Effects of microplastics on DBPs formation under the chlorination of natural organic matters.

Microplastics have attracted extensive attention and concern because they inflict damage on human beings and the environment. When the microplastics enter the water system, they inevitably flow into the water treatment system and encounter disinfectants during the disinfection procedure. Chlorine can react with microplastics to form different kinds of disinfection byproducts (DBPs). O-containing functional groups on the surface of microplastics may play a major role in DBP formation. Without O-containing functional groups, microplastics can also form DBPs but with totally different mechanisms. Reactive oxygen species (ROS, i.e., •OH) and reactive chlorine substances (RCS, i.e., Cl• and ClO•) may attack the microplastics and form DBP precursors. With relatively low surface area and very little pore volume, microplastics cannot affect the DBP formation between Suwannee River fulvic acid (SRFA) and chlorine. When SRFA exists, microplastics with few O-containing functional groups can hardly form DBPs because of the inhibition of ROS and RCS.

Sorption Behavior and Mechanisms of Organic Contaminants to Nano and Microplastics.

Nano and microplastics (NPs/MPs) have received widespread attention in recent years. Because of their large specific surface area and hydrophobicity, NPs/MPs can adsorb various organic contaminants. This article gives a brief review of the sorption behavior of organic contaminants to NPs/MPs, summarizes the possible sorption mechanisms, and analyzes the influencing factors in the environment on the sorption behavior and mechanisms of NPs/MPs. The main mechanisms of sorption of organic contaminants to NPs/MPs are partitioning, surface sorption (hydrogen bonding, π-π interaction, electrostatic interaction, and van der Waals force), and pore filling. The sorption behavior of organic contaminants to NPs/MPs is not only affected by the properties of the NPs/MPs and the organic contaminants, but also by the solution chemistry, such as the pH, ionic strength, and dissolved organic matter.

Effects of residual carbon materials on the disinfection byproduct formation in artificial and natural waters.

As the effective adsorbents, carbon materials (CMs) are typically used in the removal of disinfection byproduct (DBP) precursors during the water treatment by adding CMs before disinfection procedure. However, after the separation of CMs from the treated water by flocculation, sedimentation, and filtration, a small amount of loaded activated carbon could be released into the water treatment system and affect the DBP formation in the following disinfection. In this study, three CMs, including coal-made activated carbon (CAC), sawdust charcoal (SCC), and hydroxylated multiwall carbon nanotubes (OH-MWCNT), were used to explore the effects of residual CMs in the formation of DBPs. The results indicated that some DBP precursors could be irreversibly adsorbed into the pore structure of CMs and hardly to be extracted and determined, then affected the DBP formation in the water system. In the chlorination process of surface water samples, CMs have similar effects on the formation of DBPs. However, given that water samples contain a variety of complex substances, the effects of residual CMs on the formation of DBPs were also slightly changed.

Effects of carbon materials on the formation of disinfection byproducts during chlorination: Pore structure and functional groups.

Release of carbon materials (CMs) into water and wastewater treatment systems occurs due to their increasing utilization as adsorbents for water treatment. When the CMs, mixed with natural organic matter (NOM), interact with disinfectants used during water treatment (e.g. chlorine), the released CMs can affect the formation of disinfection byproducts (DBPs). In this study, three common CMs were investigated to reveal their possible effects and the mechanisms of DBP formation during the chlorination of NOM. The experimental results indicate that DBPs generation decreased by 10-40% in the presence of CMs when Suwannee River humic acid (SRHA) was chlorinated. The adsorption of SRHA by CMs was hypothesized as the major cause for the DBPs inhibition. CMs could irreversibly adsorb DBP precursors in their mesopores through π-π bonding and hydrophobic effects. OH groups on the surface of CMs were shown to be critical for DBPs inhibition through linking with the OH or COOH groups on the surface of NOM via hydrogen bonding. The study also showed that water chemistry parameters, such as pH and salinity, can affect DBP formation by changing the adsorption of NOM onto CMs. With diverse NOM components, the presence of CMs resulted in decreased formation of trichloromethane from 57.1 µg/L to 23.8, 38.4, and 40.4 µg/L when coal-made activated carbon (CAC), wheat straw-made BC pyrolyzed at 300 °C (WSBC300), and multiwalled carbon nanotubes (MWCNTs), respectively, were added to surface water; and from 30.6 µg/L to 20.0, 19.2, and 13.2 µg/L when CAC, WSBC300, and MWCNTs, respectively, were added to wastewater.

Formation of disinfection byproducts as affected by biochar during water treatment.

Biochar (BC) is as an emerging and promising adsorbent for the removal of pollutants from aqueous solutions in water treatment given its porous structure, large surface area, and numerous O-functional groups. However, the effects of BC on the formation of disinfection byproducts (DBPs) during the disinfection process of water treatment remains largely unknown. This study investigated the influence of aqueous solution chemistry on DBP formation in the presence of BC during chlorination. BC samples prepared from different biomass precursors (wheat straw, peanut shells, and shaddock peel) with different pyrolysis temperatures were compared, and the effects of aqueous solution chemistry were systematically investigated. Results indicated that DBPs could be formed during disinfection with BC. Certain intermediate DBP products would undergo base catalysis to form trichloromethane (TCM) via hydrolysis as pH increased. This phenomenon would increase TCM content, as well as decrease chloral hydrate and 1,1-dichloro-2-propanone content. The increment in inorganic ion (NaCl) content showed negligible effects on DBP formation during BC chlorination. DBP formation was restrained in the presence of humic acid (HA) because the number of active sites on BC that participated in the reaction decreased when BC adsorbed HA.