HEALTH AND SANITATION
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<< Continued from page 49
• Ceramic filters Ceramic water filtration systems generally consist of a porous ceramic membrane , a plastic or ceramic receptacle , and a plastic tap . Water is poured into the upper portion of the receptacle , or directly into the membrane , where gravity pulls it through the pores in the ceramic membrane and into the lower portion of the receptacle . Water is safely stored in the receptacle until it is accessed through the tap . There are two main types of ceramic filters , the candle filter and the pot filter , which differ in the shape and assemblage of the ceramic membrane :
a )
b )
Ceramic pot filters . The pot filter system is simpler , and consists of a single concave membrane , which sits inside the rim of the receptacle . Several field trials carried out in different countries have found ceramic pot filters to be effective in reducing diarrhoea . A study carried out in three regions of Guatemala reported that 91 % of the filtered water tested was free of faecal coliforms . In Nicaragua , water quality analysis was performed on 24 filters in seven communities . Of 15 homes that had E . coli in their water , eight ( 53 %) tested negative for E . coli after filtration . In Cambodia , water quality tests were carried out after 1 000 ceramic filter pots were distributed , and results showed that after up to one year in use , 99 % of the filters produced water falling into a ‘ low-risk ’ range of fewer than 10 E . coli per 100ml .
Ceramic candle filters . Candle filter systems consist of an upper receptacle that sits above and is separated from the storage receptacle . Candle elements , which are cylindrical , hollow ceramic membranes , are attached to the barrier that divides the two receptacles . The only way in which water can flow into the lower receptacle is if it enters the candle elements , which is where filtration takes place . In a randomised , controlled trial conducted among 80 households , in one community during the six-month design life of the ceramic filter elements , faecal water contamination was consistently lower among intervention households than control households . Geometric mean themotolerant coliform ( TTC ) was 2.9 / 100ml versus 32.9 / 100ml , p < 0.0001 . Overall , 70.6 % of samples from the intervention households met WHO guidelines for zero TTC / 100ml compared to 31.8 % for control households .
• Nanofiltration ( NF ) membranes Nanofiltration ( NF ) membranes are an effective technology to remove dissolved organic contaminants . This type of treatment offers an attractive approach to meeting multiple objectives of advanced water treatment , such as the removal of disinfection by product precursors , natural organic matter ( NOM ), endocrine disrupting chemicals , and pesticides . Disadvantages of using nanofilters include the decrease of permeate flux ( membrane fouling ), which is a major obstacle to the application of NF membranes to water treatment . Fouling worsens membrane performance and ultimately shortens membrane life , resulting in increased operational cost . Membrane filters applied as post treatment helps to remove pathogens and suspended solids . Advances in low-pressure-driven membrane technologies such as microfiltration ( MF ) and ultrafiltration ( UF ) have been used in water and wastewater treatment due to their high efficiency , ease of operation and small footprint . A study evaluated the efficiency of a polyvinyl ( alcohol ) ( PVA ) nanofiber membrane / activated carbon column , for the treatment of harvested rainwater .
Results indicated that total coliform counts in the unfiltered tank water samples collected from the two rainwater tanks had an average of 6 × 102 CFU / 100ml . After filtration , total coliform numbers were reduced significantly ( p = 0.008 ) as a ≥99 % decrease was observed for all the first litres of filtered tank water samples in comparison to the unfiltered tank water samples . Furthermore , in separate experiments , molecular techniques were utilised to investigate the bacterial and viral removal efficiencies from RWH tanks .
Genus-specific PCR assays revealed the presence of potentially pathogenic bacteria , commonly associated with tank water . Results indicated that Klebsiella spp ., Legionella spp ., Pseudomonas spp ., and Yersinia spp . were detected in all the unfiltered tank water samples and were then sporadically detected in the filtered tank water . Legionella spp . and Yersinia spp . were the most persistent genera , as these bacteria were detected in all the unfiltered tank water samples and in 85 and 80 % of the 20 filtered tank water .
The PCR assays and BLAST analysis also confirmed the presence of bovine adenovirus 3 in all of the tank water samples collected before microfiltration for both tanks sampled . Other adenovirus strains detected in the rainwater tanks included simian adenovirus B isolate BaAdV-1 and human adenovirus 40 strain M-364 . Moreover , once the tank water had undergone filtration through the PVA nanofiber membrane / activated carbon column , the presence of adenovirus was indicated in 75 % of the filtered tank water samples . Even though the system was able to remove indicator organisms in an efficient manner , the removal of opportunistic bacteria such as Yersina and the removal of viruses were very poor .
• Reverse osmosis Reverse osmosis is a natural phenomenon in which water passes through a semipermeable barrier from a side with lower solute concentration to a higher solute concentration side . Water flow continues until chemical potential equilibrium of the solvent is established . At equilibrium , the pressure difference between the two sides of the membrane is equal to the osmotic pressure of the solution . To reverse the flow of water ( solvent ), a pressure difference greater than the osmotic pressure difference is applied ; as a result , separation of water from the solution occurs as pure water flows from the high concentration side to the low concentration side . PA
www . plumbingafrica . co . za August 2018 Volume 24 I Number 6