Causes and consequences of the variations in natural organic matter properties

<p>Natural organic matter (NOM) is commonly contained in surface water bodies, including those that serve as sources for drinking water treatment plants (DWTPs). The composition of NOM may be very diverse, and can be further divided into humic substances (HS) and algal organic matter (AOM). Recently, increasing content of AOM is becoming a challenge for many DWTPs, owing to the global proliferation of cyanobacteria and algae. This phenomenon is most often attributed to climate changes and enhanced input of nutrients to aquatic environments.</p><p>We investigated the evolution of NOM character in a selected water reservoir (located in the Vysočina Region, Czech Republic), that serves as an irreplaceable drinking water source, for a period of 12 years (starting in the year 2006). Besides the quantitation of NOM, it was divided into fractions according to its character, i.e., VHA (very hydrophobic acids), SHA (slightly hydrophobic acids), CHA (charged hydrophilics), and NEU (neutral hydrophilics). Within the observed timescale, the relative proportion of VHA and SHA (that both belong to HS) decreased, while CHA and NEU (associated to AOM) significantly increased and comprised majority since 2016. Additionally, seasonal variations were also observed. This points out to the rising occurrence of phytoplankton in the reservoir, while its seasonal dynamic must not be neglected.</p><p>To elucidate the dependence of AOM properties on the species and the growth phase, we investigated the composition of AOM produced by green alga, diatom, and cyanobacteria. They were grown under laboratory conditions and harvested at different growth phases; extracellular and cellular AOM (EOM and COM, resp.) was investigated separately. The distinct AOM fractions were analysed in terms of peptide-protein and non-proteinaceous content, hydrophilicity/hydrophobicity, specific UV absorbance (SUVA), and molecular weights (MW). In general, both EOM and COM of all the species was mainly hydrophilic and had low SUVA values; however, the proportions of peptides-proteins and non-proteinaceous fraction and MW distribution greatly differed. For example, EOM and COM of the cyanobacteria (Microcystis aeruginosa and Merismopedia tenuissima) contained larger portions of peptides-proteins and had wider MW distributions than the green alga (Chlamydomonas geitleri) or the diatom (Fragilaria crotonensis). Changes were observed also along their growth phase.</p><p>Additionally, we studied coagulation behaviour of the distinct NOM fractions (i.e., HS versus AOM, and also AOM peptides-proteins and non-proteinaceous fraction separately), since coagulation is an essential treatment steps at most DWTPs supplied by surface waters. It has shown that the non-proteinaceous fraction (corresponding to NEU) is the most difficult to coagulate (max. removal efficiency of 25%), while the removal of AOM peptides-proteins (corresponding to CHA) reached up to approx. 80%. HS were removed with 65% efficiency. It is of note that substantial optimization of coagulation conditions (especially the dose of coagulant and coagulation pH) was a nuisance, and that the coagulation optimums differed between the NOM fractions.</p><p>Thus, our results imply that continuous characterization of NOM is essential for an effective control over the processes at DWTPs.</p>

Characterization of dissolved organic matter in the secondary effluent of pulp and paper mill wastewater before and after coagulation treatment

Meeting the regulatory discharge standards for pulp and paper mill wastewater has become ever more difficult because of its recalcitrant and colored dissolved organic matter (DOM). In this study, the variation of DOM from the secondary effluent of pulp and paper mill wastewater before and after coagulation was investigated based on hydrophobicity/hydrophilicity, apparent molecular weight (MW) and fluorescence. DOM fractions of the secondary effluent were all with the apparent MW <20 kDa. Particularly, the hydrophobic acids (HOA) fraction, mainly composed of humic-like materials, was the major component, and it also had the highest color and SUVA254 (UV254 to dissolved organic carbon ratio). Hydrophilic bases (HIB) and hydrophilic neutrals (HIN) fractions were the other important parts besides HOA. Coagulation can remove all DOM fractions to different extent, and it was more effective for organic compounds with MW > 5 kDa. The removal efficiencies of humic-like, fulvic-like and soluble microbial by-product-like constituents in HOA and HIB fractions were much higher than in other fractions. Even so, the coagulation effluent still contained large amounts of contaminants with complicated fluorophores and apparent MW <5 kDa, and HOA and HIN fractions were also the major parts in the coagulation effluent.

Analysis of Genotoxicity and Characterization of Dissolved Organic Matter in the Aniline Industrial Wastewater

Effluent of aniline wastewater treatment from a company was isolated and fractionated by resin adsorption method into six different fractions. These fractions are operationally categorized as hydrophobic acids (HOA), hydrophobic bases (HOB), hydrophobic neutrals (HON), hydrophilic acids (HIA), hydrophilic bases (HIB) and hydrophilic neutrals (HIN). The dissolved organic carbon (DOC), ultraviolet-visible (UV) and genotoxicity of each fractions were determined. The results showed that hydrophobic matter is the main fractions of DOC and makes the main contributions to the genotoxicity of effluent of aniline wastewater treatment.

Identifying Membrane Foulants in Chemical Cleaning Solutions

The main objective of this study was to investigate foulants in chemical cleaning solutions of membrane (CCSM). Sodium hydroxide (NaOH), sodium hypochlorite (NaOCl), hydrochloric acid (HCl) were used as chemical agents respectively. Hydrophobicity, molecular weight distribution and metal ions of foulants in CCSM were analyzed as the major characters for membrane fouling. Results reveal that alkali cleaning can remove both hydrophobic and hydrophilic fractions of natural organic matters (NOM), and acid cleaning mainly removes hydrophilic organic matters. Medium molecular weight of very hydrophobic acids (1-10 kDa) and different molecular weight of neutral hydrophilic acids (100-1000 Da & >300kDa) in NOM can lead to membrane irreversible fouling. Acid cleaning is relatively effective for the reduction of inorganic foulants. The main metal ions in acid cleaning solutions are K ,Ca, Al and Mn, which are responsible for membrane inorganic fouling.

Natural organic matter fractionation along the treatment of water for human consumption

The main objective of this study was to characterize the organic matter present in raw water and along the treatment process, as well as its seasonal variation. A natural organic matter fractionation approach has been applied to Lever water treatment plant located in Douro River, in Oporto (Portugal). The process used was based on the sorption of dissolved organic matter in different types of ion exchange resins, DAX-8, DAX-4 and IRA-958, allowing its separation into four fractions: very hydrophobic acids (VHA), slightly hydrophobic acids (SHA), charged hydrophilic (CHA) and hydrophilic neutral (NEU). The dissolved organic carbon (DOC) determination was used to quantify dissolved organic matter. Samples were collected monthly, during approximately one year, from raw water captured at the surface and under the bed of the river, and after each step of the treatment: pre-filtration in sand/anthracite filters, ozonation, coagulation/flocculation, counter current dissolved air flotation and filtration (CoCoDAFF) and chlorination. The NEU fraction showed a seasonal variation, with maximum values in autumn for the sampling points corresponding to raw water captured at the surface and under the bed of the river. It was usually the predominating fraction and did not show a significant decrease throughout the treatment. Nevertheless their low concentration, the same occurred for the CHA and VHA fractions. There was an overall decrease in the SHA fraction throughout the water treatment (especially after CoCoDAFF and ozonation) as well as in the DOC. The TSUVA254 values obtained for raw water generally varied between 2.0 and 4.0 L mgC-1 m-1 and between 0.75 and 1.78 L mgC-1 m-1 for treated water. It was observed a decrease of TSUVA values along the treatment, especially after ozonation. These results may contribute to a further optimization in the process of treating water for human consumption.

Contribution of different effluent organic matter fractions to membrane fouling in ultrafiltration of treated domestic wastewater

In the present work, effluent organic matter (EfOM) in treated domestic wastewater was separated into hydrophobic neutrals, colloids, hydrophobic acids, transphilic acids and neutrals and hydrophilic compounds. Their contribution to dissolved organic carbon (DOC) was identified. Further characterization was conducted with respect to molecular size and hydrophobicity. Each isolated fraction was dosed into salt solution to identify its fouling potential in ultrafiltration (UF) using a hydrophilized polyethersulfone membrane. The results show that each kind of EfOM leads to irreversible fouling. At similar delivered DOC load to the membrane, colloids present the highest fouling effect in terms of both reversible and irreversible fouling. The hydrophobic organics show much lower reversibility than the biopolymers present. However, as they are of much smaller size than the membrane pore opening, they cannot lead to such severe fouling as biopolymers do. In all of the isolated fractions, hydrophilics show the lowest fouling potential. For either colloids or hydrophobic substances, increasing their content in feedwater leads to worse fouling. The co-effect between biopolymers and other EfOM fractions has also been identified as one of the mechanisms contributing to UF fouling in filtering EfOM-containing waters.

Evaluation of DBPs Formation Potential during Chlorination of Dissolved Organic Matter Fractions Isolated from Eutrophic Water

Dissolved organic matter (DOM) in water from eutrophic water source was isolated into four classes as hydrophilic substances (HIS), hydrophobic acids (HOA), hydrophobic neutrals (HON), and hydrophobic bases (HOB). The formation of Trihalomethanes (THMs) and Haloacetic acids (HAAs) in chlorination of different DOM fractions was evaluated. The dominate species of THMs and HAAs were chloroform (CF) and trichloroacetic acid (TCAA) in the chlorination of raw water. There were close linear relationship between THMs/HAAs yields and SUVA254 values. Increasing of contact time and chlorine dosage enhanced the formation of THMs/HAAs yields from different DOM fractions. The increase of pH leads to more formation of THMs, and the highest production of HAAs was observed at pH 7.