Biotransformation of rice husk into organic fertilizer through vermicomposting

Biotransformation of rice husk into organic fertilizer through vermicomposting

Ecological Engineering 41 (2012) 60–64 Contents lists available at SciVerse ScienceDirect Ecological Engineering journal homepage:

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Ecological Engineering 41 (2012) 60–64

Contents lists available at SciVerse ScienceDirect

Ecological Engineering journal homepage:

Short communication

Biotransformation of rice husk into organic fertilizer through vermicomposting Su Lin Lim a , Ta Yeong Wu a,∗ , Edwin Yih Shyang Sim a , Pei Nie Lim a , Charles Clarke b a b

Chemical Engineering Discipline, School of Engineering, Monash University, Jalan Lagoon Selatan, Bandar Sunway, 46150 Selangor Darul Ehsan, Malaysia School of Science, Monash University, Jalan Lagoon Selatan, Bandar Sunway, 46150 Selangor Darul Ehsan, Malaysia

a r t i c l e

i n f o

Article history: Received 22 July 2011 Received in revised form 2 January 2012 Accepted 30 January 2012 Available online 28 February 2012 Keywords: Eudrilus eugeniae Market refused fruit Rice husk Vermicompost Solid waste management

a b s t r a c t Rice husk (RH) is an abundant agricultural solid waste as a result of rice-milling process. The present study investigated the potential of converting RH amended with market refused fruit (market refused banana (B), honeydew (H) or papaya (P)) into vermicompost using Eudrilus eugeniae. RH was mixed with market refused fruit in an equal ratio to produce three different treatments (1B:1RH, 1H:1RH and 1P:1RH) for laboratory screening of solid wastes. Generally, the application of E. eugeniae permitted an increase in calcium (6.9–99.0%), potassium (15.0–121.4%), phosphorus (2.4–49.5%) and carbon (6.5–69.0%) in final vermicompost after 9 weeks of vermicomposting. However, decreases in magnesium (3.7–45.7%) and nitrogen (6.9–23.7%) were also observed in final vermicomposts. Among all the RH treatments, RH which was mixed with market refused papaya (1P:1RH) showed better quality vermicompost with higher nutritional status. It was also found that RH which was amended by market refused fruit (1B:1RH, 1H:1RH or 1P:1RH), especially market refused papaya, encouraged the growth of earthworm as compared to the treatment with RH alone. The present data reveal that vermicomposting is a feasible technology for bio-transforming RH into value-added material, namely vermicompost. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Rice (Oryza sativa or Oryza glaberrima) is one of the major food crops in the world, especially in East and South Asia, Middle East, Latin America and West Indies. The inedible rice husk (RH) would always be removed during the rice-milling process and it is considered as waste by-product with little economic value because the efforts to utilize RH has been handicapped by its tough, woody, abrasive and resistance to degradation nature, low nutritive properties as well as high ash content (Sun and Gong, 2001). It is reported that for every ton of rice produced, about 0.23 tons of RH is formed (Chandrasekhar et al., 2003). The rigorous development of the rice milling industries in the world has resulted the generation of RH up to 120 million metric tons per year and the continuous generation of RH may present a major disposal problem in most of the rice production countries (Foo and Hameed, 2009). Extensive research has been carried out to reuse RH but most of the research was conducted in laboratory scale and it is unknown to the researcher if the proposed method could be used to cater for the increasing quantity of RH. One of the methods that could be used to transform large quantity of RH into value added product is composting. However, the high lignin content of the RH can prolong

∗ Corresponding author. Tel.: +60 3 55146258; fax: +60 3 55146207. E-mail addresses: [email protected], [email protected] (T.Y. Wu). 0925-8574/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.ecoleng.2012.01.011

the composting process. Leconte et al. (2009) found that the time required for the stability of RH with poultry manure in composting was about 180 days. Thus, other safe disposal and environmentally friendly management of RH, such as vermicomposting, was investigated in this study. Vermicomposting is a microbial composting of organic wastes through earthworm activity (Domínguez et al., 2001). Microbes are responsible for the biochemical degradation of organic matters whilst earthworms are the important drivers to condition the substrate and alter the biological activity (Domínguez et al., 2002). In comparison with typical type of composting, vermicomposting results in bioconversion of solid wastes into two useful products: the earthworm biomass and the vermicompost that exhibits lower mass in lesser processing time and greater fertilizer value with high humus content and lesser phytotoxicity (Garg and Gupta, 2009; Sim and Wu, 2010). To the best of our knowledge, limited study has been attempted to investigate the potential of reusing RH as feed stock in vermicomposting. Market refused fruits were used as amendments in this present study because the stock culture of Eudrilus eugeniae was grown using papaya as feedstock. Also, it was proven by Prabha et al. (2007) and Lim et al. (2011) that E. eugeniae can be cultured very well on fruit wastes. Thus, the appropriate combination of market refused fruit with RH might provide suitable condition for E. eugeniae to live in. Therefore, the aim of this study was to investigate the suitability of E. eugeniae in vermicomposting of RH

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together with market refused fruits, in which case the latter were found abundantly in local markets.


ground in a blender and stored in polythene bags (at 4 ◦ C) before chemical analysis was conducted. 2.3. Vermicompost analysis

2. Materials and methods 2.1. Earthworm and collection of organic waste E. eugeniae was obtained from ESI Agrotech, Malaysia. E. eugeniae was chosen in this study because E. eugeniae is a fast-growing earthworm that could convert organic waste rapidly (Domínguez et al., 2001). Stock earthworms were grown in the laboratory under ambient temperature on partially decomposed market refused papaya and ground RH in the ratio of 20:1. The organic wastes used in this study were RH and market refused fruits, namely market refused banana (B), honeydew (H) and papaya (P). RH was obtained from Kilang BERNAS, Sekinchan while the fruits were collected from Selayang Wholesale Market, Kuala Lumpur, Malaysia. The market refused fruits were kept in refrigerator (at 4 ◦ C) before they were used as feed stock in vermicomposting. 2.2. Experimental set up The experiments were conducted in triplicate in rectangular plastic containers (17 cm × 14 cm × 12 cm), which were kept in dark laboratory. The temperature in the laboratory was maintained at around 25 ± 2 ◦ C, which is the optimum temperature for E. eugeniae (Khwairakpam and Bhargava, 2009a). The containers were filled from bottom to top with pebbles (1 cm height), saw-dust (2 cm height) and soil (4 cm height). The lid and bottom of each container were punched several holes for aeration. Moisture content was maintained around 50% for all treatments by periodic sprinkling of distilled water. RH and/or market refused fruits (market refused B, H or P) were ground and blended together with 50 mL distilled water in equal ratio to produce three different combinations of treatment, namely B:RH (1:1), H:RH (1:1) and P:RH (1:1). Four control treatments, consisting of individual wastes (RH, B, H and P) were also set up. The physico-chemical characteristics of all treatments are presented in Table 1. For vermicomposting experiments, 10 non-clitellate E. eugeniae (∼0.70 g each) were selected from the stock culture and released into each experimental container. The worms were fed weekly up to 7 weeks with substrate material according to their weight at 0.75 g-substrate/g-worm/day (Ndegwa et al., 2000). Vermicomposting was conducted up to 63 days (9 weeks). The growth (and mortality, if any) of earthworm was observed weekly and the data of growth (in terms of quantity and biomass) was recorded for each experimental container. Earthworm biomass and quantity were measured according to Lim et al. (2011). About 100 g of homogenized wet substrates (free from earthworms, hatchlings and cocoons) were collected on the first and final day of vermicomposting for analysis. The samples were oven dried at 60 ◦ C for 48 h,

pH and electrical conductivity (EC) were measured using digital pH and conductivity meters in 1:10 (w/v, substrate:water extract) aqueous solution (Khwairakpam and Bhargava, 2009a). Total organic carbon (TOC) was determined using partially oxidation method (Walkley and Black, 1934). Total Kjeldahl nitrogen (TKN) was measured using Micro-Kjeldahl method (Shaw and Beadle, 1949). Total calcium, magnesium and potassium were measured by ignition method using atomic absorption spectrophotometer (Adi and Noor, 2009), while the total phosphorus was determined using colorimetric method (John, 1970). 2.4. Statistical analysis One-way ANOVA was used to analyze the significant difference between treatments. Tukey’s HSD test was also performed to identify the homogenous type of treatments for the various parameters. The probability levels used for statistical significance were P < 0.05 for the tests. The statistical analysis in this study was conducted using PASW® Statistics 18. 3. Results and discussion 3.1. Growth and reproduction of E. eugeniae in different treatments Table 2 shows the maximum growth rate and individual weight of E. eugeniae in different feeding materials. It is clear that E. eugeniae fed with RH amended with any market refused fruits were generally higher than the other treatments done in the past. In this study, the earthworm showed significant difference in growth parameters, i.e. maximum growth rate (mg/worm/day) (ANOVA; F = 4.955, P < 0.05) and maximum individual weight (mg/worm) (ANOVA; F = 7.138, P < 0.05). As shown in Table 2, 1P:1RH treatment produced the highest growth rate (48.57 mg/worm/day) whilst RH treatment had the lowest growth rate (9.29 mg/worm/day). Statistically, the maximum growth rate only showed significant difference between 1P:1RH and RH treatments (ANOVA/Tukey’s; P < 0.05). The maximum individual weight was the highest and lowest for treatment B and RH, respectively. There was significant difference between RH treatment with B, H, 1H:1RH and 1P:1RH treatments only. Earthworm productivity is an important indicator in vermicomposting process and the difference in growth rate among different treatments seems to be closely related to feed quality (Suthar, 2010). Generally, feedstock with high polyphenolic and lignin contents (such as RH treatment in this study) is not favourable for most of the earthworm species (Ganesh et al., 2009). Also, high polyphenolic and lignin contents inhibit microbial activities and hence slow

Table 1 Initial physico-chemical characteristics of different treatments (mean ± SD, n = 3). Treatment


B H P RH 1B:1RH 1H:1RH 1P:1RH

7.51 7.46 7.45 7.62 7.76 7.43 7.59

EC (␮S/cm) ± ± ± ± ± ± ±

0.15a 0.10a 0.47a 0.24a 0.35a 0.09a 0.22a

274.7 219.7 368.0 230.3 257.0 264.0 253.0

± ± ± ± ± ± ±

48.4ab 28.0a 83.2b 26.2a 15.1ab 14.0ab 17.6a

Calcium (g/kg) 15.30 14.33 14.60 13.30 15.00 14.03 13.70

± ± ± ± ± ± ±

0.75ab 0.15ab 0.70ab 0.26a 1.05b 1.23ab 0.28a

Potassium (g/kg) 1.87 1.60 1.60 1.40 1.53 1.53 1.65

± ± ± ± ± ± ±

0.21b 0.17ab 0.17ab 0.10a 0.12ab 0.06ab 0.21ab

Magnesium (g/kg) 1.47 1.37 1.30 1.33 1.53 1.33 1.40

Mean value followed by different letters is statistically different (ANOVA; Tukey’s test, P < 0.05).

± ± ± ± ± ± ±

0.06a 0.06a 0.00a 0.06a 0.15a 0.12a 0.00a

Phosphorous (g/kg) 1.03 0.93 0.97 0.83 0.93 0.93 0.90

± ± ± ± ± ± ±

0.25a 0.06a 0.12a 0.06a 0.00a 0.06a 0.14a

TOC (g/kg) 265.77 232.47 253.77 232.07 247.57 250.50 270.45

± ± ± ± ± ± ±

12.88a 15.50a 12.45a 6.76a 4.20a 12.72a 38.68a

TKN (g/kg) 6.67 6.40 6.23 7.60 6.53 6.23 6.85

± ± ± ± ± ± ±

0.06a 0.10a 0.15a 1.97a 0.12a 0.06a 0.21a


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Table 2 Comparison of maximum growth rate and maximum individual weight of E. eugeniae with different feeding materials (mean ± SD). Feeding materials

Maximum growth rate (mg/worm/day)

Maximum individual weight (mg)


Rubber leaf litter 1 Jowar straw:1 bajra straw:2 sheep manure Farmyard manure 1 Kitchen waste:1 leaf litter

28.80 7.24

2570 1210.6

Chaudhuri et al. (2003) Suthar (2007)

1220.4 1522.9 1044.59 1147.39

Suthar (2007) Suthar (2007) Suthar (2008) Suthar (2008)

1211.47 1261.25 1031 133 892 1704 1920.00 ± 608.11b 1540.00 ± 141.42b 866.15 ± 130.04ab 385.00 ± 21.21a 1005.00 ± 120.21ab 1610.00 ± 353.55b 1625.00 ± 162.63b

Suthar (2008) Suthar (2008) Coulibaly and Zoro Bi (2010) Coulibaly and Zoro Bi (2010) Coulibaly and Zoro Bi (2010) Coulibaly and Zoro Bi (2010) Present Study Present Study Present Study Present Study Present Study Present Study Present Study

1 Millet straw:2 cow dung 1 (Pulse bran + wheat straw):2 cow dung 1 Mixed crop residues:1 cow dung Cattle shed manure Cow wastes Sheep wastes Pig wastes Chicken wastes B H P RH 1B:1RH 1H:1RH 1P:1RH

7.39 9.80 6.16 6.98 9.94 10.62 0.084 0.111 0.109 0.113 16.43 ± 13.13ab 15.71 ± 14.14ab 14.06 ± 2.93ab 9.29 ± 5.06a 29.29 ± 3.03ab 41.43 ± 9.09ab 48.57 ± 12.12b

Mean value followed by different letters is statistically different (ANOVA; Tukey’s test, P < 0.05).

down N mineralization and decomposition (Baggie et al., 2000), which coexist with vermicomposting process. Thus, RH that contains 22% lignin (Chandrasekhar et al., 2003) and 0.50% polyphenol (Baggie et al., 2000) would make the husk difficult to be reused as a sole feedstock in vermicomposting. 3.2. Physico-chemical changes during vermicomposting process In this present study, pH of all the final vermicompost showed alkaline conditions after 63 days of vermicomposting (Table 3). Earthworms do not affect the pH of organic substrates but they do exert physiological control such as secreting intestinal Ca and excreting NH4 –N for maintaining neutral pH in their digestive tract (Mainoo et al., 2009). The increase of pH in the final vermicompost for all the treatments could be due to the degradation of shortchained fatty acids and intensive mineralization of nitrogen by the microbes (Tognetti et al., 2007a). There was significant variation (P < 0.05) in pH for all treatments. EC reflects the salinity of an organic amendment and it is a good indicator of the applicability of vermicompost for agricultural purposes (Lazcano et al., 2008). The present study shows a decrease in EC for all treatments (Table 3). This decrease in EC could be due to the production of soluble metabolites such as ammonium (NH4 + ) and precipitation of dissolved salts (Lazcano et al., 2008). Tognetti et al. (2007b) and Lazcano et al. (2008) also reported a similar decrease in EC for vermicomposting of municipal organic waste and cattle manure, respectively. In general, the RH mixtures became more stabilized and nutrient rich material after 63 days of vermicomposting. According to Khwairakpam and Bhargava (2009a), interaction between

earthworms and microorganisms is the major reason that encourages the degradation of organic matter and release of microbial nutrients. In this current study, E. eugeniae converted the RH mixture (especially 1P:1RH) into fine agronomic fertilizer, which showed significant difference (P < 0.05) from treatment of RH for calcium, magnesium and phosphorus. Calcium was observed to be increasing in the range of 6.9–99.0% for all treatments except 1B:1RH treatment (Table 3). Final vermicompost obtained from the treatment of 1P:1RH showed the highest content of calcium as compared to the other RH treatments. A similar increase in calcium was reported by some researchers who used E. eugeniae in vermicomposting process (Khwairakpam and Bhargava, 2009b; Lim et al., 2011). According to Spiers et al. (1986), the gut flora in the earthworm might use calcium oxalate as an energy source, releasing calcium ions that were subsequently absorbed in the calciferous areas of the gut to form calcium bicarbonate. The bicarbonate produced in excess of earthworm metabolic requirement was excreted as cast material, thus increasing the calcium contents in final vermicompost. The slight decrease in calcium content for 1B:1RH treatment could be due to leaching of cations by excess water that drained through the feed mixtures as reported by Kaushik and Garg (2003). The final potassium content increased (15.0–121.4%) in all treatments (Table 3). A similar increase of potassium was reported by several researchers using E. eugeniae in vermicomposting (Khwairakpam and Bhargava, 2009b; Lim et al., 2011). Increase of potassium content in the vermicompost suggests that earthworms has symbiotic gut microflora with secreted mucus and water to increase the degradation of ingested substrates and release of easily assailable metabolites (Khwairakpam and Bhargava, 2009b).

Table 3 Final physico-chemical characteristics of vermicompost obtained from different treatments (mean ± SD, n = 3). Treatment


B H P RH 1B:1RH 1H:1RH 1P:1RH

8.46 8.22 8.27 7.91 7.96 8.03 8.08

EC (␮S/cm) ± ± ± ± ± ± ±

0.14b 0.07ab 0.09 ab 0.12a 0.13a 0.10a 0.25ab

261.0 172.9 95.7 186.1 236.7 216.7 206.0

± ± ± ± ± ± ±

93.8b 29.0ab 6.7a 12.8ab 37.9b 11.8b 34.1ab

Calcium (g/kg) 30.45 22.90 20.60 18.65 14.95 15.00 24.90

± ± ± ± ± ± ±

0.35d 0.57bc 0.57bc 1.20ab 1.9a 1.56a 2.26c

Potassium (g/kg) 2.15 2.05 2.60 3.10 2.30 1.85 3.10

± ± ± ± ± ± ±

0.49ab 0.35ab 0.14ab 0.00b 0.28ab 0.35a 0.14b

Magnesium (g/kg) 1.70 1.65 1.40 1.20 1.05 1.10 1.35

Mean value followed by different letters is statistically different (ANOVA; Tukey’s test, P < 0.05).

± ± ± ± ± ± ±

0.00d 0.07d 0.00c 0.00b 0.07a 0.00ab 0.00c

Phosphorous (g/kg) 1.35 1.25 1.45 0.85 0.83 0.85 1.25

± ± ± ± ± ± ±

0.07b 0.07b 0.21b 0.07a 0.04a 0.07a 0.07b

TOC (g/kg) 313.55 333.85 270.45 393.10 314.00 364.85 313.15

± ± ± ± ± ± ±

24.96ab 10.11abc 6.15a 26.02c 8.63ab 25.53bc 2.76ab

TKN (g/kg) 7.55 6.85 7.25 5.80 5.35 5.80 6.30

± ± ± ± ± ± ±

0.07b 1.06ab 0.07b 0.00ab 0.21a 0.57ab 0.14ab

S.L. Lim et al. / Ecological Engineering 41 (2012) 60–64


Fig. 1. Images of 1P:1RH (a) before and (b) after 63 days of vermicomposting process.

Statistically, only treatment 1H:1RH is significantly different (P < 0.05) from RH and 1P:1RH treatments. A slight increase of magnesium (by 7.7–20.4%) was only observed in H, B and P (Table 3). Some studies also reported an increase in magnesium content by using E. eugeniae in vermicomposting process. For example, one recent study reported that vermicomposting with E. eugeniae along with enrichment was superior to enhance the magnesium content in vermicompost, which was derived from water hyacinth (Christopher Lourduraj and Joseph, 2010). It is interesting to note that the reduction of magnesium (by 3.7–45.7%) was observed in all RH treatments. Until now, no direct contribution of earthworm in magnesium metabolism is known. It is hypothesized that fungal and microalgal hyphae, which easily colonize on freshly deposited worm casts, are contributing to trace level of magnesium in ready vermicompost (Suthar, 2010). Thus, the reduction of magnesium in the final vermicompost in treatment which were supplied with RH could be due the unsuitable environment for the fungus and other microbes to live in the RH, which usually contains higher content of lignin that resists to degradation in nature. However, further investigation is required to confirm this assumption. Slight increase of phosphorus (by 2.4–49.5%) was observed in all control and 1P:1RH treatments (Table 3). The 1P:1RH treatment was statistically significant as compared to the other RH treatments. Mineralization and mobilization of phosphorus by bacterial and faecal phosphatase activity of earthworms could be the main reason of phosphorus increase in vermicompost (Tripathi and Bhardwaj, 2004). When organic matter passes through the gut of earthworm, some phosphorous is converted into more available form. The release of phosphorous in available form is performed partly by earthworm gut phosphatase and further release of phosphorous might be attributed to the phosphorus solubilizing microorganisms present in the worm casts (Suthar, 2008). On the other hand, the slight decrease of phosphorus for 1B:1RH and 1H:1RH treatments is probably due to the nature of the amendment material and activities of P mineralizing microflora in decomposing wastes (Suthar, 2010). Table 3 shows that TOC was higher (by 6.6–69.4%) in the final vermicompost. Tognetti et al. (2007a) also found that an increase of TOC content happened in the vermicompost, which was consisted of municipal organic waste and biosolids (in the ratio of 3:1) after 40 days of vermicomposting using Eisenia fetida. As suggested by Tripathi and Bhardwaj (2004), the increase in carbon could be due to the additional carbon from mucus and death of worms in culture medium. The difference between RH and the other treatments was statistically significant, except for H (P = 0.102) and 1H:1RH (P = 0.687) treatments. The present study also showed that H, B and P exhibited higher content of TKN (by 7.0–16.4%) in final vermicompost (Table 3). Earlier studies have reported that vermicomposting will usually enhance the TKN content of the final vermicompost due to the nitrogen additions by earthworms

in the form of mucus, enzymes or nitrogenous excretory products (Tripathi and Bhardwaj, 2004). Table 3 also shows that the reduction of nitrogen content (by 6.9–23.7%) was not statistically significant between RH treatments. It is postulated that RH which contains higher content of lignin discourages nitrogen mineralization as compared to market refused fruits. Thus, most of the available nitrogen in the initial substrate would be used and transformed into earthworm protein, leading to lower nitrogen content in the final vermicompost (Fernández-Gómez et al., 2010). 3.3. Physical structure of feed mixture and vermicompost The vermicompost obtained from 1P:1RH treatment was granular and darker in colour (Fig. 1b) than the initial waste mixtures (Fig. 1a) after 63 days of vermicomposting. The final vermicompost was also odour free. These observations were consistent with those reported by Khwairakpam and Bhargava (2009a) as well as Yadav and Garg (2009). However, some RH residues still could be observed in the final vermicompost (Fig. 1b), indicating that the feed substrate was not fully vermicomposted. It is suggested that the duration of vermicomposting process should be extended to ensure the complete biotransformation of RH by E. eugeniae. 4. Conclusions The present study shows that vermicomposting can be used as a potential tool to bio-convert RH into vermicompost. However, it is suggested that the RH should be mixed and blended with easily degraded substrate before it could be applied as an initial feedstock in vermicomposting. In general, RH mixtures yielded better quality vermicompost. Among all the RH mixtures, RH which was mixed with an equal amount of market refused papaya (1P:1RH) showed better quality vermicompost with higher nutritional status as compared to the other RH treatments. From this study, it is found that RH which was amended by market refused fruits encouraged the growth of earthworms as compared to the RH treatment. Future study on pre-composting of RH is recommended to investigate the effectiveness of both thermophilic composting and mesophilic vermicomposting in biodegradation of RH that consists of high lignin content. In conclusion, this study provides a sound basis to demonstrate that vermicomposting can be regarded as a green technology to convert agro-industrial waste into value-added materials for sustainable farming. Acknowledgements The authors would like to thank Monash University, Sunway campus for supporting this study under Seeding Fund E-CSPERS-006 E-2-11 and providing both S.L. Lim and P.N. Lim with postgraduate scholarships.


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