Options for the use of recovered N- and P-fertiliser in agriculture

Transcription

1 Options for the use of recovered N- and P-fertiliser in agriculture Daniel Klein, Institute of Sanitary and Environmental Engineering, TU Braunschweig

2 Global backgrounds of nutrient recovery Fertiliser markets are very volatile; example: DAP 1,000 US$/t 500 US$/t Phosphorus is a limited resource Global agricultural production depends on fertiliser Wastewater contains approx. 30% of global N- and P-demand Source: Indexmundi 2013

3 (Technical) Options for nutrient recovery P-recovery: Different options and approaches from lab- to full scale Prim. Sed. AST Sec. sedim. PS Excess Sludge 2 b 1 N-recovery: NH 3 -stripping for separate treatment of N-rich streams such as sludge liquor; various full-scale applications Sludge Thickening Digestion Stripping is not yet considered as N-recovery Dewatering System boundaries usually end with the fertiliser production Aim of this study: Closing the gap between fertiliser production and -use 2a 3 4 Incineration Source: Pinnekamp et al 2005, modified

4 Case study Braunschweig Long-lasting experience (~ 60 years) with wastewater irrigation and sludge reuse Farmers in the irrigation area are organised in the Wastewater Board of Braunschweig access to agricultural data and contact to agricultural stakeholders WWTP: Separate treatment of sludge liquor Reduction of the WWTP loads Recovery of N and P and use as fertiliser

5 The wastewater treatment and -reuse system of BS Nutrient recovery MAP-precipitation NH 3 -stripping (production of DAS) Cosubstrates Digester gas Sludges Cogeneration unit Digester towers Digester Heat & Energy Digested sludge: (winter) (summer) External use of dewatered sludge Dewatering Process water Biogas plant Energy crops and other Irrigation (3.000 ha) Wastewater wwtp WWTP Treated wastewater (Former) Sewage Field Former sewage field Recipient Sources: Abwasserverband Braunschweig; SE/BS, W. Küchenthal (biogas plant) 5

6 In- and output of MAP-precipitation and NH 3 -stripping Due to the direct use of digested sludge in summer, dewatering and nutrient recovery is only needed / possible in winter Operation of nutrient recovery: 175 days/year Daily amount of sludge liquor: 613 m³ In- and output parameters: Parameter Input of recovery step Nutrient recovery [t/a] Fertiliser production (and recovery ratio in %) NH 4 -N 1,000 mg/l (90%) 96.5 t/a of N 1,110 t/a ammonium sulphate (DAS)* PO 4 -P 180 mg/l (100%) 19 t/a of P (44 t P 2 O 5 ) 152 t/a MAP** *40.9%-solution with a N-concentration of 8.7% **with 12.5% phosphorus

7 The agricultural demand of fertiliser The demand of mineral fertiliser has been assessed for the four main crops of the irrigation area: Using the field record system of the farmers, the fertiliser demand could be specified according to type, date of application...

8 Phosphorus: Demand of P- fertiliser of the four main crops DAP other A 70 B 15 [t] Demand of DAP (as P 2 O 5 ) t] other P-fertiliser (as P 2 O 5 ) [t Apart from corn/maize, no demand of P-fertiliser (due to sludge irrig.) Fertiliser demand in early spring only

9 Phosphorus: Setting up substitution concepts Only one P-fertiliser (DAP) is used in substantial amounts The application of DAP is limited to the fertilisation of corn/maize during sowing in March/April Phosphorus bound in MAP is as available to plants as other P- fertiliser (DAP, TSP) Quality of MAP usually better than mineral P-fertiliser MAP from nutrient recovery Cd Cr Cu Pb Zn U min No data max No data Industrial fertiliser Triple superphosphate No data Diammonium phosphate (DAP) Data sources: Montag (2008), Steinmetz et al (2012), Esemen (2012), Bannick et al (2001), Dittrich & Klose (2008)

10 Phosphorus: Application of MAP as a substitute of DAP The whole MAP-production of ~45 t/a P 2 O 5 is used for the fertilisation of corn/maize P-demand of 15 t P 2 O 5 still has to be covered by DAP P-demand and supply (as P2O5) [t] demand still to be covered by DAP DAP-demand of corn Application of/substitution by MAP

11 Nitrogen: Demand of N-fertiliser of the four main crops UAN A -Demand [t] UAN Corn Wheat Sugar beet Rye B CAN-De emand [t] CAN C 35 D 50 Urea Urea-Demand [t] [t] other Nitrogen demand other 0 0

12 Nitrogen: Setting up substitution concepts The demand of N-fertiliser is higher than the amount of N recovered on the WWTP (> 300 t/a, compared to approx. 100 t/a) Ammonium sulphate (DAS) is not yet used as a nitrogen fertiliser Urea, CAN and UAN could theoretically be substituted by DAS For the following example, only UAN is substituted Both DAS and UAN are liquid fertiliser application technology has not to be changed Due to the different properties of DAS compared to UAN (high sulphur content; NH 4 -N only), only a part of the UAN-demand is substituted by DAS

13 Nitrogen: Application of DAS as a substitute of UAN Example: Substitution of one (!) UAN application in April by DAS for wheat Due to the high UAN-demand of wheat, only 28% are (in this case) substituted by DAS N-dema and and supply [t] UAN-demand of wheat Use of DAS Use of UAN af ter substitution Application of DAS (28%) Application of UAN (72%) 0

14 Side effects of the substitution concepts Different concentrations of the target nutrients: MAP: 29% P 2 O 5 DAP: 46% P 2 O 5 UAN: 28-30% N DAS: 8,6% N leads to higher application costs In both cases, the substitution also affects other nutrients Mg, N in case of the substitution MAP DAP S in case of the substitution DAS UAN This leads to benefits and/or additional costs The value of the fertilisers produced on the WWTP depend on their specific use / substitution concept

15 Value of MAP and DAS considering the side effects Value of MAP within the specific substitution concept Value providing the same amount of P: 315 /t - Higher application costs Additional N-fertiliser Benefit of Mg-application + 42 Final value: 290 /t Value of DAS within the specific substitution concept Value providing the same amount of N: 77 /t - Higher application costs Additional demand of lime - 12 Final value: 48.6 /t

16 Other substitution concepts / other locations MAP Value providing the same amount of P: XYZ /t +/- Application costs +/- X +/- Benefit/costs N-fertiliser +/- Y + Benefit of Mg-application + Z Final value: XYZ /t DAS Value providing the same amount of N: XYZ /t +/- Application costs +/- X + Benefit of Sulphur + Y - Additional demand of lime - Z Final value: XYZ /t Depending on fertiliser market Depending on soil/location Depending on substituted fertiliser

17 Value vs. price of the fertilisers If MAP and DAS are sold for their specific final value (in this case, 290 /t and 48.6 /t), there is no economic benefit on the agricultural side On the other side, the would be no benefit (of the agricultural use!) on the WWTP if the prices of MAP and DAS are lower than the achievable prices if sold to industry (max. 100 /t and 25 /t) All prices between = Win-Win-Situation for both stakeholders MAP DAS Maximum price = value as a substitute for DAP / UAN 290 /t /t Minimal price = value if sold to industry /t 25 /t

18 Conclusions By considering the agricultural demands, specific concepts for the use of MAP and DAS could be set up The value of MAP and DAS depend on the substitution concept and the framework of their use (application costs, consideration of other nutrients,...) There is an (economic) benefit of the agricultural reuse for... the agricultural side, if the prices of MAP/DAS are lower than the prices of the substituted fertilisers... the WWTP, if the prices are higher than the prices if MAP/DAS are sold to industry Win-Win-Situations for both stakeholders can be created Since nutrient recovery is considered to be close to economic feasibility, even small (additional) benefits could be the decisive aspect

19 Options for the use of recovered N- and P-fertiliser in agriculture Thank you for your attention Sources: Abwasserverband Braunschweig; SE/BS, W. Küchenthal