Adsorption behavior and mechanism of 2,4,6-trichlorophenol on nut shell activated carbon

The adsorbable organic halides (AOX) produced during chlorine dioxide bleaching are highly toxic and difficult to degrade. Currently, AOX generation is mainly reduced by controlling conditions during bleaching. Studies on AOX removal in the natural environment are rarely reported. In this study, the adsorption of 2,4,6-trichlorophenol (2,4,6-TCP) on nut shell activated carbon was investigated. The effects of activated carbon dosage, adsorption time, and temperature on the removal of 2,4,6-TCP were examined. The optimal adsorption conditions was activated carbon dosage 0.20 g × L-1, adsorption time 130 min, and temperature 25 °C. The removal efficiency of 2,4,6-TCP was 91.5%. The adsorption kinetics and isothermal adsorption were studied, and a thermodynamic equation was established. The adsorption was more consistent with a pseudo-second-order kinetic model and Freundlich adsorption isotherm model. Thermodynamic studies showed that the adsorption of 2,4,6-TCP on activated carbon was a spontaneous exothermic process. These findings provide a new method for AOX removal in natural environments.

Reducing the formation of adsorbable organic halides using an ammonium thiosulfate chlorine dioxide bleaching process

Reducing the formation of adsorbable organic halides during chlorine dioxide bleaching (the first stage chlorine dioxide bleaching, D0) is necessary to obtain clean bleaching processes. A new bleaching agent, ammonium thiosulfate (AT), was investigated to determine its potential for reducing the amount of adsorbable organic halides (AOX). Upon investigating the optimal reaction conditions for an effective reduction in AOX, the authors determined that adding 0.20% of AT 10 min after the beginning of the bleaching reaction, while maintaining a pH of 4 and a temperature of 70°C, yielded the best results. Under these conditions, AOX formation decreased by 22.0%. The bleaching effluent after the addition of AT was analyzed via gas chromatography-mass spectrometry, which showed an inhibited production rate of chlorobenzene and chlorophenol, which are both highly toxic and difficult-to-degrade compounds. Therefore, AT not only reduces AOX formation during the bleaching process, but also minimizes the difficulty of treating bleaching effluent. The results of this study provided a new, clean method for reducing AOX formation during chlorine dioxide bleaching.

Predicting Residual Adsorbable Organic Halides Concentrations in Industrial Wastewater Using Typical Wastewater Parameters

The aim of this study was to predict the residual adsorbable organic halides (AOX) concentration in an industrial wastewater using conventional, easy-to-measure wastewater parameters. In a pilot test unit, the wastewater was subjected to ozonation at various intensities, resulting in an AOX-removal and hence varying AOX concentrations. In first instance, the parameters used for modeling were selected using Pearson and Spearman correlations. Secondly, multiple linear regression (MLR) was used as a modeling tool to predict both the soluble and total AOX concentration in wastewater samples. To prevent overfitting, a 10-fold cross-validation was carried out. It was found that both the soluble and the total AOX concentration can be predicted using typical wastewater parameters. The measured parameters were pH, chloride concentration, Water-Soluble Organic Carbon concentration (WSOC), UV-VIS spectrum, turbidity, and Solids Removable by Filtration (SRF). Out of these parameters, the following parameters were found to be significant for prediction of the total AOX concentration: turbidity; SRF; UV-VIS absorbance at 200; 227, and 250 nm; and pH. UV-VIS absorbance at 200 and 227 nm and turbidity of the wastewater were found to contribute significantly to the final model. For the soluble AOX concentration, the significant parameters were turbidity; SRF; absorbance at 200, 227, and 250 nm; pH, and chloride concentration. Here, UV-VIS absorbance at 200 and 227 nm were found to contribute significantly to the final model. The obtained final models had an adjusted R2 of 0.921 and 0.916 for the total and soluble AOX, respectively. As a result of the obtained models, both AOX concentrations can be predicted using parameters that are easier to determine. This allows for a significant reduction in wastewater sampling and analysis time and offers the opportunity to optimize the ozone dosing in the wastewater treatment process in the future.

The reaction of lignin model compounds during enzymatic bleaching with a Curvularia verruculosa haloperoxidase: impact on chlorination

Recent developments in enzymatic bleaching processes have led to replacement strategies of harsh chemicals by haloperoxidases. For this purpose, it is important to control the haloperoxidase-mediated formation of adsorbable organic halides (AOX). In this study, we studied the chlorination of monomeric and dimeric lignin model substrates. Guaiacol, acetovanillone, veratryl alcohol, pinoresinol and adlerol were treated with Curvularia verruculosa haloperoxidase and compared to a sodium hypochlorite treatment. High-performance liquid chromatography-diode array detection-mass spectrometry (HPLC-DAD-MS) analysis was employed for the characterization of the reaction products. Our results show that while treatment with haloperoxidases in the presence of sodium chloride and hydrogen peroxide leads to no improvement in AOX formation compared to chemical treatment with NaOCl, addition of ammonium chloride substantially lessens chlorination and promotes β-O-4 ether bond cleavage. The use of ammonium chloride in conjunction with enzymatic haloperoxidase-based bleaching could be a route to minimize lignin chlorination.

Kandungan Hexenuronic Acid pada Pulp serta Pengaruhnya terhadap Kualitas Pulp dan Air Limbah: Tinjauan

Proses pemasakan kayu dengan cara alkali aktif akan menghasilkan hexenuronic acid (HexA) yang berasal dari grup glucuronoxylan, tepatnya 4-O-methylglucuronoxylan pada hemiselulosa. Proses hidrolisis HexA menghasilkan dua jenis senyawa furan, yaitu 2-furancarboxylic acid (FA) dan 5-formyl-2-furancarboxylic acid (FFA). Proses hidrolisis HexA hasil proses pemasakan dan terkandung dalam pulp dan kertas merupakan salah satu penyebab proses penguningan pada kertas akibat adanya paparan kelembapan dan panas dari lingkungan. Selain itu, kandungan HexA pada pulp juga dapat meningkatkan konsumsi bahan kimia pada proses produksi pulp dan kertas, terutama pada proses pemutihan dan pengujian parameter bilangan Kappa, serta dapat berkontribusi pada kandungan senyawa organik klorin terlarut dalam air limbah industri pulp dan kertas. Metode untuk menurunkan kandungan HexA dari pulp dan kertas antara lain dengan mengaplikasikan proses oksidatif kimia pada proses pemutihan atau dengan menggunakan proses enzimatis. Kandungan HexA yang rendah, akan dapat mempertahankan pulp dan kertas dari terjadinya proses penguningan, menghemat konsumsi bahan kimia serta menurunkan kandungan adsorbable organic halides (AOX) pada air limbah.Kata kunci: hexenuronic acid, pemasakan kayu, bilangan Kappa, AOX, enzimatis Hexenuronic Acid Content on Pulp and its Effects on Pulp Quality and Wastewater: a ReviewAbstractThe wood active alkali cooking process will produce hexenuronic acid (HexA) originating from 4-O-methylglucuronoxylan of the glucuronoxylan group in hemicellulose. Hydrolysis process of HexA produces two types of furan compounds, namely 2-furancarboxylic acid (FA) and 5-formyl-2-furancarboxylic acid (FFA). The HexA hydrolysis process contained in pulp and paper resulting from the cooking process is one of the causes of the yellowing process on paper due to exposure to moisture and heat from the environment. In addition, the HexA content of pulp can also increase the consumption of chemicals in the pulp and paper production process, especially in the bleaching process and testing of Kappa number parameters, and can also contribute to the content of organic chlorine soluble compounds in the waste water of the pulp and paper industry. There are several methods for reducing the HexA content of pulp and paper including by applying the oxidative chemical process to the bleaching process or by using an enzymatic process. Low HexA content, will be able to maintain pulp and paper from the occurrence of the pulp yellowing process, save on chemical consumption and reduce the adsorbable organic halides (AOX) content in wastewater.Keywords: hexenuronic acid, wood cooking, Kappa number, AOX, enzymatic

Coagulation optimization for DOC removal: pilot-scale analysis of UF fouling and disinfection byproduct formation potential

A pilot-scale study was performed to evaluate a coagulant dose which had been optimized for biopolymer (i.e., foulant) removal on subsequent ultrafiltration (UF) fouling, as well as disinfection by-product (DBP) precursor removal. Polyaluminum chloride (PACl) dosages were selected based on a point of diminishing returns for biopolymer removal (0.5 mg/L) and directly compared to that applied at full-scale (6 mg/L). Membrane fouling (reversible and irreversible) was measured as resistance increase over a 48 hour filtration period. DBP formation potential (total trihalomethanes (TTHMs), haloacetic acids (HAA9) and total adsorbable organic halides (AOX)) were measured in both raw and treated waters. Results of the study indicate that application of a PACl dose optimized for biopolymer reduction (0.5 mg/L) resulted in 65% less irreversible UF fouling when compared to 6 mg/L. The addition of PACl prior to the membrane resulted in up to a 14% reduction in DBP precursors relative to the UF membrane alone. A similar level of DBP precursor reduction was achieved for both 0.5 and 6 mg/L dosages. The results have implications for cost savings, which may be realized due to decreased chemical use, as well as increased membrane life associated with lower irreversible fouling rates.

Effects of boundary conditions on the cleaning efficiency of riverbank filtration and artificial groundwater recharge systems regarding bulk parameters and trace pollutants

Drinking water is often produced from surface water by riverbank filtration (RBF) or artificial groundwater recharge (AGR). In this study, an AGR system was exemplarily investigated and results were compared with those of RBF systems, in which the effects of redox milieu, temperature and surface water discharge on the cleaning efficiency were evaluated. Besides bulk parameters such as DOC (dissolved organic carbon), organic trace pollutants including iodinated X-ray contrast media, personal care products, complexing agents, and pharmaceuticals were investigated. At all studied sites, levels of TOC (total organic carbon), DOC, AOX (adsorbable organic halides), SAC (spectral absorption coefficient at 254 nm), and turbidity were reduced significantly. DOC removal was stimulated at higher groundwater temperatures during AGR. Several substances were generally easily removable during both AGR and RBF, regardless of the site, season, discharge or redox regime. For some more refractory substances, however, removal efficiency turned out to be significantly influenced by redox conditions.