Characteristic of wet method of phosphorus recovery from polish sewage sludge ash with nitric acid

Abstract

Sewage Sludge Ash (SSA) is a concentrated source of phosphorus and can be successfully recycled via a number of different routes. This paper presents research results on phosphorus recovery from differently combusted sewage sludge with the use of nitric acid extraction. Different SSA forms from Polish thermal utilization stations were compared. It was revealed that sewage treatment technology as well as combustion technology influence many physical and chemical parameters of ashes that are crucial for further phosphorus recovery from such waste according to the proposed method. Presented research defines extraction efficiency, characterized extracts composition and verifies the possibility of using SSA as cheaper and alternative sources of phosphorus compounds. Gdynia, Kielce and Kraków SSA have the best properties for the proposed technology of phosphorus recovery with high extraction efficiency greater than 86%. Unsuitable results were obtained for Bydgoszcz, Szczecin Slag and Warszawa SSA. Extraction process for Łódź and Szczecin Dust SSA need to be improved for a higher phosphorus extraction efficiency greater than 80%.Phosphorus content in extracts varies from 1.6 to 103.4 g PO 4 3-per 1 dm 3 , nitrogen content was 167,4 g per 1 dm 3 while the K content reached 0.2 to 2.37 g per 1 dm 3 . The lowest content of Fe, Ni, Cr, Cd is noted in extracts after phosphorus recovery from Gdynia SSA, where the phosphorus content is also at the highest level.The proposed solution can be considered as waste minimization technology by the rational recycling of phosphorus and could be used in industry to produce fertilizers.

Recovery of phosphorus from incinerated sewage sludge ash by combined two-step extraction and selective precipitation

“…Current worldwide available phosphate ore reserves are predicted to be depleted within the next 50-100 years [1][2][3] while Chinese phosphate ore might be exhausted within 37 years [4]. After mining, only 10% of P is consumed by human activities [5], and then the consumed-P and waste-P are disposed as waste streams [6].…”

“…Although land-spreading remains the dominant form of sewage sludge disposal, during the last 20 years there has been a trend at a global level away from landfilling and sea disposal towards incineration of sewage sludge [8]. Incineration is especially attractive in densely-populated regions and effectively reduces the volume of waste, eliminates odour problems, produces a sterile ash and allows for potential energy recovery from the organic solids in the sludge [9,10]. Almost all of the P in sewage sludge remains in the inorganic fly ash produced by sewage sludge incineration [3,11,12].…”

“…Incinerated sewage sludge ash (ISSA) consists of small glassy particles partially sintered together into irregularly shaped porous agglomerates containing Fe, Al, Si and P [13,14]. The P is preferentially deposited on the surface of particles, thus facilitating ease of recovery [5,10,15]. The main crystalline phases containing P in ISSA are whitlockite, beta-tricalcium phosphate mineral and AlPO 4 [5,16,17].…”

Comparison of Phosphorus Extraction from Sludge Incinerated Bottom Ash and Sludge Incinerated Fly Ash Using Sulfuric Acid

“…2b, SIFA had a relatively smooth surface. This type of structure was resistant to the reaction between the extraction agent and ash because of a lower surface of interphase contact (Gorazda et al, 2016). Therefore, the SIBA with a rough and porous surface showed a higher efficiency to extract P than SIFA with the relatively smooth surface when the ratio of leachate/solid ash was relatively low.…”

“…Therefore, choosing a proper extraction agent is critical for a successful P extraction using wet chemical methods. There are many different types of agents, such as H 2 SO 4 (Ottosen et al, 2016;Liang et al, 2019), HCl (Xu et al, 2012), HNO 3 (Sano et al, 2012;Gorazda et al, 2016), and oxalic acid (Liang et al, 2019). Among these extractants, H 2 SO 4 is widely used because of its low cost and highefficiency extraction yield.…”