In the daily activities that are carried out both in cities and in the countryside, large amounts of wastewater are generated and they return to nature, becoming a source of pollution. This is why the different types of wastewater treatment are the most widely applied solution to eliminate polluting waste from wastewater that returns to nature. I invite you to continue reading.
Sewage treatment
To decontaminate the wastewater generated in the different daily activities in cities and fields, these waters have to go through the Wastewater Treatment plants. These treatments are the application of a series of physical, chemical and biological methods that eliminate the contaminating agents present in the water coming from human use.
Sewage water
Residual waters are waters that originate from human activities that cause a negative impact on water quality. Within the category of Residual Waters, the wastewater from domestic, industrial, agricultural, and mining activities is included, as well as rainwater and river water that mixed with the aforementioned water.
The FAO (Food and Agriculture Organization of the United Nations), defines Residual Water as: It is that water that cannot be used immediately for the purpose for which it was used in view of its quality and quantity, …However, one user's Wastewater, at a given time, may be a source of supply for another user at a different location. Within Residual Water, cooling water is not included.
Due to the high negative impact of Residual Waters on the environment, they have to go through a channeling system. As is the case with urban wastewater, it is channeled through a sewage system that takes it to the wastewater treatment plants for purification before being spilled into natural water sources. Despite its importance, some countries do not carry out this type of treatment.
It may happen that in some urban residential areas or in the countryside that the Residual Waters that originate from housing or some areas that have not been installed the central sewage system, these waters are treated on the same site, by means of septic tanks, and sometimes (although very rarely) in septic drainage fields, sometimes with biofilters.
Sewage or sewage
Sewage or sewer water is a type of Residual Water, which originates from houses, schools, businesses and other places, in which man uses clean water for his own use and then discards it through drains and sewers. or sewers. So this discarded water can no longer be immediately used by other users. Those sewage or sewage waters contaminated with feces and urine are called "black waters".
Features
In nature, water can be composed of different amounts of other substances in various concentrations ranging from a few mg/liter of water from precipitation to about 35 mg/liter of seawater. Along with these substances originating in nature, the wastewater is mixed, which goes with impurities caused by the waste-generating process, which is what is called discharge. These waters can be contaminated by domestic and industrial waste.
These are distinguished by their physical appearance in: colloidal fraction, suspended fraction and soluble fraction. The suspended and colloidal fractions are analyzed through the total suspended solids test (TSS). These fractions are 1% of the suspended solids in the wastewater and are grouped into organic and inorganic.
- Organic solids are classified in two ways: nitrogenous and non-nitrogenous. The nitrogenous, are those that contain nitrogen in their molecule, here proteins, ureas, amines and amino acids are grouped. Non-nitrogenous organic solids are made up of cellulose, fat (lubricants) and soaps.
- To quantify the concentration of organic solids in the water, the biochemical oxygen demand is measured for 5 days BOD5, this indicator allows to measure, in principle, the carbonaceous organic material, and the BOD indicator20 It allows to measure the biochemical oxygen demand at a temperature of 20°C in organic and nitrogenous materials.
- Inorganic anions and cations and organic compounds.
Bacteriology
Due to the pathogenic agents that sewage or sewage may contain, the measurement of its bacteriology and the Treatment of these Residual Waters is carried out, with the purpose of eliminating pathogenic organisms from human beings and that reach the water through the excreta. In this way, cut off a possible cause of biological contamination by eliminating the epidemiological cycle of transmission. These pathogenic organisms are: Total coliforms; fecal coliforms; Salmonella and Viruses.
suspended matter and dissolved matter
When the water is going to be treated in the wastewater treatment plant, the quantities and composition of matter in suspension and dissolved matter must be known. For this, the differences between the two must be known:
- To determine suspended matter, physicochemical treatments must be applied to separate it, these treatments are versions of sedimentation and filtration. For solid suspended matter, it is about solid-liquid divisions through gravity or filter media and, when it comes to fatty matter, LL separation is applied, commonly by flotation.
- The dissolved material can be organic, the treatment that is usually applied for this case is the insolubilization method as cellular or inorganic material (it is transformed by an S-L separation). For this, expensive physicochemical treatments such as reverse osmosis are used.
The treatments applied depend on the type of contaminants, due to this, for suspended matter, whether organic or inorganic, sedimentation and filtration are used in different modalities. To analyze the dissolved matter, biological treatments are applied, and sometimes chemical oxidation, when it is organic matter, and when the material is inorganic, membrane methods (osmosis) are applied.
Processes in Wastewater Treatment
The purification of the Residual Waters is carried out in plants where the division of the contaminants is carried out, this treatment through physical, chemical and biological processes, which have the function of discarding the contaminants that may be in the effluent water of the drinking use.
During the Wastewater Treatments in treatment plants, the decontamination or purification of the served or residual water is carried out by separating most of the contaminants and a small percentage is left to be eliminated by nature at the place of destination. Because of this, the type of treatment will depend on the natural self-purification capacity of the recipient site.
This natural self-purification will depend on the flow rate of the receiving body where the wastewater will arrive, as well as its oxygen content, and its reoxygenation process. For this reason, the purpose of Wastewater Treatment is to generate liquid effluents that return to the environment and can be used again, as well as a solid effluent or mud, which is called sludge or biosolid, which can be reused.
Residual waters come from houses, industries, businesses, hospitals, among others. Residual water can receive treatment in the same place where it comes from, through septic tanks and can also be treated in municipal treatment plants.
The installation of Wastewater Treatment plants, both public and private, is regulated by national, regional and local laws, which allow the monitoring of regulations and controls. In the case of industrial tributaries that contain Residual Water, they have to go through specialized processes for the type of industrial compounds.
The steps for the Wastewater Treatment to be carried out begin with the extraction of the largest organic and inorganic solids, that is, the garbage, from the water current. For this, grids are placed, this garbage or waste can be crushed or compacted by equipment designed for this. This material goes through desanding, in which solids such as sand and other smaller and denser solids are separated. Then, it goes through a primary sedimentation in which the suspended solids in the Residual Water are extracted.
To first remove dissolved metals such as lead and phosphorus, a Wastewater Treatment with precipitation reactions is applied. Followed by the gradual transformation of the dissolved biological material into a solid biological mass by the use of bacteria, which is found in the water. Once this secondary sedimentation is finished, the water goes through a tertiary treatment, which consists of disinfection and filtering. The final product or final discharge discharged into a natural water source such as a river, lake, or into the ground or subsoil.
Stages of Wastewater Treatment
Wastewater Treatment is carried out through several processes, three stages and even more, these are called treatments: primary, secondary and tertiary, namely:
- Primary treatment consisting of settling solids.
- Secondary or biological treatment, which is applied to the organic matter that is dissolved in the wastewater, converting it into suspended solids in the water and in this way it is easier to eliminate them.
- The tertiary treatment that is an added step and disinfection, microfiltering or passing through lagoons is done.
In addition to the sewage or residual water that originates from the daily activities of human beings, when they bathe, cook, wash their hands and clothes and other activities, in this type of water, water from the areas must also be added. or industrial and commercial centers of cities or towns.
Residual or served waters are also classified depending on their origin in: "grey water and black water" which are produced in large quantities in developed and populated areas, being the "black water" the one that is discharged from toilets, sanitary and urinals, on the other hand, the "gray water" originates in the sinks, sinks, bathtubs, the latter can be reused as irrigation water and also for cleaning the toilet, in this case it is transformed into black water.
Residual or served water also includes surface water that falls due to precipitation. In the municipalities and towns, the wastewater contains water from residential, commercial and industrial centers, and can be mixed with the water that falls in the rains, when the water channeling pipes are of mixed use residual-rainfall.
This system is called combined or unit sewer systems. At present, due to the sanitary regulations of Residual or Sewage Water in countries such as the United States, Canada, the United Kingdom and some other countries in Europe and America such as Argentina, this type of sewer is becoming less common every day with respect to its use in last.
In these countries the Wastewater is discharged and transported through separate sewer systems that are called "separate sewer systems", called sanitary sewers and in the United States storm sewer systems. Also, this type of sewage system is called fetid sewers and surface water sewers. In other European countries they are called sewers and storm drains.
Through the rainwater, various polluting elements that are along the way can be dragged, when it moves over the roofs and the surface of the ground, such as heavy metals, inorganic elements, oils, organic waste. By regulation in some places rainwater receives or passes through some levels of Wastewater Treatment, before being discharged into the environment.
In the treatment of rainwater, sedimentation tanks, wetlands and separators are used to remove or eliminate coarse solids, called vortex separators. In Wastewater Treatment plants, it is a relatively simple process and it is similar in all countries, namely: it begins with physical treatment, goes through sieving, then gas removal, precipitation with or without coagulants, separation and filtering of solids and at the end iron chloride is added to remove the phosphorus and precipitate the sludge or biosolids.
The biological process
The Treatment of Wastewater through biological treatment is carried out through anaerobic biodigestion and artificial wetlands in which the biodegradable organic matter found in the Wastewater is used, from which it takes the nutrients of the bacteria. that are under controlled conditions and in this way keep the contaminants you find at bay.
In this type of biological treatment, it is carried out through several treatment phases in which all use microorganisms, mainly using bacteria, this with the aim of eradicating the soluble components in the water. This biological treatment takes advantage of the ability of microorganisms to absorb organic matter, nitrogen and phosphorus, which are dissolved in the wastewater, and use them for their own development. At the time of their reproduction, they multiply among themselves, forming large flocs that are eliminated in a short time.
The common thing is the suppression of soluble and colloidal organic matter, which biodegrades, in addition to those nitrogenous and phosphorous compounds. Biological treatment is widely used, both in wastewater from cities, as well as in some industrial waters, due to the simplicity of the treatment and its low cost.
Chemical process
Chemical treatment is usually carried out with operations to remove solids, such as filtration. This chemical process is one of the Wastewater Treatments, which is applied in almost all plants with the aim of increasing the quality of the effluent, this certifies that the environment meets the best conditions for bacterial activity to take place.
The chemical methods used in Wastewater Treatment are conditioned by the particularities of each effluent; a chemical precipitation phase is usually added to remove the phosphorus and level the pH. Similarly, in those processes where the amount of carbon is low and is required for the biological modification of nitrate into nitrogen, an external carbon source can be added.
In order to improve and guarantee the chemical processes that are carried out in a Residual Water Treatment plant, the dosing stations are built with materials resistant to corrosion of the chemical products that are used in the process according to the specifications. You have to be very precise in the safety protocols that are used and the designs of the chemical product storage tanks, the pumps for the doses, the mixers and the pipe network.
Excess iron from drinking water
The methods applied to eliminate the excess of iron ore in drinking water are carried out with the modification of chlorinated water in a basic solution catalyzed with slaked lime; get the iron to rust and ferric precipitation from the basic solution. Simultaneously, the OCI ion removes pathogens from excess iron deposited in the water.
Separation of oxygen from water
To change the state of liquid water to water vapor in the thermal power plants, boilers that resist high temperatures are installed in the treatment plants. Because oxygen is an oxidizing element, hydrogen is used as a reducing agent to eliminate oxygen.
Phosphate removal
For Domestic Wastewater Treatment, the removal of phosphates is considered. For the removal of phosphates in domestic wastewater, the method is to remove phosphates with calcium hydroxide or slaked lime. One way phosphates can occur is in their hydrogen phosphate ion form.
Elimination of nitrates
For the elimination or separation of nitrates in both domestic and industrial waters, the treatment is carried out with the combination of two processes, one of nitrification and the other of denitrification, from the combination of these procedures a biodegradable and reusable sludge or sludge results. .
Types of Wastewater Treatment
Wastewater Treatment is carried out in three stages or cycles to separate contaminating agents and solid compounds. These consist of three stages, being these the primary, secondary and tertiary stages.
primary treatment
Through the primary treatment applied to Residual Water, the aim is to eliminate fats, sands and larger solids, as well as oils. This primary treatment is carried out by means of machinery and, due to what is called a mechanical procedure.
Separation of solids by screening
Screening is used in this first cycle to remove solids. In this stage, balls, washing machines, plastic containers, such as bottles, and others are removed or eliminated. With the elimination of larger solid elements, fats and oils, it has the purpose of reducing and avoiding the possible inconveniences of obstruction of water pipes of the treatment plant, either by reducing the flow of water or damaging equipment.
Filtered with sand and gravel
This phase is also called maceration, the Residual Water passes through a sand channel where the speed is controlled so that the stones and sand of the residual water can grab particles, in the Residual Water organic matter is still maintained. The equipment used is a sand collector.
This cycle is carried out at the beginning of the treatment with the function of removing sand and stones in time to avoid damage to the pumps and other equipment of the treatment plant. In some plants and procedures for treating wastewater, they may also have a sand classifier, together with a conveyor to take the sand to a container and then expel it. The sand that reaches the collector can come from the incinerator through an incinerator for processing in the sludge plant, on other occasions the sand is transferred to an embankment.
solids maceration
The Residual Water already treated in the first stage is passed through rotating screens to separate floating material and other larger objects, such as: leftover food, corn cobs and others. These objects are collected and go to the sludge treatment plant or are transferred to the field and incinerated.
Solids maceration consists of cutting the solids into smaller pieces by means of rotating blades that are located in rotating cylinders and are part of the treatment plant equipment that can transform this garbage into particles. These equipments are expensive to purchase, maintain and unreliable compared to physical screens.
sedimentation
Many treatment plants are equipped with large circular or rectangular tanks, these tanks are called primary sedimentation tanks or primary clarifiers, where the sedimentation of the waste takes place. These tanks are very large so that fecal, plastic and fat residues fall into them and remain on the surface and be skimmed or eliminated.
The function of the first stage is to produce a homogeneous liquid that can go through a biological treatment and the biodegradable sludge can be processed separately. To achieve this first stage, the tanks or plants are equipped with mechanized scrapers, which transport the sludge or sludge produced to a hopper located at the base of the tank, from here it is pumped to other parts to go through secondary treatment.
secondary stage
In this phase or secondary stage, its objective is to eliminate as much as possible of the biological component found in Residual Water, which comes from feces, urine, food remains, detergents and other residual waste. The Wastewater Treatment plants of the city halls or municipalities are equipped to carry out this aerobic process on organic waste.
Sludge or activated sludge
The tanks to treat activated sludge or activated sludge have mechanisms that allow dissolved oxygen to be processed and encourage the growth of organic or biological organisms that help eliminate a large proportion of organic matter and also trap material particles.
The oxidizing filter
In the old treatment plants and some variable load receiving plants, they have within their equipment drip filter beds, in which the Residual Water is discharged on the surface of a deep bed made of coal, limestone or with plastic. These structures have a large surface to be able to store the fats of biological material that are formed.
This biological substance is removed by rotating perforated arms that start from a central axis. Treated Wastewater drips into the bed and is collected in drains at the base. These drains provide oxygen that is directed up the bed, this allows the medium to remain aerobic. On the surface, a layer is formed composed of bacteria, protozoa, and fungi that benefit from feeding on organic compounds in the Residual Water. This layer of organisms feeds on insects and earthworms.
Rotary and spiral system
This type of rotary and spiral system is part of the equipment of small wastewater treatment plants. These have a slow revolution that has a part of their system flooded in the waters. Through these rotary presses, a floc or lump is formed based on organic matter that is added and united during the process. This biological floc offers the substrate that is needed.
Moving Bed Biological Reactor (MBBR)
This reactor takes the incorporation of the inert material in activated sludge vessels with the aim of providing active material and gathering the biological material or biomass. This creates a growth system with some advantages:
- Increase and maintain the high biomass population
- Increase system efficiency without having to increase the concentration of mixed liquor solids.
- Stop specifying the operating cost in the activated sludge return line (RAS).
anoxic filters
Biological or anoxic aerated filters, these filters allow to reduce the biological reduction of carbon, nitrification and denitrification. Biological aeration filters (BAFs) typically have a reactor filled with filter media. The biological media are suspended or in a layer at the bottom of the filter.
This medium has two objectives, the first to contain the active biomass that binds to the filter and also the suspended solids of the filter. During this process, the carbon and the transformation of the ammonia that occurs in an aerobic environment and in opportunities achieved in a single reactor are reduced, as well as the transformation of the nitrate in an anoxic form. According to the design it can be operated in high flow or low flow.
Membrane Biological Reactor System
The membrane biological reactor (MBR) system has the objective of achieving the elimination of contaminants found on the surface and dissolved solids. This consists of a barrier of semi-permeable coatings. Its performance is related to its effective reduction of nutrients from the passage of activated sludge. The cost of the membrane biological reactor system is generally high compared to that of a traditional Wastewater Treatment.
sedimentation
The last step of the secondary stage consists of separating the biological flocs from the filter material, and generating treated Wastewater with a small amount of biological matter and suspended matter. In plants located in rural areas, it is carried out in the secondary sedimentation tank.
Tertiary Stage
This third stage is carried out to complete the Wastewater Treatment and seeks to guarantee the quality of the effluent, according to the indicators established by environmental regulations, before being discharged into the sea, river, field or any other receiving environment. This treatment or tertiary stage can be applied several times in the treatment plant. When the disinfection of Wastewater is carried out in the final process, it is called polishing the effluent.
sand filtration
This filtering step of the sand is carried out so that it retains the greatest amount of residue or garbage that is in the Residual Water. Residual toxins are retained by excess activated carbon during filtering.
Lagooning
This purification process called lagooning, has the objective of carrying out in an artificial environment the natural purification that occurs in lakes, rivers or the sea. During this step, the lagoons offer sedimentation and a greater biological contribution when the residual water is stored in puddles or artificial lagoons. They are artificial aerobic lagoons where colonization by natural macrophytes, such as reeds, occurs. Invertebrates of the Daphnia and Rotifera genera are also present, which collaborate in the retention of particles.
To carry out the lagoon step in the third stage of the Wastewater Treatment, there must be enough space, the installation cost is low. However, it is not very efficient to disinfect large amounts of water.
artificial wetlands
These artificial wetlands are used to increase aerobic biological improvement, these can be reed beds or other similar structures. These constructed wetlands can be used to replace the secondary stage in small populations, as well as for phytoremediation. An example of a constructed wetland is used at Chester Zoo in England, to clean the drain in the elephant cage which consists of a bed of reeds.
Nutrient separation
Wastewater can have high amounts of phosphorus and nitrogen that can affect fish and invertebrates, as is the case with the presence of ammonia. Likewise, produce eutrophication, that is, the growth of algae in the lagoons that affects the light and oxygen of the water for other living organisms.
The high density of algae has a negative impact, because it generates toxins, and when they die they are consumed by bacteria that reduce the amount of oxygen in the water, making it difficult for fish and other aquatic life to obtain it. These conditions of the Residual Waters when they reach the low seas, rivers and lakes, then by incorporating the nutrients can lead to the loss of many fish to the contamination of the waters. Due to this, a reduction of phosphorus and nitrogen has to be done by means of biological and chemical precipitation.
The elimination of nitrogen is carried out through the biological oxidation of nitrogen transforming ammonia to nitrate, this occurs through nitrification that entails nitrifying bacteria such as Nitrobacter and Nitrosomonus, by reduction the nitrate is transformed into gaseous nitrogen through from denitrification that is released into the atmosphere.
For these transformations or conversions to occur, they have to be carried out under fairly controlled conditions and guarantee the formation of new biological communities. To reduce nitrogen, sand filters, lagoons, artificial wetlands can be used by means of reed beds or sheets. Sometimes the tertiary stage is performed only for the transformation of toxic ammonia into nitrate.
Anaerobic oxidation is a decomposition process that occurs without the presence of oxygen, this oxidation is carried out by nitrates, nitrites, sulfates and CO2 that accept electrons. In denitrification, facultative bacteria use nitrates and nitrites in conditions of absence of oxygen or anoxic, which as final products form CO2, water and nitrogen.
Enhanced Biological Phosphorus Removal is used to remove phosphorus biologically. Bacteria "polyphosphate accumulating organisms" are used that are applied to absorb and accumulate a high amount of phosphorus within their cells. When withdrawing from Residual Water, this biomass through biosolids or sludge is reused as fertilizer. Phosphorus is also removed by chemical precipitation through ferric chloride, to remove iron, and with alum, to remove aluminum.
However, the chemical sludge resulting from the treatment is difficult to work with and applying chemicals at this stage is costly. This entails that the operation is more difficult and less clean, by this method of chemical removal of phosphorus, however, it requires a smaller trace than doing it by biological removal and easier to operate.
Purpose of disinfection
Disinfection in this third phase of Wastewater Treatment has the objective of eliminating the largest number of organisms before being discharged again into natural spaces. This step will be effective depending on the turbidity of the water, its pH and other qualities that influence the quality of the treated water. Also the disinfection applied, the concentration and exposure time with the disinfectant, as well as other environmental conditions.
The effectiveness of the cloudy water disinfection treatment is lower in view of the fact that the organic matter can prevent the ultraviolet light rays from acting on certain organisms and also have less contact times, eliminating fewer toxic organisms present in the Residual Water. The most used techniques to disinfect are with ozone, chlorine, ultra violet light. Chloramine is used to disinfect drinking water, it is not used in the disinfection of Residual Water due to its permanence in these liquids.
In the United States, wastewater has been disinfected with chlorine for a long time, in view of its high long-term efficiency and its economy. However, disinfection carried out with chlorine has the disadvantage that the organic material present in the residual medium can be transmuted into chlorinated organic compounds that can become carcinogenic or environmental contaminants.
In a natural water body where organic chlorine is applied, residual chlorins or chloramines may have the ability to treat organic matter. It should be noted that residual chlorine is dangerous for aquatic species, due to this the natural aquatic body has to be chemically treated for dechlorination, which makes this treatment more complex and expensive.
In the United Kingdom, disinfection is carried out with ultraviolet light (UV), in view of the negative impact caused by chlorine in Wastewater Treatment and organic chlorination in rivers, lakes and other aquatic environments that are receptors. UV acts by altering the genetic structure of the pathogenic agent, be it a bacterium or a virus or another, preventing them from reproducing.
However, disinfection with ultraviolet light has the disadvantage of maintenance and frequent replacement of the lamp and also requires a very well treated effluent or Wastewater to ensure that target organisms are not shielded or protected from ultraviolet light radiation. .
When oxygen (O2) passes through a high-voltage potential and is transformed into ozone (O3), because a third oxygen atom is added. Ozone is an unstable and reactive element that oxidizes many of the organic matter they get. Due to this, it destroys many microorganisms that cause diseases. Another advantage of using ozone is that it is safer to use and because of its low need for storage.
This is because chlorine has to be stored in very safe places, since it is a very poisonous material. Instead the ozone is placed as required. Likewise, disinfection with ozone generates less by-products than when disinfection is done with chlorine. The disadvantage of disinfection using ozone is cost.
Package plants and batch reactors
To reduce the space required for the operation of a Wastewater treatment plant, treat solid waste, analyze intermittent flow and achieve high environmental standards, package treatment plants and batch reactors have been designed and built.
These plants carry out the three or two of the stages of Wastewater Treatment in a combined manner. They are widely used plants in the United Kingdom, and are put into operation in small towns. These plants are a good option to add them in the designs of the buildings, so that they do the Treatment of the Residual Waters of the same.
To explain the operation of this type of plant and sequential batch reactor, in general, in the process the activated sludge joins the wastewater that is entering and after joining they are aerated and produce a wastewater and sludge of high quality. The biodegradable sludge or sludge that is dumped is aerated and filtered and part is reused. These batch plants and batch reactors are increasingly used in different countries of the planet.
The disadvantages of these package plants is that an exact control has to be kept for the combination of the treatments and then, there must be a total synchronization of the steps, as well as when mixing and aerating. This synchronization is achieved by digitized controls and sensor-driven assistance throughout the plant. This type of package plant with high-tech sensors is impractical in places where controls are inadequate, maintenance is low, or the power supply is intermittent.
These packaged Wastewater Treatment plants, due to the way they process the biological load, are referred to as low-loaded or high-loaded. This can be explained because in highly charged systems, when the biological stage is carried out, it is presented with a high amount of organic material and, then, the mixed material of the floc and organic is oxygenated for a few hours to be charged again. In the case of being a low loaded system, the biological phase contains a low biological load and is mixed with the floc for a relatively long term.
sludge treatment
Coarse primary sludge and secondary biosolids deposited during Wastewater Treatment must be disposed of safely. Usually the deposited material is unexpectedly contaminated with toxic organic and inorganic materials, such as heavy materials. The objective of the digestion phase is to reduce the amount of organic matter and the amount of microorganisms present in the toxic solids. For this, the following treatments must be applied: anaerobic digestion, aerobic digestion, and fertilization.
anaerobic digestion
This anaerobic digestion process is carried out by bacteria that do not require oxygen to grow. This anaerobic digestion can be carried out by different processes such as thermophilic digestion, in this digestion the sludge or sludge is fermented in tanks at 55°C; and mesophilic digestion than sludge fermentation is at 36°C, with a shorter retention time. On the other hand, thermophilic digestion is more expansive in reference to temperature.
Through anaerobic digestion, gas is produced, it has a high amount of methane that can be used as fuel, with which tanks, micro turbines or engines can be recharged that allow the operation of different processes on site.
These anaerobic digestion processes in the Wastewater Treatment plants produce a greater amount of electrical energy than is required for the operation of the plant. This methane production is a benefit of the anaerobic process. However, the disadvantage is the high cost of the process and the time it takes to generate electricity, around 30 days.
Its advantages
This type of treatment allows it to support a high amount of organic loads even when it operates in periods of very short hydraulic resistance, because it can allow long periods without recharging the system and also gather a high amount of biomass in the system. The rooting of the technology of this system depends on its design and operation. That in exchange for the aerobic system, aerobic zones and stabilized sedimentation are required.
In reference to the volume to carry out the anaerobic process, it only requires less than 80% of the amount of sludge compared to aerobic systems and even produces gas. Which is given the name of methane gas, and can be used in the same plant because it does not require a large amount of electrical energy during its operation.
Due to this methane gas can be used as alternative energy. As a complement, the indicated nutritional requirements are used, which are low, and not the demanded amount of industrial waste required by the aerobic system.
Regarding the infrastructure requirements, with respect to the different aerobic systems, the space requirements are low, this is because the anaerobic process can be carried out in relatively small spaces when compared to the aerobic process.
This Wastewater Treatment system is used at Goldbar in Edmonton in Alberta, Canada. Experience has shown that useful amounts of electricity can be produced from organic sludge under laboratory conditions by electrochemical activation of naturally occurring bacteria.
This technique has the potential to be an ecological way of generating energy and even electricity. However, to be an efficient fuel, a microbial cell has to maximize the contact area between the effluent or waste material and the bacterial coated surface of the anode, which would lead to lower process yields.
aerobic digestion
Unlike the previous process, aerobic digestion is carried out in the presence of oxygen. Under conditions of the presence of oxygen, some bacteria rapidly absorb organic matter and transform it into carbon dioxide. When the organic matter is finished, these bacteria die and serve as food for saprophytic bacteria. This phase of the process is called endogenous respiration and a reduction of solids occurs.
This aerobic digestion process is faster and the investment costs are lower. However, due to the high costs of the aerobic digestion process, in view of the energy costs required for aeration and the constant oxygen requirement for this process.
Formation of manure or compost
The formation of fertilizer or compost is a process that can be carried out in the aerobic stage that is carried out by uniting the solid elements of the Residual Water with material that provides carbon such as: wood chips, sawdust, and others. Aerobic bacteria in the presence of oxygen consume wastewater solids and carbon and generate heat.
Anaerobic and aerobic digestion processes can destroy pathogenic microorganisms and parasites to a level that allows the digested solids to be added to the soil as compost material for agriculture and as soil amendment material, much the same. to the mob
thermal depolymerization
During thermal depolymerization, aqueous pyrolysis is applied, which is the chemical decomposition of organic matter from which complex organisms are transformed into oil. The hydrogen in the water is inserted between natural polymers, such as proteins, fats and cellulose. Containing fuels such as: methane, butane and propane, as a result of the mixture of carbon and hydrogen.
The level of inorganic salts of nitrates and phosphates remain in the water after the Wastewater Treatment, in high quantities, so an additional treatment has to be carried out again. The energy used to store the material is recovered and due to this the heat and pressure of the process is activated from the light fuel gases. The oil is further processed into lighter oil refining, such as some diesel and heating oils, for sale.
When you want to select a type of treatment of the solid material present in the Wastewater, it will be determined by the amount of solids present and other characteristics. However, the production of fertilizer is the most frequent that is obtained in small quantities from aerobic digestion and in larger quantities through anaerobic digestion.
sludge drying
During the Wastewater Treatment from the solid organic matter, a sludge is produced that, due to its high water content, has to undergo an additional treatment to bring it to a suitable degree of drying for its final deposition. The usual thing is that these sludges are dried or dehydrated to reduce the volumes of the material that will be transported to the place to be deposited.
To achieve this drying and eliminate excess water, the material must be passed through the lagoons and drying beds that have the function of producing the cake that can be deposited on the ground or lead to be incinerated; For this, the mud or sludge is mechanically filtered as it passes through the screens of the cloth to achieve a firm cake, and then centrifuged where the thick sludge is centrifuged again to separate the solid and liquid part.
This sludge or sludge is disposed of through liquid injection to land or by deposition, stockpiling or embankment. Some professionals and technicians have conflicting opinions regarding the incineration of sludge, due to the polluting and toxic gases that would go into the air due to the emissions during the burning of the sludge. For this reason, coupled with the high cost of fuel that has to be used, carrying these less conspicuous and few built means of treatment for the deposition of sludge.
In Australia, in the treatment plants after centrifugation of the sludge, it is possible to completely dry the sludge by means of sunlight, saving costs. This allows the sludge or biosolids that the Wastewater brings to be rich in nutrients, which are offered to farmers for use as fertilizer or compost. This has made it possible to reduce the amount accumulated by the process each year.
Wastewater photobiopurification
The process of photobiopurification of Residual Water is carried out during the hours of sunlight and the presence of organisms that carry out photosynthesis in the purification process. This wastewater purification process carried out through photobiopurification is carried out by the microorganisms that photosynthesize such as microalgae and cyanobacteria, which are taken to the photobioreactors, which are reactors designed in a way that takes advantage of sunlight and in this way these microorganisms spread.
The reception environment
The deposition of Residual Water that has passed through Residual Water Treatment into nature has an impact on bodies of water such as lakes and rivers. This is because the processes that are carried out during the treatment seek to simulate nature with respect to the steps that it takes to purify the water that will then be channeled until it is reincorporated back into a body of water or into the earth.
If they have not been saturated, the bacteria will dissipate the organic contaminants, this leads to a decrease in the oxygen levels of the water, which will impact the receiving water, altering this ecosystem in its entirety. The consequences are that the bacteria in the natural environment feed on organic pollutants and the populations of pathogenic microorganisms decrease due to the conditions of the natural environment due to the action of predators, due to the action of ultraviolet light and other factors.
Because of this, if it turns out that the natural environment has the right conditions to dilute the pollutants that the wastewater carries, part of the Wastewater treatment will not be required. Although in recent times it has been shown that the scarcely low levels of some pollutants such as: hormones for animal use, hormones for fertility in humans and synthetic materials, can negatively alter the natural environment and this is a threat to human health, if this water is reused for drinking water.
The environmental regulations of the United States regulate and prohibit uncontrolled discharges or discharges of Wastewater into the natural environment and the characteristics of the Wastewater that is going to be returned to the natural environment must be known. Currently and in the future, the increase in uncontrolled wastewater discharges in developing countries is a major threat.
Water treatment in the world
At present, Wastewater Treatment is deficient and this situation has been dragging on more or less since the XNUMXs. The researchers respond to this situation because this occurs due to overpopulation, the problem of water scarcity, and the high economic costs involved in the construction of a Residual Water Treatment plant.
The consequences of this situation of deficit in Wastewater Treatment worldwide, is the significant increase in mortality, especially from diseases that can be warned. This increase in the mortality rate is a negative impact among children and some adults in underdeveloped countries, especially in the continents of Africa and Asia.
Since the beginning of the third millennium in the year 2000, the United Nations reported that around 2.640 billion people received water from insufficient Wastewater Treatment. In the world at that time it meant 44% of the world population. However, in Africa and Asia it was already likely that more than half of the population did not have access to any type of wastewater treatment system.
Your environmental impact
Wastewater originating in municipalities, cities or towns of domestic and industrial origin, are carriers of a large amount of suspended and diluted solids that are usually: organic and inorganic materials such as nutrients, disease-carrying microorganisms, fats and oils, and others. toxic products.
It should be noted that waste of human origin, which is not treated promptly since it is disposed of at its place of origin, as well as that which is collected and transferred, represents a threat of parasitic infection, especially when there is direct contact with the feces.
Carrying diseases due to hepatitis infections and other gastrointestinal diseases, such as cholera and typhoid, the latter due to contamination of the water and therefore the food. Unfortunately, it has been shown that urban rainwater precipitation can have high concentrations of pollutants.
The negative impact on the environment is high when wastewater is inadequately treated before being discharged into the environment and in some cases reused, maintaining the same threats that the quality of the water near the place of discharge offers. If this discharge is in a place of receiving waters, it means a threat of dangerous added impacts, such as the alteration of the aquatic and marine ecosystem due to the high amount of solids, the decrease in oxygen levels caused by the decomposition of matter organic.
Likewise, both freshwater and marine organisms can be negatively affected by toxic substances, which due to the effects of bioaccumulation can pass from one organism to another in the food chain. If the discharge occurs and reaches confined waters, such as lakes and bays, due to the high amount of nutrients they can cause eutrophication and consequently the overpopulation of aquatic plants and due to this the decrease in oxygen and light affecting the life of the fish and recreational use of these waters.
On the other hand, the solid waste that comes from Residual Waters that went through the Residual Water Treatment, such as gravel, sludge or secondary and primary sludge and sifted material, are polluting agents of soils and waters, when they are not managed properly. right way.
The projects carried out for different types of wastewater treatment are carried out to reduce or avoid the effects and negative impacts of the aforementioned contaminating agents, both for human beings and for the natural environment. It should be noted that when these different types of wastewater treatment are carried out effectively, they offer a positive impact on the environment.
The positive environmental impacts are reflected in a decrease in the deterioration and dangers for public health, a better quality of the waters where the treated Residual Waters are discharged and, consequently, an increase in the amount of benefits of the receiving waters.
In addition, the incorporation of a wastewater collection and treatment system allows better monitoring and more effective control of wastewater from industries through pre-treatment and subsequent connection to the public sewer network, and Being well treated, they have the potential for the beneficial reuse of treated Wastewater and treated sludge.
In addition to these positive impacts, the indirect impacts that can be generated by Wastewater Treatment can be listed, which can be the creation of new service places for development, increase and improvement in production and profitability for fishermen, a increase in tourist and recreational activities and therefore in economic benefits.
In addition, improvement of agricultural, livestock and forestry activities and the reduction of the use of chemical fertilizers, as fertilizers from residual sludge are used, and a decrease in the demand for water from other water sources other than reused water. of the effluent.
From this exhibition of beneficial impacts as a result of Wastewater Treatment, arguments can be presented for the qualitative measurement of the justification of the costs involved in planning the development of some type of Wastewater or Sewage Treatment.
The benefits of this type of project for human health can be calculated, by calculating the costs that would be avoided or reduced due to medical expenses and reduced absence from work due to illness, which would be the result of good Water Treatment. Residuals.
In the same way, the lower costs of the Treatment of Residual or served water of domestic and industrial origin, and the increase in profitability in fishing activities, tourism and other recreational activities can help to monitor gradual measurements of the benefits achieved. for the improvement in the quality of the receiving waters.
In the case of being a place with a high demand for housing, the benefits offered by plots with integrated Wastewater Treatment services can be reported, with respect to what the costs of installing a plant imply in advance with respect to the costs that would have to be calculated for the adaptation and subsequent installation in unplanned communities.
Above all, because the Wastewater Treatment Plant projects that are not well planned, located, calculated, outlined, built, put into operation and properly maintained, end up being projects to improve the quality of the sewage or wastewater that in Instead of benefiting, they have a negative impact, both due to the high economic investment and the negative environmental impacts it causes.
Sociocultural aspects
For a project for the development and operation of a Wastewater Treatment plant, it implies a well-located land surface, given that its location may result in an involuntary repopulation or relocation of people who used to live in that place. Likewise, the treatment and dumping activities for the elimination of Residual Waters may occasionally produce disturbances in the surroundings of the plant.
This may occur because, in general, the selected spaces and populations are vulnerable community groups with fewer possibilities and capacity to face the costs of relocating a treatment plant and also their living environment has already been affected.
For this reason, during its planning, design and construction, care must be taken in the location of the installation of the treatment plant and where it will be eliminated so that odors or noise do not affect and disturb the residents who live close to it. plant.
For this reason, their relocation must be managed with some sensitivity, and a mitigation plan for the project must be provided, ways to compensate or remedy the negative impacts on the entire environment and quality of life. These forecasts must be taken into account in a project of this type, in order to avoid significant risks.
Choosing the right technology
To determine the selection of the appropriate technology for Wastewater Treatment, several aspects must be taken into account, namely: technical, institutional, social and economic aspects. Taking into account the technical and institutional dimension and scope, the choice of an inappropriate technology is one of the factors that have led to the consideration of the ineffectiveness or failure of this system.
The wastewater treatment project itself creates a hostile environment for electrical, electronic, and mechanical equipment. Continuous maintenance must be carried out, and therefore support material must be provided, such as: spare parts, technical laboratory, specialized advisory personnel, trained technical personnel, and adequate and timely budget.
For all that has been explained, in the most technical countries, the installed Wastewater Treatment plants are the projects of this type with the simplest technology, which are chosen and put into operation, due to the low cost of maintenance and for providing a service less complicated.
These considerations must be taken into account in developing countries, where some element may be lacking at any given time for the proper development of a project of this type and especially its long-term maintenance. So, this should be the first thing to consider when selecting technologies to choose the right treatment plant and pumping station.
Similarly, in small towns and rural areas, the technical options have to be the simplest and, above all, to provide a good service, it is very important that institutional considerations maintain a balance with social ones. Local agencies must have the capacity to respond and timely management of wastewater or sewage sanitation programs or systems.
As well as educating the community regarding Wastewater Treatment and proper maintenance of the facilities, since it can be a social and institutional combination that brings success to the project. This is because it is important to know the preferences and social and traditional practices, given that some can be modified through environmental educational programs and, others, due to being cultural traditions since ancient times, are less subject to change.
The economic aspect is decisive when selecting the technology, however, this has to be analyzed from two points of view. In general, the less complicated or simpler technologies are usually selected because they are easier to handle and have lower operating and maintenance costs.
However, it is good to analyze that even if the opposite is believed, when a large amount of land has to be acquired for the stabilization tanks, a cheaper system can fail, being finally more expensive than another that due to its technology is more expensive and its more reliable operation.
Wastewater treatment by biotechnology
The natural process of purification of Residual Water consists of anaerobic bacteria feeding on the organic compounds that are present in Residual or served water. The opportune work of these bacteria is what led to conceive the Wastewater Treatment projects by the biological method of biodigestion, which through several processes put the bacteria in contact with the Residual Water so that they are catalysts and accelerate the natural process of biodigestion.
This is achieved by using a fixed film of bacteria in different places studied by engineers and biologists, so that during the process they have higher numbers of contacts with the water, at the time it is being treated. When the water comes into contact with the bacteria, biodigestion is caused using less time than the natural process.
In different types of treatment plants, in which rollers, packages, modules or mills are used, this film or fixed layer has the same objective. The way in which the natural process is accelerated is what determines the different technologies used for the different treatment plants. In addition, the space indicated for the construction of a Wastewater Treatment plant that meets this characteristic.
With respect to other types of technologies and methods to carry out the purification of Residual Water, this method where the fixed film is used is undoubtedly one of the most used technologies, due to its size, ease of use, maintenance, cost and size. of the precise space for its construction and installation.
Bibliographies and journals on this treatment
The book «Water Analysis and Treatment Tests. Principles and Applications» written by the author Rafael Marín Galvín, explains through studies and essays the principles, applications and treatment of wastewater. The book is divided into three parts, be these: In the first part he writes about the physical and chemical principles of the process, making a descriptive analysis of them.
The second part describes the applications, from the taking of water samples and the detailed description of the different methods used for its analysis, be these analytical, physicochemical and microbiological methods, as well as the most used to determine water quality. In the third part, he presents a series of treatment essays, starting with the fundamentals of the main processes for water purification. It also presents tests of the most used treatments in the laboratory.
Another book is published by the editorial Bellisco (2013), where the author shows a wide group of machinery designed and specialized to work and put into operation the purification stations or plants for the treatment of drinking water, as well as for the desalination plants of the Water.
Specialized Technical Magazines
The magazine A comparison of requirements, is one of the specialized magazines on the study of the different Types of Wastewater Treatments, in which works by professionals specialized in the subject are presented. Some topics discussed are: the prevention that must be considered due to accidents that may occur when applying chemicals that damage the natural environment.
In the magazine published in the United Kingdom called Water and Health published between 2003-2012, it is a magazine that was dedicated to publishing articles to educate and disseminate the consequences of the use of chemical substances on the health of human beings and in the development of the countries of the planet.
The UN and Water Treatment
Among the objectives proposed in 2015 to guarantee sustainable development, the United Nations Organization (UN), raised the objective of, Guaranteeing the availability of water and its sustainable management and sanitation for all. Regarding its sanitation, I characterize that it is the result of the urban sewage and drainage system and its purification for its discharge into natural water bodies.
The UN for 2017, presented a figure on the deplorable conditions of water management and sanitation and the health of human beings. He noted that around 2400 billion people lack adequate water treatment services, such as toilets and latrines. Entailing that 34% of a total of 7.000 million people who inhabit the earth, do not have basic water sanitation services.
In addition, more than 80% of the Wastewater that is produced throughout the planet is returned to nature, without having gone through a Type of Wastewater Treatment, where it is purified and polluting agents are eliminated. Finally, every day around 1.000 children die from health problems such as digestive tract diseases and predictable diarrhea caused by untreated water.
Wastewater Treatment in Spain
Unfortunately, Spain does not escape the inadequate management of Residual Water, the problem dates from 1991, in which the regulations of that time stipulated that municipalities with more than 15.000 inhabitants had to avoid the discharge of contaminated water into the seas and rivers by carrying out the Wastewater treatment. However, in current times a problem related to this issue was detected in 9 towns, most of them located in Andalusia, for which they had to pay a fine to the European Commission of the European Union.
For the European country, this is the largest amount that has had to be paid to Brussels, and it should be an effective wake-up call for the Iberian country, not only because of the economic impact. If not also, due to the lack of proper collection and treatment of Residual Water due to the well-known risks that its poor management implies for health, the deterioration of river water and the discharge of pollutants into the seas.
For the well-being of the health of Spaniards and environmental quality, it is vital to accelerate the planning, design, construction and operation of treatment plants and collectors to carry out the biological treatment of Residual Water and comply with the application of the strategy of circular economy promoted by the European Commission: purifying and reusing water.
Wastewater Treatment in Venezuela
The Vitalis environmental foundation, in a publication made for the celebration of World Water Day, highlighted the importance of wastewater management and the importance of its waste. As is known, wastewater originates from homes, schools, health institutions, businesses, industries, agriculture, mining and other projects. Many of these wastewaters reach nature without any type of treatment, contaminating natural spaces, losing a large number of ecosystems and species of fauna and flora.
In Venezuela, Wastewater Treatment is considered, according to the director of the Vitalis Foundation, one of the country's main environmental problems, given that around 25% of wastewater is that which reaches nature after having been treated at a treatment plant.
The professional pointed out that in Caracas, the country's capital and where the largest urban concentration is, few treatment plants are installed, resulting in the majority of these untreated wastewater being discharged into the Tuy River basin, from there transferred to flow into The Caribbean Sea.
According to Martínez, the Venezuelan capital only has the Wastewater treatment plant (experimental type) installed in the Faculty of Engineering of the Central University of Venezuela and that of the POLAR Group Company, in the Los Cortijos urbanization. For the president of Vitalis, and founder of the Venezuelan Association for Water, Diego Díaz M., he suggests that instead of wasting large amounts of Residual Water, what has to be done is to reduce the amount that is produced and manage to reuse most of it. amount.
He suggested that the wastewater in the house can be reused as gray water, to clean the house, clean the patio, water the plants, clean the toilet, of course depending on how the house is. Likewise, in urban spaces, these gray or residual waters can be reused in parks and gardens, for street cleaning, in industries and agricultural crops, for example. In addition to this, both professionals agree to promote the construction of treatment plants in the country and thus reduce the negative environmental impact of these waters in the country.
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