Eleven million tonnes of waste are produced yearly by the European pulp and paper industry, of which 70% originates from the production of deinked recycled paper.Wastes are very diverse in composition and consist of rejects, different types of sludges and ashes in mills having on-site incineration treatment. The production of pulp and paper from virgin pulp generates less waste but the waste has similar properties to waste from the production of deinked pulp, although with less inorganics. Due to legislation and increased taxes, landfills are quickly being eliminated as a final destination for wastes in Europe, and incineration with energy recovery is becoming the main waste recovery method. Other options such as pyrolysis, gasification, land spreading, composting and reuse as building material are being applied, although research is still needed for optimization of the processes. Due to the large volumes of waste generated, the high moisture content of the waste and the changing waste composition as a result of process conditions, recovery methods are usually expensive and their environmental impact is still uncertain. For this reason, it is necessary to continue research on different applications of wastes, while taking into account the environmental and economical factors of these waste treatments.

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1I n paper manufacturing flocculation can be defined as the formation of aggregates or flocs from the raw materials presented in a papermaking furnish. These interactions include fibres-fibres; fines-fibres; fillers-fibres; fillers-fines; and dissolved and colloidal fraction with all other furnish constituents. Fibre flocculation is mainly due to mechanical processes and it has an important influence on formation. However, fines and fillers interaction is dominated by the electrostatic interactions between particles and chemicals, and are the main influence on retention. Adhesion and occlusion of fines and fillers in the mechanical network mainly affect drainage. Dissolved and colloidal material flocculation is also due to electrostatic interactions with the added polyelectrolytes and it will mainly affect the efficiency of the chemicals and the runnability of the process and the quality of the final product when deposits are formed. Flocculation is extremely important in papermaking and it can be considered the intermediate state between the raw materials and the final product. For this reason, flocculation control has become an increasingly important issue in the paper industry over the years. The goal is to achieve the optimum flocculation that allows papermakers to obtain good retention and drainage at the same time as good formation. In the past, the optimum was considered the right equilibrium between these opposite effects; however, nowadays, the aim is to optimize these opposing effects in a sequential way. In other words, manipulating the chemicals and the turbulence in order to first flocculate the suspension, then break down the flocs, and then to re-flocculate the suspension in an optimum manner. This approach facilitates low mechanical flocculation and high chemical flocculation. Considering that the raw materials and the papermaking conditions are fixed for a given product and paper machine, there are only a few variables that can be controlled to improve flocculation, from the point of view of floc properties, size and strength to shear stress. Among these variables are consistency, type of chemical additive and addition point (Gess, 1998;Blanco, 1994).On the other hand, trends in papermaking such as a move towards closed-water systems, a higher use of recovered paper, faster machines, etc., also affect flocculation. For example, accumulation of anionic trash, fluctuating pH and temperature, increase of conductivity and turbulence, and so forth. These changes may affect pulp fractions, polymer characteristics, flocculation mechanism and floc properties. Therefore, the efficiency of the polymer can be dramatically affected. These effects most often result in a degradation of the additive efficiency and sometimes hinder the effectiveness of the various additives (Blanco et al., 1998;Vendries and Pfromm, 1998 One of the most important parameters that influences flocculation and, therefore, floc properties, is the flocculant characteristics. Flocculant additives operate via different flocculation mecha...

Flocculation studies of precipitated calcium carbonate induced by cationic polyacrylamides (C-PAMs) were carried out using light diffraction scattering (LDS). The effect of both polymer charge density and concentration on the flocculation process and on flocs density was investigated. As expected, results show that high charge density C-PAM induces flocculation by bridging and patching mechanisms simultaneously, while medium charge density C-PAM acts mainly according to the bridging mechanism. Consequently, the mass fractal dimensions of the flocs produced by high charge density C-PAM are higher. Results also show the effect of flocculant concentration: flocculation rate decreases and denser flocs are obtained as flocculant concentration increases. The results obtained so far allowed a preliminary quantitative evaluation of flocculation kinetics. In the flocculation curve, two regions corresponding to different kinetics were identified: a first region dominated by particle aggregation and a second region dominated by flocs stabilization. Therefore, LDS is considered a useful tool to evaluate flocculants performance. A strategy was developed that resulted in the use of LDS to retrieve, in a single test, information on the evolution with time of flocs dimension and structure, flocs resistance and flocculation kinetics. All the tests were performed under turbulent conditions similar to the ones prevailing in process equipment.