Bioenergy waste residues as alternatives to conventional inorganic fertilisers for sustainable food production in sub-Saharan Africa

土壤提供、支持和调节环境中的基本过程，包括养分循环、植物生长，并对确保大气的纯度以及水的供应和质量具有重大影响。通过提供这些生态系统服务，至关重要的全球生物多样性得以维持，并最终维持了人类的生计。然而，通过密集的农业做法，如过度施用磷肥和氮肥，对土壤进行开发，导致土壤退化，从而导致土壤肥力下降，威胁到未来的全球粮食安全。磷是作物生长所需的一种重要的不可再生元素，农业现在几乎完全依赖于磷来维持目前的粮食生产水平。磷的提取和加工也对环境造成极大的破坏，它来自一种不可再生的来源，对这种来源的需求正在迅速增加，而且所需的数量没有替代品。氮肥的生产也是一个高度能源密集型和不可持续的过程，与化石燃料的价格和可用性密切相关。到2050年，全球人口预计将达到90亿，人类迫切需要平衡对能源和自然资源日益增长的需求，以及对生态系统及其提供的重要服务的可持续管理。非洲国家每天产生大量的垃圾，其中大部分被倾倒或填埋。西非主要的废物管理公司中联重科（Zoomlion）报告称，大多数非洲城市产生的废物中有机含量很高。例如，在加纳，大约66%的垃圾是有机的。非洲国家可以通过废物转化能源来改变其能源格局，但需要有政治和制度上的承诺。令人鼓舞的是，近年来，许多非洲国家的政府正在逐步接受绿色增长的发展道路，其中一些国家已经将绿色经济行动纳入其国家发展计划的主流。这些步骤标志着非洲废物转化能源发展的巨大前景，因为绿色增长发展行动促进了经济、社会和环境发展。由此产生的问题是如何处理废物转化为能源过程中的残余废物流，包括厌氧消化、生物乙醇生产中的有机残留物、燃烧木材产生的灰烬和木炭产生的烟灰。在与撒哈拉以南非洲的科学家和决策者讨论这个问题时，很明显，土壤很容易因环境条件（极端干湿、淋滤、侵蚀、有机物流失）和人为影响（化肥和农药施用、土地使用、森林砍伐、倾倒废物和污染）而退化。然而，保持土壤健康和肥力对于持续的粮食生产、家庭和社区福利以及地方和国家经济至关重要。需要将重点转向更可持续的农业系统，利用循环和回收的养分产品，将OM纳入改善土壤结构和生物多样性，以及改善作物-土壤管理以获取养分。通过使用这些生物能源残留物，土壤将对环境影响变得更有弹性，并将提供一种可持续的替代昂贵且有限的人造氮肥和开采磷肥。

Soils provide, support and regulate fundamental processes in the environment, including nutrient cycling, plant growth, andhave a strong influence on ensuring purity of the atmosphere, as well as water supply and quality. Through the delivery of these ecosystem services, vital global biodiversity and, ultimately, the sustenance of the human population is maintained. However, exploitation of soils through intensive agricultural practices such as the over application of phosphorus and nitrogen fertilisers, has resulted in their degradation and, as a result, a diminishment of soil fertility, threatening future global food security.Phosphorus is a vital, non-renewable element required for crop growth, upon which agriculture is now almost entirely dependent to maintain current levels of food production. The extraction and processing of phosphorus, is also extremely environmentally damaging, and originates from a non-renewable source for which demand is rapidly increasing with no alternative available in the volume required. The production of nitrogen fertiliser is also a highly energy intensive and unstainable process, is tied strongly to the price and availability of fossil fuels. As the global population is expected to reach 9 billion by 2050, humanity faces an urgent need to balance an ever increasing demand for energy and natural resources, with the sustainable management of ecosystems and the vital services that they provide.A huge amount of waste is generated daily in African countries, much of which is dumped or landfilled. Zoomlion, a major waste management company in West Africa, have reported that there are high levels of organic content of waste generated in most African cities. In Ghana, for example, about 66% of the total waste generated is organic. African countries can transform their energy landscape through waste-to-energy, but there needs to be political and institutional commitment. It is encouraging to note that in recent times a lot of governments in Africa are gradually embracing the Green Growth development pathway, with some having already mainstreamed Green Economy actions in their national development plans. These steps signal great prospects for waste-to-energy development in Africa because Green Growth developmental actions foster economic, social and environmental development. The knock on from this is what to do with the residual waste streams from waste-to-energy processes including anaerobic digestate, organic residues from bioethanol production, ash from burning wood and soots from charcoal. In discussing this with scientists and policy makers from sub-Saharan Africa, it is clear that soils are vulnerable to degradation through environmental conditions (extremes of wetting and drying, leaching, erosion, loss of organic matter) and anthropogenic impacts (fertiliser and pesticide application, land use, deforestation, dumping of wastes and pollution). However, the maintenance of soil health and fertility is crucial to continued sustainable production of food, welfare of families and communities and local and national economies. A shift in emphasis to more sustainable farming systems, utilising recycled and recovered nutrient products, incorporating OM to improve soil structure and biodiversity, and improved crop-soil management for nutrient acquisition are needed. By using these bioenergy residues, soils will become more resilient to environmental impacts and will offer a sustainable alternative to expensive and finite made N and mined P fertilisers.