**Abstract**

Industries play a major role in the development of countries′ economy. However, they are known as the biggest source of water pollution in the whole world. In fact, several industries use a huge amount of water in their manufacturing operations, and then, they reject a large volume of wastewaters such as tanneries, brassware, olive mills … etc. The sewage of these industries may contain organic/inorganic matters or toxic components that harm human health and the environment. Therefore, the treatment of these effluents is necessary. For that, there are many treatment processes, including biological and physicochemical processes or both. The choice of adequate process is depending on many reasons, especially on the biodegradability degree of each effluent, as well as the presence of recalcitrant pollutants. Nevertheless, biological technologies, particularly bioremediation, are recently an emerging technology for the elimination of recalcitrant pollutants like heavy metals. Furthermore, these biotechnologies are simple, efficient, eco-friendly and inexpensive. Therefore, this environmental biotechnology may be a new approach for the treatment of industrial sewage, so, it can successfully replace physicochemical technologies that are very expensive.

**Keywords:** Industries, sewage, biological technologies, physicochemical processes

## **1. Introduction**

Water is so essential in our daily life. However, water resources and their quality are progressively decreasing because of human activities, and then several countries are threatened by water scarcity, including Morocco. So, the rational management of these water resources is a big challenge in the whole world. Nowadays, the treatment and reuse of wastewater are known as the best solutions to deal with this lack of water. The constraint of this issue is pollution, especially industrial pollution, because industries generate high toxic substances, which may reduce the performance of the treatment [1]. For example in Morocco, the large hydraulic basin 'Sebou' receives more than 40% of pollution from industries of Fez city such as tanneries, textiles, brassware, olive mill … etc.

Industries release organic and inorganic pollutants namely heavy metals, dyes, polyphenols … etc. Heavy metals are toxic, in which their toxicity depends on several factors, particularly the metal dose and the time exposition. Arsenic, cadmium, chromium, lead, and mercury, have ranked as carcinogenic metals, because they may damage multiple organs even at lower exposure doses [2]. Likewise, textile dyes are highly toxic and potentially carcinogenic [3]. Thus, they can lead to various animal and human diseases, as well as the environmental degradation. Therefore, recalcitrant substances harm the environment and human health, and then their removal from wastewaters is mandatory.

The literature has shown several physicochemical and biological processes for the treatment of industrial sewage. Among physicochemical processes, there is coagulation [4], electrocoagulation [5], forward osmosis [6], chemical precipitation [7], adsorption [8], and oxidation [9]. As for biological systems, there are many technologies such as sequencing batch reactor [10], bioaugmentation [11], biosorption [12], membrane bioreactor [13], anaerobic digestion [14]… etc. In fact, each process has its advantages and disadvantages; hence the process performance is highly dependent on the nature of the effluent and the flow to be treated. For example, physical–chemical treatments are known for their high performance, but they are very expensive and can generate another serious pollution. Biological treatments are also efficient and ecological, but the presence of recalcitrant substances in huge amount can decrease their efficient. So, the issue is complex, because it is necessary to find a treatment process that will be eco-friendly, efficient, and economical at the same time.

Taking into account the above, this chapter focuses on various physicochemical and biological processes for the treatment of industrial sewage. Moreover, this chapter will show the effectiveness of biological technologies for the removal of toxic substances.

### **2. Treatment of industrial wastewaters**

The treatment of industrial effluents is essential before their discharge into the natural environment. Several physicochemical and biological treatments of these effluents have been studied in the literature. These techniques have been considered simple, efficient, or even advanced, but each system has certain advantages over the other. Moreover, these treatment systems can be applied independently or combined.

### **2.1 Physicochemical treatments**

### *2.1.1 Membrane filtration*

### *2.1.1.1 Reverse osmosis*

This technology is based on the use of a semi-permeable membrane, wherein pollutants will be captured. This treatment system is known for its high purification rate, and it may be used for the treatment of all industrial sewage [15]. A study has shown that reverse osmosis is an advanced and promising technique for industrial wastewaters. Despite the qualities of this treatment system, it presents certain disadvantages, particularly the high cost.

### *2.1.1.2 Membrane filtration*

Currently, this technique is well developed; it is based on the physical separation of pollutants under hydraulic pressure. This treatment system is very efficient *Biological versus Physicochemical Technologies for Industrial Sewage Treatment… DOI: http://dx.doi.org/10.5772/intechopen.100325*

for industrial sewage treatment such as pharmaceutical [16], textile [17], pulp and paper effluents [18]…etc. The separation is based on three principles, which are adsorption, electrostatic phenomenon, and sieving [19].

According to the membrane′s pore size, there are three filtration types:


Otherwise, the membrane can be mineral (metallic, ceramic, etc.) or organic (polyamides, cellulose acetate, etc.). Its structure can be uniform (Isotropic) or composite (Anisotropic). Indeed, organic membranes are the most used because of their low cost, but mineral membranes can resist extreme conditions (Temperature, pH, etc.).

Consequently, membrane filtration has several qualities, namely the removal of micro-organisms, heavy metals, turbidity, dyes, and also odors from industrial sewage. Despite these advantages, the technique has also some limits such as rapid membrane fouling, production of high amount of sludge, high investment costs, and high energy consumption.

### *2.1.2 Coagulation-flocculation*

The coagulation-flocculation process involves the use of coagulant and flocculant agents that can regroup the pollutants together as heavy flocs. These flocs will be eliminated by precipitation or filtration. These agents may be iron or aluminum chemicals. According to Junio et al. [4], coagulation-flocculation is a simple, fast, and effective technique for removing pollutants from industrial wastewaters. In this study, ferric chloride was used as a coagulant agent for the treatment of tannery sewage, wherein the abatement rates of COD and suspended solids were above 80%. Nevertheless, this technique has several disadvantages, namely the production of high sludge and the increase of acidity and conductivity within the treated effluent. On the other hand, the use of bio-coagulants and bio-flocculants is a new approach of this technique in order to reduce the massive use of chemicals and their harmful effects. According to previous study, cactus juice can be used as a bio-flocculant to reduce chromium, in which chromium VI removal was around 98% [22].

### *2.1.3 Electrocoagulation*

Electrocoagulation has considered as a new alternative of chemical coagulation, and it is a promising process for the treatment of industrial sewage [23]. This technique is based on the principle of soluble anodes, and it induces the electrochemical separation of pollutants. These anodes are often made of aluminum or iron, from where metal cations (Fe3+ or Al3+) are generated by imposing an electric current between these anodes. These metal cations react as a coagulant to destabilize the suspended particles, and then, the formation of flocs that will subsequently precipitate. Indeed, this technique has several advantages, but the production of sludge in high amount and the consumption of high energy are its main disadvantages.
