Derbal Kerroum, Bencheikh-LeHocine Mossaab and Meniai Abdesslam Hassen

University Mentouri Constantine,

Algeria

1. Introduction

The pollution of water, air and soil by municipal, industrial and agricultural wastes is a major concern of public autorithies who imperatively have to encourage the development of effective and non expensive treatment technologies. Although it is not recent, the process based on the anaerobic digestion (bio-methanisation) for the treatment of the waste organic fraction, is getting very attractive from the environmental and the economical points of view. It consists of a biological degradation of the organic matter, under anaerobic conditions, where a biogas, mainly methane (CH4) is evolved, and hence providing a renewable source of energy which may be used in the production of electricity and heat.

Generally various types of residual sludges and solid wastes are generated by human activities. They are composed of organic matter which may or may not be easily biodegradeable, inorganic matter, inert soluble and non soluble matter, toxic matter, etc. In order to treat these solid wastes, it is first required to characterise them and second to choose a treatment mode depending on their types and their possible final destinations. According to the physical state, one may distinguish solid wastes (dehydrated sludges, domestic wastes, etc.), liquid wastes (effluents from food, fresh liquid sludges, etc.) and suspensions (sludges from water treatment plant). Classification in terms of the sources may be as follows: [18]

mineralised organic matter. The sludge characterisation is essential for the choice of the most adequate treatment method as well as for the prediction of each treatment stage performance. Generally distinction is made between primary sludges which are recovered by simple waste waters decantation, and are of high concentrations in mineral and organic matter, and the biological or secondary sludges resulting from a biological treatment of waters. These latter have different compositions, depending on the nature of the degraded substrate, the operation load of the biological reactor and the eventual stabilising treatment.

For the treatment of the different pollution types, vvarious techniques and processes of different chemical, biological and physico-chemical natures as well as a coupling of the last two, are developed. The treatment and the final elimination consist of a sequence of unit operations with a great number of possible options among which the best one is to be chosen, taking into account the upstream (nature, characteristics, and waste quantities) and downstream (local possibilities of final eliminations) constraints as well as the cost.

The present study is more concerned by the biodegradable organic solid wastes which are characterised by a high organic matter concentration, recommanding a biological treatment.

One of technologies to carry out the treatment of the organic fraction of this organic waste is anaerobic digestion (bio-methanization, this process is presented with more details in the next sections of this chapter), which consists of a biological degradation in an anaerobic phase of the organic matter into biogas with a high methane percentage. This technology is becoming essential in the reduction of organic waste volume and the production of biogas, a renewable source of energy. It can be used in a variety of ways, with a heating value of approximately 600 -800 Btu/ft and a quality that can be used to generate electricity, used as fuel for a boiler, space heater, for refrigeration equipment, or as a cooking and lighting fuel.