Industrial Wastewater Treatment Guide: Expanded Edition

Browse everything you ever wanted to know about industrial wastewater treatment (and more):

• What are industrial wastewater treatment systems?
• How do industrial wastewater treatment systems work?
• Contaminants wastewater treatment systems typically remove
• How to know if your industrial facility needs a wastewater treatment system
• How much do industrial wastewater treatment systems cost?
• Membrane filtration and industrial wastewater treatment
• Ion exchange and industrial wastewater treatment
• Biological technologies and industrial wastewater treatment
• Zero liquid discharge and industrial wastewater treatment
• Brine and industrial wastewater treatment 

What Are Industrial Wastewater Treatment Systems?  

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An industrial wastewater treatment system is a system made up of several individual technologies that address your specific wastewater treatment needs.

An efficient and well-designed wastewater treatment system should be able to handle:

• process variations in contamination and flow
• variations in water chemistry needs and required chemical volumes adjustments
• possible changes in water effluent requirements

The exact components of a industrial wastewater treatment system will depend on the wastewater characterization in relation to regulatory requirements for discharge from the plant, but in general, a basic wastewater treatment system typically includes some type of:

• clarifier to settle suspended solids that are present as a result of treatment
• chemical feed to help facilitate the precipitation, flocculation, or coagulation of any metals and suspended solids
• filtration to remove all the leftover trace amounts of suspended solids (again, the level of filtration needed will depend on the degree of suspended solids removal required to pass local discharge regulations)
• Final pH adjustment and any post treatment
• control panel (depending on the level of automated operation needed)

Depending on the needs of your plant and process, these standard components are usually adequate, however, if your plant requires a system that provides a bit more customization, there might be some features or technologies you will need to add on.

How Do Industrial Wastewater Treatment Systems Work? 

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Specific treatment processes vary, but a typical industrial wastewater treatment facility process will usually include one or more of the following steps:

• coagulation; a process where various chemicals are added to a reaction tank to remove the bulk suspended solids and other various contaminants
• flocculation; when coagulated particles are slowly stirred together with long-chain polymers, creating visible, settleable particlesthat resemble snowflakes
• sedimentation; a large circular device that promotes a very slow settling process creating sludge that is pumped out of the bottom into a handling or dewatering operation
• sand filtration; feed water is passed through, trapping the particles
• membrane filtration; can also be used after the clarifiers instead of the gravity sand filter, or it can replace entire clarification process altogether eliminating the entire clarifier/filtration train
• lime softening; raises the pH, causing hardness and metals in the water to precipitate out
• ion exchange softening; a strong acid cation exchange process whereby resin is charged with a sodium ion, and as the hardness comes through, it has a higher affinity for calcium, magnesium, and iron so it will grab that molecule and release the sodium molecule into the water
• disinfection; (or chlorination) kills the bacteria in the water
• distribution; the wastewater is either pumped into a holding tank where it can be used based on the demands of the facility or fed into a distribution system of water towers and various collection and distribution devices

Wastewater and effluent regulations differ everywhere you go, and these are some of the most common steps in a wastewater treatment plant. Typically, there are special process steps to treat for a specific issue, such as the removal of certain metals or organics, or to reduce TDS for recycling, etc. For these various problems specific to your individual needs, careful consideration must be given for the proper method of treatment.

Contaminants Wastewater Treatment Systems Typically Remove

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A wastewater treatment system might be made up of the technologies necessary to remove any number of the following:

• biochemical oxygen demand; or BOD, refers to the amount of dissolved oxygen needed by aerobic biological organisms to break down organic matter into smaller molecules
• nitrates and phosphates; in large amounts can lead to an increase BOD and extensive weed growth, algae, and phytoplankton, which causes eutrophication and environmental dead zones
• pathogens; bacteria, viruses, fungi, or any other microorganisms present in wastewater leading to all kinds of health issues, including acute sickness, severe digestive problems, or death
• metals; mostly found in wastewater as a result of various industries and manufacturing processes, when left in wastewater in high concentrations, metals can cause extensive damage to the environment and human health
• total suspended solids; (TSS) can decrease levels of oxygen in aquatic environments and kill off insects and also scale and foul piping and machinery
• total dissolved solids; (TDS) are any anions, cations, metals, minerals, or salts found in wastewater. They can cause issues with aquatic life, irrigation and crops, and they can also seep into groundwater. TDS can be generated in wastewater from just about any industry
• synthetic chemicals; when pesticides and other chemicals are used or made in the manufacturing process, they can be transmitted to humans and the environment through wastewater, causing damage to the environment and human health. Some common chemicals found in wastewater include diethylstilbestrol, dioxin, PCBs, DDT, and other pesticides

In a general sense, your facility will need to remove any contaminants that will harm your reuse or discharge regulations, which will vary based on your facility’s needs and who is doing the regulating.

How to Know If Your Industrial Facility Needs a Wastewater Treatment System

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Not properly treating wastewater can potentially harm the environment, human health, and a facility’s process or products (especially if the wastewater is being reused). It can also cause a company to incur heavy fines and possible legal action if wastewater is being improperly discharged into a POTW (publicly owned treatment works) or to the environment (usually under a National Pollutant Discharge Elimination System, or NPDES, permit). But how do you know if a facility really needs a wastewater treatment system? 

Your system needs will depend on three things:

1. Wastewater characterizations of the production facility

One of the major factors that will determine whether or not a facility requires a wastewater treatment system is what the wastewater characteristics of the facility are, or what kind of contaminants are present. Some of the major contaminant offenders include:

• heavy BOD, oils, and grease
• suspended solids and/or metals such as zinc, iron, lead, and nickel
• inorganic contaminants

If your facility has any of these, chances are it requires some type of wastewater treatment system. The presence of these contaminants can be problematic in a variety of ways and discharging these impurities is often strictly regulated.

2. Regulatory requirements for discharge from the plant

Regulations for your wastewater will vary depending on what your facility is doing with it. Three common scenarios include:

• releasing wastewater into the environment; if your facility plans to release your wastewater into the environment in the United States, you will need to do so under a National Pollutant Discharge Elimination System or NPDES permit and other local regulations
• discharging wastewater into the local municipality; your local municipality might take your effluent, but chances are they’ll want you to clean it first. Check with your local publicly owned treatment works (POTW) to be sure you’re meeting their qualifications
• reusing wastewater for your process; if you plan to reuse your wastewater for use in your production facility, such as for boiler feed or cooling tower water, then you’ll likely need to remove at least some of the contaminants. By doing so, you will avoid costly damage to your equipment and problematic issues such as organic growth, fouling, scaling, and corrosion.

3. Results of a treatability study and/or pilot test

A wastewater treatability study is a study or test that will determine how the wastewater can be treated for your process. If the study is done correctly, it will clearly identify the contaminants present in your wastewater stream, helping you decide if a system is necessary and ensuring the proper treatment solutions are considered and implemented in your wastewater treatment system. This streamlines the process and takes out any guesswork, ensuring your facility is considering the best possible solution for your unique situation.

How much do industrial wastewater treatment systems cost?

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Because wastewater treatment is a highly complex, custom solution, several factors go into choosing the right treatment options. So, what might you need for your plant and how much do they cost?

All in all, there are two main factors that drive the cost of a wastewater treatment system:

• What is the quality of the plant’s effluent (levels of contaminants) and what are the local maximum and average monthly discharge limits to the environment or POTW?
• What amount of water do you need to process per day and how fast? (This is your required peak gallons per minute, or GPM.)

If you can answer these questions, it will help you narrow down what your needs might be and provide a better sense of the budget you might be looking at. 

The quality of your effluent and the equipment needed to treat it

One of the largest factors that will determine the cost of your wastewater treatment system is the equipment that will go into the actual makeup of the system.

Here are some important questions to address:

• Does your plant process foods that leave you with wastewater heavy in BOD, oils, and grease?
• Does your process include the manufacturing of metals that contaminates the wastewater with suspended solids and metals such as zinc, iron, lead, and nickel?
• Do you see high levels of inorganic contaminants or need to remove BOD or COD (chemical oxygen demand)?

All these factors will determine what type of wastewater treatment system you need.

For example, if your plant runs a plating operation, some of the issues we often see are the need for pH stabilization, suspended solids, and metals removal.

Flow rates in relation to the capital cost of your system

In general, if your plant runs consistently at a lower flow rate, you’re usually looking at a lower capital cost for your wastewater treatment system.

If your plant generally runs a greater flow in a shorter amount of time, your capital cost is usually higher for equipment.

Flow rates are always factored into the wastewater treatment system cost, so be sure you measure this as efficiently as possible prior to requesting a quote in order to get an accurate cost estimate for your system. Typically, inlet buffering tanks are installed to minimize the peaks in flow and concentration of contaminants

Other factors

Other important factors to consider when pricing a wastewater treatment system include:

• up-front planning; the cost of engineering for this type of project can typically run 10–15% of the cost of the entire project and is usually phased in over the course of the project, with most of your investment being allocated to the facility’s general arrangement, mechanical, electrical, and civil design
• space requirements; keep in mind that sometimes your plant location can affect the cost of your system. For example, if your plant is located in a place that is very expensive when it comes to space, you might want to aim for a smaller footprint, if possible
• installation rates; be aware of the cost to install the system and factor this into your budget. In areas where installation costs are high you may want to consider prepackaged modules versus build-in-place facilities
• level of system automation needed; choose between a higher level of automation where you won’t need an operator present for much of the time (which eliminates much of the human error), or a lower level of automation with less capital cost, but with added labor, this can end up costing you more in the long run
• turnkey and prepackaged systems; if you are able to order your wastewater treatment system prepackaged, this will typically save you about three months in construction time at about the same cost or less
• shipping the system to your plant; factor in about 5–10% of the cost of the equipment for freight. This can vary widely depending upon the time of year you are purchasing your system in addition to where your plant is located
• operation costs; particular technology packages cost a certain amount to purchase up front, but you need to also factor in system operating costs over time
• other possible costs and fees; keep in mind what other hidden costs and fees might be, for example taxes on the system or additional purchasing fees and utility costs or connection fees
• When it comes to treating your wastewater, even though the treatment option and costs can be complex, all in all, you are looking at a $500,000 to $1.5 million system at 150,000 GPD when you factor in all the needed equipment, engineering, design, installation, and startup.

 

Membrane Filtration and Industrial Wastewater Treatment

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As global demands for clean water increase, more and more industrial facilities are looking toward membrane filtration solutions, such as reverse osmosis, nanofiltration, microfiltration, or ultrafiltration to help manage wastewater treatment. Using membrane filtration can help your facility reuse wastewater and virtually eliminate discharge fees and can be much more efficient than some conventional treatments.

Since there are a variety of options that will depend on what industry the plant serves (oil and gas, petrochemical, food and beverage, etc.), along with which part of the process the filtration is needed and what contaminants need to be removed, this blog article breaks down what to consider when going through the process:

Reverse Osmosis (RO)

Reverse osmosis, also known as RO, is a membrane technology that uses a semipermeable medium to remove certain ions and particles from a liquid stream. RO removes contaminants based on their particle size and charge—generally anything that is 0.0001 µm or larger, including:

• bacteria
• calcium
• colloidal particles
• fluoride
• iron
• manganese
• organic material
• pyrogens
• salt
• viruses

Because of its filtration properties, RO is often used to:

• clean wastewater to acceptable effluent standards or for reuse
• concentrate solvents used in the food and beverage industry, such as whey
• create ultrapure process water streams, such as required in the microelectronics industry
• desalinate seawater or other brine solutions
• generate potable drinking water

RO is also the reverse process of osmosis, a phenomenon that occurs naturally when a lower-solute stream (with a higher-water concentration) migrates toward a higher-solute stream (with a lower-water concentration) through a semipermeable membrane to achieve concentrate equilibrium.

Nanofiltration (NF)

While RO and NF are both membrane technologies that uses a semipermeable medium to remove certain ions and particles from a liquid stream, they can be distinguished based on the size of particulates that each is able to remove. Comparatively, RO and NF are capable of removing finer contaminants than microfiltration and ultrafiltration, with applications including the removal of:

• hardness
• heavy metals
• nitrates
• organic macromolecules
• radionuclides
• sulfates
• total dissolved solids (TDS)

Nanofiltration, however, delivers slightly coarser filtration than RO, with the ability to remove particles as small as 0.002 to 0.005 μm in diameter, including pesticide compounds and organic macromolecules, while retaining minerals that RO would otherwise remove.

Nanofiltration membranes are capable of removing larger divalent ions such as calcium sulfate, while allowing smaller monovalent ions such as sodium chloride to pass through.

Because of its filtration properties, nanofiltration is often used to:

• concentrate and demineralize valuable byproducts, such as metals from wastewater
• generate potable drinking water
• remove nitrates
• remove pesticides from ground or surface water
• soften water

Microfiltration (MF)

MF membranes are available in pore sizes ranging from 0.1 to 10 μm. MF porosity is the highest in the membrane filtration family, with the result that MF membranes allow water, ions, dissolved organic material, small colloids, and viruses to pass through, while retaining larger contaminants such as:

• algae
• bacteria
• pathogenic protozoa, including Giardia lamblia and Crypotosporidium
• sediment, including sand, clay, and complex metals/particles

Ultrafiltration (UF)

UF membranes are available in pore sizes ranging from 0.001 to 0.1 μm. Owing to the smaller pore size of its membranes, UF removes a more comprehensive range of contaminants than MF does, while leaving behind ions and organic compounds of low molecular weight. UF is suited for removal of very fine particles, including:

• endotoxins
• plastics
• proteins
• silica
• silt
• smog
• viruses

Ion Exchange and Industrial Wastewater Treatment

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Ion exchange (IX) systems are used across a variety of industries for water softening, purification, and separation purposes. While the chemistry of individual ion exchange reactions varies from one application to the next, IX is a treatment process where dissolved ions are replaced by other, more desirable, ions of a similar electrical charge.

It is often an important solution for wastewater treatment because of the selectivity of its process. Below, we describe what ion exchange systems are, how they work, and why they’re important to wastewater treatment systems.

What is an ion exchange system?

IX systems separate ionic contaminants from solution through a physical-chemical process where undesirable ions are replaced by other ions of the same electrical charge. This reaction occurs in an IX column or vessel where a process or waste stream is passed through a specialized resin that facilitates the exchange of ions.

A common example is a water softening IX system, where the goal is to remove scale-forming calcium or magnesium ions from solution. When the solution is passed through an IX resin composed of concentrated sodium ions, the calcium and magnesium ions are effectively captured from solution and held by the resin, while the sodium ions are released from the resin into the effluent stream.

What’s included in a basic ion exchange system?

A well-designed IX system conforms to the conditions of a specific application in both physical design specifications and in the chosen IX resin material. Common components of a basic IX vessel include:

• IX resin
• Inlet distribution system
• Regenerant distribution system
• Retention elements
• PLC, control valves and piping

IX resins are the most critical factor in IX system design. The substances present in the feed stream, as well as other process conditions, will determine the geometric shape, size, and material used in the IX resin.

How does ion exchange work?

By definition, ions are charged atoms or molecules. When an ionic substance is dissolved in water, its molecules dissociate into cations (positively charged particles) and anions (negatively charged particles). Taking advantage of this characteristic, IX selectively replaces ionic substances based on their electrical charges. This is accomplished by passing an ionic solution through an IX resin that serves as a matrix where the ion exchange reaction is allowed to take place.

Most commonly, IX resins take the form of tiny, porous microbeads, though they are sometimes available as a sheet-like membrane. IX resins are fashioned from organic polymers, such as polystyrene, which form a network of hydrocarbons that electrostatically bind a large number of ionizable groups. As the process or waste stream flows through the IX resin, the loosely held ions on the surface of the resin are replaced by ions with a higher affinity for the resin material.

Over time, the resin becomes saturated with the contaminant ions, and it must be regenerated or recharged. This is accomplished by flushing the resin with a regenerant solution. Typically consisting of a concentrated salt, acid, or caustic solution, the regenerant reverses the IX reaction by replenishing the cations or anions on the resin surface, and releasing the contaminant ions into the wastewater.

What contaminants do ion exchange systems remove?

The most common application of IX is sodium zeolite softening, though other popular applications include high-purity water production, dealkalization, and metals removal. IX can be an extremely effective strategy for removal of dissolved contaminants, though IX resins must be carefully chosen based on the substances present in the feed stream, as listed below.

Cationic resins

Cation exchangers can be classified as either strong acid cation (SAC) resins or weak acid cation (WAC) resins, both of which are extensively used for demineralization. SAC resins are also commonly used for softening, while WAC resins are used for dealkalization applications.

Contaminants removed by cation resins typically include:

• Calcium (Ca²⁺)
• Chromium (Cr³⁺ and Cr⁶⁺)
• Iron (Fe³⁺)
• Magnesium (Mg²⁺)
• Manganese (Mn²⁺)
• Radium (Ra²⁺)
• Sodium (Na⁺)
• Strontium (Sr²⁺) 

Anionic resins

Anion exchangers can be classified as either strong base anion (SBA) resins or weak base anion (WBA) resins. SBA resins are frequently used for demineralization, while WBA resins are often used for acid absorption. Contaminants removed by anion resins typically include:

• Arsenic
• Carbonates (CO₃)
• Chlorides (Cl^–)
• Cyanide (CN^–)
• Fluoride
• Nitrates (NO₃)
• Perchlorate (ClO_4-)
• Perfluorooctane sulfonate anion (PFOS)
• Perfluorooctanoic acid (PFOA)
• Silica (SiO₂)
• Sulfates (SO₄)
• Uranium

Specialty resins

While specialty IX resins are highly effective for specific industrial applications, their greater specificity generally means greater expense and narrower adoption than conventional IX resins. Chelating resins, for example, are used extensively for concentration and removal of metals in dilute solutions, such as Cobalt (Co²⁺) and Mercury (Hg and Hg²⁺). Similarly, magnetic ion exchange (MIEX) resins are often deployed for the removal of natural organic matter from feed water.

Biological Technologies and Industrial Wastewater Treatment

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For an industrial company producing waste as part of its process, some type of wastewater treatment system is usually necessary to ensure safety precautions and discharge regulations are met. The most appropriate wastewater treatment system will help a facility avoid harming the environment, human health, and a facility’s process or products (especially if the wastewater is being reused). It will also help the facility curb heavy fines if wastewater is being improperly discharged into a POTW (publicly owned treatment works) or to the environment (usually under a NPDES, or National Pollutant Discharge Elimination System, permit).

Typically used as a secondary wastewater treatment method after the initial larger contaminants have been settled and/or filtered out, biological wastewater treatment systems can be efficient and economical technologies for breaking down and removing organic contaminants from heavily organic-laden wastes, such as those produced in the food and beverage, chemical manufacturing, oil and gas, and municipal industries.

But “what is a biological wastewater treatment system and how does it work?”

Since this subject can be extremely multifaceted and complex, this article will break down the basics as an overall introduction to some of the more common biological wastewater treatment methods used industrially today.

What is a biological wastewater treatment system?

In a simplified, top-level answer to this question, a biological wastewater treatment system is a technology that primarily uses bacteria, some protozoa, and possibly other specialty microbes to clean water. When these microorganisms break down organic pollutants for food, they stick together, which creates a flocculation effect allowing the organic matter to settle out of the solution. This produces an easier-to-manage sludge, which is then dewatered and disposed of as solid waste.

Typically broken out into three main categories, biological wastewater treatment can be:

1. aerobic, when microorganisms require oxygen to break down organic matter to carbon dioxide and microbial biomass
2. anaerobic, when microorganisms do not require oxygen to break down organic matter, often forming methane, carbon dioxide, and excess biomass
3. anoxic, when microorganisms use other molecules than oxygen for growth, such as for the removal of sulfate, nitrate, nitrite, selenate, and selenite

The organic contaminants these microorganisms decompose are often measured in biological oxygen demand, or BOD, which refers to the amount of dissolved oxygen needed by aerobic organisms to break down organic matter into smaller molecules. High levels of BOD indicate an elevated concentration of biodegradable material present in the wastewater and can be caused by the introduction of pollutants such as industrial discharges, domestic fecal wastes, or fertilizer runoff.

When pollutant levels are elevated, BOD can deplete the oxygen needed by other aquatic organisms to live, leading to algal blooms, fish kills, and harmful changes to the aquatic ecosystem where the wastewater is discharged. Because of this, many facilities are required to treat their wastes, perhaps biologically, prior to discharge—but it’s the level of organic and inorganic pollutants in relation to their discharge requirements that will dictate what specific unit operations a facility’s biological wastewater treatment system will need and how they are sequenced and operated.

In short, biological wastewater treatment systems optimize the naturally occurring process of microbial decomposition to break down industrial wastewater contaminants so that they, along with other unwanted materials, can be removed. They also often replace (and are sometimes used alongside) physical and chemical treatments, which can be among the pricier treatment alternatives.

How does a biological wastewater treatment system work?

Depending on the chemical makeup of the wastewater in relation to the effluent requirements, a biological wastewater treatment system might be composed of several different processes and numerous types of microorganisms. They will also require specific operational procedures that will vary depending on the environment needed to keep biomass growth rates optimal for the specific microbial populations. For example, it often is required to monitor and adjust aeration to maintain a consistent dissolved oxygen level to keep the system’s bacteria multiplying at the appropriate rate to meet discharge requirements.

In addition to dissolved oxygen, biological systems often need to be balanced for flow, load, pH, temperature, and nutrients. Balancing a combination of system factors is where the biological treatment process can become very complex. Below are examples of some common types of biological wastewater treatment systems, including a brief description of how they function within an industrial wastewater treatment regimen to give you an idea of the types of technologies and systems that might benefit your industrial facility.

Aerobic wastewater treatment technologies

Activated sludge was first developed in the early 1900s in England and has become the conventional biological treatment process widely used in municipal applications but can also be used in other industrial applications. Wastewaters from the primary treatment phase enter an aeration tank where it is aerated in the presence of suspended (freely floating) aerobic microorganisms. The organic material is broken down and consumed, forming biological solids that flocculate into larger clumps, or flocs. The suspended flocs enter a settling tank and are removed from the wastewater by sedimentation. Recycling of settled solids to the aeration tank controls levels of suspended solids, while excess solids are wasted as sludge. Activated sludge treatment systems typically have larger space requirements and generate large amounts of sludge, with associated disposal costs, but capital and maintenance costs are relatively low, compared to other options.

Fixed-bed bioreactors, or FBBRs, developed as forced-air industrial treatment systems in the 1970s and 80s, consist of multiple-chambered tanks in which the chambers are packed tight with porous ceramic, porous foam, and/or plastic media; the wastewater passes through the immobilized bed of media. Of all biological treatment systems, FBBRs can hold the most contaminant-eating microbes in the smallest volume, which makes FBBRs space-saving and energy-efficient technologies ideal for treating wastewaters from medium to medium-high BOD feed levels down to very low effluent levels. The media is engineered to have a high enough surface area to encourage a robust biofilm formation with long solids lifespan, resulting in low sludge formation and lowest sludge disposal costs. A well-engineered fixed-bed will allow wastewater to flow through the system without channeling or plugging. Chambers can be aerobic and still have anoxic zones to achieve aerobic carbonaceous removal and full anoxic denitrification at the same time. More advanced biological processes can be facilitated with these systems (for example, nitrification, denitrification, deselenation, sulfide-reduction, and anammox), by having unique bacterial populations colonize the biofilm media in separate tank chambers, which can be uniquely configured to treat your facility’s specific wastewater constituents.

Moving bed bioreactors, or MBBRs, invented in the late 1980s in Norway, already has been applied in over 800 applications in more than 50 countries, with approximately half treating domestic wastewater and half treating industrial wastewater. MBBRs typically consist of aeration tanks filled with small moving polyethylene biofilm carriers held within the vessel by media retention sieves. Today the plastic biofilm carriers come from many vendors in many sizes and shapes, are typically half- to one-inch diameter cylinders or cubes and are designed to be suspended with their immobilized biofilm throughout the bioreactor by aeration or mechanical mixing.

Because of the suspended moving bio-film carriers, MBBRs allow high BOD wastewaters to be treated in a smaller area with no plugging. MBBRs are typically followed by a secondary clarifier, but no sludge is recycled to the process; excess sludge settles, and a slurry removed by vacuum truck, or settled solids are filter pressed and disposed as solid waste.

MBBRs are often used to remove the bulk of BOD load upstream of other biological treatment processes or used in situations where effluent quality is less important; they are not used for polishing BOD to low effluent levels. They are used for treating wastewaters produced in food and beverage facilities, meat processing and packing plants, petrochemical facilities, and refineries.

Membrane bioreactors, or MBRs, came into common use in the 1990s once membrane modules were submerged directly in the aeration tank, and air scour was implemented to keep the membranes from fouling. MBRs are advanced biological wastewater treatment technologies that combine conventional suspended-growth activated sludge with membrane filtration, rather than sedimentation, to separate and recycle the suspended solids. As a result, MBRs operate with much higher mixed-liquor suspended solids (MLSS) and longer solids residence times (SRTs), producing a significantly smaller footprint with a much higher quality effluent compared to conventional activated sludge.

MBRs primarily target BOD and total suspended solids (TSS). MBR system design varies depending on the nature of the wastewater and the treatment goals, but a typical MBR might consist of aerobic (or anaerobic) treatment tanks, an aeration system, mixers, a membrane tank, a clean-in-place system, and either a hollow fiber or flat sheet ultrafiltration membrane. As a result of its many parts and cleaning processes, MBRs are known for high capital, high operating, and high maintenance costs.

Biological trickling filters are used to remove organic contaminants from both air and wastewater. They work by passing air or water through a media designed to collect a biofilm on its surfaces. The biofilm may be composed of both aerobic and anaerobic bacteria that breakdown organic contaminants in water or air. Some of the media used for these systems include gravel, sand, foam, and ceramic materials. The most popular application of this technology is municipal wastewater treatment and air remediation to remove H2S at municipal sewer plants, but they can be used in many situations where odor control is important.

Anaerobic Wastewater Treatment Technologies

Upflow anaerobic sludge blankets, or UASBs, use anaerobic bacteria to, as mentioned in the intro of this article, breakdown organics without the use of oxygen, resulting in combustible methane-bearing biogas, treated effluent, and anaerobic sludge. With UASB systems, the general idea is that wastewaters are pumped into the base of the system, where the organics in the wastewater flow through a blanket of sludge before entering the upper gas-liquid-solids (GLS) separator, where collection hoods capture the biogas while allowing the suspended solids to settle and return to the lower reaction zone, while the cleaned effluent overflows out of the top of the system. The biogas (methane and carbon dioxide) is either flared or used to generate steam or electricity for use in other processes at the facility.

The UASB process creates less sludge than aerobic biosystems and therefore needs to be cleaned out and emptied less than other biological treatment systems, but they require skilled operators to maintain optimal hydraulic and anaerobic conditions for UASBs to operate properly. Expanded granular sludge beds, or EGSBs, are a similar process, but EGSBs use a stronger upward force to encourage more wastewater-to-sludge contact.

Anaerobic digesters also use anaerobic bacteria to break down organic waste without oxygen and produce biogas, mostly for sewage treatment, and there are a variety of anaerobic digesters available. They each perform the same process in slightly different ways. Examples include covered lagoons, fixed-film, suspended and submerged media, and continuous stirred tank reactors.

Zero liquid discharge and industrial wastewater treatment

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Not every industrial facility that produces wastewater will require zero liquid discharge (ZLD). It is usually looked to as a last resort because it can be a complex process that requires a high initial investment.

If a facility is located on a site that has severe water scarcity issues and/or astronomical discharge fees, it might be worthwhile to pursue, but in the instances it’s not mandated (some local and/or federal regulations might require ZLD), careful consideration must be made as to whether or not it will benefit your facility.

What is a zero liquid discharge treatment system?

A ZLD treatment system utilizes advanced technological water treatment processes to limit liquid waste at the end of your industrial process to, as the name suggests, zero.

An efficient and well-designed ZLD treatment system should be able to:

• handle variations in waste contamination and flow
• allow for required chemical volumes adjustments
• recover around 95% of your liquid waste for reuse
• treat and retrieve valuable byproducts from your waste (i.e. salts and brines)
• produce a dry, solid cake for disposal

A ZLD treatment system will also help your facility meet stringent effluent requirements, such as the U.S. Environmental Protection Agency’s Steam Electric Power Generating Effluent Guidelines. Just keep in mind your facility’s requirements will vary based on whether you are discharging into a publicly owned treatment works (POTW) or to the environment under a National Pollutant Discharge Elimination System (NPDES permit).

What’s included in a basic ZLD treatment system?

The exact components of a ZLD treatment system will largely depend on (1.) the volume of dissolved material present in the waste, (2.) the system’s required flow rate, and (3.) what specific contaminants are present. But in general, a basic ZLD treatment system typically includes some type of:

• clarifier and/or reactor to precipitate out metals, hardness, and silica
• chemical feed to help facilitate the precipitation, flocculation, or coagulation of any metals and suspended solids
• filter press to concentrate secondary solid waste after pretreatment or alongside an evaporator
• ultrafiltration (UF) to remove all the leftover trace amounts of suspended solids and prevent fouling, scaling, and/or corrosion down the line of treatment
• reverse osmosis (RO) to remove the bulk of dissolved solids from the water stream in the primary phases of concentration
• brine concentrators to further concentrate the reject RO stream or reject from electrodialysis to further reduce waste volume
• evaporator for vaporizing access water in the final phases of waste concentration before crystallizer.
• crystallizer to boil off any remaining liquid, leaving you with a dry, solid cake for disposal

Depending on the needs of your plant and process, these standard components are usually adequate, however, if your plant requires a system that provides a bit more customization, there might be some features or technologies you will need to add on. Because of the broad range of industries that use ZLD and the various waste streams produced, ZLD is a highly custom process and these add ons will depend on your facility’s individual needs.

How does a ZLD treatment system work?

Specific treatment processes vary, but a typical ZLD treatment facility process will usually include the following steps:

Pretreatment and conditioning 

Pretreatment is used to remove simple things from the wastewater stream that can be filtered or precipitated out, conditioning the water and reducing the suspended solids and materials that would otherwise scale and/or foul following treatment steps.

Typically this treatment block consists of some type of clarifier and/or a reactor to precipitate out metals, hardness, and silica. Sometimes this step requires the addition of caustic soda or lime to help with coagulation, a process where various chemicals are added to a reaction tank to remove the bulk suspended solids and other various contaminants. This process starts off with an assortment of mixing reactors, typically one or two reactors that add specific chemicals to take out all the finer particles in the water by combining them into heavier particles that settle out. The most widely used coagulates are aluminum-based such as alum and polyaluminum chloride.

Sometimes a slight pH adjustment will help coagulate the particles, as well.

When coagulation is complete, the water enters a flocculation chamber where the coagulated particles are slowly stirred together with long-chain polymers (charged molecules that grab all the colloidal and coagulated particles and pull them together), creating visible, settleable particles that resemble snowflakes.

The gravity settler (or sedimentation part of the ZLD treatment process) is typically a large circular device where flocculated material and water flow into the chamber and circulate from the center out. In a very slow settling process, the water rises to the top and overflows at the perimeter of the clarifier, allowing the solids to settle down to the bottom of the clarifier into a sludge blanket. The solids are then raked to the center of the clarifier into a cylindrical tube where a slow mixing takes place and the sludge is pumped out of the bottom into a sludge-handling or dewatering operation. The settlers can also be designed using a plate pack for smaller footprint.

Depending on the material in the feed, additional reactors or chemistry may be required for the reduction of metals or silica. Careful consideration must be given to the pretreatment step for a successful ZLD system.

Ultrafiltration (UF) can also be used after the clarifiers instead of the gravity sand filter, or it can replace entire clarification process altogether. Membranes have become the newest technology for treatment, pumping water directly from the wastewater source through the UF (post-chlorination) and eliminating the entire clarifier/filtration train.

Out of this process comes a liquid that is then filter-pressed into a solid, resulting in a solution much lower in suspended solids and without the ability to scale up concentration treatment.

Phase-one concentration 

Concentrating in the earlier stages of ZLD is usually done with membranes like reverse osmosis (RO), brine concentrators, or electrodialysis.

The RO train will capture the majority of dissolved solids that flow through the process, but as mentioned in a prior article about common problems with ZLD, it’s important to flow only pretreated water through the RO system, as allowing untreated water to go through the semipermeable membranes will foul them quickly. Brine concentrators, on the other hand, are also used to remove dissolved solid waste but they are usually able to handle brine with a much higher salt content than RO. They are pretty efficient for turning out a reduced-volume waste.

Electrodialysis can also be used at this part of the ZLD treatment system. It’s a membrane process that uses positively or negatively charged ions to allow charged particles to flow through a semipermeable membrane and can be used in stages to concentrate the brine. It is often used in conjunction with RO to yield extremely high recovery rates.

Combined, these technologies take this stream and concentrate it down to a high salinity while pulling out up to 60–80% of the water.

Evaporation/crystallization

After the concentration step is complete, the next step is generating a solid, which is done through thermal processes or evaporation, where you evaporate all the water off, collect it, and reuse it. Adding acid at this point will help to neutralize the solution so, when heating it, you can avoid scaling and harming the heat exchangers. Deaeration is often used at this phase to release dissolved oxygen, carbon dioxide, and other noncondensible gases.

The leftover waste then goes from an evaporator to a crystallizer, which continues to boil off all the water until all the impurities in the water crystallize and are filtered out as a solid.

Recycled water distribution/solid waste treatment

If the treated water is being reused in an industrial process, it’s typically pumped into a holding tank where it can be used based on the demands of the facility. The ZLD treatment system should have purified the water enough to be reused safely in your process.

The solid waste, at this point, will enter a dewatering process that takes all the water out of the sludge with filter or belt presses, yielding a solid cake. The sludge is put onto the press and runs between two belts that squeeze the water out, and the sludge is then put into a big hopper that goes to either a landfill or a place that reuses it. The water from this process is also typically reused.

Brine and industrial wastewater treatment

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If you’re new to handling brine waste and are looking for more information about properly treating it for recycling or discharging, you might be wondering “what is brine waste, and how can it be treated or disposed of?”

This section provides a general overview of what brine waste is, how it occurs or is made, and how it should be treated prior to use in production and/or discharge so you can better understand the proper way to handle these often-problematic streams.

What is brine waste?

In general, “brine” is any solution with an extremely high concentration of salts such as sodium chloride, which can occur either naturally (as with seawater, deep-water ocean pools, salt lakes, etc.) or as a byproduct of industry. These byproducts, or “brine waste” streams, are typically highly concentrated salt solutions that, in some cases, contain more than twice the amount of concentrated salts than natural brine solutions. Brine waste can also carry various contaminants, which differ depending on which process the brine waste is a byproduct of.

Brine waste streams can be some of the most challenging to treat or discharge because their composition and purification requirements can be rather dynamic and complex.

Some examples of brine waste created as a byproduct of industry include:

• cooling tower and boiler effluent
• reverse osmosis (RO) and ion exchange waste/reject streams
• produced water from extracting oil and natural gas
• chlor-alkali and chemical plant waste
• acid rock and mine drainage
• food preservation and manufacturing waste streams
• desalination waste from potable water creation
• irrigation runoff

Brine waste is typically either recycled for use in the facility’s process or treated for disposal. For example, solutions with a high concentration of salt are known to reduce thermal conductivity, so brine waste is often recycled and reused as a cooling agent for steel heat exchangers in many power plants. This type of brine is often treated to remove dissolved oxygen and other harmful contaminants since brine waste can be highly corrosive to plant machinery and piping if untreated, and the presence of dissolved oxygen and other contaminants can increase that risk.

Varying salt concentrations in the brine stream will also determine how the temperature, pressure, and other threshold limitations will need to be adjusted during production, so facilities that use brine as part of their process often run frequent tests to ensure the relevant purification requirements are consistently met. It’s an arduous process that often requires round-the-clock monitoring. For this reason, it’s extremely important to have your water treatment specialist evaluate what the brine is being used for in addition to where and how it is being recycled and/or discharged to ensure its composition remains appropriate for the process or disposal at hand.

Recycling brine waste for reuse 

As mentioned earlier in the article, many industrial processes require brine in part of their process, such as hydrometallurgy, sodium hypochlorite, lithium carbonate, and chlor-alkali manufacturing plants, to name a few. Some facilities even use leftover brine for irrigation or deicing.

Regardless what your facility is using the recycled brine waste for, keep in mind that brine leftover from production often accumulates contaminants along the way, such as:

• silica
• heavy metals
• hardness
• organic compounds
• sulfates, nitrates, and phosphates
• suspended solids

The brine waste can be pretreated with coagulants, polymers, additives, and pH adjustment to settle out many of the larger contaminants, including metals, sulfates, and other suspended solids that can foul membranes and cells down the production line. Other contaminants, such as calcium, can scale equipment, so depending on the manufacturing process and brine requirements, there are several membrane and ion exchange technologies that can prevent these issues and produce a useful brine stream adequate for your process.

For example, if a chlor-alkali plant is looking to reuse brine waste that is contaminated with metals like iron, vanadium, or manganese, they will often have trouble with the fouling of downstream equipment, which can often lead to unscheduled plant downtime and other delays. The brine stream might be treated with specialty chelating resins that target specific metals for removal without being exhausted by sodium, thereby removing the unwanted contaminants while preserving the salt concentration in the brine solution.

When it comes to facilities that produce lithium carbonate or lithium hydroxide, specialty ion exchange resins can be used to remove unwanted metals and other contaminants, and the brine stream can then be further treated with high-pressure membranes that can separate out and concentrate the lithium carbonate and lithium hydroxide, so the technologies and methods of purification and/or separation vary greatly depending on the quality of the brine waste and the brine composition required for production.

Treating brine waste for discharge

Most brines are technically considered nontoxic, but industrial brine waste released in heavy concentrations to the environment or to local publicly owned treatment works (POTW) can cause an assortment of issues if untreated. For example, if the waste contains more than just sodium, it can possibly harm aquatic life in local waterways. In some cases, simply diluting the brine waste prior to discharging might be a practical solution. It can also be against discharge regulations, which can cause your facility to pay a heavy fine.

Most discharge regulations will require a reduction in the amount of sodium, total suspended solids, and contaminants in general, which can often be treated with membrane technology such as ultrafiltration followed by reverse osmosis. Because of the high concentration of salt in brine, pretreatment is often used to help protect downstream filtration units and equipment.

Another option for treating brine waste is evaporation. This can be done in an outdoor evaporation pond or with a technique called vacuum evaporation. By evaporating the effluent under vacuum, the boiling point is reduced (thereby saving energy) and what’s left is a crystalized mass of salt and, separately, a purified water stream. This method can be useful for drying brine filtrates thoroughly, and it can be implemented in tandem with other treatments to boost effectiveness.

Whichever method your facility uses to treat its brine waste for discharge, make sure it is done so in compliance with the facility’s POTW or National Pollutant Discharge Elimination System permits.

Common technologies for treating brine waste

These are the technologies are commonly used to treat brine waste, which can vary depending on what contaminants are present and whether the facility is treating the brine for discharge or recycling and/or reusing in its process.

Membrane filtration

One of the more cost-effective technologies for treating brine waste, membrane filtration is still widely used across various industries. When treating brine, it’s common to see systems that begin with ultrafiltration (UF) and end with reverse osmosis (RO).

When UF is used prior to RO, it effectively removes various contaminants while protecting downstream membranes from premature wear and fouling. UF membranes are available in pore sizes ranging from 0.001 to 0.1 μm, which means UF removes a more comprehensive range of contaminants than some other membranes (such as microfiltration) while leaving behind ions and organic compounds of low molecular weight. UF is suited for removal of very fine particles, including proteins, colloidal silica, and silt.

The stream is then passed through an RO system, which is a membrane technology that uses a semipermeable medium to remove certain ions and particles from a liquid stream that are 0.0001 µm or larger, including salt. This produces a high-quality water stream in addition to a highly concentrated stream of waste, which can be used or discarded, depending on the needs of the facility.

This sequence of membrane treatment is effective for protecting equipment and minimizing chemical costs and system downtime for cleaning and is generally considered a low energy–consuming technology.

Evaporation and crystallization

After brine is concentrated by membrane filtration, thermal processes or evaporation are often used as the next step to dry solids. Excess water is evaporated off, collected, and reused (adding acid at this point will help to neutralize the solution so, when heating it, you can avoid scaling and harming the heat exchangers). Deaeration is often used at this phase, as well, to release dissolved oxygen, carbon dioxide, and other noncondensible gases to further protect equipment from corrosion and other harmful occurrences.

The leftover waste then goes from an evaporator to a crystallizer, which continues to boil off all the water until all the impurities in the water crystallize and are filtered out as a solid. This process is often used in facilities that aim for zero liquid discharge, but it’s generally reserved for only facilities that require it (most likely due to stringent environmental and discharge regulations) as it is considered a costly and high energy–consuming process.

Ion exchange 

Ion exchange (IX) systems are used across a variety of industries for water softening, purification, and separation purposes. These systems separate ionic contaminants from solution through a physical-chemical process where undesirable ions are replaced by other ions of the same electrical charge. This reaction occurs in an IX column or vessel where a process or waste stream is passed through a specialized resin that facilitates the exchange of ions.

When contaminant removal needs are highly specific, many times IX is ideal. Chelating resins are the most common type of specialty resin and are often used for brine softening.

Weak acid cation (WAC) exchange resins are also often used to remove cations associated with alkalinity (temporary hardness) and are therefore also ideal for softening brine. Facilities can also use various proprietary resins to separate contaminants, such as metals, from the brine stream to support production and manufacturing of lithium carbonate and lithium hydroxide.

Electrodialysis is also a form of ion exchange that can be used in the brine treatment system. It’s a membrane process that uses positively or negatively charged ions to allow charged particles to flow through a semipermeable membrane and can be used in stages to concentrate the brine. It is often used in conjunction with RO to yield extremely high recovery rates. Combined, these technologies can concentrate a brine stream down to a high salinity while pulling out up to 60–80% of the water.

Other things to consider when treating brine waste

As mentioned previously, when looking at basic separation for a contaminated brine stream, you will always be left, essentially, with a more purified brine (such as a sodium chloride stream). The cost to treat a brine stream like this can be relatively low and would include treatments such as:

• membrane filtration
• precipitation
• carbon adsorption of organics
• oil and water separation

Using IX, the facility can take out easy-to-remove contaminants, which might leave you with something like a sodium chloride or brine sulfate brine stream, which is a salt stream that doesn’t easily precipitate.

These technologies are relatively low cost compared to removing the salt directly out of the brine (such as with sodium chloride or sodium nitrate). In these instances, it’s very difficult to remove the salts and almost always involve high-pressure membrane systems to concentrate the brines (pulling the water out of the brine).

In situations where membrane filtration won’t be effective, evaporation and crystallization will help remove the water from the brine, but such thermal polishing processes are exponentially more expensive when it comes to purchasing the relative technology in addition to high operational and energy usage costs.

Essentially, by trying to solve one problem your facility can easily create another.

The only true ways to dispose of brine are to reuse it or dilute and slowly release it back into the environment. For example, if you have a very large river near your facility that is available of discharging your treated brine, you can slowly bleed the brine in, dissolving it back into the body of water with a minimal impact to the river. If you have a smaller stream, your facility will not be able to do this; doing so could pose catastrophic harm to the environment, killing off fish and other wildlife in the surrounding areas. In some areas, where permitted, waste brines can be deep-well injected although this option is becoming more restricted.

Facilities can reuse brine, but recycling it will concentrate it more, which would leave you discharging a smaller stream with a higher concentrate of salt and TDS.

As always, it is usually best to discuss any treatment options with a water-treatment professional who is able to analyze your facility’s needs, specifically, and help you determine the best treatment options, as they can be highly individual.