Mr. Amitabh Kant, CEO of NITI Ayog, said that India’s wastewater treatment market stood at USD 2.4 billion in 2019 and is projected to reach USD 4.3 billion by 2025. The development of Sewage Treatment plants has been a significant objective of various government programs like Namami Gange, Atal Mission of Rejuvenation and Urban Transformation (AMRUT), and Swachh Bharat Abhiyan. The total capacity of Sewage Treatment Plants in India is 6,190 MLD, and another 1742.6 MLD, sewage treatment capacity, is under construction. According to CPCB, states of Maharashtra, Gujarat, Uttar Pradesh, NCT of Delhi, and Karnataka are the top 5 states which have installed significant sewage treatment facilities. With increasing awareness of water scarcity, government and non-government organizations take proactive measures to overcome the considerable generation of wastewater.
Sewage Treatment Plants remove pollutants, contaminants, and hazardous substances from the sewage water and produce clean water. The treated water fulfills various water needs like agricultural, horticultural, and industrial. However, Sewage water treatment Plants come with several advantages and disadvantages.
Traditionally sewage was removed and collected manually. Nowadays, sewage is extracted, organized, and transported using technology and can be handled by minimum workers. In addition, modern Sewage Treatment Plants can treat massive amounts of sewage, reducing the long work hours.
Sewage contains significant amounts of organic matter, which is used to generate energy. Sludge is pre-treated, and then anaerobic digestion breaks it down. Anaerobic digestion produces methane gas, which provides power to the grid. It can provide energy to run the Sewage Treatment Plant and supply power to the residential areas. Sewage gas can also be configured as a combined heat and power plant (CHP), and CHP mode increases the plant’s overall efficiency.
The sludge gathered for treatment carries a colossal amount of biodegradable matter, nitrogen, and phosphorous. Therefore, when the sludge is treated with the sludge drying method, it leads to biodegradable fertilizer. This fertilizer is suitable for agricultural and gardening use.
Less than 50% of the Indian population has access to safe drinking water, and annually about 37.7 million Indians are affected by water-borne diseases. In addition, untreated sewage is released in ponds, lakes, and rivers and directly affects the underprivileged Indian population. Sewage Treatment reduces the health risk of the people as it removes most of the contaminants from wastewater before release in the natural water stream.
Sewage Treatment Plants treat water in various steps to remove large solid particles, chemicals, hazardous substances, and microorganisms. As a result, the treated water is safe for re-use and minimizes water needs and pollution.
Sewage Treatment Plants comprise numerous types of waste that have several smells. Foul odor generally originates from organic decomposition. The prominent smell is of sewage, and other aromas include hydrogen sulfide (rotten eggs), ammonia, mercaptans, and other chemicals. Most of the scent is retained in the plant’s boundary, affecting employees, and some smell drifts towards the surrounding area. They are worse during summertime when the temperature is high.
An optimum amount of microorganisms can help in sewage treatment. However, the concentration of bacteria may rise in some situations and affects the treatment process. For example, they might slow down the process or stop it completely. In addition, sometimes, the treatment process can create variants of bacteria that are resistant to antibiotics that can kill other microbes. Moreover, they increase rapidly, and sewage provides them with an optimum environment.
According to CPCB, the estimated conventional cost for a Sewage Treatment Plant comes to rupees 1 crore per million liters daily (MLD). So, for example, a Sewage Treatment Plant with 500 MLD capacity will require 500 crores to be set up.
Sewage Treatment Plants require a continuous power supply to function properly. For example, plants with more than 200 MLD capacity need a 1 megawatt power supply. Therefore, interruption in power supply damages the mechanism of Sewage Treatment Plants.
Annual maintenance costs of Sewage Treatment Plants are high. For example, the yearly maintenance of plants with a minimum capacity of 100 MLD requires rupees 70 lakh to 2 crores.
‘STPs are costly affairs and can only be maintained when a comprehensive financial structure of maintenance is available. An STP needs all its sections to be fully functional in order to treat sewage,” says A.B. Akolkar, Member secretary, CBCP.
Though Sewage Treatment Plats treat water for re-use, they still leave an environmental footprint. The left-over residues after sewage treatments must be eradicated, leading to pollution. Moreover, fumes of Green House Gases, CO2, and N2O are released into the environment and contribute 26% of the carbon footprint.
Sewage Treatment Plants require large land areas for construction, and authorities impose regulations of boundaries which becomes a problem for area selection for plants. Moreover, the direct flow of sewage to sewage treatment plants is a concern mainly in urban areas where drainage systems and old.
Sewage Treatment Plant has its pros and cons. Although it treats water in less time, produces energy, fertilizers, reduces public health risk, and reduces water pollution, it also produces a pungent smell, hybrid bacteria, requires huge capital, land area, and leaves an environmental footprint. However, advancement in technology will reduce the disadvantages of Sewage Treatment Plants and enhance the efficiency of STPs.
Every stage in a wastewater treatment process is important to achieve the desired treatment results. However, primary treatment and tertiary are critical to the overall process. In the primary treatment process solids are reduced to a large extent. Without this step, subesequent treatment would be less effective. In tertiary treatment, harmful microbiological matter is rendered killed or inactive so that it will not cause sickness to those organisim that encounter it.
These wastewater treatment methods, are coagulation and disinfection respectively. Each of these processes has multiple ways that they can be accomplished, either by chemical or non-chemical techniques. Each of these wastewater treatment methods has their own benefits and disadvantages.
Coagulation
Wastewater influents contain varying levels of total dissolved solids (TDS) and total suspended solids (TSS). Course screening and grit chambers will reduce the TSS but must be followed by a more refined solids removal process. Sedimentation and filtration are methods that have been used in the past, but these methods cannot remove many of the smallest particles.
Coagulation has become a popular method of reducing both the TSS and in some cases TDS of wastewater. This process involves destabilizing the charged particles in the solution. Because of their similar electrical charges, the particles repel one another and prevent them from settling quickly. To destabilize this electrical charge, an opposite charge must be applied to the solution, enabling the colloids and other minerals to aggregate.
There are currently two well-known methods of coagulation:
Chemical Coagulation
Chemical coagulation is a well known method of particle coagulation. This process warrants the addition of a number of chemical additives to achieve the desired destabilized state. Alum, Ferric chloride, Ferric sulfate, Ferrous sulfate, and Lime are some of the additives used to neutralize the charged particles. Other supplements include polymers, which act as an aid for the aggregation of solids.
Pros
The main consideration behind the use of chemical coagulation is that it speeds up the time it would take for the solids to settle on their own. Therefore, decreasing the overall detention time of the wastewater treatment process.
Chemical coagulation can also aid the settling of finer colloidal particles and mineral contaminants. These particles typically may not settle during a sedimentation process and would pass through a subsequent filtration system.
Cons
Chemical coagulation is, at its core, an additive process. Though it can reduce the amounts of solids in a solution, it still requires the addition of chemicals to achieve this. Adding these substances can be quite complex and require extensive jar testing. The dosages need to be fairly exact in order to properly process the influent optimally. Dosage can require continuous adjustment based on the varying composition of the wastewater source.
The addition of chemicals also results in the production of a large volume of sludge that will need to be treated and disposed of following treatment. This sludge is also hazardous due to the nature of the constituents being added. The volume and toxicity of the sludge can drive up disposal costs as its not easily dewatered.
Electrochemical Coagulation
More recently, electrochemical coagulation has entered the scene in wastewater treatment in a more optimized form. After pH adjustment if needed, this process involves the supply of specific power to a series of metallic media. The anodes and cathodes can either be the same material or different from one another. This material is optimized depending on the influent water makeup. Aluminum and iron are two such materials that can be used in this process. The electrodes release charged ions into the solution during oxidation, which leads to the destabilization of the particles in the solution.
Pros
Electrocoagulation is a straight forward process. It has few moving parts, thus it can be remotely monitored with reduced oversight and maintenance. The process can also typically be adjusted to accommodate for differing amounts of particles without much effort if required.
The EC process is also able to target multiple contaminants using a single system and in certain cases with a single treatment pass. Its lack of typical chemical addition, produces smaller volumes of sludge that are typically non-hazardous, easily dewatered, and less expensive to process and dispose of.
Cons
An EC system can require the addition of acids or bases for pH adjustment, so it is not completely free of additives. Also, due to the nature of the process, the electrodes are sacrificial and will corrode over time, requiring replacement. It can utilize a CIP process for plate cleaning, which would use acid in its cleaning cycle. The nature of the process also requires electrical power. While it may not require much at one time, in some places in the world, power may be more expensive which can increase operating cost.
Disinfection
In the tertiary wastewater treatment process, the effluent may contain bacteria, viruses, mold, cysts or other pathogens that other treatment processes cannot remove. Before the treated water can be discharged into any body of water, the microbiological contaminants need to be inactivated or killed. There are several wastewater treatment methods of disinfection available, but the two most commonly used are chlorine and ultraviolet light.
Chlorine Disinfection
Most are familiar with the use of a chlorine compound to shock treat swimming pools. Chlorine is a toxic agent to biological organisms and kills them by oxidation. It penetrates the surface of pathogens and once inside, begins to interact with intracellular enzymes and proteins, rendering them nonfunctional. The micro-organism will either die or fail to reproduce.
Pros
Chlorine is relatively inexpensive and readily available. In addition, because it is such a powerful oxidizing agent, it can be quite effective at rendering large quantities of harmful micro-organisms inert with suitable reaction time.
Cons
Chlorine is quite volatile, and can result in disinfection by-products (DBPs) that can be harmful to humans, animals and aquatic life. It requires careful handling to be shipped, stored, and used safely. Viruses, Giardia lamblia, and cryptosporidium are unaffected by chlorine disinfection treatment.
UV Disinfection
Ultraviolet light disinfection systems are prevalent in many applications in recent times for their non chemical disinfection capabilities. At particular wavelengths, UV light can disrupt a pathogen’s DNA by breaking its molecular bonds. Normal cellular function becomes impossible in this state, leaving microbiological organism, cysts, and viruses virtually inert.
Pros
UV disinfection is an entirely physical process so there are no hazardous chemicals to handle. There is no harmful residual byproducts that could be generated in the treated water. It is highly effective against most viruses, bacteria, spores, and cysts and requires shorter contact time than other tertiary wastewater treatment methods. In addition, it has a compact footprint for its disinfection capability.
Cons
Due to the use of light to decontaminate a solution, high concentrations of total suspended solids (TSS) can render it ineffective. This is a non-issue if the preceding treatment process is effective at removing TSS. Low doses of UV light can be ineffective against some viruses, spores, and cysts, so they would require longer contact times or higher intensity exposure. There is also the potential for photoreactivation to occur in the micro-organisms whereby the organisms repair themselves following treatment if the UV dose is not powerful enough.
Summary Table of Pros and Cons
Coagulation
Disinfection
Chemical
Electrochemical
Chlorine
UV
Pros
Lower precipitation time
Removal of fine particles
Simple process and design
Easily adjustable
Low sludge production, non-hazardous
Targets multiple contaminants
Easily available
Inexpensive
Powerful oxidizing agent
No harmful residual effects
no chemicals to handle
effective against most viruses, spores, and cysts,
requires little space
shorter contact time
Cons
Additive process
Complex dosing
High hazardous sludge volume
Some pH adjustment
Sacrificial electrodes
Electricity use may be expensive
Taste and odor
Can create DBPs
Volatile
Can’t remove all pathogens (ie viruses,cysts)
Ineffective if TSS is too high
Low doses can be ineffective against some viruses, spores, and cysts,
Photoreactivation possible
Based on the given information, Genesis Water Technologies, Inc. sees great potential in using sustainable non-chemical water treatment processes. We are proud to design, engineer and supply our GWT specialized Electrochemical treatment systems and UV disinfection systems in suitable treatment trains for municipal and industrial water & wastewater treatment applications.
If you would like to know more about these treatment options and how they could benefit your organizations water or wastewater treatment goals, please contact us. You can reach us at 1-877-267-3699 or send us an email to customersupport@genesiswatertech.com for a no cost initial consultation to discuss your application.
For more information, please visit lithium ion battery for solar storage, Scalable single phase string inverter, Advanced single phase string inverter.