Environmental implications, potential value, and future of food-waste anaerobic digestate management: A review

Globally, the valorisation of food waste into digestate through the process of anaerobic digestion is becoming increasingly popular. As a result, a large amount of food-waste digestate will need to be properly utilised. The utilisation of anaerobic digestion for fertiliser and alternative uses is essential to obtain a circular bioeconomy. The review aims to examine the environmental management of food-waste digestate, the value of digestate as a fertiliser and soil conditioner, and the emerging uses and improvements for post-anaerobic digestion reuse of digestate. Odour emissions, contaminants in food waste, emission and leaching of nutrients into the environment, and the regulations, policies, and voluntary initiatives of anaerobic digestion are evaluated in the review. Food-waste digestate can provide essential nutrients, carbon, and bio-stimulants to soils and increase yield. Recently, promising research has shown that digestates can be used in hydroponic systems and potentially replace the use of synthetic fertilisers. The integration of anaerobic digestion with emerging uses, such as extraction of value-added products, algae cultivation, biochar and hydrochar production, can further reduce inhibitory sources of digestate and provide additional economic opportunities for businesses. Moreover, the end-product digestate from these technologies can also be more suitable for use in soil application and hydroponic use.

Investigation of the aerobic biochemical treatment of food waste: A case study in Zhejiang and Jiangsu provinces in China

Food waste production is increasing rapidly and becoming a global concern. In areas with small production volumes and scattered production sources, the use of biochemical processors can be a beneficial supplement to the centralized treatment method for the in-situ treatment of wastes to effectively improve the efficiency of resource utilization. China is an important case study for this global issue; however, the implementation and outcomes of this process are not clear in China. In this study, field investigation and laboratory analysis were carried out on 14 biochemical processors in four representative regions of the Jiangsu and Zhejiang Provinces. The results showed that biochemical processors mostly used high-temperature aerobic fermentation, accounting for more than 80% of the commonly used procedures. The fermentation period was relatively short and ranged from 48 h to 10 days. Only 21.4% of devices were equipped with relatively complete secondary pollution-control units, which introduced the risk of secondary pollution during operation. The fermentation products exhibited common characteristics of acidity, high salt levels, and low maturity, rendering them unsuitable for agricultural use directly prior to an additional secondary fermentation process. Therefore, it is necessary to unify the design standards of biochemical processors and develop acid-resistant thermophilic microbial inoculants to increase fermentation efficiency. Thus, this study has significant implications in regulating food waste and serves as a theoretical and practical reference point to promote its in-situ treatment.