Effect of low temperature thermal pre-treatment on the

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Effect of low temperature thermal pre-treatment on the solubilization of organic matter, pathogen inactivation and mesophilic anaerobic digestion of poultry sludge a

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Juan E. Ruiz-Espinoza , Juan M. Méndez-Contreras , Alejandro Alvarado-Lassman & Sergio A. Martínez-Delgadillo

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Departamento de Ciencias Básicas, Universidad Autónoma Metropolitana - Azcapotzalco, Distrito Federal, México b

Division de Estudios de Posgrado e Investigación, Instituto Tecnológico de Orizaba, Orizaba, México Version of record first published: 04 Jul 2012

To cite this article: Juan E. Ruiz-Espinoza, Juan M. Méndez-Contreras, Alejandro Alvarado-Lassman & Sergio A. MartínezDelgadillo (2012): Effect of low temperature thermal pre-treatment on the solubilization of organic matter, pathogen inactivation and mesophilic anaerobic digestion of poultry sludge, Journal of Environmental Science and Health, Part A: Toxic/Hazardous Substances and Environmental Engineering, 47:12, 1795-1802 To link to this article: http://dx.doi.org/10.1080/10934529.2012.689237

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Journal of Environmental Science and Health, Part A (2012) 47, 1795–1802 C Taylor & Francis Group, LLC Copyright  ISSN: 1093-4529 (Print); 1532-4117 (Online) DOI: 10.1080/10934529.2012.689237

Effect of low temperature thermal pre-treatment on the solubilization of organic matter, pathogen inactivation and mesophilic anaerobic digestion of poultry sludge 2 ´ JUAN E. RUIZ-ESPINOZA1, JUAN M. MENDEZ-CONTRERAS , ALEJANDRO ALVARADO-LASSMAN2 1 ´ and SERGIO A. MARTINEZ-DELGADILLO 1

Departamento de Ciencias B´asicas, Universidad Aut´onoma Metropolitana - Azcapotzalco, Distrito Federal, M´exico Division de Estudios de Posgrado e Investigaci´on, Instituto Tecnol´ogico de Orizaba, Orizaba, M´exico

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Treatment of poultry industry effluents produces wastewater sludge with high levels of organic compounds and pathogenic microorganisms. In this research, the thermal pre-treatment of poultry slaughterhouse sludge (PSS) was evaluated for low temperatures in combination with different exposure times as a pre-hydrolysis strategy to improve the anaerobic digestion process. Organic compounds solubilization and inactivation of pathogenic microorganisms were evaluated after treatment at 70, 80 or 90◦ C for 30, 60 or 90 min. The results showed that 90◦ C and 90 min were the most efficient conditions for solubilization of the organic compounds (10%). In addition, the bacteria populations and the more resistant structures, such as helminth eggs (HE), were completely inactivated. Finally, the thermal pre-treatment applied to the sludge increased methane yield by 52% and reduced hydraulic retention time (HRT) by 52%. Keywords: Anaerobic sludge digestion, organic matter solubilization, pathogen inactivation, thermal pre-treatment.

Introduction The poultry industry is one of the fastest growing segments of the animal industry in the world. Poultry slaughtering uses large quantities of water in various washing and cleaning operations. Slaughterhouse effluents have a high concentration of biodegradable organics, particulates and dissolved forms, which include blood, feathers, viscera, soft tissues removed during trimming and cutting, bones, soil and various cleaning and sanitizing compounds.[1] Poultry slaughterhouse sludge commonly contains a large portion of these wastes, which typically contain high levels of organic matter, nutrients and a high concentration of pathogenic microorganisms. These high levels are due to the poultry manure wastes (9.8 and 6.2 log units of fecal coliforms and salmonella, respectively[2]), which require inactivation by conventional or unconventional technologies before using them as fertilizers or disposing of them. This type of sludge has been treated with anaerobic digestion. This digestion process involves the transformation of organic matter to biogas that is primarily methane Address correspondence to Juan E. Ruiz-Espinoza, De´ partamento de Ciencias B´asicas, Universidad Autonoma Metropolitana-Azcapotzalco, Av. San Pablo #180, CP02200, D.F. M´exico; E-mail: [email protected] Received December 3, 2011.

(55–80%) but has drawbacks that include long hydraulic retention times (20–30 d) and limited inactivation of the pathogenic microorganisms. This process has two modalities that occur at different operating temperatures; the mesophilic process occurs at 35◦ C, and the thermophilic process occurs at 55◦ C. The mesophilic process has been successfully used to degrade organic matter; however, it can inactivate only two log units of pathogenic microorganisms, producing class B biosolids.[3] The thermophilic process is capable of supporting large organic loads (greater than 4 kg VS m−3 d−1) and inactivates large concentrations of pathogenic microorganisms, producing class A biosolids. The main disadvantage to the thermophilic process is that it consumes a large amount of energy due to the temperatures that is required for the process. The application of pre-treatment techniques has been increasing in importance in recent years.[4] Thermal pre-treatment is a method suggested to improve the solubilization of organic matter,[5] sludge dewaterability,[6] sludge sanitation and to reduce sludge viscosity with the subsequent enhancement of sludge handling.[7] However, most investigations have used high pretreatment temperatures ranging from 120–200◦ C[8–15] and different treatment times ranging from 30–60 min. These optimum treatment conditions (temperature and time) require a high level of energy, which is the largest drawback for this method.

1796 The application of low-temperature thermal treatment (1000 MPNg−1 TS). The main factors causing pathogen decay during treatment of the biowaste include temperature, retention time,

PSS raw

65

PSS treated

60

Fecal coliformes (LogMPN g -1TS)

Volatile Solids (%)

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Mesophilic anaerobic digestion of poultry sludge

Reduction 38% VS (USEPA)

55 50 45 40 35 0

5

10

15 20 Time (days)

25

30

Fig. 5. Removal of volatile solids in raw sludge and treated sludge.

11 10 9 8 7 6 5 4 3 2 1 0

Fecal Coliforms Biosolids A and B Biosolids C

25

35

45

55

65

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Temperature (°C)

Fig. 7. Fecal coliforms inactivation at different temperatures.

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Fig. 8. Salmonella spp. inactivation at different temperatures.

reactor configuration, microbial competition, pH value and chemical interaction, which explain the previously described effect.[23] The wastewater treatment process commonly involves a disinfection step, which significantly decreases the microorganism concentration. However, many of the pathogenic microorganisms found in wastewater are either bound to solids or trapped in the sludge floc matrix from the absorption, coagulation, or precipitation processes.[24] Thus, the PSS studied here contains a higher concentration of pathogenic microorganisms than those present in the treated water due to the physicochemical characteristics of the sludge (PSS), which provide better conditions for the survival of pathogenic microorganisms (e.g., Salmonella and helminth eggs). Figure 8 presents the thermal inactivation of Salmonella spp., which follows a similar trend when compared with the fecal coliforms. The initial concentration of 4.5 log units of Salmonella spp. in the raw sludge was reduced to 1.4

Fig. 9. Helminth eggs inactivation at different temperatures.

Ruiz-Espinoza et al. log units at 55◦ C, but this residual concentration is not sufficient to meet any biosolids classification. As shown, treatments with temperatures at 65◦ C or higher can produce class A biosolids. Several researchers have reported bacterial inactivation with different hygienization processes. Bonjoch and Blanch[25] showed the resistance of fecal coliforms and Enterococci populations to mesophilic anaerobic digestion (MAD), composting and pasteurization in municipal wastewater sludge (MWS). Menert et al.[26] used thermal pre-treatment with MAD of sludge and found a significant inactivation of heterotrophic, coliforms, E. coli and Clostridia bacteria. Lang and Smith[27] reported the time and temperature inactivation kinetics of enteric bacteria in sewage sludge. However, most published work does not present results about “helminth egg” inactivation, although these eggs are the most resistant to the inactivation because they have a highly impermeable eggshell that is highly resistant to “chlorination,” a commonly used wastewater inactivation processes; dramatic changes in temperature (−15◦ C to 40◦ C); ultraviolet radiation processes; and the application of low concentration ozone. Figure 9 shows the average results from four tests involving the inactivation of Ascaris suum eggs using thermal inactivation performed with different contact times and temperatures. As shown, the treatments at 90◦ C for 90 min reduced the helminth egg concentration from 35 up to less than 1 HE g−1 TS, which meets the class A biosolids limit. By contrast, treatments of 30 to 60 min resulted in class B biosolids, which have restrictions for use in areas with human contact. The inactivation of helminth eggs is due to the temperature, which causes membrane damage and releases cellular material.

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Mesophilic anaerobic digestion of poultry sludge

Fig. 10. VS removal efficiency during the PSS digestion and increase of OLR.

Fig. 11. Daily biogas production during the PSS digestion and increase of OLR.

Increased organic loading in mesophilic anaerobic PSS digestion improvement with thermal pre-treatment

Additionally, the methane yield reached an average value of 0.81 LCH4 g−1 VSremoved . This methane yield is similar to that obtained by Jolis (2008),[28] who showed a methane yield between 0.8 and 1.1 LCH4 g−1 VSdestroyed for municipal sludge that underwent a thermal hydrolysis pretreatment at 170◦ C for 25 min. The methane yield in this work is justified because the studied PSS contains a high proportion of nondigested material, including blood that was not collected, animal fats and waste from poultry feed. Most of the material is solubilized when this sludge is treated by thermal pre-treatment, allowing for a higher digestion velocity and favoring an increase in the process treatment capacity.

Figure 10 shows the behavior of VS removal together with the increase of organic load rate (OLR) in a semicontinuous flow reactor that was operated for approximately 90 days. In the first operation period (1–30 d), the reactor was fed with thermally pre-treated PSS and a low initial organic load (1 kgVS m−3d−1). For this experiment, an average VS removal of 58% and an average biogas production of 2.14 L d−1 were obtained (Fig. 11). During this period, biogas yield (1 Lbiogas g−1 VSremoved ) and methane yield (0.82 LCH4 g−1 VSremoved ) were also obtained (Table 3) and were very similar to those obtained in the preliminary batch digestion (Fig. 6). The second period (31–60 d) began after the initial adaptation phase. During this second period OLR increased to 2 kg VS m−3 d−1, while VS removal slightly decreased due to this new OLR. However, a 50% reduction in HRT was required (11 d) to attain the stabilization criterion in this period. In the third period of this process, the system was fed 3 kg VS m−3d−1, and the system was able to quickly adapt to the new organic load. However, the removal efficiency decreased by 9% in comparison with the initial period because the system had an OLR that was 300% higher than that in the first 30 days. During this operation period (60–90 d), the biogas production was 5.2 L d−1, the VS removal averaged 49.9%, and the HRT was reduced to 7.6 d, which were associated with the OLR.

Conclusion These results demonstrate that applying a low-temperature thermal pre-treatment (90◦ C for 90 min) to PSS increases the organic matter hydrolysis rate to a sufficient degree to significantly reduce the hydraulic retention time of the anaerobic digestion and increase the biogas and methane production in comparison with raw sludge digestion. Under these conditions, thermal pre-treatment can fully inactivate the dense pathogens and helminth eggs. In addition, the biosolids comply with the permissible limits for class A biosolids, which can be used in agricultural soil without any restrictions. Treatment of PSS at temperatures and exposure times lower than those recommended in this study can produce sludge with surviving bacteria and pathogen

Table 3. Performance parameters during the increase of OLR in PSS anaerobic digestion. Average Operation period 1 2 3

Continuous operation (d)

HRT (d)

OLR kg VSm−3d −1

Biogas production (Ld −1)

VS removal (%)

1-30 31-60 61-90

22.0 11.0 7.6

1 2 3

2.14 ± 0.25 3.6 ± 0.27 5.2 ± 0.34

58.81 ± 3.42 51.78 ± 2.82 49.9 ± 2.73

Biogas yield Methane yield (L g−1VS rem.) (L g−1VS rem.) 1.00 ± 0.14 1.05 ± 0.10 1.04 ± 0.09

0.82 ± 0.12 0.81 ± 0.08 0.81 ± 0.07

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populations, which can pose a serious human health risk during handling of the sludge and for land application of the biosolids. It is possible to reduce the energy consumption, and thus reduce the costs of this process, because the thermal pretreatment temperature used was less than 100◦ C. This proposed technology can be successfully adopted in developing countries for the sustainable treatment of wastewater sludge with high densities of pathogen microorganisms. Finally, the biogas obtained can be used as a source of energy in thermal pre-treatment.

Ruiz-Espinoza et al.

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Acknowledgments

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This work was supported by the FONDO MIXTOCONACYT-VER. (Project 128276-2009-03).

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