La disputa de/desde el Estado

The following summary of recommendations to filter manufacturers is based on the knowledge summarized in this report.

1) FACTORY SETUP: Before establishing a factory, it is recommended that a production manager visit a fully functioning filter factory. An experienced filter technician and local potters should be involved when setting up a factory and developing the mixture ratio. 2) WATER: A reliable source of reasonably clean water is required for filter

manufacturing. Both production and flow rate testing water should be tested for heavy metals, inorganic chemicals, arsenic, and microbiological contaminants at project outset and yearly, or more regularly if the factory is using an intermittent or less safe source. In addition, flow rate testing water should be evaluated for turbidity.

3) RAW MATERIALS: A reliable source for raw materials, including clay, burn-out materials, and any additional materials added to the filter mixture should be identified and materials should be evaluated during initial sourcing, yearly, when characteristics vary, or if a change in filter quality is observed. Evaluations should be documented and analyzed, and a variation greater than 10% or a change in filter characteristics or quality must be followed-up with microbiological confirmation of filter effectiveness. 4) MATERIALS PROCESSING: Both clay and burn-out material should be processed

onsite to a consistent powdered form using a 25 or 30 mesh sieve. Additional materials, such as sand, grog, or laterite, should be processed and included

consistently according to the factory filter mixture ratio. Both raw and processed materials should be stored safely and under appropriate conditions.

5) ESTABLISHING RATIO: The appropriate clay:burn-out ratio should be determined at project outset, and used consistently throughout production and any changes in ratio should be confirmed with microbiological testing of finished filters. To confirm

clay:burn-out ratio, a minimum of 9 prototype filters from 3 different batches should be tested and achieve 99% (2-log) reduction of microbiological indicators. The effluent water from prototype filters should be tested for heavy metals and inorganic chemicals before starting production.

6) MIXTURE PREPARATION: In preparing the filter mixture, raw materials should be measured by weight, not volume, and the burn-out material should be dehydrated before it is weighed. Materials should be mixed in a mortar mixer operating at 40-50 rpms, if available. Before adding water, mixed dry materials should be inspected visually for even distribution of clay and burn-out material and again after water has been added. The mixture should be processed through a pug mill, if available. Filter mixture should be wedged or kneaded before pressing. A standard weight of filter mixture should be used to press each filter. Filters should be pressed the same day that the filter material is prepared, and filters manufactured from the same batch of filter mixture should be kept together throughout production and fired in the same kiln load. 7) FILTER PRESSING AND DRYING: A press with a high-quality mold should be used to

press the filter mixture into shape. Freshly pressed filters should be handled as little as possible to prevent deformation or warping. Filters should be stored in conditions that allow them to dry slowly and evenly, protected from direct sun, wind, and rain. Artificial drying from a wet stage is not recommended. Once leather-hard, the surface of the filter may be touched up and each filter should be stamped with a batch, filter number, and logo. Filters should be inspected visually after pressing and periodically throughout the drying process for even drying, deformation, and cracks, holes or other flaws. Once beyond the leather-hard stage, filters should never be patched: rejected filters should be destroyed, and the mixture should not be reused to make filters.

8) KILNS: The Mani kiln is recommended for filter production, but other fuel efficient, reliable kilns that fire evenly and consistently may be used. Kiln capacity should be tailored to the projected level of production taking into consideration mixture batch size, daily production capacity, and factory storage capacity. Production can be smoothly coordinated if kiln capacity matches the number of filters that will be produced in 2 days, so that a production run can be fired in one firing and time is allowed for the firing and cooling of the kiln(s). Kiln temperature mapping should be carried out on a new kiln, annually, or if firing results (filter quality) are inconsistent. Effort should be made to acquire fuel from sustainable sources. Experimentation with and the use of agricultural waste or alternative fuel sources is encouraged.

9) FIRING: Filters should be completely dry before being fired and should be stacked using spacers to promote heat circulation and even heating and cooling to reduce the chances of warping or cracking and minimize carbon marks on the filters. The firing temperature and firing curve appropriate for the local clay and burn-out material should be established and followed, and a firing log should be maintained. To ensure

processes are properly carried out, firing should be slow and closely monitored during the critical phases of water smoking, combustion of the burn-out material, and burning out of carbon. Fewer than 10% of filters should crack per firing. It is not recommended that a black core be allowed to remain within filter walls. Kiln temperature and heatwork should be should be monitored visually, with pyrometric cones (the three cone

method), draw trials, and a pyrometer with thermocouples. The use of these methods will help monitor heat distribution in the kiln, aid in consistent firings, and provide information to document and compare firings, aid in troubleshooting, and help increase fuel efficiency.

10) HEALTH AND SAFETY: Employees should be required to follow national and local health and safety regulations in addition to the guidelines outlined in each section of this report. In particular, anyone exposed to airborne particles should be required to wear face masks, remembering that very fine silica dust can remain airborne for several hours. In addition, preventative measures should be taken to reduce the suspension of dust including cleaning with water (as opposed to dry sweeping) and securing the collection bag to the hammermill during operation. Wearing goggles can prevent eye irritation from dust. When working with machinery, long hair should be tied back, and loose clothing, which could get caught, should not be worn. Earplugs should be worn when working with or near loud machinery. When looking into a hot kiln safety goggles that protect from ultraviolet and infrared light should be worn. When working with liquid silver, gloves and an apron should be worn and when working with powdered silver, a face mask, protective eyewear, gloves, and an apron should be worn.

11) DOCUMENTATION: Materials evaluations, production, and firing logs should be maintained. Materials should be evaluated regularly. A detailed production log that documents the manufacturing process and the results of quality control evaluations and tests should be maintained for each filter. A firing log should be kept to document each firing and the location of each filter in the kiln should be recorded. Recommended items to record are suggested throughout this report and example logs are included in Annex G.

12) INSPECTING AND TESTING FILTERS: Visual inspections should be carried out before each major step of the manufacturing process, observations should be recorded on a filter log, and filters which do not pass should be destroyed. Indirect indicator tests including auditory, pressure, and flow rate testing should be carried out and

documented for 100% of filters destined for sale or distribution. Filters should be saturated before testing their flow rate. Flow rate can be determined either by measuring the drop in water level with a T-stick or measuring the water that passes through a suspended filter after 1-hour. Filters that do not meet the minimum flow rate may be refired in attempt to increase the flow rate. The flow rate of each filter should be documented and average flow rates should be monitored over time.

13) MICROBIOLOGICAL TESTING: Each factory should establish a microbiological testing schedule that includes both independent laboratory testing and in-house testing. Microbiological testing should be carried out before silver application. A minimum of 0.1% of the filters should be tested in a laboratory. A minimum of a 2-log reduction in TC, TTC, and/or E. coli should be achieved. Additional testing should be

carried out at the factory on a minimum of 1% of filters (minimum one from each batch). Results should show either a 2-log reduction or fewer than 10 CFU/100 mL of TC, TTC, and/or E. coli. Filters that do not pass quality control tests should be destroyed so they cannot be mistaken for effective filters and used.

14) SILVER APPLICATION: Colloidal silver should be applied to filters to prevent bacterial growth in the filter (Silversty-Rodriguez 2008) and potentially increase the

microbiological reduction through the filter. Silver should be applied to filters that have passed all other quality control inspections to avoid wasting silver on noncompliant filters and reduce the amount of silver released into the environment. Colloidal silver should be diluted with nonchlorinated boiled, filtered, bottled or deionized water, preferably with a low calcium concentration (to prevent the aggregation of silver particles). Approximately 64 mg of colloidal silver should be applied to each filter by brushing on 302 mg of a 211 ppm solution. Powdered, liquid, and diluted silver should be stored in a dark, airtight container to protect it from oxidation and ultra-violet light. Because there are potential problems with dissociation of silver nitrate from the filter, the use of silver nitrate is not recommended until further research has been carried out. 15) THE FILTER UNIT AND PACKAGING: Receptacles should be large enough to provide

enough space below the bottom of the filter to contain the volume of water that fits inside the filter. Lids should fit well so that insects, dust, and debris cannot gain access to the filter or filtered water. The tap should be of high quality and located to maximize the amount of water that can be dispensed yet clear a surface the receptacle is placed on. Plastic receptacles should be made of food grade material and clay receptacles should be coated with colloidal silver diluted to application strength. Filter elements should be placed in a bag. Packaging of filter units should be developed to minimize breakage.

16) OPERATION AND MAINTENANCE INSTRUCTIONS: Filter manufacturers should recommend that filter owners wash the receptacle and tap with the first three flushes of water from the filter since: 1) the first few batches contain a higher concentration of silver; 2) the receptacle and tap could have become contaminated during transport; and, 3) the initial water has a bitter taste, which might discourage filter acceptance. Operation and maintenance instructions should be provided with each filter unit and should state: cleaning frequency should be as needed or when flow rate slows; the receptacle, tap, and lid should be cleaned when the filtering element is cleaned, and not more frequently, unless needed; hands should be washed before cleaning the filter; once removed from the receptacle, the filter element can be placed rim down on the inside of the lid; the receptacle, tap, and lid can be cleaned with bleach or soap (except clay receptacles); and, cleaning products should not be used on the filter element and only the inside of the element should be cleaned and scrubbed, the outside should not be touched.

17) ONGOING EVALUATIONS: Factories are encouraged to obtain certification from local authorities and carry out internal and/or external reviews after the installation of a new factory, before the initial release of filters for consumer use, and annually. Factories are encouraged to work with academic researchers, international or local NGOs, health clinics, national health organizations, or other relevant institutions to continue to prove the performance of their filters. Production should be well documented to aid factories

in troubleshooting, identify changes in materials characteristics, increase efficiency, reduce the risk of having to stop production to resolve a quality control issue, and to have manufacturing details available for researchers studying filters.