Industrial wastewater treatment describes the processes used fortreating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater (or effluent) may be reused or released to asanitary sewer or to asurface water in the environment. Some industrial facilities generate wastewater that can be treated insewage treatment plants. Most industrial processes, such aspetroleum refineries, chemical andpetrochemical plants have their own specialized facilities to treat their wastewaters so that the pollutant concentrations in the treated wastewater comply with the regulations regarding disposal of wastewaters intosewers or into rivers, lakes oroceans.[1]: 1412 This applies to industries that generate wastewater with high concentrations of organic matter (e.g. oil andgrease), toxic pollutants (e.g. heavy metals,volatile organic compounds) or nutrients such asammonia.[2]: 180 Some industries install a pre-treatment system to remove some pollutants (e.g., toxic compounds), and then discharge the partially treated wastewater to the municipal sewer system.[3]: 60
Most industries produce somewastewater. Recent trends have been to minimize such production or to recycle treated wastewater within the production process. Some industries have been successful at redesigning their manufacturing processes to reduce or eliminate pollutants.[4] Sources of industrial wastewater include battery manufacturing, chemical manufacturing, electric power plants,food industry, iron and steel industry, metal working, mines and quarries, nuclear industry,oil and gas extraction,petroleum refining andpetrochemicals, pharmaceutical manufacturing,pulp and paper industry, smelters,textile mills, industrialoil contamination, water treatment andwood preserving. Treatment processes include brine treatment, solids removal (e.g. chemical precipitation, filtration), oils and grease removal, removal of biodegradable organics, removal of other organics, removal of acids and alkalis, and removal of toxic materials.
Industrial facilities may generate the following industrial wastewater flows:[citation needed]
Industrial wastewater could add the following pollutants to receiving water bodies if the wastewater is not treated and managed properly:
The specific pollutants generated and the resultant effluent concentrations can vary widely among the industrial sectors.[citation needed]
Battery manufacturers specialize in fabricating small devices for electronics and portable equipment (e.g., power tools), or larger, high-powered units for cars, trucks and other motorized vehicles. Pollutants generated at manufacturing plants includes cadmium, chromium, cobalt, copper, cyanide, iron, lead, manganese, mercury, nickel, silver, zinc, oil and grease.[13]
A centralized waste treatment (CWT) facility processes liquid or solid industrial wastes generated by off-site manufacturing facilities. A manufacturer may send its wastes to a CWT plant, rather than perform treatment on site, due to constraints such as limited land availability, difficulty in designing and operating an on-site system, or limitations imposed by environmental regulations and permits. A manufacturer may determine that using a CWT is more cost-effective than treating the waste itself; this is often the case where the manufacturer is a small business.[14]
CWT plants often receive wastes from a wide variety of manufacturers, including chemical plants, metal fabrication and finishing; and used oil and petroleum products from various manufacturing sectors. The wastes may be classified ashazardous, have high pollutant concentrations or otherwise be difficult to treat. In 2000 theU.S. Environmental Protection Agency published wastewater regulations for CWT facilities in the US.[15]
The specific pollutants discharged byorganic chemical manufacturers vary widely from plant to plant, depending on the types of products manufactured, such as bulk organic chemicals, resins, pesticides, plastics, or synthetic fibers. Some of the organic compounds that may be discharged arebenzene,chloroform,naphthalene,phenols,toluene andvinyl chloride.Biochemical oxygen demand (BOD), which is a gross measurement of a range of organic pollutants, may be used to gauge the effectiveness of a biological wastewater treatment system, and is used as a regulatory parameter in some discharge permits. Metal pollutant discharges may includechromium,copper,lead,nickel andzinc.[16]
Theinorganic chemicals sector covers a wide variety of products and processes, although an individual plant may produce a narrow range of products and pollutants. Products include aluminum compounds; calcium carbide and calcium chloride; hydrofluoric acid; potassium compounds; borax; chrome and fluorine-based compounds; cadmium and zinc-based compounds. The pollutants discharged vary by product sector and individual plant, and may include arsenic, chlorine, cyanide, fluoride; and heavy metals such as chromium, copper, iron, lead, mercury, nickel and zinc.[17]
Fossil-fuel power stations, particularlycoal-fired plants, are a major source of industrial wastewater. Many of these plants discharge wastewater with significant levels of metals such aslead,mercury,cadmium andchromium, as well asarsenic,selenium andnitrogen compounds (nitrates andnitrites). Wastewater streams includeflue-gas desulfurization,fly ash,bottom ash andflue gas mercury control. Plants with air pollution controls such aswet scrubbers typically transfer the captured pollutants to the wastewater stream.[18]
Ash ponds, a type of surface impoundment, are a widely used treatment technology at coal-fired plants. These ponds use gravity tosettle out large particulates (measured astotal suspended solids) from power plant wastewater. This technology does not treat dissolved pollutants. Power stations use additional technologies to control pollutants, depending on the particular wastestream in the plant. These include dry ash handling, closed-loop ash recycling,chemical precipitation, biological treatment (such as anactivated sludge process), membrane systems, and evaporation-crystallization systems.[18] Technological advancements inion-exchange membranes andelectrodialysis systems has enabled high efficiency treatment offlue-gas desulfurization wastewater to meet recent EPA discharge limits.[19] The treatment approach is similar for other highly scaling industrial wastewaters.[citation needed]
Wastewater generated from agricultural andfood processing operations has distinctive characteristics that set it apart from common municipal wastewater managed by public or privatesewage treatment plants throughout the world: it isbiodegradable and non-toxic, but has high BOD andsuspended solids (SS).[20] The constituents of food and agriculture wastewater are often complex to predict, due to the differences in BOD andpH in effluents from vegetable, fruit, and meat products and due to the seasonal nature of food processing and post-harvesting.[citation needed]
Processing of food from raw materials requires large volumes of high grade water. Vegetable washing generates water with high loads ofparticulate matter and some dissolvedorganic matter. It may also contain surfactants and pesticides.
Aquaculture facilities (fish farms) often discharge large amounts of nitrogen and phosphorus, as well as suspended solids. Some facilities use drugs and pesticides, which may be present in the wastewater.[21]
Dairy processing plants generateconventional pollutants (BOD, SS).[22]
Animal slaughter and processing produces organic waste from body fluids, such asblood, andgut contents. Pollutants generated include BOD, SS,coliform bacteria, oil and grease,organic nitrogen andammonia.[23]
Processing food for sale produces wastes generated from cooking which are often rich in plant organic material and may also containsalt,flavourings,colouring material andacids oralkali. Large quantities of fats, oil and grease ("FOG") may also be present, which in sufficient concentrations can clog sewer lines. Some municipalities require restaurants and food processing businesses to usegrease interceptors and regulate the disposal of FOG in the sewer system.[24]
Food processing activities such as plant cleaning, material conveying, bottling, and product washing create wastewater. Many food processing facilities require on-site treatment before operational wastewater can be land applied or discharged to a waterway or a sewer system. High suspended solids levels of organic particles increase BOD and can result in significant sewer surcharge fees. Sedimentation, wedge wire screening, or rotating belt filtration (microscreening) are commonly used methods to reduce suspended organic solids loading prior to discharge.[citation needed]
Glass manufacturing wastes vary with the type of glass manufactured, which includesfiberglass,plate glass,rolled glass, and glass containers, among others. The wastewater discharged by glass plants may include ammonia, BOD,chemical oxygen demand (COD),fluoride, lead, oil, phenol, and/or phosphorus. The discharges may also be highly acidic (low pH) or alkaline (high pH).[25]
Theproduction of iron from its ores involves powerfulreduction reactions in blast furnaces. Cooling waters are inevitably contaminated with products especiallyammonia andcyanide. Production ofcoke from coal in coking plants also requireswater cooling and the use of water in by-products separation. Contamination of waste streams includes gasification products such asbenzene,naphthalene,anthracene, cyanide, ammonia,phenols,cresols together with a range of more complexorganic compounds known collectively aspolycyclic aromatic hydrocarbons (PAH).[26]
The conversion of iron or steel into sheet, wire or rods requires hot and cold mechanical transformation stages frequently employing water as a lubricant and coolant. Contaminants includehydraulic oils,tallow and particulate solids. Final treatment of iron and steel products before onward sale into manufacturing includespickling in strong mineral acid to remove rust and prepare the surface fortin orchromium plating or for other surface treatments such asgalvanisation orpainting. The two acids commonly used arehydrochloric acid andsulfuric acid. Wastewater include acidic rinse waters together with waste acid. Although many plants operate acid recovery plants (particularly those using hydrochloric acid), where the mineral acid is boiled away from the iron salts, there remains a large volume of highly acidferrous sulfate orferrous chloride to be disposed of. Many steel industry wastewaters are contaminated by hydraulic oil, also known assoluble oil.[citation needed]
Many industries perform work on metal feedstocks (e.g. sheet metal,ingots,bar stock) as they fabricate their final products. The industries include automobile, truck and aircraft manufacturing; tools and hardware manufacturing; electronic equipment and office machines; ships and boats; appliances and other household products; and stationary industrial equipment (e.g. compressors, pumps, boilers). Typical processes conducted at these plants includegrinding,machining,coating and painting,chemical etching and milling,solvent degreasing,electroplating andanodizing. Wastewater generated from these industries may containheavy metals (common heavy metal pollutants from these industries include cadmium, chromium, copper, lead, nickel, silver and zinc), cyanide and various chemical solvents, oil, and grease.[27][28]
The principal waste-waters associated withmines andquarries are slurries of rock particles in water. These arise from rainfall washing exposed surfaces and haul roads and also from rock washing and grading processes. Volumes of water can be very high, especially rainfall related arisings on large sites.[29] Some specialized separation operations, such ascoal washing to separate coal from native rock usingdensity gradients, can produce wastewater contaminated by fine particulatehaematite andsurfactants.Oils and hydraulic oils are also common contaminants.[30]
Wastewater from metal mines and ore recovery plants are inevitably contaminated by the minerals present in the native rock formations. Following crushing and extraction of the desirable materials, undesirable materials may enter the wastewater stream. For metal mines, this can include unwanted metals such aszinc and other materials such asarsenic. Extraction of high value metals such asgold andsilver may generateslimes containing very fine particles in where physical removal of contaminants becomes particularly difficult.[31]
Additionally, the geologic formations that harbour economically valuable metals such ascopper and gold very often consist of sulphide-type ores. The processing entails grinding the rock into fine particles and then extracting the desired metal(s), with the leftover rock being known as tailings. These tailings contain a combination of not only undesirable leftover metals, but also sulphide components which eventually form sulphuric acid upon the exposure to air and water that inevitably occurs when the tailings are disposed of in large impoundments. The resultingacid mine drainage, which is often rich in heavy metals (because acids dissolve metals), is one of the manyenvironmental impacts of mining.[31]
The waste production from the nuclear and radio-chemicals industry is dealt with asRadioactive waste.[citation needed]
Researchers have looked at the bioaccumulation ofstrontium byScenedesmus spinosus (algae) in simulated wastewater. The study claims a highly selectivebiosorption capacity for strontium of S. spinosus, suggesting that it may be appropriate for use of nuclear wastewater.[32]
Oil and gas well operations generateproduced water, which may contain oils, toxic metals (e.g.arsenic,cadmium,chromium, mercury, lead), salts, organic chemicals and solids. Some produced water contains traces ofnaturally occurring radioactive material.Offshore oil and gas platforms also generate deck drainage, domestic waste and sanitary waste. During the drilling process, well sites typically dischargedrill cuttings anddrilling mud (drilling fluid).[33]
Pollutants discharged atpetroleum refineries andpetrochemical plants includeconventional pollutants (BOD, oil and grease,suspended solids), ammonia, chromium, phenols and sulfides.[34]
Pharmaceutical plants typically generate a variety of process wastewaters, including solvents, spent acid and caustic solutions, water from chemical reactions, product wash water, condensed steam, blowdown from air pollution control scrubbers, and equipment washwater. Non-process wastewaters typically include cooling water and site runoff. Pollutants generated by the industry includeacetone, ammonia, benzene, BOD, chloroform, cyanide,ethanol,ethyl acetate,isopropanol,methylene chloride,methanol, phenol and toluene. Treatment technologies used include advanced biological treatment (e.g. activated sludge with nitrification),multimedia filtration, cyanide destruction (e.g.hydrolysis),steam stripping and wastewater recycling.[35]
Effluent from thepulp and paper industry is generally high insuspended solids and BOD. Plants thatbleach wood pulp for paper making may generatechloroform,dioxins (including2,3,7,8-TCDD),furans, phenols, andchemical oxygen demand (COD).[36] Stand-alone paper mills using imported pulp may only require simple primary treatment, such assedimentation ordissolved air flotation. Increased BOD or COD loadings, as well as organic pollutants, may require biological treatment such asactivated sludge orupflow anaerobic sludge blanket reactors. For mills with high inorganic loadings like salt, tertiary treatments may be required, either general membrane treatments likeultrafiltration orreverse osmosis or treatments to remove specific contaminants, such as nutrients.
The pollutants discharged by nonferroussmelters vary with the base metal ore.Bauxite smelters generatephenols[37]: 131 but typically usesettling basins and evaporation to manage these wastes, with no need to routinely discharge wastewater.[37]: 395 Aluminum smelters typically dischargefluoride,benzo(a)pyrene,antimony andnickel, as well as aluminum. Copper smelters typically generatecadmium, lead, zinc, arsenic and nickel, in addition to copper, in their wastewater. Lead smelters discharge lead and zinc. Nickel and cobalt smelters discharge ammonia and copper in addition to the base metals. Zinc smelters discharge arsenic, cadmium, copper, lead, selenium and zinc.[38]
Typical treatment processes used in the industry are chemical precipitation, sedimentation and filtration.[37]: 145
Textile mills, includingcarpet manufacturers, generate wastewater from a wide variety of processes, includingcleaning and finishing,yarn manufacturing and fabric finishing (such asbleaching,dyeing,resin treatment,waterproofing andretardant flameproofing). Pollutants generated by textile mills include BOD, SS, oil and grease, sulfide, phenols and chromium.[39]Insecticide residues in fleeces are a particular problem in treating waters generated in wool processing. Animal fats may be present in the wastewater, which if not contaminated, can be recovered for the production of tallow or further rendering.[citation needed]
Textile dyeing plants generate wastewater that contain synthetic (e.g., reactive dyes, acid dyes, basic dyes, disperse dyes, vat dyes, sulphur dyes, mordant dyes, direct dyes, ingrain dyes, solvent dyes, pigment dyes)[40] and natural dyestuff, gum thickener (guar) and various wetting agents, pH buffers and dye retardants or accelerators. Following treatment with polymer-based flocculants and settling agents, typical monitoring parameters include BOD, COD, color (ADMI), sulfide, oil and grease, phenol,TSS and heavy metals (chromium,zinc, lead, copper).
Industrial applications where oil enters the wastewater stream may include vehicle wash bays, workshops, fuel storage depots, transport hubs and power generation. Often the wastewater is discharged into local sewer or trade waste systems and must meet local environmental specifications. Typical contaminants can include solvents, detergents, grit, lubricants and hydrocarbons.
Many industries have a need to treat water to obtain very high quality water for their processes. This might include pure chemical synthesis or boiler feed water. Also, some water treatment processes produce organic and mineral sludges fromfiltration andsedimentation which require treatment.Ion exchange using natural or synthetic resins removescalcium,magnesium andcarbonate ions from water, typically replacing them withsodium,chloride,hydroxyl and/or other ions. Regeneration of ion-exchange columns with strong acids and alkalis produces a wastewater rich in hardness ions which are readily precipitated out, especially when in admixture with other wastewater constituents.
Wood preserving plants generate conventional and toxic pollutants, including arsenic, COD, copper, chromium, abnormally high or low pH, phenols, suspended solids, oil and grease.[41]
The various types of contamination of wastewater require a variety of strategies to remove the contamination.[1] Most industrial processes, such aspetroleum refineries, chemical andpetrochemical plants have onsite facilities to treat their wastewaters so that the pollutant concentrations in the treated wastewater comply with the regulations regarding disposal of wastewaters into sewers or into rivers, lakes or oceans.[1]: 1412 Constructed wetlands are being used in an increasing number of cases as they provided high quality and productive on-site treatment. Other industrial processes that produce a lot of waste-waters such aspaper and pulp production have created environmental concern, leading to development of processes to recycle water use within plants before they have to be cleaned and disposed.[42]
An industrial wastewater treatment plant may include one or more of the following rather than the conventional treatment sequence of sewage treatment plants:
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Brine treatment involves removing dissolvedsalt ions from the waste stream. Although similarities to seawater or brackish waterdesalination exist, industrial brine treatment may contain unique combinations of dissolved ions, such as hardness ions or other metals, necessitating specific processes and equipment.
Brine treatment systems are typically optimized to either reduce the volume of the final discharge for more economic disposal (as disposal costs are often based on volume) or maximize the recovery of fresh water or salts. Brine treatment systems may also be optimized to reduce electricity consumption, chemical usage, or physical footprint.
Brine treatment is commonly encountered when treating cooling tower blowdown,produced water fromsteam-assisted gravity drainage (SAGD), produced water fromnatural gas extraction such ascoal seam gas, frac flowback water,acid mine or acid rock drainage, reverse osmosis reject,chlor-alkali wastewater, pulp and paper mill effluent, and waste streams from food and beverage processing.
Brine treatment technologies may include: membrane filtration processes, such asreverse osmosis;ion-exchange processes such aselectrodialysis orweak acid cation exchange; or evaporation processes, such as brine concentrators andcrystallizers employingmechanical vapour recompression and steam. Due to the ever increasing discharge standards, there has been an emergence of the use ofadvance oxidation processes for the treatment of brine. Some notable examples such asFenton's oxidation[45][46] andozonation[47] have been employed for degradation of recalcitrant compounds in brine from industrial plants.
Reverse osmosis may not be viable for brine treatment, due to the potential for fouling caused by hardness salts or organic contaminants, or damage to the reverse osmosis membranes fromhydrocarbons.
Evaporation processes are the most widespread for brine treatment as they enable the highest degree of concentration, as high as solid salt. They also produce the highest purity effluent, even distillate-quality. Evaporation processes are also more tolerant of organics, hydrocarbons, or hardness salts. However, energy consumption is high and corrosion may be an issue as the prime mover is concentrated salt water. As a result, evaporation systems typically employtitanium orduplex stainless steel materials.
Brine management examines the broader context of brine treatment and may include consideration of government policy and regulations,corporate sustainability, environmental impact, recycling, handling and transport, containment, centralized compared to on-site treatment, avoidance and reduction, technologies, and economics. Brine management shares some issues withleachate management and more generalwaste management. In the recent years, there has been greater prevalence in brine management due to global push for zero liquid discharge (ZLD)/minimal liquid discharge (MLD).[48] In ZLD/MLD techniques, a closed water cycle is used to minimize water discharges from a system forwater reuse. This concept has been gaining traction in recent years, due to increased water discharges and recent advancement in membrane technology. Increasingly, there has been also greater efforts to increase the recovery of materials from brines, especially from mining, geothermal wastewater or desalination brines.[49][50][51][52][53][54] Various literature demosntrates the vaibility of extraction of valuable materials like sodium bicarbonates, sodium chlorides and precious metals (like rubidium, cesium and lithium). The concept of ZLD/MLD encompasses the downstream management of wastewater brines, to reduce discharges and also derive valuable products from it.
Most solids can be removed using simple sedimentation techniques with the solids recovered asslurry or sludge. Very fine solids and solids with densities close to the density of water pose special problems. In such case filtration orultrafiltration may be required. Althoughflocculation may be used, usingalum salts or the addition ofpolyelectrolytes. Wastewater from industrial food processing often requires on-site treatment before it can be discharged to prevent or reduce sewer surcharge fees. The type of industry and specific operational practices determine what types of wastewater is generated and what type of treatment is required. Reducing solids such as waste product, organic materials, and sand is often a goal of industrial wastewater treatment. Some common ways to reduce solids include primary sedimentation (clarification),dissolved air flotation (DAF), belt filtration (microscreening), and drum screening.
The effective removal of oils and grease is dependent on the characteristics of the oil in terms of its suspension state and droplet size, which will in turn affect the choice of separator technology. Oil in industrial waste water may be free light oil, heavy oil, which tends to sink, and emulsified oil, often referred to as soluble oil. Emulsified or soluble oils will typically required "cracking" to free the oil from its emulsion. In most cases this is achieved by lowering the pH of the water matrix.
Most separator technologies will have an optimum range of oil droplet sizes that can be effectively treated. Each separator technology will have its own performance curve outlining optimum performance based on oil droplet size. the most common separators are gravity tanks or pits, API oil-water separators or plate packs, chemical treatment via dissolved air flotations, centrifuges, media filters and hydrocyclones.
Analyzing the oily water to determine droplet size can be performed with a video particle analyser.
Hydrocyclone separators operate on the process where wastewater enters the cyclone chamber and is spun under extreme centrifugal forces more than 1000 times the force of gravity. This force causes the water and oil droplets (or solid particles) to separate. The separated materials is discharged from one end of the cyclone where treated water is discharged through the opposite end for further treatment, filtration or discharge. Hydrocyclones can also be utilised in a variety of context from solid-liquid separation to oil-water separation.[56][57][58][59]
Biodegradable organic material of plant or animal origin is usually possible to treat using extended conventionalsewage treatment processes such asactivated sludge ortrickling filter.[1][60] Problems can arise if the wastewater is excessively diluted with washing water or is highly concentrated such as undiluted blood or milk. The presence of cleaning agents, disinfectants, pesticides, or antibiotics can have detrimental impacts on treatment processes.[citation needed]
Theactivated sludge process is a type of biologicalwastewater treatment process for treatingsewage or industrial wastewaters usingaeration and a biologicalfloc composed of bacteria andprotozoa. It is one of several biological wastewater treatment alternatives insecondary treatment, which deals with the removal of biodegradable organic matter and suspended solids. It uses air (oroxygen) andmicroorganisms tobiologically oxidize organic pollutants, producing a waste sludge (orfloc) containing the oxidized material.
The activated sludge process for removing carbonaceous pollution begins with an aeration tank where air (or oxygen) is injected into the waste water. This is followed by a settling tank to allow the biological flocs (the sludge blanket) to settle, thus separating the biological sludge from the clear treated water. Part of the waste sludge is recycled to the aeration tank and the remaining waste sludge is removed for further treatment and ultimate disposal.
A trickling filter consists of a bed ofrocks,gravel,slag,peat moss, or plastic media over which wastewater flows downward and contacts a layer (or film) ofmicrobial slime covering the bed media.Aerobic conditions are maintained by forced air flowing through the bed or by natural convection of air. The process involvesadsorption of organic compounds in the wastewater by the microbial slime layer, diffusion of air into the slime layer to provide the oxygen required for the biochemicaloxidation of the organic compounds. The end products includecarbon dioxide gas, water and other products of the oxidation. As the slime layer thickens, it becomes difficult for the air to penetrate the layer and an inner anaerobic layer is formed.[citation needed]
Synthetic organic materials including solvents, paints, pharmaceuticals, pesticides, products fromcoke production and so forth can be very difficult to treat. Treatment methods are often specific to the material being treated. Methods includeadvanced oxidation processing,distillation, adsorption,ozonation, vitrification,incineration, chemical immobilisation or landfill disposal. Some materials such as some detergents may be capable of biological degradation and in such cases, a modified form of wastewater treatment can be used.
Acids and alkalis can usually beneutralised under controlled conditions. Neutralisation frequently produces aprecipitate that will require treatment as a solid residue that may also be toxic. In some cases, gases may be evolved requiring treatment for the gas stream. Some other forms of treatment are usually required following neutralisation.
Waste streams rich inhardness ions as from de-ionisation processes can readily lose the hardness ions in a buildup of precipitated calcium and magnesium salts. This precipitation process can cause severefurring of pipes and can, in extreme cases, cause the blockage of disposal pipes. A 1-metre diameter industrial marine discharge pipe serving a major chemicals complex was blocked by such salts in the 1970s. Treatment is by concentration of de-ionisation waste waters and disposal to landfill or by careful pH management of the released wastewater.
Toxic materials including many organic materials, metals (such as zinc, silver,cadmium,thallium, etc.) acids, alkalis, non-metallic elements (such as arsenic orselenium) are generally resistant to biological processes unless very dilute. Metals can often be precipitated out by changing the pH or by treatment with other chemicals. Many, however, are resistant to treatment or mitigation and may require concentration followed by landfilling or recycling. Dissolved organics can beincinerated within the wastewater by the advanced oxidation process.
Molecular encapsulation is a technology that has the potential to provide a system for the recyclable removal of lead and other ions from polluted sources. Nano-, micro- and milli- capsules, with sizes in the ranges 10 nm–1μm,1μm–1mm and >1mm, respectively, are particles that have an active reagent (core) surrounded by a carrier (shell).There are three types of capsule under investigation:alginate-based capsules,carbon nanotubes, polymer swelling capsules. These capsules provide a possible means for the remediation of contaminated water.[61]
To remove heat from wastewater generated bypower plants ormanufacturing plants, and thus to reducethermal pollution, the following technologies are used:
Some facilities such as oil and gas wells may be permitted to pump their wastewater underground throughinjection wells. However, wastewater injection has been linked toinduced seismicity.[63]
Economies of scale may favor a situation where industrial wastewater (with pre-treatment or without treatment) is discharged to the sewer and then treated at a large municipal sewage treatment plant. Typically, trade waste charges are applied in that case. Or it might be more economical to have full treatment of industrial wastewater on the same site where it is generated and then discharging this treated industrial wastewater to a suitable surface water body. This effectively reduces wastewater treatment charges collected by municipal sewage treatment plants by pre-treating wastewaters to reduce concentrations of pollutants measured to determine user fees.[64]: 300–302
Industrial wastewater plants may also reduce raw water costs by converting selected wastewaters to reclaimed water used for different purposes.
Theinternational community has defined the treatment of industrial wastewater as an important part ofsustainable development by including it inSustainable Development Goal 6. Target 6.3 of this goal is to "By 2030, improvewater quality by reducingpollution, eliminating dumping and minimizing release ofhazardous chemicals and materials, halving the proportion ofuntreated wastewater and substantially increasing recycling andsafe reuse globally".[65] One of the indicators for this target is the "proportion of domestic and industrial wastewater flows safely treated".[66]
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