Particle Size (nm) Surface charge concentration duration Major findings References
AgNP 25.2 (citrate coated), 27 (GA coated), 21 (PVP coated) n/a 0.2,2, 20 mg/L 4 hrs Gum Arabic and citrate coated AgNPs were more toxic to cultured N. Europaea Arnaout et al, 2012
AgNP 15 nm (TEM) n/a 0.5 mg Ag/L 3 months Freshly prepared AgNPs are beneficial for microbial diversity and biomass concentration Sheng at al,2018
AgNP
32.3 (GA) TEM 15.5 (Citrate) TEM
n/a
0.2 mg/L, 2 mg/L
1) Coated AgNPs were less toxic than AgNO3; 2)2 mg/L dose caused significant reduction in N-removal;
Alito & Gunsch, 2014
AgNP 14 nm n/a (PVA coated) 1 mg/L 800 s test 1) 1 mg/L of Ag inhibited nitrifying bacteria growth, AgNP > Ag+; 2) No evidence of membrane damage Choi et al, 2008
AgNP 21 (TEM), 29 (DLS) n/a, (PVA coated) 1 mg/L shock loading Short term batch test and bioreactor test (25 days) 1mg/L AgNP inhibited nitrification by 41.4%; decreased abundance of AOBs and NOBs Liang et al,2010
AgNP
6.0±2.0 (STEM) 10.6±0.3
-26.2±1.0 mV
0.1 mg/L, continuous loading
60 days
No impacts on activated sludge performance
Zhang et al,, 2014
AgNP
118.5±1.2 (DLS, in Milli-Q water)
1.0 mg/L, 5.0 mg/L
27 days (1 mg/L) 36 days (5mg/L)
No effects on nitrification, denitrification or COD removal. Sludge settling abilities affected.
Qiu et al, 2016
AgNP 14 (TEM) n/a 0-10 mg/L 1.5 hr AgNPs of 0.25 to 10 mg/L inhibited ammonia oxidation by 4-50% Giao et al, 2012
AgNP
13.0±3.3 (as synthesized) 63.5±15.2 (glucose feed) 79.2±18.1 (ammonia feed) -24.0±2.8 mV (as synthesized) 15.5±1.7 mV (glucose feed) -11.5±1.4 mV(ammonia feed)
0.1-50 mg/L
24 hrs; 50 days
1).Concentration-depedent inhibition of N-removal and COD removal; effects started at concentrations below 1 mg/L; 2. Nitrification was more severely inhibited; 3) nitrifying bacteria more sensitive to AgNP than heterotrophic bacteria
Jeong et al, 2014
AgNP
7±3; 40±14 (TEM)
n/a (Na2ATP coated, PVA-coated)
0-10 mg/L
3 hrs (N. Europaea cell culture)
1).Size and coating-dependent ammonia oxidation inhibition; 2. Toxicity due to release Ag ion and AgNP dispersity; 3. Cell membrane damage
Yuan et al, 2013
AgNP
7±3 (TEM)
n/a (PVP coated)
0.1, 1 and 5 mg/L
125 days (0.1 mg/L) 40 days (1 mg/L) 30 days (5 mg/L)
No impact on nitrification & denitrification; significantly inhibited P-removal; toxicity attributed to dissolved silver
Yuan et al, 2015
AgNP
Synthesized NPs: < 10 nm (TEM) 38±10 (DLS) Commercial NPs: < 100 Synthesized:-25±0.88 mV Commercial: n/a
0-15 mg/L
21 hr (respirometry)
Commercial AgNPs showed no effects on sludge respiration; synthesized AgNPs has an IC50 value of 3.2-22.1 mg/L
Geyil and Cecen, 2016
AgNP n/a n/a 0-30 mg/L 290 days 1. > 5 mg/L Ag NPs inhibited COD and P removal, not N removal; 2) Decreased enzymatic activities (AMO, NOR, NIR, NR, PPX and PPK); 3) dose-dependent ROS production and LDH release Xu et al, 2017
AgNP
10 ±5 (DLS) 20 (TEM)
-36.1 mV
0.1, 1, 10
50 days
1.0 and 10 mg/L AgNP decreased COD, N and SOP removal; 2. AgNP inhibited EPS production; reduced the SOUR and increased LDH release, reduced nitrifyer abundance
Zhang et al, 2016
AgNP 44.61 (TEM) n/a 30 mg/L 14 hrs 1).30 mg/L reduced nitrite production by 90%; 2. IC50 value of 10.5 mg/L for AOB activity inhibition Michel et al, 2017
AgNP 20 (DLS) n/a 1-100 mg/L 12 hr, 22 days 1).short-term exposure led to 21-24.9% reduction in ammonia oxidation in flocculent sludge; 2)long-term exposure significantly inhibited ammonia oxidation, denitrification and oxygen uptake rate; 3) no effect on granular sludge Gu et al, 2014
CuNP
336 (wastewater) < 100 (TEM)
-24.6 mV
1 mg/L
180 days
1 mg/L led to: 1)inhibited N & P removal; 2) decreased AMO and NOR activity; 3)no effects on denitrification or its enzymes; 4)microbial shift and decreased ecological network interactions
Wang et al, 2017
CuNP 220±25 (DLS) n/a 0-10 mg/L 92 days 5 mg/L or high led to 1) enhanced N removal; 2) enhanced denitrification enzyme activity, 3) increased number of denitrifiers; 4) decreased glycogen metabolism Chen et al, 2012
NZVI n/a Zero charge 20, 50 and 200 mg/L 10 hrs 200 mg/L inhibited ammonia removal and increased LDH release; no significant effects at 50 mg/L and below Wu et al, 2013
NZVI & AgNP mixture
35 (nominal) 60 (DLS)
n/a
5, 50 and 100 mg/L
60 days
Nitrification inhibition at 100 mg/L, slight decrease in AMO and NOR activity
Yazdanbakhsha et al, 2019