Farm/Industrial/Municipal Waste: Prospects of Nutrient (Phosphorus) Recovery
External supply of plant nutrients is a must to achieve intensification of agricultural sector, thereby meeting food demand of growing global population. However, non-substitutable nutrient like phosphorus (P) with finite natural reserve makes recovery of
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Baruah (*) Department of Energy, Tezpur University, Napaam 784028, Assam, India e-mail: [email protected] H. West School of Biosciences, University of Nottingham, Sutton Bonington Campus, Leicestershire LE12 5RD, UK M. Clarke School of Geography, University of Nottingham, University Park, Nottingham NG7 2RD, UK © Springer Nature Singapore Pte Ltd. 2018 S.K. Ghosh (ed.), Utilization and Management of Bioresources, DOI 10.1007/978-981-10-5349-8_21
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1 Introduction At the current population growth rate, the associated food consumption is seen to grow at an annual growth rate of 3.1% (Heffer and Prud’homme 2014). Food and Agriculture Organization of the United Nations estimated a required growth of 60% in current agricultural production to meet the food demand (FAO 2013). For agricultural intensification, nutrient supplementation is a must, which is given through chemical fertiliser. Phosphorus (P) is one plant macronutrient which is supplied through chemical fertiliser. This is an agricultural input, without which the escalating food demand for growing population cannot be expected to meet, as it is non- substitutable in agriculture. P being a non-substitutable input in agriculture, agro-ecosystem stands for 80–90% of the world total P consumption (Childers et al. 2011). Presently the only source of commercial P fertiliser is natural phosphate rock. Considering the indispensable role of P in agriculture, its limiting nature in soil and limited availability as P rock, sustainable use of P has drawn growing attention. This necessitates trapping or conservation of P from non-conventional P-rich sources with the help of efficient and economically viable processes. One of the most investigated methods for the recovery of P is through production of solid recoverable phosphate mineral or as a salt precipitate from different P-rich sources. In this context, ‘struvite’ or magnesium ammonium phosphate (MAP/ MgNH4PO4 6H2O) is a prospective value added P source. Struvite precipitation requires the presence of Mg2+, NH4+ and PO43− in alkaline medium in an optimum molar ratio of 1:1:1 (Rahaman et al. 2008). A pH range of 8–11 is considered favourable (Kabdasli et al. 2009). Precipitation of P as struvite is governed by many factors such as pH, presence of impurities, solution strength, mixing energy, temperature, residence time of suspension during crystallisation and effect of seeding material (Doyle et al. 2003; Nelson et al. 2003; Capdevielle et al. 2013). There are a number of P sinks in nature, where P ends up depositing during its circulation through biogeochemical cycle such as farm waste, municipal waste and industrial effluents. It is important to identify and investigate the suitability of these sources as a source of P recovery. Anaerobic digestate or biogas slurry is such an inevitable by-product of bioenergy conversion technology, ‘anaerobic digestion’ that generates biogas as a main product and which needs immediate managerial attention. The physico-chemical characteristics of digestat
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