**Abstract**

The valorization of different organic residues like municipal solid wastes, sewage sludge and olive mill wastewater is becoming more and more worrying in the different modern communities and is becoming relevant and crucial in terms of environmental preservation. The choice of the treatment technique should not be only from the point of view of economic profitability but, above all, must consider the efficiency of the treatment method. Thus, an attempt to remove polyphenols from olive mill wastewater would have a double interest: on the one hand, to solve a major environmental problem and to recover and valorize the olive mill wastewater for advanced applications in food processing and soil amendments. It is also interesting to think of associating two harmful wastes by co-composting such as sewage sludge-vegetable gardens, sewage sludge-municipal solid waste, and green wastes-olive mill wastewater…, to get a mixed compost of good physical–chemical and biological qualities useful for agricultural soil fertilization. Finally, in order to be more practical, we will describe specifically in this chapter a new variant of composting and co-composting technology intended for waste treatment that is very simple, inexpensive and easy to implement.

**Keywords:** Valorization, Wastes, Olive mill wastewater, Compost, Soil fertilization

### **1. Introduction**

Compost makes up a stable, hygienized and humus-rich product resulting from the mixing of various municipal, plant or animal residues, gradually fermented to ensure the decomposition of organic matter (OM), and used as a fertiliser, amendment or growing medium. Thus, compost is the resulting product of a complex microbial process of decomposition and transformation of biodegradable organic residues. This process operated under varied microbial communities that develop and grow in aerobic conditions [1–3]. Fermentable organic wastes are coming in many forms and with different proportions and accessibility to microorganisms. The raw materials used in composting are much diversified, we can cite as examples raw manure, bedding, feed residues, straw, various crop residues, olive pomace and varied products from agro-food industries [4].

Composting is a biochemically continuous phenomenon of organic matter mineralisation or oxidation in the presence of oxygen. The mineralisation or oxidation is achieved by microorganisms that use oxygen from the air and organic carbon for all their all-metabolite biosynthesis. To make the degradation or the oxidation easy, two operations may be implemented. These two operations are always considered as optional. First, the waste can be sorted to separate the fermentable fraction from the non-recyclable one. Second, the waste may be mechanically shredded to improve the structure of the waste mass; thus, on the one hand, the waste shredding facilitated the biodegradation, reduced the treatment time and make handling more pleasant; and the second hand to make homogenisation of the waste mass easy by allowing a uniform distribution of the different waste components. Once the residual substrate has been prepared, fermentation that resides at the heart of the process, is started. This fermentation leads to a rapid decomposition of easily biodegradable organic matter that generates some fewer complex molecules. Subsequently, the substrate biodegradation leads to slower maturation. These steps are commonly known as the processes of humification and stabilisation of the compost [5]. Once the compost has reached maturity, it will undergo screening and sieving. This operation is allowed to give two products: a commercial product known as compost and a refusal product to refine and/or to landfill. All these mentioned operations are well conducted in all common composting processes. Despite, some precise differences could be existed and lie in the location of the screening phase and the choice of the fermentation system. The originality aim of this book chapter is to describe, in the composting plant implemented under semi-arid pedoclimatic conditions, a description of new and simple process of composting and co-composting of municipal solid wastes, olive mill wastewater, waste farm and garden cutting, straw and sewage sludge. All these residual materials resulting from the main human activities commonly known at the present state in modern societies, with especially the olive mill wastewater resulting from oleiocultural activities, will be considered in this a new process of composting description, mainly characterized as simple to implement and to monitor [6, 7].

Indeed, the process is directed in two principal successive steps: step of prefermentation (uncontrolled fermentation) and step of maturation (controlled fermentation), respectively.

#### **2. General composting process operation**

Composting is a complex bio-physical–chemical operation that comprises biodegradation of organic waste under controlled conditions of temperature, humidity and aeration. Two important following one another biophysical phenomenon could include the common composting process. The first process brings the organic residues to the state of fresh compost. An intense aerobic degradation concern essentially the decomposition of fresh organic matter at a high temperature of 50–70°C under the action of thermophilic bacteria; while the second process is done by a less sustained degradation mainly achieved by mesophilic bacteria. These bacteria transform the fresh compost into a mature compost, rich in humus. This maturation phenomenon, which takes place at lower temperatures of 35–45°C, leads to the biosynthesis of humic compounds by fungi.

The composting process of organic residues takes place in three distinct and important phases. First, the temperature rises rapidly to around 40°C or 45°C following the respiration of aerobic mesophilic microorganisms; in parallel, the most degradable compounds such as sugars and starch are consumed. Second, the temperature rises progressively to around 60°C or 70°C and the mesophilic

**49**

will be inhibited.

*Co-Composting of Various Residual Organic Waste and Olive Mill Wastewater for Organic Soil…*

microorganisms will be replaced by thermophilic ones, anaerobic fermentation by aeration of the waste mass must be avoided; pathogens, parasites and weed seeds will be destroyed by the temperature. Third, the degradation is complete when aeration no longer increases the temperature, the amount of material easily operational by the microflora becomes scarce and the biosynthesis of humic compounds becomes predominant, and at the end the thermophilic species in favour of more common species disappears and appearance of new mesophilic species [8].

**3. Physical-chemical parameters monitored during the composting** 

The principal physical–chemical parameters of the process monitoring are summarised in the parameters that condition the good development and progress of microbiological activities, and their monitoring is essential to test the effective conduct and behaviour of the composting process [9, 10]. This is achieved by optimising nutrient supply and regulating pH, temperature, water content and aeration

The waste particle size is an important parameter to consider in the composting process since (i) it determines the size and volume of the pores created by the arrangement of the particles in the waste matrix, (ii) it is involved in increasing the specific surface area of the raw organic matter, (iii) it facilitates the diffusion of oxygen inside the compost waste matrix, thus allowing homogenisation of the waste, and at last (iv) it is the site of main microbiological activities that take place

This parameter shows the real proportion of oxygen in the interstices of the waste mass. It is critical to the oxidation of the organic matter, and directly related to the size, humidity and aeration of the waste during composting. Oxygen requirements decrease along composting whether they are proportionate to the organic matter gradually disappearing over the mineralisation process. However, maintaining and preserving good aeration avoids the start of an anaerobic process that could induce the generation of malodorous compounds. Moisture in the waste mass always interacts negatively with the system aeration. The supply of oxygen allows the drop in humidity. If this humidity is high, a probable temperature rise will take place leading to a significant improvement in the substrate mass homogeneity. The minimum threshold of oxygen needed to maintain aerobic conditions is of the order

Humidity is both a raw material-related parameter and a monitoring parameter. It hosts the development of the microbial flora within the compost. The optimal water content during composting is around 60%. However, high water content promotes anaerobic fermentation. If the water content exceeds 70%, the water fills the voids and space, making oxygen exchange very difficult. On the other hand, if this prevailing humidity drops below 20%, the decomposition of organic matter

*DOI: http://dx.doi.org/10.5772/intechopen.97050*

**process**

conditions.

**3.1 Grain size of wastes**

on the surface of the organic particles.

**3.2 Interstices oxygen rate**

of 5% as reported by Jammes [9].

**3.3 Prevailing humidity in the waste mass**

*Co-Composting of Various Residual Organic Waste and Olive Mill Wastewater for Organic Soil… DOI: http://dx.doi.org/10.5772/intechopen.97050*

microorganisms will be replaced by thermophilic ones, anaerobic fermentation by aeration of the waste mass must be avoided; pathogens, parasites and weed seeds will be destroyed by the temperature. Third, the degradation is complete when aeration no longer increases the temperature, the amount of material easily operational by the microflora becomes scarce and the biosynthesis of humic compounds becomes predominant, and at the end the thermophilic species in favour of more common species disappears and appearance of new mesophilic species [8].
