organic materials, including living organisms. Soil degradation lowers crop production and is caused by a variety of human factors including;

acidification, salinization, contamination, desertification, erosion.

114 We are interested in the following factors:

 Salinization: the result of continual irrigation of soil; In poorly drained soil, after the water evaporates, salt is left behind, and plants die because they are unable to take water away from the salty soil.

 Nutrient Depletion: plants remove nutrients and minerals from soil as they grow. If not properly managed by crop rotation or fertilizing the soil, nutrients will become depleted.

 Soil Depletion: caused by improper use of pesticides and over-fertilizing; chemicals can disrupt the food web, reducing soil’s biodiversity, and ultimately ruining the soil.

[edit] E.7.2 Describe the relevance of the soil organic matter (SOM) in preventing soil degradation, and outline its physical and biological functions.

SOM refers to the organic constituents in the soil. This includes plant and animal tissue, partial decomposition products and soil biomass. Chemicals found in SOM from decomposition of plants are high molecular mass organics such as Polysaccharides, proteins, sugars, and amino acids. The end product of decomposition is humus. Humus is the organic decomposition layer which plants live on. It has a mixture of simple and more complex organic chemicals from plants, animals, or microbial origin.

How SOM prevents soil degradation:

 helps soil to retain moisture, and dark color helps to retain heat and warm the soil during the spring.

 contains mineral nutrients that it exchanges with plants (at the roots).

 it improves the soil structure

 it reduces soil erosion.

Biological functions of SOM:

 humus provides a source of nutrients (such as N, P, and S) to the soil. Nitrogen provides proteins, Phosphoros provides enzymes, Sulfur provides amino acids.

Physical functions of SOM:

 SOM can retain several times its mass of water (like a sponge). Therefore more SOM means more water, making the soil more stable.

115 Chemically, SOM acts like clay with cation exchange capacity (CEC): it contains active sites that enable it to bind to nutrient cations. Humus also has the ability to maintain a constant pH by acting as a buffer.

[edit] E.7.3 List common organic soil pollutants and their sources

Here is a list of common soil pollutants and their major sources:

 Agrichemicals: from pesticides, herbicides and fungicides.

 Polyaromatic hydrocarbons: from incomplete combustion of coal, oil, gas, wood and garbage.

 Polychlorinated biphenyls (PCBs): from transformers and generators (they are used as a coolant).

 Organotin compounds: from bactericides and fungicides (used in paper, wood, textile and anti-fouling paint).

 Hydrocarbons and other VOCS: from transport, solvents and industrial processes.

[edit] E8 Waste

In document Diseño de las instalaciones de un Centro de Salud (página 134-138)