(438h) Analysis of the Production of Biofertilizers from Colombian Lignocellulosics Feedstocks

According to the United Nations the world population could reach 9.15 billion persons by 2050 (Food and Agriculture Organization of the United Nations 2012). This fact means a great challenge for the agriculture since it would be necessary to supply the food demand in quality as well as in quantity and at least the 50% of the requirements should come from already cultivated soils (Food and Agriculture Organization of the United Nations and International Fertilizer Agency 2002). These intensive farming practices lead to the gradual impoverishment of the soil because of the extraction of the required nutrients by the harvested plants (Rasool, Kukal et al. 2007). In this sense, the use of fertilizers leads to increase the crop yields and soil productivity and to replace land nutrients that have been already used by previous plant growth. The use of these agrochemicals is influenced not only by the population growth but also by the economic growth, the agriculture production, the prices and governmental policies (Food and Agriculture Organization of the United Nations 2008). In 2010 the world demand of fertilizers reached the 170.7 million tones, while in 2011 was of approximately 157.7 million tones (Food and Agriculture Organization of the United Nations 2011).

Despite of the above mentioned benefits of using agrochemicals in agriculture practices, the excessive use and poor application methods of chemical fertilizers can cause unwanted side effects. One of them is the high environmental cost, since its regular use can deplete the soil reducing its porosity as well as contaminate underground water and contribute significantly to the green house gas (GHG) emissions (Chirinda, Olesen et al. 2010). Other side effect is the volatile price, tending to high prices due to petroleum dependency in the case of the nitrogen-based fertilizers and the lack of the deposits and high extraction costs in the case of the potash and phosphorous-based fertilizers (Consejo Nacional de Política Económica y Social 2009). Especially for Colombia, the wholesale prices of agrochemicals such as the urea, diammonium phosphate (DAP) and potassium chloride (KCl) ranges from 25 to 35% above the international prices, while the retail price is 15% higher than the wholesale price (Suárez 2013). These facts together with the inefficient and non-sustainable use of fertilizers (Approximately 70-75% of the nitrogen and phosphorous applications, respectively, are lost by soil fixation (Consejo Nacional de Política Económica y Social 2009)) and the share percentage of these agrochemicals into the production costs (15-30%) per hectare, have been put at risk of become unviable the Colombian agriculture

As an alternative to this situation, in this work the use of lignocellulosic residues coming from agroindustrial processes to produce biofertilizers through anaerobic digestion was techno-economic, environmental and experimental assessed. Three agroindustrial Colombian residues have been selected to carry out this study: orange peel, coffee husk and plantain empty fruit bunches. The raw materials were characterized by measuring moisture content (AOAC 928.09 method), klason lignin content (TAPPI 222 om-83 method), acid-soluble lignin content (TAPPI 250UM-85 method) holocellulose content (ASTM Standard D1104 method), cellulose content (TAPPI 203 os-74 method), ash content (TAPPI Standard T211 om-93 method), total nitrogen content (kjeldahl method), potash content (colorimetric method) and phosphorous content (colorimetric method).

Besides, the anaerobic digestions were also experimentally carried out. The process started with the pretreatment of the stream with ammonia in order to remove part of the lignin and to enhance the hydrolysis of the biomass, preserving the most of the fermentable fraction. The pretreatment process was performed at 51°C, with ammonia at 14.8% in a 1:10 solid to liquid ratio and a residence time of 27 h. Ammonia pretreatment presents some advantages compared to other pretreatment processes: It is an abundant, less expensive and less corrosive chemical (than, say, sulfuric acid); it has high selectivity for lignin reactions and preserves carbohydrates due to the mild basic nature; the residual ammonia left after evaporation is approximately 1.0% and a potential nitrogen source for fermentation; there is no neutralizing waste such as irrecoverable salts or wash streams created in the process; and there is no formation of furfural or furfural derivatives which are potential inhibitors of anaerobic digestion (Li, Merrettig-Bruns et al. 2014).

After the pretreatment, the resulting streams was filtered and submitted to the anaerobic digestion process in a 50 L bioreactor at 35°C during 20 days (Borja, Martín et al. 2005). As products of the anaerobic digestion, besides biogas, a slurry composed by a liquid and a solid fraction is obtained. The nitrogen, potash and phosphorus, valuable nutrients present in the original raw material, are recovered in the form of liquid effluent from the digester and can be used for foliar application. In the case of the solids, which also contain these nutrients, may be applied to agricultural land. The obtained biofertilizers were characterized by measuring the moisture content, free carbonates (qualitative method), organic matter (Walkey-Black method), nitrogen content, potash content, phosphorous content and C/N ratio. All the experiments were carried out in the Biotechnology and Agrobusiness Institute at the Universidad Nacional de Colombia at Manizales.

Then, for each raw material the techno-economic and environmental assessments of the anaerobic digestion process was carried out using simulation tools. For the techno-economic analysis, the main simulation tools used were the commercial package Aspen Plus v8.0 and Aspen Economic Analyzer V8.0 (both from Aspen Technology, Inc., USA). Specialized package for performing mathematical calculations especially for kinetic analysis such as Matlab was also used. In the case of the environmental analysis, the Waste Reduction Algorithm WAR, developed by the National Risk Management Research Laboratory from the U.S was used. Besides, the Green House Gas (GHG) emissions associated to the process was developed. This procedure was completed following the IPPC Guidelines. The GHG emissions were calculated using equivalent factors of 14 for CH₄, 4.5 for CO, 196 for NO_x. Also GHG emissions were calculated for external energy requirements. Finally, the results were compared with the base case of gasification.

The results show that the anaerobic digestion is a feasible technique to process lignocellulosic residues in order to obtain biofertilizers by recovering the nutrients from the original raw material. Besides, the cost and environmental analyses lead to conclude that the processes are profitable and environmental friendly.

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