The BIG Phosphorus Conference & Exhibition Removal and Recovery 4-5 July, Old Trafford, Manchester. Cohen, Y. 1 and Enfält, P. 1

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1 ASH2 PHOS CLEAN COMMERCIAL PRODUCTS FROM SLUDGE ASH Cohen, Y. 1 and Enfält, P. 1 1 EasyMining Sweden, Sweden Corresponding Author yariv.cohen@ragnsells.com Abstract EasyMining Sweden AB has developed a process for phosphorus recovery from sludge ash named Ash2 Phos. The process is based on wet chemical processing and is suitable for processing ash of mono-incinerated sewage sludge, as well as ash from co-incineration of sewage sludge and waste according to a specific concept. Phosphorus is first recovered in form of clean intermediate calcium phosphate. Several options exists for converting the intermediate calcium phosphate into final commercial phosphorus products. Keywords Ash, Phosphorus, Recovery Introduction One important target for a sustainable society is to close the phosphorus cycle, i.e. to recirculate phosphorus removed in wastewater treatment plants back to agriculture. Phosphorus is a limited resource essential for life, for which there is no substitution. One major precondition for sustainable phosphorus recycling is to produce as clean and safe recovered products as possible. The absence of environmental pollutants is one critical feature, but there are additional conditions that must be fulfilled to achieve fully sustainable phosphorus recycling. These include the following: (1) costeffective waste treatment and transport, allowing equitable redistribution of phosphorus to arable land; (2) significant fertilizing effect of products that can replace mineral fertilizers; and (3) safe and clean recycled products that have no adverse effect on crops, soils or the environment (Kirchmann et al., 2005, 2016; Cohen et al., 2011). The main task of wastewater treatment plants is to produce clean water. Sewage sludge is a waste by-product, from water cleaning and therefore is neither an optimal fertilizer nor a clean product. Sewage sludge contain environmental pollutants and high metal content which limit the plant availability of phosphorus. The high water and low nutrient content in sewage sludge is limiting for long distance transportation of large volumes which is also an obstacle for using sewage sludge on agricultural land. By incineration of sewage sludge the volume and weight is reduced by approx. 90% but the metals are enrichment in the ash. The low plant availability of phosphorus in ash restricts the possibility to use ash on arable land. We believe that technological development of phosphorus extraction from sludge ash is the way forward to obtain sustainable phosphorus recycling in society, characterized by efficient processes producing clean and high quality products.

2 EasyMining Sweden AB (a company in the Ragn-Sells group) has developed a process for phosphorus recovery from sludge ash named Ash2 Phos. The process is based on wet chemical processing of sludge ash and is suitable for processing ash of mono-incinerated sewage sludge, as well as ash from co-incineration of sewage sludge and waste according to a specific concept (Bäfver et al., 2013). Ragn-Sells is Sweden s largest sewage sludge handling company treating ca tons of dewatered sewage sludge annually. Material and Methods Sludge ash is mainly composed of five elements: phosphorus, calcium, iron, aluminium and silicon in form of oxides and other inorganic forms. During the development of the Ash2 Phos process, the focus was on separating these five inorganic elements to enable a cost effective phosphorus recovery processes characterized by: (1) high phosphorus recovery rate; (2) high quality of recovered phosphorus product (low heavy metal content); (3) recovery of phosphorus in form of commercial products; (4) favorable mass-balance (cheap raw materials e.g. waste acid, lime); and (5) focus not only on phosphorus but also on recovery of iron and aluminium in form of commercial products. A schematic illustration of the Ash2 Phos process can be seen in figure 1. Figure 1. Schematic illustration of the Ash2 Phos process The process starts by dissolving the sludge ash in acid. Commercial hydrochloric acid or sulfuric acid can be used for that purpose. The process is also adapted to enable the use of waste acid from waste incineration plants such as scrubber acid from flue gas treatment. Dissolution of phosphorus and

3 calcium from sludge ash is generally high (Cohen, 2009), exceeding ninety percent. Dissolution of aluminium is up to eighty five percent and that of iron is up to forty percent. The next processtep is removal of recoverable elements from the obtained solution. Phosphorus, iron and aluminium are removed from the solution by precipitation steps in a unique combination. Thereafter, the solution is neutralized and treated for removal of heavy metals. The non-dissolved residue which mainly consists of inorganic silicates can after separation and washing be used e.g. in the cement industry. The recoverable elements are thereafter separated from each other by dissolution and precipitation reactions in a process which is characterized by internal recirculation of chemicals. The main chemical consumed in this process is lime. The recoverable elements are separated into three intermediate products: calcium phosphate, ferric hydroxide and aluminium hydroxide. The final step is conversion of intermediate products into final products. Several options exists depending on the form of the desired end-products. The intermediate calcium phosphate can be converted into calcium chloride and ammonium phosphate (mono-ammonium phosphate, MAP, or diammonium phosphate, DAP) by addition of hydrochloric acid and ammonia using the CleanMAP process. The CleanMAP process (also developed by EasyMining Sweden AB) enables energy effective production of pure and well defined ammonium phosphates of technical grade (figure 2). Technical grade of ammonium phosphates has lower metal content and is fully water soluble compared to the fertilizer grade which is the large volume commodity for phosphorus fertilizers, table 1. Table 1: Difference between fertilizer grade and technical grade mono-ammonium phosphate Fertilizer grade MAP (NP 11:21) Technical grade MAP (NP 12:26) 21% P (48% P2O5) 26% P (59% P2O5) Heavy metals proportional to raw material content Very low heavy metal content Contains impurities as calcium, gypsum etc. No impurities 10-20% of P not water soluble 100% water soluble Only spreading/use as solids Spreading/use as solid or dissolved Other options include conversion of the intermediate calcium phosphate into animal feed additives such as mono-calcium phosphate (MCP) or dicalcium phosphate (DCP) by reaction with an acid (phosphoric acid, hydrochloric acid or sulfuric acid) according to a suitable process. The intermediate calcium phosphate can also be used as a raw material for production of other phosphorus products such as phosphoric acid or superphosphates. Intermediate ferric hydroxide is converted into ferric chloride by reaction with hydrochloric acid. The final ferric chloride product can be used as a coagulant for phosphorus removal in wastewater treatment plants (WWTP). Intermediate aluminium hydroxide can be converted into aluminium sulfate or aluminium chloride by reaction with sulfuric acid or hydrochloric acid respectively (figure 3).

4 Results and Conclusions The Ash2 Phos process was tested in pilot trails for treatment of both ash of mono-incinerated sewage sludge and co-incinerated sewage sludge according to the above described concept. The recovered final products are of high commercial quality (table 2). Work is ongoing to upscale the process to a full-scale production plant in Sweden or Scandinavia. The concept for sewage sludge co-incineration is based on preparation of a fuel by mixing dewatered sewage sludge and a waste material with a high energy value and a low ash content to not dilute the phosphorus concentration in the resulting ash. The fuel mixture can thereafter be incinerated in existing waste incinerators. This approach enables utilizing the large existing waste incineration capacity in Sweden for incineration of sewage sludge with subsequent phosphorus recovery without requirements for large investments in dedicated sewage sludge incineration plants. The approach to focus not only on recovery of phosphorus but also on recovery of iron and aluminium for use as phosphorus precipitation chemicals in WWTP s is beneficial according to our view. Use of precipitation chemicals in wastewater treatment enables high phosphorus removal rate and reduction of energy consumption in the biological treatment. Combined chemical and biological treatment is probably the best for the environment. In Europe, a considerable amount of phosphorus is lost to the recipient (ca 18%) due to inefficient phosphorus removal. With the use of coagulants, 90% of the lost phosphorus could be captured and recovered from sludge ash. Therefore, the feature of the Ash2 Phos process which enables efficient phosphorus recovery independent on the use of coagulants in WWTP s is beneficial for a sustainable phosphorus management. Figure 2. Photos showing the intermediate calcium phosphate product (left) and the final mono-ammonium phosphate product (right)

5 Figure 3. Photos showing the final ferric chloride product (left) and the final aluminium sulphate product (right) Table 2: Elemental composition of recovered intermediate calcium phosphate and the final mono-ammonium phosphate product Element Unit Intermediate calcium phosphate final mono-ammonium phosphate Al mg/kg ,5 As mg/kg 31,2 <0,2 Ca mg/kg <5 Cd mg/kg <0.09 <0,01 Co mg/kg 1,19 <0,01 Cr mg/kg 14,6 <0,07 Cu mg/kg 29 <0,2 Fe mg/kg ,9 Hg mg/kg <0.2 <0,02 Ni mg/kg 5,38 0,339 P mg/kg Pb mg/kg 1,74 <0,1 Na mg/kg ,2 F % 0,014 - N tot mg/kg

6 References Bäfver, L., Renström, C., Fahlström, J., Enfält, P., Skoglund, N. and Holmén, E. (2013) Sludge fuel mixtures Combustion and extraction of phosphorus. Waste Refinery, Project nr WR-59, ISSN Cohen, Y. (2009), Phosphorus dissolution from ash of incinerated sewage sludge and animal carcasses using sulphuric acid. Environmental Technology 30: Cohen, Y., Kirchmann, H. and Enfa lt, P. (2011). Management of Phosphorus Resources Historical Perspective, Principal Problems and Sustainable Solutions, Integrated Waste Management - Volume II, Mr. Sunil Kumar (Ed.), InTech, DOI: / Kirchmann, H., Nyamangara, J., and Cohen, Y. (2005) Recycling municipal wastes in the future: From organic to inorganic forms? Soil Use Manage. 21: Kirchmann, H., Börjesson, G., Kätterer, T. and Cohen, Y. (2016), From agricultural use of sewage sludge to nutrient extraction: A soil science outlook. Ambio, doi: /s