To meet the needs of a fast growing global population, agriculture and livestock production have been intensified, resulting in environmental pollution, climate change, and soil health declining. Closing the nutrient circular loop is one of the most important sustainability factors that affect these issues. Apart from being a serious environmental issue, the discharge of N and P via agricultural wastewater is also a major factor that disturbs nutrient cycling in agriculture. In this study, the performance, in terms of recovery, of N and P (individually, as well as simultaneously) from agricultural wastewaters via struvite has been comparatively summarized. Details on the hindrances to nutrient recovery through struvite formation from agricultural effluents, along with strategies to overcome these hindrances, are provided. In addition, various strategies for recovery performance intensification and operational cost reduction are comprehensively discussed. This work will provide scientists and engineers with a better idea on how to solve the bottlenecks of this technique and integrate it successfully into their treatment systems, which will ultimately help close the nutrient loop in agriculture.
The manifestations of rapid population growth, urbanization, improved standards of living, and concurrent intensification of socioeconomic activities on overall environmental health are well recognized and acknowledged (Cordell et al., 2009; Clarke, 2013). Global cereal production has doubled in the past 40 years, mainly from the increased yields resulting from greater inputs of fertilizer, water, pesticides, and so on. This has increased the global per capita food supply and alleviate hunger in poverty-stricken areas (Alexandratos and Bruinsma, 2012). During this process, however, the increase in nitrogenous fertilizer application and exhaustion of the limited reserves of rock phosphate have been quite considerable. At present, the annual fertilizer consumption of rock phosphate is reported to be over one million tons, while the use of N fertilizer could be three times as much (Rahman et al., 2011). Moreover, it is estimated that within 100 years, mined P rocks will be completely exhausted (Cordell and White, 2014”). Global cycling of these nutrients has been altered, owing to their widespread use in intensive agriculture, in ways that can contribute to severe environmental issues. Predominantly, nutrients can escape from farm fields to the surrounding soils, air, and waterways, when applied in excess of the plants' needs (Deng et al., 2006). Hence, the notion of a closed-loop nutrient cycle provides a simple, persuasive, and elegant approach for realizing efficient natural resource management-improved human well-being, and long-term food security (Maurer et al., 2006). The closing of the nutrient loop includes a wide range of ongoing efforts to make sure that nutrients are applied at times and places that align with the requirements of the plants. It also includes efforts to recover nutrients in usable forms from waste effluents and recycle them into cropping systems (Yorgey, 2014). The logic is that by recovering nutrients from waste effluents, a more “closed” system for sustainable agricultural development can be created.