Comparative study on DBPs formation profiles of intermediate organics from hydroxyl radicals oxidation of microbial cells

Magnetic Fe3O4 nanoparticles enhance cyanobactericidal effect of allelopathic p-hydroxybenzoic acid on Microcystis aeruginosa by enhancing hydroxyl radical production

Recently, considerable progress has been made in the environmental application of nanotechnology. However, little is known about how nanomaterials might affect the cyanobacterial suppression potential of allelochemicals. In this study, a microcosm was employed to simulate and verify the effect of magnetic Fe₃O₄ nanoparticles (MFN) on the inhibitory influence of allelopathic hydroxybenzoic acid (p-Ha) on bloom-forming Microcystis aeruginosa. MFN had a hormetic effect on cyanobacterial growth. At a neutral concentration of 182 mg/L, MFN enhanced the algal suppression by p-Ha and decreased the IC₅₀ by half, which was significantly and positively associated with the amount of OH. Furthermore, adding MFN induced a stronger physiological response than treatment with only p-Ha. The cellular integrity was severely disrupted for the cyanobacterium M. aeruginosa. The total protein content decreased rapidly to inactivate the algae by limiting the amounts of extracellular microcystin and polysaccharide released. The modification of the effect of p-Ha by MFN was reflected by the intracellular NO content of M. aeruginosa. In addition, the typical radical scavengers ascorbic acid and 5,5-dimethyl-1-pyrroline N-oxide decreased OH production to weaken algal suppression under the combined treatment with p-Ha and MFN. By contrast, the addition of Fe³⁺ and increasing the light intensity triggered the generation of OH and strong cyanobacterial suppression. Thus, MFN could enhance the cyanobacterial control efficiency of p-Ha and decrease the input of allelochemicals in the field. These findings suggest a novel mode of allelochemical modification by nanomaterials as a promising cyanobactericide for harmful algal bloom management.

Intermittent light and microbial action of mixed endogenous source DOM affects degradation of 17β-estradiol day after day in a relatively deep natural anaerobic aqueous environment

All kinds of wastewaters containing steroid estrogens (SEs) and mixed endogenous source dissolved organic matter (DOM) enter natural water environments with intermittent illumination where microbial action occurs in a relatively deep natural aqueous environment. The role of mixed endogenous source DOM in SEs' biodegradation and photochemical degradation in such environments was studied using 17β-estradiol (E2) in laboratory experiments under anaerobic conditions. The experimental results show that microbial action can improve the optical properties and electron transfer capability of mixed endogenous source DOM, promoting photodegradation and biodegradation. Intermittent illumination attenuates DOM's electron transfer capacity and its chromophore groups, but it improves the bioavailability of low molecular weight dissolved organic matter which promotes microbial growth under anaerobic conditions. DOM-mediated co-degradation by light and microbial action over three days was better than either individually. The presence of Fe(III) promoted electron transfer, and Fe(III)-DOM complexes accelerated energy transfer under irradiation, enhancing photodegradation. Any remaining estrogens will continue to degrade, most effectively in well-aerated waters with sufficient illumination.

Removal of organics by combined process of coagulation-chlorination-ultrafiltration: optimization of overall operation parameters

To gain the run parameters of the combined process of coagulation/in situ chlorination/ultrafiltration (UF) so that the system can remove as much organic contaminants as possible without serious membrane fouling, the impacts of operation conditions in coagulation and pre-chlorination unit were investigated in a pilot-scale test. The characteristics of organics in UF influent were examined by excitation emission matrix spectroscopy to find out fouling behavior of different natural organic matter compositions to UF membrane. Thereafter, the operation parameters of different processing units of the hybrid device were optimized by response surface methodology (RSM). The results showed that the tests with the agitation speed of 40 r min^-1 had the lowest membrane fouling rate and the highest COD_Mn removal, in addition, inappropriate dosage of sodium hypochlorite in membrane influent might exert negative impacts on membrane by lowering UV₂₅₄ rejection, especially during the high algae laden period. The predominant factors of membrane fouling were the existence of tryptophan protein-like substances and the soluble microbial products. Optimum values of the mechanical rotation speed in coagulation unit, chemical dosage in pre-chlorination unit, and membrane flux in UF unit of the integrative process were 41.79 r min^-1, 1.40 mg L^-1, and 82.26 LMH, respectively.

Formation of iodo-trihalomethanes (I-THMs) during disinfection with chlorine or chloramine: Impact of UV/H2O2 pre-oxidation

Ultraviolet/hydrogen peroxide (UV/H₂O₂) pre-oxidation has the potential to induce reactions with dissolved organic matter (DOM) and alter the generation of disinfection byproducts (DBPs). This study evaluated the influence of UV/H₂O₂ pretreatment on the formation of iodo-trihalomethanes (I-THMs) during disinfection with chlorine or chloramine. The changes of precursors, I^- and Br^-, after UV/H₂O₂ pretreatment were investigated, and then, the formation and speciation of I-THMs during chlorination or chloramination after pre-oxidation were explored. Additionally, the effects of UV doses and H₂O₂ concentrations on the formation and speciation of I-THMs were studied. It was found that UV/H₂O₂ pretreatment could change larger molecular weight (MW) DOM to smaller MW species, which had less aromatic organic compounds and fluorescence substances. Additionally, insignificant transformations of I^- and Br^- were observed after UV/H₂O₂ treatment. Compared to direct disinfection, UV/H₂O₂ pretreatment resulted in 23.0 ± 3.5% reduction in I-THMs formation during post-chlorination while an enhancement was observed during post-chloramination at a UV dose of 460 mJ/cm² and 20 mg/L H₂O₂. Moreover, total I-THM concentration increased from 43.7 ± 2.4 to 97.6 ± 14.9 nM with the increase of UV doses from 0 to 1400 mJ/cm² during the post-chlorination process, while reduced when the UV fluence was >460 mJ/cm² during the post-chloramination. Additionally, the generation of I-THMs during both post-chlorination and post-chloramination was positively related to the H₂O₂ levels from 0 to 20 mg/L in the UV/H₂O₂ pretreatment.

Membrane Fouling and Rejection of Organics during Algae-Laden Water Treatment Using Ultrafiltration: A Comparison between in Situ Pretreatment with Fe(II)/Persulfate and Ozone

In this study, in situ pretreatments with ozone and Fe(II)/persulfate were employed to suppress membrane fouling during the filtration of algae-laden water and to improve the rejection of metabolites. Both ozonation and Fe(II)/persulfate pretreatments negatively impacted the cell integrity, especially ozonation. Fe(II)/persulfate pretreatment improved the removal of dissolved organic carbon and microcystin-LR, but ozonation resulted in a deterioration in the quality of the filtered water. This suggests that the Fe(II)/persulfate oxidation is selective for organic degradation over cell damage. With ozonation, 2-methylisoborneol and geosmin were detected in the filtered water, and the irreversible fouling increased. The intracellular organic release and generation of small organic compounds with ozonation may be the reason for the increased membrane fouling. Fe(II)/persulfate oxidation substantially mitigated the membrane-fouling resistance at concentrations over 0.2 mM compared to the membrane-fouling resistance without oxidation. The combined effect of oxidation and coagulation is likely the reason for the excellent fouling control with Fe(II)/persulfate pretreatment. Membrane fouling during the filtration of algae-laden water is successively governed by complete-blocking and cake-filtration mechanisms. Ozonation caused a shift in the initial major mechanism to intermediate blocking, and the Fe(II)/persulfate pretreatment (>0.2 mM) converted the dominant mechanism into single-standard blocking.

Microcystis aeruginosa-laden water treatment using enhanced coagulation by persulfate/Fe(II), ozone and permanganate: Comparison of the simultaneous and successive oxidant dosing strategy

In this study, the application of enhanced coagulation with persulfate/Fe(II), permanganate and ozone for Microcystis-laden water treatment was investigated. Two oxidant dosage strategies were compared in terms of the organic removal performance: a simultaneous dosing strategy (SiDS) and a successive dosing strategy (SuDS). To optimize the oxidant species, oxidant doses and oxidant dosage strategy, the zeta potential, floc size and dimension fraction, potassium release and organic removal efficiency during the coagulation of algae-laden water were systematically investigated and comprehensively discussed. Ozonation causes most severe cell lysis and reduces organic removal efficiency because it releases intracellular organics. Moreover, ozonation can cause the release of odor compounds such as 2-methylisoborneol (2-MIB) and geosmin (GSM). With increasing doses, the performance of pollutant removal by coagulation enhanced by persulfate/Fe(II) or permanganate did not noticeably improve, which suggests that a low dosage of persulfate/Fe(II) and permanganate is the optimal strategy to enhance coagulation of Microcystis-laden water. The SiDS performs better than the SuDS because more Microcystis cell lysis occurs and less DOC is removed when oxidants are added before the coagulants.