Leaching-bed reactor for producing stabilised plant growing media from dairy manure

Recovering dairy manure fibre for use as a higher value plant growing media offers an economically attractive manure management alternative. Market realisation can occur only if physical properties are altered to be more in line with the peat moss industry standard as, and pathogens along with indices for pathogen growth, such as nutrients and readily biodegradable volatile solids, are removed. However, available technologies for reducing pathogen counts, such as composting, require considerable reaction time and energy inputs. In this study a two-step leaching-bed system was developed to process raw fibrous dairy solids to produce a fibre product with higher quality that could readily be used as plant growing media. The effects of leaching temperature and flow rate were studied at 100 litre reactor scale. The leaching process was also optimised to reduce water usage and improve process efficiency. The optimal operating conditions obtained include (1) a leaching temperature of 50 °C at a leaching rate of 4 l h−1 per kg dry solids using a 50/50 ratio of recycled and fresh water; (2) first step washing time of 1 h with recycled water, and second step washing time of 3 h with fresh water. Under the optimal conditions, indicator coliform bacteria were reduced by 1.6 log units, and the physical properties of the fibre product were positively altered to be similar to those of peat moss. Subsequent growth trials demonstrated the potential of this process and the performance of the developed product for use as a plant-growing medium.