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、植物生长和营养物质，土壤对确保大气的纯净以及水的供应和质量有很大影响。通过提供这些生态系统服务，维持至关重要的全球生物多样性，并最终维持人类人口的生计。然而，通过过度使用磷肥和氮肥等集约化农业措施开发土壤，导致土壤退化，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至关重要的不可再生元素，农业现在几乎完全依赖于此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，其来源是一种不可再生的来源，其需求正在迅速增加，所需的数量没有其他选择。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获得性密切相关。到2050年，全球人口预计将达到90亿，人类迫切需要在不断增长的能源和自然资源需求与生态系统的可持续管理和它们提供的重要服务之间取得平衡。非洲国家每天产生大量废物，其中大部分被倾倒或填埋。西非一家主要的废物管理公司中联重科报告称，大多数非洲城市产生的垃圾中有机含量很高。例如，在加纳，产生的垃圾中约66%是有机垃圾。非洲国家可以通过将垃圾转化为能源来改变其能源格局，但需要有政治和体制上的承诺。令人鼓舞的是，最近非洲许多国家政府正在逐步采用绿色增长发展道路，其中一些政府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垃圾转化为能源的发展前景广阔，因为绿色增长发展行动促进了经济、社会和环境发展。由此引发的连锁反应是如何处理垃圾转化为能源的过程中产生的残余废物流，包括厌氧消化系统、生物乙醇生产过程中的有机残留物、燃烧木材的灰烬和木炭产生的烟尘。在与撒哈拉以南非洲的科学家和政策制定者讨论这一问题时，显然土壤容易受到环境条件(极端的湿干、淋溶、侵蚀、有机质损失)和人为影响(化肥和农药的使用、土地使用、砍伐森林、倾倒废物和污染)的退化。然而，保持土壤健康和肥力对于持续的粮食可持续生产、家庭和社区的福利以及地方和国家经济至关重要。需要将重点转移到更可持续的耕作系统，利用回收和回收的营养产品，加入有机质来改善土壤结构和生物多样性，以及改善作物-土壤管理以获得养分。通过使用这些生物能源残留物，土壤将变得对环境影响更具弹性，并将提供一种可持续的替代方案，取代昂贵的有限制造的N和P化肥。

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.