Compostingis a biological phenomenon causing the decomposition of organic substrates resultingin stabilization at elevated temperatures due to biological heat production generatinga stable and final product that is free of pathogens. The naturalcomposting process is rather time-consuming, shortage of land and generation oflarge quantity of waste require a quicker and effective treatment of thesewastes. Investigations have reported that inoculation of waste with cellulolyticbacteria could be a considered a useful strategy for reduction in compostingtimeperiod, enhance the properties of final product and achieve compoststability (Lia et al., 2017). While, an improper inoculum may produce negative seedinfluence and produce toxins for in-situ microorganisms 11–13. A suitable microbial inoculation canimprove the quality of the compost by generation of desired enzymes with decreasein the operation time thus, reducing the production costs 4–9. As,the major constituents of MSW is organic being cellulose, hemicellulose,lignin, starch and protein compounds they undergo degradation by specificenzymes.
Microbial activity is achieved through the action of theseenzymes, responsible forthe hydrolysis of complex macromolecules present in the organic wastes. The process is then continued byrelease of simple water-soluble compounds to support microbialgrowth. A key role isplayed by enzymes to mediate the biochemical process in the biologicaldegradation of organic matter1-2, determinethe physical and chemical changes in the compost affecting the rate ofcomposting and product quality of important nutritional elements like C,N or P. This enzymatic activity can be directly influenced by factors such as pH, moisture,nutrient availability, temperature and the chemical properties 17,22–24. The dehydrogenase activity is considered to be a general indexof biological activity on account of its role on the oxidative phosphorylationprocess, and therefore in the respiratory metabolism of microorganisms (Delgado et al., 2004).On the contrary, b-glucosidases, phosphatases, proteases and ureases arerelated to specific cycles. b-Glucosidases are involved in the carbon cyclethrough the hydrolysis of glucosides, while phosphatases release phosphategroups from organic compounds.
Proteases and ureases take part in nitrogenmineralization. Both of them hydrolyze nitrogen compounds intoammonia, using low molecular weight proteins and urea as a substrate,respective. Therefore,the enzyme activity characterization and quantification during composting isessential to reflect the dynamics of the process in terms of organic matter decompositiongenerating information about compost maturity3-4. In addition, theenzymatic activity determination when compared to other analytical compoststability evaluation techniques is easier, fast and less expensive5.Also, the Mesophilic and thermophilic microorganisms affect the composting withtheir succession being an important parameter for effective management of theprocess6-7.
At each phase ofcomposting, the enzymatic activities correlated with variations in compositionof microbial community (Ryckeboer et al., 2003a),directly relate to rate of waste decomposition and,therefore, provide information aboutthe product stability (Mondini et al., 2004) and maturity(Tiquia, 2002, 2005). Microbialactivity is achieved through the action of the enzymesthat are responsible forthe hydrolysis of the organic matter. The enzymesreleased by the microorganismsduring composting break down several organic mattercharacterized by acomplex structure, finally leading to the solubilisationof simple water solublecompounds 3.
As a consequence, enzymatic activitiesgive information on therate of decomposition of organic matter and, therefore,on product stability 14. Important enzymes involved in the composting processinclude dehydrogenasewhich reflects microbial activity, B-glucosidases whichhydrolyze glucosides,urease involved in N-mineralization, and phosphatasesthat removephosphate and sulfate groups from organic matter 3 4.Characterizing microbialcommunities along the process is important for achievingthe effectivemanagement of a composting process and it may providevaluable informationregarding process evolution and biodegradation rate 56. The investigation ofthe significant enzymes (e.g., dehydrogenases, ?-glucosidases,phosphodiesteraseand ureases) provides data for a correct estimation ofthe events that take placethroughout the composting process 7.
Although several researchers 1 3 8 have studied thedynamics of the microbialcommunities, little is known about the relationshipbetween microbial diversityand enzyme activities during composting of the organicfraction of municipalsolid waste (MSW). The present work thus aims atconstructing a fuller pictureof the microbial and enzyme activities in a small-scalecomposting system. In spite of many pitfallsaffiliated with C/N ratio, it is generally considered as an index of compostmaturity 8. Also for determining compost maturity a C/N ratio < 20 isgenerally considered as a benchmark and a reliable parameter. With all thisbackground information present investigation was carried out to understand theeffect of inoculation of cellulolytic bacteria and cowdung addition in terms ofmicrobial population dynamics and the extracellular enzyme activity in twodifferent seasons during the composting of municipal solid waste. To ascertain the effectiveness ofinoculation and degree of decomposition in composting process certain enzymessuch as cellulases, ureases, dehydrogenases, phosphatases, catalases, amylasesand proteases can be assayed.