Sustainable nutrient recovery from animal manure: A review of current best practice technology and the potential for freeze concentration

Abstract

Current trends of livestock expansion and associated mass production of manure bring a net import of nutrients that have led to a significant excess in many areas. The implementation of an efficient and more economical technology solution to recover and re-use nutrients from raw or digested wastes is essential and will reduce the need for fossil-fuel based fertilizers. From a waste management standpoint, the identification of nutrient recovery technologies is considered one of the main challenges within a circular economy context. Several traditional techniques exist for manure treatment such as, gasification, thermochemical conversion, composting, hydrothermal carbonization, and liquefaction. However, these technologies face many challenges related to energy consumption and recovered nutrient quality. In this context, freeze concentration (FC) is an emerging technique that can be applied to recover water and concentrate nutrients from waste liquid effluents. This technology brings advantages such as high concentration factor and low energy usage. However, freeze concentration technology is only semi-industrialised and for most applications remains at the development stage. Many studies have been conducted to design and develop processes and applications that target the improvement of both productivity and efficiency, which makes freeze concentration an attractive research subject to the scientific community. Combination of freeze concentration technology with another technology, such as membranes, to generate a more efficient hybrid process must also be considered. This approach of resource recovery from animal manure would ultimately create a more sustainable and circular economy. This paper evaluates the current state-of-the-art and processing strategies related to the treatment of livestock waste materials and contains an up-to-date and critical review on nutrient-rich effluent valorization technologies; focusing on the latest technological progress to recover nutrients from animal manure and introduces the potential that freeze concentration offers, which has only been marginally explored to date. This work makes a comparative analysis of the different processes in terms of their efficiency, cost, energy consumption, operational management, and the results obtained from both bench and large-scale experiments; making it possible to determine the current best practice procedures for the treatment of animal manure.