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Water Treatment Operations
Published in Frank R. Spellman, Handbook of Water and Wastewater Treatment Plant Operations, 2020
Lime softening has been widely used in the United States for reducing hardness in large water treatment systems. Lime softening, excess lime treatment, split lime treatment, and lime-soda softening are all common in municipal water systems. All of these treatment methods are effective in reducing arsenic. Arsenite or arsenate removal is pH dependent. Oxidation of arsenite is the predominant form. Considerable amounts of sludge are produced in a lime softening system and its disposal is expensive. Large capacity systems may find it economically feasible to install recalcination equipment to recover the reuse of the lime sludge and reduce disposal problems. Construction of a new lime softening plant for the removal of arsenic would not generally be recommended unless hardness must also be reduced.
Treatment of Coal Industry Effluents
Published in Mihir Kumar Purkait, Piyal Mondal, Chang-Tang Chang, Treatment of Industrial Effluents, 2019
Mihir Kumar Purkait, Piyal Mondal, Chang-Tang Chang
The technology of mechanical dehydration is quite efficient at present. The main applications in the project are belt pressure filter, centrifugal dehydrator, plate and frame filter, etc. The sludge produced by the sewage treatment of biochemical system is mainly flocculation sludge and biological excess sludge, which is dehydrated by a belt-type pressure filter. The power consumption is low, and the equipment costs are comparatively lower. The sludge produced by lime softening is inorganic sludge, containing inorganic particles, which causes more abrasion to the equipment. Choosing a box, plate, and frame filter press to improve the solid content of mud cake is more preferred. At present, a screw-type dehydrator and centrifugal dehydrator are widely used. Due to the high precision of centrifuge manufacturing, most of the imported products are used.
Inorganic Chemicals in Drinking Water
Published in Joseph Cotruvo, Drinking Water Quality and Contaminants Guidebook, 2019
Water softening is a common practice both in the home and in larger-scale facilities. Precipitative lime softening with calcium hydroxide and lime-soda ash softening are used by municipal water plants that soften. POE softening with a cation exchange resin is a common practice. Cation exchanged softened water is not necessarily aggressive to metal pipe because the total ionic composition remains high. POU RO softening is not a good option in the home. POE RO softening would cause the water to be aggressive toward metal pipe and fixtures.
Integrated bio-oxidation and adsorptive filtration reactor for removal of arsenic from wastewater
Published in Environmental Technology, 2019
Kalyani Kamde, Rashmi Dahake, R.A. Pandey, Amit Bansiwal
Arsenic exists in metalloid, inorganic and organic form in the environment. The behavior of arsenic species will change depending on the biotic and abiotic conditions in water. The inorganic species are highly mobile and several hundred times as toxic as organic arsenicals [14]. However, two predominated oxidation state naturally occurs in water are oxyanions of trivalent arsenic [As (III)] and pentavalent arsenic [As (V)] with a minor amount of methyl and dimethyl arsenic compounds being detected. As (III) is 25–60 times as toxic as As (V) and difficult to remove by conventional physicochemical treatment processes [15–17]. As per the available literature, various technologies are available for the removal of arsenic in contaminated water. The oxidation/precipitation, electrocoagulation/co-precipitation, lime-softening, metal–oxide adsorption, reverse-osmosis, nano-filtration, ion-exchange resin, coagulation-microfiltration are the most commonly used technologies. These processes have numerous drawbacks, which include selective or partial metal removal and high capital and operational cost with increased disposal of residual metal sludge, making them unsuitable and unsustainable [18]. Nowadays, extensive research has been conducted towards identifying new technologies for arsenic removal.
Statistical optimization of arsenic biosorption by microbial enzyme via Ca-alginate beads
Published in Journal of Environmental Science and Health, Part A, 2018
Suchetana Banerjee, Anindita Banerjee, Priyabrata Sarkar
Many procedures such as oxidation/precipitation, sorption onto activated carbon, co-precipitation/ coagulation, lime softening, reverse osmosis, ion-exchange, membrane techniques have been used for arsenic removal although the above methods have certain drawbacks e.g., high operational cost, lower efficiency, production of harmful chemical sludge and limited tolerance to pH change.[5–8] Mechanisms and degree of arsenic adsorption depend greatly on the speciation of the inorganic arsenic forms which in turn depends on the pH and the redox potential (Eh) of the solution.[9] Organisms have developed several tolerance mechanisms to survive in the toxic arsenic-containing environments such as detoxifying reduction of As (V) to As(III) by the cytoplasmic ars operon that is often located on plasmids or transposons that synthesizes the arsenate reductase enzyme.[10–12] Substantial research on microbiological processes that regulate the mobilization and distribution of As in aquatic environments has been carried out. Pseudomonas species along with other organisms are known to have high metal binding capability as well as very high As (V) tolerance and can be used as metal-adsorbing agents.[13,14]
Bioremoval of mercury (II) from aqueous solutions by Phragmites australis: Kinetic and equilibrium studies
Published in Journal of Dispersion Science and Technology, 2018
Gökben Başaran Kankiliç, Ayşegül Ülkü Metin, Yaşar Aluç, Ogün Bozkaya
Mercury, listed as toxic heavy metal, is often found in the form of mercury vapor in the atmosphere while the inorganic salts or organic form of mercury complexes are encountered mostly in soil, water, sediment or biota.[1] In aquatic ecosystems, inorganic mercury is found in two ionic states Hg(I) and Hg (II). Both of them are soluble in water and bioavailable.[2] Hg (II) state is the most common form, which is found as HgCl2.[3] With rapid industrial development, mercury contamination is increasing steadily in waste waters and aquatic ecosystems through a wide variety of activities such as metal plating, mining, batteries, combustion of fossil fuels, paint manufacture, photographic industries, pulp and paper industries, steel pigments, fertilizers, municipal waste.[4–6] It has been reported that discharge of the mercury can cause some harmful effects to the humans and animals such as neurological, renal and cardiovascular disorders.[7,8] In consequence of the detrimental effects, removal of mercury ions from aquatic ecosystems is an important issue. Several types of techniques are used for this purpose such as chemical precipitation, ozonation, electrolysis, cation exchange membranes, lime softening, reverse osmosis, enhanced ultrafiltration, adsorption and biosorption.[9–12] In all these methods Biosorption, which basically refers to the use of biological material as sorbent, has attracted a great deal of attention as the best alternative method against the known conventional techniques, relying upon lesser cost, effectiveness, easiness in design, user-friendliness, environmental sensitivity and no formation of toxic secondary compounds.[13–15] Biomaterials such as fungi, bacteria, algae, lichens and aquatic macrophytes have been used for biosorption of metal ions from aqueous solutions and wastewater in several studies.[16–19]