Over the next decade the UK will experience significant, imposed changes in the quantity of sewage sludge produced and in the means available for its disposal. Existing practices are being reappraised and new technologies are being explored to cope with a predicted 40% increase in the quantity for disposal. Thermal drying of sludge undoubtedly has a role to play in coping with this demand.The two principal process types, i.e. direct and indirect heat application, are appraised in depth and a comparison is drawn. A case study is identified to examine the energy demands of the process, including the potential for heat recovery and for resource reuse. The environmental impact of a typical process is also examined.
Abstract. Remote communities in the Nepalese mountains above 2500 m a.s.l. belong to the most precarious in the world. Inhabitants struggle for the minimum in terms of safe drinking water, food and sanitation. Reliable, affordable and clean energy for cooking, room heating and warm water for personal hygiene is often lacking and dependency on firewood very high. The remoteness and unlikeliness of electric grid connection in the coming decades make a diversified energy supply from renewable local resources crucial. Small-scale anaerobic digestion (AD) of organic substrates has been used for long in rural areas of developing countries to produce biogas as energy source and recover residue as organic fertilizer. AD is challenging at high elevations due to year around lower ambient temperatures and lower annual biomass production per area compared to lowlands. Nevertheless, examples of operational household AD exist even above 3000 m a.s.l. in the Andes. Here we compare firewood consumption with biogas potential from organic substrates in a community with 39 households at 3150 m a.s.l. in Jumla District, Nepal. In five households with varying numbers of members and animals kept, mean firewood use and its energy content per capita (cap) and day (d) were 2.1 kg or ca. 25 MJ in spring and 2.3 kg or ca. 28 MJ in winter. Easily available substrates include cow, sheep and horse dung from overnight shelters and human excrements from pit latrines, amounting on average to 1.7 kg wet weight (kg ww ) cap À1 d À1 in spring and 2.2 kg ww cap À1 d À1 in winter. Adjusted to normal conditions (Nm 3 at 0°C, 1013.15 hPa), these substrates yielded on average 0.08 Nm 3 cap À1 d À1 biogas in spring and 0.12 Nm 3 cap À1 d À1 in winter (35-60% methane content) in biochemical methane potential (BMPs) tests at 36°C. This could provide up to 60% of basic cooking needs on average and up to 75% in a "typical" household in terms of members and animals kept. Of the overall thermal energy needs including also room heating ca. 10-20% could be covered, substituting 0.1-0.4 (mean: 0.2) kg firewood cap À1 d À1 . If only animal dung and human excrements are considered, no competition for resources arises as residues can still be used as organic fertilizer. This study supports the design and introduction of planned pilot digesters integrated into on-going community development including pit latrines for substrate availability, greenhouses as possible way of thermal insulation, and planned pico-hydropower plants to use excess electricity during the night for digester heating.
In March 1990 a pilot ultra‐violet disinfection plant was installed at the sewage‐treatment works in Bellozanne, Jersey. The pilot plant was set up to test the ability of the process to meet certain defined objectives and, ultimately, to enable the island authorities to satisfy stringent water quality objectives in the receiving waters of St Aubins Bay.
The pilot study simulated an open channel installation using medium pressure ultra‐violet lamps parallel to the direction of flow. The pilot plant was supplied by Trojan Technologies Inc.
The pilot study met its objectives and confirmed the design parameters for a full‐scale plant installation to follow.
About 35 years ago the island of Jersey in the Channel Islands set about rationalizing and modernizing its sewage‐treatment operations. Treatment was carried out in one central, advanced sewagetreatment works producing a Royal Commission effluent which received nominal dilution in a small stream before discharging into the sea in one of the foremost bathing areas on the island.
In 1989, a thorough investigation was carried out on the options to secure an environmentally acceptable solution to effluent disposal. The investigation concluded that disinfection, in combination with a change to the outfall discharge point, offered the most cost‐effective solution. Alternative disinfection techniques were identified, which recognized the nature and sensitivity of the receiving waters and the limited space available on the site. Only ultraviolet disinfection was suitable.
An ultraviolet disinfection system depends on the exposure of the micro‐organisms causing disease to their germicidal wavelength. Light of this wavelength (about 253.7 nanometres) is absorbed by the nucleic acids in the cell which damages or rearranges the genetic information, effectively rendering the cell unable to replicate and resulting in the death of the cell.
In over 300 installations in North America the system has proven to be reliable, simple, economic and, above all, environmentally acceptable.
An ultraviolet disinfection system is currently being installed at Bellozanne, Jersey.
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