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INTRODUCTION
The textile industry in Morocco produces considerable amounts of sludge and the management of liquid sludge becomes a major issue for industrial plants due to increased environmental regulations.
Color removal is one of the most important steps in wastewater treatment process, which is generally achieved through the coagulation process using suitable coagulants. Generally, the coagulants used in the conventional methods are calcium oxide Ca(OH)2, aluminum salts (Al2(SO4)3 and AlCl3), and iron salts (FeCl3 and Fe2(SO4)3) (Berradi et al. 2014). Due to these chemicals, there is a possibility that a secondary pollution problem will arise because of excessive chemical use in the treatment.
The use of alkali pretreatment is often critical for the performance of the separation process (Saveyn et al. 2005; Hjorth et al. 2008). Aggregation of particles into flocs improves separation, i.e. higher quality of the liquid phase (in terms of purity) and increased capacity of the separation. In addition, alkali pretreatment can cause the alignment of the sludge colloidal particles, leading to a reduction in their affinity for water and the water-holding capacity of the sludge flocs. Therefore, the use of calcium oxide during the pretreatment could be an interesting option for enhancing the handling capacity of the sludge. An addition of calcium oxide to the sludge could allow the utilization of larger volumes of sludge for coal-sludge slurry (CSS) and offer economic benefit as an alternative to conventional energy sources. The effects of calcium oxide on the surface properties of municipal wastewater sludge and its co-slurrying ability with coal were reported by Wang et al. (2013). In their study, the rheological measurements were carried out to analyze the flow behavior of the sludge containing different amounts of calcium oxide. The characteristic viscosity of the coal raw-sludge slurry (R-CSS) was 1,635.3 mPa s. After modification of the sludge with 2 wt% of calcium oxide for 24 h, the CSS viscosity decreased to 1,184.4 mPa s.
There is also a great interest in sludge valorization for the manufacture of building materials. The stabilization process of dewatered domestic sewage sludge by the addition of calcium oxide to produce material for the cement industry was conducted by Valderrama et al. (2013).
Various rheological studies were carried out on the stabilization of sewage sludge with calcium...