Sergio Piccinini
Giuseppe Moscatelli Claudio Fabbri
CRPA – Research Centre on Animal Production - Reggio E. - Italy
Nitrogen recovery from digestate with ammonia stripping : results of 27 tests
ManuREsource 2013 Manure management
and valorization
December 5‐6, 2013 Bruges, Belgium International conference
Layout of the stripping treatment in an anaerobic digestion scheme
Slurry and biomass Anaerobic Digestion
S/L Separation
Stripping
Ammonium sulfate Liquid fraction
Composting Drying
(optional)
Agronomic use
Liquid fraction with low ammonia
Solid fraction Fertilizer
Industry Combined Heat and Power (CHP)
Digestate
Layout and characteristics of the stripping pilot plant.
•Recirculation of air
•SemiBatch
•Acid Scrubber
•Temp: 60°C
•HRT: 6 ore
•Capacity reactor: 1 m3 of slurry
•Air flow rate=100-250 m3/h.m3 of slurry
Pilot plant stripping reactor
Air insuffator
Anti foam
Heat exchanger
Pilot plant stripping reactor
Hot (60°C) stripping of
ammonia, without the chemical
raising of pH, on several tests with 9 types of clarified digestate (9 types x 3
repetitions)
Experimental programme carried out
A.D. Plant Power S / L separator
A.D. plant 1 330 kWel Screw press Cattle manure and slurry (100%)
A.D. plant 2 999 kWel Screw press
Cattle slurry (25%) Energy crops (60%) Agoindustrial by-product (15%)
Pig slurry (90%)
Corn flour and molasses (4%) Cattle slurry (6%) A.D. plant 3 999 kWel Screw press Energy crops (100%)
A.D. plant 4 630 kWel Sieve drum press
Pig slurry (70%) Energy crops (15%)
Cattle slurry (15%)
999 kWel Sieve drum press Cattle slurry and manure (70%) Energy crops (30%) A.D. plant 5 999 kWel Screw press Energy crops (100%)
A.D. plant 6 250 kWel Centrifuge
A.D. plant 9 250 kWel Screw press
Pig slurry (30%) Energy crops (30%)
Cattle slurry (40%)
Input Substrate to Anaerobic Digestion
A.D. plant 7 60 kWel Screw press Cattle slurry (100%) A.D. plant 8
Characterisation of clarified digestate before and after stripping tests
pH TS TKN pH TS TKN
[-] [g/kg] [mg/kg] [mg/kg] [%TKN] [-] [g/kg] [mg/kg] [mg/kg] [%TKN]
Average 8,09 48,3 3339 1944,7 58,2% 8,59 49,5 2481 1049,7 42,3%
S.D. 0,05 0,6 33 4,7 0,5% 0,06 1,4 44 52,9 1,9%
Average 8,11 54,6 4324 2594,3 60,0% 8,70 58,2 3326 1503,7 45,2%
S.D. 0,05 0,4 31 1,2 0,4% 0,01 1,3 39 15,0 0,3%
Average 7,98 69,0 4341 2131,3 49,1% 8,67 71,9 3621 1251,7 34,6%
S.D. 0,11 1,5 56 60,9 0,8% 0,15 0,8 74 15,9 0,5%
Average 7,92 53,7 5476 3769,7 68,9% 8,63 53,9 4135 2171,7 52,5%
S.D. 0,26 5,7 92 64,8 2,2% 0,09 9,3 34 147,9 3,7%
Average 7,81 65,5 4672 2223,3 47,7% 8,46 71,1 3786 1296,7 34,2%
S.D. 0,07 3,3 420 95,6 2,7% 0,06 2,6 215 91,9 0,9%
Average 7,88 15,6 2110 1602,0 76,0% 8,43 15,2 1460 792,7 54,3%
S.D. 0,09 2,5 73 33,3 1,1% 0,06 2,0 33 21,1 1,2%
Average 7,73 36,8 2391 1366,0 57,1% 8,48 34,7 1890 933,0 49,4%
S.D. 0,07 1,3 18 46,4 1,5% 0,03 2,4 15 11,4 1,0%
Average 7,91 43,5 3514 1928,3 54,9% 8,54 48,3 2892 1315,7 45,5%
S.D. 0,11 2,6 138 44,8 1,4% 0,02 1,1 119 87,8 2,6%
Average 7,75 13,9 1747 1361,0 78,1% 8,74 14,2 1276 761,7 60,1%
S.D. 0,08 0,6 83 57,2 5,9% 0,10 0,8 151 30,7 4,8%
A.D. plant 7
A.D. plant 8 A.D. plant
1
A.D. plant 2
A.D. plant 3
A.D. plant 4
A.D. plant 5
A.D. plant 6
Thesis NH4
+ -N
A.D. plant 9
Clarified Digestate POST-Stripping NH4
+ -N Clarified Digestate PRE-Stripping
Ammonia-N and TKN Removal efficiency observed in the 27 tests (average value and standard deviation -in brackets - of the 3 repetitions of each 9 types of clarified digestates treated)
NH4+
‐ N TKN
Power [dm3] [dm3] [%] [%]
A.D. plant 1
(330 kWel) 310 (11) 263 (6) 603 (19) 276 (12) 54.3 (1.5) 31.6 (1.1)
A.D. plant 2
(999 kWel) 301 (2) 289 (4) 780 (4) 435 (3) 44.3 (0.7) 26.6 (0.6)
A.D. plant 3
(999 kWel) 301 (2) 262 (11) 641 (21) 328 (12) 48.8 (0.8) 24 (0.6)
A.D. plant 4
(630 kWel) 301 (2) 276 (24) 1135 (11) 600 (87) 47.1 (8.2) 32.5 (6.5)
A.D. plant 5
(999 kWel) 303 (8) 245 (8) 674 (42) 317 (32) 52.9 (2.5) 25.2 (1)
A.D. plant 6
(250 kWel) 316 (14) 205 (53) 506 (19) 162 (44) 68.1 (7.8) 51.7 (5.4)
A.D. plant 7
(60 kWel) 339 (5) 273 (4) 463 (14) 254 (6) 45 (0.6) 25.7 (0.9)
A.D. plant 8
(999 kWel) 320 (9) 275 (22) 617 (3) 362 (53) 41.3 (8.3) 22.7 (5)
A.D. plant 9
(250 kWel) 318 (7) 211 (19) 433 (24) 160 (7) 63 (0.5) 49.2 (3.7)
NH4+
‐ N initial
NH4 + ‐ N final
N removal efficiency
[g]
Types of clarified digestates from 9
A.D. plants
Clarified digestate to stripping
Effluent after stripping
Average trend of the ammonia concentration and removal during the experiments at 60 °C
Relationship between removal efficiency of ammonia and total solids content in the influent
The removal efficiency of nitrogen is strongly influenced
by the content of total solids present in the clarified digestate
Relationship between content of ammonia in the influent and removal efficiency of ammonia
The greater the ammonia content in the digestate, higher the stripping efficiency
Results: characteristics of ammonium sulphate solution extracted from scrubber
pH: 4.29
TS: 36.4 %
TKN: 73.27 g/kg (20.1 % TS),
about 90% as ammonia
Results: some problems
• Foam formation (but controlled by the slurry mixing system designed to reduce this
problem);
• Ammoniun sulphate dilution in the scrubber’s tank, for condensation of the water vapor from air stripping flow;
• Accumulation of organic matter on the reactor
walls and bottom.
• The results of experiments show feasible the stripping of clarified digestate by air insufflation and heating, without chemical raise of the pH; efficiencies, however, are not very high;
• The lower the solids content in the digestate, the greater the efficiency of stripping;
• The greater the nitrogen content and the percentage of ammonia in the digestate, higher the stripping efficiency;
• The ammonia stripping after anaerobic digestion therefore has three advantages: the anaerobic digestion converts most of the organic nitrogen into ammonia, reduces organic acids (less foam) and makes available waste heat from CHP unit.
