Academic literature on the topic 'Filters and filtration – Aquaculture ; Manganese dioxide'

Most drinking water production plants use rapid sand filters for the removal of manganese from groundwater. The start-up of manganese removal on newly installed sand media is slow, taking several weeks till months. Reducing this period in order to prevent the loss of water during this phase has become an issue of concern. In this study pilot and bench scale experiments were conducted to investigate the mechanism, influence of operational conditions (e.g. filtration rate, manganese loading) and measures that enhance manganese removal capacity of the sand media. Other filter media were investigated with the objective of finding suitable substitutes for the sand. The development of the adsorptive/catalytic coating the sand media in a pilot plant was very slow, notwithstanding the relatively high pH of 8. Low manganese concentration and more frequent backwashing resulted in a longer start up period of the manganese removal. It can not be excluded, that nitrite has a negative effect as well. Measurements in the lab and bench scale tests show that the rate of adsorption/oxidation of manganese in the top layer of the filter bed is too low to explain the complete manganese removal in the filters. It is likely that the adsorptive catalyst in the top layer has partly been covered with ferric hydroxide. From the Freundlich's isotherms determined for 6 different filter media, a crushed medium consisting of mainly manganese dioxide and some silica, iron and aluminium (Aquamandix) followed by iron oxide coated sand, containing some manganese, demonstrated highest adsorption capacities at pHs 6 and 8. These materials can therefore be potential substitutes for sand in situations of slow start-up of manganese removal.

A downflow column test (5 cm bed depth and 5 min bed contact time), employing tap water spiked with Escherichia coli (ca. 50 CFU/mL) and with or without natural turbidity (50 NTU), was used to screen filtration/adsorption media, prepared from locally available materials (bituminous coal, lignite,manqanese ore and iron ore, both raw as well as pretreated/impregnated with alum,ferric hydroxide, lime or manganese dioxide), in terms of their capacity to remove bacteria and turbidity from water. Based on bacteria removal and turbidity data, ferric hydroxide impregnated lignite (Fe-1ignite) and alum pretreated or lime impregnated manganese ore (alum-Mn ore or lime-Mn ore) ranked top among the twenty media tested, showing 100% removal of Escherichia coli with effluent turbidity not exceeding 5 NTU. In terms of chemical characteristics that may affect the aesthetic quality of drinking water, both Fe-lignite and lime-Mn ore were acceptable; however, Fe-lignite showed the least change in the filtered water quality. Effects of pH (5 – 10), ionic strength (0.005–0.0125) and temperature (20 – 35°C) on Escherichia coli sorption by Fe-lignite were investigated in batch sorption tests. In column tests using canal water with 3 min contact time, Fe-lignite produced filtered water with 0–4 CFU/mL coliforms and turbidity not exceeding 5 NTU. Fe-lignite was found to be a potentially useful media for domestic water filters in rural areas of the developing countries.

The aim of this project was to investigate the usage of manganese dioxide ore as a bio-filter media to remove metabolites in aquaculture closed system, and to determine whether manganese toxicity would at the same time represent a risk to fish. Initial work investigated the physical properties of manganese dioxide and its chemical interaction with ammonia and nitrite in the absence of biological activity. Subsequently, two pilot-scale pressurised filters were installed in a commercial scale hatchery in order to compare the metabolite removal performance of manganese dioxide against silicate sand in the presence of biological activity commonly found in aquaculture conditions. The investigation suggests that Mn medium is more reliable in converting ammonia to nitrate without producing a residual output of nitrite. The superior performance ofMn media compared with sand appears to be mainly related to the physical structure of the manganese ore. Furthermore, the Mn medium did not appear to be soluble in the ambient conditions normally found in aquaculture-closed system. From the design point of view, due to the higher ammonia and nitrite removal rates, a shorter retention time and a lower volume of media are required in the case of manganese dioxide technology compared with sand media. As a result, it is much easier to size a biofilter with Mn media. Manganese systems have a comparable total costs to conventional sand media, but using the Mn technology provides a more reliable control of toxic nitrite, thereby reducing risks offish loss and hence with reduced expected production costs.