**Abstract**

The tannery effluents are characterized by high toxic pollutants such as sulfides; used in the tanning of animal's skin. The mean objective of this work is the evaluation of the pollution degree of various operating units, and the treatment of tannery effluent generated from unhairing-liming unit. According to physicochemical characterization, this effluent was largely basic and very loaded in sulfides, which have harmful effects on human health and the environment as well. Otherwise, the microbiological characterization showed an absence of pathogenic bacteria and a low concentration of mesophilic aerobic flora, because of this effluent toxicity. Thus, the treatment of this effluent is indispensable before its reject into the environment. In fact, chemical precipitation is a promising approach for the treatment of this effluent. In this regard, ferric chloride was used as chemical agent to reduce and removal sulphide ions from this effluent. As result, this treatment gave an excellent abatement rate of sulphide, which reached more than 90% using a pH of 8.5 and a ferric chloride concentration of 1.4 mol/L.

**Keywords:** Tannery, sulfides, characterization, chemical precipitation, ferric chloride

## **1. Introduction**

The leather industry plays an important role in the global economy, particularly in African countries [1, 2], particularly in Morocco [3]. Besides, the tanning industry is an important activity, which involves the processing of leather animal skin by removing fat and hair through different operations namely unhairing-liming, rinsing, delimingbating and tanning … etc. This tanning process led skins unalterable and rigid [4]. Two methods of tanning are used, chrome tanning and vegetable tanning. At a global level, between 70% and 80% of leather is produced by chrome tanning [5, 6]. Tannery industries use a lot of chemicals and produce huge volumes of wastewater and solid waste [7]. Consequently, tanning industries have been known as a pollution source in the whole world, including Morocco. In fact, they always reject into the environment a large amount of wastewaters, which is loaded with toxic pollutants such as sulfides.

Sulfides can be reduced to hydrogen sulfide (H2S). This toxic gas can poison all living beings, especially humans. Indeed, prolonged sulfide inhalation may cause degeneration of the olfactory nerve and cause death just after few breaths. Plus, the inhalation of this gas even in small amounts can lead to a loss of consciousness [8–13]. Thus, the discharge of these tannery effluents, without prior treatment, harms human health and the environment too. For that, the treatment of these effluents has been very necessary.

Several previous research works have proven some treatment processes for these effluents such as activated carbon adsorption [14], ions exchange [15–18], chemical precipitation using ferric chloride [19, 20], coagulation [21], electrocoagulation [7, 22], sequencing batch reactor [23], bio-augmentation [24] … etc. However, all these studies are only focused on chromium removal from these effluents, and they ignored the elimination of sulfides even they also very toxic.

In this regard, the objective of this chapter was the evaluation of the quality of tannery effluents rejected from different tanning operations. Then, the treatment of wastewater loaded in sulfide and generated from unhairing-liming operation.
