Optimising nutrient extraction from chicken manure and compost

Optimising nutrient extraction from chicken manure and compost

The global production of chicken manure is estimated to be 457 million tonnes per year. Chicken manure contains most nutrients that could be applied as a fertiliser to plants. Chicken manure has a high salinity level, high nitrogen and phosphorus content, low C/N ratio and contains pathogens. Hence, the disposal of chicken manure requires appropriate management to avoid environmental contamination. The main disposal practices are direct application to agricultural lands or composting. However, both of these methods require a high standard of management. This research investigates strategies for optimising nutrient extraction by leaching chicken waste. If the leachate can be extracted and treated effectively, then it may be applied to crops using an irrigation system where the rate and time of application are more readily controlled.

There are a range of methods used to extract soluble nutrients from animal manure at different scales. The main nutrient extraction methods produce either a manure leachate or manure tea. However, the quality (both nutrient and pathogen levels) of the leachate or tea is a function of the waste material properties and the extraction method used. Hence, the aim of this research was to identify strategies which optimised the extraction of the soluble nutrients from chicken manure or compost.

Fresh chicken manure and compost (ranging in age from 1 to 18 weeks) was packed into small columns which were subsequently leached. The leachate extracted from fresh manure and week 1 compost was found to contain higher concentrations of soluble nutrients than leachate derived from the week 6 and 18 composts. However, the leachate from the fresh manure also contained high levels of sodium and the leachate from both fresh manure and the young composts contained pathogens. On the other hand, leachate extracted from the older composts (≥4 weeks old) was free of pathogens. Further column studies were conducted to (a) evaluate the effect of column length and packing density on the nutrient extraction, (b) identify strategies for eliminating pathogens in the leachate and (c) evaluate the effect of increasing the hydraulic pressure in the extraction process. In general, the concentration of soluble nutrients in the leachate was found to increase with both column length and packing density. To evaluate the sterilisation options, a range of treatments (hot water, acetic acid and hydrogen peroxide) were applied during leaching and different treatments (acetic acid, hydrogen peroxide, heating and ozone) were applied to the extracted leachate. The most effective treatments were found to involve leaching with hot water (although the concentration of soluble nutrients was greatly reduced) or applying ozone to the extracted leachate (which did not affect the nutrient levels). While the application of a low hydraulic pressure during leaching reduced the time required to extract nutrients the concentration of soluble nutrients per unit volume of leachate was reduced due to a reduced contact time.

This work has identified the effect of the waste material properties and extraction methodology on nutrients in the leachate. However, further work is required to (a) better understand the optimal column length to packing density ratio and the extraction pressure appropriate for specific waste materials, (b) evaluate strategies to mitigate the potential effect of high sodium levels found in the leachate, (c) evaluate the efficacy of
nutrient extraction improvements, including the use of a recirculating leaching system, and (d) refine the nutrient extraction system design for commercial scale use.