Sri Chandana Panchangam

The impact of semiconductor, electronics and optoelectronic industries on downstream perfluorinated chemical contamination in Taiwanese rivers

This study provides the first evidence on the influence of the semiconductor and electronics industries on perfluorinated chemicals (PFCs) contamination in receiving rivers. We have quantified ten PFCs, including perfluoroalkyl sulfonates (PFASs: PFBS, PFHxS, PFOS) and perfluoroalkyl carboxylates (PFCAs: PFHxA, PFHpA, PFOA, PFNA, PFDA, PFUnA, PFDoA) in semiconductor, electronic, and optoelectronic industrial wastewaters and their receiving water bodies (Taiwans Keya, Touchien, and Xiaoli rivers). PFOS was found to be the major constituent in semiconductor wastewaters (up to 0.13 mg/L). However, different PFC distributions were found in electronics plant wastewaters; PFOA was the most significant PFC, contributing on average 72% to the effluent water samples, followed by PFOS (16%) and PFDA (9%). The distribution of PFCs in the receiving rivers was greatly impacted by industrial sources. PFOS, PFOA and PFDA were predominant and prevalent in all the river samples, with PFOS detected at the highest concentrations (up to 5.4 microg/L).

High levels of perfluorochemicals in Taiwan's wastewater treatment plants and downstream rivers pose great risk to local aquatic ecosystems.

We studied perfluorochemicals (PFCs) in the influents and effluents of two municipal wastewater treatment plants (MWWTPs) and in the effluents of an industrial wastewater treatment plant (IWWTP). The impact of IWWTP effluents on the receiving rivers (the Nanmen and Keya Rivers) was evaluated by measuring PFC levels in the surface waters of both rivers and the sediments of the Nanmen River. Perfluorooctane sulfonate (PFOS) (293 ng L(-1)) and perfluorohexanoic acid (406 ng L(-1)) were identified as the compounds present in greatest concentrations in the influents and effluents of both MWWTPs, which are largely influenced by domestic sources. High concentrations of PFCs (up to 1,0000 ng L(-1)) were found in IWWTP effluents and receiving rivers, with more perfluoroalkyl sulfonates (PFASs) found than perfluoroalkylcarboxylic acids (PFCAs). This study confirms the IWWTP as the point source of the persistent contamination of the Nanmen and Keya Rivers. Sediments of the Nanmen River were also impacted by IWWTP discharges, with high concentrations of PFOS (up to 9,0000 ng kg(-1)). PFCAs with longer carbon chains exhibited preferred partitioning onto the sediments. The occurrence of higher PFC concentrations in Taiwans aquatic media compared to other countries stresses the necessity for PFC risk management. Accordingly, a preliminary risk assessment was performed using the predicted no-effect concentration (PNEC) and indicative maximum permissible concentration (iMPC). The likelihood of ecological risk due to PFOS was plausible at a risk quotient of 1.21, as calculated using iMPC. Given our findings of high environmental PFC concentrations, rapid and meaningful steps should be taken to reduce entry of PFCs into Taiwans aquatic environment.

Decomposition of perfluorocarboxylic acids (PFCAs) by heterogeneous photocatalysis in acidic aqueous medium.

Decomposition of perfluorocarboxylic acids (PFCAs) is of prime importance since they are recognized as persistent organic pollutants and are widespread in the environment. PFCAs with longer carbon chain length are particularly of interest because of their noted recalcitrance, toxicity, and bioaccumulation. Here in this study, we demonstrate efficient decomposition of three important PFCAs such as perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA) and perfluorodecanoic acid (PFDA) by heterogeneous photocatalysis with TiO(2) as a photocatalyst in acidic aqueous solutions. The PFCAs were decomposed into shorter carbon chain length PFCAs and fluoride ions. Photoholes of excited TiO(2) generated upon UV-irradiation are found to be the oxidation sites for PFCAs. Therefore, creation and sustenance of these photoholes in the acidic aqueous medium has enhanced the decomposition of PFCAs. Heterogeneous photocatalytic treatment achieved more than 99% decomposition and 38% complete mineralization of PFOA in 7h. The decomposition of other PFCAs was as high as 99% with a defluorination efficiency of 38% for PFDA and 54% for PFNA. The presence of perchloric acid was found to enhance the decomposition by facilitating the ionization of PFCAs. The oxygen present in the medium served both as an oxidant and an electron acceptor. The mechanistic details of PFCA decomposition and their corresponding mineralization are elaborated.

Sonication-assisted photocatalytic decomposition of perfluorooctanoic acid.

Decomposition of perfluorinated chemicals is of significant interest in both scientific and industrial perspectives. Here, we report the decomposition of perfluorooctanoic acid (PFOA) under sonication-assisted photocatalysis by utilizing commercial TiO(2) (RdH) and home-made TiO(2) (sol-gel) as photocatalysts at ambient temperature, pressure and near neutral pH with the irradiation of 254nm UV light. PFOA was decomposed into fluoride ions and to several perfluorinated carboxylic acids (PFCAs) with a shorter carbon chain length such as perfluoroheptanoic acid (PFHpA), perfluorohexanoic acid (PFHxA), perfluoropropanoic acid (PFPA), and trifluoroacetic acid (TFA). The efficiency of sonication-assisted photocatalysis was found to be 64%. In all the cases, higher efficiencies were obtained when sol-gel TiO(2) was used as a photocatalyst than the commercial RdH TiO(2) catalyst. The specific surface area is three times higher for sol-gel TiO(2) than commercial RdH TiO(2) and appears to be the probable reason for the observed differences in the corresponding efficiencies. It is also interesting to note that pH plays a determining role in the decomposition of PFOA and correspondingly photocatalyses were carried out under different controlled pH. Perfluoroalkyl radicals are presumably oxidized by superoxide and hydroxyl radicals generated during the TiO(2)-mediated photocatalysis at pH 4 and 10, respectively. The role of sonication in sonication-assisted photocatalysis was construed to be an aid to photocatalysis than a tool itself. Sonication enhances photocatalysis through physical dispersion of TiO(2) and eases mass transfer which keeps on rejuvenating the TiO(2) surface.

Biodegradation and bio-sorption of antibiotics and non-steroidal anti-inflammatory drugs using immobilized cell process

In the present study, the removal mechanisms of four antibiotics (sulfamethoxazole, sulfadimethoxine, sulfamethazine, and trimethoprim) and four non-steroidal anti-inflammatory drugs (acetaminophen, ibuprofen, ketoprofen, and naproxen) in immobilized cell process were investigated using batch reactors. This work principally explores the individual or collective roles of biodegradation and bio-sorption as removal routes of the target pharmaceuticals and the results were validated by various experimental and analytical tools. Biodegradation and bio-sorption were found as dominant mechanisms for the drug removal, while volatilization and hydrolysis were negligible for all target pharmaceuticals. The target pharmaceuticals responded to the two observed removal mechanisms in different ways, typically: (1) strong biodegradability and bio-sorption by acetaminophen, (2) strong biodegradability and weak bio-sorption by sulfamethoxazole, sulfadimethoxine, ibuprofen and naproxen, (3) low biodegradability and weak bio-sorption by sulfamethazine and ketoprofen, and (4) low biodegradability and medium bio-sorption by trimethoprim. In the sorption/desorption experiment, acetaminophen, sulfamethoxazole and sulfadimethoxine were characterized by strong sorption and weak desorption. A phenomenon of moderate sorption and well desorption was observed for sulfamethazine, trimethoprim and naproxen. Both ibuprofen and ketoprofen were weakly sorbed and strongly desorbed.

Removal of perfluorooctanoic acid and perfluorooctane sulfonate via ozonation under alkaline condition.

The elimination of recalcitrant, ubiquitous perfluoroalkyl acids (PFAAs) such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) is desirable for reducing potential human health and environmental risks. We here report the degradation of PFOA and PFOS by 85-100% via ozonation under alkaline condition being studied at environmentally relevant contaminant concentrations of 50 μg L(-1) to 5 mg L(-1), with enhanced removal rates by addition of hydrogen peroxide. Enhanced removal is achieved by ozonation pretreatment for 15 min at the ambient pH (i.e. 4-5), followed by elevation of pH to 11 and continued ozonation treatment for 4h. The ozonation pretreatment resulted in increased degradation of PFOA by 56% and PFOS by 42%. The results indicated hydroxyl radical-driven degradation of PFOA and PFOS in both treatments by ozone and peroxone under alkaline conditions. Wastewaters from electronics and semiconductor fabrication plants in the Science Park of Hsinchu city, Taiwan containing PFOA and PFOS have been readily treated by ozonation under alkaline condition. Treatment of PFAAs by ozone or peroxone proves to be efficient in terms of energy requirement, contact time, and removal rate.

Sorption of Perfluorooctanoic Acid (PFOA) onto Sediment in the Presence of Dissolved Natural Organics

The abundance of perfluorooctanoic acid (PFOA) in the aquatic environment makes it important to understand the influence of important parameters affecting the partition of PFOA onto sediment. With a focus on the influence by dissolved organic matter (DOM), we investigated the sorption of PFOA to river sediment downstream of a semiconductor and optoelectronic industrial complex that discharged wastewater with a considerable amount of PFOA in it. The dominant components of the sediment were silica oxide (∼14%) and iron oxide (∼2%). The sorption density of PFOA was not significantly affected by solution pH and ionic strength. The combinations of low pH-high ionic strength and high pH-low ionic strength favored partitioning of PFOA to the sediment. The sorption density of PFOA to sediment ranged from 0.41 to 1.43 µg/m2, with the presence of DOM in the aqueous phase reducing the affinity of PFOA toward the sediment. The sorption of PFOA seemed to be facilitated not by electrostatic but by hydrophobic interactions. The PFOA-sediment sorption equilibration required a duration exceeding 12 d. This study revealed DOM as an important solution-specific parameter in sorption studies. The influence of DOM on PFOA sorption provides a useful reference to understand PFOA partition in the aqueous environment. Supplemental materials are available for this article. Go to the publishers online edition of Separation Science & Technology to view the free supplemental file.

Recovery of metallic copper by integrated chemical reduction and high gradient magnetic separation

The recovery of metals from waste effluents is necessary for pollution prevention and sustainable practice. High gradient magnetic separation (HGMS) is seen as a viable method. We investigated the capture of valence copper from aqueous copper ion by HGMS in combination with a chemical reduction process. When a copper solution (3.9 or 15.6 mM) was exposed to excess of dithionite (mole ratio of 1:3) in the presence of ammonia (mole ratio of 4) and amended with MnCl2 (2.5 g/L) and the mixture passed through a flow reactor under a strong magnetic field (10000 Gauss), valence copper was obtained and captured in the reactor with well over 95% yields. The chemical reduction reactions were unaffected by the presence of MnCl2 while the amount of MnCl2 (0, 20 and 32 mM) has significantly varied the copper recovery efficiency, especially in the case of high initial copper ion concentration (15.6 mM). Formation of MnO2 flocs was found to have a detrimental effect on copper removal efficiency. The HGMS method offers a tool of resource recovery for copper from waste effluents.

Effects of water washing on removing organic residues in bottom ashes of municipal solid waste incinerators

Due to their potential toxicity and odourous nature, the residual organics in municipal solid waste incinerators are recently gaining attention as an important issue of resources recovery apart from their complex mixture of organic counterpart. Studies of the organic fractions in municipal solid waste incinerator residues have been limited. In this study, extended solid-phase extraction of the water-washed bottom ash and liquid-phase extraction of the washing water were carried out with regard to bottom ash samples from three mass-burning incinerators in Taipei County (Taiwan) during four consecutive seasons of year 2008-2009. Supercritical fluid extraction and Soxtec extraction techniques along with GC-MS were successfully used to characterize the residual organics in weathered and washed bottom ashes. Supercritical fluid extraction provided the quantification of aliphatics and aromatic compounds such as hexanoic acid and benzaldehyde, respectively. Soxtec extraction was useful for qualitative analysis of aromatic and aliphatic groups in the ashes and many of which were odourous and toxic compounds. By mixing one unit weight (g) bottom ash with two unit volume (mL) water for 15 min, total organic carbon in the bottom ash was greatly reduced (e.g., from 4.1 to 1.8 wt.%). Among the removed were foul odour-causing compounds such as pyridine and quinoline derivatives, while some aromatic compounds such as 4-hydroxybenzaldehyde and low-molecular-weight aliphatics such as hexanoic acid remained. The results here suggest that washing with water can be an effective pre-treatment step for removing odour-causing and environmental concerned organics.

Effect of Ultrasound on Membrane Filtration and Cleaning Operations

The impact of ultrasound (US) on membrane filtration and cleaning were studied and compared at various operating parameters of nominal pore sizes of 10 and 100 kDa membrane, trans-membrane pressure (TMP) of 100 and 140 kPa, and US frequencies of 20 kHz and 40 kHz. An average of 15%–20% increase of permeability was observed when US (20 kHz) was applied to assist membrane filtration on 10 kDa membrane and 100 kPa trans-membrane pressure (TMP). However, an insignificant improvement was observed in the case of larger pore size membrane at higher TMP (140 kPa). US also augmented the membrane cleaning process effectively. Lower frequency 20 kHz US exhibited a higher flux recovery (>90%) than the high frequency 40 kHz (59%) using the 10 kDa pore size membrane with US-assisted membrane cleaning. Important factors influencing optimization of US effectiveness lie heavily on its configuration and operation. The experimental results as supported with SEM images demonstrate that US-assisted filtration and cleaning are most effective when membrane pore size, US frequency, and TMP are lower.