Drum Filter Description

Description
Sand, anthracite, sandstone, and charcoal are used as granular media for water filtration in POU devices such as bucket, drum or barrel, roughing, and cistern filters. These granular media are usually negatively charged and may be mixed with positively charged metal oxides and hydroxides of iron, aluminum, calcium and magnesium for more effective adsorption of negatively charged viruses and bacteria. These filters may also contain antibacterial elements such as silver.

Performance

Amount of Water Treated
Granular media and rapid rate filters are available in a variety of scales for household and community-level use. The most widely used commercial bucket filtration system provides enough water for 10 people per day. Drum or barrel filters typically have a 200 liter capacity, though a version designed by UNICEF provides 40 liters of treated water a day. Roughing filters are operated at relatively low flow rates, but typically large enough to provide water for an entire community.

Contaminant Removal
Granular media and rapid rate filters typically remove up to 90 percent of turbidity and enteric bacteria and more than 99 percent of larger parasites. Roughing filters can remove 50 to 85 percent of bacteria in highly turbid water. Combining the filter media with a positively charged ingredient can result in up to 99 percent viral and bacterial removal. Filters containing granulated vegetable matter such as burnt rice hull ash have been shown to reduce turbidity and general bacteria by 90 percent, with E. Coli reductions reported at 90 to 99 percent.

Ease of Use
Bucket filters consist of two or three buckets, one of which is perforated at the bottom and filled with granulated media. Water is passed through this bucket into an empty bucket. Initially, enough water should be passed through the filtering bucket to clean the media. The media also needs to be cleaned or replaced every few weeks to remove accumulated contaminants and microbes. Drum or barrel filters come in a variety of designs, most of which have a pour-through design. These filters require regular cleaning through backwashing, a process of forcing water through the filter, which may be technically difficult. Roughing filters also require regular backwashing to work effectively. Roughing filters are most often used on a community level because of their need for operational and maintenance skill and labor. If a regular maintenance schedule is not followed, users may be unaware that any of these filters needs cleaning until signs of contamination are evident.

Costs

Bucket filters can be locally built at low cost using sand or other local granular media. Commercial bucket filters are also available. The most widely used version consists of two 19 liter buckets and filters and costs $50 US, with replacement filters that cost $20 US. These bucket filter systems are often subsidized by NGOs to make them affordable. Drum or barrel filters cost $0.001 to $0.10 US per liter of water treated.

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