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Fecal sludge was prepared by mixing tapwater with feces and urine collected from volunteers. The feces and urine constituted 0.65 and 1.6% (w/w), respectively, of the mix, equivalent to 30 L flushwater, 0.5 L urine and 200 g feces per person and day. Feces were kept frozen until use. At preparation, feces and urine were measured separately into 8- and 50-mL tubes and mixed with ammonia solution or urea to reach 2–10% ammonia solution and 0.05–1.5% urea (Table 1). Different treatment concentrations were used at the different temperatures, thereby covering the different knowledge gaps in treatment efficiency of ammonia and carbonate at the temperatures tested. In the treatments with urea, urease enzymes were added (∼500 U/g urea). Finally, the tubes were filled with tapwater to the desired volume, aiming at minimised headspace. The tubes were sealed with an O-ring in the lid to prevent ammonia losses. After preparation, the tubes with urea addition were shaken at 50 rpm for 3 hours in 37 °C to hydrolyse the urea, which was confirmed by ammonia measurement. The tubes were then stored cold (5 °C) until the addition of pathogens.

Table 1

Treatment time required for 4 log10 reduction of Ascaris egg viability and 7 log10 reduction of Salmonella spp., number of samples (#), ammonia activity (NH3, mM) and carbonate activity (, mM) and pH for the different treatments

Temp.Treatment4 log red. Ascaris (days)#7 log red. Salmonella (days)#NH3 (mM)pH
32 °C 10% ammonia <0.21 915 11.2 
32 °C 0.4% urea 20 2.1 50 (61–41) 9.0 (9.2–8.9) 
32 °C 0.15% urea NR (24) 112 12 13 (23–7) 0.5 8.6 (8.9–8.3) 
32 °C 0.05% urea NR (30) NR (30) 12 2 (4–2) 0.1 7.9 (8.3–7.9) 
32 °C no treatment NR (51) NR (51) 13 1 (2–1) 0.02 7.7 (8.6–7.7) 
32 °C  control 67a,b – – 9.0 
32 °C NH3 control 19a – – 73 9.0 
32 °C  control 15a – – 62 9.0 
32 °C Control NRa (40) – – 9.0 
28 °C 1.5% urea 17 1.4 196 9.3 
28 °C 0.75% urea 28 2.8 92 9.2 
28 °C 0.4% urea 45 4.2 39 9.0 
28 °C 0.15% urea NR (48) 399 11 12 (19–8) 0.5 8.6 (8.9–8.4) 
28 °C 0.05% urea NR (102) NR (85) 11 1 (2–1) 0.0 7.9 (8.1–7.9) 
28 °C no treatment NR (152) NR (85) 10 0.4 (2–0.5) 0.01 7.7 (8.5–7.7) 
23 °C 10% ammonia <9 <0.7 1,205 11.3 
23 °C 1.5% urea 52 1.4 171 9.3 
23 °C no treatment NR (152) NR (152) 11 0.7 (3–0.2) 0.03 8.1 (8.8–7.5) 
17 °C 3% ammonia 73 0.7 355 10.7 
17 °C 2% ammonia 82 1.4 225 10.6 
17 °C 1.5% urea 130 1.4 149 9.3 
17 °C 0.75% urea 216 2.8 62 9.2 
17 °C no treatment NR (204) NR (108) 10 1 (2–0.3) 0.04 8.3 (8.8–7.3) 
11 °C  control NRa (220) – – 9.0 
11 °C NH3 control 159a – – 550 9.0 
11 °C  control 200a – – 304 9.0 
11 °C Control NRa (220)       
10 °C 10% ammonia 100 2.1 1,107 11.3 
10 °C 5% ammonia 131 4.2 570 11.0 
10 °C 1.5% urea NR (108) 3.5 94 (99–92) 9.3 (9.4–9.3) 
10 °C no treatment NR (204) 28 0.3 (1–1) 0.03 8.2 (8.8–7.4) 
4 °C 10% ammonia 149 2.1 1,064 11.3 
4 °C 5% ammonia 188 620 11.0 
4 °C 1.5% urea NR (204) 3.5 71 (69–69) 9.4 (9.3–9.4) 
4 °C no treatment NR (204) 28 0.4 (1–1) 0.05 8.6 (8.8–7.4) 
Temp.Treatment4 log red. Ascaris (days)#7 log red. Salmonella (days)#NH3 (mM)pH
32 °C 10% ammonia <0.21 915 11.2 
32 °C 0.4% urea 20 2.1 50 (61–41) 9.0 (9.2–8.9) 
32 °C 0.15% urea NR (24) 112 12 13 (23–7) 0.5 8.6 (8.9–8.3) 
32 °C 0.05% urea NR (30) NR (30) 12 2 (4–2) 0.1 7.9 (8.3–7.9) 
32 °C no treatment NR (51) NR (51) 13 1 (2–1) 0.02 7.7 (8.6–7.7) 
32 °C  control 67a,b – – 9.0 
32 °C NH3 control 19a – – 73 9.0 
32 °C  control 15a – – 62 9.0 
32 °C Control NRa (40) – – 9.0 
28 °C 1.5% urea 17 1.4 196 9.3 
28 °C 0.75% urea 28 2.8 92 9.2 
28 °C 0.4% urea 45 4.2 39 9.0 
28 °C 0.15% urea NR (48) 399 11 12 (19–8) 0.5 8.6 (8.9–8.4) 
28 °C 0.05% urea NR (102) NR (85) 11 1 (2–1) 0.0 7.9 (8.1–7.9) 
28 °C no treatment NR (152) NR (85) 10 0.4 (2–0.5) 0.01 7.7 (8.5–7.7) 
23 °C 10% ammonia <9 <0.7 1,205 11.3 
23 °C 1.5% urea 52 1.4 171 9.3 
23 °C no treatment NR (152) NR (152) 11 0.7 (3–0.2) 0.03 8.1 (8.8–7.5) 
17 °C 3% ammonia 73 0.7 355 10.7 
17 °C 2% ammonia 82 1.4 225 10.6 
17 °C 1.5% urea 130 1.4 149 9.3 
17 °C 0.75% urea 216 2.8 62 9.2 
17 °C no treatment NR (204) NR (108) 10 1 (2–0.3) 0.04 8.3 (8.8–7.3) 
11 °C  control NRa (220) – – 9.0 
11 °C NH3 control 159a – – 550 9.0 
11 °C  control 200a – – 304 9.0 
11 °C Control NRa (220)       
10 °C 10% ammonia 100 2.1 1,107 11.3 
10 °C 5% ammonia 131 4.2 570 11.0 
10 °C 1.5% urea NR (108) 3.5 94 (99–92) 9.3 (9.4–9.3) 
10 °C no treatment NR (204) 28 0.3 (1–1) 0.03 8.2 (8.8–7.4) 
4 °C 10% ammonia 149 2.1 1,064 11.3 
4 °C 5% ammonia 188 620 11.0 
4 °C 1.5% urea NR (204) 3.5 71 (69–69) 9.4 (9.3–9.4) 
4 °C no treatment NR (204) 28 0.4 (1–1) 0.05 8.6 (8.8–7.4) 

For treatments with decreasing pH (>0.2 units decrease), initial and final values of pH and NH3 activity are given in brackets. For treatments with no reduction, i.e. less than 0.3 log10 reduction (NR), the study duration is given in brackets (days).

aTime for reduction of 3log10.

bExtrapolated value, ∼0.5 log10 reductions observed.

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