Silver doped TiO2 nanoparticles have been prepared by liquid impregnation (LI) and
photodeposition (PD) methods and characterized by surface analytical methods such as
scanning electron micrographs (SEM) and X-ray diffraction (XRD). The photocatalytic activity
of silver doped TiO2 was tested by photocatalytic degradation of C.I. Acid Red 88 (AR88) as a
model compound from monoazo textile dyes. Results show silver doped TiO2 is more efficient
than undoped TiO2 at photocatalytic degradation of AR88. The positive effect of silver on the
photoactivity of TiO2 at degradation of AR88 may be explained by its ability to trap electrons.
This process reduces the recombination of light generated electron-hole pairs at TiO2 surface.
Silver content has an optimum value 2% in LI and 0.5% in PD methods for achieving high
photocatalytic activity. The AR88 decomposition with Ag-photodeposited method was much
higher than that of deposited with LI method.
The effect of ultrasonic waves (US) was studied on the degradation of Malachite Green (MG)
as a model contaminant from textile industry by direct photolysis with ultraviolet (UV) radiation
and UV/H2O2 processes. The US (35 kHz) and UV (253.7 nm) radiations were carried out with
an ultrasonic bath and a 15 W low-pressure mercury lamp, respectively. Degradation of MG
follows pseudo-first order kinetics in all cases. The apparent reaction rate constant (kap) for
UV/US process is greater than sum of the UV and US processes but it is relatively low for
practical uses. However UV/H2O2 treatment more efficiently decomposes this organic
contaminant and combining this process with US can improve its efficiency. kap is influenced
by variation of operational parameters such as power density, temperature, initial
concentration of MG and H2O2 for US/UV/H2O2 process and activation energy was 9 kJ mol-1
in the range of 294-307 K for this process. UV-vis spectral change of MG showed
hypsochromic shift occurred with increasing sonication time, suggested N-demethylation
process of MG.
C.I. Acid Orange 7 (AO7) commonly used as a textile dye and could be degraded by UV/ZnO,
UV/H2O2 and UV/H2O2/Fe (III) (photofenton) processes. In the photocatalytic degradation of
dye by UV/ZnO process, effect of some parameters such as UV irradiation time, presence of
ZnO and UV irradiation, pH, concentrations of ZnO, dye, H2O2 and ethanol was examined and
first order reaction rate constant was calculated equal to 2.39×10-2 min-1 at experimental
condition. The semi-log plot of dye concentration versus time was linear, suggesting first order
reaction. Efficiency of photodegradation process in the absence of ZnO photocatalyst and UV
light was small. Increasing the UV irradiation time increased AO7 removal. Ethanol had
inhibitory effect on this process. Maximum AO7 removal was seen at neutral pH area. In the
UV/H2O2 process, effect of some parameters such as presence of H2O2 and UV irradiation,
amount of H2O2, effect of pH and addition of bicarbonate on the efficiency of dye removal
were examined. Absence of each of UV irradiation or H2O2 decreased AO7 removal efficiency
near to zero. Increasing H2O2 concentration increased dye removal to some extent but at
higher H2O2 concentrations, dye removal efficiency did not increase. Increasing pH to value
about 9 increased the AO7 removal efficiency and increasing bicarbonate anion concentration
decreased it. Rate constant of AO7 removal by this process was calculated to be equal to
4.221×10-1 min-1 at experimental condition. Also, the order of UV/ H2O2/Fe (III) > UV/ H2O2 >
UV/Fe (III) > H2O2/Fe (III), was seen for AO7 removal efficiency of these processes.
Increasing Fe (III) and oxalate concentration increased dye removal efficiency.
In the present study, the wet oxidation of zinc and copper cyanide complexes (cyanide
concentration of 1,000 mg dm-3) was conducted in a hydrothermal reactor, under oxygen
atmosphere of which the pressure was set to 1 MPa. The pH of the reaction solution was kept
in the range of 11 to 12 and the reaction temperature was changed from 383 K to 423 K. In the
experiments, mainly the effect of reaction time on the cyanide decomposition was investigated.
As a result, it was found that cyanide decomposition increased with an increase in the
temperature and cyanide decompositions of 99.9 % and 96.1 % were achieved after 8 hours at
423 K for Na2[Zn(CN)4] and Na3[Cu(CN)4], respectively. In the case of Na2[Zn(CN)4], mainly
HCOO- and NH4+ were identified as the decomposition products. By contrast, in the case of
Na3[Cu(CN)4], carbon of CN- was transformed either to H2CO3 or HCOO-, and nitrogen was
converted to NH4+, N2 or NO2-. Based on these results, the decomposition mechanisms of
Na2[Zn(CN)4] and Na3[Cu(CN)4] at a temperature of 423 K and pressure of 1 MPa were
The combinations of H2O2/Fe+2, UV/H2O2/Fe+2 and UV/H2O2 process were investigated on
treatment of oil recovery industry wastewater. Treatment of oil recovery industry wastewater,
a typical high pollution strength industrial wastewater (chemical oxygen deman (COD): 21000
mg l-1, biological oxygen demand (BOD): 8000 mg l-1, oil and grease:1140 mg l-1, total
dissolved solids (TDS): 37000 mg l-1, total suspended solids: 2580 mg l-1), was carried out by
batch oxidation processes.
The optimal mass ratio for H2O2/Fe+2 yielding the highest COD removal was found to be 8.658
corresponding to 200.52 g 1-1 H2O2 and 23.16 g l-1 Fe+2 concentrations for 60 minutes
reaction time. Fenton process gave a maximum COD reduction of 86% (from 21000 to 2980
mg l-1) and the combination of UV/H2O2 gave a COD reduction of 39% (from 21000 to 12730).
The percentage of removal, after the total reaction time (3.5h), H2O2: 8.4 g l-1 and Fe+2: 0.05g
l-1, in the photo Fenton process, corresponded to 81 % of the total initial COD (4200 mg l-1).
The oxidative ability of the UV/Fe+2/H2O2 process (81%) was greater than that of the UV/H2O2
process (55%) for 80% diluted wastewater. COD removal efficiency for UV/H2O2 process
(COD/H2O2=1/2 (w/w)) was 90%, 55%, and 39 when initial COD was 1050, 4200, and 21000
mg l-1, respectively, whereas COD removal was 943, 2320, and 8270 mg l-1, respectively.
Wastewaters from fossil fuel refining, pharmaceuticals, and pesticides are the main sources of
phenolic compounds. Those with more complex structures are often more toxic than the simple
phenol, and yet little is known about the treatment of wastewater containing a mixture of
phenolic pollutants. . The present study was aimed at assessing the efficacy of UASB and SBR
for the treatment of mixtures of phenolics compounds.
The experiments were conducted in a laboratory scale UASB reactor, which had a volume of
1.414 l. A gas-liquid solid separator, GLSS was provided at the top of the reactor. The reactor
was operated at constant HRT of 24 h throughout the study. The reactor was seeded with
digested sewage sludge obtained from Okhla Sewage Treatment Plant, New Delhi, India.
Initially the microbial culture was acclimatized to phenol concentration of 600 mg l-1 in UASB.
Thereafter, different phenol: m-cresols ratio were introduced, 10:1, 4.5:1, 2.7:1, 1.75:1 and
1.2:1 and the performance of the reactor was evaluated under each case. The second
experiment was conducted in a laboratory scale SBR reactor with a working volume of 1.4 l.
The effluent was drawn from a volumetric exchange ratio of 50%. A fine bubble aerator in the
bottom of the column was used to introduce air. The reactor was seeded with aerobic digested
sludge obtained from Star Paper Mill, Saharanpur, UP, India. A constant HRT of 12h was kept
throughout the study. Reactor was operated sequentially with fill, react, settle and draw periods
for a cycle of 6h. In order to establish a viable biomass and minimize any potential toxic effects
due to presence of phenolic compounds, the sludge was fed with phenol as batch culture up to
1000 mg l-1 concentration. After acclimatization, different phenol: m cresol ratio were
introduced 6.5:1, 2:1, 1.1:1, 0.5:1 and the performance of the reactor was evaluated under
each case. A start up period of 40 days was required to acclimatize the anaerobic bacterial at
HRT of 24 hrs for phenol concentration of 200 mg l-1. UASB reactor successfully biodegraded
phenol and m-cresol up to a maximum ratio (1.25:1) (300: 250 mg l-1) with 80% efficiency. A start up period of 30 days was required to acclimatize aerobic bacteria with phenol to
concentration up to 1000 mg l-1 as batch culture. The maximum phenol and m-cresol up to (1.1: 1)
(800: 700 mg l-1) was successfully treated with efficiency of 95% in SBR.The results indicates
that anaerobic treatment by UASB and aerobic treatment by SBR can be successfully used for
phenol/cresol mixture, representative of major substrates in chemical and petrochemical
wastewater and the results shows proper acclimatization period is essential for the degradation
of m - cresol and phenol. Moreover, SBR was found as a better alternative than UASB reactor
as it is more efficient and higher concentration of m cresols can be successfully degraded.
The present paper aims at a treatment technique designed for special industrial wastewaters
contaminated with only traces of halogenated organic compounds (HOCs) – concentrations
which are nevertheless large enough to make a discharge into municipal sewage works
impossible. Our research follows the idea to detoxify the water by a selective destruction of
the HOCs by hydrodehalogenation (HDH) reactions on palladium-containing nano-catalysts.
Detoxification means that persistent HOCs are converted into organic compounds which can
easily be removed by biodegradation in a wastewater treatment plant.
A novel promising trend in environmental research is the application of nano-reagents (such
as zero-valent iron) and nano-catalysts. As known from nano-sized metal particles, nanocatalysts
have the advantage of very high reaction rates due to high specific surface areas
and low mass-transfer restrictions. For special applications in wastewater treatment we were
able to generate extremely active palladium catalysts on the basis of ferromagnetic carrier
colloids. The magnetic nano-sized carriers (such as zero-valent iron or magnetite) were
spiked with traces of Pd (0.1 wt.-%). These nano-catalysts have been successfully tested in
different reactor systems at the laboratory scale. Using Pd on nano-scale supports leads to
enormous activity of the catalyst which is several orders of magnitude higher than reached in
conventional fixed-bed reactors. The ferromagnetism of the carriers enables a separation of
the catalysts from the treated water by means of magneto-separation. This gives the chance
to reuse the catalyst several times.
The preferred reductant for the HDH reaction is molecular hydrogen. For highly contaminated
waters, alternative hydrogen donors such as formic acid have been successfully tested.
Two novel materials have been developed and tested in initial studies for the in-situ
generation of sorption and reactive barriers for subsurface water treatment at low cost by
introducing sorbents or reagents via injection wells. Both materials are based on finely-ground
activated carbon with a particle size of D50 = 0.8 μm which is quasi-soluble, i.e. it forms stable
colloidal solutions in water over a wide concentration range. With these activated carbon
colloids, an approved material of environmental technology is now applicable for injection into
contaminated aquifers to form sorption barriers by controlled deposition on aquifer sediment
directly in the flow passages. A new remediation strategy can be followed – the in-situ
generation of a permeable AC sorption barrier in contaminated aquifers.
Based on the colloidal carbon particles, a second material has been developed which
combines the sorption properties of the activated carbon carrier and the reactivity of the zerovalent
iron deposits. This CARBO-IRON (20 wt-% zero-valent iron) has proved its suitability as
a dehalogenation reagent applicable for both plume and source treatment.
A simple model is presented for the dynamic calculation of the sludge blanket height and
concentrations of suspended solids (diluted, sludge blanket and return sludge) in circular
secondary settling tanks. The model combines a mass balance equation with three empirical
equations, which account for the main processes. These equations form a non-linear,
dynamic system, which cannot be solved explicitly; thus, a trial-and-error method is adopted.
Field data were obtained from a full-scale treatment plant in transient and steady state
conditions and were used in the calibration, the verification and the application of the model.
Model calibration involved the determination of only two coefficients, which were found to be
relatively constant in various operating conditions. Model verification and application were
successful showing a satisfactory agreement with field data. A discrepancy of the model to
over-predict sludge blanket height during sudden hydraulic overloads was noted and
Granular sludge is the key factor for an efficient operation of an upflow anaerobic sludge
blanket (UASB) reactor. In order to monitor the granularity of anaerobic sludge, the
determination of the granule size distribution is of vital importance. Another critical parameter
for the UASB reactor performance is the sludge bed porosity. For this reason, several
techniques have been proposed, however they are either tedious, imprecise or expensive and
hardly applicable in full scale treatment plants. There was then the need for a simple and low
cost technique. This technique involves the determination of the settling velocities of a sludge
sample and of extrapolating the corresponding diameters using a mathematical algorithm. In
the proposed algorithm, the granules density was calculated, the flow regime was examined
and finally the granule size distribution was obtained. Some very important correlations were
suggested by the experimental results. The granule density and diameter as well as the
sludge bed porosity were strongly correlated with the VSS/TSS ratio.