Developing persulfate-activator soft solid (PASS) as slow release oxidant to remediate phenol-contaminated groundwater

The research objective was to develop a persulfate-activator soft solid (PASS) as a biodegradable slow-release oxidant to treat phenol-contaminated groundwater. PASS was prepared by graft copolymerization of acrylic acid (AA) and acrylamide (AM) onto 1% (w/v) sodium alginate mixed with 500 mg L−1 sodium persulfate and 5 mg L−1 ferrous sulfate. The physical and chemical properties of PASS were characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, the water content and swelling ratio. Various variables, including the ratio of AA/AM, pH, temperature and the type of groundwater cations affecting PS release, were investigated. The maximum PS release in DI water was 98% in the ratio of PASS 1 (AA/AM, 75/25), 96% at pH 3, 83% at 25 °C, and 80% with Na+. The major factors controlling PS release were the AA/AM ratio and pH. PASS 1 can be stable in size and shape for 6–8 days and completely degraded within 34 days. The degradation rates of 10 mgL−1 phenol using PASS produced the highest kobs values for each variable at a ratio of PASS 1 (k = 0.1408 h−1), pH 7 (k = 0.1338 h−1), 25 °C (k = 0.1939 h−1), and Ca2+ (k = 0.1336 h−1). The temperature of the groundwater was key to driving the reaction between PS and phenol. PASS 1 was applied in simulated phenol-contaminated groundwater via horizontal tanks containing Ottawa sand. The results indicated 93.2% phenol removal within 72 h in a narrow horizontal flow tank and 41.7% phenol removal in a wide horizontal flow tank with aeration

Developing a Slow-Release Permanganate Composite for Degrading Aquaculture Antibiotics

Copious use of antibiotics in aquaculture farming systems has resulted in surface water contamination in some countries. Our objective was to develop a slow-release oxidant that could be used in situ to reduce antibiotic concentrations in discharges from aquaculture lagoons. We accomplished this by generating a slow-release permanganate (SR-MnO4-) that was composed of a biodegradable wax and a phosphate-based dispersing agent. Sulfadimethoxine (SDM) and its synergistic antibiotics were used as representative surrogates. Kinetic experiments verified that the antibiotic-MnO4- reactions were first-order with respect to MnO4- and initial antibiotic concentration (second-order rates: 0.056–0.128 s-1 M-1). A series of batch experiments showed that solution pH, water matrices, and humic acids impacted SDM degradation efficiency. Degradation plateaus were observed in the presence of humic acids (\u3e20 mgL-1), which caused greater MnO2 production. A mixture of KMnO4/beeswax/paraffin (SRB) at a ratio of 11.5:4:1 (w/w) was better for biodegradability and the continual release of MnO4-, but MnO2 formation altered release patterns. Adding tetrapotassium pyrophosphate (TKPP) into the composite resulted in delaying MnO2 aggregation and increased SDM removal efficiency to 90% due to the increased oxidative sites on the MnO2 particle surface. The MnO4- release data fit the Siepmann–Peppas model over the long term (t \u3c 48 d) while a Higuchi model provided a better fit for shorter timeframes (t \u3c 8 d). Our flow-through discharge tank system using SRB with TKPP continually reduced the SDM concentration in both DI water and lagoon wastewater. These results support SRB with TKPP as an effective composite for treating antibiotic residues in aquaculture discharge water

Dual Activation of Peroxymonosulfate Using MnFe\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e/g‑C\u3csub\u3e3\u3c/sub\u3eN\u3csub\u3e4\u3c/sub\u3e and Visible Light for the Efficient Degradation of Steroid Hormones: Performance, Mechanisms, and Environmental Impacts

Single activation of peroxymonosulfate (PMS) in a homogeneous system is sometimes insufficient for producing reactive oxygen species (ROS) for water treatment applications. In this work, manganese spinel ferrite and graphitic carbon nitride (MnFe2O4/g-C3N4; MnF) were successfully used as an activator for PMS under visible light irradiation to remove the four-mostdetected- hormone-contaminated water under different environmental conditions. The incorporation of g-C3N4 in the nanocomposites led to material enhancements, including increased crystallinity, reduced particle agglomeration, amplified magnetism, improved recyclability, and increased active surface area, thereby facilitating the PMS activation and electron transfer processes. The dominant active radical species included singlet oxygen (1O2) and superoxide anions (O2 •−), which were more susceptible to the estrogen molecular structure than testosterone due to the higher electron-rich moieties. The self-scavenging effect occurred at high PMS concentrations, whereas elevated constituent ion concentrations can be both inhibitors and promoters due to the generation of secondary radicals. The MnF/PMS/vis system degradation byproducts and possible pathways of 17β-estradiol and 17α-methyltestosterone were identified. The impact of hormone-treated water on Oryza sativa L. seed germination, shoot length, and root length was found to be lower than that of untreated water. However, the viability of both ELT3 and Sertoli TM4 cells was affected only at higher water compositions. Our results confirmed that MnF and visible light could be potential PMS activators due to their superior degradation performance and ability to produce safer treated water

Enrofloxacin and Sulfamethoxazole Sorption on Carbonized Leonardite: Kinetics, Isotherms, Influential Effects, and Antibacterial Activity toward \u3ci\u3eS. aureus\u3c/i\u3e ATCC 25923

Excessive antibiotic use in veterinary applications has resulted in water contamination and potentially poses a serious threat to aquatic environments and human health. The objective of the current study was to quantify carbonized leonardite (cLND) adsorption capabilities to remove sulfamethoxazole (SMX)- and enrofloxacin (ENR)-contaminated water and to determine the microbial activity of ENR residuals on cLND following adsorption. The cLND samples prepared at 450oC and 850oC (cLND450 and cLND550, respectively) were evaluated for structural and physical characteristics and adsorption capabilities based on adsorption kinetics and isotherm studies. The low pyrolysis temperature of cLND resulted in a heterogeneous surface that was abundant in both hydrophobic and hydrophilic functional groups. SMX and ENR adsorption were best described using a pseudo-second-order rate expression. The SMX and ENR adsorption equilibrium data on cLND450 and cLND550 revealed their better compliance with a Langmuir isotherm than with four other models based on 2.3-fold higher values of qmENR than qmSMX. Under the presence of the environmental interference, the electrostatic interaction was the main contributing factor to the adsorption capability. Microbial activity experiments based on the growth of Staphylococcus aureus ATCC 25923 revealed that cLND could successfully adsorb and subsequently retain the adsorbed antibiotic on the cLND surface. This study demonstrated the potential of cLND550 as a suitable low-cost adsorbent for the highly efficient removal of antibiotics from water

Adsorptive–Photocatalytic Performance for Antibiotic and Personal Care Product Using Cu\u3csub\u3e0.5\u3c/sub\u3eMn\u3csub\u3e0.5\u3c/sub\u3eFe\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e

The amount of antibiotics and personal care products entering local sewage systems and ultimately natural waters is increasing and raising concerns about long-term human health effects. We developed an adsorptive photocatalyst, Cu0.5Mn0.5Fe2O4 nanoparticles, utilizing co-precipitation and calcination with melamine, and quantified its efficacy in removing paraben and oxytetracycline (OTC). During melamine calcination, Cu0.5Mn0.5Fe2O4 recrystallized, improving material crystallinity and purity for the adsorptive–photocatalytic reaction. Kinetic experiments showed that all four parabens and OTC were removed within 120 and 45 min. We found that contaminant adsorption and reaction with active radicals occurred almost simultaneously with the photocatalyst. OTC adsorption could be adequately described by the Brouers–Sotolongo kinetic and Freundlich isotherm models. OTC photocatalytic degradation started with a series of reactions at different carbon locations (i.e., decarboxamidation, deamination, dehydroxylation, demethylation, and tautomerization). Further toxicity testing showed that Zea mays L. and Vigna radiata L. shoot indexes were less affected by treated water than root indexes. The Zea mays L. endodermis thickness and area decreased considerably after exposure to the 25% (v/v)-treated water. Overall, Cu0.5Mn0.5Fe2O4 nanoparticles exhibit a remarkable adsorptive–photocatalytic performance for the degradation of tested antibiotics and personal care products

Removing PAHs from urban runoff water by combining ozonation, adsorption, and biodegradation

The water quality of lakes and rivers associated with metropolitan areas is declining from increased inputs of urban runoff that contain polycyclic aromatic hydrocarbons (PAHs). Our objective was to develop a treatment technology that removes PAHs from urban runoff. We accomplished this by developing a flow-through system that uses ozone (O3) to quickly transform PAHs in a runoff stream and then removes the O3-transformed PAHs via adsorption to either activated carbon or carbon nano-onions (CNOs); adsorbed PAH products are then further biodegraded. To quantify the efficacy of this approach, 14C-labeled phenanthrene and benzo(a)pyrene, as well as a mixture of 16 PAHs were used as test compounds. These PAHs were pumped from a reservoir into a flow-through reactor that continuously ozonated the solution. Outflow from the reactor then went to a chamber that contained either activated carbon or CNOs that adsorbed the O3-treated PAHs and allow clean water to pass. By adding a microbial consortium to the CNOs following adsorption, we observed that bacteria were able to degrade the adsorbed products and release more soluble, transformed products back into solution. Control treatments confirmed that parent PAH structures were not biologically degraded following CNO adsorption and that O3-treated PAHs were not released from the CNO in the absence of bacteria. For phenanthrene, we identified diphenaldehyde as the product of ozonation and diphenaldehydehdric acid as the biological product released from the CNOs. We then compared the biodegradability of these products to the parent structures in unsaturated soil microcosms. Results showed that the parent phenanthrene structure was more biodegradable (Σ 14CO2 released = 51%) than the transformed products (34.5 - 36.7%) but for the 5-ring benzo(a)pyrene, the products produced by ozone (22.3%) or released from the CNO following biological treatment (35.2%) were significantly more biodegradable than the parent compound (2.7%). As an alternative to using activated carbon or CNOs, we also verified that the ozonated product (diphenyldehyde) could be biologically mineralized in a bioreactor and that mineralization rates improved with acclimation of the microbial population. These results support the combined use of ozone and biological degradation as a means of removing PAHs from urban runoff

Using slow-release permanganate candles to remediate PAH-contaminated water

Surface waters impacted by urban runoff in metropolitan areas are becoming increasingly contaminated with polycyclic aromatic hydrocarbons (PAHs). Slow-release oxidant candles (paraffin–KMnO4) are a relatively new technology being used to treat contaminated groundwater and could potentially be used to treat urban runoff. Given that these candles only release permanganate when submerged, the ephemeral nature of runoff events would influence when the permanganate is released for treating PAHs. Our objective was to determine if slow-release permanganate candles could be used to degrade and mineralize PAHs. Batch experiments quantified PAH degradation rates in the presence of the oxidant candles. Results showed most of the 16 PAHs tested were degraded within 2–4 h. Using 14C-labled phenanthrene and benzo(a)pyrene, we demonstrated that the wax matrix of the candle initially adsorbs the PAH, but then releases the PAH back into solution as transformed, more water soluble products. While permanganate was unable to mineralize the PAHs (i.e., convert to CO2), we found that the permanganate-treated PAHs were much more biodegradable in soil microcosms. To test the concept of using candles to treat PAHs in multiple runoff events, we used a flow-through system where urban runoff water was pumped over a miniature candle in repetitive wet–dry, 24-h cycles. Results showed that the candle was robust in removing PAHs by repeatedly releasing permanganate and degrading the PAHs. These results provide proof-of-concept that permanganate candles could potentially provide a low-cost, low-maintenance approach to remediating PAH-contaminated water

Developing slow-release persulfate candles to treat BTEX contaminated groundwater

The development of slow-release chemical oxidants for sub-surface remediation is a relatively new technol­ogy. Our objective was to develop slow-release persulfate-paraffin candles to treat BTEX-contaminated ground­water. Laboratory-scale candles were prepared by heating and mixing Na2S2O8 with paraffin in a 2.25 to 1 ra­tio (w/w), and then pouring the heated mixture into circular molds that were 2.38 cm long and either 0.71 or 1.27 cm in diameter. Activator candles were prepared with FeSO4 or zero-valent iron (ZVI) and wax. By treat­ing benzoic acid and BTEX compounds with slow-release persulfate and ZVI candles, we observed rapid trans­formation of all contaminants. By using 14C-labeled benzoic acid and benzene, we also confirmed mineraliza­tion (conversion to CO2) upon exposure to the candles. As the candles aged and were repeatedly exposed to fresh solutions, contaminant transformation rates slowed and removal rates became more linear (zero-order); this change in transformation kinetics mimicked the observed dissolution rates of the candles. By stacking per­sulfate and ZVI candles on top of each other in a saturated sand tank (14 × 14 × 2.5 cm) and spatially sampling around the candles with time, the dissolution patterns of the candles and zone of influence were determined. Results showed that as the candles dissolved and persulfate and iron diffused out into the sand matrix, ben­zoic acid or benzene concentrations (Co = 1 mM) decreased by \u3e90% within 7 d. These results support the use of slow-release persulfate and ZVI candles as a means of treating BTEX compounds in contaminated groundwater. Includes Supplementary Materials

Improving the treatment of non-aqueous phase TCE in low permeability zones with permanganate

Treating dense non-aqueous phase liquids (DNAPLs) embedded in low permeability zones (LPZs) is aparticularly challenging issue for injection-based remedial treatments. Our objective was to improve thesweeping efficiency of permanganate (MnO4−) into LPZs to treat high concentrations of TCE. This wasaccomplished by conducting transport experiments that quantified the penetration of various perman-ganate flooding solutions into a LPZ that was spiked with non-aqueous phase14C-TCE. The treatments weevaluated included permanganate paired with: (i) a shear-thinning polymer (xanthan); (ii) stabilizationaids that minimized MnO2rind formation and (iii) a phase-transfer catalyst. In addition, we quantifiedthe ability of these flooding solutions to improve TCE destruction under batch conditions by develop-ing miniature LPZ cylinders that were spiked with14C-TCE. Transport experiments showed that MnO4−alone was inefficient in penetrating the LPZ and reacting with non-aqueous phase TCE, due to a distinctand large MnO2rind that inhibited the TCE from further oxidant contact. By including xanthan withMnO4−, the sweeping efficiency increased (90%) but rind formation was still evident. By including thestabilization aid, sodium hexametaphosphate (SHMP) with xanthan, permanganate penetrated 100% ofthe LPZ, no rind was observed, and the percentage of TCE oxidized increased. Batch experiments usingLPZ cylinders allowed longer contact times between the flooding solutions and the DNAPL and resultsshowed that SHMP + MnO4−improved TCE destruction by ∼16% over MnO4−alone (56.5% vs. 40.1%).These results support combining permanganate with SHMP or SHMP and xanthan as a means of treatinghigh concentrations of TCE in low permeable zones. [Includes supplementary materials