Alice Antony

Bioanalytical assessment of the formation of disinfection byproducts in a drinking water treatment plant

Disinfection of drinking water is the most successful measure to reduce water-borne diseases and protect health. However, disinfection byproducts (DBPs) formed from the reaction of disinfectants such as chlorine and monochloramine with organic matter may cause bladder cancer and other adverse health effects. In this study the formation of DBPs through a full-scale water treatment plant serving a metropolitan area in Australia was assessed using in vitro bioanalytical tools, as well as through quantification of halogen-specific adsorbable organic halogens (AOXs), characterization of organic matter, and analytical quantification of selected regulated and emerging DBPs. The water treatment train consisted of coagulation, sand filtration, chlorination, addition of lime and fluoride, storage, and chloramination. Nonspecific toxicity peaked midway through the treatment train after the chlorination and storage steps. The dissolved organic matter concentration decreased after the coagulation step and then essentially remained constant during the treatment train. Concentrations of AOXs increased upon initial chlorination and continued to increase through the plant, probably due to increased chlorine contact time. Most of the quantified DBPs followed a trend similar to that of AOXs, with maximum concentrations observed in the final treated water after chloramination. The mostly chlorinated and brominated DBPs formed during treatment also caused reactive toxicity to increase after chlorination. Both genotoxicity with and without metabolic activation and the induction of the oxidative stress response pathway showed the same pattern as the nonspecific toxicity, with a maximum activity midway through the treatment train. Although measured effects cannot be directly translated to adverse health outcomes, this study demonstrates the applicability of bioanalytical tools to investigate DBP formation in a drinking water treatment plant, despite bioassays and sample preparation not yet being optimized for volatile DBPs. As such, the bioassays are useful as monitoring tools as they provide sensitive responses even at low DBP levels.

Comparison of treatment options for removal of recalcitrant dissolved organic matter from paper mill effluent.

Recycling paper mill effluent by conventional water treatment is difficult due to the persistence of salt and recalcitrant organics. Elimination of dissolved organic matter (DOM) from paper mill effluent was studied using three treatment options, ion exchange resin (IER), granular activated carbon (GAC) and nanofiltration (NF). The removal efficiency was analysed based on hydrophobicity, molecular weight and fluorogenic origin of the DOM fractions. For IER, GAC and NF treatments, overall removal of dissolved organic carbon was 72%, 76% and 91%, respectively. Based on the hydrophobicity, all the three treatment methods majorly removed hydrophobic acid fractions (HPhoA). Further, IER acted on all fractions, 57% of HPhoA, 44% of transphilic acid and 18% of hydrophilics, substantiating that the removal is by both ion exchange and adsorption. Based on the molecular weight, IER and GAC treatments acted majorly on the high molecular weight fractions, whereas NF eliminated all molecular weight fractions. After GAC adsorption, some amount of humic hydrolysates and low molecular weight neutrals persisted in the effluent. After IER treatment, amount of low molecular weight compounds increased due to resin leaching. Qualitative analysis of fluorescence excitation emission matrices showed that the fulvic acid-like fluorophores were more recalcitrant among the various DOM fractions, considerable amount persisted after all the three treatment methods. Three treatment methods considerably differed in terms of removing different DOM fractions; however, a broad-spectrum process like NF would be needed to achieve the maximum elimination.

Removal Efficiency and Integrity Monitoring Techniques for Virus Removal by Membrane Processes

Membranes are a mechanical form of disinfection that works by physical separation of the target pathogen. In theory, an intact membrane is a barrier to pathogens that are larger in size than the pore size of the membrane. However, in practice the pore size distribution or molecular weight cutoff will provide an indication of the separation efficiency and in many cases complete rejection of the virus is not demonstrated by various membrane processes. The general mechanism of pathogen removal by membrane processes is predominantly achieved by size exclusion, influenced by the physicochemical properties of the membrane, surface properties of the pathogens, and the solution environment. However, in order to evaluate the intrinsic performance of the membranes for a specific objective, a standard protocol with defined set of operating conditions is required. Any anomaly with the membrane surface (e.g., abnormally big pores, compromised glue line, holes) and the filtration system (e.g., compromised O-rings, broken mechanical seals) will result in microbial contamination risk of the product water. Therefore, monitoring membrane treatment system integrity is essential for the protection of public health from microbial risk. The demand for real-time monitoring is increasing as the usage of membrane-processed water is on the rise. Monitoring membrane integrity can be achieved by regular noncontinuous direct integrity testing performed on the membrane itself, or continuous indirect tests carried out on the filtrate. These monitoring techniques provide ongoing assurance that the water quality objectives are continually met. Existing integrity monitoring techniques have been shown in various instances to be reliable and sensitive for detecting contaminants of 1.0 μm and larger, while enteric virus particles are in the size range 0.01–0.04 μm. Some of the indirect monitoring techniques are capable of detecting a membrane breach less than 1 μm, but the practical challenge resolution is typically around 1–2-log. Similarly, the process control monitoring parameters lack sensitivity and therefore virus breakthrough occurs even before a loss of integrity is detected. At present it is difficult to demonstrate virus removal without conducting challenge tests due to a lack of sufficiently sensitive process monitoring. On the other hand, regulators are under increasing pressure to grant log removal credits for enteric viruses to membrane treatment processes due to the inability of present integrity tests to verify ongoing removal of virus-sized particles. Therefore, finding reliable and sensitive integrity tests for viruses is a high-priority issue in the water treatment sector. The authors aim to review the present state of knowledge on the process efficiencies of virus removal by membrane processes and the associated membrane integrity monitoring practices for virus-sized particles. Some of the knowledge gaps and research needs associated with the existing guidelines and standing protocols for integrity monitoring are also identified.

Diagnosis of dissolved organic matter removal by GAC treatment in biologically treated papermill effluents using advanced organic characterisation techniques

Granular activated carbon (GAC) exhaustion rates on pulp and paper effluent from South East Australia were found to be a factor of three higher (3.62cf. 1.47kgm(-3)) on Kraft mills compared to mills using Thermomechanical pulping supplemented by Recycled Fibre (TMP/RCF). Biological waste treatment at both mills resulted in a final effluent COD of 240mgL(-1). The dissolved organic carbon (DOC) was only 1.2 times higher in the Kraft effluent (70 vs. 58mgL(-1)), however, GAC treatment of Kraft and TMP/RCF effluent was largely different on the DOC persisted after biological treatment. The molecular mass (636 vs. 534gmol(-1)) and aromaticity (5.35 vs. 4.67Lmg(-1)m(-1)) of humic substances (HS) were slightly higher in the Kraft effluent. The HS aromaticity was decreased by a factor of 1.0Lmg(-1)m(-1) in both Kraft and TMP/RCF effluent. The molecular mass of the Kraft effluent increased by 50gmol(-1) while the molecular mass of the TMP/RCF effluent was essentially unchanged after GAC treatment; the DOC removal efficiency of the GAC on Kraft effluent was biased towards the low molecular weight humic compounds. The rapid adsorption of this fraction, coupled with the slightly higher aromaticity of the humic components resulted in early breakthrough on the Kraft effluent. Fluorescence excitation-emission matrix analysis of the each GAC treated effluent indicated that the refractory components were higher molecular weight humics on the Kraft effluent and protein-like compounds on the TMP/RCF effluent. Although the GAC exhaustion rates are too high for an effective DOC removal option for biologically treated pulp and paper mill effluents, the study indicates that advanced organic characterisation techniques can be used to diagnose GAC performance on complex effluents with comparable bulk DOC and COD loads.

Evaluation of ion exchange resins for the removal of dissolved organic matter from biologically treated paper mill effluent

In this study, the efficiency of six ion exchange resins to reduce the dissolved organic matter (DOM) from a biologically treated newsprint mill effluent was evaluated and the dominant removal mechanism of residual organics was established using advanced organic characterisations techniques. Among the resins screened, TAN1 possessed favourable Freundlich parameters, high resin capacity and solute affinity, closely followed by Marathon MSA and Marathon WBA. The removal efficiency of colour and lignin residuals was generally good for the anion exchange resins, greater than 50% and 75% respectively. In terms of the DOM fractions removal measured through liquid chromatography-organic carbon and nitrogen detector (LC-OCND), the resins mainly targeted the removal of humic and fulvic acids of molecular weight ranging between 500 and 1000 g mol(-1), the portion expected to contribute the most to the aromaticity of the effluent. For the anion exchange resins, physical adsorption operated along with ion exchange mechanism assisting to remove neutral and transphilic acid fractions of DOM. The column studies confirmed TAN1 being the best of those screened, exhibited the longest mass transfer zone and maximum treatable volume of effluent. The treatable effluent volume with 50% reduction in dissolved organic carbon (DOC) was 4.8 L for TAN1 followed by Marathon MSA - 3.6L, Marathon 11 - 2.0 L, 21K-XLT - 1.5 L and Marathon WBA - 1.2 L. The cation exchange resin G26 was not effective in DOM removal as the maximum DOC removal obtained was only 27%. The resin capacity could not be completely restored for any of the resins; however, a maximum restoration up to 74% and 93% was achieved for TAN1 and Marathon WBA resins. While this feasibility study indicates the potential option of using ion exchange resins for the reclamation of paper mill effluent, the need for improving the regeneration protocols to restore the resin efficiency is also identified. Similarly, care should be taken while employing LC-OCND for characterising resin-treated effluents, as the resin degradation is expected to contribute some organic carbon moieties misleading the actual performance of resin.

Influence of nitrones on corrosion inhibition and hydrogen permeation through mild steel in acidic solutions

A few nitrones such as N‐benzilidene aniline‐N‐oxide, N‐(O‐hydroxy benzilidene) aniline‐N‐oxide (HN) and N‐(α‐naphthylidene) aniline‐N‐oxide (NN) have been synthesised and investigated for evaluating their efficiency as inhibitors for the corrosion of mild steel in 1M HCl at different concentrations of nitrones ranging from 0.025‐1.0mM and at different temperatures ranging from 30‐70°C. Among these compounds NN gives the best performance even at higher temperatures. Potentiodynamic polarisation studies reveal the fact that all compounds behave as mixed type inhibitors. Hydrogen permeation studies reveal the fact that all the compounds bring down the permeation current. The absorption of these compounds on the mild steel surface from 1M HCl obeys Temkin’s absorption isotherm.

Evaluating the impact of recycled fiber content on effluent recycling in newsprint manufacture.

This paper investigates the effect of using recycled fiber (RCF) in newsprint production on the effluent quality and its treatability using membrane operations for internal and external recycling and reuse. Increased chemical usage in RCF for deinking had significant impact on the silica and sodium content of the effluent which in turn limits the membranes operation. Increasing the RCF content from 0% to 50% is estimated to increase the silica content from 4 to 119mgL(-1) and sodium content from 135 to 500mgL(-1). A process model was developed to calculate the impact of these excess chemicals on the greenhouse gas (GHG) emission and brine disposal for an integrated membrane plant design producing 4MLday(-1) of recycled water. As the ratio of RCF increased from 0% to 50% in the mill process, the operating pressure increased for nanofiltration (NF) and reverse osmosis (RO). Additionally, organics presence in the feed increased the NF operating pressure above the simulated value and reduced the silica removal efficiency by 15%. Incorporation of lime coagulation pretreatment was found to be essential to operate RO at high recoveries with relatively GHG emissions. Without pretreatment, as RCF content increased from 0% to 50%, RO recovery decreased from 80% to 22% and the expended GHG increased from 0.9 to 3.5kgCO2m(-3). Although the excess sodium concentration limits the brine disposal for irrigation purposes, a partial blending of the treated wastewater with other process streams resulted in the reduction of sodium absorption ratio by 20%.

Degradation of polymeric membranes in water and wastewater treatment

Abstract: This chapter reviews the mechanisms and attendant operating problems associated with degradation of polymeric membranes in water treatment applications. Information is presented on the possible modes of membrane failure and associated operational issues in full scale applications. Specific details of the degradation mechanism for various membrane polymers in different aqueous environments are presented, in addition to information on tools to monitor, detect and prevent membrane degradation.

Influence of substituent groups on performance of N-benzylidine phenylamine-N-oxide as corrosion inhibitor of mild steel in acidic solutions

AbstractN-benzylidine phenylamine-N-oxide (nitrone) and eight of its derivatives with substituents in the para position of the α phenyl group were synthesised and their inhibition of the corrosion of mild steel in 1M HCl was investigated by weight loss, potentiodynamic polarisation studies, hydrogen permeation measurements, and impedance measurements. Determination of inhibition efficiency in the presence of these compounds at different temperatures clearly indicates that the dimethyl derivative shows the best performance even at temperatures as high as 70°C. Potentiodynamic polarisation studies clearly reveal the fact that nitrone and its derivatives act as mixed type inhibitors. All of these compounds are found to reduce the permeation of hydrogen through mild steel in HCl solution. Values of double layer capacitance and charge transfer resistance were derived from Nyquist plots obtained from ac impedance studies. The adsorption of these compounds on the mild steel surface obeys Temkins adsorption isot...