Pal Groundwater Arsenic Remediation

Treatment Technology and Scale UP
1. Auflage 2015
ISBN: 978-0-12-801377-9
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 326 Seiten

Arsenic abatement from groundwater in locations with a central water distribution system is relatively simple. The real challenge is selecting the most effective and affordable treatment and scale up option for locations which lack the appropriate infrastructure. Groundwater Arsenic Remediation: Treatment Technology and Scale UP provides the latest breakthrough groundwater treatment technologies and modeling and simulation methods for project scale up and eventually field deployment in locations which lack the proper central water distribution system to ensure arsenic free groundwater. - Covers the different removal methods, such as chemical, adsorption, separation by membranes, and membrane distillation - Includes the state-of-the-art modeling & simulation methods for optimization and field deployment - Provides economic and comparative analysis of each arsenic treatment technology

Professor Parimal is currently serving as HAG Professor (Higher Administrative Grade) and the senior most professor in the Department of Chemical Engineering, National Institute of Technology Durgapur, A Govt. of India Autonomous Institute of National importance. A Master of Technology from the Department of Chemical Engineering, Indian Institute of Technology Kharagpur, he joined academia in 1990 with a few years field experience in Indian Oil Corporation Limited the most profitable and largest petroleum industry in India. He holds PhD degree from Jadavpur University, Kolkata. Professor Pal developed a dozen of membrane-based green technologies and software for chemical and allied process industries. He has already earned patent rights of half a dozen novel technologies and copyright of two process optimization and control software. Dr. Pal supervised around one and a half dozen doctoral and postdoctoral thesis work.

Autoren/Hrsg.

Pal, Parimal

Leseproben

Chapter 2 Chemical Treatment Methods in Arsenic Removal
Abstract
This chapter describes physico-chemical treatment of arsenic-contaminated groundwater. The forms of arsenic, the underlying principles of chemical coagulation, and precipitation and separation of arsenic from the aqueous phase, which are central to this arsenic removal technology, are elaborated in this chapter. Based on the theoretical understanding, mathematical modeling and simulation are done to help scale up the method for the practical field. Finally, development of software meant for optimization and control of the whole physico-chemical process is presented. Keywords Arsenic removal chemical precipitation destabilization optimization and control Contents 2.1 Different forms of arsenic in groundwater   26 2.2 Chemical precipitation   27 2.2.1 Alum precipitation   28 2.2.2 Lime softening   29 2.2.3 Iron precipitation   29 2.2.4 Enhanced coagulation   31 2.2.5 Coprecipitation   31 2.3 Physical separation   31 2.3.1 Diffuse-double-layer theory   32 2.3.2 Destabilization of colloids and settling of particles   34 2.3.2.1 Double layer compression   35 2.3.2.2 Adsorption and neutralization of charge   35 2.3.2.3 Enmeshment-precipitation   35 2.3.2.4 Interparticle bridging   35 2.3.3 Filtration   35 2.3.3.1 Rapid sand filtration   35 2.3.3.2 Backwashing   36 2.4 Modeling and simulation of the physico-chemical processes for scaleup   36 2.4.1 Introduction   36 2.4.2 Operation of the treatment plant   37 2.4.3 Measuring arsenic concentration in water   39 2.4.4 Computation of percentage removal of arsenic   39 2.4.5 Modeling and simulation of physico-chemical treatment process   40 2.4.5.1 Process kinetics and modeling basis   40 2.4.5.2 Modeling the process   41 2.4.5.3 Material balance for the oxidizer unit   42 2.4.5.4 Component mass balance of arsenic   43 2.4.5.5 Component mass balance of oxidant   43 2.4.5.6 Material balance of the coagulator and flocculator   43 2.4.5.7 Material balance for the sedimentation unit   44 2.4.5.8 Filtration unit   45 2.4.6 Determination of the model parameters   45 2.4.6.1 Computation of flow rate and concentration of oxidant   45 2.4.6.2 Computation of root mean square velocity gradient (G) in the coagulator/flocculator   46 2.4.6.3 Computation of average flock size (dQM) in the coagulator-flocculator unit   46 2.4.6.4 Computation of flow rate and concentration of coagulant   46 2.4.6.5 Determination of settling velocity and superficial velocity in sedimentation unit   47 2.4.6.6 Determination of the filtration pressure drops due to filter cake and filter medium   48 2.4.6.7 Effects of the operating parameters   48 2.4.6.8 Effect of pH   50 2.4.6.9 Effect of oxidant dose   51 2.4.6.10 Effect of coagulant dose   52 2.4.6.11 Effect of feed concentration   53 2.4.7 Performance of the system and the model   54 2.5 Optimization and control of treatment plant operations   55 2.5.1 Development of the optimization and control software   55 2.5.2 The overall procedure of computation and output generation   56 2.6 The numerical solution scheme and error monitoring   56 2.6.1 Software description   56 2.6.2 Software input   58 2.6.3 Software output   63 2.6.4 Running the software   63 2.6.4.1 Software analysis   63 2.7 Techno-economic feasibility analysis   65 Nomenclature   68 References   69 2.1 Different forms of arsenic in groundwater
Arsenic can occur in the environment in various forms and oxidation states (–3, 0, + 3, + 5) but in natural water, arsenic occurs mainly in inorganic forms such as oxyanions of trivalent arsenite or as pentavalent arsenate. The two oxidation states common in drinking water in the form of arsenate and arsenite are part of the arsenic (H3AsO4) and arseneous (H3AsO3) acid systems, respectively. These two forms depend upon oxidation-reduction potential and pH of the water. At typical pH values of 5.0–8.0 in natural waters, the predominant arsenate species are 2AsO4– and 42–, and the arsenite species is H3AsO3. Under oxidizing conditions, 42– dominates at a high pH regime, whereas H3AsO4 predominates at a low pH regime. 2AsO4– predominates at a low pH (< 6.9). This means that As(III) remains as a neutral molecule in natural water. Arsenates are stable under aerobic or oxidizing conditions, while arsenites are stable under anaerobic or mildly reducing conditions. In reducing waters, arsenic is found primarily in the trivalent oxidation state in the form of arseneous acid, which ionizes according to the following equations: The acid base dissociation reactions of arsenic acid can be described as: Surface water is also found to be contaminated with arsenic by the anthropogenic sources to various degrees since arsenic is also used in agriculture (pesticide), industrial applications, mining activities, and feed additives. 2.2 Chemical precipitation
Arsenic can be separated from aqueous solutions through chemical precipitation, exploiting the insolubility of some arsenic compounds. Most dominant arsenic compounds that are precipitated out in this way are arsenic sulphide, ferric arsenate, and calcium arsenate, where pH plays a very crucial role in such precipitation. In the neutral pH regimes, the inorganic arsenic compounds of Cu(II), Zn(II), Pb(II), and Fe(II) are more stable [1]. In chemical precipitation, the As(V) is the dominant form. Iron (II) arsenate [2] is highly insoluble and stable for its successful adoption [2]. A large number of calcium arsenate compounds can be very effectively precipitated out from aqueous solutions of As(V) by raising pH through the addition of lime. But compounds such as those precipitated out at a pH above 8 are often not very stable, particularly in the atmospheric carbon dioxide environment where soluble carbonates are easily formed. More complex arsenic compounds such as apatite structured calcium phosphate arsenate or ferric arsenite have been found to be more appropriate forms of arsenic precipitation and subsequent stabilization. Chemical precipitation in general is considered to be a permanent, efficient, and easy-to- monitor method that can have immediate results. Simultaneous removal of many metal contaminants is possible with the chemical precipitation method. Chemical precipitation may be very useful for large-scale treatment of high-arsenic water, but is not suitable for deep elimination of arsenic up to the level...