Stringent laws and frequent checks by authorities reflect growing environmental concerns. Thus, for instance, the pH of wastewater of industries such as textiles can deviate only minimally from the neutral point when discharged into a receiving watercourse or sewerage system.
Various chemicals are available to neutralize the high alkaline textile industrial wastewater depending upon the application. In most cases, Sulfuric Acid (H2SO4) is used. The end user must consider the concentration to be used, must carefully analyze all the chemistries involved, must review manufacturers' warnings and instructions, and must consider common safety measures for hazardous liquids.
The process of treating wastewaters with chemicals comprises use of either acids or bases or substances capable of forming them on addition to wastewater. Various chemicals are available for industrial neutralization depending upon the application and whether neutralization of an acidic or basic solution is being carried out.
The most commonly used neutralization chemicals for acid or base neutralization are 98% Sulfuric acid and 50% Sodium hydroxide. In many cases these are very good choices. However, there are many considerations when selecting chemicals and these may not always be the best selection. The selection of the chemicals used for the neutralization of an acid or base is almost as important as the design of the neutralization system. Some of the major points to consider in the selection of chemicals are listed below:    Health and Safety    Cost and Convenience    Physical Properties of neutralizing chemicals    Storage Environment
An explanation of chemical selection criteria is as follows:
Health and Safety: Mixing of chemicals can lead to extreme hazardous/noxious reactions. For example, addition of an acid to cyanide bearing solution results in release of deadly HCN gas. Cost and Convenience: Acids and bases work in most applications. Sulfuric acid (H2SO4), for example, is less costly and more potent than nitric acid. Concentration is also an important consideration in cost assessment. H2SO4 for example, can be purchased in concentrations ranging from near 0 to 98%. Higher concentrations are generally less expensive.Physical Properties: The physical properties of the selected reagent must be considered carefully. 50% Sodium hydroxide (NaOH), for example, begins to freeze at temperatures below 60° F. Decreasing the concentration to 25% eliminates this concern altogether. Hydrochloric acid (HCl), for example, gasses out severely and is highly corrosive and will attack all metallic objects. Therefore, if HCl is used it must be properly vented or used outdoors where the gasses can easily dissipate.Storage Environment: Storage issues such as the types of tanks and secondary containment available, familiarity of operators in handling hazardous chemicals, the dangers of refilling storage containers or procedures for transferring from bulk containers are of concern.
The most commonly used neutralizing chemicals are listed below:    Acids: Sulfuric Acid, Hydrochloric Acid, Nitric Acid, Phosphoric Acid and Carbon Dioxide which forms Carbonic Acid in water    Bases: Sodium Hydroxide (Caustic Soda), Calcium Hydroxide, Calcium Carbonate (Lime or Limestone), Ammonium HydroxideNeutralization with Acids    Sulfuric Acid is the most widely used and produced chemical in the world. Available in concentrations ranging from 0% to 98%, sulfuric acid is most economical of all and used universally for neutralization reactions. It is easier and safer to use than HCl or HNO3 and is more potent than all of the other acids except for phosphoric acid. Sulfuric acid is typically used in concentrations ranging from 25% to 96%. However, 30% to 50% concentrations of sulfuric acid are generally recommended.    Hydrochloric Acid (HCl), also known as muriatic acid, is the second most commonly used acid in industry, sulfuric acid being the primary choice since it is more effective and relatively inexpensive. At a maximum available concentration of 37%, HCl is about ⅓ as potent as sulfuric acid, thus making it relatively more expensive to use. Depending on temperature and agitation, HCl at concentrations above 10% evolves hydrogen chloride vapors which combine with the water vapors present in the air. The gas thus formed, is highly corrosive and attacks all metallic objects including building structures, sprinkler heads, copper wiring, stainless steel, etc. Therefore, it must be properly vented or used outdoors where the gasses can easily dissipate.    Nitric Acid (HNO3) though a widely used chemical in many industries it does not enjoy the popularity of hydrochloric or sulfuric acid, as it is more expensive to use than either of them. Nitric acid evolves noxious gas which on combines with water vapors present in the air. The gas is highly corrosive and attacks all metallic objects including building structures, sprinkler heads, copper wiring, stainless steel, etc. Therefore, it must be properly vented or used outdoors where the gasses can easily dissipate.    Phosphoric Acid (H3PO4), very widely used in the production of agricultural fertilizers and detergent products it is a relatively inexpensive acid. However it still does not compete well with sulfuric and hydrochloric acid as it is a weak acid and does not fully disassociate in water at normal concentrations. This renders it safer to use compared to sulfuric or hydrochloric acid and the evolution of gasses is rare. It tends to buffer neutralization reactions and this makes for a slower reaction that is easier to control. Due to its cost (as compared to sulfuric acid) and availability, phosphoric acid is not commonly used in neutralization system.    Carbon Dioxide (CO2), the third most concentrated gas found in earth's atmosphere, CO2 is itself not an acid. It forms carbonic acid (H2CO3) when dissolved in water; and it is this carbonic acid that brings about the neutralization of alkalinity in solution. The most appealing feature of CO2 is that it will not lower the pH of water below 7.0 for all practical purposes. Additionally CO2 is non corrosive. However as it is heavier than air asphyxiation is a hazard. Carbon dioxide is difficult to use and its use is limited because the gas must be dissolved into solution to be used. This requires the use of a carbonator, or some method to dissolve the gas into solution. Significant out-gassing also occurs, which does not hold a problem unless the process also requires the settling of solids. In cement pouring operations large amounts of alkaline wastewaters are generated. It is an excellent choice for such applications as the site is temporary, the gas is nonhazardous, can be used in-line assuming retention and mixing is considered and is self-buffering so regardless of dosage it will not lower the pH below 7.5-7.0.Alkaliphiles
Several microorganisms exhibit more than one pH optimum for growth depending on growth conditions, particularly nutrients, metal ions, and temperature. The term “alkaliphile” is used for microorganisms that grow optimally or very well at pH values above 9. The first paper concerning an alkaline enzyme of alkaliphilic microorganisms was published in 1971 (Horikoshi, K. (1971) Production of alkaline enzymes by alkalophilic microorganisms. Part 1. Alkaline protease produced by Bacillus No, 221. Agric. Biol. Chem. 36, 1407–1414). Over the past two decades, our studies have focused on the enzymology, physiology, ecology, taxonomy, molecular biology and genetics of alkaliphilic microorganisms. Industrial applications of these microorganisms have also been investigated extensively and some enzymes, such as alkaline proteases, alkaline amylases and alkaline cellulases, have been put to use on an industrial scale (Horikoshi, K. and Akiba, T. (1982) Alkalophilic Microorganisms: A New Microbial World. Springer-Verlag, Heidelberg, Tokyo, Horikoshi, K. (1991) Microorganisms in Alkaline Environments, Kodansha-VCH, Tokyo, Weinheim, N.Y., Cambridge, Basel).
Subsequently, many microbiologists have published numerous papers on alkaliphilic microorganisms in various fields. Cell surface of alkaliphiles can maintain the intracellular pH values neutral in alkaline environments of pH 10–13. In 1995, using alkaliphilic Bacillus C-125 mutants that are alkaline sensitive developed new host vector systems, and genes responsible for alkaliphily have been investigated (Kudo, T., Hino, M., Kitada, M. and Horikoshi, K. (1990) DNA sequences required for the alkalophily of Bacillus sp. strain C-125 are located close together on its chromosomal DNA. J. Bacteriol. 172, 7282–7283, Seto, Y., Hashimoto, M., Usami, R., Hamamoto, T., Kudo, T. and Horikoshi, K. (1995) Characterization of a mutation responsible for an alkali-sensitive mutant, 18224, of alkaliphilic Bacillus sp. strain C-125. Biosei. Biotechnol. Biochem. 59, 1364–1366).
Although alkaliphiles have been used for a number of industrial applications, there is no research publication regarding neutralization of textile industrial wastewater using them. U.S. patent application Ser. No. 09/160422, (1998) discloses a biological neutralization process by using a mixture of bacteria in the presence of sugars.