8 research outputs found
Effects of aeration rate and detention time on thermophilic aerobic digestion of mixed sludge and its dewaterability
Thermophilic aerobic digestion (TAD) is a possible alternative for
rapid sludge degradation and producing Class A biosolids. Aeration rate
and detention time are two of the important parameters in TAD processes
due to rapidly growing thermophilic bacteria population, limited
solubility of oxygen at high temperatures and the need to prevent
cooling of TAD process. Also the current knowledge and understanding of
dewatering TAD biosolids are limited and incompelet.The objectives of
this study were to investigate the effects of various aeration rates
and detention time on some characteristics of mixed sewage sludge. Four
glass-cylindrical digesters with 7 liters of sludge in each, placed in
a water bath and were operated at 55 °C with the aeration rates of
2.14, 3.00, 3.86 and 4.71 volume of air per volume of sludge per hours.
It was found the increase in aeration rate decreased the required
detention time in order to meet the Class A sludge regulations to
reduce vector attraction. The values of Oxidation-Reduction Potential
(ORP) were changed from negative values to positiv ones and the values
of pH were increased from around neutral to slightly basic, but this
increases were occured at different detention times. TAD affected
dewaterability of mixed sewage sludge and produced biosolids with
higher specific resistance to filtration (lower dewaterability) than
undigested sludge. Thermophically digested sludge has a good setteling
behavior and air drying on sand bed
Decolorization And Biological Degradation Of Azo Dye Reactive Red2 By Anaerobic/Aerobic Sequential Process
This study investigates the anaerobic treatability of reactive Red2 in
an anaerobic/aerobic sequential process. Laboratory scale anaerobic
baffled reactor and fixed activated sludge reactor were operated at
different organic loadings and hydraulic retention times. The effects
of shock dye concentration on the chemical oxygen demand and color
removal efficiencies were investigated in the anaerobic baffled
reactor. The effect of hydraulic retention time on the color and
chemical oxygen demand removal efficiencies were also investigated in
the aerobic reactor. The studies were carried out in continuous mode
and the effluent of the anaerobic baffled reactor was used as feed for
the fixed activated sludge reactor. Chemical oxygen demand removal
efficiency of 54.5% was obtained at HRT =1 day in the anaerobic
reactor. The average color removal was 89.5%. Chemical oxygen demand
removal efficiency of 69% was obtained at HRT =7 h in the aerobic fixed
activated sludge reactor. A slight decrease of the color was also
observed in the aerobic reactor. This investigation has shown that
successful treatment of a highly colored wastewater is possible in the
anaerobic baffled reactor. Also the results showed that, anaerobic
biological system has higher efficiency in dye removal than fixed
activated sludge system, while aerobic system has higher efficiency in
chemical oxygen demand removal comparing with the anaerobic baffled
reactor
F--F-Journal-JOURNA~10001.mdi
Abstract Thermophilic aerobic digestion (TAD) is a possible alternative for rapid sludge degradation and producing Class A biosolids. Aeration rate and detention time are two of the important parameters in TAD processes due to rapidly growing thermophilic bacteria population, limited solubility of oxygen at high temperatures and the need to prevent cooling of TAD process. Also the current knowledge and understanding of dewatering TAD biosolids are limited and incompelet.The objectives of this study were to investigate the effects of various aeration rates and detention time on some characteristics of mixed sewage sludge. Four glass-cylindrical digesters with 7 liters of sludge in each, placed in a water bath and were operated at 55 º C with the aeration rates of 2.14, 3.00, 3.86 and 4.71 volume of air per volume of sludge per hours. It was found the increase in aeration rate decreased the required detention time in order to meet the Class A sludge regulations to reduce vector attraction. The values of Oxidation-Reduction Potential (ORP) were changed from negative values to positiv ones and the values of pH were increased from around neutral to slightly basic, but this increases were occured at different detention times. TAD affected dewaterability of mixed sewage sludge and produced biosolids with higher specific resistance to filtration (lower dewaterability) than undigested sludge. Thermophically digested sludge has a good setteling behavior and air drying on sand bed. Key words: Sludge processing, thermophilic aerobic digestion, Class A biosolid, oxidation-reduction potential (ORP), sludge dewaterability, specific resistance to filtration (SRF) Abstract Thermophilic aerobic digestion (TAD) is a possible alternative for rapid sludge degradation and producing Class A biosolids. Aeration rate and detention time are two of the important parameters in TAD processes due to rapidly growing thermophilic bacteria population, limited solubility of oxygen at high temperatures and the need to prevent cooling of TAD process. Also the current knowledge and understanding of dewatering TAD biosolids are limited and incompelet. The objectives of this study were to investigate the effects of various aeration rates and detention time on some characteristics of mixed sewage sludge. Four glass-cylindrical digesters with 7 liters of sludge in each, placed in a water bath and were operated at 55 º C with the aeration rates of 2.14, 3.00, 3.86 and 4.71 volume of air per volume of sludge per hours. It was found the increase in aeration rate decreased the required detention time in order to meet the Class A sludge regulations to reduce vector attraction. The values of oxidation-reduction potential (ORP) were changed from negative values to positiv ones and the values of pH were increased from around neutral to slightly basic, but this increases were occured at different detention times. TAD affected dewaterability of mixed sewage sludge and produced biosolids with higher specific resistance to filtration (lower dewaterability) than undigested sludge. Thermophically digested sludge has a good setteling behavior and air drying on sand bed
Effectiveness Of Chitosan As Natural Coagulant Aid In Treating Turbid Waters
During the last decade, there has been a concern about the relation
between aluminum residuals in treated water and Alzheimer disease, and
more interest has been considered on the development of natural
coagulants such as chitosan. Chitosan, a natural linear
biopolyaminosaccharide, is obtained by alkaline deacetylation of
chitin. The present study was aimed to investigate the effects of alum
as coagulant in conjunction with chitosan as coagulant aid on the
removal of turbidity, hardness and Escherichia coli from water. A
conventional jar test apparatus was employed for the tests. The optimum
pH was observed between 7 to 7.5 for all turbidities. The optimum doses
of alum and chitosan when used in conjunction, were 10mg/L and 1mg/L,
5mg/L and 0.5mg/L, and 5mg/L and 0.5mg/L in low, medium and high
turbidities, respectively. Turbidity removal efficiency was resulted
between %74.3 to %98.2 by alum in conjunction with chitosan. Residual
Al+3 in treated water was less than 0.2 mg/L, meeting the international
guidelines. The results showed that turbidity decrease provided also a
primary Escherichia coli reduction of 2-4 log units within the first 1
to 2 hr of treatment. Hardness removal efficiency decreased when the
total hardness increased from 102 to 476mg/L as CaCO3. At low initial
turbidity, chitosan showed marginally better performance on hardness,
especially at the ranges of 100 to 210 mg/L as CaCO3. In conclusion,
coagulant aid showed a useful method for coagulation process. By using
natural coagulants, considerable savings in chemicals and sludge
handling cost may be achieved
Survey on possibility of Disinfection of Isfahan North Wastewater Treatment Plant Effluent by Low and Medium Pressure Ultraviolet Systems in Pilot ScaleSystems in Pilot Scale
"n "n "nBackgrounds and Objectives:Today, due to health, environmental and economical problems, of chlorine application, UV radiation is better option than chlorine for disinfection of effluent. The aim of this study was disinfection of secondary effluent with UV radiation."nMaterials and Methods: Two types of UV disinfection system including low pressure (LP) and medium pressure (MP) was used to disinfection of Isfahan North Wastewater Treatment Plant (INWWTP) effluent without pretreatment. Single and combined lamps were operated to evaluate the removal of total and fecal coliforms (TC and FC), and fecal streptococcus (FS). TSS, iron, hardness, UV absorption and transmittance were analyzed in order to observe the fouling of the quartz sleeves. "nResults: After using LP lamp with dose of 161 mws/cm2, TC and FC content was declined to standard level (1000 TC, and 400 FC/100ml). In addition, disinfection with MP lamp was led to FS content of 400 MPN/100 mL. Combination of LP and MP, with dose of 460 mws/cm2 could be met the environmental requirements of TC & FC, and the FS count was reached to 400 MPN/100 mL with dose of 237 mws/cm2. Maximum photo-reactivation percentage of coliforms after LP and MP lamps were appeared 15 and 3 percent respectively, while it was not observed for FS."nConclusion: High fluctuation in secondary effluent quality of INWWTP mainly TSS concentration was caused to decline of the UVT value. Therefore, disinfection of effluent by LP, MP and even combined both systems are not applicable in conventional UV dose. Hence, using advanced process unit before UV disinfection system is necessary for removal of TSS
Removal of hexavalent chromium (VI) from aqueous solutions using surface modified nanozeolite A
Chromium (VI) adsorption behavior and capacity by surface modified
nanozeolite A has been investigated. Surface modification was performed
and the morphology of modified and unmodified nanozeolite was studied
using Scanning Electron Microscope (SEM) and Transmission Electron
Microscope (TEM). Adsorption isotherms were studied under different
conditions (pH, adsorbent dose, adsorbate concentration and interaction
time). The Langmuir monolayer adsorption capacity (q m ) was found to
be 14.16 mg Cr(VI) per gram at pH = 3.0 at room temperature. Chromate
adsorption on surface modified nanozeolite A was found to be inversely
proportional to the pH. Effect of competitive ions was studied and it
was found that there is no significant competition between chromate
adsorption and presence of competitive ions. Results revealed that
Langmuir model is in good agreement with experimental re-sults. Results
of examinations on a polluted natural sample showed that surface
modified nanozeolite A could reduce chromium (VI) concentration to
acceptable criteria. Based on results, surface modified nanozeolite A
is an effective sorbent for removing chromate from aquatic solution and
the adsorption ability is enhanced by surface modification
Performance of Moving Bed Biofilm Reactors for Biological Nitrogen Compounds Removal from Wastewater by Partia; Nitrification-Dentrifiction Process
In this research, the continuously operated laboratory scale Kaldnes
(k1) moving bed biofilm reactors (MBBRs) under partial
nitrification-denitrification process were used for treatment of
synthetic wastewater containing ammonium and glucose. The Anoxic and
Aerobic reactors were filled to 40 and 50 %( v/v) to attach and retain
biomass with k1 biofilm carriers, respectively. The favorite internal
recycle ratio and hydraulic residence time (HRT) to eliminate nitrogen
compounds were 300% of inflow rate and 20 hours, respectively. Optimal
dissolved oxygen (DO) was 1-1.5 mg/L in the aerobic reactor. No sludge
was returned into the system and only an internal recycling was
performed from aerobic to anoxic reactor. The results showed that the
maximum and average specific nitrification rate (SNR) in the aerobic
reactor were 49.4 and 16.6 g NOx-N/KgVSS.day, respectively and the
maximum and average specific denitrification rate (SDNR) as 156.8 and
40.1gNOx-N/KgVSS.day in the anoxic reactor, respectively. The results
also showed that it is possible to reach a stable partial nitrification
with high ratio of NO2-N/NOx-N (80% to 85%) during high load ammonium
and low DO concentration (>1.5 mg/L) in the aerobic reactor. During
optimum conditions, the average removal efficiency of total nitrogen
(TN), ammonia and soluble organic carbon (SCOD) occurred as 98.23%,
99.75% and 99.4%, respectively. This study showed that the partial
nitrification/denitrification process in the moving bed biofilm
reactors system has an acceptable performance for treatment of
wastewater with high load of organic carbon and organic nitrogen
compounds
Removal of cadmium and humic acid from aqueous solutions using surface modified nanozeolite A
The sorption of cadmium and humic acids from aqueous solutions using
surface-modified nanozeolite A has been investigated under various
examination conditions. The morphology of untreated and treated
nanozeolite was studied under scanning electron microscope and
transmission electron microscope. Isotherms of cadmium adsorption onto
surface-modified nanozeolite A were studied at different pH, solid to
liquid ratio, adsorbate concentration and interaction time. Kinetic and
equilibrium studies were conducted and the equilibrium data have been
analyzed using Langmuir and Freundlich isotherm models. The study
revealed that experimental results were in agreement with the
Freundlich model. The Langmuir monolayer adsorption capacity was found
to be 1666.67 g cadmium and 6.75 g humic acid per gram of modified
nanozeolite A, which is higher than that of reported value for other
zeolites. The sorption ability was enhanced by surface modification and
reduction in size and enabled the zeolite to adsorb cadmium. The
adsorption of cadmium and humic acid on nanozeolite was found to be the
highest at pH 6 and 3, respectively. Results showed that solid to
liquid ratio and pH are the most important factors for cadmium and
humic acid removal, respectively. Effect of competitive ions was
studied and results showed that there is no competition between cadmium
and humic acid sorption and presence of these ions