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Characteristics of rice straw and sewage sludge as composting materials in Valencia (Spain)
Bioresource Technology 95 (2004) 107–112
Short Communication
Characteristics of rice straw and sewage sludge as composting materials in Valencia (Spain) Maria Iranzo a, Jose V. Ca~ nizares, Luis Roca-Perez b,c, Isabel Sainz-Pardo a, Salvador Mormeneo a, Rafael Boluda b,c,* a
b
Departament de Microbiologia (Pharmacy Faculty), Universitat de Valencia, Avda. Vicent Andres i Estelles s/n, 46100 Burjassot, Valencia, Spain Departament de Biologia Vegetal (Pharmacy Faculty), Universitat de Valencia, Avda. Vicent Andres i Estelles s/n, 46100 Burjassot, Valencia, Spain c CIDE (CSIC-UV-GV), Camıde la Marjal s/n 46470 Albal, Valencia, Spain Received 28 April 2003; accepted 27 January 2004 Available online 5 March 2004
Abstract This work supports the idea that composting can be useful for minimizing the rice straw and sewage sludge environmental impact. Several physical, chemical and microbiological properties of these raw materials were analyzed. The characteristics of the rice straw were complementary to those of the sewage sludge for the application of composting. The C/N ratios suitable for a rapid increased in microbial activity were the lowest (17–24). A temperature of 62 C during 48 h removed pathogenic microorganisms from rice straw and sewage sludge mixture. The results obtained in the present work suggested that these materials could be use in the composting process. 2004 Published by Elsevier Ltd. Keywords: Rice straw; Sewage sludge; C/N ratio; Blend-sanitation
1. Introduction The increase in the production of waste in society is of rising concern at different levels of the population; this increase can be diminished by means of various alternatives (elimination, purification and/or recycling). Wastes would cease to be a problem if an added value were attributed to them (Menzies and Chaney, 1974; Catroux et al., 1983; Lue-Hing et al., 1992). The treatment and/or utilization of hazardous by-products is considered a vital issue in the protection of the health of mankind and the environment. There are three basic questions to be considered: What does the term ‘‘hazardous’’ mean?; Which is the best available technology to eliminate the danger? and, what advantages are to be obtained simultaneously? (Yong et al., 1992). The danger of a waste product depends on its chemical, physical or biological nature, but often this only depends on how it is disposed of. *
Corresponding author. Tel.: +34-96-3544927; fax: +34-96-3544926. E-mail address: [email protected] (R. Boluda).
0960-8524/$ - see front matter 2004 Published by Elsevier Ltd. doi:10.1016/j.biortech.2004.01.013
Every autumn, more than 100 million kg straw from rice cultivation in the Albufera Natural Park (ANP) are disposed of, traditionally by burning in situ, causing real environmental problems. This practice produces huge clouds of smoke that affect all the adjacent municipalities, with a population corresponding to almost a third of the Valencian Community (including the city of Valencia). The problems are varied and even affect health (respiratory, cardio-respiratory and allergic disorders). In some countries, for example Japan, the emissions from burning of rice residuals have been related to the appearance of respiratory diseases such as bronchial asthma (Arai et al., 1998; Torigoe et al., 2000). This problem is not exclusive to Valencian agriculture and generally affects other rice-growing areas, both at national (the Ebro Delta in Catalonia) and international level (Japan, China, etc.). Different approaches have been described for the utilization of rice straw: paper production, construction materials, incorporation in soil, compost, energy source, animal feed, etc. However, competition with other resources prevents the immediate use of this agricultural
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M. Iranzo et al. / Bioresource Technology 95 (2004) 107–112
waste for these purposes, with the result that its use is still a remote possibility (Han, 1978; Haug, 1993). Other residuals with serious effects upon environmental problems are the sludge waste from urban and industrial sewage reprocessing plants. These materials present different characteristics whose composition depends on the type and origin of the waters to be purified. They contain a large amount of organic material and nutrients, but often toxic elements and pathogenic microorganisms that must be monitored when sludges used. The production of compost from this waste to obtain organic additives for use in agricultural systems has been the object of several studies (Catroux et al., 1983; Davis et al., 1983; Berglund et al., 1983; Williams et al., 1985; Haug, 1993; Escrig et al., 1994); currently, the subject is the focus of ongoing research (Beltrame et al., 1999; Eweis et al., 1999; Akhtar and Malik, 2000; Gagliardi and Karns, 2000; Jezierski et al., 2000; Lazzari et al., 2000) given the importance of the problem and its social and environmental implications, leading to the regulation of its utilization at European, national and regional level. The modern conception of environmental management has as its base the recycling of residues and in this context composting arises as a safe form of treatment of some wastes and the reusability of the nutrients contained in them. The most common applications of composting are the treatment of agricultural residues, garden and kitchen waste, solid municipal waste and sewage plant sludge; currently, they are also being applied to solid biorecovery. This process presents the great advantage of eliminating pathogenic microorganisms during the thermophilic phase, increasing the quality of the end product. The disadvantages of composting are the need for maintenance and the production of emissions into the air due to the temperatures that are developed; nevertheless, these are easier to deal with than in treatment in beds. It is also important to control moisture in order to keep biological activity optimal. Nonetheless, compared with non-biological treatment processes, such as incineration and bio-mass plants, composting is much cheaper and its technology is much simpler to apply (Eweis et al., 1999). Given all the above, the use of composting to eliminate the residual straw from rice growing in the ANP, appears, in principle, to be a technically and economically feasible measure. In the Mediterranean area, mainly in dry land, the soils have a very low organic matter content (Sanchez et al., 1994). The need to recycle this type of residues and maintain the appropriate levels of organic matters in the soils in order to prevent their degradation is therefore evident, but the disadvantage of the shortage, increasingly greater, of natural organic products arises. In this sense, the materials from composting of solid urban residues have been the subject of much research and
many of them are already in very good conditions for recycling, notably minimizing any problem of contamination (Fortun and Fortun, 1995). There is practically no substance existing in nature that is not used by one microorganism or another (Iranzo et al., 2001); it is therefore necessary to identify the microorganisms present in the different processes, as several different species of microbe are usually involved (Hugenholtz et al., 1998; Radajewski et al., 2000). The project: ‘‘Use of rice straw and sewage sludge composting. Study of the microorganisms involved for process optimization’’ (GV-CAPA00-03, 2001–2004) aims to offer a technical and economically viable solution to two serious problems in the Valencia area by means of the transformation of sewage reprocessing biological waste into organic compost, utilizing the residual straw from rice cultivation as structural agent material. Transforming these materials into an organic soil supplement is a viable alternative for their treatment and utilization. The aim of the present work was to show some preliminary results that justify the use of composting process in rice straw and sewage sludge recycling. Thus we have been studied the physical, chemical and microbiological characteristics of these materials.
2. Methods A total of 30 rice straw samples from different ANP zones were collected (12 from the 1999 harvest, 12 from 2000 and 6 from 2001). In each zone we performed a random sampling of plants, taking about 1 kg of straw. The samples were oven-dried at 60 C, pulverized and stored until analyses were performed, except a sub sample that was refrigerated at 4 C until moisture, microbiological and respirometry analyses were performed. As for sewage sludge, 7 samples (4 from 2000 and 3 from 2001) from the sewage treatment plant (EMARSA) in Valencia (Spain) were collected. Each sample was divided into two parts: one of then, was refrigerated (4 C) until moisture, mineral nitrogen, saturated paste, microbiological and respirometry analyses were performed; the other one, was carry out on oven-dried at 60 C during 48 h and pulverized. The moisture content (oven-dried at 105 C for 24 h), total organic matter (weight loss on ignition at 550 C for 72 h), oxidizable organic carbon (Walkley–Black method) and total nitrogen (Kjeldahl method) were determined (Page et al., 1982).The pH and electrical conductivity was measured in a 1:2.5 and 1:5, respectively, water soluble extract (w:v). In saturated paste extract, sewage sludge-distilled water (2:1, fw:v), NO3 -N (formation in sulfuric acid of a red nitro compound the concentration of which is determined by photometry) and NH4 -N (indophenol blue method) were measured.
M. Iranzo et al. / Bioresource Technology 95 (2004) 107–112
In order to determine the total content of P, K, Ca, Mg, Na, Fe, Mn, Cu, Zn, Ni, Pb, Cd, Cr and Hg, sewage sludge was digested with an acid mixture of HNO3 and HClO4 , and rice straw only with nitric acid. The phosphorous concentration was determined colourimetrically as molybdovanadate phosphoric acid and total S of samples were measured with CE instruments EA 1110 CNHS elemental analyzer. The rest of elements were determined by flame atomic absorption spectrometry (AAS, Perkin Elmer 2080), except Ni, Pb, Cr and Cd in the rice straw, which were determined by graphite chamber (GC) AAS and the Hg by GC AAS by generation of hydrides. For all analyses three replicates were performed per sample. The respiration activity of microorganism was determined on different initial C/N (17, 24 and 40) raw materials blends and sewage sludge by manometric measurement of oxygen consumption during the simultaneous absorption of CO2 in caustic soda solution (1 N) OxiTop -C (WTW, Weilheim, RFA) (Platen and Wirtz, 1999). Samples were incubated at 20 C and moisture was 60%. Two replicates were performed per sample. The total number of microorganisms were determined by isolation and identification. It was carried out using the procedure described by Soriano et al. (2001).
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In order to study the temperature effect over some pathogen microorganisms. We incubated 500 g fresh material blend (sewage sludge and rice straw, 1:4 v/v) during 72 h at 43 C (Blend-1) and 48 h at 62 C (Blend-2).
3. Results and discussion The results obtained when analyzing the physical, chemical and biological properties of the rice straw and the sewage sludge are shown in Table 1. Sewage sludge samples are of different dates, even thought the moisture content, pH, electrical conductivity (EC), organic matter, oxidizable organic C, total N, nitrate and ammonia display scant variability. Thus, the values of organic matter and total N are within the ranges reported by Felip o and Garau (1987). The low C/N relation and the high P content indicates that sewage sludge is an important source of N and P for the aerobic microorganisms responsible for the composting process. On the other hand, analysis of the mineral elements reveals a greater variability, emphasizing the high heavy metal content that is usual in residues of urban and industrial origin. However, their levels do not exceed the quality
Table 1 Physical, chemical and microbiological characterization of raw materials Parameter
Sewage sludge Range
Mean (SD)
Range
Mean (SD)
Total moisture, % Moisture to 60 C, % Mineral residue, % EC 25 C, dS m1 1:5 Density, g cm3 pH 1:2.5 Total organic matter, % Oxidizable organic C, % C/N N total, % NO 3 , ppm NHþ 4 , ppm P2 O5 , % K2 O, % CaO, % MgO, % Na2 O, % S, % Fe, mg kg1 Mn, mg kg1 Zn, mg kg1 Cu, mg kg1 Ni, mg kg1 Pb, mg kg1 Cd, mg kg1 Cr, mg kg1 Hg, mg kg1 Bacteria, CFU g1 Fungi, CFU g1
76.2–79.0 72.0–77.0
76.5 (2.7) 74.5 (2.0) – 5.94 (1.06) 1.0 (0.1) 7.21 (0.12) 48.6 (5.1) 26.0 (2.0) 7.3 (0.1) 3.53 (0.01) 663 (52) 1731 (148) 4.71 (0.27) 0.24 (0.10) 7.3 (3.6) 0.50 (0.25) 0.21 (0.05) – 39,438 (6777) 166 (15) 1429 (366) 378 (50) 57.0 (8.0) 154 (35) 1.82 (1.00) 222 (31) 2.08 (0.65) 5.1 · 1011 (2.6 · 1011 ) ND
11.00–20.00 10.0–13.7 12.1–15.2
12.7 11.8 (3.0) 14.3 (2.1) – 0.06 (0.03) – 80.3 (2.2) 33.6 (0.94) 46.8 (15.4) 0.93 (0.45) – – 0.19 (0.07) 1.55 (0.44) 0.32 (0.14) 0.20 (0.09) 0.50 (0.32) 0.15 (0.05) 174.2 (95.5) 72.2 (38.6) 32.2 (13.0) 4.32 (1.57) 3.00 (1.67) 0.75 (1.60) 0.12 (0.15) 6.0 (2.83) ND 3.23 · 106 (1.4 · 106 ) 3.75 · 106 (5.05 · 106 )
4.5–6.6 0.9–1.1 7.1–7.4 42.0–59.4 23.0–27.1 7.1–7.3 3.50–3.70 599–702 15.5–18.0 4.41–5.02 0.14–0.35 3.5–11.2 0.20–0.80 0.15–0.27 30,264–39,438 147–186 1036–1700 322–450 49–66 110–200 0.94–3.23 191–253 1.30–2.64
Rice straw
0.05–0.10 78.1–85.0 32.1–35.6 30.0–58.3 0.60–1.30
0.12–0.35 0.91–2.10 0.46–0.60 0.10–0.30 0.10–0.97 0.09–0.22 100–430 50–130 20–50 3.5–7.5 1.2–5.5 0.00–4.00 0.00–0.30 2.8–9.1 1.80 · 106 –5.00 · 106 8.7 · 103 –9.5 · 106
All data are expressed on dry weight. SD: standard deviation, –: not determined, EC: electrical conductivity, ND: not detected.
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cumulative O 2 uptake (mg g-1)
standards for sewage sludge destined to composting (BOE, 1990). For sewage sludge to be composted, it is necessary to incorporate a second material as a structuring agent that must have complementary properties, such as a high C/N ratio as well as balancing moisture (Epstein et al., 1981). Beside this, straw residues from rice cultivation are rich in organic matter content (80%) and oxidizable organic C (34%) and have a high C/N ratio (very variable and near the average of 50), which means a feasible carbon source for the microorganisms which able to survive the composting conditions. In addition, their physical properties make a good quality structuring agent for mixing with sewage sludge. Thus, the blend of these materials will have pH, C/N and moisture values suitable for the development of microorganisms implicated in composting process. In order to assess, in an initial approach, the microbiological flora of both residuals, their biological activity was studied by means of bacterial and fungi total counts. The results obtained are shown in Table 1. The number of bacteria is considerably higher in the sewage sludge (5.1 · 1011 CFU g1 d.w.) than in the rice straw (3.23 · 106 CFU g1 d.w.), while the fungi is not detected and 3.75 · 106 CFU g1 d.w. for this materials respectively. In order to optimize the C/N ratio in a initial raw materials mixture during biosolids composting, three different C/N ratio (17, 24 and 40) blends were studied by evaluation the effect of C/N ratio on microbial activity. The results obtained show in Fig. 1. It is noteworthy that all C/N mixes showed higher microbial activity than sewage sludge (9.35 mg O2 g1 d.w.) which is obvious. Several authors indicate that the optimal C/ N ratio for composting process ranged between 25 and 30 (Dıaz et al., 1993; Haug, 1993; Negro et al., 2000; Rodrıguez, 2001). Microbial respiration of our three different blends and the sewage sludge (Fig. 1) showed that at 36 h cumulative O2 uptake to C/N-16 ratio was 28 mg O2 g1 d.w., while to C/N-24 was 21 mg O2 g1 d.w., and C/N-40 was 12 mg O2 g1 d.w. Our results
indicate that C/N ratio has a greater influence on the microbial activity of rice straw and sewage sludge blends since a low C/N ratio induces a higher oxygen consumption than other larger ratios. This fact is due to (1) a low C/N ratio in ecosystem increased the microorganism growth (Begone et al., 1997) and therefore the O2 uptake is increased, (2) and also that a low C/N ratio provide a better homogeneity of mixture and consequently a great microbiological attach. The preliminary results of characterization of microorganisms have led to the isolation of two species of fungi that are able to develop only in the presence of rice residues (Rhodotorula glutinis and Aspergillus sp.). On the other hand, sewage sludge has a potential amount of pathogen microorganisms (fecal coli forms, Salmonella, parasites, etc.). In our research we found Salmonella spp., Enteric Bacteria and Streptococci (Table 2). Fortunately, these biological agents are controlled by the maintenance of high temperatures during several days, at the active phase, in which the composting process is developed. The regulations on compost quality proposed by US EPA for Class A sludge, expound that the time/temperature conditions for the inactivation of microorganisms indicate that 30 min at 60 C reduces by around 6 log 10 the number of coli forms and Salmonella; whereas for fecal streptococci, 67 C or more than 30 min is required to reach the same level of inactivation. A tem-
Table 2 Temperature influence on pathogenic microorganisms presences Microorganisms
Rice straw
Sewage sludge
Blend-1a
Blend-2b
Staphylococci Streptococci Enteric Bacteria Salmonellas
– – – –
+ + ++ +
++ ++ +++ ++
+ * * *
–: not determined; +++: abundant; ++: frequent; +: presence; *: absence. a 43 C/72 h (temperature/time). b 62 C/48 h (temperature/time).
35 30 25 C/N-40
20
C/N-24
15 10
C/N-17
5
sewage sludge
0 0
10
20
30
40
Time (h) Fig. 1. Microbial activities of raw materials blends at different initial C/N (17, 24 and 40) ratios and sewage sludge.
M. Iranzo et al. / Bioresource Technology 95 (2004) 107–112
perature of 60 C for 30 min provides a similar level of reduction for the nematode Ascaris lumbricoides, considered one of the most heat-resistant parasites (Haug, 1993). Our results (Table 2) showed that blend-1, which was incubated at 62 C/48 h agreed with to EPA regulations, since it did not show the presence of Staphylococci, Salmonella spp., Enteric Bacteria and Streptococci. By contrast blend-2 did not reach the adequate temperatures, which confirms the importance of composting termophilic phase for pathogenic reduction. 4. Conclusion The results obtained in the present work when studying the physical, chemical and microbiological properties of rice straw and sewage sludge allow us to conclude that these materials are suitable for being used in the composting process. The characteristics of the rice straw are complementary to those of the sewage sludge for the application of this process and the obtaining of compost or organic supplement suitable for being used in agriculture in accordance with current legislation. In addition, the C/N ratio suitable for a rapid increased in microbial activity was the lowest (16–24). On the other hand, the results suggest that the time/temperature conditions that are reached during the thermophilic phase can be highly effective in eliminating the pathogenic microorganisms present in blend of raw materials. These results support the idea that the use of composting process for minimizing the environmental impact of these wastes. Further work is required to validate these results in full-scale composting operations.
Acknowledgements This work has been undertaken thanks to a projected awarded by the Valencian Regional Government (Generalitat Valenciana) (GV-CAPA00-03). L. Roca-Perez and I. Pardo-Sainz were supported by doctoral fellowships from the Generalitat Valenciana, and J.V. Ca~ nizares was supported by a post-doctoral ‘‘Primo-Y ufera’’ fellowship from Jose and Ana Royo Foundation. References Akhtar, M., Malik, A., 2000. Roles of organic soil amendments and soil organisms in the biological control of plant–parasitic nematodes: a review. Bioresource Technol. 74, 35–47. Arai, T., Takaya, T., Ito, Y., Hayakawa, K., Tshima, S., Shibuya, C., Nomura, M., Yoshimi, N., Shibayama, M., Yasuda, Y., 1998. Bronchial asthma induced by rice. Int. Med. 37 (1), 98–101. Begone, M., Harper, J.L., Towsend, C.R., 1997. Descomponedores y detritıvoros. In: Ecologıa: Individuos, poblaciones y comunidades. Omega, Barcelona, pp. 391–421.
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Beltrame, K.G., Aloisi, R.R., Vitti, G.C., Boluda, R., 1999. Compostaje de un lodo biol ogico de la industria cervecera con aireaci on forzada y virutas de eucalipto. Edafologıa 6, 85–93. Berglund, S., Davis, R.D., L’Hermite, P., 1983. Utilization of sewage sludge on land rates of application and long-term effects of metals. In: Proceedings of a Seminar Held at Uppsala. D. Reidel Publishing Company, Lancester. BOE (Boletın Oficial del Estado), 1990. Boletın Oficial del Estado, Madrid, Spain. Catroux, G., Hermite, P., Suess, E., 1983. The influence of sewage sludge application on physical and biological properties of soil. In: Proceedings of a Seminar Held in Munich 1981. D. Reidel Publishing Company, Amsterdam, The Netherlands, p. 253. Davis, R.D., Hucker, G., L’Hermite, P., 1983. Environmental effects of organic and inorganic contaminants in sewage sludge. Reidel Publishing Company, Dordrecht, The Netherlands. Dıaz, L., Savage, G., Eggerth, L., Golueke, C., 1993. Composting and recycling municipal solid waste. Lewis publishers, CalRecovery, Inc., California, USA. Epstein, E., Paar, J.F., Sikora, G.B., Wilson, G.B., 1981. The aerated method of sludge composting. In: Goldstein, J. (Ed.), Composting Theory and Practice for City, Industry and Farm. JG Press, Emmaus, pp. 117–124. Escrig, I., Hernandez, F., Boluda, R., 1994. Contaminaci on por metales pesados en suelos tratados con lodos de depuradora. Metodos de extracci on. In: II Congr. Intern. de Suelos Contaminados, IHOBE, Vitoria-Gasteiz, Spain. Eweis, J.B., Ergas, S.J., Chang, D.P.Y., Schroeder, E.D., 1999. Principios de Biorrecuperaci on. Mc Graw Hill, Madrid. p. 327. Felip o, M.T., Garau, M.A., 1987. La Contaminaci o del s ol. Quaderns d’Ecologia Aplicada, Diputaci ode Bar celona, Barcelona, Spain, p. 85. Fortun, C., Fortun, A., 1995. Utilizaci on de compost de residuo s olido urbano para disminuir la degradaci on de los suelos. Edafologıa 1, 27–34. Gagliardi, J.V., Karns, J.S., 2000. Leaching of Escherichia coli O157: H7 in diverse soils under various agricultural management practices. Appl. Environ. Microbiol. 66, 877–883. Han, Y.W., 1978. Microbial utilization of straw (a review). Adv. Appl. Microbiol. 23, 119–153. Haug, R., 1993. The Practical Handbook of Compost Engineering. Lewis Publishers, Florida. p. 717. Hugenholtz, P., Goebel, B.M., Pace, N.P., 1998. Impact of cultureindependent studies on the emerging phylogenetic view of bacterial diversity. J. Bacteriol. 180, 4765–4774. Iranzo, M., Sainz-Pardo, I., Boluda, R., Sanchez, J., Mormeneo, S., 2001. The use of microorganisms in environmental remediation. Ann. Microbiol. 51, 135–143. Jezierski, S., Czechowsky, F., Jerzykiewicz, M., Drozd, J., 2000. EPR investigations of structure of humic acids from compost, soil, peat and soft brown coal upon oxidation and metal uptake. Appl. Magn. Reson. 18, 127–136. Lazzari, L., Sperni, L., Bertin, P., Pavoni, B., 2000. Correlation between inorganic (heavy metals) and organic (PCBs and PAHs) micropollutant concentrations during sewage sludge composting processes. Chemosphere 41, 427–435. Lue-Hing, C., Zenz, D.R., Kuchenrither, R., 1992. Municipal sewage sludge management. In: Proceedings of Utilization and Disposal. Technomic Publ. Co. Inc., Lancaster. Menzies, J.B., Chaney, R.L., 1974. Waste characteristics. In: Factors Involved in Land Application of Agricultural and Municipal Wastes. Nat. Prog. Sttaff Soil, Water and Air Sciences, Beltsville, Maryland, p. 200. Negro, M.J., Villa, F., Aibar, J., Alarc on, R., Ciria, P., 2000. Producci on y gesti on del compost. Informaciones tecnicas del departamento de agricultura de la direcci on general de tecnologı a agraria. Gobierno de Arag on. Nr. 88, Zaragoza.
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Short Communication
Characteristics of rice straw and sewage sludge as composting materials in Valencia (Spain) Maria Iranzo a, Jose V. Ca~ nizares, Luis Roca-Perez b,c, Isabel Sainz-Pardo a, Salvador Mormeneo a, Rafael Boluda b,c,* a
b
Departament de Microbiologia (Pharmacy Faculty), Universitat de Valencia, Avda. Vicent Andres i Estelles s/n, 46100 Burjassot, Valencia, Spain Departament de Biologia Vegetal (Pharmacy Faculty), Universitat de Valencia, Avda. Vicent Andres i Estelles s/n, 46100 Burjassot, Valencia, Spain c CIDE (CSIC-UV-GV), Camıde la Marjal s/n 46470 Albal, Valencia, Spain Received 28 April 2003; accepted 27 January 2004 Available online 5 March 2004
Abstract This work supports the idea that composting can be useful for minimizing the rice straw and sewage sludge environmental impact. Several physical, chemical and microbiological properties of these raw materials were analyzed. The characteristics of the rice straw were complementary to those of the sewage sludge for the application of composting. The C/N ratios suitable for a rapid increased in microbial activity were the lowest (17–24). A temperature of 62 C during 48 h removed pathogenic microorganisms from rice straw and sewage sludge mixture. The results obtained in the present work suggested that these materials could be use in the composting process. 2004 Published by Elsevier Ltd. Keywords: Rice straw; Sewage sludge; C/N ratio; Blend-sanitation
1. Introduction The increase in the production of waste in society is of rising concern at different levels of the population; this increase can be diminished by means of various alternatives (elimination, purification and/or recycling). Wastes would cease to be a problem if an added value were attributed to them (Menzies and Chaney, 1974; Catroux et al., 1983; Lue-Hing et al., 1992). The treatment and/or utilization of hazardous by-products is considered a vital issue in the protection of the health of mankind and the environment. There are three basic questions to be considered: What does the term ‘‘hazardous’’ mean?; Which is the best available technology to eliminate the danger? and, what advantages are to be obtained simultaneously? (Yong et al., 1992). The danger of a waste product depends on its chemical, physical or biological nature, but often this only depends on how it is disposed of. *
Corresponding author. Tel.: +34-96-3544927; fax: +34-96-3544926. E-mail address: [email protected] (R. Boluda).
0960-8524/$ - see front matter 2004 Published by Elsevier Ltd. doi:10.1016/j.biortech.2004.01.013
Every autumn, more than 100 million kg straw from rice cultivation in the Albufera Natural Park (ANP) are disposed of, traditionally by burning in situ, causing real environmental problems. This practice produces huge clouds of smoke that affect all the adjacent municipalities, with a population corresponding to almost a third of the Valencian Community (including the city of Valencia). The problems are varied and even affect health (respiratory, cardio-respiratory and allergic disorders). In some countries, for example Japan, the emissions from burning of rice residuals have been related to the appearance of respiratory diseases such as bronchial asthma (Arai et al., 1998; Torigoe et al., 2000). This problem is not exclusive to Valencian agriculture and generally affects other rice-growing areas, both at national (the Ebro Delta in Catalonia) and international level (Japan, China, etc.). Different approaches have been described for the utilization of rice straw: paper production, construction materials, incorporation in soil, compost, energy source, animal feed, etc. However, competition with other resources prevents the immediate use of this agricultural
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waste for these purposes, with the result that its use is still a remote possibility (Han, 1978; Haug, 1993). Other residuals with serious effects upon environmental problems are the sludge waste from urban and industrial sewage reprocessing plants. These materials present different characteristics whose composition depends on the type and origin of the waters to be purified. They contain a large amount of organic material and nutrients, but often toxic elements and pathogenic microorganisms that must be monitored when sludges used. The production of compost from this waste to obtain organic additives for use in agricultural systems has been the object of several studies (Catroux et al., 1983; Davis et al., 1983; Berglund et al., 1983; Williams et al., 1985; Haug, 1993; Escrig et al., 1994); currently, the subject is the focus of ongoing research (Beltrame et al., 1999; Eweis et al., 1999; Akhtar and Malik, 2000; Gagliardi and Karns, 2000; Jezierski et al., 2000; Lazzari et al., 2000) given the importance of the problem and its social and environmental implications, leading to the regulation of its utilization at European, national and regional level. The modern conception of environmental management has as its base the recycling of residues and in this context composting arises as a safe form of treatment of some wastes and the reusability of the nutrients contained in them. The most common applications of composting are the treatment of agricultural residues, garden and kitchen waste, solid municipal waste and sewage plant sludge; currently, they are also being applied to solid biorecovery. This process presents the great advantage of eliminating pathogenic microorganisms during the thermophilic phase, increasing the quality of the end product. The disadvantages of composting are the need for maintenance and the production of emissions into the air due to the temperatures that are developed; nevertheless, these are easier to deal with than in treatment in beds. It is also important to control moisture in order to keep biological activity optimal. Nonetheless, compared with non-biological treatment processes, such as incineration and bio-mass plants, composting is much cheaper and its technology is much simpler to apply (Eweis et al., 1999). Given all the above, the use of composting to eliminate the residual straw from rice growing in the ANP, appears, in principle, to be a technically and economically feasible measure. In the Mediterranean area, mainly in dry land, the soils have a very low organic matter content (Sanchez et al., 1994). The need to recycle this type of residues and maintain the appropriate levels of organic matters in the soils in order to prevent their degradation is therefore evident, but the disadvantage of the shortage, increasingly greater, of natural organic products arises. In this sense, the materials from composting of solid urban residues have been the subject of much research and
many of them are already in very good conditions for recycling, notably minimizing any problem of contamination (Fortun and Fortun, 1995). There is practically no substance existing in nature that is not used by one microorganism or another (Iranzo et al., 2001); it is therefore necessary to identify the microorganisms present in the different processes, as several different species of microbe are usually involved (Hugenholtz et al., 1998; Radajewski et al., 2000). The project: ‘‘Use of rice straw and sewage sludge composting. Study of the microorganisms involved for process optimization’’ (GV-CAPA00-03, 2001–2004) aims to offer a technical and economically viable solution to two serious problems in the Valencia area by means of the transformation of sewage reprocessing biological waste into organic compost, utilizing the residual straw from rice cultivation as structural agent material. Transforming these materials into an organic soil supplement is a viable alternative for their treatment and utilization. The aim of the present work was to show some preliminary results that justify the use of composting process in rice straw and sewage sludge recycling. Thus we have been studied the physical, chemical and microbiological characteristics of these materials.
2. Methods A total of 30 rice straw samples from different ANP zones were collected (12 from the 1999 harvest, 12 from 2000 and 6 from 2001). In each zone we performed a random sampling of plants, taking about 1 kg of straw. The samples were oven-dried at 60 C, pulverized and stored until analyses were performed, except a sub sample that was refrigerated at 4 C until moisture, microbiological and respirometry analyses were performed. As for sewage sludge, 7 samples (4 from 2000 and 3 from 2001) from the sewage treatment plant (EMARSA) in Valencia (Spain) were collected. Each sample was divided into two parts: one of then, was refrigerated (4 C) until moisture, mineral nitrogen, saturated paste, microbiological and respirometry analyses were performed; the other one, was carry out on oven-dried at 60 C during 48 h and pulverized. The moisture content (oven-dried at 105 C for 24 h), total organic matter (weight loss on ignition at 550 C for 72 h), oxidizable organic carbon (Walkley–Black method) and total nitrogen (Kjeldahl method) were determined (Page et al., 1982).The pH and electrical conductivity was measured in a 1:2.5 and 1:5, respectively, water soluble extract (w:v). In saturated paste extract, sewage sludge-distilled water (2:1, fw:v), NO3 -N (formation in sulfuric acid of a red nitro compound the concentration of which is determined by photometry) and NH4 -N (indophenol blue method) were measured.
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In order to determine the total content of P, K, Ca, Mg, Na, Fe, Mn, Cu, Zn, Ni, Pb, Cd, Cr and Hg, sewage sludge was digested with an acid mixture of HNO3 and HClO4 , and rice straw only with nitric acid. The phosphorous concentration was determined colourimetrically as molybdovanadate phosphoric acid and total S of samples were measured with CE instruments EA 1110 CNHS elemental analyzer. The rest of elements were determined by flame atomic absorption spectrometry (AAS, Perkin Elmer 2080), except Ni, Pb, Cr and Cd in the rice straw, which were determined by graphite chamber (GC) AAS and the Hg by GC AAS by generation of hydrides. For all analyses three replicates were performed per sample. The respiration activity of microorganism was determined on different initial C/N (17, 24 and 40) raw materials blends and sewage sludge by manometric measurement of oxygen consumption during the simultaneous absorption of CO2 in caustic soda solution (1 N) OxiTop -C (WTW, Weilheim, RFA) (Platen and Wirtz, 1999). Samples were incubated at 20 C and moisture was 60%. Two replicates were performed per sample. The total number of microorganisms were determined by isolation and identification. It was carried out using the procedure described by Soriano et al. (2001).
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In order to study the temperature effect over some pathogen microorganisms. We incubated 500 g fresh material blend (sewage sludge and rice straw, 1:4 v/v) during 72 h at 43 C (Blend-1) and 48 h at 62 C (Blend-2).
3. Results and discussion The results obtained when analyzing the physical, chemical and biological properties of the rice straw and the sewage sludge are shown in Table 1. Sewage sludge samples are of different dates, even thought the moisture content, pH, electrical conductivity (EC), organic matter, oxidizable organic C, total N, nitrate and ammonia display scant variability. Thus, the values of organic matter and total N are within the ranges reported by Felip o and Garau (1987). The low C/N relation and the high P content indicates that sewage sludge is an important source of N and P for the aerobic microorganisms responsible for the composting process. On the other hand, analysis of the mineral elements reveals a greater variability, emphasizing the high heavy metal content that is usual in residues of urban and industrial origin. However, their levels do not exceed the quality
Table 1 Physical, chemical and microbiological characterization of raw materials Parameter
Sewage sludge Range
Mean (SD)
Range
Mean (SD)
Total moisture, % Moisture to 60 C, % Mineral residue, % EC 25 C, dS m1 1:5 Density, g cm3 pH 1:2.5 Total organic matter, % Oxidizable organic C, % C/N N total, % NO 3 , ppm NHþ 4 , ppm P2 O5 , % K2 O, % CaO, % MgO, % Na2 O, % S, % Fe, mg kg1 Mn, mg kg1 Zn, mg kg1 Cu, mg kg1 Ni, mg kg1 Pb, mg kg1 Cd, mg kg1 Cr, mg kg1 Hg, mg kg1 Bacteria, CFU g1 Fungi, CFU g1
76.2–79.0 72.0–77.0
76.5 (2.7) 74.5 (2.0) – 5.94 (1.06) 1.0 (0.1) 7.21 (0.12) 48.6 (5.1) 26.0 (2.0) 7.3 (0.1) 3.53 (0.01) 663 (52) 1731 (148) 4.71 (0.27) 0.24 (0.10) 7.3 (3.6) 0.50 (0.25) 0.21 (0.05) – 39,438 (6777) 166 (15) 1429 (366) 378 (50) 57.0 (8.0) 154 (35) 1.82 (1.00) 222 (31) 2.08 (0.65) 5.1 · 1011 (2.6 · 1011 ) ND
11.00–20.00 10.0–13.7 12.1–15.2
12.7 11.8 (3.0) 14.3 (2.1) – 0.06 (0.03) – 80.3 (2.2) 33.6 (0.94) 46.8 (15.4) 0.93 (0.45) – – 0.19 (0.07) 1.55 (0.44) 0.32 (0.14) 0.20 (0.09) 0.50 (0.32) 0.15 (0.05) 174.2 (95.5) 72.2 (38.6) 32.2 (13.0) 4.32 (1.57) 3.00 (1.67) 0.75 (1.60) 0.12 (0.15) 6.0 (2.83) ND 3.23 · 106 (1.4 · 106 ) 3.75 · 106 (5.05 · 106 )
4.5–6.6 0.9–1.1 7.1–7.4 42.0–59.4 23.0–27.1 7.1–7.3 3.50–3.70 599–702 15.5–18.0 4.41–5.02 0.14–0.35 3.5–11.2 0.20–0.80 0.15–0.27 30,264–39,438 147–186 1036–1700 322–450 49–66 110–200 0.94–3.23 191–253 1.30–2.64
Rice straw
0.05–0.10 78.1–85.0 32.1–35.6 30.0–58.3 0.60–1.30
0.12–0.35 0.91–2.10 0.46–0.60 0.10–0.30 0.10–0.97 0.09–0.22 100–430 50–130 20–50 3.5–7.5 1.2–5.5 0.00–4.00 0.00–0.30 2.8–9.1 1.80 · 106 –5.00 · 106 8.7 · 103 –9.5 · 106
All data are expressed on dry weight. SD: standard deviation, –: not determined, EC: electrical conductivity, ND: not detected.
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cumulative O 2 uptake (mg g-1)
standards for sewage sludge destined to composting (BOE, 1990). For sewage sludge to be composted, it is necessary to incorporate a second material as a structuring agent that must have complementary properties, such as a high C/N ratio as well as balancing moisture (Epstein et al., 1981). Beside this, straw residues from rice cultivation are rich in organic matter content (80%) and oxidizable organic C (34%) and have a high C/N ratio (very variable and near the average of 50), which means a feasible carbon source for the microorganisms which able to survive the composting conditions. In addition, their physical properties make a good quality structuring agent for mixing with sewage sludge. Thus, the blend of these materials will have pH, C/N and moisture values suitable for the development of microorganisms implicated in composting process. In order to assess, in an initial approach, the microbiological flora of both residuals, their biological activity was studied by means of bacterial and fungi total counts. The results obtained are shown in Table 1. The number of bacteria is considerably higher in the sewage sludge (5.1 · 1011 CFU g1 d.w.) than in the rice straw (3.23 · 106 CFU g1 d.w.), while the fungi is not detected and 3.75 · 106 CFU g1 d.w. for this materials respectively. In order to optimize the C/N ratio in a initial raw materials mixture during biosolids composting, three different C/N ratio (17, 24 and 40) blends were studied by evaluation the effect of C/N ratio on microbial activity. The results obtained show in Fig. 1. It is noteworthy that all C/N mixes showed higher microbial activity than sewage sludge (9.35 mg O2 g1 d.w.) which is obvious. Several authors indicate that the optimal C/ N ratio for composting process ranged between 25 and 30 (Dıaz et al., 1993; Haug, 1993; Negro et al., 2000; Rodrıguez, 2001). Microbial respiration of our three different blends and the sewage sludge (Fig. 1) showed that at 36 h cumulative O2 uptake to C/N-16 ratio was 28 mg O2 g1 d.w., while to C/N-24 was 21 mg O2 g1 d.w., and C/N-40 was 12 mg O2 g1 d.w. Our results
indicate that C/N ratio has a greater influence on the microbial activity of rice straw and sewage sludge blends since a low C/N ratio induces a higher oxygen consumption than other larger ratios. This fact is due to (1) a low C/N ratio in ecosystem increased the microorganism growth (Begone et al., 1997) and therefore the O2 uptake is increased, (2) and also that a low C/N ratio provide a better homogeneity of mixture and consequently a great microbiological attach. The preliminary results of characterization of microorganisms have led to the isolation of two species of fungi that are able to develop only in the presence of rice residues (Rhodotorula glutinis and Aspergillus sp.). On the other hand, sewage sludge has a potential amount of pathogen microorganisms (fecal coli forms, Salmonella, parasites, etc.). In our research we found Salmonella spp., Enteric Bacteria and Streptococci (Table 2). Fortunately, these biological agents are controlled by the maintenance of high temperatures during several days, at the active phase, in which the composting process is developed. The regulations on compost quality proposed by US EPA for Class A sludge, expound that the time/temperature conditions for the inactivation of microorganisms indicate that 30 min at 60 C reduces by around 6 log 10 the number of coli forms and Salmonella; whereas for fecal streptococci, 67 C or more than 30 min is required to reach the same level of inactivation. A tem-
Table 2 Temperature influence on pathogenic microorganisms presences Microorganisms
Rice straw
Sewage sludge
Blend-1a
Blend-2b
Staphylococci Streptococci Enteric Bacteria Salmonellas
– – – –
+ + ++ +
++ ++ +++ ++
+ * * *
–: not determined; +++: abundant; ++: frequent; +: presence; *: absence. a 43 C/72 h (temperature/time). b 62 C/48 h (temperature/time).
35 30 25 C/N-40
20
C/N-24
15 10
C/N-17
5
sewage sludge
0 0
10
20
30
40
Time (h) Fig. 1. Microbial activities of raw materials blends at different initial C/N (17, 24 and 40) ratios and sewage sludge.
M. Iranzo et al. / Bioresource Technology 95 (2004) 107–112
perature of 60 C for 30 min provides a similar level of reduction for the nematode Ascaris lumbricoides, considered one of the most heat-resistant parasites (Haug, 1993). Our results (Table 2) showed that blend-1, which was incubated at 62 C/48 h agreed with to EPA regulations, since it did not show the presence of Staphylococci, Salmonella spp., Enteric Bacteria and Streptococci. By contrast blend-2 did not reach the adequate temperatures, which confirms the importance of composting termophilic phase for pathogenic reduction. 4. Conclusion The results obtained in the present work when studying the physical, chemical and microbiological properties of rice straw and sewage sludge allow us to conclude that these materials are suitable for being used in the composting process. The characteristics of the rice straw are complementary to those of the sewage sludge for the application of this process and the obtaining of compost or organic supplement suitable for being used in agriculture in accordance with current legislation. In addition, the C/N ratio suitable for a rapid increased in microbial activity was the lowest (16–24). On the other hand, the results suggest that the time/temperature conditions that are reached during the thermophilic phase can be highly effective in eliminating the pathogenic microorganisms present in blend of raw materials. These results support the idea that the use of composting process for minimizing the environmental impact of these wastes. Further work is required to validate these results in full-scale composting operations.
Acknowledgements This work has been undertaken thanks to a projected awarded by the Valencian Regional Government (Generalitat Valenciana) (GV-CAPA00-03). L. Roca-Perez and I. Pardo-Sainz were supported by doctoral fellowships from the Generalitat Valenciana, and J.V. Ca~ nizares was supported by a post-doctoral ‘‘Primo-Y ufera’’ fellowship from Jose and Ana Royo Foundation. References Akhtar, M., Malik, A., 2000. Roles of organic soil amendments and soil organisms in the biological control of plant–parasitic nematodes: a review. Bioresource Technol. 74, 35–47. Arai, T., Takaya, T., Ito, Y., Hayakawa, K., Tshima, S., Shibuya, C., Nomura, M., Yoshimi, N., Shibayama, M., Yasuda, Y., 1998. Bronchial asthma induced by rice. Int. Med. 37 (1), 98–101. Begone, M., Harper, J.L., Towsend, C.R., 1997. Descomponedores y detritıvoros. In: Ecologıa: Individuos, poblaciones y comunidades. Omega, Barcelona, pp. 391–421.
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