versão impressa ISSN 1405-7743
Ing. invest. y tecnol. v.8 n.1 México jan/mar. 2007
Ingeniería en México y en el mundo
Organic Bed Biofiltration: A new Technology for Simultaneously Deodorization of Liquid and Gaseous Effluents on Pig Farms
1 Centre de Recherche Industrielle du Québec (CRIQ)
2 Centre de Recherche Industrielle du Québec (CRIQ)
Recibido: marzo de 2006
Aceptado: septiembre de 2006
El rápido crecimiento de la industria porcina ha originado serios problemas ambientales asociados a los olores ofensivos, generados en las instalaciones de producción y durante el almacenamiento, el transporte y la descarga de las aguas residuales porcinas. Entre las alternativas de tratamiento existentes, la biofiltración en lecho orgánico representa una tecnología de alto potencial para la desodorización y el tratamiento de los efluentes líquidos y gaseosos producidos en las granjas porcinas. Trabajos de investigación y desarrollo tecnológico fueron realizados durante seis años en una granja porcina situada en Quebec, Canadá, con el objetivo de adaptar y optimizar el funcionamiento del proceso de biofiltración BIOSORMC Estiercol al tratamiento simultáneo de efluentes líquidos y gaseosos generados por esta agroindustria. Estos trabajos se efectuaron a una escala industrial utilizando un sistema de biofiltración de 560 m3 . Los resultados obtenidos muestran que el proceso BIOSORMC Estiercol es una tecnología robusta, simple y eficiente que ofrece una solución global al problema de gestión de los olores ofensivos. Efectivamente, esta tecnología reduce más del 95% de la carga contaminante (NH3, H2S) y más del 80% de la intensidad de los olores generados por la granja porcina.
Descriptores: Estiércol de puerco, olores ofensivos, efluentes líquidos y gaseosos, análisis olfactométricos, desodorización, tratamiento, biofiltración.
The growth of pig industry has caused a great problem of undesirable odours, particularly in and around production buildings, storage areas and when the pig manure is spread. Among manure treatment options, organic bed biofiltration represents a very promising technique for the deodorization and treatment of pig manure. Research and development work to optimize the BIOSORTMManure, a biofiltration process for simultaneously treatment of liquid and gaseous effluents on pig farms, have been realized on the site of a piggery (Île d'Orléans, Québec,Canada) using a 560 m3 biofiltration system. The results obtained show that the BIOSORTMManure process is an efficient, simple and performing technology bringing a global solution to odours pig manure problems. Actually, the process reduce over 95% the polluting load from the gas of the pig farm (NH3, H2S), the BIOSORTMManure process eliminates over 80% the odour intensity coming from the production installations, the storage, the transportation and the spread ing of the manure.
Keywords: Pig manure, odours, liquid and gaseous effluents, olfactometrical analysis, deodorization, treatment, biofiltration.
The agricultural sector is grappling with a growing problem associated with the odour pollution that it generates. One of the most affected sectors is the porcine production industry, which currently represents the most blatant nonpoint source pollution management problem. Pig production has grown considerably in Quebec, with the number of pigs almost tripling in the last 25 years. This development has led to a surplus of pig manure to be discharged in relation to the available spreading area and consequently, a water, air and soil pollution problem, along with undesirable odours primarily generated by the production building and the storing and spreading of pig manure. Considering the intensity and duration of the odours, the proposed weighting of odour sources for Quebec is 20% for the building, 10% for the storage, 5% for the collection and 65% for the spreading (O'Neill and Stewart, 1985; Héduit, 1989; Buelna et al., 1993).
The main source of odour in terms of pig installations comes from the manure and their management. Even though there are over 150 volatile combinations in pig manure (Merkel et al., 1969; Schaeffer et al., 1977; Yasuhara et al., 1983), the main components are methane, carbon dioxide, ammonia and hydrogen sulphide (Lee, 1976; McQuitty et al., 1983; Lasbleiz,1989). According to their detection limit and their olfactory character, ammonia and hydrogen sulphide have been identified as being good indicators to monitor odours emanating from the treatment of pig manure (Pain et al., 1990, Martin and Laffort, 1991).
Increasingly stringent environmental standards, constantly growing public awareness of environmental problems and the conflicts associated with living with unpleasant odours, have led to enhanced research into various alternatives for treating pig manure in different countries. One alternative, the organic bed biofiltration is a very promising technology for the deodorization and treatment of liquid and gas effluents in reducing the overall odour problem at the farm (building, storage, spreading).
The biofiltration by organic media is a simultaneous AIR/WATER treatment process (Buelna et al., 1997) for the global management of porcine production effluents. The principle consists of passing the liquid (manure) and gas (foul air) effluents through an organic media biofilter (mixture of peat moss, woodchips, etc.). As a pollutant removal agent, the organic media can act in two ways, as a natural resinable to fix several types of pollutants and/or as support for various types of microorganisms capable of degrading the retained substances. These pollutants are degraded into CO2 and H2O due to the microbial activity (Bélanger et al., 1987). The constituents of the organic media, particularly the lignin and organic acids, possess numerous polar functional groups: alcohols, phenols, aldehydes, cetones, acids, ether. This polar characteristic gives it a good adsorption capacity for organic molecules and transition metals (Coupal and Lalancette, 1976). Adsorption properties can also be linked to the presence of a porous structure, conducive to physical adsorption (Tinh et al., 1971).
Given the potential of this technology, large scale research and development work has been conducted on a 150 sows farrowtofinish operation on Île d'Orléans (Québec, Canada) using an industrial biofiltration system of 560 cubic metres total volume (primary biofilter: 400 cubic metres, polishing biofilter: 160 cubic metres). This work aimed to demonstrate the overall efficiency of the BIOSORTM system to reduce odours in terms of manure produced and foul air coming from the livestock buildings.
Ammonia (NH3), hydrogen sulphide (H2S) and odour intensity (olfactometry) were subject to rigorous monitoring to establish the deodorization performance of the biofiltration system.
The system installed on the farm offers a purifying efficiency of over 95% for NH3. The measured elimination performances exceed 99% for H2S. System efficiency is maintained at around 80% 85% for odour intensity reduction. Moreover, foul air and raw manure from the livestock buildings, considered to be annoying, indeed unacceptable, are deodorized to reach an acceptable level after they pass through the biofilter (Buelna et al, 1998).
The results obtained during the longterm monitoring of the technology's purifying performance (6 years), show that the technology developed by the CRIQ is a simple and efficient treatment system adapted to the needs of agricultural enterprises, which is a substantial asset for the evolution of the sustainable development of this industry.
Materials and Methods
An industrial biofiltration system was designed, built and implemented in January 1997, to treat the liquid and gas effluents of a 150 sows farrowtofinish operation (about 3,000 pigs produced per year). The system was designed to simultaneously treat up to 12 cubic metres/d of manure and 15,000 cubic metres/h of foul air. Figure 1 shows that the pig manure is treated by first separating the liquid and solid parts in a sedimentation tank and a 1,200 cubic metres digester (existing storage tank reused for the needs of the system). The system stabilizes and deodorizes the sludge (20% of the total volume of the manure) through anaerobic digestion. The residual liquid fraction (80%) is directed to a protection prefilter. This fraction is then pumped to the surface of a 400 cubic metres primary biofilter composed of a multilayer organic bed non inoculated (70% woodchips, 30% peat moss). In order to reach a degree of purification to consider discharge to the environment, the waters are finally directed into a 160 cubic metres polishing biofilter (non inoculated, 70% woodchips, 30% peat moss). The treated water is stored in an existing tank (2,600 cubic metres) before being used to wash the gutters or for irrigation. The foul air from the production building is directed to the base of the two biofilters to perform a countercurrent treatment.
Measuring Purification Efficiency
We have used two complementary approaches to determine the deodorization performance of the biofiltration system. The first is the classic physiochemical analysis to evaluate the concentration of ammonia NH3 and hydrogen sulphide H2S, the two main compounds responsable for the odours. The second is olfactometry, a sensory analysis method that calls upon a jury to quantify the perceived odours.
The sampling method selected to characterize the foul air from the buildings housing the pigs is a selective sampling device by family of components (Le Cloirec et al., 1991). This technique consists of trapping the volatile components to be dosed with specific reactives. The ammonia trapped in the form of ammonium ions in the hydrochloric acid solution is dosed by colorimetry using the Nessler reactive according to the AFNOR NFT 90.15 norm. The sulphated components are quantified by iodometric dosage according to the SMEWW4500 S2F Iodometric Method (APHA, 1995). NNTK was analyzed in accordance with Standard Methods (1995).
To perform the sensory analysis of the gas effluents, it was used the TECNODORTM, dynamic dilution olfactometer based on the principal of the suprathreshold measure (ASTM E544 American standard, VDI 3882 German standard and AFNOR X43103 French standard). The TECNODORTM is a mobile machine that allows in situ measurement. The principle consists of having a jury of at least four people smell the odour to be evaluated. The intensity of the perceived odour is then compared with the intensity provided by a specific concentration of a reference substance (1butanol) generated by the olfactometer. The intensity of the ambient odour is then expressed as an equivalent ppb of 1butanol. For the comparative olfactometrical analysis of the liquid (raw and treated manure), we used a dynamic flux chamber (Eklund, 1992; Gholson et al., 1991) that channels the fumes and prevents their dispersion in the ambient air when the olfactometric measure is taken.
In addition to measuring the intensity of the perceived odours, we have also evaluated the hedonic character of the perceived odours, i.e. the degree of acceptability experienced by each jury member upon exposure. To do this, we used the method suggested by Martin and Laffort (1991) which consists of determining the Odour Nuisance Index (ONI).
Results and Discussion
Performance of the Eliminationof Ammonia and Hydrogen Sulphide
Table 1 shows the results obtained for the determination of ammonia concentrations (NH3) and hydrogen sulphide (H2S) present in the foul air of the livestock buildings and when it comes out of the biofilters (averages for six years).
The increased concentrations in biofilter entries observed in the fall are caused by a decrease in the farm's ventilation rates. This operation is performed in order to comply with minimum ventilation rate criteria for the winter. This rate is completely taken up by the biofilter supply fans.
Ammonia is the compound with the highest concentrations varying between 2.3 and 6.7 ppmv. Even though they appear weak, the hydrogen sulphide concentrations measured in the foul air (0.03 to 0.19 ppmv) are nevertheless higher than the perception threshold for this compound (Le Cloirec et al., 1991).
The system maintained purifying efficiencies greater than 95% for NH3 during six years of operation. The measured elimination performances exceed 99% for H2S.
Odour Reduction (Foul Air in the Live stock Buildings)
The results of the sensory measures show a net difference between the foul air and the treated air. This difference essentially resides in the intensity of the perceived odour and the level of discomfort felt by the jury. Table 2 reveals that the farm's ambient air is characterized by a strong intensity qualified as annoying, even unacceptable. The air that comes out of the biofilter provides a slight olfactory sensation that is deemed acceptable. Moreover, the air treated by biofiltration has an odour described as being like a wetland (characteristic odour of peat moss). The biofilter therefore has a dual role: it breaks down the pollutants from the farm (NH3 and H2S) and it gives the gas stream an acceptable odour. System efficiency is maintained at around 80% 85% for the reduction in odour intensity. This reduction was not affected by winter time and summer time temperatures (25°C ; +25°C) and the load applied to the biofilter.
Olfactometric Measures on the Liquid Fraction (Treated and Untreated Manure)
The results of the sensory measures also show a net difference between the raw manure and the treated manure. Figure 2 reveals that the biofiltration system reduced the odour intensity by over 4,000 ppb of 1butanol to about 600 ppb of 1butanol. In addition, the raw manure qualified as unacceptable is deodorized to reach an acceptable level after passing through the biofilter. The odour of the treated water that comes out of the biofilter also has a wetland smell (peat moss).
Distribution of the Primary Nitrogenous Forms
Loads high in N NTK were treated by the biofiltration system (see figure 3). In spite of a total entry load of 61.4 g N/m2d, the average load of liquid effluent treated was maintained at about 10 g N/m2d and that of the gas effluent did not exceed 0.1 g N/m2d, for an overall purifying efficiency of 84%. Even though several mechanisms are involved in the conversion of nitrogen during the biofiltration by supported organic media (filtration, sorption, biotransformation, volatilization), a mass balance carried out by GarzónZúñiga (2001) revealed that simultaneous nitrificationdenitrification (SND) is the most important means of transformation within the BIOSORTMManure process. In fact, the establishment of a detailed mass balance realized over a 180day period revealed that 30% of the N NTK is transformed into molecular nitrogen N2 and 10% of the N NTK is found in the form of N NO3. The microorganisms involved in the biotransformation assimilated about 16% of the N NTK for their growth and 6% of the N NTK was accumulated in the filter bed.
The results obtained during this project reveal that the BIOSORTMManure biofiltration process represents a solution to the overall problem of porcine farm odour. Its dual role enables the biofilter to break down pollutants from the farm and provide treated foul air and manure with an acceptable odour (peat moss).
The passage of gas effluents in biofilters reduces (> 95%) the concentration of target compounds (NH3 and H2S) present in the foul air of livestock buildings. Moreover, sensory measures show that the biofilter reduces the intensity (> 80%) of odours generated by livestock production activities and the management of manure (buildings, storage, transportation and spreading).
The sensory analysis method used (TECNODORTM olfactometer) resulted in an in situ evaluation of the sensation actually perceived (intensity) by integrating the hedonic aspect (pleasant or unpleasant character) of the odour.
Moreover, the biofiltration process has turned out to be a technological alternative enabling simple and efficient management of highly charged nitrogenous effluents. The longterm follow up study (6 years) shows that the technology performed well in spite of major variations in temperature and pollutant loads.
In light of these results, there is no doubt that the biofiltration process developed by the CRIQ represents a rugged, simple and efficient technology to solve the overall environmental problem associated with unpleasant odours generated by the management of pig manure. The biofiltration system is installed directly on the producer's pig farm with no impact on production control while recuperating existing storage reservoirs. This technology now makes it possible to reconcile people's environmental concerns with the pork industry's potential for growth.
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Gerardo Buelna. DoctorEngineer, Senior technical expert Treatment and Bioconversion at the Industrial Research Center of Quebec (CRIQ) and associate professor at Laval University (Quebec, Canada), is an internationally renowned expert in the treatment of gaseous and liquid effluents through biological filtration. He is the author of over 70 publications in numerous national and international magazines as well as two patents. Dr. Buelna obtained the SNC 1991 award of excellence awarded by Sciences et Techniques de l'eau (AQTE) magazine and was the recipient of the 1998 MichelJurdant award, dedicated to environmental sciences and awarded by the Association CanadienneFrançaise pour l'Avancement des Sciences (ACFAS).
Nicolas Turgeon. Holds a Bachelor's degree in civil engineering from Université Laval (Québec City) and a Master's in the environment also from Laval. He has been working as a research and development agent and project manager in the Environment Division of CRIQ since 1997. He is involved in developing Biotechniques for Air pollution Control.
Rino Dubé. Holds a Bachelor's degree in civil engineering from Université Laval (Québec City) and a Master's in the environment also from Laval. He has been working as a research and development agent in the Environment Division of CRIQ since 1995. He is involved in developing and fine tuning the organic bed biofiltration process, in particular for treating industrial and agricultural effluents.