Biomedical subjects

Khursheed Karim

Publications and source records attributed to Khursheed Karim.

9 recordsLinked to original sources

PubMed2006

Effect of shock and mixed nitrophenolic loadings on the performance of UASB reactors.

The effect of nitrophenolic shock loads on the performance of three bench-scale upflow anaerobic sludge blanket (UASB) reactors was studied using synthetic wastewater. Reactors R1, R2 and R3 were fed with 30 mg/L concentration of 2-nitrophenol (2-NP), 4-nitrophenol (4-NP) and 2,4-dinitrophenol (2,4-DNP), respectively, along with methanol (COD = 2000 mg/ L), sodium nitrate (NO3(-)-N=200mg/L), and other nutrients. The reactors were in continuous operation for more than 2 years before the shock loading study was performed. Five nitrophenolic shock loadings of 45, 60, 75, 90 and 120mg/L d were administrated by increasing the influent nitrophenolic concentration to 45, 60, 75, 90 and 120mg/L, respectively, while keeping hydraulic retention time as 24h. The shocks were given continuously for a period of 4 days before switching back to normal nitrophenolic loading (30mg/Ld). The reactors were allowed to recover to normal performance level before administrating the next nitrophenolic shock load. The study showed that the nitrophenolic shock load of as high as 120 mg/L d did not affect the reactors performance irreversibly. After resuming the normal nitrophenolic loading, it took almost 3-18 days for the reactors to recover from the shock effect. The study was further extended to assess the maximum possible mixed nitrophenolic loading (2NP:4NP:2,4:DNP = 1:1:1) to which 2,4-DNP acclimated granular sludge containing reactor (R3) can be exposed without hampering the reactor (R3) performance irreversibly. The reactor was able to achieve pseudo-steady-state at a mixed nitrophenolic loading of 180 mg/L d with more than 90% removal of all the three nitrophenols, but failed at a mixed nitrophenolic loading of 225 mg/Ld.

2,4-Dinitrophenol↗

PubMed2006

Methane production in a 100-L upflow bioreactor by anaerobic digestion of farm waste.

Manure waste from dairy farms has been used for methane production for decades, however, problems such as digester failure are routine. The problem has been investigated in small scale (1-2 L) digesters in the laboratory; however, very little scale-up to intermediate scales are available. We report production of methane in a 100-L digester and the results of an investigation into the effect of partial mixing induced by gas upflow/recirculation in the digester. The digester was operated for a period of about 70 d (with 16-d hydraulic retention time) with and without the mixing induced by gas recirculation through an internal draft tube. The results show a clear effect of mixing on digester operation. Without any mixing, the digester performance deteriorated within 30-50 d, whereas with mixing continuous production of methane was observed. This study demonstrates the importance of mixing and its critical role in design of large scale anaerobic digesters.

Agriculture↗

PubMed2005

Anaerobic digestion of animal waste: waste strength versus impact of mixing.

We studied the effect of mode of mixing (biogas recirculation, impeller mixing, and slurry recirculation) and waste strength on the performance of laboratory scale digesters. The digesters were fed with 5% and 10% manure slurry, at a constant energy supply per unit volume (8 W/m3). The experiments were conducted in eight laboratory scale digesters, each having a working volume of 3.73 L, at a controlled temperature of 35+/-2 degrees C. Hydraulic retention time (HRT) was kept constant at 16.2 days, resulting in a total solids (TS) loading rate of 3.08 g/Ld and 6.2 g/Ld for 5% and 10% manure slurry feeds, respectively. Results showed that the unmixed and mixed digesters performed quite similarly when fed with 5% manure slurry and produced biogas at a rate of 0.84-0.94 L/Ld with a methane yield of 0.26-0.31 L CH4/g volatile solids (VS) loaded. This was possibly because of the low solids concentration in the case of 5% manure slurry, where mixing created by the naturally produced gas might be sufficient to provide adequate mixing. However, the effect of mixing and the mode of mixing became prominent in the case of the digesters fed with thicker manure slurry (10%). Digesters fed with 10% manure slurry and mixed by slurry recirculation, impeller, and biogas recirculation produced approximately 29%, 22% and 15% more biogas than unmixed digester, respectively. Deposition of solids inside the digesters was not observed in the case of 5% manure slurry, but it became significant in the case of 10% manure slurry. Therefore, mixing issue becomes more critical with thicker manure slurry.

Bacteria, Anaerobic↗

PubMed2005

Anaerobic digestion of animal waste: effect of mixing.

Six laboratory scale biogas mixed anaerobic digesters were operated to study the effect of biogas recycling rates and draft tube height on their performance. The digesters produced methane at 0.40-0.45 L per liter of digester volume per day. A higher methane production rate was observed in unmixed digesters, while increased biogas circulation rate reduced methane production. However, different draft tube heights caused no difference in the methane production rate. Air infiltration (up to 15% oxygen in the biogas) was observed in the digesters mixed by biogas recirculation. Slight air permeability of tubing or leakage on the vacuum side of the air pump may have caused the observed air infiltration. The similar performance of the mixed and unmixed digesters might be the result of the low solids concentration (50 g dry solids per liter of slurry) in the fed animal slurry, which could be sufficiently mixed by the naturally produced biogas.

Analysis of Variance↗

PubMed2005

Anaerobic digestion of animal waste: effect of mode of mixing.

Laboratory-scale digesters were operated to study the effect of mixing (via biogas recirculation, impeller mixing, and slurry recirculation) on biogas production. Three sets of experiments were performed using cow manure slurry feed with either 50, 100, or 150 g/L total solids (TS) concentrations (referred in the text as 5%, 10%, and 15% manure slurry). The experiments were conducted at a controlled temperature of 35 degrees C and a hydraulic retention time of 16.2 days, resulting in TS loadings of 3.1, 6.2, and 9.3g/Ld for 5%, 10%, and 15% manure slurry feeds, respectively. Results showed that the unmixed and mixed digesters performed quite similarly when fed with 5% manure slurry and produced biogas at a rate of 0.84-0.94 L/Ld. The methane yield was found to be 0.26-0.28 L CH4/g volatile solids loaded. However, the effect of mixing and the mode of mixing became important when the digesters were fed thick manure slurry feeds (10% and 15%). Digesters fed with 10% and 15% manure slurry and equipped with external mixing produced about 10-30% more biogas than the unmixed digester. While the mixed digesters produced more biogas than unmixed digesters, digester mixing during start-up was not beneficial, as it resulted in lower pH, performance instability and prolonged start-up time. Mixing using biogas recirculation system was found not to be effective in the case of 15% manure slurry feed under the experimental conditions studied.

Animals↗

PubMed2004

Production of bioenergy and biochemicals from industrial and agricultural wastewater.

The building of a sustainable society will require reduction of dependency on fossil fuels and lowering of the amount of pollution that is generated. Wastewater treatment is an area in which these two goals can be addressed simultaneously. As a result, there has been a paradigm shift recently, from disposing of waste to using it. There are several biological processing strategies that produce bioenergy or biochemicals while treating industrial and agricultural wastewater, including methanogenic anaerobic digestion, biological hydrogen production, microbial fuel cells and fermentation for production of valuable products. However, there are also scientific and technical barriers to the implementation of these strategies.

Bacteria↗

PubMed2004

Flow pattern visualization of a simulated digester.

Mixing patterns inside a simulated flat bottom digester were imaged using the non-invasive techniques of computer automated radioactive particle tracking (CARPT) and computed tomography (CT). Mixing/agitation was provided using gas (air) recirculation at three different flow rates (Q(g)) of 28.32, 56.64 and 84.96 l/h, corresponding to superficial gas velocities of 0.025, 0.05 and 0.075 cm/s, respectively. Better mixing was observed in the upper zone near the top of the draft tube. However, at the bottom of the digester there was a total stagnancy at all the three gas flow rates. The maximum value of the time-averaged axial velocity inside the draft tube, at a gas flow rate of 84.96 l/h, was observed as 34.4 cm/s. The turbulent kinetic energy was observed to be maximum (724 dyn/cm(2)) inside the draft tube, and decreases radially toward the wall of the digester. The present study showed that the CARPT and CT techniques could be successfully used to identify the flow pattern in the digester and to calculate velocity and turbulence parameters quantitatively. On the other hand, the increase in gas circulation rate from 28.32 to 84.96 l/h did not significantly reduce the dead zones inside the flat bottom digester. To achieve the desired mixing and reactor performance, the operating conditions and reactor configuration need to be optimized.

Automation↗

PubMed2003

Continuous biotransformation and removal of nitrophenols under denitrifying conditions.

The effect of COD/NO(3)(-)-N ratio on the biotransformation and removal of 2-nitrophenol (2-NP), 4-nitrophenol (4-NP), and 2,4-dinitrophenol (2,4-DNP) was studied in bench scale upflow anaerobic sludge blanket (UASB) reactors. Sodium acetate and sodium nitrate were used as electron donor (substrate) and electron acceptor, respectively. Nitrate nitrogen loading was increased from 0.098 to 0.6 kg/m(3)d in order to keep COD/NO(3)(-)-N ratio as 20.8, 14.3, 9.8, 5.0, 4.0 and 3.33. Throughout the study, input nitrophenolic concentration and hydraulic retention time (HRT) were kept constant as 30 mg/l and 24h, respectively. 2-Aminophenol (2-AP), 4-aminophenol (4-AP) and 2-amino,4-nitrophenol (2-A,4-NP) were found as the major intermediate metabolite of 2-NP, 4-NP and 2,4-DNP, respectively. Removal of all the three nitrophenols increased with lowering of COD/NO(3)(-)-N ratio. However, nitrophenols removal got adversely affected when COD/NO(3)(-)-N ratio was reduced below 5. Maximum removal achieved were 91.63%, 90.17% and 86.10% for 2-NP, 4-NP and 2,4-DNP, respectively at a COD/NO(3)(-)-N ratio of 5. Simultaneous denitrification and methanogenesis was observed in all the reactors throughout the study.

Bioreactors↗

PubMed2002

Effects of alternative carbon sources on biological transformation of nitrophenols.

The removal of nitrophenols under denitrifying conditions was studied in bench-scale upflow anaerobic sludge blanket (UASB) reactors (R1, R2, R3 and R4) using three different carbon sources. Initially acetate was used as carbon source (substrate) in all the four reactors followed by glucose and methanol. Reactor R1 was kept as control and R2, R3, R4 were fed with 30 mg/l concentration of 2-nitrophenol (2-NP), 4-nitrophenol (4-NP), and 2,4-dinitrophenol (2,4-DNP), respectively. Throughout the study the hydraulic retention time (HRT) and COD/NO3-N ratio were kept as 24 h and 10, respectively. 2-Aminophenol (2-AP), 4-aminophenol (4-AP) and 2-amino,4-nitrophenol (2-A,4-NP) were found as the major intermediate metabolites of 2-NP, 4-NP and 2,4-DNP degradation, respectively. Methanol was found to be a better carbon source for 4-NP and 2,4-DNP degradation as compared to acetate and glucose, while 2-NP degradation was not influenced much by the change of substrate. Nitrate nitrogen removal was always more than 99%. COD removal efficiency of the nitrophenol fed reactors varied from 85.7% to 97.7%. The oxidation-reduction potential (ORP) inside the reactors dropped, up to -300 mv, with glucose as carbon source. As the reactors were switched over to methanol, ORP increased to -190 mv. The granular sludge developed inside the reactors was light brown in colour when acetate and glucose were used as substrate, which turned dark brown to black at the end of methanol run. Biomass yield in terms of volatile suspended solids was observed as 0.15, 0.089 and 0.14 g per gram of COD removal for acetate, glucose and methanol, respectively.

Acetates↗