P- Recovery in Berlin – from Pilot Scale Experiments to large Scale ...

P- Recovery in Berlin – from Pilot Scale 

Experiments to large Scale Application 

Dr. Bernd Heinzmann 

Berliner Wasserbetriebe (BWB) 

Germany 

Baltic 21 - Phosphorus Recycling and Good Agricultural Management Practice 

September 28-30, 2009 - Berlin, Germany

Content 

1. Formation of Incrustations 

in the Sludge Chain 

2. Measures for Incrustation Prevention 

3. Measures for Phosphorus Recovery 

4. The Cooperation Project with TU Berlin 

5. Assessment of the 

MAP Precipitation Product 

6. Summary 




in the Sludge Treatment 

� The wastewater purification process is used 

with an enhanced biological phosphorus removal and 

concentrated streams of digested sludge 

� Favours the formation of incrustations during sludge treatment 

� Spontaneous release or degassing of carbon dioxide of the over 

saturation of the digested sludge and the process water (centrate of the 

digested sludge) 

� These incrustations were the cause of a lot of operational problems! 



Examples of Incrustation Problems in the 

WWTP Waßmannsdorf 

Objective: Prevention of incrustations 

� safe operation of the sludge treatment process 

digester 

Heinzmann and Engel (2003) 

80 mm diameter bend joint of pump 2 after 319 

operating hours and intake aperture after 180 

operation hours of the centrate pumping station 



Studies and Trials Undertaken to Identify and 

Further to Prevent the Incrustation Problems 

in the WWTP Waßmannsdorf 

• Chemical and structural analysis of the crystalline matter: 

→ Insoluble, crystalline white MAP deposits with small portions of different 

calcium phosphate compounds 

• Technical laboratory tests to study the phosphorus dynamics in anaerobic 

sludge treatment 

(chemistry and kinetics of phosphorus precipitation during digestion) 

• Trials on the degassing of CO 2 due to aeration of the digested sludge 

• Laboratory studies that dealt with the induced precipitation of struvite and 

calcium phosphates by means of aerating digested sludge which leads to 

degassing of CO 2 , thus increasing pH value 




mixed raw-sludge 

two stage high rate digestion 

anti-incrustation agent 

MgCl 2 

digested sludge 

storage tank 

anti-incrustation agent 


September 28-30, 2009 - Berlin, Germany 


MAP 

air 

air 

centrifuge 

centrate 

dewatered sludge


• Partial separation of the MAP by 

sedimentation in the digested 

sludge storage tank of the 

WWTP 

• After a period of 3 months 

around 30 tons of MAP are 

removed from the bottom by a 

vacuum truck 

• Disposal 

(costs around 140 euro / tons) 

• Cleaning is necessary before 

phosphorus recovery 



4. The Cooperation Project with TU Berlin, 

Chair of Chemical & Process Engineering 

Main Objectives: 

• optimum dimensioning of the digested sludge 

storage tank for complete precipitation and 

separation of MAP: 

→ A high yield of precipitated crystals for a 

maximum P-recovery 

→ Enhanced crystal separation from digested 

sludge 

Methods 

• Lab scale research for optimizing relevant 

parameters like aeration rate, Mg-dosing, 

geometric dimensioning, stoichiometric ratio of 

crystallization partners, yield of MAP 

• Batch and continuously pilot plant trials 



Stumpf (2009)

Pilot Plant Airlift Reactor: 

Efficient MAP-Precipitation 

Residual concentration cPO4-P [mg L-1] 

300 

200 

100 

0 

HRT = 8h cPO4-P pH 

Digested sludge 

0 1 2 3 4 5 6 7 8 

time [h] 

• About 90 - 95 % of phosphorus could be precipitated as MAP 

• An airlift reactor is suitable for an enhanced MAP-precipitation 

9,0 

8,5 

8,0 

7,5 

7,0 

6,5 

6,0 

pH-value 



Operational parameters: 

- Reactor volume 

45 L 

- Aeration rate 

500 L h -1 

- n PO4-P : n Mg = 1:1 

- Hydraulic residence 

time (HRT) = 8 h

Pilot Plant Airlift Reactor: 

Particle Size Distribution of MAP by Sieving 

Frequency distribution [%] 

50 

40 

30 

20 

10 

0 

MAP from digested sludge before 

pilot plant trials 

MAP from digested sludge after 

pilot plant trials 

0 100 200 300 400 500 600 700 800 

size [µm] 

• Similar results of the digested sludge before and after pilot plant trials 

• Slight trend to more MAP due to precipitation and further growth of the crystals 

• Average crystal sizes are still too small for a maximum separation 



P-Balance in Batch Operation – Current 

Situation at WWTP Waßmannsdorf 

Total-P in percent in digested sludge [%] 

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

0 

P-content in 

sludge 

BWB current digested sludge storage tank 

TU pilot plant airlift reactor 

ortho-P in 


P-precipitated P-separated 



P-Balance in Continuous Operation 

Total-P in percent in digested sludge [%] 

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

0 

P-content in 

sludge 

BWB optimized digested sludge storage tank 

(not yet in operation) 

TU pilot plant airlift reactor 

ortho-P in 


P-precipitated P-separated 



?

Designing of an Optimized 

Digested Sludge Storage Tank 

Current: 

Optimized: 

Stumpf et al. (2009) 

Objective: 

• Optimizing the MAP precipitation 

• Improvement of the MAP 

separation 

� Circulation - flow caused by air 

injection; mixing 

� Stripping the CO 2 

� pH rises, precipitated MAP as 

crystals 

� MAP is released through a coneshaped 

bottom 



Pictures of the Optimized Digested 

Sludge Storage Tank under Construction 

at the WWTP Waßmannsdorf 



Further Separation of the MAP from the 

Digested Sludge 

• Hydro-cyclone 

• Cyclone separator with immersed spiral pipe 

• Centrifuge, e.g. : 

- Sedimentation instruments; Vertical centrifuge 

(discontinuous centrifuge); Horizontal centrifuge 

(with/ without rotation - discontinuous centrifuge); 

Shearing centrifuge (continuous centrifuge) and 

Sieves screw extrusion centrifuge (continuous 

centrifuge) 

• Sieves: 

- Rotary type screen; Upstream classification; 

Bended sieves and Screw extrusion press 



Trials for further Separation of the MAP from 

the Digested Sludge using Hydro-cyclones 

� A centrifugal separation by means of hydro-cyclones 

� MAP crystal density is 1.7 kg/dm3 

� Particle size distribution is 95 % > 0.063 mm 

►To achieve separation of particles > 0.05 mm 

Supernatant 

outflow 

Influent 

Base 

outflow 



Cleaning of the separated MAP Precipitation 

Product 

� Investigation of an optimal cleaning or treatment 

process for the separated MAP precipitation 

product by 

� Washing 

� Belt filter squeezer 

� Drying 

Outflow with high concentrated MAP 

of hydro-cyclone 



Microscope Photos of MAP Crystals in 

the Base Outflow of the Hydro-Cyclone 

Crystals with typical 

orthorhombic shape 



Large Scale Trials for Cleaning MAP from 

Digested Sludge in a Grid Washing Tank 



Results of Washing Trials 

• Decreasing TOC-concentration by increasing water inflow 

• Fluidized-bed height not relevant for an efficient cleaning of MAP-crystals 



Content 


in the Sludge Chain 



4. The Cooperation Project with TU Berlin 

5. Assessment of the 

MAP Precipitation Product 

6. Summary 



Comparison of Nutrients in the washed and unwashed MAP 

Precipitation Product, after the Separation by Hydro-Cyclone, 

with minimum Contents of different Fertilisers defined by the 

German Fertiliser Regulation 

Content [%] 

20 

15 

10 

5 

0 

Unwashed MAP after hydro-cyclone 

Washed MAP after hydro-cyclone 

Superphosphate 

Dicaliumphosphate with magnesium 

NP-fertilizer 

P 2 O 5 N total MgO 



Supernatant Überlauf Unterlauf Base 

outflow outflow 

Influent Zulauf

Comparison of Heavy Metal Content 

(in % based on P) in digested Sludge and 

in unwashed MAP Precipitation Product 

% Heavy metal / kg Phosphorus 

2,5 

2 

1,5 

1 

0,5 

0 

digested Sludge 

im Faulschlamm 

MAP 

im MAP 

Lead Chrome Copper Nickel Zinc Cadmium Mercury 



Phosphorus - Availability with regard to 

German Ryegrass – Lolium perenne 

Investigations of the phosphorus availability 

of the MAP precipitation product compared to 

synthetic MAP and calcium phosphate: 

→ two soils with a pH-value of 6.6 und 7.1 

→ special kind of grass German Ryegrass 

(Lolium perenne): 

• Good mobility of phosphorus in the fertilized 

soil 

• Good availability 

• Satisfying growth 

(Richards and Johnston, 2001) 



6. Summary 

� Process for an induced precipitation of MAP is applied 

● Prevention of further incrustations 

● Fixing of significant amounts of phosphorus in the MAP 

� Substantial reduction of the remaining P-load in the wastewater purification 

process 

� Partial separation by gravity of the MAP already in the digested sludge 

storage tank 

� Assessment of the MAP precipitation product for reuse as fertilizer: 

nutrients, pollutants, (solubility) and plant availability 

� Process optimization before a continuous technical application in the 

WWTP Waßmannsdorf 



� The Cooperation Project with TU Berlin 

(Chair of Chemical & Process Engineering) 

for optimal dimensioning of the digested sludge storage tank 

for continuously complete precipitation and separation of MAP 

� Optimal design of the digested sludge storage tank regarding to air 

injection, aeration rate, the flow pattern, geometric dimensioning, MAP 

precipitation (crystallisation and growth) and Mg-dosing, stoichiometric ratio 

of crystallization partners, yield of MAP 

� Construction of the optimized sludge storage tank 

� Further MAP separation in a subsequent second step, 

e.g. by hydro - cyclone 

� Optimal cleaning for the separated MAP precipitation product by washing 



Thank you for your attention!

P- Recovery in Berlin – from Pilot Scale Experiments to large Scale ...

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