Phosphorous and Silica Recovery from Rice Husk Poultry Litter Ash: A Sustainability Analysis Using a Zero-Waste Approach

Ash from Poultry Manure Incineration as a Substitute for Phosphorus Fertiliser

The goal of the tests was to separate a phosphate concentrate from ash and to assess its fertiliser use efficiency in anthropogenic land. Ash obtained from poultry manure incineration is an interesting fertiliser, as it contains both of the necessary nutrients, i.e., phosphorus and potassium. The ash selected for the tests contained 15.73 wt% P₂O₅, and 6.75 wt% K₂O. CaO also constituted the main component (44.79 wt%). Phosphorus in crystalline form was present as hydroxyapatite and carbonate apatite. The first stage, applied in order to separate a phosphate concentrate from ash, involved a number of physicochemical methods: (i) a method based on grain wettability differences; (ii) a method based on grain density differences; and (iii) methods based on size distribution differences. Wet sieving made it possible to separate a fraction with a P₂O₅ content of 24.56 wt%. The second stage, applied to assess fertiliser use efficiency, involved cassette tests as well as pot and field cultivation using as fertiliser, the obtained product as well as raw ash and commercial ones. Therefore, the conducted research allowed for the development of a methodology for the management of ash from the incineration of a poultry manure and their use as a substitute for phosphorus fertiliser. The tested material was applied in various doses. Using the obtained phosphate concentrate at a dose of 95 g/m³ resulted in a comparable yield as in the case of the commercial fertiliser at a dose recommended by the producer (75 g/m³). Unprocessed ash had to be used in larger amounts, i.e., 165 g/m³, to have a comparable yield as a commercial fertiliser.

Properties of Animal-Origin Ash—A Valuable Material for Circular Economy

In the presented paper, two types of animal-origin biomass, cow dung and chicken litter, are characterized in terms of combustion-related problems and ash properties. It was found that these parameters strongly depend on the farming style. Whether it is cow dung or chicken litter, free-range raw materials are characterized by higher ash contents than industrial farming ones. Free-range samples contain chlorine at lower levels, while industrial farming samples are chlorine rich. Free-range samples are characterized by the predominant content of silica in the ash: 75.60% in cow dung and 57.11% in chicken litter, while industrial farming samples contain more calcium. Samples were classified by 11 “slagging indices” based on the ash and fuel composition to evaluate their tendencies for slagging, fouling, ash deposition and bed agglomeration. Furthermore, an assessment was made against the current EU law regulations, whether the ashes can be component materials for fertilizers. The phosphorus concentration in the investigated ashes corresponds to 4.09–23.73 wt% P2O5 and is significantly higher in industrial chicken litter samples. The concentrations of Hg, Cu, As, Ni, Cd and Pb in all samples are below the limits of the UE regulations. However, concentrations of Cr in all samples and Zn in industrial chicken litter exceed these standards.