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About Coagulation and Flocculation...   - More

About Coagulation and Flocculation In wastewater treatment operations, the processes of coagulation and flocculation are employed to separate suspended solids from water. Although the terms coagulation and flocculation are often used interchangeably, or the single term "flocculation" is used to describe both; they are, in fact, two distinct processes. Knowing their differences can lead to a better understanding of the clarification and dewatering operations of wastewater treatment.

Finely dispersed solids (colloids) suspended in wastewaters contain negative electric charges on their surfaces, causing them to repel each other. Since this prevents these charged particles from colliding to form larger masses, (called "flocs"), they do not settle. To assist in the removal of colloidal particles from suspension, chemical coagulation and flocculation are required. These processes, usually done in sequence, are a combination of physical and chemical procedures. Chemicals are mixed with wastewater to promote the aggregation of the suspended solids into particles large enough to settle or be removed.


Coagulation is the destabilization of colloids by neutralizing the forces that keep them apart. Cationic coagulants, such as CaČ+, provide positive electric charges to reduce the negative charge of the colloids. As a result, the particles collide to form larger particles (flocs). Rapid mixing is required to disperse the coagulant throughout the liquid.

Flocculation, is the action to form bridges between the flocs. and bind the particles into large agglomerates or clumps. For example, bridging can occurs when segments of a polymer chain adsorb on different particles and help particles aggregate.


Once suspended particles are flocculated into larger particles, they can usually be removed from the liquid by sedimentation, provided that a sufficient density difference exists between the suspended matter and the liquid. Such particles can also be removed or separated by media filtration, straining or floatation. When a filtering process is used, the addition of a flocculant may not be required since the particles formed by the coagulation reaction may be of sufficient size to allow removal. The flocculation reaction not only increases the size of the floc particles to settle them faster, but also affects the physical nature of the floc, making these particles less gelatinous and thereby easier to dewater.


About Phosphorus, brought by sludge to the crops   - More

Phosphorus (P) is required by every living plant and animal cell. It is one of the primary nutrients essential for plant growth and crop production. Deficiencies in available P in soils are a major cause of limited crop production. When P fertilizers are added to soils deficient in the available form of this element, increased crop and pasture yields ordinarily follow.

Phosphorus. is a non-renewable resource. It can't be artificially produced. It occurs in nature as phosphate. It is made up of a phosphorus atom and four oxygen atoms (PO4) and carries three negative charges. The phosphate ion combines with various atoms and molecules within living organisms to form many different compounds essential to life.

Some examples of phosphate's role in living matter include:

  • Giving shape to DNA (deoxyribonucleic acid), which is a blueprint of genetic information contained in every living cell. A sugar-phosphate backbone forms the helical structure of every DNA molecule.

  • Playing a vital role in the way living matter provides energy for biochemical reactions in cells. The compound adenosine triphosphate (ATP) stores energy living matter gets from food (and sunlight in plants) and releases it when it is required for cellular activity. After the energy, in the form of a high-energy phosphate bond, is released the ATP becomes a lower-energy adenosine diphosphate (ADP) or a still lower-energy adenosine monophosphate (AMP) molecule. These will be replenished to the higher-energy ATP (or ADP) state with the addition of phosphate by various mechanisms in living cells.

Humans get phosphate from the foods they eat.

Plants get phosphate from the soil along with nitrogen, potassium and a number of other nutrients they need to thrive. Fertilizer is added to nutrient-deficient soil to replenish these vital chemicals. Sludge are also able to play this major role.

Phosphorus enters the organic food chain from the soil through the roots of plants.


Functions of Phosphorus in Plants

In the plant, phosphorus is essential for a number of physiological functions that are involved with energy transformations. Phosphorus is a component of many cell constituents and plays a major role in several key processes, including photosynthesis, respiration, energy storage and transfer, cell division, and cell enlargement. Adequate phosphorus is needed for the promotion of early root formation and growth. Phosphorus also improves crop quality and is necessary for seed formation.


Calcium Nutrition in Plants  - More

Calcium Nutrition in Plants The role of calcium in plants is quite similar to that in people; it is essential for good growth and structure. Insufficient calcium levels lead to deterioration of the cell membrane; the cells become leaky resulting in the loss of cell compounds and eventually death of the cell and plant tissue.

Calcium, in addition to its role in cell structure, also plays a role in regulating various cell and plant functions as a secondary messenger. This function as a secondary messenger assists in various plant functions from nutrient uptake to changes in cell status to help the plant react to the impact of environmental and disease stresses.

Adjusting soil pH based on soil test results is essential in soil fertility.
Without adequate soil pH plant nutrient uptake and plant nutrition are compromised.
However in the case of a crop that requires calcium for quality, total calcium availability is more important than soil pH.
The ideal % saturation for calcium should be around 70% for most crops. Howeverand, certain crops will require more calcium.

In the case of many soils, pH is elevated by more than calcium based reagents. Maintaining the proper balance between calcium and magnesium requires understanding the difference between soil types and predictable availability of the cations.


Calcium and Nutrient Uptake

Calcium also plays a role in the plant very similar to a hormone in the regulation of various cell functions.
One such function is in the regulation of the protein pump that regulates the uptake and movement of nutrients into the root and throughout cells within the plant. At the root level, calcium activates stimulation of the protein channels that take up nutrients. Adequate availability of calcium at the root surface is required for this process to work effectively.

Aluminum toxicity disrupts the availability of calcium and magnesium. In crops where magnesium is important for quality factors, aluminum will reduce available magnesium increasing potential for early death and poor uptake of phosphorus. Raising pH reduces the amount of aluminum that is released in the soil and made available to the root.


Calcium and Disease Mitigation

In plant nutrition, calcium is often referred to as the plant's first line of defense. Many organisms that infect plants do so by penetrating the cell tissue with enzymes known as pectinase, which dissolve pectins. The higher the calcium content in plants, the higher the concentration of pectins holding cells together and the greater the ability to withstand these enzymes.
Adequate levels of calcium in plants also aid in the plant's ability to isolate an infection.


Calcium and Nutrient Uptake

It has long been understood that calcium plays a major role in the quality of many crops.



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