HEALTH AND SANITATION
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• 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