Saswati Chakraborty

Fixed-bed column study for hexavalent chromium removal and recovery by short-chain polyaniline synthesized on jute fiber.

Fixed-bed column studies were conducted to evaluate performance of a short-chain polymer, polyaniline, synthesized on the surface of jute fiber (PANI-jute) for the removal of hexavalent chromium [Cr(VI)] in aqueous environment. Influent pH, column bed depth, influent Cr(VI) concentrations and influent flow rate were variable parameters for the present study. Optimum pH for total chromium removal was observed as 3 by electrostatic attraction of acid chromate ion (HCrO(4)(-)) with protonated amine group (NH(3)(+)) of PANI-jute. With increase in column bed depth from 40 to 60 cm, total chromium uptake by PANI-jute increased from 4.14 to 4.66 mg/g with subsequent increase in throughput volume from 9.84 to 12.6L at exhaustion point. The data obtained for total chromium removal were well described by BDST equation till 10% breakthrough. Adsorption rate constant and dynamic bed capacity at 10% breakthrough were observed as 0.01 L/mgh and 1069.46 mg/L, respectively. Adsorbed total chromium was recovered back from PANI-jute as non-toxic Cr(III) after ignition with more than 97% reduction in weight, minimizing the problem of solid waste disposal.

A mechanistic insight into enhanced and selective phosphate adsorption on a coated carboxylated surface

Trimesic acid (benzene-1,3,5-tricarboxylic acid, TMA) coated on basic alumina surface showed a significant and selective adsorption of phosphate from aqueous solution. Focus has been given on the selective adsorption and recovery of phosphate from a wide pH range solution which is the major drawback of phosphate removal in the known literature methods. TMA coated alumina exhibited high adsorption efficiency even with low phosphate concentration (approximately 1.0 mg/L) as well as low pH (approximately 1.0). Moreover, probable mechanism of high and consistent phosphate immobilizing capacity throughout a broad pH range (pH approximately 1.0-8.0) is discussed in detail. Adsorbed phosphate could be desorbed completely from adsorbent surface by treating with high alkaline solution. Discussion of adsorption process with two kinetic models revealed a fast kinetic rate and preference of second order model. A competitive study with other anions (chloride, nitrate and bromide) exhibited a high selective removal of phosphate over other anions. Influence of pH and temperature were also studied. Adsorption followed Langmuir isotherm model mostly and was thermodynamically favorable at even higher temperature (50 degrees C).

Kinetic analysis of phenol, thiocyanate and ammonia-nitrogen removals in an anaerobic-anoxic-aerobic moving bed bioreactor system.

A simulated wastewater containing phenol (2500 mg/L), thiocyanate and ammonia-nitrogen (500 mg/L) was treated in an anaerobic (R1)-anoxic (R2)-aerobic (R3) moving bed biofilm reactor system at different hydraulic retention time (HRT) intervals (total HRT 3-8 days, R1: 1.5-4 days; R2: 0.75-2 days and R3: 0.75-2 days) and feed thiocyanate (SCN(-)) concentrations (110-600 mg/L) to determine substrate removal kinetics. In R1, phenol and COD reduction and specific methanogenic activity were inhibited due to the increase of SCN(-) in feed. Bhatia et al. model having inbuilt provision of process inhibition described the kinetics of COD and phenol utilization with maximum utilization rates of 0.398 day(-1) and 0.486 day(-1), respectively. In R2 and R3 modified Stover-Kincannon model was suitable to describe substrate utilization. In R2 respective maximum SCN(-), phenol, COD and NO(3)(-)-N utilization rates were 0.23, 5.28, 37.7 and 11.82 g/L day, respectively. In aerobic reactor R3, COD, SCN(-) and NH(4)(+)-N removal rates were, respectively, 10.53, 1.89, and 2.17 g/L day. The minimum total HRT of three-stage system was recommended as 4 days.

Anaerobic-anoxic-aerobic sequential degradation of synthetic wastewaters.

This study was conducted in a continuous three-stage system of anaerobic (R1)-anoxic(R2)-aerobic (R3) reactors with synthetic wastewater containing phenol (1000 mg/L), chemical oxygen demand (COD) (3000 mg/L), CN− (30 mg/L), SCN−(400 mg/L), and NH4+-N (600 mg/L) as principal pollutants and well-acclimated heterogeneous microbial cultures. The final effluent was partially returned to R2 with a recycle ratio of 1. Anaerobic stage served to detoxify the feed by removing up to 80% of cyanide. Complete SCN− removal and denitrification could be achieved in the anoxic stage by utilizing phenol as an internal source of carbon. Nitrification efficiency of 93% was obtained in the aerobic reactor. The results demonstrated that the three-stage system can give the desired final treated effluent quality (0 mg/L of phenol, 0.2 mg/L of CN−, 210 mg/L of COD, and 20 mg/L of NH4+-N) and that the NO3−-N concentration can be lowered by a higher recycle ratio.

Trimesic acid coated alumina: an efficient multi-cyclic adsorbent for toxic Cu(II).

Biodegradable and eco-friendly organic acid, benzene-1,3,5-tri-carboxylic acid (trimesic acid), coated on commercial basic alumina, was used as adsorbent to remove toxic Cu(II) ion from aqueous solution. Adsorbent preparation was optimized and was characterized by SEM, EDX, FT-IR, and powder XRD pattern. Effect of various regulating parameters like reaction pH, adsorbent dose and initial Cu(II) concentration was studied in detail. Adsorption isotherms followed the Langmuir isotherm model and adsorption was thermodynamically favourable. Maximum adsorption capacity (Qm) for Cu(II) ion has been achieved as 10.80 mg/g. Detail kinetic study revealed that it followed second-order rate. Desorption of Cu(II) ion and re-usability of the adsorbent was also studied.

A comparative metal ion adsorption study by trimesic acid coated alumina: A potent adsorbent

Benzene-1,3,5-tri-carboxylic acid (trimesic acid, TMA) coated on basic alumina has been shown to be an effective adsorbent for Fe(III) and Fe(II) from aqueous solution. A comparative study on the adsorption of Fe(III) and Fe(II) revealed that TMA coated alumina is more selective towards Fe(III) than Fe(II). The maximum adsorptions of Fe(III) and Fe(II) were 26.6 mg/g and 8.4 mg/g, respectively. Fe(III)/Fe(II) adsorption was also compared in some cases with adsorption of Co(II) and Ni(II). Maximum uptakes (Qm) for Co(II) and Ni(II) were found much lower (approximately 1 mg/g) than Fe(III)/Fe(II). pH dependent studies have revealed that Fe(III) was adsorbed efficiently at high acidic condition (pH approximately 1.5) compared to Fe(II), Co(II) and Ni(II), while temperature did not have significant effect on the adsorption processes. Adsorption of Fe(III) and Fe(II) was quite rapid and thermodynamically favourable. Adsorption processes fitted well in Langmuir isotherm model and followed second order rate kinetics in all cases.

Stability of continuous and fed batch sequential anaerobic–anoxic–aerobic moving bed bioreactor systems at phenol shock load application

ABSTRACT The stability of two sequential moving bed bioreactor systems operated in anaerobic–anoxic–aerobic continuous moving bed bioreactor (CMBR: R1–R2–R3) and semi-continuous fed batch moving bed bioreactor (FMBR: B1–B2–B3) modes was assessed for phenol shock load (PSL) applications in the presence of thiocyanate and ammonia. Both the systems were exposed to 3000 mg phenol/L (PSL-I) and 3500 mg phenol/L (PSL-II) for 3 days each from initial 2500 mg phenol/L without any intermediate concentration at 6 days HRT (hydraulic retention time). The effect of PSL-I on R1 was reversible within 10–12 days. At PSL-II, R1 required 2 days stop of feed for stability and resumed removal efficiency of phenol (15%) and COD (3%). R2 remained robust to sustain both PSLs and recovered within 15 days from peak influent concentrations of 1727 mg phenol/L (removal: 67%) and 324 mg SCN−-/L (removal: 68–70%). In B1, effluent COD increased by 2%, though effluent phenol decreased by 3% than the pre-shock condition after PSL-I exposure. B2 acted similar to R2 when exposed to PSLs. The effect of PSL-I on R3 and B3 was negligible. However, at PSL-II R3 became vulnerable for nitrification, whereas phenol, COD and SCN− removal remained unaffected. In B3, PSL-II caused a decrease in phenol, SCN− and NH+4−N removal. In B3, stop of feed for 4 days also did not improve nitrification. The performance of the CMBR system was better than that of the FMBR system for organic shock load exposure in the presence of multiple pollutants.

Pyridine influence on a sequential anaerobic–anoxic–aerobic FMBR system for phenol, thiocyanate and ammonia removal

ABSTRACT A synthetic wastewater containing various pyridine concentrations (25–250 mg/L) was treated in a sequential anaerobic(B1)–anoxic(B2)–aerobic(B3) fed batch moving bed reactor (FMBR) system. Pyridine was associated with phenol (1500 mg/L), SCN− (800 mg/L), chemical oxygen demand (COD) (5400–5430 mg/L) and NH4+–N (500 mg/L) at hydraulic retention time (HRT) of 6 (B1: 3 days; B2 and B3: 1.5 days each) days. In B1, pyridine removal was 10–12% from influent concentration of 25–100 mg/L and beyond that, it was zero. Removal of phenol (53–39%) and COD (33–22%) occurred in B1, but pyridine above 50 mg/L inhibited both. In B2, 68–90% of pyridine removal occurred along with phenol (>98%), COD (>67%), SCN− (>85%) removal and denitrification. In B2, with an increase in pyridine loading removal rate of phenol, COD and nitrate increased, whereas SCN− removal decreased beyond pyridine loading of 0.031g/L day. In B3, nitrification decreased with high generation of free ammonia. Pyridine degradation in B1, B2 and B3 follows the Stover–Kincannon model with a maximum substrate removal rate of 111.1, 333.3 and 23.81 g/L day, respectively. Thiocyanate removal in B2 and ammonia removal in B3 follows the Bhatia inhibition model with a maximum substrate removal rate of 0.641 and 0.528/day, respectively. The overall efficiency of the FMBR system remained unaffected up to 250 mg pyridine/L at 6 days HRT.

Effect of air flow rate on development of aerobic granules, biomass activity and nitrification efficiency for treating phenol, thiocyanate and ammonium

The impact of air flow rate on aerobic granulation was evaluated for treating toxic multiple pollutants; phenol (400 mg L-1), thiocyanate (100 mg L-1) and ammonia nitrogen (100 mg L-1) by using three lab scale sequencing batch reactors (SBRs) (R1, R2 and R3). Larger granules (2938.67 ± 64.91 μm) with higher biomass concentration (volatile solids of 4.17 ± 0.09 g L-1), higher granule settling velocity (55.56 ± 1.36 m h-1) and lower sludge volume index (35.25 ± 1.71 mL gTSS-1) were observed at optimal air flow rate of 2.5 L min-1 (R2). Confocal laser scanning microscopic images illustrated the extended fluorescence for extracellular polymeric substances in R2. In R2, partial nitrification was achieved. Phenol was completely removed in all the reactors while partial removal of SCN- and no nitrification were observed with a decrease (1.5 L min-1) and an increase (3.5 L min-1) in air flow rates (R1 and R3, respectively). This study provides an experimental contribution to examine the effect of optimal combination of aeration and toxic multiple pollutants, governing characteristics and nitrification efficiency of granules along with SBR performance in an economic way in terms of optimal air supply.

Effects of cycle time and fill time on the performance of an anaerobic-anoxic-aerobic-fed batch moving-bed reactor.

Performance of a fed batch moving-bed reactor system arranged in anaerobic (B1)–anoxic (B2)–aerobic (B3) mode was investigated using cycle time (18–36 h), gradual fill time (total 5–18.5 h; B1: 1–3.7 h; B2 and B3: 2–7.4 h each) and instantaneous fill time as variable parameters. During cycle time variation, total hydraulic retention time changed from 4.5 to 9 days (B1: 2.25–4.5 days; B2 and B3: 1.13–2.25 days each). Synthetic wastewater contained phenol (1500 mg/l), thiocyanate (SCN− 800 mg/l at gradual fill and 100 mg/l at instantaneous fill) and ammonia ( 500 mg/l). Phenol and chemical oxygen demand (COD) removals in B1 increased with increase in cycle time and gradual shorter filling showed higher performance than gradual long filling and instantaneous filling. In B2, simultaneous removals of phenol, SCN, COD and -N were achieved and effects of cycle time and fill times were not profound. In B3, removal efficiency increased with increase in both cycle time and gradual fill time. The minimum cycle time of 30 h and total hydraulic retention time of 7.5 days and total fill time of 12.5 h were recommended. A modified Stover–Kincannon model showed the highest correlation for removal of substrates in B1, B2 and B3.