Solutions

Targets of arsenic removal
  • Efficient removal of arsenic particullary arsenic(III) and arsenic (V)
  • Reasonable investment and operating costs
  • Low requirements of Operating and Maintenance
  • Feasible handling of the arsenic loaded process residues

Overview principle technologies of arsenic removal

technologieso_arsenic_removal

Arsenic Removal Units (ARU)
     -  Small units for house or villages, operated by hand pumps
Arsenic Removal Plant (ARP)
     -  Small and big plants, operated by electric pumps / machines

 

Technologies arsenic removal – flocculation

 

Flocculation – Co-precipitation
  • Usage of mainly alumina and ferric salt  as inorganic flocculant
  • Flocculation as allumina or ferric hydroxide
  • adsorption / co-precipitation of arsenic with flocculated hydroxides
  • Sedimentation and/or fitration of the flocculated / precipitated products
  • The mainly used method in bigger treatment plants
Application of Flocculation – Co-precipitation  methods
  • Flocculation by ferric-III-chloride
  • Flocculation by ferric-III-sulfate;
  • Lime softening and flocculation (inefficient and very high amount of arsenic enriched sludge)
  • The effeciency of ferric-III-salts is better especially for the removal of arsenic (III)
  • Problem:  Environmental-friendly disposal of arsenic enriched sludge
Operating of small arsenic removal unit 
  • Adding calcium or sodium hypochloride (bleaching powder), for oxydation of arsenic(III) and disinfection (option)
  • Adding of  e.g. ferric sulphate
  • Mixing / stirring: at first powerfull then slowly
  • Sedimentation of arsenic enriched sludge
  • Upflow filtration to remove small flocs
Flocculation_Co-precipitation_ methodsSource: Mitigation and Remedy og Groundwater arsenic  Menance in India; National Institute of Hydrology, India  June 2010

 

Technologies arsenic removal – adsorption

Adsorption
Adsorption of arsenic on the surface of metal oxides and hydroxides or activated carbon
Adsorption material
-  Adsorption by Iron Based Sorbents (IBS)
  • Granulated Ferric Hydroxide (GFH) mainly synthetic granular products, based on neutralisation of Ferric-III-chlorid with sodium hydroxid
  • Iron coated sand, developed by BUET Bangladesh University of Engineering and Technology); up to 25 mg Fe / g sand
Adsorption by activated allumina (AA)
  • Granular Aluminum trioxid, prepared by dehydration of aluminum hydroxide at high temperature AA can be regenerated 3 upto 4 time by sodium hydroxide and sulfuric acid
 -  Adsorption by activated Carbon

 

Operating of adsorbent  removal unit 
  • Primary treatment and enrich oxygen of the water if required
  • The water pass the adsorbent from top to bottom
  • Back wasch from bottom to top if adsorbent blocked
  • Replace the adsorbent if it is arsenic loaded

small_arsenic_filter_columnssmall_arsenic_filter_columns1

  Examples of  small arsenic filter columns

 

function_adsorbent_filter_column
Principle function of adsorbent  filter column

 

Technologies arsenic removal – oxidation

Oxidation  [Combination of iron and arsenic removal]
  -  Oxidation of arsenic (III) to arsenic (V)
  -  Oxidation and precipitation of iron as ferric hydroxide
  -  Co-precipitation / adsorption arsenic with ferric-hydroxide
iron and arsenic removal
Application of Oxidation methods
  -  SORAS small (micro) scale method
  -  In-situ Oxidation; increase oxigen in aquifer to oxidize As(III) and iron and adsorp As(V) by the the formed FeOH insitu (investigated by DPHE-DANIDA in Bangladesh)
Source: Mitigation and Remedy og Groundwater arsenic  Menance in India; National Institute of Hydrology, India  June 2010
SORAS – simple method to remove arsenic
  • Small (micro) scale method, ussage 0.5 – 2 l PET bottles
  • Addition of some drops of lemon juice (citric acid)
  • Bottles are laid in the sun for about 6 hour
  • formation of ferric-III-citrate and photooxidation As(III) to As(V)
  • Precipitation of  ferric hydroxide which adsorp As(V)
  • Decantation in bottle and filtrate by textile or clay filter
  • SORAS is dependent on  the iron content of the ground water
    e.g. Bangladesh: Fe content high ð As elimination 80 – 90 %
    e.g. Argentinia, Chile: Fe content low ð As elimination 50 – 90 %

Oxidation methods Oxidation methods1

 

 

 

 

Source:
- M. Wegelin et.all, SORAS – a simple arsenic removal  process Swiss Federal Institute for Env. Science and Technology (EAWAG)
- M.I Litte et.all, present. Arsenic removal by solar oxidation, Nat. Atomic Commission, Argentinia;

Technologies arsenic removal – ARU

Examples of Arsenic removal units (ARU) -  excuted in West bengale / India

Examples of Arsenic removal units (ARU)excuted in West bengale_IndiaExamples of Arsenic removal units (ARU)excuted in West bengale_India Examples of Arsenic removal units (ARU)excuted in West bengale_India1

Source: Mitigation and Remedy og Groundwater arsenic  Menance in India; National Institute of Hydrology, India  June 2010

Technologies arsenic removal – Expierences India

Existing ARU and APP (state 2010) 
  • About 80 ARUs, each covering about 15,000 people, operated by hand pumps
  • About 2,400 ARUs, each covering about 600 – 800 people, operated by hand paump
  • About 1,900 APRs in different places
Assessment/Evaluation of operation
  • An evaluation of the the operating and sustainablity of the ARUs and APRs had shown that 80 to 90 % of the units and plant didn‘t work satisfying  and useful
  • The main reason is a non-satisfying Operating and Maintenance O&M;

Groundwater arsenic  Menance in India

Source: Mitigation and Remedy of Groundwater arsenic  Menance in India; National Institute of Hydrology, India  June 2010
Targets future activities and developments
  • Improve of effectiveness in arsenic removal
  • Reduce of capital and operating costs of the systems
  • Make the technologies more user friendly
  • Overcome maintenance problems and
  • Resolve the management of  arsenic enriched residues

 

Overview Disinfection methods

Overview Disinfection methods

  • primary disinfection:       Basic disinfection
  • Secondary disinfection: Keep the disinfection status in the water distribution system  to prevent a re-growing of pathogens

Comparison of Disinfection methods

Comparison of Disinfection methods

Source: www.lenntech.com/processes/disinfection/disinfection.htm

Remarks to the factors of the comparison
  • Environmentally friendly: risks for human and environmental
  • By products: forming of harmfull byproducts caused by chemical reactions of disinfection substances
  • Fluids: disinfection efficiency in fluids
  • Surface: disinfection efficiency on surfaces (e.g. pipe surfcaes)

Ultra Violett1

Membrane Filtration

  • Pressure driven filtration
  • Pore sized filter media (see graphic) Micro Filtration (MF)  /  2 – 0.3 bar  /  0.05 – 2 µm Ultra Filtration  (UF) /   5 – 1 bar     /  0.001 – 0.1 µm Reverse Osmosis (RO) / 10 – 40 bar
  • Usual used for disinfection: UF and MF (less viruses)
New membrane technologies for rural areas in developing countries
  • GDM Gravity-Driven Membran Technology Development of Swiss EAWAG
  • Low pressure Ultra Filtration UF
  • Siemens Memcor Membran Technology
  • Minimum required pressure  0.5 m  (0.05 bar)
  • Maximum required presure   4    m  (0.4 bar)
  • Pore size: 0.04 µm
  • Easy and safety operating
  • Inactivate: bacteria, protozoa, partial virus

Membrane Filtration2 Membrane Filtration Membrane Filtration1

 

 

 

 

 

 

 

Source: Water treatment  and pathogenic control  (WHO 2004)