Hydroxyl (OH) radical is proposed as an important factor in the ozonation of water. It is necessary for the utilization of ozonation in the water treatment process to quantitatively determine the interaction among ozone, OH radical and dissolved substances during ozonation. In this study, the effect of humic acid on OH radical generation during ozonation was evaluated with ESR/spin-trapping/stopped-flow technique using resorcinol as a model compound of humic substances. The OH radical was trapped with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a stable adduct, DMPO-OH. The initial velocity (ν0) of DMPO-OH generation increased as a function of ozone and resorcinol concentrations. The relation among ozone, resorcinol concentrations and the initial velocity (ν0) of DMPO-OH generation was kinetically analyzed using a power law equation and the following equation was obtained: ν0 ([DMPO-OH] 10-6 M/s) = (9.55 × 10-5) × [resorcinol (10-6 M)] × [ozone (10-6 M)]1.9 + (3.09 × 10-5) × [ozone (10-6 M)]1.72. The equation fitted the experimental results very well. This equation indicated that in the presence of 1 μM resorcinol, 1/3 of ozone concentration is enough to produce the same initial velocity of OH radical generation as that without resorcinol. The kinetic equation for the enhancing effect of resorcinol obtained in the present study should provide useful information to optimize the condition in ozone treatment process of water containing humic substances.
Anaerobic decolorization of two kinds of dye, viz., azo type represented by Methyl Orange (MO) and anthraquinone type represented by Reactive Blue 4 (RB4) was performed using digested sludge under mesophilic (35°C) and thermophilic (55°C) conditions. Decolorization of dye was investigated to compare the efficiency and extent of decolorization, and additionally to evaluate the effect of temperature and dye on decolorizing microorganisms. Glucose was used as an electron donor in terms of co-substrate without the addition of other nutrients. Under thermophilic treatment, high efficiency of decolourisation was shown in both of the dyes at high concentration, 1000 mg·L-1of MO and 600mg·L-1 of RB4 compared with mesophilic treatment. MO, 200mg·L-1, was decolorized 95-98% under both mesophilic and thermophilic conditions. High decolorizing efficiency of RB4, 100mg·L-1, obtained under thermophilic conditions, was 80% when compared with mesophilic conditions (70%). The reduced form of MO showed an auto-oxidizing effect with pink to violet color when exposed to air, while RB4 showed no auto-oxidizing reaction. The inhibition of MO was effected on sugar conversion to fatty acids, and CH4 productivity resulted in slow reduction of TOC. While RB4 inhibited only on methane productivity, in which TOC reduction was similarly used as control. Due to the increase of temperature, methanogenesis was inhibited and which low CH4 production, whereas an increase of decolorizing efficiency on both dye decolorization and a high rate of TOC reduction was observed.
Ten mg-AC/L aqueous solutions of 18 kinds of agricultural chemicals (ACs), such as organophosphorus, organochlorine and amidic chemicals, were prepared and underwent the biodegradation test. The samples attained through the test were considered to contain various decomposition products, hereafter referred to as composite samples. Mutagenicity and mutagen formation potential (MFP) were measured for the composite samples, and the test results revealed that the ACs tested in the present study do not produce mutagens as a result of undergoing the biodegradation test. However, 12 out of 18 samples manifested statistically significant MFP. All of the 12 ACs, except for iminoctadine-triacetate, were aromatic compounds. Specific activities for thiram and DDVP, which were reported to be mutagenic, were measured, showing 320 net rev./mg and 190 net rev./mg respectively. Compared with these values, MFP of the composite samples attained from ferimzone, pyridiphenthion, bentazone, bensultap, and napropamide were greater. Accordingly, it was suggested that some ACs, though they were non-mutagenic compounds, could form strong mutagens when they were biodegraded in a water environment, and the decomposition products subsequently intruded into the raw water for water supply, and the water was then chlorinated at a purification plant.
The use of zero-valent iron (ZVI) represents one of the latest innovative technologies for groundwater remediation. The reactivity of ZVI is enhanced when the particle size is in the nanometer range. However, nanoscale ZVI has limited field applications for in-situ groundwater remediation such as permeable reactive barriers due to its powdery form. Therefore, a method of adhering nanoparticles on a supporting material was suggested. In this paper, functionalized mesoporous silica beads were created using 3-mercaptopropyltrimethoxy silica, tetrabutyl orthosilicate, and cetyltrimethyl ammonium bromide, and their physical and chemical characteristics were measured. The highly active ZVI nanoparticles were adhered on these mesoporous silica beads. The reactivity of the resulting material was tested using nitrate solution. The reductive reaction of nitrate indicated that the degradation of nitrate appeared to be pseudo-first order with a high reaction rate constant of 0.1619 h-1. The reaction constant decreased to 0.0122 h-1 after 3 h of experiment due to mass transfer limitation. The higher dose of the supported nanosized ZVI increased the removal rate as well as the removal efficiency of nitrate.
Groundwater is one of the most important sources for drinking water. Arsenic (As) contamination of groundwater is a serious problem worldwide, especially in Bangladesh, India and South East Asia. Adsorption using appropriate and readily available adsorbents is a promising method for the removal of arsenic with applicability in rural areas. This work aims to study the removal of arsenic from synthetic groundwater using an adsorption column by sequential combination of laterite (LA) and iron-modified activated carbon (AC-Fe) as adsorbents. The effect of ratio LA/AC-Fe, flow rate, initial arsenic concentration and pH to the breakthrough time were investigated. Adsorption equilibrium and adsorption kinetics were also studied through batch experiment. The result was found to be an efficient and feasible approach for arsenic treatment from groundwater for ready applicability in rural areas.
Certain aquatic and/or terrestrial plants have been used as artificial floating island systems in water pollution control. This research was carried out to confirm the release of anti-cyanobacterial allelochemicals from aquatic and terrestrial plants suitable for artificial floating island systems. A series of cyanobacterial assays using the culture solution extracts of umbrella plant (Cyperus alternifolius) and Canna (Canna generalis) demonstrated the release of anti-cyanobacterial allelochemicals. GC/MS analysis of the solid extract of C. alternifolius culture solution indicated the existence of 9 phenolic compounds [resorcinol, 3-hydroxy benzoic acid, 4-hydroxy benzoic acid, (4-hydroxyphenyl) acetic acid, vanillic acid, protocatechuic acid, p-coumaric acid, gallic acid, and ferulic acid], and 4 carboxylic compounds (azelaic acid, butanedioic acid, dehydroabietic acid, and malic acid) in which anti-cyanobacterial compounds were involved.
Recently, nitrite has been recognized as one of the considerable inhibitors of biological phosphorus removal. In fact, there are several reports on inhibitory effect of nitrite. While unfortunately, the reported critical levels of nitrite widely spread. So the real effect of nitrite has not yet been well understood. In this study, several batch tests were conducted to obtain stable and quantitative relation between the size of nitrite exposure and the size of inhibition. The obtained results are as follows; 1) Nitrite inhibits aerobic phosphate uptake of PAOs, but the inhibition is not direct inhibition by nitrite but indirect inhibition caused by reduced respiration, 2) PAOs with higher anoxic activity can reduce the inhibitory effect of nitrite, possibly because of aerobic nitrite denitrification, 3) Nitrite inhibition of aerobic phosphate uptake is successfully expressed by the model including aerobic nitrite denitrification rates. These results strongly suggest that unstable nitrite inhibition of aerobic phosphate uptake is caused by widely distributed anoxic activities of PAOs.