Laundry wastewater

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Wastewater comes out of the laundry process with additional energy (heat), lint, soil, dyes, finishing agents, and other chemicals from detergents. [1] Some laundry wastewater goes directly into the environment, due to the flaws of water infrastructure. The majority goes to sewage treatment plants before flowing into the environment. Some chemicals remain in the water after treatment, which may contaminate the water system. Some have argued they can be toxic to wildlife, or can lead to eutrophication.

Contents

General influences of laundry wastewater

As of 2023, the United States has 2,538 industrial laundry facilities [2] which may discharge an average of 400 m3 of wastewater every day. [3] Annually, about 5.11 km3 laundry wastewater is produced.

Treatment of laundry wastewater

There are several parameters in the evaluation of laundry wastewater: temperature, pH-value, suspended substances, Cl2, sediment substances, total nitrogen, total phosphorus, nitrogen ammonia, chemical oxygen demand(COD), biochemical oxygen demand(BOD5), anionic surfactants. [4]

Chemicals in detergents

Several common detergent ingredients are surfactants, builders, bleach-active compounds and auxiliary agents. The surfactants can be classified into anionic, cationic and nonionic surfactants. The most widely used surfactant linear alkylbenzene sulfonate (LAS) is an anionic surfactant. In builders, sodium triphosphate, zeolite A, sodium nitrilotriacetate (NTA) are the most important substances. Bleach-active compounds are usually sodium perborate and sodium percarbonate. Enzymes and fluorescent whitening agents are added into detergents as auxiliary agents. [1]

Mechanism

Environmental harm of surfactants

Surfactants are surface active agents, as they have both hydrophilic and lipophilic properties and are widely used in various washing process. With the lipophilic tails, surfactants are biologically active. Anionic surfactants have the ability of binding to bioactive macromolecules like enzymes, DNA, peptides, causing changes of surface charge and the folding of polyp eptide chain(structure o different. Cationic surfactant can bind to the inner membrane of bacteria, and by this way disorganize the bacteria through their long alkyl chain. Nonionic surfactants are able to bind to both proteins and phospholipid membrane, leading to leakage of low molecular mass compounds by increasing the permeability of membranes and vesicles. This may result in serious damage in cells or even cell death. [5]

LAS and its biodegradation

Linear alkylbenzene sulfonate (LAS) with the formula of C12H25C6H4SO3Na, also known as sodium dodecylbenzene sulfonate, is the most widely used anionic surfactant in laundry detergent because it has minimal environmental impact for its readily biodegradation.

A complete biodegradation under aerobic conditions consists of two steps, primary biodegradation and ultimate biodegradation. The first step begins from the terminal carbon in the alkyl chain as omega-oxidation, which can start from one or both ends, then is followed by beta-oxidation. After the first step the residual is sulfophenyl(di)carboxylates (SP(d)Cs), a large molecule which can be involved in the second step. The second step occurs only when the required bacteria exist. The ring cleavage of benzene and the further desulphonation of the mono- and dicarboxylic sulphophenyl acids happen. After the two-step biodegradation, LAS is degraded into carbon dioxide, water, inorganic salts and residual biomass. During the biodegradation, several specific bacteria and oxygen are required in both omega-oxidation of the alkyl chain and the benzene ring cleaving process, so this biodegradation can only happen in aerobic conditions. [6] In anaerobic conditions in treatment process, LAS shows no change. Researchers also prove that biodegradation process is restricted in 20–40 mg/L and even inhibited at a higher concentration, which leads to the incomplete biodegradation of LAS in sewage treatment plants. [7]

Omega-oxidation of LAS biodegradation Omega-LAS.jpg
Omega-oxidation of LAS biodegradation
Beta-oxidation of LAS biodegradation Beta-LAS.jpg
Beta-oxidation of LAS biodegradation

Harm of builders to the environment

Builders in detergents are water softeners, which can remove calcium and magnesium ions by complexation or precipitation in hard water which contains high levels of calcium and magnesium.

Sodium triphosphate , with a formula of Na5P3O10, is a largely used builder in laundry detergents, which can lead to eutrophication caused by phosphorus (P). P is needed for energy transfer, the formation of DNA, RNA and many other intermediary metabolites. Only P in orthophosphate can be assimilated by autotrophs, other P compounds like sodium triphosphate can be chemically or enzymatically hydrolyzed to orthophosphate. [8] The mechanism is shown below. [9]

Degradation of sodium triphosphate with enzyme Hydrolytic degradation of sodium triphosphate.jpg
Degradation of sodium triphosphate with enzyme

Excessive phosphorus can make for excessive production of autotrophs, like algae and cyanobacteria, leading to eutrophication in an inorganic nutrient pathway. Nutrient enrichment in lakes and reservoirs results in the microscopic floating plants, algae and formation of dense mats of larger floating plants that can produce oxygen by photosynthesis. When they die and sink to the bottom, they consume oxygen in decomposition. Bacteria thriving in this process consume oxygen. With the depletion of oxygen, fishes die and anaerobic bacteria produce methane, hydrogen sulfide and ammonia, which can destroy the ecosystem.

Related Research Articles

<span class="mw-page-title-main">Detergent</span> Surfactants with cleansing properties

A detergent is a surfactant or a mixture of surfactants with cleansing properties when in dilute solutions. There are a large variety of detergents, a common family being the alkylbenzene sulfonates, which are soap-like compounds that are more soluble in hard water, because the polar sulfonate is less likely than the polar carboxylate to bind to calcium and other ions found in hard water.

<span class="mw-page-title-main">Surfactant</span> Substance that lowers the surface tension between a liquid and another material

Surfactants are chemical compounds that decrease the surface tension or interfacial tension between two liquids, a liquid and a gas, or a liquid and a solid. Surfactants may function as emulsifiers, wetting agents, detergents, foaming agents, or dispersants. The word "surfactant" is a blend of surface-active agent, coined c. 1950.

A lysis buffer is a buffer solution used for the purpose of breaking open cells for use in molecular biology experiments that analyze the labile macromolecules of the cells. Most lysis buffers contain buffering salts and ionic salts to regulate the pH and osmolarity of the lysate. Sometimes detergents are added to break up membrane structures. For lysis buffers targeted at protein extraction, protease inhibitors are often included, and in difficult cases may be almost required. Lysis buffers can be used on both animal and plant tissue cells.

<span class="mw-page-title-main">Sodium triphosphate</span> Chemical compound

Sodium triphosphate (STP), also sodium tripolyphosphate (STPP), or tripolyphosphate (TPP),) is an inorganic compound with formula Na5P3O10. It is the sodium salt of the polyphosphate penta-anion, which is the conjugate base of triphosphoric acid. It is produced on a large scale as a component of many domestic and industrial products, especially detergents. Environmental problems associated with eutrophication are attributed to its widespread use.

In organic chemistry, ethoxylation is a chemical reaction in which ethylene oxide adds to a substrate. It is the most widely practiced alkoxylation, which involves the addition of epoxides to substrates.

<span class="mw-page-title-main">Sulfonic acid</span> Organic compounds with the structure R−S(=O)2−OH

In organic chemistry, sulfonic acid refers to a member of the class of organosulfur compounds with the general formula R−S(=O)2−OH, where R is an organic alkyl or aryl group and the S(=O)2(OH) group a sulfonyl hydroxide. As a substituent, it is known as a sulfo group. A sulfonic acid can be thought of as sulfuric acid with one hydroxyl group replaced by an organic substituent. The parent compound is the parent sulfonic acid, HS(=O)2(OH), a tautomer of sulfurous acid, S(=O)(OH)2. Salts or esters of sulfonic acids are called sulfonates.

<span class="mw-page-title-main">Laundry detergent</span> Type of detergent used for cleaning laundry

Laundry detergent is a type of detergent used for cleaning dirty laundry (clothes). Laundry detergent is manufactured in powder and liquid form.

<span class="mw-page-title-main">Amphiphile</span> Hydrophilic and lipophilic chemical compound

An amphiphile, or amphipath, is a chemical compound possessing both hydrophilic and lipophilic (fat-loving) properties. Such a compound is called amphiphilic or amphipathic. Amphiphilic compounds include surfactants. The phospholipid amphiphiles are the major structural component of cell membranes.

<span class="mw-page-title-main">Organosulfate</span> Organic compounds of the form R–O–SO₃ (charge –1)

In organosulfur chemistry, organosulfates are a class of organic compounds sharing a common functional group with the structure R−O−SO−3. The SO4 core is a sulfate group and the R group is any organic residue. All organosulfates are formally esters derived from alcohols and sulfuric acid although many are not prepared in this way. Many sulfate esters are used in detergents, and some are useful reagents. Alkyl sulfates consist of a hydrophobic hydrocarbon chain, a polar sulfate group and either a cation or amine to neutralize the sulfate group. Examples include: sodium lauryl sulfate and related potassium and ammonium salts.

Dodecylbenzene is an organic compound with the formula C
12
H
25
C
6
H
5
. Dodecylbenzene is a colorless liquid with a weak oily odor that floats on water.

<span class="mw-page-title-main">Cleaning agent</span> Substance used to remove dirt or other contaminants

Cleaning agents or hard-surface cleaners are substances used to remove dirt, including dust, stains, foul odors, and clutter on surfaces. Purposes of cleaning agents include health, beauty, removing offensive odor, and avoiding the spread of dirt and contaminants to oneself and others. Some cleaning agents can kill bacteria and clean at the same time. Others, called degreasers, contain organic solvents to help dissolve oils and fats.

<span class="mw-page-title-main">Lauryldimethylamine oxide</span> Chemical compound

Lauryldimethylamine oxide (LDAO), also known as dodecyldimethylamine oxide (DDAO), is an amine oxide–based nonionic surfactant, with a C12 (dodecyl) alkyl tail. It is one of the most frequently-used surfactants of this type. Like other amine oxide–based surfactants it is antimicrobial, being effective against common bacteria such as S. aureus and E. coli, however, it is also non-denaturing and may be used to solubilize proteins.

A soap substitute is a natural or synthetic cleaning product used in place of soap or other detergents, typically to reduce environmental impact or health harms or provide other benefits.

A methylene blue active substances assay, or MBAS assay, is a colorimetric analysis test method that uses methylene blue to detect the presence of anionic surfactants in a sample of water. An anionic surfactant detected by the color reaction is called a methylene blue active substance (MBAS).

Paint has four major components: pigments, binders, solvents, and additives. Pigments serve to give paint its color, texture, toughness, as well as determining if a paint is opaque or not. Common white pigments include titanium dioxide and zinc oxide. Binders are the film forming component of a paint as it dries and affects the durability, gloss, and flexibility of the coating. Polyurethanes, polyesters, and acrylics are all examples of common binders. The solvent is the medium in which all other components of the paint are dissolved and evaporates away as the paint dries and cures. The solvent also modifies the curing rate and viscosity of the paint in its liquid state. There are two types of paint: solvent-borne and water-borne paints. Solvent-borne paints use organic solvents as the primary vehicle carrying the solid components in a paint formulation, whereas water-borne paints use water as the continuous medium. The additives that are incorporated into paints are a wide range of things which impart important effects on the properties of the paint and the final coating. Common paint additives are catalysts, thickeners, stabilizers, emulsifiers, texturizers, biocides to fight bacterial growth, etc.

<span class="mw-page-title-main">Alkylbenzene</span> Family of organic compounds

An alkylbenzene is a chemical compound that contains a monocyclic aromatic ring attaching to one or more saturated hydrocarbon chains. Alkylbenzenes are derivatives of benzene, in which one or more hydrogen atoms are replaced by alkyl groups. The simplest member, toluene, has the hydrogen atom of the benzene ring replaced by a methyl group. The chemical formula of alkylbenzenes is CnH2n-6.

<span class="mw-page-title-main">Alkylbenzene sulfonate</span> Class of chemical compounds

Alkylbenzene sulfonates are a class of anionic surfactants, consisting of a hydrophilic sulfonate head-group and a hydrophobic alkylbenzene tail-group. Along with sodium laureth sulfate, they are one of the oldest and most widely used synthetic detergents and may be found in numerous personal-care products and household-care products . They were introduced in the 1930s in the form of branched alkylbenzene sulfonates (BAS). However following environmental concerns these were replaced with linear alkylbenzene sulfonates (LAS) during the 1960s. Since then production has increased significantly from about one million tons in 1980, to around 3.5 million tons in 2016, making them most produced anionic surfactant after soaps.

Phosphates in detergent refers to the use of phosphates as an ingredient in a detergent product. The advantage of using phosphates in a consumer laundry detergent or dishwashing detergent is that they make detergents more efficient by chelating calcium and magnesium ions. The disadvantage of using phosphates is that they remain in wastewater and eventually make their way to a natural body of water. While phosphates are low toxicity, they instead cause nutrient pollution and feed the algae. This leads to eutrophication and harmful algal bloom.

<span class="mw-page-title-main">Polycarboxylates</span> Any polymer with repeating carboxylate side chains

Polycarboxylates are linear polymers with a high molecular mass and with many carboxylate groups. They are polymers of acrylic acid or copolymers of acrylic acid and maleic acid. The polymer is used as the sodium salt.

α-Olefin sulfonate Class of chemical compounds

α-Olefin sulfonates are a group of anionic surfactants, which are used as detergents. The compounds contain a - mostly linear, primary - alkyl R and a monovalent cation M, preferably sodium. The most frequently used example of this group of substances is sodium α-olefin sulfonate.

References

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