Verification of NOM removal in MIEX-NF system for advanced water treatment

Identifying the critical activated carbon properties affecting the adsorption of effluent organic matter from bio-treated coking wastewater

Activated carbon is widely used to remove effluent organic matter (EfOM) from bio-treated coking wastewater. However, the critical carbon properties affecting adsorption performance are still unclear. Nine commercial powdered activated carbons (PACs) with different pore structures, surface functional groups, and surface charges were used to adsorb EfOM from bio-treated coking wastewater, which was fractionated according to their molecular weight (MW) and hydrophobicity. Good correlations were observed between the adsorption of biopolymers (MW > 20,000 Da, 7 %) and macropore volume (>50 nm), as well as between the adsorption of humics (MW = 1000 ~ Da, 36 %) and mesopore volume (2-50 nm), suggesting that the adsorption sites of EfOM depended on their molecular size. Higher isoelectric points and fewer acidic groups promoted the adsorption of the most negatively charged hydrophobic acids (HPOA, 39.5 %). According to variation partitioning analysis (VPA), mesopore-macropore greatly contributed to the adsorption capacities of EfOM (71.3 %), whereas the sum of phenolic hydroxyl and carboxyl (26.3 %) and isoelectric point (12.2 %) affected the normalized adsorption capacities of EfOM. In conclusion, PAC with a higher mesopore volume, fewer acidic groups, and a higher isoelectric point was desirable for removing EfOM from bio-treated coking wastewater. This study provides guidance for the selection of PAC for the removal of EfOM from bio-treated coking wastewater.

Designing sustainable membrane-based water treatment via fouling control through membrane interface engineering and process developments

Membrane-based water treatment processes have been established as a powerful approach for clean water production. However, despite the significant advances made in terms of rejection and flux, provision of sustainable and energy-efficient water production is restricted by the inevitable issue of membrane fouling, known to be the major contributor to the elevated operating costs due to frequent chemical cleaning, increased transmembrane resistance, and deterioration of permeate flux. This review provides an overview of fouling control strategies in different membrane processes, such as microfiltration, ultrafiltration, membrane bioreactors, and desalination via reverse osmosis and forward osmosis. Insights into the recent advancements are discussed and efforts made in terms of membrane development, modules arrangement, process optimization, feed pretreatment, and fouling monitoring are highlighted to evaluate their overall impact in energy- and cost-effective water treatment. Major findings in four key aspects are presented, including membrane surface modification, modules design, process integration, and fouling monitoring. Among the above mentioned anti-fouling strategies, a large part of research has been focused on membrane surface modifications using a number of anti-fouling materials whereas much less research has been devoted to membrane module advancements and in-situ fouling monitoring and control. At the end, a critical analysis is provided for each anti-fouling strategy and a rationale framework is provided for design of efficient membranes and process for water treatment.

Residual chemical oxygen demand (COD) fractionation in bio-treated coking wastewater integrating solution property characterization

The refractory nature of residual COD in bio-treated coking wastewater (BTCW) creates barriers for its further treatment and reclamation. It is necessary to fractionate the residual COD in BTCW associated with characterization of solution properties. In this paper, a stepwise process composed of membrane filtration, coagulation, adsorption and ozonation was proposed to fractionate residual COD in the BTCW, in which the COD was stepwise reduced to near zero. In addition, the correlation between COD and water quality indexes as well as solution properties were discussed together with a safety assessment of the water quality. Results showed that the residual COD fractionation percentage contributed by suspended solids, colloids, dissolved organics and reductive inorganic substances in the BTCW was 43.7%, 22.1%, 26.2% and 4.9%, respectively. By stepwise fractionating of these substances, the residual COD was reduced from 168.8 to 5.2 mg L^-1, and the UV₂₅₄ value decreased from 1.90 to 0.15 cm^-1. In addition, the particle size of the dominant substances contributing to the residual COD was smaller than 450 nm. Among these substances, the hydrophobic fraction accounted for 78.66% (in the term of TOC). Three-dimensional excitation-emission matrix (3D-EEM) analysis showed that hydrophobic neutral substances (HON) were the main fluorescence constituent in the BTCW, which was highly removable by adsorption. The residual COD after adsorption was mainly composed of reductive inorganic substances. Apart from pursuit of high COD removal rates, more emphasis should be given to the removal of toxic COD. Correlations were observed between the residual COD and water quality indicators as well as solution properties, providing a guideline for optimized removal of residual COD in the BTCW. In summary, these results gave a referential information about the nature of residual COD in the BTCW for the selection of advanced treatment technologies and the management of water quality safety.

Multi-spectral characterization of natural organic matter (NOM) from Manitoba surface waters using high performance size exclusion chromatography (HPSEC)

The main objective of this research was to develop an algorithm that would be able to relate ultraviolet absorbing moieties in potable water to trihalomethanes (THMs) and other water quality parameters. The characterization was carried out using high performance size exclusion chromatography (HPSEC) to separate water samples based on apparent molecule weight (AMW); while the developed algorithm utilized multi-spectral information extracted from 7 Manitoba source waters, and from samples treated with strong base ion-exchange (IX). AMW components between 2.2-4 k Da were strongly associated with the formation of THMs, and more strongly with chlorinated byproducts, determined using Spearman and Pearson coefficients. associations were not improved upon removal of the raw samples from the dataset, indicating that the applied methodology is not specific to IX treatment. Strong associations were also found between initial wavelengths of 226-239 nm and final wavelengths of 257-273 nm, which suggests that absorbing moieties in these ranges are prime precursors in the reaction mechanism to form THMs. A closer look noted that chlorinated THMs were more strongly associated than THMs in general; with brominated byproducts following closely to profiles of UV₂₅₄ - indicating these parameters are closely related.

Removal of Microcystin-LR from spiked natural and synthetic waters by anion exchange

Cyanobacterial blooms are becoming a serious challenge across the globe due to changing climate and rainfall patterns as a consequence of human activities. In the present study, the fundamental interactions involved during the removal of Microcystin-LR (MCLR), one of the most commonly occurring cyanobacterial toxins, were investigated by employing strongly basic anion exchange (IX) resins. Several factors including the stoichiometric coefficients, competitive fractions and solute affinities were determined under various concentrations of inorganic ions and natural organic matter. The results indicated that suphates were the most competitive fractions with high affinity (α (affinity coefficient) values ~ 9) followed by nitrates (α ~ 4.7) and NOM fractions (α ~ 4.5, p < 0.05). The Equivalent Background Concentration Mode (EBC), that arises from the Ideal Adsorption Solution Theory (IAST), indicated a competitive fraction of ~2 μeq/L NOM, which approximates to <10% of the initial NOM concentrations, indicating a small fraction of the NOM resulting in the competitive effect. Further, studies with natural surface waters indicated that the MCLR uptake could be modeled using the IAST-EBC model and the IX resin could simultaneously removal of >90% of NOM, inorganic ions and MCLR at resin dosages of 3.6 meq/L or higher.

An overview of the uses of high performance size exclusion chromatography (HPSEC) in the characterization of natural organic matter (NOM) in potable water, and ion-exchange applications

Natural organic matter (NOM) constitutes the terrestrial and aquatic sources of organic plant like material found in water bodies. As of recently, an ever-increasing amount of effort is being put towards developing better ways of unraveling the heterogeneous nature of NOM. This is important as NOM is responsible for a wide variety of both direct and indirect effects: ranging from aesthetic concerns related to taste and odor, to issues related to disinfection by-product formation and metal mobility. A better understanding of NOM can also provide a better appreciation for treatment design; lending a further understanding of potable water treatment impacts on specific fractions and constituents of NOM. The use of high performance size-exclusion chromatography has shown a growing promise in its various applications for NOM characterization, through the ability to partition ultraviolet absorbing moieties into ill-defined groups of humic acids, hydrolysates of humics, and low molecular weight acids. HPSEC also has the ability of simultaneously measuring absorbance in the UV-visible range (200-350 nm); further providing a spectroscopic fingerprint that is simply unavailable using surrogate measurements of NOM, such as total organic carbon (TOC), ultraviolet absorbance at 254 nm (UV₂₅₄), excitation-emission matrices (EEM), and specific ultraviolet absorbance at 254 nm (SUVA₂₅₄). This review mainly focuses on the use of HPSEC in the characterization of NOM in a potable water setting, with an additional focus on strong-base ion-exchangers specifically targeted for NOM constituents.

Unraveling complex removal behavior of landfill leachate upon the treatments of Fenton oxidation and MIEX® via two-dimensional correlation size exclusion chromatography (2D-CoSEC)

The complex removal behavior of stabilized landfill leachate was explored for the treatments of Fenton oxidation (FnO) and magnetic ion exchange (MIEX^®) resin using two-dimensional correlation size exclusion chromatography (2D-CoSEC) and fluorescence excitation emission matrix-parallel factor analysis (EEM-PARAFAC). The overall removal rates of the bulk parameters (∼45% for dissolved organic carbon and ∼78% for UV absorbance) were similar between the two treatment options, while distinct differences were found with respect to different molecular sizes and chemical composition. The resin treatment eliminated humic substances (HS) and low molecular weight acid (LMWA) fractions to a greater extent than other fractions (i.e., HS: 62% and LMWA: 99%), while low molecular weight neutral (LMWN) and biopolymers (BP) fractions were more effectively treated by the FnO with the removal rates of 56% and 92%, respectively. The 2D-CoSEC further revealed that the sequential or preferential changes of different size fractions with increasing the resin or H₂O₂ were opposite between the two treatment options in the order of HS → LMWA → LMWN → BP for MIEX^®. Due to their complementary roles in treating leachate, the combined processes removed a wider ranges of different molecular sizes compared to the single operation.

Advanced Oxidation Processes and Nanofiltration to Reduce the Color and Chemical Oxygen Demand of Waste Soy Sauce

Currently, the ozone (O3) oxidation efficiency in the treatment of waste soy sauce provides 34.2% color removal and a 27.4% reduction in its chemical oxygen demand (COD). To improve the O3 oxidation efficiency, hydrogen peroxide (H2O2) is used to cause a H2O2/O3 process. In H2O2/O3 process experiments, a previously optimized pH of 11 and applied O3 dose of 50 mg L−1 were used and the H2O2/O3 ratio was varied between 0.1 and 0.9 in intervals of 0.2. The results show that an H2O2/O3 ratio of 0.3 results in the highest efficiencies in terms of color removal (51.6%) and COD reduction (33.8%). Nanofiltration (NF) was used to pretreat the waste soy sauce to improve color removal and COD reduction. The results showed that NF with an NE-70 membrane results in 80.8% color removal and 79.6% COD reduction. Finally, the combination of NF and H2O2/O3 process resulted in the best treatment efficiency: 98.1% color removal and 98.2% COD reduction. Thus, NF & H2O2/O3 process can be considered as one of the best treatment methods for waste soy sauce, which requires high intrinsic color removal and COD reduction efficiencies.

Characterization of effluent organic matter from different coking wastewater treatment plants

Effluent organic matter (EfOM) in bio-treated wastewater generally has negative impacts on advanced wastewater treatment processes. Thus, a comprehensive characterization of EfOM would help determine feasibility of wastewater treatment. The aim of this work was to characterize EfOM originating from four coking wastewater treatment plants (WTPs) in China, using specific UV absorbance (SUVA), EfOM fractionation, size exclusion chromatography, and excitation-emission matrix (EEM) fluorescence spectroscopy. It was found that the predominant species in all the EfOM samples were hydrophobic compounds with high SUVA values. The molecular weight (MW) distribution of the sampled EfOM was in the range of 300-1500 Da, and stronger UV absorbance was observed in the high MW (＞ 500 Da) region. The EEM fluorescence spectra showed that aromatic compounds accounted for a large proportion of the sampled EfOM based on the fluorescence regional integration technique. The abovementioned analysis highlights the similarities in the characteristics of the EfOM originating from different coking WTPs, regardless of treatment plant design. Meanwhile, significant differences between the characteristics of the EfOM in coking wastewater and municipal wastewater were observed.

Removal of natural organic matter (NOM) from water by ion exchange - A review

Natural organic matter (NOM) is present in underground and surface waters. The main constituents of NOM are humic substances, with a major fraction of refractory anionic macromolecules of various molecular weights. The NOM concentration in drinking water is typically 2-10 ppm. Both aromatic and aliphatic components with carboxylic and phenolic functional groups can be found in NOM, leading to negatively charged humic substances at the pH of natural water. The presence of NOM in drinking water causes difficulties in conventional water treatment processes such as coagulation. Problems also arise when applying alternative treatment techniques for NOM removal. For example, the most significant challenge in nanofiltration (NF) is membrane fouling. The ion exchange process for NOM removal is an efficient technology that is recommended for the beginning of the treatment process. This approach allows for a significant decrease in the concentration of NOM and prevents the formation of disinfection byproducts (DBPs) such as trihalomethanes (THMs). This article provides a state-of-the-art review of NOM removal from water by ion exchange.

Membrane processes

The membrane processes have played important role in the industrial separation process. These technologies can be found in all industrial areas such as food, beverages, metallurgy, pulp and paper, textile, pharmaceutical, automotive, biotechnology and chemical industry, as well as in water treatment for domestic and industrial application. Although these processes are known since twentieth century, there are still many studies that focus on the testing of new membranes’ materials and determining of conditions for optimal selectivity, i. e. the optimum transmembrane pressure (TMP) or permeate flux to minimize fouling. Moreover the researchers proposed some calculation methods to predict the membrane processes properties. In this article, the laboratory scale experiments of membrane separation techniques, as well their validation by calculation methods are presented. Because membrane is the “heart” of the process, experimental and computational methods for its characterization are also described.

Disolved organic matter (DOM) removal from bio-treated coking wastewate using a new polymeric adsorbent modified with dimethylamino groups

In the current study a new recyclable aminated hyper-cross-linked polymeric adsorbent (A-HPA) was prepared for effective removal of DOM from BTCW. Possibly benefited from its unique structure of polystyrene matrix, sufficient aminated groups and high specific surface area, A-HPA could remove DOM from BTCW through the synergetic effect of π-π interactions, acid-base interactions and micropore filling, and exhibited the highest removal efficiency than the other adsorbents. Moreover, the exhausted A-HPA was amenable to effective regeneration by using acid and alkaline solution, allowing for repeated use with a constant removal efficiency. Field application of continuous 3-year fixed-bed runs demonstrated that A-HPA is capable of effectively removing DOM from BTCW with no significant capacity loss, and the treated effluent can be partially used as recycled water in production. All the above results demonstrated that A-HPA adsoption could serve as a good choice for the advanced treatment of bio-treated sewage effluent.

An evaluation of organic substance fraction removal during ion exchange with Miex-DOC resin

In this study, the usefulness of Miex-DOC resin in eliminating organic substances and their fractions from water sources for drinking water was evaluated. The objects of study were samples from three surface water sources and one infiltration water source taken at water treatment plants before treatment in technical conditions. In particular, the effectiveness of removing biodegradable and non-biodegradable fractions as a function of resin dosages and water-resin contact times was evaluated. The ion exchange process with the Miex-DOC resin achieved a high effectiveness in removing aromatic non-biodegradable organic substances, and therefore a reduction in UV254 absorbance. The biodegradable fraction is much less susceptible to removal yet its removal effectiveness allows for a significant reduction in hazards connected with secondary microorganism development. The results of this study indicate the possibility of using ion exchange with the Miex-DOC resin for effective removal of disinfection by-product precursors.

Effective removal of effluent organic matter (EfOM) from bio-treated coking wastewater by a recyclable aminated hyper-cross-linked polymer

Effluent organic matter (EfOM) is a complex matrix of organic substance mainly from bio-treated sewage effluent and is considered as the main constraint to further advanced treatment. Here a recyclable aminated hyper-cross-linked polymeric adsorbent (NDA-802) featured with aminated functional groups, large specific surface area, and sufficient micropore region was synthesized for effective removal of EfOM from the bio-treated coking wastewater (BTCW), and its removal characteristics was investigated. It was found that hydrophobic fraction was the main constituent (64.8% of DOC) in EfOM of BTCW, and the hydrophobic-neutral fraction had the highest SUVA level (7.06 L mg(-1) m(-1)), which were significantly different from that in the domestic wastewater. Column adsorption experiments showed that NDA-802 exhibited much higher removal efficiency of EfOM than other polymeric adsorbents D-301, XAD-4, and XAD-7, and the efficiency could be readily sustained according to continuous 28-cycle batch adsorption-regeneration experiments. Moreover, dissolved organic matter (DOM) fractionation and excitation-emission matrix (EEM) fluorescence spectroscopy study indicated that NDA-802 showed attractive adsorption preference as well as high removal efficiency of hydrophobic and aromatic compounds. Possibly ascribed to the presence of functional aminated groups, relatively large specific surface area and micropore region of the unique polymer, NDA-802 possesses high and sustained efficiency for the removal of EfOM, and provides a potential alternative for the advanced treatment.