Wastewater Evaporators

Chapter One – What is a Wastewater Evaporator?

A wastewater evaporator is a method of removing water from water-based waste by converting the water in the waste to a vapor and leaving contaminants. The function of a wastewater evaporator is to reduce the volume of waste materials.

The handling of wastewater is a highly sensitive business that is closely regulated with precise specifications. Wastewater evaporator manufacturers work closely with governmental agencies to assist in the removal of toxic industrial waste.

Chapter Two - How a Wastewater Evaporator Works

A wastewater evaporator uses thermodynamics and mass transfer to remove water from waste material. Thermodynamic wastewater evaporation involves heating the waste material sufficiently to turn water into a vapor using different sources of fuel.

Once the water has been changed to a vapor, it is mass transferred in droplets by a blower as unfiltered water vapor.

Wastewater evaporation has become an effective method for removing contaminants and concentrating liquid waste. It can remove salts, heavy metals, and hazardous materials. Wastewater evaporators have been found to be more efficient than solar evaporation ponds that take up large areas of land and work very slowly.

How a Wastewater Evaporator Works

Feed:

Wastewater is fed into the treatment tank from a holding tank in the amount necessary for the operation.

Feed Pump:

The feed pump moves the wastewater into the wastewater evaporator and can be activated by a toggle switch or using an auto fill system.

Heat:

The wastewater evaporation process depends on heated steam created by a heat exchanger, which increases vaporization and concentration. The heat in the evaporator creates a flat or even boil across the surface of the solution.

The temperature rises to a level for maximum concentration of the waste, at which time the evaporator signals that it needs to be emptied.

Blower:

The blower on a wastewater evaporator draws air into the evaporator tank to remove water vapors and assist in the heating process. The blower compartment on the unit below can be seen in the lower right corner.

Compressor:

Compressors are used to assist in the vaporization process and can be positive displacement, centrifugal, or axial. Wastewater evaporators that use a compressor need to have an outside steam source such as a boiler or heater in the feed tank.

Mist Eliminator:

The mist pad or eliminator removes contaminants from the process that may be in the form of oil or other possible substances. They are made from corrosion resistant materials and can be designed to be self-cleaning.

Heat Production in a Wastewater Evaporator

Gas:

The burner is ignited in the combustion chamber and sends hot gases to a chimney in the evaporator tank, which heats the wastewater to the boiling point.

Electric:

Units that use electricity have the heat exchanger located in the wastewater evaporator tank to create to heat the wastewater.

Oil:

Oil powered wastewater evaporators operate on the same principle as gas with oil being the fuel. The oil burns in a combustion chamber and moves through tubes in the heat exchanger from which they enter the chimney where they are combined with air to heat the evaporation tank.

Steam

Steam heats the coils for the heat exchanger. As it condenses, heat transfers to the wastewater and is discharged releases the vapors through the mist eliminator.

Chapter Three - Industrial Use of Wastewater Evaporators

One of the primary uses for wastewater evaporators is for removing oily waste from water used for parts washers. Removing oil from parts washer water is only one of the many uses for wastewater evaporators. They are widely used by a variety of industries from food processing to power generators.

Uses for Wastewater Evaporators

Metal Finishing:

There are several types of wastewater from metal finishing, which include tumbling, stamping, die casting, and polishing. Metal finishing wastewater contains difficult to treat chelating agents that need to be removed. To avoid chemically treating wastewater or filtering, some companies pay to have it hauled away, a very expensive solution. Though wastewater evaporators cannot completely solve the problem, they significantly reduce the cost of disposal.

Food industry:

There are several applications for wastewater evaporators in the food industry. Though wastewater from food production is non-toxic and biodegradable, it does contain biochemical oxygen demand and solids from the many foods that are processed. Vegetable washing and animal slaughter produce dissolved organic materials that need to be removed from water before it can be reused or discharged.

Pharmaceutical:

The pharmaceutical industry requires clean water because chemists need pure water in the production process. Regulating agencies set standards for the purity of water to be used when producing drugs. The contaminants produced from pharmaceutical production are hazardous and dangerous, which makes wastewater evaporation equipment a necessity.

Paint Production:

Water is a necessary part of the paint manufacturing process for water based paints and cooling of ball mills for the production of oil based paints. Wastewater from paint production contains high amounts of alkaline from cleaning and from cooling towers. The wastewater from paint production is small in volume but highly concentrated with pollutants.

Part Cleaning:

Parts cleaning is water-based and produces brownish gray and clear water that has a soapy appearance with settled solids and oil. Parts produced for automotive and other manufacturing applications are washed before being sent on to assembly. Water from the process contains pollutants that have to be removed.

Graphic Arts:

Wastewater from graphic arts is produced from offset and flexo plates, ink, and cylinder etchings.

Machine Coolant:

Machining coolants are used to cool tools and parts being fabricated overheat during processing. Coolants are water-soluble oils, water-soluble synthetics, and oil. In the normal process, coolant is constantly fed through the machine until it is no longer useful and needs to be cleaned. It is then fed into an evaporator to evaporate the water leaving metals and oil in the evaporator tank.

Landfill Leachate:

Landfills have dissolved organic and inorganic matter, heavy metals, and other organic compounds. The type of landfill and its age determines the amount of leachate, liquids that drain or leach in the landfill. The wastewater from landfills can have serious negative environmental effects and requires treatment. The treatment of leachate wastewater at one location may be totally different than at another one. Wastewater evaporators are perfect for this application since they can adapt to variations in the wastewater stream.

Chapter Four – Types of Wastewater Evaporators

The purpose of vaporization is to change a liquid to a vapor. Though vapor and gas may seem interchangeable, vapor is unlike gas because it begins as a liquid and is transformed into a vapor. When a liquid is changed to a vapor below its boiling point, the process is referred to as evaporation.

Factors that influence evaporation:

• Concentration in the air
• The concentration of other substances in the air
• Temperature
• Air flow rate – the higher the air flow, the greater the rate of evaporation
• Molecular forces – the stronger the force keeping molecules together, greater energy has to be applied.

Types of Wastewater Evaporation

Natural Wastewater Evaporation:

Water that is placed in an outdoor pond will naturally evaporate by solar heat and wind. Natural evaporation requires a great deal of space.

Forced Air Evaporator:

A forced air evaporator has a feed pump, evaporation tank with a heater, a circulation pump, blower, mixing tube, mist eliminator, and air outlet. Wastewater is pumped into the evaporator tank and is heated. Air and wastewater are mixed and pass to the evaporator tank where it goes through the mist eliminator and out the air outlet.

Boiler Blow Off Evaporator:

The boiler blow-off for evaporators is not used for collecting or removing suspended solids. In this method, solids are dissolved as vapor at 212o F and blown into the atmosphere.

Boiling Water in a Tank:

Boiling water evaporation consists of boiling water at its boiling point and exhausting the steam through an exhaust pipe. This method cannot remove dried solids.

Steam Tube Evaporator:

The concept of the steam tube evaporator is based on the same principle as the boiling tank evaporator. The difference between the methods is that heated exhaust gases are passed through the wastewater, which improves heat transfer.

Liquid Thermal Oxidation:

The liquid thermal oxidation method involves spraying liquid waste, under pressure, near a flame. At 1250o F, all volatile organic compounds (VOC) are oxidized and dissolved, while solids are oxidized to ash. Contaminants are changed to inorganic ash.

Heat Exchanger Evaporator:

In a heat exchanger, high temperature oil, that has been heated in an oil filled coil, is pumped to a coil inside the tank containing contaminated waste.

Vacuum Wastewater Evaporator:

Vacuum wastewater evaporators lower the pressure in the evaporation tank below the pressure in the atmosphere reducing the boiling point of the wastewater. The process removes the need for heat and can be used with liquids that have a high boiling point. Vacuum wastewater evaporators are a safe and efficient method of removing contaminants.

Leachate Wastewater Evaporator:

Leachate wastewater evaporators are designed to reduce leachate volume. They remove water from the leachate and drive off the cleaned vapors, while leaving sludge and solids behind.

Chapter Five – Benefits of Wastewater Evaporator Technology

Though there are several techniques for wastewater disposal, wastewater evaporators are slowly gaining popularity. Unlike chemical treatments and other processes, wastewater evaporators are environmentally friendly and can remove salts, heavy metals, and hazardous materials in the water purification process.

With the rise of technology, there has been an increase in the need for proper wastewater disposal due to the nature of water-mixed chemicals in creating highly technical instruments.

Benefits of Wastewater Evaporators

Energy Efficient:

Wastewater evaporators work on a 1:1 ratio where the amount of energy used to extract water is the same as the amount of water being extracted. This ratio can be improved by using multiple effects, such as taking the steam from one operation and using it for another.

Zero Liquid Discharge:

National, state, and local governments have regulations regarding the discharge of industrial wastewater that are upgraded regularly. Wastewater evaporators can achieve zero wastewater discharge to more than meet local and national regulations.

Total Dissolved Solids (TDS):

TDS refers to the parts per million or milligrams per liter of contaminants in water. Wastewater processed by an evaporator can produce less than 10 mg/L or as few as 2 mg/L. These levels allow the processed water to be reused and recycled to the manufacturing process.

Cost:

When compared to chemical precipitation systems, wastewater evaporators are far more efficient and cost effective. While a chemical treatment process can work at 395 Liters per minute (L/m), a wastewater evaporator can process 190 L/m.

Flexibility:

Every industry and wastewater site have different concerns and issues. What may work at one location may not apply to another. Wastewater evaporators can adapt to any conditions and can be programmed to handle any form of contaminants.

Volume of Waste:

The most significant benefit of a wastewater evaporator is its ability to reduce the volume of waste materials by removing the moisture from the materials. One of the issues that waste management operations are facing is the ever decreasing amount of area available for waste disposal. The elimination of water from waste greatly reduces its volume.

Inclusion

Added to the flexibility of a wastewater evaporation system is its ability to work independently or be added to an existing system. Its adaptability and being able to be engineered into existing processes saves on costs and improves the overall wastewater disposal process.

Comparison of Other Wastewater Disposal Methods

Natural Evaporation:

Natural evaporation has been used for many years as a means of evaporating water in ponds to leave hazardous materials behind. Though it is environmentally sound, the process takes very long and can contaminate the surrounding environment.

Sewage Discharge:

For many centuries, people simply threw dirty water into rivers and streams without realizing the consequences. As environmental concerns have grown, regulations have been enacted to strictly control the discharge of wastewater into sewers and public waters.

Removal to be Dumped:

This is still a viable option for removing waste products from industrial operations. It is simply a matter of sending waste to a landfill or regulated disposal site. The process is costly and avoids the fact that over 70% of waste contains water that could be removed to lower the volume of the waste.

Filtration:

Through the technical developments, more highly refined filters have been developed to remove the most minute particulates. Though it has become a viable system for purifying water, it is not always reliable and has to be closely monitored, which increases labor costs.

Reverse Osmosis (RO):

Reverse osmosis was one of the first methods for removing contaminants from water. The process involves forcing wastewater through a semi-permeable fabric. The process traps large particles and allows small ones to pass through. The problem with the RO process is what to do with the water that is left behind and unable to pass through the membrane.

Chemicals:

The use of chemicals to treat wastewater is over 70 years old and was one of the first methods used as a treatment method. As clean water regulations have grown, chemical treatment methods have become less and less useful since the process cannot safely remove a sufficient number of contaminants and leaves residual chemicals.

Evaporation:

Wastewater evaporation is simple, efficient, and cost effective. It takes little time to install and can immediately be put to use. Engineers from manufacturers take samples of a company’s wastewater and program wastewater evaporators to fit a specific application.

Chapter Six – Wastewater Evaporator Regulations

Requirements for wastewater evaporators are dependent on legislation regarding clean water. The first Clean Water Act (CWA) was passed in 1972 as the Federal Water Pollution Control Act to be administered by the Environmental Protection Agency (EPA).

The goal of the CWA is to eliminate untreated water discharge from cities and factories. The scope and oversight of the EPA has grown over the years to include more wastewater locations than those of cities and factories. It has come to encompass agriculture, logging, paper production, and fertilizers.

National Pollutant Discharge Elimination System (NPDES)

The NPDES is a department of the EPA and issues permits regarding the level of water purity from wastewater treatment facilities. A permit licenses a treatment system to discharge a regulated amount of pollutants under strictly controlled conditions.

Types of NPDES Permits

Individual: An individual permit has requirements that apply to a specific location or facility. The permit is issued after a study of the conditions and operations of the location and has a regulated timeline of less than five years, at which time it has to be renewed.

General: A general permit, which can be referred to as a group permit, applies to wastewater treatment operations in a geographical area. They are designed for companies that have several locations with wastewater treatment and avoids the need for a permit for each location.

For a state to oversee wastewater processes, it applies to the EPA through NPDES to receive authority to regulate wastewater management. To receive authorization, a state has to submit a report on its program for approval.

Several states have passed legislation with stipulations regarding wastewater processing, with some being more stringent than others.

Conclusion

• A wastewater evaporator is a method of removing water from water based waste by converting the water in the waste to a vapor and leaving contaminants.
• A wastewater evaporator uses thermodynamics and mass transfer to remove water from waste material.
• One of the primary uses for wastewater evaporators is for removing oily waste from water used for parts washers.
• Requirements for wastewater evaporators are dependent on legislation regarding clean water.