WHY WASTE WATER TREATMENT IS IMPORTANT?

 

Wastewater treatment protects humans and ecosystem

Wastewater contains elements toxic to humans and the ecosystem. Wastewater treatment facilities help to purify the water and eliminate situations like what is currently seen in developing countries. Unclean water poses significant health risks, accounting for 1.7 million deaths annually, of which over 90 percent are in developing countries.² Several water-related diseases, including cholera and schistosomiasis, remain widespread across many developing countries, where only a very small fraction (in some cases less than 5 percent) of domestic and urban wastewater is treated prior to its release into the environment³.

Wastewater treatment also protects the ecosystem. Fish and aquatic life require fresh water. When their water environment is laden with wastewater, they cannot survive. If chemicals, such as nitrogen and phosphates, enter streams, rivers or large bodies of water in excessive amounts, it causes excessive plant growth which release toxins into the water. This leads to oxygen depletion and dead zones; areas where fish and other aquatic life can no longer exist.

Chemical treatment in wastewater treatment plants includes neutralisation, disinfection, phosphate precipitation, nitrogen elimination, deicing and manganese removal.

Neutralisation is used to produce the prescribed pH value, which is achieved by adding an acid, e.g. HCL, or a base, e.g. milk of lime.

During disinfection , pathogens are killed by adding chlorine or chlorine dioxide. The irradiation of the wastewater with UV light is a good alternative to adding chemicals, but it is used less frequently. Phosphate elimination: Our wastewater is frequently contaminated with phosphates from detergents, fertilisers, food additives and faeces. If they remain in the wastewater, they lead to overfertilisation of water bodies and enrichment with nutrients, which can lead to useless plant growth (eutrophication) harmful to the ecosystem. Phosphates are removed with a chemical precipitation or flocculation process. The phosphate precipitation is partly triggered by the addition of aluminium or iron salts in the sand collector or in the secondary wastewater treatment tank. The metal-phosphate flocks that are formed during this secondary clarification are then taken out of the wastewater together with the activated sludge. Depending on the mode of operation, the phosphate can also be "fished" with the help of microorganisms from the wastewater. In this case we speak of a biological phosphorus elimination, which is, however, still rarely used.

Chemical water purification also includes nitrogen elimination: it is used to remove nitrogen compounds that are harmful to water, such as ammonia and ammonium, from waste water. Nitrogen compounds remove the vital oxygen from the water and can even cause fish to die when discharged into water bodies. Nitrogen is eliminated by nitrification and denitrification: During nitrification, ammonium is converted to nitrite with the addition of anaerobic bacteria and oxygen – and then to nitrate in a second stage. The subsequent denitrification is also triggered by the addition of anaerobic microorganisms. These decompose the nitrate to nitrogen gas via enzymatic activities, which then is returned to the atmosphere.

Deferrisation: To reduce the iron content of the wastewater to the prescribed value, iron (II) cations are oxidised by the addition of oxygen. To trigger the oxidation process, caustic soda must also be added to the wastewater.

Manganese removal: Manganese is usually present in wastewater as manganese hydrogen carbonate. The addition of oxygen forms poorly-soluble manganese IV compounds, which can be easily removed from the water.

1.    Energy Production and Conservation. Energy and water consumption has always had challenges finding an adequate balance between the two. But it’s still completely possible. Currently, energy use at a water or wastewater facility can be 30 to 50 percent of the site’s total energy consumption. Technology has expanded in order to find other alternative energy consumption routes, as well as ways to utilize less energy overall.

2.    Nutrient Management. Thanks to changing regulations and increasingly strict limits have brought nutrient management to light as a major topic within the water and wastewater treatment industries.

3. Residuals and Biosolids. Removing toxic waste from water has always been a challenge for the water and wastewater industries, accounting for more than 50 percent of treatment costs. But if the waste is claimed, cleaned and reused, there could be additional revenue to be made.
4. Water Reclamation and Reuse. Reusing treated wastewater has become a huge trend within the industry lately, working for both drinking water and other water purposes. Water shortages across the country have made been a huge burden that reusing treated wastewater has been able to fill. The pressure to use less water overall has led to the consistent use of reusable wastewater.
5. Water Supply and Water Management. When water is scarce due to the geographic location of an area, water supply and water management must be heavily considered. It’s imperative to find out how much water is available and where it’s located, as well as where it’s coming from. Water management is essential because someone has to balance the use between industrial water and consumer water.
6. Stormwater, Green Infrastructure, and Wet Weather Management. Stormwater management has been on the eyes of both the water and wastewater industry lately. Heavy wet-weather events are often hazardous to the rain systems put in place, which is why it’s important to find a place for all of that extra water to go without harming any nearby communities. Green infrastructure solutions and growing regulations are some of the solutions to this problem.

WHY TREAT WASTEWATER?

Wastewater can contain chemical, biological or physical pollutants. This can make it unsafe for human uses. It can potentially cause severe illness if untreated wastewater gets into the public drinking supply. Most wastewater is usually released back into the environment after treatment.

WHAT TREATMENT PROCESSES ARE USED?

There are several steps you would normally take when treating wastewater in a municipal facility. According to NYC Environmental Protection, wastewater from New York City goes through five distinct processes that include preliminary, primary and secondary treatments, as well as disinfection and sludge treatment. Most treatment facilities employ similar steps or combine steps when treating wastewater.

1. PRELIMINARY/PRIMARY

Many communities have a waste water treatment plant that incorporates a series of processes to remove pollutants from water used in homes, small businesses, industries, and other facilities. All waste water first goes through the primary treatment process, which involves screening and settling out large particles.

Preliminary treatment normally includes screening the water to remove large objects and debris. Wastewater pretreatment can include everything from twigs and rocks to bottles and diapers. For industrial users, nation pollutant discharge elimination system (NPDES) sets wastewater pretreatment standards that are more strict.

2. SECONDARY

The waste water then moves on to the secondary treatment process, during which organic matter is removed by allowing bacteria to breakdown the pollutants. The treated waste water is then usually disinfected with chlorine to remove the remaining bacteria.

This is where your treatment options begin to diverge. Coagulation, along with flocculation, are methods that require a combination of chemicals. These processes cause particles to stick together so at a later point they can be more easily filtered out. Aluminum sulfate is a chemical often used in this process. After these insoluble fragments settle at the bottom through sedimentation, the purified water is filtered out. Filtration involves using a variety of filters to catch particles as the water flows through.

More about the primary and secondary treatment of wastewater here.

 

 

3. DISINFECTION

This is sometimes referred to as the tertiary treatment phase. Chlorine and chloramines are chemicals often used during the water treatment disinfection process. UV radiation is also sometimes used to disinfect water.

4. SLUDGE TREATMENT

The final stage of treating water will often include removing a sludge that is sometimes referred to as biosolids. According to Water Use it Wisely, the byproduct of sludge dewatering systems is sometimes used for agricultural purposes.

 

WHAT TREATMENT METHODS ARE BEST?

The previous section details the processes involved in treating wastewater. Biotech articles states that the specific methods used generally fall into three categories.

BIOLOGICAL

Biological methods are normally put in place when the water will be used for drinking purposes. Aerobic treatment and fermentation are both biological methods.

PHYSICAL

Physical methods include sedimentation, aeration and filtration. Sand filters are sometimes used in the oil water separation process to remove oil and grease particles.

CHEMICAL

Chlorine is the chemical most often used in treating sewage and other types of wastewater. The process is called chlorination. This is the most effective means of destroying a variety of viruses and bacteria. A method known as neutralization is effective when treating industrial wastewater. Lime is sometimes used when treating acidic water.

What treatment solutions you’ll need will likely be determined by the type of wastewater, what contaminants are in the water and what the water will be used for after it’s treated. The best methods for treating wastewater should always coincide with regulations required in the state and locality where your facility is located. The methods used should also be as environmentally safe as possible.

FUTURE WATER TREATMENT METHODS

Water treatment is a critical foundation of society. By expanding access to clean drinking water, safe water for home use and recycled water for agricultural purposes, water treatment improves the quality of life and security of millions of Americans each year. As technology has become more advanced, several unique and promising water treatment methods have begun to emerge, from systems for drought conditions to devices for hiking.

1. DESALINIZATION

2. SONO ARSENIC FILTERING

3. LIFESTRAW

4. MEMBRANE FILTRATION TECHNOLOGY

5. ULTRAVIOLET IRRADIATION TECHNOLOGY

Water treatment is a complex and critical service that has historically been expensive and time-consuming. Luckily, these five promising technologies have the potential to make clean drinking water much more accessible to communities around the world in the coming years.

Stage One — Bar Screening

Removal of large items from the influent to prevent damage to the facility’s pumps, valves and other equipment.
The process of treating and reclaiming water from wastewater (any water that has been used in homes, such as flushing toilets, washing dishes, or bathing, and some water from industrial use and storm sewers) starts with the expectation that after it is treated it will be clean enough to reenter the environment.

The quality of the water is dictated by the Environmental Protection Agency (EPA) and the Clean Water Act, and wastewater facilities operate to specified permits by National Pollutant Discharge Elimination System (NPDES). According to the EPA, The Clean Water Act (CWA) establishes the basic structure for regulating discharges of pollutants into the waters of the United States and regulating quality standards for surface waters. Under the CWA, EPA sets wastewater standards for industry. The EPA has also developed national water quality criteria recommendations for pollutants in surface waters. EPA's National Pollutant Discharge Elimination System (NPDES) permit program controls discharges.

As an example of expected standards, the Biochemical Oxygen Demand (BOD) of average wastewater effluent is 200 mg/L and the effluent after treatment is expected to be >30 mg/L. It is crucial a wastewater facility meets these expectations or risk stiff penalty.

The physical process of wastewater treatment begins with screening out large items that have found their way into the sewer system, and if not removed, can damage pumps and impede water flow. A bar screen is usually used to remove large items from the influent and ultimately taken to a landfill.

Stage Two — Screening

Removal of grit by flowing the influent over/through a grit chamber.
Fine grit that finds its way into the influent needs to be removed to prevent the damage of pumps and equipment downstream (or impact water flow). Too small to be screened out, this grit needs to be removed from the grit chamber. There are several types of grit chambers (horizontal, aerated or vortex) which control the flow of water, allowing the heavier grit to fall to the bottom of the chamber; the water and organic material continue to flow to the next stage in the process. The grit is physically removed from the bottom of the chamber and discarded.

Stage Three — Primary Clarifier

Initial separation of solid organic matter from wastewater.
Solids known as organics/sludge sink to the bottom of the tank and are pumped to a sludge digestor or sludge processing area, dried and hauled away. Proper settling rates are a key indicator for how well the clarifier is operating. Adjusting flow rate into the clarifier can help the operator adjust the settling rates and efficiency.

After grit removal, the influent enters large primary clarifiers that separate out between 25% and 50% of the solids in the influent. These large clarifiers (75 feet in diameter, 7½ inches at the edges and 10½ feet in the center as an example) allow for the heavy solids to sink to the bottom and the cleaner influent to flow. The effectiveness of the primary clarification is a matter of appropriate water flow. If the water flow is too fast, the solids don’t have time to sink to the bottom resulting in negative impact on water quality downstream. If the water flow is too slow, it impacts the process up stream.

The solids that fall to the bottom of the clarifier are know as sludge and pumped out regularly to ensure it doesn’t impact the process of separation. The sludge is then discarded after any water is removed and commonly used as fertilizer.

Stage Four — Aeration

Air is pumped into the aeration tank/basin to encourage conversion of NH3 to NO3 and provide oxygen for bacteria to continue to propagate and grow.
Once converted to NO3, the bacteria remove/strip oxygen molecules from the nitrate molecules and the nitrogen (N) is given off as N2↑ (nitrogen gas).

At the heart of the wastewater treatment process is the encouragement and acceleration of the natural process of bacteria, breaking down organic material. This begins in the aeration tank. The primary function of the aeration tank is to pump oxygen into the tank to encourage the breakdown of any organic material (and the growth of the bacteria), as well as ensure there is enough time for the organic material to be broken down. Aeration can be accomplished with pumping and defusing air into the tank or through aggressive agitation that adds air to the water. This process is managed to offer the best conditions for bacterial growth. Oxygen gas [O2] levels below 2 ppm will kill off the bacteria, reducing efficiency of the plant. Dissolved oxygen monitoring at this stage of the plant is critical. Ammonia and nitrate measurements are common to measure how efficient the bacteria are in converting NH3 to N2↑.

A key parameter to measure in wastewater treatment is Biochemical Oxygen Demand (BOD). BOD is a surrogate indicator for the amount of organic material present and is used to determine the effectiveness of organic material breakdown. There are a number of other tests used to ensure optimal organic material breakdown (and BOD reduction) such as measuring pH, temperature, Dissolved Oxygen (DO), Total Suspended Solids (TSS), Hydraulic Retention Time (flow rate), Solids Retention Time (amount of time the bacteria is in the aeration chamber) and Mixed Liquor Suspended Solids. Ongoing and accurate monitoring is crucial to ensure the final required effluent BOD.

Stage Five — Secondary Clarifier

Treated wastewater is pumped into a secondary clarifier to allow any remaining organic sediment to settle out of treated water flow.
As the influent exits the aeration process, it flows into a secondary clarifier where, like the primary clarifier, any very small solids (or fines) sink to the bottom of the tank. These small solids are called activated sludge and consist mostly of active bacteria. Part of this activated sludge is returned to the aeration tank to increase the bacterial concentration, help in propagation, and accelerate the breakdown of organic material. The excess is discarded.

The water that flows from the secondary clarifier has substantially reduced organic material and should be approaching expected effluent specifications.


Stage Six — Chlorination (Disinfection)

Chlorine is added to kill any remaining bacteria in the contact chamber.
With the enhanced concentration of bacteria as part of the aeration stage, there is a need to test the outgoing effluent for bacteria presence or absence and to disinfect the water. This ensures that higher than specified concentrations of bacteria are not released into the environment. Chlorination is the most common and inexpensive type of disinfection but ozone and UV disinfection are also increasing in popularity. If chorine is used, it is important to test for free-chlorine levels to ensure they are acceptable levels before being released into the environment.


Stage Seven — Water Analysis & Testing

Testing for proper pH level, ammonia, nitrates, phosphates, dissolved oxygen, and residual chlorine levels to conform to the plant’s NPDES permit are critical to the plant’s performance.
Although testing is continuous throughout the wastewater treatment process to ensure optimal water flow, clarification and aeration, final testing is done to make sure the effluent leaving the plant meets permit specifications. Plants that don`t meet permit discharge levels are subject to fines and possible incarceration of the operator in charge.


Stage Eight — Effluent Disposal

After meeting all permit specifications, clean water is reintroduced into the environment.
Although testing is continuous throughout the wastewater treatment process to ensure optimal water flow, clarification and aeration, final testing is done to make sure the effluent leaving the plant meets permit specifications. Plants that don`t meet permit discharge levels are subject to fines and possible incarceration of the operator in charge.