Production of biochar from poultry and swine solid waste

Production of biochar from poultry and swine solid waste2018-06-29T15:53:21+00:00

The livestock industry in the Biobío Region concentrates 1.5 million birds (mainly laying hens) and 93 thousand pig heads (Source: INE, 2015). One of its challenges is to move towards a sustainable production, being management of waste (e.g., slurry, manure, sawdust, chips and feathers) the critical stage from environmental and social points of view.

Although there are others options for waste treatment (e.g., use as fertilizer, composting or anaerobic digestion), none completely resolves the problems associated with its generation, (e.g., odors emitted by decomposing nitrogen compounds).

An obvious alternative for recovery of guano is biochar production by slow pyrolysis. Biochar is a carbonaceous material that can be obtained from different types of biomass through a process of thermal decomposition in a reduced or oxygen-free environment at moderate temperatures (<700°C). It has beneficial properties for agricultural use by improving water and nutrient retention of the soil and stimulating metabolic activity of microbial biomass in the soil.

In this context, the project “Production of biochar and thermal energy as a mechanism for the recovery of solid waste from poultry and swine farms in the Biobío Region” sought to establish a techno-economic basis for the implementation of a pyrolysis system to simultaneously produce biochar and thermal energy from poultry and swine residues.

The biochar product must have adequate characteristics to be used in the agricultural sector in a safe and stable manner. Therefore, the effect of temperature and reaction time on product yield and the properties of interest (pH, electrical conductivity, available phosphorus) as well as scale-up capacity, were analyzed. In addition, agricultural tests were conducted to determine the behavior of biochar in soils typical of the Biobío Region and its contribution to crop development.

The laboratory-scale study determined that the best pyrolysis conditions for biochar generation are 500°C and residence time of 10 minutes. Under these conditions, bird guano had a higher biochar yield than pig guano. The difference in yields reflects their different ash contents.

The pyrolysis process was shown to promote an increase in the pH and amount of available phosphorus, while toxicity tests indicated that neither type of biochar is harmful for sensitive seeds, even in large quantities. Regarding biological activity, a microbial biomass increase was observed, to a greater extent in the case of guano biochar. At the greenhouse level, dry-matter-based yield was measured for a forage grass crop; use of biochar significantly improved biomass yield, especially the bird biochar (2 to 6 times greater than control).

A livestock waste processing flow diagram was also developed, it includes the stages of drying, pyrolysis, pyrolysis gas combustion, energy integration and clear-up combustion gas. The effect of raw material moisture on energy requirements was also evaluated. The process was found to be autothermal for humidity levels below 65% and 57% for poultry and pig guano, respectively.

The preliminary economic evaluation considered a period of 5 years and 2 plant sizes, taking account of the reality of small and medium-sized enterprises (SMEs) in the Region: one of 3.8 tons biochar/year and another of 0.5 tons biochar/year. The resulting sales prices ranged from 300 to 900 USD/ton, depending on plant size. According to market data, the average international sales price of biochar is 2.500 USD/ton, whereas fertilizer prices in Chile are 400-950 USD/ton; this makes both plant sizes viable.

The technological alternative for recovery of organic residues from poultry and swine farms through slow pyrolysis shows therefore that it is a technically, economically and environmentally viable option for SMEs in the Biobío Region. It can be replicated successfully in the rest of the country as well.