Page 147 - New Trends in Eco efficient and Recycled Concrete

Sewage sludge ash
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Jordi Paya ´, Jose ´ Monzo ´, Marı´a Victoria Borrachero and Lourdes Soriano
Chemistry in Building Materials Research Group (GIQUIMA), Concrete Science and
Technology Institute (ICITECH), Universitat Polite `cnica de Vale `ncia, Valencia, Spain

5.1 Introduction

The increase in the human population and the development of new technologies,
materials and processes have caused an increase in the demand for resources. The
mismanagement and extensive use of these resources cause detrimental environ-
mental problems. To minimise the impact on the environment, it is necessary to
ensure the elimination of dangerous substances into nature.
The demand for water and the subsequent generation of huge quantities of waste-
water, both of urban origin and of industrial origin, requires the development of
diverse technologies for the elimination of contaminants present in wastewater. In
remote times, nature itself could manage the self-purification of wastewater since
the amount generated was small. However, industrial development and the concen-
tration of people in large cities has resulted in the self-purifying capacity of rivers,
lakes and seas being exceeded.
One of the most notable characteristics of wastewater, especially those of urban
origin, is its high concentration of organic matter, both soluble and insoluble. The
oxygen demand (chemical oxygen demand, COD, and biological oxygen demand,
BOD) caused by this organic matter decreases dissolved oxygen levels in the
receiving water (river, lake or sea), causing the death of many species and limiting
the possibility of using that natural resource.
To minimise the impact of wastewater, various wastewater treatment processes
(WWTP) have been developed, such as pre-treatments, primary treatments, second-
ary treatments and tertiary treatments (Ramalho, 2013; Gupta et al., 2012). These
treatments allow, on the one hand, the reduction of the impact on the environment
and, on the other hand, increasing the possibility of reusing treated water (for exam-
ple, in the area of agriculture).
Pre-treatment consists of the elimination of large elements present in the waste-
water through bars and screens. Likewise, fats and oils that remain on the surface
of water can also be eliminated in order to improve the exchange of air with the
atmosphere in later stages. In this case, the type of waste generated can be consid-
ered as a waste similar to urban solid waste.
Primary treatment consists mainly of a physical/chemical sedimentation pro-
cesses in such a way that the insoluble particles, both organic and inorganic, can be
New Trends in Eco-efficient and Recycled Concrete. DOI: https://doi.org/10.1016/B978-0-08-102480-5.00005-1
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