This creates a large amount of wastewater treatment, which is usually led to the next sewage treatment plant via sewage pipes. In this article, you will find out what wastewater treatment is exactly and which points you should definitely pay attention to.Every Pakistani citizen uses 130 to 150 liters of water every day. He uses it for showering, bathing, washing and flushing the toilet
WHAT IS WASTEWATER TREATMENT?
Wastewater treatment is the term used to describe all processes that contribute to the removal of foreign substances in the wastewater. Wastewater from houses, public buildings, and businesses contain organic and chemical compounds, heavy metals, drug residues, and solids. These include, for example, plastic splinters, toilet paper and kitchen waste. Under no circumstances may the foreign matter get into the water or into the groundwater. Therefore, the wastewater must first be subjected to wastewater treatment. This takes place in technical systems using mechanical, biological, and chemical processes. The treated wastewater is then channeled into special bodies of water (receiving waters) or by means of seepage into the groundwater.
Wastewater is the collective name for various types of contaminated water that is discharged from the place of origin via pipes. This mainly includes rainwater from the rain gutter and dirty water from the household (washing water, rinsing water, feces). The wastewater is transported to the sewage treatment plant via underground pipelines. There, all foreign substances are removed in several cleaning stages. These include
foreign substances
- organic compounds (proteins, fats, carbohydrates, and other nitrogen and phosphorus compounds)
- Nutrients (glucose, uric acid)
- Pollutants (heavy metals, poisons, pathogenic microorganisms, drugs, microplastics)
- disruptive substances (sand, clay, salts)
The biodegradable nutrients and organic compounds reduce the oxygen content in the water and can thus cause increased algae growth. They also often cause unpleasant odors.
HOW DOES WASTEWATER TREATMENT WORK?
Wastewater from private households is mostly treated in municipal sewage treatment plants. Households that are not connected to the public sewer system often have their own small biological sewage treatment plants. This is the case, for example, in remote locations. In the private small sewage treatment plants, outdated, non-aerated systems are still in use in addition to the biological wastewater treatment plants with a ventilated purification stage that are customary today. Wastewater from industrial companies is treated in special sewage treatment plants.
HOW A SEWAGE TREATMENT PLANT WORKS
The modern sewage treatment plant cleans the wastewater in three stages. The primary treatment includes mechanical wastewater treatment. In this first cleaning stage, larger solids are fished out of the wastewater using mechanical devices such as rakes and sand traps. The wastewater treatment is continued by mechanical drainage (screenings press) and subsequent disposal. The sand settles in the sand trap. It is then washed mechanically in the sand trap. It can then be recycled. The finer solids sink to the bottom of the primary clarifier and form the sewage sludge there. This flows through pipes when it has reached a certain height in the pool. It is then drained and taken to the digestion tower for recycling. The suspended matter is directed into the second clarifier via overflows.
Second Cleaning Stage
During the second cleaning stage (biological wastewater treatment), soluble organic substances are broken down by bacteria. The degradation of feces, leftover food, and organic dirt from the laundry by bacteria is only possible with a supply of oxygen. This is fed directly into the wastewater as compressed air. The bacteria digest carbon, releasing water and CO2. They also generate energy by breaking down biological substances. Since they always have enough food, they multiply accordingly and form the activated sludge. At this stage of wastewater treatment, there are only 5 to 10% organic substances, phosphorus, and nitrogen compounds in the pre-clarified water. This residue is almost completely removed from the water in the third cleaning stage.
Chemical Cleaning
It involves the metabolism of nitrogen by certain types of bacteria. The phosphorus is eliminated using a chemical process. Aluminum chloride or iron sulfate are usually used for precipitation. These metal compounds make the phosphorus insoluble in water, so that it sinks to the bottom. Then you can dispose of it. Some sewage treatment plants also use activated carbon to filter residual hormones and drugs from the purified water. Occasionally, ozone is used to kill pathogenic microorganisms and neutralize drugs.
SMALL SEWAGE TREATMENT PLANTS
Special legal requirements apply to the much smaller private sewage treatment plants. The biological systems work, for example, by means of a fixed bed or SBR processes, as a membrane activation reactor or plant-based sewage treatment plant. After the biological treatment, the operators divert the water into receiving water or via canals into the receiving water. Small biological wastewater treatment plants function in a similar way to municipal wastewater treatment plants. Each stage of the cleaning process is carried out in its own chamber. If the biological system is not only suitable for breaking down carbon (cleaning class C) but also for breaking down urea and proteins into nitrate, it complies with the requirements for cleaning class N.
Systems that work with the fixed bed process generate a bacterial biofilm, while in SBR systems the microorganisms swim in the wastewater. The oxygen required for the biological cleaning stage is supplied by introducing air into the dirty water. In the small wastewater treatment plants, some of the biofilm and sewage sludge is returned to the primary clarification chamber (first stage). The 95% purified water then flows off over the surface of the ground or is pumped into the sewage system.
Particularly powerful, fully automatic small sewage treatment plants also carry out denitrification (cleaning class D), phosphate removal (cleaning class + P), and sanitation (cleaning class + H). These special requirements usually apply to systems that are used in drinking water protection areas. By the way: Scientists have been calling for a fourth treatment stage to be introduced in public and private sewage treatment plants for years. The reason: at least a hundred drugs can be detected in the dirty water. These get into drinking water and food via the bodies of water.
WHAT IS THE POINT OF WASTEWATER TREATMENT?
The aim of wastewater treatment is to restore normal water quality. In this way, one prevents the pollution of public waters by an excess of introduced nutrients and harmful substances. Therefore, industrial direct dischargers must also comply with certain limit values. For phosphorus this is 2 mg / l, for nitrogen compounds 18 mg / l: Only clean water is suitable as drinking water.
The microorganisms living in the sewage sludge of the plants not only purify the water supplied: they can even be used to generate electricity. As scientists discovered a few years ago, metal-reducing bacteria generate energy and act as microbial fuel cells. They produce electrons when the heavy metals are broken down. If masses of these microorganisms colonize electrodes, electricity flows through them. In 10 to 20 years they should then be used as large bio cells to produce the electricity required in the sewage treatment plant.
Sewage sludge dewatered to 70% dry matter has a coal-like consistency. It is therefore already suitable for generating energy through combustion. The hydrothermal carbonization saves 80% electricity compared to conventional drying processes. In addition, you only have to dispose of 25 percent of the digested sludge from the sewage treatment plant when it is recycled. The sludge water left behind during dewatering generates digester gas (biogas) and can also be used to recover phosphorus. The low-energy biomass will in future replace the costly dried sewage sludge as a substitute for fossil fuels.
WHAT DO YOU HAVE TO PAY ATTENTION TO WHEN TREATING WASTEWATER?
When it comes to waste water treatment, a distinction is made between normal wastewater that occurs in residential buildings and commercial wastewater that arises during production. The former usually does not require any special treatment. However, wastewater from industrial and commercial operations usually still contains problematic substances. These converge beforehand in special devices (separators). The remaining wastewater is then separated.
Gastronomy businesses, for example, have to drain their dirty water into pipes with a grease trap. All greasy and other food waste collects in this device before the water reaches the sewage treatment plant for cleaning. Sewage pipes at petrol stations must be equipped with oil and gasoline separators. Inorganic compounds occur in the metal industry, organic substances in breweries. Special processes are used to remove it from the dirty water.
Commercial wastewater treatment takes place in accordance with the special properties of the contaminated water and the location of the plant. Membrane processes make water reuse possible because they meet the high demands on water quality. Manufacturing companies are interested in recovering the valuable substances contained in wastewater. During decanting, the dirt particles of different sizes in the industrial wastewater are separated by centrifugal force using rotating sieves. If the wastewater contains many different heavy metals, hydroxide precipitation is used. The resulting metal sulfides can then be removed from the water without any problems.