Ash and sludge are the main waste materials from the pulp and paper industry. A typical plant generates between 800 and 900 tons/month with disposal costs of 18.000 to 54.000 USD. This situation was the starting point for proposing two CORFO projects (line 2 and line 4), “Technologies for the recovery of solid waste for the paper industry” in 2011 and “Packaging and transfer of technology to obtain a soil improver from the solid waste of the pulp and paper industry”, which our department executed since 2013.

The main result was a soil improver, and a proposal of a sustainable, effective and competitive solution alternative to traditional fertilizers, which can be applied in agricultural plantations and eroded lands.

In this context, one of the partner companies, CMPC Celulosa, decided to continue the research and evaluate different mixtures of by-products in their processes. Based on this, together with CMPC Forestal, the performance of different mixtures (in pellet form) was evaluated using appropriate dose levels and methodologies of forest plantations themselves.

Five types of pellets were prepared, according to CMPC specifications, using a variety of residual by-products (fly ash, Dregs & Grits, cellulose effluent treatment sludge) and other additives to solve soil acidity problems and improve concentrations of macro- (N, P, K, S, Ca, Mg) and micro-nutrients (B, Mn, Zn, Na).

The pellets did not cause problems in their elaboration, and we were able to establish the feasibility of their production on an industrial scale. Their physical and chemical properties were determined, as well as moisture retention, mineralization and incubation, and the results of leaching tests were obtained. It was concluded that the pellets did facilitate the delivery and use of essential nutrients for crop development and did allow a more efficient use of nitrogen; on one hand, this improves the yield of crops and, on the other, it reduces contamination of water tables by N-NO3 leaching.