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Sewage Sludge Ash

An Alternative Source of Phosphate

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Sewage Sludge Ash

An Alternative Source of Phosphate

Rechten: Alle rechten voorbehouden

Samenvatting

As an essential nutrient for food production, phosphate is largely used in fertilizers to enhance crop growth (Baishya et al., 2016; Hasanuzzaman et al., 2018). Regardless of its enormous demand, the only concentrated P source is phosphate rock and the resource is finite (Cordell & White, 2011; Smit et al., 2009). There are no large reserves of phosphate rock left in Europe. Most of European countries import phosphate rock from North Africa and Russia (Ridder et al., 2012). The dependency on a non-recyclable source of phosphate today raises the urgency and ambition among European countries to find alternative sources of phosphate. The aim is to find and develop alternative sources to secure the balance between the demand and supply of phosphate in the future (M. A. de Boer et al., 2018; Schröder et al., 2010).

According to Smit et al. (2010), there is a non-negligible 30 Mkg of P in the Netherlands obtained from society (household and industry waste) and agriculture, but less than 2 Mkg is being recycled. Among the alternative sources, wastewater treatment plants (WWTPs) have currently the highest potential source of P-recycling. Several research studies have addressed the development of P-recovery methods and technologies (Hartmann et al., 2020; Kumar et al., 2021; Zapata & Zaharah, 2002). Approximately 14 000 tons of P2O5 total contains in 1 500 000 tons of sludge treated in a year (Ministerie van Economische zaken, 2011; Smit et al., 2009). The phosphorus pentoxide or P2O5 is a natural occurring form of elementary phosphorus. It is commonly used in the fertilizer industry to determine the P-content in phosphate rock or other phosphate sources. In 1996, the regulation of P-removal in sewage water treatment plants (SWTP) is applied in the Netherlands to prevent eutrophication (Bunce et al., 2018). The regulation is followed by the prohibition of landfilling and land application of sewage sludge in 1997, leaving incineration as the only viable way for sludge disposal (Mitchell & Beasley, 2011).

The phosphate is captured from the sludge through adsorption, chemical precipitation, enhanced biological phosphorus removal, and constructed wetland (Ramasahayam et al., 2014). Metal compounds, such as aluminum chloride and iron chloride, are commonly used to flocculate and precipitate phosphate in wastewater (Bratby, 2006). Meanwhile polyphosphate accumulating organisms (PAO) are utilized for the enhanced biological phosphorus removal (EBPR). According to Tarayre et al. (2016), the PAOs, which generally are bacteria, are maintained in an aerobic phase. Under this condition, the PAOs take up phosphate and store it in the intercellular polyphosphate form. The dilute solid suspension from both chemical and biological treatment is then incinerated at around 700°C for 3 hours (Kauwenbergh et al., 2007). The incinerated ash is known as sewage sludge ash (SSA) or incinerated sewage sludge ash (ISSA) with around 22- 26% P2O5 content. The amount is considered to be comparable to the amount of P2O5 in phosphate rock (National Research Council, 2000).

The possible use of SSA as alternative phosphate source is being investigated by ICL Fertilizers as one of the leading global chemical company in plant nutrition. They mark the beginning of their research and development of sewage sludge ash (SSA) as the alternative phosphate source by opening the ICL Phosphate Recycling Unit in Amfert. The ash is obtained from two different companies, HVC and SNB. The amount of SSA produced by HVC (Dordrecht) and SNB (Moerdijk) is respectively ±22 000 tons/year and ±35 000 tons/years (Ruijter, 2018). The Gewijzigde veldcode 4 amount of phosphate rock imported and consumed at the ICL Amfert plant is around 100.000 tons/year . Although the demand of phosphate rock is still bigger than the current production of SSA per year, partial reduction of phosphate rock import can reduce the production cost and lower the dependency on phosphate rock (M. A. de Boer et al., 2018; Schröder et al., 2010).

The project aims to produce fertilizers using alternative phosphate sources, such as sewage sludge ashes (SSA) and produce circular and sustainable phosphate fertilizers. The products need to fulfill the quality standards of products made from standard phosphate rock. The development progress on laboratory and plant-scale will be explained and discussed in this report. The discussion will be divided into the two main steps of phosphate fertilizer manufacturing, acidulation and granulation. The report includes the effects of different material addition in each step, such as water and acid in the acidulation process. Furthermore, the report details the influence of changes and main parameters. Finally, the report gives recommendations and suggestions for the upcoming research.

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OrganisatieDe Haagse Hogeschool
OpleidingTIS Process & Food Technology
AfdelingFaculteit Technologie, Innovatie & Samenleving
PartnerICL
Datum2021-10-13
TypeBachelor
TaalEngels

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