Kinetic and mechanistic investigation of geosmin and 2-methylisoborneol degradation using UV-assisted photoelectrochemical

Establishing electro-functionalized gravity-driven ceramic membrane filtration (EGDCM) for decentralized treatment of algae-laden brackish water: Comparison of in-situ electro-oxidation and ex-situ electro-coagulation

Algae-laden brackish water (ABW) has remarkably threatened drinking water safety in warm coastal areas. Although gravity-driven ceramic membrane filtration (GDCM) exhibits high potential in ABW treatment during decentralized water supply, membrane fouling is still a critical problem. Herein, GDCM was skillfully electro-functionalized (EGDCM) by in-situ electro-oxidation (ISEO) based on self-fabricated Ti/SnO2-Sb dimensionally stable anode (DSA) (EO-EGDCM) and ex-situ electro-coagulation (ESEC) based on iron anode (EC-EGDCM) in this study. EO-EGDCM with KMnO4 augment (MnEO-EGDCM) was also established for comparison. Results show that ISEO increased GDCM membrane permeability by 22 %, while EC-EGDCM membrane flux was nearly 4.8 times that of GDCM. ISEO enhanced the early removal of organic pollution, and KMnO4 facilitated the active chlorine oxidization of ammonia and algal toxins on electrified Ti/SnO2-Sb DSA by suppressing the transformation of free chlorine to less reactive chloramines. Both algae cell permeabilization and intracellular organic matter release were enhanced by ISEO. But SEM-EDS, CLSM and biomass analysis evidenced that membrane biological process, which was improved by 32 %∼323 % by electrical stimulation, developed porous structures in the fouling layer in EO-EGDCM/MnEO-EGDCM. According to energy consumption and carbon emissions evaluation, GDCM was confirmed as an energy-saving system for treating ABW with the consumption of only 3.47 × 10-3 kWh/m3. Electricity demand was increased for EGDCM but still considerably lower than that for other algae-laden water treatment processes. EC-EGDCM reduced energy consumption and carbon emission by around 80 % compared to EC-EGDCM/MnEO-EGDCM. Electro-functionalization was a promising option to improve GDCM treatment of ABW via multiple mechanisms but further optimization was still required.

The analytic hierarchy process method to design applicable decision making for the effective removal of 2-MIB and geosmin in water sources

Numerous utilities encounter issues with taste and odor that alter the public's impression of the safety of drinking water. The creation of certain components in water naturally due to global climate change is another source of taste and odor components, in addition to industrial emissions. Geosmin and 2-methylisoborneol (2-MIB), both of which are generated by blue-green algae and actinomycetes, are two substances that contribute to the musty and earthy smells in drinking water sources. Unfortunately, current conventional treatment plants only partially remove 2-MIB and geosmin. Therefore, to protect the environment and public health, more up-to-date or optimized treatment methods should be applied to outdated treatment facilities. Best treatment practices, evaluation standards, and decision-making approaches, however, are still shrouded in mystery. The goal of this study was to identify the most effective treatment options for 2-MIB and geosmin. By using the analytical hierarchy process (AHP), a total of 22 assessment criteria were found and prioritized. A thorough literature search led to the identification of potential treatment options, and their effectiveness was evaluated. These options and priority rankings were decided upon using AHP in the decision-making process. Advanced oxidation techniques came out on top in the final priority ranking, followed by membrane filtering, adsorption, oxidation, hybrid processes, and traditional treatment methods. The applied analytical decision techniques may also be used to choose the optimal treatment options, even though the results are particular to 2-MIB and geosmin.

Identification of odor-causing compounds in six species of odor-producing microalgae separated from drinking water source with distinct fishy odor: Insight into microalgae growth and odor characteristics

Fishy odor, as an offensive and unpleasant odor, could occur in drinking water source with poor nutrition, it is usually considered to be associated with odor-producing microalgae. However, the specific relations among fishy odor, fishy odorants and responsible microalgae were not elucidated comprehensively. In this paper, the odor-causing compounds generated from six microalgae with fishy odor characteristic, isolated in drinking water source Tongyu River, were identified simultaneously. The sensory evaluation result indicated that Tongyu River was principally related to fishy odor (odor intensity 6.5-7.6). Correspondingly, seven, nine, seven, six, seven and seven olfactory detection peaks (ODP) were screened by combining data of GC/O/MS and GC/GC/TOFMS in Cyclotella, Cryptomonas ovate, Melosira, Dinobryon sp., Synedra and Ochromonas sp., which were isolated in Tongyu River and cultured in laboratory. Totally twenty odor-causing compounds, including hexanal, 2-hexenal, 3-hexen-1-ol, heptanal, 1-octen-3-one, 2,4-heptadienal, 2-tetradecanone, 3,5-octadien-2-one, octanal, 1-octen-3-ol, 2-octenal, nonanal, 2,4-octadienal, 2-nonenal, decanal, 2,6-nonadienal, 2-decenal, undecanal, 2,4-decadienal and dodecanal, were screened and identified in all isolated microalgae. Additionally, fishy odor intensity for all identified microalgae increased obviously as microalgae cell number increased and microalgae cell ruptured in cultivation cycles through pearson and spearman correlation analysis. For the first time, twenty odor-causing compounds associating with fishy odor were recognized from six isolated microalgae, which would provide more scientific basis and theoretical support for preventing and treating fishy odor episode of drinking water source.

Mechanism study on the effect of peracetic acid (PAA), UV/PAA and ultrasonic/PAA oxidation on ultrafiltration performance during algae-laden water treatment

In this work, peracetic acid (PAA), ultraviolet (UV)/PAA and ultrasonic (US)/PAA pre-oxidation were applied to enhance ultrafiltration (UF) performance during algae-laden water treatment. The results showed that 10 mg/L PAA, exhibiting an optimal performance with membrane fouling resistance reduced by 76.26%. Low dosage of UV/PAA can effectively control fouling by enhancing the degradation of dissolved organics. Though more radicals were generated with the increasing dosage of PAA during the UV/PAA process, flux deterioration was occurred when PAA dosage over 10 mg/L, owing to a negative correlation between fouling resistance and algal integrity loss. Compared with UV, US exhibited a worse activation effect on PAA with less reactive radicals produced. Even worse, US can stimulate the stress metabolism of algal cells with slightly integrity loss, which then resulted in an exacerbation of permeate quality. Fouling mechanism analysis revealed that the delay formation of cake layer with membrane fouling alleviation mainly through efficient degradation of macromolecular organics. The investigation of synergistic and individual effect of EOM degradation, algae rupture and IOM release on the filtration performance revealed that EOM degradation was the primary mechanism for fouling control while algae rupture rather than IOM release was crucial for membrane fouling aggravation. This indicates that moderate oxidation, with property of high organic degradation and low cell rupture, was the working principal and objectives for algae-laden water treatment. Additionally, it was found that the ·OH radicals produced during UV/PAA process can efficiently degrade representative odors. In general, pretreatments of PAA and low dosages of UV/PAA showed promising prospects in improving the UF performance of algae-laden water and treating algal secretions.