Insight into the recovery of nutrients from organic solid waste through biochemical conversion processes for fertilizer production: A review

The safe disposal of organic solid waste (OSW) has been regarded as utmost concern in this period of green economy and the concept of producing high quality fertilizers with an enriched nutrient content is at present identified prospectively in many countries. When OSW are improperly disposed, considerable amounts of nutrients which are locked in the OSW are reduced or lost. These valuable nutrients which are lost might be recuperated through suitable biochemical technologies and employed as nutrient-rich fertilizers in agricultural fields for maintaining soil fertility. This work aimed to review macro-nutrients (N, P, K) and micro-nutrients (Ca, Mg, Na, Fe, Cu, Mn, Zn, B, Mo, S) recycling during biochemical conversion technologies e.g. composting and vermicomposting of OSW for the production of fertilizer. This work also elucidates the possible ways of enriching the nutrient content in vermicompost, the effects of possible mechanisms on earthworms linking to nutrients enrichment and the quality assessment of composts and vermicomposts in terms of nutrient content. Generally, it would appear that vermicomposts can have ‘‘added-value’’ characteristics since vermicomposting of OSW could efficiently amplify the nutrients content and vermicomposts could be inferred as a superior organic fertilizer with high nutritional content of agronomic importance in contrast to composts. The high nutrient content in vermicompost could be explicated by earthworm gut-borne microorganisms which mixed with organic matter (OM) during their passage in the intestine and those microorganisms consecutively have a vital role in the biochemical alterations of nutritive elements. This review recommends the importance of obtaining a comprehensive insight on the earthworm activity entailed in vermitechnology, especially the mechanisms they accomplish for the nutrients enrichment. Conclusively, the need for further scientific research aimed at outlining Mg and Na metabolisms by earthworm mechanism and also other trace elements (Fe, Cu, Mn, Zn, B, Mo, S) in vermicomposting processes is greatly recommended which will thus provide a meaningful direction for future study.