Home Page Link DFID logo
Back
  Biological Removal Of Iron From Borehole Handpump Water Supplies
 

R Number:  R6253
Contractor:  Silsoe College, Cranfield University
Dates:         1 July 1995 to 28 February 1997
The development and testing of a handpump-attachable biofilter for the removal of iron from groundwater. A successful design would be affordable, in the context of borehole-handpump water supply projects, and maintainable at the village level.

Executive Summary
Objectives

The stated outputs of this project were as follows:

  • The development of a working prototype filter design appropriate for attachment to handpumps.
  • The development of a simple, routine maintenance strategy to ensure sustainable operation.
  • The development and testing of training materials aimed at village level operation and maintenance.
  • The dissemination of the accrued information such that it can reach the widest possible audience.
    • Methodology

    3 pilot-scale experimental filters were fabricated over the period January-October 1996. The filters were filled with sand of different particle size and to different depths. Groundwater was supplied to the filters for 6 hours per day. Because filters become clogged with iron deposits and gases, they need to be cleaned periodically. Various cleaning techniques were tried. The total iron concentrations of influent and effluent water samples were determined daily. The discharge from the filter was measured twice daily. Occassional measurements of temperature, pH and dissolved oxygen were also made.

    Results

  • All of the experimental filters were capable of reducing iron concentrations from an average of 7.3 mg/l to * 0.3 mg/l (WHO recommended concentration of iron).
  • The filters containing the 1.18 mm sand were the most consistent. Over the full experimental period, the 0.15 m deep bed achieved the WHO limit on 47% of operational days and the 0.1 m deep bed achieved the WHO limit on 49% of operational days.
  • Once operational procedures had been optimised, the 0.15 m deep bed containing 1.18 mm sand proved to be very reliable, meeting the WHO limit on 83% of operational days from June 1996 until the end of the experiment in September 1996. This compares to a success rate of 58% for the 0.10 m deep bed containing 1.18 m sand from the beginning of June 1996 until the end of the experiment in October 1996.
  • The filter containing the larger sand size (1.3 mm) proved to be much less consistent, only achieving the WHO limit on 5% of operational days.
  • The biological iron removal process is consistently able to achieve >95% removal at surface loadings up to approximately 1.27 m/hr. At rates greater than this, iron removal is less predictable.
  • Flow through all filters tested diminished with time due to clogging by trapped gases and iron precipitates. When the filters are cleaned every week, we may expect flow rates to fall to one half of their clean value.
  • Once clogged, it proved possible to re-establish flow rates using a range of simple cleaning methods.
  • Stirring would feature in any proposed filter design as it disturbs and releases iron biofilm and trapped gases. Following stirring, there must be a mechanism for removing disturbed particulates from the filter.
    • Conclusions
    Objectives achieved

    The development of a working prototype filter design appropriate for attachment to handpumps

    Studies with experimental filters indicate that biological iron removal is an effective and, over the experimental period, a sustainable process. A working prototype design has been developed, based on the results of experimental filters. The design has been coupled to handpumps in limited trials in UK and Uganda. The system shows promise but is unlikely to prove acceptable to users unless the problem of a delay in the delivery of an acceptable flow of filtered water is overcome. This requires further development.

    The development of a simple, routine maintenance strategy to ensure sustainable operation

    Studies with experimental filters indicate that a combination of stirring and backwashing/bailing on a weekly basis is capable of sustaining acceptable flow rates, without adversely affecting filtered water iron concentrations. It is not yet possible to confirm whether these experimental protocols can be translated into simple and routine cleaning strategies as certain design/operational questions remain unanswered.

    The development and testing of training materials aimed at village level operation and maintenance

    A set of guidelines have been developed for use by organisations interested in testing the prototype filter design. The document provides advice on design, operation and maintenance. The operation and maintenance advice contained within the were field tested in Uganda in April 1997.

    The dissemination of the accrued information such that it can reach the widest possible audience

  • Distribution of filter guidelines to interested parties on the mailing list.
  • The guidelines and accompanying information to be transformed into a website on the internet.
  • The preparation of at least 1 scientific journal paper and 1 popular article.
    • Further Information
    List of Publications
    Tyrrel, S.F., Gardner, S.J., Howsam, P., & Carter, R.C. (1998) Biological removal of iron from well-handpump water supplies. Waterlines 6 (4), 29-31.
    Follow-up Activities

    Further development of the filter

    The delay that the current design creates, in obtaining an acceptable outlet flow rate must be dealt with if the filter is ultimately to be accepted by users. Two potential solutions have been devised, one of which, the reduction of the volume of stored water above the sand using floating ballast is currently being worked on. This problem re-emphasises the point that it is hydraulic/engineering factors which are fundamental to the success of handpump-attached filters rather than the process of biologically-enhanced iron removal itself.

    A small amount of further development work has been undertaken since the completion of the R6253 project. Further work is still needed if this research is to reach its potential. Private sector participation (handpump or water filter manufacturers) in further research would be welcomed.

    A number of handpump-attached iron removal filters have been developed around the world but the technology is still not well-known. This may be, in part, due to the fact that the technology has not, as yet, been perfected. Another factor may be lack of promotion. It arguable that technologies are best promoted by commercial manufacturers. A sensible next step would be to attempt turn the prototype into a manufacturable and marketable product.

    Future development and consumer testing of the filter could thus be jointly supported by DFID and a commercial manufacturer.

    Contact Details for Further Information
    Sean Tyrrel
    Water Management Group
    Silsoe College
    Cranfield University
     Silsoe. MK45 4DT
    UK

     

    Tel: 01525 863288
    Fax: 01525 863300
    Email: s.tyrrel@cranfield.ac.uk