Preferential binding between intracellular organic matters and Al13 polymer to enhance coagulation performance

Changes of characteristics and disinfection by-products formation potential of intracellular organic matter with different molecular weight in metalimnetic oxygen minimum

Metalimnetic oxygen minimum (MOM) occurs in reservoirs or lakes due to stratification and algal blooms, which has low dissolved oxygen (DO) levels and leads to the deterioration of water quality. The transformation mechanism and the impact on the water quality of intracellular organic matter (IOM) derived from algae are poorly understood under MOM conditions. In this study, IOM extracted by Microcystis aeruginosa was divided into five components according to molecular weight (MW), and the changes of characteristics and correlated disinfection by-products formation potential (DBPFP) were analyzed and compared under MOM conditions. The removal efficiency of dissolved organic carbon (DOC) in the <5 kDa fraction (66.6%) was higher than that in the >100 kDa fraction (41.8%) after a 14-day incubation under MOM conditions. The same tendency also occurred in Fmax and DBPFP. The decrease in Fmax was mainly due to the decline in tryptophan-like and tyrosine-like for all IOM fractions. The diversity of microorganisms degrading the MW > 100 kDa fraction was lower than others. Besides low MW fractions, these findings indicated that more attention should be paid to high MW fractions which were resistant to biodegradation under MOM conditions during water treatment.

Decomposition of Al13 promoted by salicylic acid under acidic condition: Mechanism study by differential mass spectrometry method and DFT calculation

Decomposition of the polycation Al₁₃O₄(OH)₂₄(H₂O)₁₂⁷⁺ (Al₁₃) promoted by ligand is a vital subject to advance our understanding of natural and artificial occurrence and evolution of aluminum ions, especially in the case of acidic condition that dissolved Al³⁺ species can be released from the Al-bearing substances. However, the microscopic pathway of synchronous proton-promoted and ligand-promoted decomposition process for Al₁₃ is still in the status of ambiguity. Herein, we applied differential mass spectrometry method and DFT calculation to study the initial detailed process of Al₁₃ decomposition under the presence of proton and salicylic acid (H₂Sal). Mass results showed that the mononuclear Al³⁺-H₂Sal complexes dominated the resulting Al species, whereas the monodentate complex Al₁₃HSal⁶⁺ was not observed in the spectra. The difference of decomposition levels between the ligand/Al ratio 0.2 and 0.5 cases revealed that proton and ligand performed synergistic effect in initial Al₁₃ decomposition process, and the proton transfer determined the ring closure efficiency. The ring closure reaction is the prerequisite for the collapse of Al₁₃ structure and detachment of the mononuclear complex. DFT calculations reveal that hydrogen bond plays an important role in inducing the formation of chelated complex accompanying proton transfer. Attachment of protons at the bridging OH^- can elongate and weaken the critical bond between targeted Al³⁺ and µ₄-O^2- resulting from delocalization of electron pairs in the oxygen atom. These results demonstrate the detailed mechanism of Al₁₃ composition promoted by ligand and proton, and provide significant understanding for further application and control of Al₁₃.

Impact of pre-oxidation on the formation of byproducts in algae-laden water disinfection: Insights from fluorescent and molecular weight

Pre-oxidation has been reported to be an effective way to remove algal cells in water, but the released algal organic matter (AOM) could be oxidized and lead to the increment in disinfection by-product (DBP) formation. The relationship between pre-oxidation and AOM-derived DBP formation needs to be approached more precisely. This study compared the impact of four pre-oxidants, ozone (O₃), chlorine dioxide (ClO₂), potassium permanganate (KMnO₄) and sodium hypochlorite (NaClO), on the formation of nitrogenous (N-) and carbonaceous (C-) DBPs in AOM chlorination. The characterization (fluorescent properties, molecular weight distribution and amino acids concentration) on AOM samples showed that the characterization properties variations after pre-oxidation were highly dependent on the oxidizing ability of oxidants. The disinfection experiments showed that O₃ increased DBP formation most significantly, which was consistent with the result of characterization properties variations. Then canonical correspondent analysis (CCA) and Pearson's correlation analysis were conducted based on the characterization data and DBP formation. CCA indicated that C-DBPs formation was highly dependent on fluorescent data. The formation of haloacetic acids (HAAs) had a positive correlation with aromatic protein-like component while trichloromethane (TCM) had a positive correlation with fulvic acid-like component. Pearson's correlation analysis showed that low molecular weight fractions were favorable to form N-DBPs. Therefore, characterization data could provide the advantages in the control of DBP formation, which further revealed that KMnO₄ and ClO₂ were better options for removing algal cells as well as limiting DBP formation.

Disinfection by-product (DBP) research in China: Are we on the track?

Disinfection by-products (DBPs) formed during water disinfection has drawn significant public concern due to its toxicity. Since the first discovery of the trihalomethanes in 1974, continued effort has been devoted on DBPs worldwide to investigate the formation mechanism, levels, toxicity and control measures in drinking water. This review summarizes the main achievements on DBP research in China, which included: (1) the investigation of known DBP occurrence in drinking water of China; (2) the enhanced removal of DBP precursor by water treatment process; (3) the disinfection optimization to minimize DBP formation; and (4) the identification of unknown DBPs in drinking water. Although the research of DBPs in China cover the whole formation process of DBPs, there is still a challenge in effectively controlling the drinking water quality risk induced by DBPs, an integrated research framework including chemistry, toxicology, engineering, and epidemiology is especially crucial.

Enhanced coagulation for mitigation of disinfection by-product precursors: A review

The unintended formation of disinfection by-products (DBPs) has received considerable attention as it may pose risks to human health. Coagulation is the most common process for removing particulates as well as dissolved organic matter (DOM) (i.e., DBP precursors) during drinking water and wastewater treatments. With the improvement of water quality standards and the increased fluctuation in source water quality, conventional coagulation becomes challenging. Thus, significant efforts have been made to enhance coagulation to promote the removal of DOM in source water and mitigate the formation of DBPs in drinking water. This review provides a brief summary of the properties of DBP precursors and summarizes the effectiveness of enhanced coagulation involving three types of coagulants (metal-based coagulants, organic polymers, and organic-inorganic hybrid coagulants) in controlling the formation of DBPs during chlor(am)ination disinfection. Metal-based coagulants can achieve a reduction in DBP formation potential of approximately 20%-60% in natural water under enhanced coagulation conditions. Both the organic polymers (used as coagulant aids) and novel hybrid coagulants increase the removal of DOM and exhibit high potential for mitigating DBP formation. In addition, integrated treatments combining coagulation with other treatment processes (e.g., oxidation, membrane filtration, ion exchange, and adsorption) to enhance DBP precursor removal are evaluated in terms of performance, mechanisms, and features. Advanced treatments, such as membrane filtration and activated carbon adsorption, are effective coagulation-assisted processes, and can further control chlorinated DBPs; however, the elevated formation of bromate or highly brominated DBPs is of particular concern.

Influences of Dimethyl Phthalate on Bacterial Community and Enzyme Activity in Vertical Flow Constructed Wetland

Dimethyl phthalate (DMP), belonging to the family of Phthalate esters (PAEs), is a plasticizer and has been widely used in the world for many years. Nowadays, it has become a ubiquitous environmental pollutant and is listed as an environmental priority pollutant by China’s Environmental Monitoring Center. The purpose of this study is to estimate the responses of the bacterial community and enzyme activity to DMP contamination in three vertical flow constructed wetlands (VFCW), namely the constructed wetland A (planted with Pennisetum sinese Roxb), constructed wetland B (planted with Pennisetum purpureum Schum.), and constructed wetland C (unplanted), respectively. The results showed that the relative percentages of some genera associated with nitrogen metabolism and the function of degrading aromatic hydrocarbons were increased by DMP contamination, such as Dechloromonas agitata, Pleomorphomonas sp., Denitratisoma oestradiolicum, Plasticicumulans lactativorans, Novosphingobium sp., Alicycliphilus denitrificans, and Thauera sp. Meanwhile, principal coordinate analysis (PCA) analysis showed that the addition of DMP divided 12 samples into two groups as followed: one was the DMP group containing a-1, a-2, b-1, b-2, c-1 and c-2 while the other was no DMP group including A-1, A-2, B-1, B-2, C-1 and C-2. It indicated that DMP was the main reason for this change. In addition, by monitoring the activity of substrate enzymes, the activity of urease, phosphatase, catalase, and invertase in the wetlands before and after the experiment, these were significantly higher in the upper layer than in the lower layer and maintained high activity. Ultimately, the average influent concentration of DMP in three VFCWs was 8.12 mg/L and the average removal efficiency of the effluent was over 90%. Our results suggested that DMP was an important factor affecting the microbial community structure of wetland and the upper layer of the VFCW was the main site for the degradation of DMP. VFCW has great potential for the removal of the high concentration of DMP and it can be a good choice for the treatment of PAEs.

The role of hydraulic conditions of coagulation and flocculation on the damage of cyanobacteria

Limited information exists on the damage of harmful cyanobacteria cells, such as Raphidiopsis raciborskii and Dolichospermum circinale, caused by the hydraulic conditions at water treatment plants especially when it comes to the mechanical stresses imposed by coagulation and flocculation. To close this gap, this study evaluated the impacts of rapid and slow-mixing on R. raciborskii and D. circinale cells and trichomes. The hydraulic conditions used during the experiment were selected based on AWWA, which are widely applied in the absence of specific treatability tests. Cellular integrity was evaluated by the Erythrosine B staining method and logistic regression was used to study the association between organism integrity and hydraulic conditions (i.e., velocity gradient and mixing time). Wilcoxon rank-sum test was used to verify if there was a significant reduction of the trichome length and cell integrity. Rapid-mixing (velocity gradient of 750 s^-1 for 60 s) reduced the odds of finding intact D. circinale to <50%, whereas the odds of finding intact R. raciborskii cells did not significantly decrease. The odds of finding intact cells of R. raciborskii were 124 times greater than D. circinale. Rapid-mixing also reduced the length of D. circinale trichomes by approximately 50% but did not significantly decrease R. raciborskii trichomes. Slow-mixing did not significantly affect organisms or trichomes of either species. The results indicate that AWWA recommendations for coagulation may cause damage to D. circinale but not to R. raciborskii, suggesting that the operation of water treatment plants could be adjusted according to the dominant cyanobacterium present in the reservoir to avoid cell rupture and metabolite release.

Aerobic denitrification performance of strain Acinetobacter johnsonii WGX-9 using different natural organic matter as carbon source: Effect of molecular weight

The aim of this study was to investigate the effect of natural organic matter (NOM) including humic acid (HA) and fulvic acid (FA), intracellular organic matter (IOM) extracted from Microcystis aeruginosa (MA) and Chlorella sp. (CH), and their different molecular weight (MW) fractions on the aerobic denitrification performance of bacterial strain WGX-9 by monitoring nitrogen removal efficiency and testing changes in organic matter with HA, FA, MA-IOM and CH-IOM as the sole carbon source. Strain WGX-9 was identified as Acinetobacter johnsonii and exhibited excellent aerobic denitrification capability. The nitrate removal efficiency with IOM as the sole carbon source was relatively higher than that with NOM as the sole carbon source. The prepared NOM and extracted IOM samples were separated into six fractions with MW cut-offs of 100, 30, 10, 5 and 1 kDa. The fraction of MW > 100 kDa contributed the largest amount to the MW distribution, accounting for 77.11%, 29.00%, 44.97% and 24.81% of HA, FA, MA-IOM, and CH-IOM, respectively. Nitrate removal efficiency was improved with decreasing MW of organic matter. For example, nitrate removal efficiency was 26.50%, 32.41%, 27.88% and 43.89% using HA, FA, MA-IOM, and CH-IOM fractions of MW > 100 kDa as the carbon source, whereas with MW < 1 kDa, it increased to 36.67%, 37.88%, 60.90%, and 68.90%, respectively. This is probably because the smaller MW fraction is more suitable for bacterial growth. These results demonstrate that the strain WGX-9 can utilize lower MW organic matter, which lays the foundations for nitrogen removal in actual drinking water reservoirs.