BRUSSELS, March 1, 2014 (PPI Magazine) - Forestry companies, especially those producing pulp and paper, generate tons of waste daily from their production processes. The main residuals include sludge from treatment plants; bark and chips from wood, biomass boiler ash, dregs and grit, which is the buildup of calcium carbonate in the recausticizing phase.
The final destination of this waste has been a major concern of the companies, environmental agencies and society in general. The use of landfills is limited in terms of space and imposed legislative restrictions. The waste can be extremely damaging to the environment and produces a high concentration of toxic slurry, for which there is no final disposition.
The application of waste material to the soil in forest plantations helps to reduce waste disposal in landfills and minimize the discharge of pollutants into rivers. It also helps to generate significant yield increases in plantations as well as mitigating the effect on the soil, considering the large phyto-remediation capacity of trees subjected to a cutting cycle of seven years.
Applying these wastes to forested areas is advantageous when compared with its application on agricultural crops, because there are extensive areas of plantations close to pulp and paper mills. Moreover, forest plantations are often located in low fertility soils; forest crops are not intended for the human food chain; the root system has great ability to remove nutrients from the soil; there is an immobilization of nutrients, especially nitrogen, in woody biomass and sequestration CO 2; and, it is easy to apply biosolids on forest plots at any time.
Therefore, among the various existing alternatives for the disposal of sludge and other waste generated by industries, forest use is presented as one of the most appropriate given the high concentration of nutrients and organic matter in these wastes.
In fact, the sludge should not be applied directly in agricultural or forest areas without being first subjected to a series of biological treatments to reduce their organic content and to stabilize the material. In 2007, the Water Environmental Federation (WEF) recommended the use of the term biosolids to define the sludge that passes through a biological treatment process and which presents a potential for beneficial use in agro-forestry systems, with no risk to human and animal health.
One method to allow a better use of sludge in forests is composting and a subsequent mixing of this material with other wastes such as dregs and grits that have a high concentration of calcium. This mixture also allows for the dilution of toxic elements in specific waste.
For composting, it is necessary to blend the sludge with high concentration of organic matter such as wood chips and bark (biomass) to increase its carbon/nitrogen ratio and which would initiate the thermal phase of the composting process. Several studies have been conducted using biosolids as fertilizer in eucalyptus plantations. There are various approaches that make it relevant to the pulp and paper industry. The first deal with urban waste, contributing to solving the serious problem related to the fate of the huge amounts of sludge produced daily. This includes sewage and other waste produced in the manufacturing processes of several industries.
The ecological approach, associated with nutrient cycling, when sewage sludge is targeted toward agro-forest ecosystems, which can benefit by adding this component rich in organic matter and nutrients.
Finally, there is the silvicultural approach related to the effect of biosolids applied to the timber produced in rapid growth plantations. Related economic studies can provide data needed for the analysis of the cost/benefit ratio, essential for decision making by the forester.
An extensive program for the scientific evaluation of the application of sewage sludge as fertilizer in forests has been developed in recent years by IPE F / ESALQ (Piracicaba, Brazil) and some vertically integrated forestry companies. The benefits and risks of this operation in eucalypt plantations were evaluated1,2,4. The results have been quite promising since they show gains in timber production in the order of 30%, without the environmental damage, such as nitrate leaching or accumulation of heavy metals in soil, river or subsurface water. The biosolids used in this study came from the Barueri sewage treatment plant, where processed sewage sludge is mostly from industrial sources.
The potential of biosolids as a source of nutrients in forest plantations is high and also has the advantage of releasing nutrients slowly, increasing the efficiency of its use by the trees. Nutrient losses by leaching and erosion are low, because the forests are perennial crops and have a wide root system configuration that preserves the nutrients in the ecosystem. Therefore, it is interesting that the application of waste is practiced when the forest is already of a certain age, with an existing good root formation.
The use of biosolids as fertilizer allows the recycling of nutrients such as phosphorus, potassium and nitrogen that can be complementary and an alternative to a chemical fertilizer source. In most cases where the soil conditions are not suitable for growing trees, periodic sludge application has the potential not only to increase production in the short term (a forest cycle) and productivity of the site in the long term3. There is initially a rapid response in tree growth due to immediate absorption of nutrients readily available, similar to chemical fertilization. Subsequently, the nutrients are released slowly by the decomposition of organic matter in the sludge, which is desirable in forests due to its long production cycle.
In Brazil, one pulp and paper mill now applies sewage sludge from the Jundiaí treatment plants in its regional forests in São Paulo State. It was the first forestry company to get approval for sludge application from biological treatment systems in agricultural areas from the environmental agency. This precedent will allow forestry companies to begin to use sludge from their wastewater treatment plants. Several other companies are already producing and testing treated waste and compost in their forests.
However, it would be reckless to indiscriminately use sludge, dregs, grit or biomass ash in the forest. Some possible nutritional imbalances, due to a high concentration of one or more specific nutrients, or even the application of an overly high dose can reduce the productivity of wood rather than increase it. On the other hand, it is important to conduct an economic evaluation for each of the waste streams generated in the manufacturing process, focusing primarily on the amount of nutrients and its moisture (due to transport costs).
The main steps to integrate the use of an array of industrial waste in an ecologically and economically viable manner are:
1) Quantify the generation of each residue in the industrial manufacturing process;
2) Know the generation process for each residue (what are the chemicals used in the process);
3) Conduct chemical and physical analysis of all potential waste, separating macro and micro nutrients, moisture, pH, organic matter, etc. It is important to characterize the material according to the most restrictive legislation. Sometimes the law can derail forestry or agricultural waste used due to non-standard results (pH, sodium concentration, content of heavy metals, etc.);
4) Make the mixture of sludge to chip/bark to increase the C/N ratio of the material and start the composting process;
5) At the end of the composting process, mix wastes as dregs, grit and biomass ash. It is important that the proportion of mixed waste generation is the same material produced in each manufacturing process. Thus, there will be no leftover waste disposal.
6) Define an economic transport radius based on moisture and nutrient content of the finished compost;
7) Evaluate the use of mineral fertilizers as complementary sources of nutrients, if necessary;
8) Recommend some possible adjustments in the manufacturing process to improve the quality of a specific residue (moisture from boiler ash, for example, may be very high and potassium concentration in waste can be significantly reduced in the case of washing the material after its burning);
9) Determining a dose range to be applied, based on the nutrients and toxic potential content of other elements;
10) Install field experiments to analyze operating results and define recommendations.
The composting process should normally be employed for pathogen reduction and vector attraction, leaving the final product with the following characteristics: complete elimination of probable pathogens, absence of odor; drastic reduction in moisture content of the material, and good particle size, facilitating distribution in the field. Furthermore, mixing the waste in the same proportion generated in the plant allows a unique distribution of the product in the field, thereby significantly reducing the costs of transport and application.
Vanderlei Benedetti, Engenheiro Florestal, Jequitibá Assessoria Florestal Ltda., firstname.lastname@example.org
1. BENEDETTI , V. POGGIANI, F. The applicability of urban sewage sludge in Eucalyptus Plantations In: Seminário Internacional: "Site Management and Productivity in Tropical Plantation Forests", November, 24 to 26 - 2004, Piracicaba e Itatinga/SP, IPE F/PTSM /CIFOR, 2004.
2. GUEDES, M. C. POGGIANI, F. Variação nos teores de nutrientes em eucalipto fertilizado com lodo de esgoto (biossólido). Scientia Forestalis, No. 63, p: 13-23, Junho de 2003.
3. HENRY , C.L. CO LE, D.W. Use of biosolids in the forest: technology, economics and regulations. Biomass and Bioenergy. Vol. 13, Nos. 45. p.269-217. 1997.
4. POGGIANI, F., GUEDES, M.C.; BENEDETTI , V. Aplicabilidade de biossólido em plantações florestais: I. reflexo no ciclo dos nutrientes. In: BETTIO L, W. e CAMARGO, O. A. (Eds): Impacto Ambiental do Uso Agrícola do Lodo de Esgoto. Jaguariúna: EMBRAPA Meio Ambiente, 2000, cap. 8, p.163-178.
5. WEF (Water Environmental Federation), Biosolids Recycling - What are biosolids?http://www.wef.org/LearnAboutWater/ForThePublic/FactSheets/FactSheetDocuments/BiosolidsRecycling.htm