Nihar Biswas

Removal of phenolic compounds from synthetic wastewater using soybean peroxidase

Abstract Experiments were conducted to investigate the efficiency of using soybean peroxidase (SBP) to remove several different phenolic compounds from unbuffered synthetic wastewater. The phenol derivatives studied included parent phenol, chlorinated phenols, cresols, 2,4-dichlorophenol and 4,4′-isopropylidenediphenol (commonly known as bisphenol A). Optimum conditions to achieve at least 95% removal of these compounds were determined for the following parameters: pH, SBP dose in the absence and presence of polyethylene glycol (PEG), hydrogen peroxide to substrate ratio, and PEG dose. Experimental results showed that SBP efficiently removed aromatic compounds from synthetic wastewater in the presence of hydrogen peroxide. An increase in the hydrogen peroxide to substrate ratio beyond the optimum resulted in enzyme inactivation in all cases except for bisphenol A. The optimum pH for different phenolic compounds ranged from 5.5 to 8. For each substrate, the optimum enzyme dose in the presence of PEG varied significantly. The studies showed that PEG only slightly reduced the amount of SBP required for 95% removal of the substrate. For most of the substrates, an increase in PEG dose beyond the optimum dose did not significantly change the removal efficiency.

A model for the Protective Effect of Additives on the Activity of Horseradish Peroxidase in the Removal of Phenol

Horseradish peroxidase has been proven effective in removing phenolic compounds in wastewater and additives such as polyethylene glycol have been found very effective in reducing the minimum enzyme dose required. The effect of additives on horseradish peroxidase-catalyzed removal of phenol was investigated in this study. In the absence of additive, active enzyme is predominantly inactivated by the polymer product formed during the reaction. The specific activity of horseradish peroxidase is higher due to the presence of additive. Experiments suggest that additives combine with the polymerization products formed during the reaction, because additives have a higher partition affinity with the polymer products than peroxidases. Most of the polymer product is coupled with additive so that less enzyme interacts with the polymer product. Horseradish peroxidase still combines with polymer products and becomes inactivated but at a much slower rate when additives are present. Consequently, the enzyme activity is protected by the additives.

REACTOR DEVELOPMENT FOR PEROXIDASE CATALYZED POLYMERIZATION AND PRECIPITATION OF PHENOLS FROM WASTEWATER

Abstract Horseradish peroxidase enzyme catalyzes the oxidation of toxic aromatic compounds, especially phenols and aromatic amines, in the presence of hydrogen peroxide. The reaction products polymerize to form high molecular weight materials which readily precipitate from solution; hence, providing a means for the treatment of wastewaters which contain aromatic compounds. The catalytic lifetime of horseradish peroxidase enzyme can be extended by optimizing treatment conditions such as pH and temperature and by maintaining a low instantaneous enzyme concentration in the reaction mixture. The enzyme catalyzed polymerization process was implemented in a continuous stirred tank reactor (CSTR) configuration because reactant and enzyme concentrations are lowered immediately upon entering the reactor causing a reduction in inactivation of HRP through free radical bonding and compound III formation. Catalytic turnovers achieved in single and multiple CSTRs in series were significantly higher than those observed in batch reactors when sufficient retention time was provided.

Comparison of additives in the removal of phenolic compounds by peroxidase-catalyzed polymerization

Several additives, polyethylene glycol, gelatin and some polyelectrolytes, were studied to compare their behaviour in the removal of phenolic compounds from aqueous solution by horseradish-peroxidase-catalyzed polymerization. The effects of additives on optimum pH range, horseradish-peroxidase saving, reaction stoichiometry and minimum additive requirements were investigated. The fate of additive after reaction was also studied. The experimental results showed that all tested additives significantly reduced the horseradish-peroxidase requirement. Comparison among them revealed that polyethylene glycol was the best choice from all perspectives. It saved more peroxidase and had no negative overdose effect shown by gelatin and polyelectrolytes. At minimum polyethylene glycol dose, there was little polyethylene glycol remaining in solution after completion of reaction. However, a considerable amount of gelatin remained in solution even at the minimum gelatin dose. Also, gelatin produced more precipitate than polyethylene glycol.

Sulfide Production by Sulfate Reducing Bacteria with Lactate as Feed in an Upflow Anaerobic Fixed Film Reactor

The sulfate reducing bacteria (SRB) have the capability of reducing sulfate (SO4-2) under anaerobic conditions into sulfide (S-2) which can precipitate metals as metal sulfides. The optimum conditions for sulfide production by SRB utilizing lactate, in an upflow anaerobic fixed film reactor (UAFFR) were not previously established. The main objective of this research was to investigate these conditions for the growth of SRB to ensure the highest sulfide production under consistent behaviour of the system. Substrate containing lactate as the organic carbon source along with sulfate, nitrogen and phosphorus as the required nutrients was used as a feed to the UAFER which was seeded with SRB. It was found that an optimum sulfide production occurred with an organic loading rate (OLR) of 6 kg d-1 m-3, while the theoretical oxygen demand to sulfate ratio (ThOD/SO4) ranged from 1.5 to 2.25. Also, the optimum total nitrogen and phosphorus demands were determined to be about 250 and 50 mg L-1 respectively. A total nitrogen concentration above 600 mg L-1 started showing toxicity and lowered the sulfide production. The optimum ThOD:N:P for sulfide production and growth of SRB in the UAFFR was 100:5:1 under optimum conditions.

A Short Review of Techniques for Phenol Removal from Wastewater

Phenolic compounds are priority pollutants with high toxicity even at low concentrations. In this review, the efficiency of both conventional and advanced treatment methods is discussed. The applicability of these treatments with phenol and some common derivatives is compared. Conventional treatments such as distillation, absorption, extraction, chemical oxidation, and electrochemical oxidation show high efficiencies with various phenolic compounds, while advanced treatments such as Fenton processes, ozonation, wet air oxidation, and photochemical treatment use less chemicals compared to the conventional ones but have high energy costs. Compared to physico-chemical treatment, biological treatment is environmentally friendly and energy saving, but it cannot treat high concentration pollutants. Enzymatic treatment has proven to be the best way to treat various phenolic compounds under mild conditions with different enzymes such as peroxidases, laccases, and tyrosinases. This review covers papers from 2013 through January 2016.

Immobilized enzyme catalyzed removal of 4-chlorophenol from aqueous solution

Abstract The ability of horseradish peroxidase enzyme attached on three different reactor matrices: cellulose filter paper, nylon balls and nylon tubing, to remove 4-chlorophenol from aqueous solution is evaluated. The enzymatic reaction is extremely fast and the reaction products remained on the reactor matrix. Detachment or release of the reaction products from the reactor matrix is not observed. Results indicate that, over 80% removal efficiency can be obtained as long as enzyme activity is not limiting in the reactor. Systematic recycle batch reactor studies reveal that, initial reaction rates exhibit saturation with substrate concentration under conditions of excess peroxide. Inactivation of enzyme active sites by reaction intermediates is observed in the reactor studies. Immobilized peroxidase also catalyzes the oxidation of other chlorophenols and cresols.

Optimization of phenol removal by a fungal peroxidase from Coprinus macrorhizus using batch, continuous, and discontinuous semibatch reactors

Abstract The use of a peroxidase from the fungus Coprinus macrorhizus for the removal of toxic organics from synthetic wastewater is explored in this study. Removal of phenols demonstrated a dependence of enzyme lifetime on enzyme concentration in batch reactors. Maximum removal of phenol under optimal conditions in a batch reactor at enzyme activity above 0.3 U ml −1 and up to 1.2 U ml −1 was 53% in the present study. Continuous addition of C. macrorhizus peroxidase (CMP) to the reactor over periods varying from 0.5 to 3 h did not improve the removal. Similarly, continuous addition of H 2 O 2 did not improve the removal of phenol. A colorimetric assay for H 2 O 2 indicated its depletion in the batch reactors. H 2 O 2 : phenol stoichiometry was greater than one if all the H 2 O 2 was added at the beginning of the reaction. Instability of the H 2 O 2 and possible decomposition by contaminating catalase in the sample preparation are two possibilities for its depletion. To overcome this depletion in the reactors regardless of the enzyme concentration, discontinuous addition of either CMP or H 2 O 2 or both was adopted. Significant improvement in phenol removal (90%) was obtained when either H 2 O 2 or CMP was added in three discrete aliquots over 0.5 h. With discontinuous addition of both reactants, the amount of CMP could be reduced to 0.3 U ml −1 while achieving 91% removal of phenol at equimolar concentration of H 2 O 2 . Thus, discontinuous addition of the reactant(s) increased the turnovers obtained by CMP and conserved the 1 : 1 phenol to peroxide stoichiometry in the clearance reaction. Spectral observation of the CMP utilized in this study showed the presence of a contaminating cyanide-like complex of the enzyme, as was observed by another group using a similar microbial peroxidase.

Removal of oil from emulsions using electrocoagulation

An attempt has been made to remove oil from synthetic oily wastes using electrochemical treatment. The standard jar test apparatus was used with ferric sulfate as coagulant. The effects of alternating and direct current were evaluated in terms of coagulant aid in the oil removal process. The removal efficiency was found to be as high as 96% using 150 mg/L of ferric sulphate and a direct current of 100 V applied for 16 minutes. The polarity of the electrodes and the electric field gradient played an important role in the destabilization of oil emulsion.

Revisiting turbulence in smooth uniform open channel flow

This study reexamines the mean velocity scaling as well as higher order turbulent moments in a uniform smooth open channel flow with three different aspect ratios. In the overlap region, the velocity profiles follow the classical logarithmic law. In the outer region, the mean velocity data at various aspect ratios collapse on to each other only when the length scale is suitably modified. This length scale is defined on the basis of a region of constant turbulence intensity close to the free surface and is equal to the depth of flow at large aspect ratios. The proposed new length scaling also provides for a positive value of the wake parameter. Furthermore, turbulence distributions including that of the Reynolds shear stress, and triple correlations and collapse onto a single line making them nearly independent of aspect ratio. Quadrant decomposition of the velocity data was used to quantify the differences in the turbulence structure at the three channel aspect ratios. The quadrant analysis shows that the turbulence in open channel is similar to that in both turbulent boundary layers and flow in two-dimensional channels when all turbulent events are included. When only the extreme events are considered, differences between open channel flow and turbulent boundary layers become significant. The conditional quadrant analysis reveals that the violent ejections do penetrate into the flow and they are responsible for producing large portion of the Reynolds shear stress. Some effects of aspect ratio are revealed when the ratio of the ejection to sweep events are calculated. The turbulent events with the higher aspect ratios tend to be closer to the two-dimensional channel data.