black-water

What is black water?

Have you ever wondered what black water is? What is the difference between it and gray water? How can it be reused?

Black water is considered one of the most dangerous types of wastewater because it contains many dangerous pollutants, bacteria, and pathogens, so care must be taken to treat it in the right and appropriate manner. Water is one of the most valuable and most important resources on earth. It is used in all daily practices such as drinking, cleaning, washing, agriculture, and industry. As a result of the daily consumption of this water, wastewater is produced, which are of two types:

There is gray wastewater: it is the wastewater from the laundries, showers, and kitchens
There is black wastewater: it is the water that is flushed into the toilets, and it is necessary to treat it completely in special wastewater treatment plants before it can be reused.

Black Water treatment stages:

The process of sewage treatment has witnessed some gradualness throughout history. Blackwater treatment was initially limited to primary treatment, then secondary treatment began to be used after a period of time. As for advanced treatment, it is used when needed. The following are the stages of black water treatment:

First, the initial treatment:

It includes the following stages:

Clearwater from large floating items such as sticks, and pieces of cloth.
Use strainers to get rid of heavy inorganic materials such as sand and small pebbles.
Sedimentation of organic and inorganic materials inside sedimentation tanks and the sediments are later used as fertilizer, or disposed of in a landfill, incinerated, or recycled if they are free of toxic substances.
Disinfection of water from bacteria using chlorine, ozone, or ultraviolet rays, knowing that the effects of toxic chlorine must be eliminated before water is thrown into water bodies.

Second: Secondary treatment:

It includes biological black water treatment to get rid of organic matter and transform it into masses that are deposited at the bottom of sedimentation ponds and can be used later as fertilizers. 85% or more of organic matter is removed during secondary treatment, while the percentage of organic matter that is disposed of in the primary treatment stage than 50%, and this is done in several ways, including:

Activated sludge: This method relies on pumping black water into aeration tanks where the bacteria in the wastewater are supplied with oxygen to activate them to consume the organic matter in the water.
Distillation filters: This method relies on passing black water over a surface of stones, and industrial materials on which living organisms such as bacteria that work on decomposing pollutants grow, and the bacteria are provided with the air necessary for their breathing through special filters.

Third: advanced treatment:

With the advancement of science and the development of technologies, it has become possible to rid black water of heavy metals, toxic chemicals, and other pollutants, in the following ways:

Microfiltration or micron filter: It is intended to use a microfiltration membrane to rid black water of bacteria and impurities, and the pore size of this type of filter ranges between 0.1 – 10 microns.
Chemical adsorption with carbon: It means the use of carbon to rid the black water of some soluble substances such as mineral oils.
Evaporation and distillation: It means separating the impurities from the water depending on the difference in its boiling point. The water is heated and converted into water vapor free of impurities, then it is condensed again.
Chemical precipitation: It means separating a solid from a solution by changing the nature of the solvent and reducing the solubility of the substance in it, or changing the nature of the solid to become insoluble.

The uses and benefits of treated water:

  • Conservation of potable water and expansion of agriculture.
  • Reducing the need for artificial fertilizers due to the presence of necessary elements in that treated water.
  • Use in cities and urban areas: in irrigation of public and private parks, sports facilities, street cleaning, and fire protection systems.
  • Agricultural uses: such as food crops prepared and not intended for trade, pastures, milking animals, seeds, ornamental flowers, aquaculture.
  • Industrial uses: such as recycling cooling towers, making concrete.
  • Recreational uses: golf courses and snowmaking.
  • Environmental uses: groundwater recharge in wetlands and forestry.

What can you do to stop the spread of diseases caused by black water pollution?

There are several things you can do to prevent the spread of diseases caused by water pollution in African countries. The most effective way is to properly dispose of black water in wastewater treatment plants instead of rivers or other bodies of water. This will help reduce the levels of pollution found within these waterways.

Another way to help prevent further river pollution is to use grey water irrigation systems on your farm. This will help recycle the black water and use it as fertilizer which improves soil health and reduces soil erosion rates.

Recycling black water in irrigation systems on farms is a very common practice in Japan, one of the most polluted areas in Asia. This results in lower input costs as well as higher crop yields due to recycled black water fertilization practices. Using treated black water can reduce soil loss due to erosion as well as improve aeration because it reduces evaporation rates when stored for long periods.

Properties of Raw Wastewater

pH:

This is a measure of the acidity of the water once it leaves the plant. Ideally, the pH of the water should match the pH of the river or lake that receives the plant’s output. Standards generally call for a pH between 6.5 and 9.

Biological Oxygen Demand:

BOD is a measure of the amount of oxygen required in the water to complete the digestion of the organic matter remaining in the waste. Ideally, the BOD should be zero. The EPA standard for secondary waste is 30 mg/L.

Dissolved Oxygen:

This is the amount of oxygen in the water as it leaves the plant. If the water does not contain oxygen, it will kill any aquatic life that comes into contact with it. The dissolved oxygen should be as high as possible and should cover the BOD. If dissolved oxygen concentrations drop below 5 mg/L (or parts per million), fish will not survive for long. Trout need at least 8 mg/L of dissolved oxygen and salmon need about 11 mg/L.

Total Suspended Solids:

This is a measure of the solids remaining in the water after treatment. Ideally, total suspended solids should be zero. The standard for total suspended solids is no more than 30 mg/L.

Total Phosphorus and Nitrogen:

This is a measure of the nutrients remaining in the water. Levels greater than 30 mg/L of nitrate can inhibit growth, weaken the immune system, and cause stress in some aquatic species. The EPA has set a maximum contaminant level of 10 mg/L for nitrate in drinking water, but the limit for children is 1 mg/L. Excess nitrate can restrict oxygen transport in the bloodstream.

Phosphorus:

This is a nutrient that causes an increase in algae blooms. In some places, levels of 1 mg/L can complicate lakes. Effluent limits typically range from 0.1 to 2 mg/L, with many set at 1.0 mg/L. Effluent from treatment plants can reach 0.1 to 0.05 mg/L with new processes and initial control levels (by banning the sale of detergents and soaps containing phosphorus).

Chlorine:

Chlorine used to kill harmful bacteria must be removed so that it does not kill beneficial bacteria in the environment. Ideally, chlorine should be undetectable.

Coliform count:

This is an indirect measure of fecal bacteria remaining in the water. Fecal coliform bacteria are more common than pathogens that pose a threat to human health. The amount of fecal coliform bacteria is related to the amount of pathogens. Ideally, this number should be zero. Note that water in the environment is not completely free of fecal bacteria – birds and other wildlife introduce some.


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