RESULTS AND DISCUSSION
4.1 PERFORMANCE OF SEQUENTIAL ANAEROBIC–ANOXIC–AEROBIC CONTINUOUS MOVING BED REACTOR (CMBR) SYSTEM
4.1.4.3. Effect of varied influent ammonia concentration on aerobic CMBR (R3)
Figure 4.29 Error in sulfate generation against thiocyanate removal rate in R2
y = 951.82x - 47.138 R2 = 0.9739
0 50 100 150 200 250
0.00 0.05 0.10 0.15 0.20 0.25 0.30
Thiocyanate removal rate (g/L.day) Error in sulfate generation (mg/L)
During the study, in R2, 415–460 mg/L sulfate evolved as byproduct from SCN– biodegradation however, sulfate generation was lower to the theoretical sulfate generation value throughout the study. Figure 4.29 shows increase in error of sulfate generation with thiocyanate removal rate in R2. During other studies with feed thiocyanate, HRT and feed phenol variation also the error was observed to be higher in R2 while R2 was showing higher thiocyanate removal rate. Other sulfur compound might have accumulated in R2 rather than sulfate/sulfide as earlier reported (Buisman et al. 1990; Mahmood et al. 2008).
ammonia removal rate of 0.28 g/L.day at NH4+–N loading rate of ~0.33 g/L.day was observed in a fluidized bed aerobic reactor from wastewater containing phenol, SCN– and CN– and NH4+–N and COD of 2500 mg/L (Jeong et al. 2006b).
Figure 4.30 Performance of R3 at varied NH4
+-N loading 0
20 40 60 80 100
0.0 0.1 0.1 0.2 0.2 0.3 0.3
NH4
+-N loading (g/L.day)
Removal (%)
0.00 0.05 0.10 0.15 0.20 0.25
Removal rate (g/L.day)
Removal Rate
Table 4.12 (a): Performance of R3 at feed NH4+–N concentration variation NH4+–N NO3––N NO2–
-N Feed
NH4+–
N S0# Se Rem S0 Se Se
NR FA UN COD
: NH4+
–N
TVS pH
100 110 25
(0)
77.27 190 200 (12)
65 (0)
0.06 4.2 7 3.8 11658 8.4
±0.2
300 221 40
(0)
81.82 189 240 (21)
80 (0)
0.09 8.9 22 2.3 11700 8.4
±0.2
500 324 48
(2.5)
85.09 173 247 (12)
100 (0)
0.12 24.6 28 2.0 12280 8.4
±0.2
600 380 65
(7.8)
82.86 131 270 (48)
118 (0)
0.17 28.0 9 1.8 12900 8.4
±0.2 S0: Influent (mg/L), Se: Effluent (mg/L), Rem: Removal (%), Gen: Generation (mg/L)
# Influent NH4+–N of R3 = {Effluent NH4+–N of R2 + 0.24x (SCN– removed in R3)};
NR: Nitrification rate (g/L.day);
FA: Free ammonia (mg/L); UN: Unaccounted nitrogen (%) Numbers in parenthesis indicate standard deviation values
The respective nitrification rate (generation of NOx––N) in R3 was 0.06–0.17 g/L.day, which increased with increase in NH4+–N loading rate. Though both the nitrification rate and NH4+–N removal rate in R3 increased with increase in NH4+–N loading rate, nitrification rate was found to be lower to NH4+–N removal rate. Some nitrogen might got lost from the reactor through incorporation to biomass or by volatilization shown as unaccounted nitrogen. In the present study, R3 received NH4+–N concentration of 380 mg/L, higher than reported threshold inhibitory concentration of 350 mg/L for nitrifying bacteria (Kim et al. 2008b) only during the experiment with initial feed of 600 mg/L NH4+–N. Accumulation of nitrite in R3 was observed and it increased from 65 mg/L to 118 mg/L with increase in influent ammonia. R3 was responsible for only 0.25–4.0% nitrogen removal [Figure 4.28 (b)] as R3 mainly contributed nitrification of NH4+–N rather than nitrogen removal from the system. FA concentration in R3 was found to increase from 4–
28 mg/L with increase in feed NH4+–N and pH in the reactor [Table 4.12(a)].
Influent COD to R3 was 428–670 mg/L with loading of 0.285–0.446 g COD/L.day. COD removal remained almost constant at 63–65% with varied loading of NH4+–N in R3. COD removal rate in R3 increased from 0.187 g/L.day to 0.283 g/L.day with increase in feed NH4+–N and COD loading. Maximum COD removal rate observed in R3 was 0.291 g/L.day at COD and NH4+–N concentration of 666 and 324 mg/L, respectively during this study. Vázquez et al. (2006a) reported maximum COD removal rate of 0.76 g/L.day (removal of 58%) in an aerobic suspended growth reactor at influent COD of 1012 mg/L and maximum SCN– degradation rate was 0.019 g/L.day at influent SCN– of 210 mg/L in presence of phenol and NH4+–N. The COD to influent NH4+–N ratio in R3 decreased from 3.88–1.76 with increase in influent NH4+–N to R3. Total biomass observed during the study that increased from 11658 mg/L to 12900 mg/L with increase in influent COD and NH4+–N indicating the biomass was capable of tolerating the toxicity exerted by the pollutants in the present study. Suspended biomass concentration in R3 was observed to increase from 3000–4900 mg/L through out the study and attached biomass was 8600 mg/L up to influent NH4+–N 324 mg/L and then decreased slightly to 7900 mg/L when influent NH4+–N was maximum of 380 mg/L.
Phenol removal in R3 was almost 50–93% releasing ~ 1 mg/L phenol in all the cases of The influent phenol to R3 was only 2–15 mg/L with phenol loading of 0.001–0.01 g/L.day.
influent NH4+–N and it seemed that NH4+–N concentration up to 380 mg/L did not affect phenol degradation in R3 in present condition. Dyreborg and Arvin (1995) reported that pseudo–critical concentration of phenol was 3.7 mg/L for nitrifying bacteria.
Table 4.12 (b): Performance of R3 at feed NH4+
–N concentration variation NH4+–
N
Phenol COD SCN– SO42–
S0 S0 Se Rem S0 Se Rem S0 Se Rem S0 Se Gen Th.
SO42
–
Err
110 2 1
(0)
50 428 147
(7.5)
65.65 2 0 (0)
100 938 950 (10)
12 3 9
221 5 1
(0)
80 513 190
(12)
62.96 5 1 (0)
80 920 930 (15)
10 7 3
324 5 1
(0)
80 666 230
(13.4)
65.47 10 1 (0)
89 888 907 (11)
19 14 5
380 15 1
(0)
93 670 245
(13)
63.43 40 2 (0)
95 880 930 (15)
50 62 –8
S0: Influent (mg/L), Se: Effluent (mg/L), Gen: Generation (mg/L), Err: Error (mg/L);
Th. SO42–: Theoretical sulfate generation {1.65*(SCN–removed)};
Numbers in parenthesis indicate standard deviation values.
Influent thiocyanate to R3 was 2–40 mg/L and R3 efficiently removed influent thiocyanate releasing 0–2 mg/L thiocyanate in effluent. SCN− loading to R3 was 0.001 to 0.026 g/L.day and removal efficiencies were 80–100% with effluent SCN– from 0–2 mg/L. With increase in influent NH4+–N to 110–379 mg/L, SCN−removal efficiency was not affected in R3 and it satisfactorily removed the SCN–. High NH4+–N removal from high NH4+–N concentration suggested that there was very little or no inhibition by phenol, SCN– and NH4+–N on nitrification and vice versa in present study. Maximum SCN–degradation rate observed in R3 was 0.025 g/L.day at maximum loading of 0.026 g SCN–/L.day. SCN– degradation rates of 0.2 and 5.0 g/L.day, respectively in aerobic suspended growth and fluidized bed reactor were observed by Hung and Palvostathis, (1997) and Jeong and
Chung, (2006a). In a suspended growth aerobic reactor maximum SCN– degradation rate was reported as 0.019 g/L.day at influent SCN– of 210 mg/L in presence of phenol and NH4+–N by Vázquez et al. (2006a) which is close to SCN– degradation rate observed in the present investigation. Banerjee (1996) observed maximum SCN– degradation rate of 0.2 g/L.day in a rotating biological contactor in presence of phenol. However in present study R3 received very low amount of SCN–than reported inhibitory value of 200 mg/L in its influent and successfully removed the same (Kim et al. 2008b).
In presence of varied influent NH4+-N, 3–62 mg/L sulfate evolved in R3 as byproduct from SCN– biodegradation along with NH4+–N. During the study, sulfate generation was similar to the theoretical sulfate generation value with low error [Table 4.12 (b)].