AlternativeLEC4

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Alternative Water Treatment (4)
Alternative disinfectants (2)
Lecture 3 Î Reminder
Disinfection of water by using Solar Irradiation
Purpose
General principles
Systems
Factors affecting performance
1
Lecture 3 reminder
Clostridium removal by membranes
More efficient than disinfection with Cl
2
or UV;
Does not create oxidation by-products;
Recommended for surface waters
Typical values of efficiency : up to 5 log
Growth on Agar
Microscopic image
2
Lecture 3 reminder
Declared removal efficiency of typical hollow fibre mebrane
Water Treatment Results:
Turbidity< 0.1 NTU
Bacteria> 4 log removal
Giardia Cysts> 4 log removal
Cryptosporidium Oocysts> 4 log removal
Virus Rejection > 4 log
Total Suspended Solids < 1 mg/L
3
„Evolution” of water disinfection
19th Century Î pathogen removal with the use of
strong oxidants (ozone gas);
Beginning of 20th Century Î implementation of long
lasting disinfectants to prevent water in a network
against bacterial growth (chlorine gas);
50Ós of 20th Century Î taste improvement (ozone
comes back)
60Ós Î disinfection/chlorination by-products recognition
(THMs, bromides etc.)
90Ós Î disinfection by-product rule (in general terms:
minimization of oxidantsÓ use)
90Ós need for inexpensive means for disinfection to be
applied in remote/underdeveloped/crisis areas
4
Solar disinfection
Purposes of investigations
Developed countries
Implementation of non-chemical means (no by-products
recognized);
Tourism/trekking;
Developing countries and remote areas:
No chemicals needed;
Lack of toxicity and/or explosion
No electricity consumption;
Relatively simple, sustainable solution;
Applicable in crisis situations
5
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