Nageswara N. Rao

Treatment of refractory organics from membrane rejects using ozonation

The reject water or retentate generated from membrane application for recovery of water from tannery wastewater treatment contains certain refractory organics. These refractory organics are present in substantial quantity in the condensate of reject water also. Hence the treatment of rejects using conventional methods is rather difficult. In this paper, an attempt has been made to treat the reject water from the reverse osmosis (RO) and nano filtration (NF) operation on tannery wastewater using ozonation treatment technique. Ozonation studies on RO and NF rejects indicate that ozone dose of 80 and 100mg/min for 60 and 70 min contact time achieves 59 and 78% chemical oxygen demand (COD) reduction, respectively. The mass balance in ozone indicates the ozone consumption for RO and NF rejects varies from 2.4 to 3.4 and 2.8 to 4.5 g/g of COD removed respectively. The results suggest that ozonation of RO and NF rejects would significantly reduce the refractory organic pollutant loading into the environment from wastewater reuse facility.

Treatment of refractory nano-filtration reject from a tannery using Pd-catalyzed wet air oxidation

We attempted catalytic wet air oxidation (CWAO) of nanofiltration (NF)-reject using Pd based catalyst viz., Pd/activated charcoal (AC) and PdCl2 with the objective of degradation of refractory organic pollutants. Refractory organic pollutants in NF-reject before and after WAO and CWAO were confirmed by GC-MS analysis. Experiments were conducted to investigate the effects of temperature, catalyst dosage and air partial pressure on the rate of removal of total organic carbon (TOC). The reaction kinetics can be conveniently described by considering two-stage first order kinetics. The use of Pd/AC afforded 85% TOC removal, the corresponding rate constant (k) was 2.90 ± 0.075 × 10(-3)min(-1) (Pd/AC, 100mg/L; T, 473.15K; Pair, 0.69 MPa). On the other hand, 75% TOC was removed with k=2.31 ± 0.075 × 10(-3)min(-1) using Pd(2+) catalyst (Pd(2+), 16.66 mg/L; T, 473.15K; Pair, 0.69 MPa). The observed rate of mineralization under Pd-catalyzed conditions was significantly higher than that of the uncatalyzed oxidation (41%) under the similar experimental conditions. Catalyst stability experiments were performed and TEM, SEM, XRD, Raman and XPS characterization data collected. Despite some morphological transformation of support, Pd catalyst was stable under CWAO conditions.

Benzoylation for the recovery of structure directing agent (di-n-propylamine) from the process effluent of aluminophosphate synthesis

Di-n-propylamine (DPA), a structure directing agent for (silico)aluminophosphate (AlPO4) synthesis, is lost into the mother liquor (ML, 5–6 wt%) from the filtration step. A simple benzoylation reaction could recover DPA as N,N,-dipropylbenzamide (DPBA). The reaction also leads to the recovery of more AlPO4 and a decrease in the pollution caused by the ML.

Transformation of azo dyes during moist heat sterilisation: a potential source of error in microbial decolourisation

This paper presents the role of moist heat sterilisation in decolourisation of azo dyes during autoclaving itself, thereby leading to over estimation of actual decolourisation through subsequent microbial process. This surprise phenomenon was probed in detail by studying the effects of temperature, pressure and role of electron donor/carbon sources on decolourisation. In the presence of 10 g/litre glucose, 75% decolourisation of Reactive Black 5 (RB-5) dye was observed after autoclaving of medium at 121°C for 15 min at 15 psi. Studies repeated with other azo dyes revealed that Reactive Orange 16 (RO-16) was affected by autoclaving whereas Reactive Red 11 (RR-11) and Reactive Red 141 (RR-141) did not show significant decolourisation. The reduction of dye was dependent on concentration of electron donor/carbon source and autoclave conditions. The results indicate that investigators must screen the dyes for decolourisation during autoclaving and choose the appropriate means of sterilisation to remove the artifice or incorporate correction factor for dye concentration at the start of experiment.