Solar drying of wastewater sludge
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Date
2011
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Publisher
Elsevier
Abstract
Drying constitutes an important process for wastewater sludge management, as it can reduce the mass
and the volume of the product and consequently the cost of storage, handling and transport. During constant
operating conditions, the drying kinetic of the sludge has shown mainly: a constant drying rate,
one or two falling rate periods and a final short period with variations along the process of the physical
properties of the product with the appearance of shrinkage and cracks phenomena. Solar drying was
benefit as using free solar energy can reduce the cost of the operation. On the other hand, it plays an
important role for the pathogen reduction until Environmental protection Agency (EPA) recommendations.
In some studied cases, the value of 1000 CFU g−1 DS, which represents the EPA Class A pathogen
requirement, for fecal coliform was attained. The general design of used solar dryers was constituted of:
a greenhouse made with transparent material and a floor, where the product is speared in thick layers.
Furthermore, fans and ventilations can be used in order to have homogeneous distribution of the air
inside the greenhouse with replacement of humidified air with fresh one. Automatic or handle mix of
the product was used once or for several times a day. In order to increase the performances of the drying
system, other ways such as heating the floor using solar water heater, infrared lamps, using heat pumps
or adding thermal energy storage systems were also tested. Covered solar drying has given better results
than open solar drying. However, the origin of the wastewater sludge affects the obtained results. Alternatively,
modeling drying systems was effectuated using heat and mass balances, applied for the air and
the dried product. Solar drying of wastewater sludge has given satisfactory results.
Description
Keywords
Solar energy, Drying kinetic, Shrinkage, Cracks, Design, Greenhouse