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Bioenergy is produced from a variety of organic materials, called biomass, such as wood, charcoal, dung and other manures for heat and power production, and agricultural crops for liquid biofuels. Most biomass is used in rural areas for cooking, lighting and space heating, generally by poorer populations in developing countries.


Cow dung, an excreta of bovine animal, is a cheap and easily available bioresource on our planet. Many traditional uses of cow dung such as burning as fuel, mosquito repellent and as cleansing agent are already known in India. Cow dung harbours a diverse group of microorganisms that may be beneficial to humans due to their ability to produce a range of metabolites. Along with the production of novel chemicals, many cow dung microorganisms have shown natural ability to increase soil fertility through phosphate solubilisation. Nowadays, there is an increasing research interest in developing the applications of cow dung microorganisms for biofuel production and management of environmental pollutants. This review focuses on recent findings being made on cow dung that could be harnessed for usage in different areas such as medicine, agriculture and industry.

Cow dung can be defined as the undigested residue of consumed food material being excreted by herbivorous bovine animal species. Being a mixture of faeces and urine in the ratio of 3:1, it mainly consists of lignin, cellulose and hemicelluloses. It also contains 24 different minerals like nitrogen, potassium, along with trace amount of sulphur, iron, magnesium, copper, cobalt and manganese. The indigenous Indian cow also contain higher amount of calcium, phosphorus, zinc and copper than the cross-breed cow (Garg and Mudgal 2007; Randhawa and Kullar 2011). Cow dung harbours a rich microbial diversity, containing different species of bacteria (Bacillus spp., Corynebacterium spp. and Lactobacillus spp.), protozoa and yeast (Saccharomyces and Candida) (Nene 1999; Randhawa and Kullar 2011). Sawant et al. (2007) have isolated many different bacterial genera such as Citrobacter koseri, Enterobacter aerogenes, Escherichia coli, Klebsiella oxytoca, Klebsiella pneumoniae, Kluyvera spp., Morgarella morganii, Pasteurella spp., Providencia alcaligenes, Providencia stuartii and Pseudomonas spp. from cow dung.

Cow dung in India is also used as a co-product in agriculture, such as manure, biofertiliser, biopesticides, pestrepellent and as a source of energy (Dhama et al. 2005a). As per ayurveda, it can also act as a purifier for all the wastes in the nature (Randhwa and Khullar 2011). Therefore in India, Cow (B. indicus) is not only just milk-producing animal but also truly considered as Gomata (mother of all) and Kamdhenu (Dhama et al. 2005a; Jarald et al. 2008). Detailed study of cow dung is gaining interest around the world and few attempts have been made for utilising its potential in the field of energy production, pharmaceutical products. The review intends to highlight the possible applications of cow dung particularly in the area ranging from energy, agriculture and environment to medicine for human welfare.

Human population is increasing worldwide giving rise to intensive farming system and unsuitable cropland management that ultimately results in reduced soil fertility (Onwudike 2010; Bedada et al. 2014). Extensive use of chemical fertilisers is suggested for replenishment of nutritional deficiencies to increase crop yield. Many disadvantages of widespread use of chemical fertilisers include increase in soil acidity, mineral imbalance and soil degradation (Kang and Juo 1980; Ayoola and Makinde 2008) and even farmers nowadays do not prefer chemical fertilisers (Bedada et al. 2014). In composting, microorganisms decompose organic substrate aerobically into carbon dioxide, water, minerals and stabilised organic matter (Bernal et al. 2009; Kala et al. 2009; Vakili et al. 2015). Compost is added into the soil to improve nutrients and water-holding capacity (Arslan et al. 2008; Vakili et al. 2015). Recently, researchers observed that addition of cow dung to biomass generated from palm oil industries improves the physical and chemical properties including nutritional composition of compost. Palm oil biomass mixed with cow dung in the ratio of 1:3 significantly improved the compost quality with respect to various parameters such as pH, electrical conductivity and C:N ratio (Vakili et al. 2015). Thus, cow dung may not only act as a substitute for chemical fertilisers because it supplements organic matter, but also as a conditioner for soil (Garg and Kaushik 2005; Yadav et al. 2013; Belanger et al. 2014). Slurry from biogas plant is also a nutrient-rich source but it cannot be used at large scale because of its drawbacks such as eutrophication and leaching of the soil nutrients (Garg et al. 2005; Wachendorf et al. 2005; Islam et al. 2010; Lu et al. 2012; Guo et al. 2014).

Organic amendments alone may not offer sufficient nutrient supply to meet the demand (Palm et al. 1997; Gentile et al. 2011; Bedada et al. 2014). One way to counter this soil fertility problem is ISFM, i.e., Integrated Soil Fertility Management, a technique that makes use of both organic and inorganic resources resulting in greater yield response and better nutrient storage (Bedada et al. 2014; Ewusi-Mensah et al. 2015). For example, combination of cow dung with NPK (15:15:15) in the concentration of 3 t/ha and 100 kg/ha, respectively, showed marked increase of 8.9 t/ha in the yield of potato tuber in comparison to control that yielded only 1.8 t/ha. The organic carbon of the soil after treatment with this combination was found to be significantly increased from 1.33 to 3.21 %. The combination also improved soil organic matter, phosphate availability, exchangeable ions, effective cation exchange capacity and pH in comparison to untreated soil (Onwudike 2010). The same combination has also been reported to increase the yield of maize (Ayoola and Makinde 2008; Bedada et al. 2014).

Many biodynamic preparations obtained from cow dung have shown antagonistic effect against plant pathogens such as Rhizoctonia bataticola (Rupela et al. 2003; Somasundaram et al. 2007; Radha and Rao 2014). An investigation by Mary et al. (1986) revealed cow dung extract to be more effective than antibiotics like Penicillin, Paushamycin and Streptomycin in controlling bacterial blight of rice. B. subtilis strains are the most predominant isolates from culturable cow dung microflora. A few reports have shown the antagonistic properties of these B. subtilis strains against plant pathogens such as Fusarium soalni, Fusarium oxysporum and S. Sclerotiorum (Basak and Lee 2002; Swain et al. 2006; Stalin et al. 2010; Swain et al. 2012). Plant pathogenic nematodes are one of the important pathogens of crops. Recently, a work by Lu et al. (2014) investigated 219 bacterial strains from cow dung for nematicidal activity against model nematode Caenorhabditis elegans and out of these, 17 strains killed more than 90 % of the tested nematode within 1 h. The strains identified included Alcaligenes faecalis, Bacillus cereus, Proteus penneri, Providencia rettgeri, Pseudomonas aeruginosa, Pseudomonas otitidis, Staphylococcus sciuri, Staphylococcus xylosus, Microbacterium aerolatum and Pseudomonas beteli. Out of these 14 strains also inhibited another nematode Meloidogyne incognita. This was for the first time that strains in the genera Proteus, Providencia and Staphylococcus from cow dung displayed nematicidal activity. Cow dung is conventionally applied in Indian subcontinental agriculture to enhance soil fertility. It not only improves the different properties of soil but also acts as a source of microorganisms producing biological nematicidal agents with no negative effect on environment. Therefore, use of cow dung should be promoted in the field of agriculture.

Cow dung contains diverse group of microorganisms such as Acinetobacter, Bacillus, Pseudomonas, Serratia and Alcaligenes spp. which makes them suitable for microbial degradation of pollutants (Adebusoye et al. 2007; Akinde and Obire 2008; Umanu et al. 2013). Cow dung slurry maintained in the ratio of 1:10 or 1:25 is able to degrade the rural, urban and hospital wastes, including oil spillage to five basic elements (Randhawa and Kullar 2011). A study by Orji et al. (2012) highlights the importance of cow dung isolates, both bacterial and fungal, for reducing total petroleum hydrocarbons to 0 % in polluted mangrove soil. The bacterial isolates involved in the process belonged to genera Pseudomonas, Bacillus, Citrobacter, Micrococcus, Vibrio, Flavobacterium and Corynebacterium, whilst fungal isolates were the species from Rhizopus, Aspergillus, Penicillium, Fusarium, Saccharomyces and Mucor. The natural ability of cow dung microflora to degrade hydrocarbons in soil contaminated with engine oil is recently being investigated by Adams et al. (2014) where total petroleum hydrocarbon reduced up to 81 % by the metabolic activities of cow dung microorganisms such as Bacillus, Staphylococcus, Pseudomonas, Flaviobacterium, Arthobacter, Enterobacter, Trichoderma, Mucor and Aspergillus spp. Umanu et al. (2013) suggested that the application of cow dung in an appropriate concentration may prove very efficient in biodegradation of water contaminated with motor oil. Some researchers also suggested the metabolic pathway for microbial degradation of polycyclic aromatic hydrocarbons. A Mycobacterium sp. isolated from contaminated soil of gaswork plant has shown the ability to degrade pyrene up to 60 % within 8 days maintained at 20 C with several degrading products such as Cis-4,5-pyrene dihydrodiol, 4-5-phenanthrene dicarboxylic acid, 1-hydroxy-2-naphthoic acid, 2-carboxybenzaldehyde, phthalic acid and protocatechuic acid were recognised (Rehmann et al. 1998; Haritash and Kaushik 2009). Lignolytic fungi Irpex lacteus has also shown the ability to degrade phenanthrene to phenanthrene-9,10-dihydrodiol (Cajthaml et al. 2002; Haritash and Kaushik 2009). All these findings indicate that cow dung can supply nutrients and energy required for microbial growth thereby resulting in the bioremediation of pollutants.

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