Showing papers on "Hydraulic retention time published in 1991"

Anaerobic biodegradation of cyanide under methanogenic conditions.

Abstract: Upflow, anaerobic, fixed-bed, activated charcoal biotreatment columns capable of operating at free cyanide concentrations of greater than 100 mg liter-1 with a hydraulic retention time of less than 48 h were developed. Methanogenesis was maintained under a variety of feed medium conditions which included ethanol, phenol, or methanol as the primary reduced carbon source. Under optimal conditions, greater than 70% of the inflow free cyanide was removed in the first 30% of the column height. Strongly complexed cyanides were resistant to removal. Ammonia was the nitrogen end product of cyanide transformation. In cell material removed from the charcoal columns, [14C]bicarbonate was the major carbon end product of [14C]cyanide transformation.

Treatment of liquid swine manure in the sequencing batch reactor under aerobic and anoxic conditions

Abstract: Laboratory studies were conductedon a sequencing batch reactor (SBR) for the treatmentof screenedliquid swine manure. The SBR was operated on the basis of a 24 hours cycle at 6 and 9 days hydraulic retention time and 20 days solids biological retention time. Nitrification and denitrification processes were carried out in the same reactor by alternating aerobic/anoxic conditions, and the tested time ratios were 19/3, 16/6, 14/8 and 10/12 (hours). The results from the overall performance indicated that above 99% NH3-N, 93% TKN, 97% COD and 97% TSS removal were achieved in the SBR treatment. Anoxic operation did not adversely affect the activity of the nitrifyers, and NO2-NO3-N concen tration increased up to 230 mg/L following air supply. However, sludge settling was poor in those reactors functioning with an anoxic period greater than 8 hours. As a result of nitrification and denitrification the removal of ammonia and nitrite plus nitrates nitrogen was 80 to 93%.

Oxidation of hydrogen sulfide by flocculated Thiobaccillus denitrificans in a continuous culture

Abstract: In a continuous fermentation, significant advantages may be gained by immobilization of microbial cells. Immobilization allows cells to be retained in the fermenter or to be readily recovered and recycled. Therefore, the hydraulic retention time and the biomass retention time are decoupled. A novel cell immobilization has been developed for the immobilization of autotrophic bacteria by coculture with floc-forming heterotrophic bacteria with growth of the latter limited by the availability of organic carbon. The result is an immobilization matrix which grows along with the immobilized autotroph. We have previously demonstrated the utility of this approach by immobilizing the chemoautotroph Thiobacillus denitrificans in macroscopic floc by coculture with floc-forming heterotrophs from an activated sludge treatment facility. Floc with excellent settling characteristics were produced. These floc have now been used to remove H(2)S from a gas stream bubbled through continuous cultures. The stoichiometry and kinetics of H(2)S oxidation by immobilized T. denitrificans were comparable to that reported previously for free-cell cultures. Oxygen uptake measurements indicated the growth of both T. denitrificans and the heterotrophs although the medium contained no added organic carbon. Continuous cultures with total biomass recycle were maintained for up to four months indicating the long-term stability of the commensal relationship between the immobilized autotroph and the heterotrophs which composed the immobilization matrix. It was observed that at any given H(2)S loading the biomass concentration reached a maximum and leveled out. The ultimate biomass concentration was dependent upon the H(2)S feed rate.

Amelioration of methane yield in cheese whey fermentation by controlling the ph of the methanogenic stage

Abstract: A two-stage, no-mix anaerobic digester of 145 L capacity was used to investigate the effect of controlling the pH of the methanogenic stage on the biogas production and the pollution potential reduction of acid cheese whey. The digester was operated at a 15-d hydraulic retention time, and a temperature of 35°C. Controlling the pH of the methanogenic stage increased the biogas production rate and methane yield by 77.77 and 289.00%, respectively. Reductions of up to 32.19, 44.44, and 35.86% in the COD, solids and nitrogen were achieved.

Ozone Application for the Improvement of UASB Reactor Effluent I. Physical-Chemical and Biological Appraisal

Abstract: Ozonation can improve the effluent characteristics of UASB (upflow anaerobic sludge blanket) reactors treating domestic sewage, by removing organic matter, solids, surfactants, color and microorganisms. In Brazil, part of the effluent of a 120 msup3; UASB reactor, fed with screened domestic sewage at an hydraulic retention time of 7 hours, was post-treated in a two-column ozonation system of 300 liters total volume. With a contact time of 50 minutes and ozone application dosage of 16.7 mg/L, the following removals were obtained at the ozonation step: 51‰ BOD, 56‰COD, 76‰ TSS, 62‰ color, and 91‰ surfactants. Pathogens and indicator organisms were inactivated to over 99.9‰. Ozonation completely destroyed Salmonella, protozoa cysts and helminth eggs and larvae.

Denitrification by thermophilic soil bacteria with ethanol as substrate in a USB reactor

Abstract: Thermophilic biological denitrification was studied in a laboratory-upflow sludge blanket reactor fed with ethanol as carbon and energy source. High denitrification efficiency (>98%) was obtained at an ethanol: nitrate ratio >2 and at a hydraulic retention time (HRT) of 5 hours. The performance of the system with respect to nitrate removal was very satisfactory (>95%), even at high nitrate (235 mg NO3-N/L) and hydraulic (3 hours HRT) loading rates applied.

Analysis and anaerobic degradation of wool scouring and olive oil mill wastewaters.

Abstract: Two types of fatty industrial wastewaters, wool scouring effluents (WSE) and olive oil mill effluents (OME) were analysed (lipids, phenols and COD), and were then treated anaerobically in laboratory-scale fixed bed filters. Approximately 50% of the organic compounds in both wastewaters was degraded at two days of hydraulic residence time. A higher biogas production was obtained when using OME rather than WSE. This experimental study confirmed that anaerobic digestion can be considered as a roughing treatment in a multi-step process for industrial fatty wastewaters.

Start‐up of sequencing batch reactors for toxic wastewater treatment

Abstract: The start‐up of sequencing batch reactors (SBR) for the treatment of phenol‐bearing wastewater was achieved in about a week without any seeding, using the culture present in raw sewage only. The mixed liquor suspended solids (MLSS) concentration was grown to about 3000 mg/1 without showing any inhibition effects at phenol concentrations as high as 800 mg/1. The effluent concentrations of phenol were consistently less than 0.5 mg/1 during most of the start‐up phase. The response of the SBR to shock loadings of phenol at concentrations up to 1600 mg/I was favorable and over 75% phenol removal was maintained at a hydraulic retention time of 1 day.

Start-up and operation of a fluidized-bed reactor oxidizing butyrate by a defined syntrophic population

Abstract: Start-up and operation of a fluidized-bed reactor were investigated with butyrate or butyrate plus acetate as sole substrates. Start-up could be enhanced by increasing the amount of inoculum and by providing balanced substrate concentrations in a wellbuffered synthetic wastewater. High-rate degradation of butyrate to methane and carbon dioxide was achieved with a maximum organic loading rate (OLR) of 34.5 kg chemical oxygen demand (COD)/m3·d at a hydraulic retention time (HRT) of 0.47 d and with a COD removal efficiency of 87%.

Treating contaminated groundwater using a fluidized‐bed reactor

Abstract: Both biological treatment and carbon adsorption have inherent advantages for remediation of groundwater contaminated with compounds such as benzene, toluene, ethylbenzene, and xylenes (BTEX). Biological treatment destroys the contaminants and is extremely cost-effective. Carbon adsorption is a positive removal mechanism that ensures a product water of high quality, but the process is relatively expensive and requires frequent carbon replacement and/or regeneration. Coupling the two processes realizes the inherent advantages of both approaches. An additional benefit of combining these removal mechanisms in a biological fluidizedbed reactor (FBR) system is that no loss of BTEX from volatilization occurs, since predissolution of oxygen is used in place of conventional aeration for the fluidized-bed process. This article summarizes preliminary performance data from a laboratory, pilot-scale biological FBR, using granulated activated carbon (GAC) as the support media (GAC-FBR), operated at various BTEX concentrations and organic loading rates. Greater than 99-percent degradation of total BTEX was achieved at an organic loading rate of 3.0 kg COD/m3-day or less and an empty bed hydraulic retention time of 5.0 minutes. System performance was extremely robust, easily handling a tenfold step increase in loading due to the combined adsorptive capability of the biofilm-coated GAC and ability to subsequently bioregenerate the GAC. Monitoring verified that no off-gas was produced during treatment.

Characterization of pollutants at source and biological treatment of a CTMP effluent

Abstract: Effluents from seventeen different sources in a CTM pulp and paper mill were collected for analysis. The pollutants in each effluent were characterized. Concentrations and loadings of BOD 5 , COD, resin and fatty acids (RFA), and other pollutant constituents in the effluent from CTMP washing were very much higher than those in the other effluents. A pollutant material balance was made around the whole mill. Laboratory scale aerobic biodegradation treatment of the CTMP washing effluent was studied under a very wide range of conditions of pH, hydraulic retention time, temperature, and level of dissolved oxygen

Efficiency of a phthalate ester in an activated sludge system

Abstract: The optimization of an organic compound removal (di‐n‐butyl phthalate, or DBP) from an activated sludge system with recycle is presented The experimental procedure has been developed using two latin squares and having as variables the hydraulic retention time (HRT), the concentration of the compound (C), and the percentage of return sludge (R) It has been found that the phthalate compound can be removed very efficiently The experimental results and the statistical analysis followed indicate that HRT and C are the variables affecting to a great extend the removal of the compound R does not appear to have a significant effect on the process, at least in the investigated range from 75% to 200% The ciliate population was analyzed using the saprobic method The microbiological results suggest that although DBP shows an inhibitory effect at higher concentrations, it does not appear to be toxic to the microorganisms

Theoretical and experimental study of a sequential batch reactor treatment of liquid swine manure

Abstract: A laboratory scale sequential batch reactor (SBR) was used to digest liquid swine manure containing 1 to 2% suspended solids. Hydraulic retention time, biological solid retention time and influent concentration were varied during the tests. The treated effluent was analyzed for suspended solids, chemical oxygen demand, ammonia, and nitrate plus nitrite. In addition, a mathematical model was developed to describe the changes in concentration with time of chemical oxygen demand, ammonia, and nitrate plus nitrite in the SBR reactor. Results of the experimental study showed that the single reactor SBR process is capable of reducing the potential polluting carbon and nitrogen components of a concentrated wastewater to a high degree when it is operating at 7 to 9 days HRT and a BSRT around 20 days. The mathematical model developed followed quite closely the changes in COD, ammonia, and oxides of nitrogen on a laboratory scale, and should be useful for assessment of SBR system designs for commercial swine manure treatment.

Anaerobic bioflocculation of wool scouring effluent

Abstract: A two-stage anaerobic bioflocculation process is investigated to successfully flocculate the emulsified wool grease from wool scouring effluent. After 110 days of continuous operation, the laboratory process gave promising results by removing between 70 and 90% wool grease and about 60 to 86% COD at a combined hydraulic residence time (HRT) of 4 to 10 days. Methane production and volatile fatty acids consumption were negligible. Most of the grease was thought to be removed by flocculation as a result of anaerobic activity. Since the supernatant of the treated effluent still contained residual grease of over 1 500 mg/L, further purification is necessary. The supernatant was easily treatable by the classical aerobic activated sludge treatment (internal sludge recycle), which removed virtually all of the residual wool grease resulting in less than 100 mg/l in the final effluent, at an HRT of 3 days.

Degradation of resorcinol in upflow anaerobic filter

Abstract: Biodegradation of resorcinol was studied in upflow anaerobic filter (UAF). Substrate and total organic carbon (TOO removal efficiencies above 90% were achieved when substrate loadings were increased from 0.38 kg to 2.07 kg/m3/d. Gas yield was around 0.54 m3/kg COD removed. The system remained unaffected even at an influent resorcinol concentration of 2000 mg/1. Decrease in hydraulic retention time (HRT) upto 16 h did not influence the performance of the filter. Low effluent suspended solids (< 50 mg/1) indicated that solids washout was minimum and the system operated at high solids retention time (SRT).

Treatment of Tapioca Starch Wastewater By Anaerobic Digestion Coupled With Membrane Separation Process

Abstract: This study thus looks into two treatment processess : i) Anaerobic digester coupled with hollow fibre membrane unit. Treatment of starch waste with anaerobic digester-membrane system was studied. area of hollow fibre membrane unit of known pore size was immersed into laboratory-scale anaerobic digestion system. The pore size of membrane was varied from 0.03 to m. The hydraulic retention time of anaerobic digester was varied from 1.5 to 10 days. The effect of hydraulic retention time on treatment efficiency was significant while effect of membrane size was not significant. The gas production was about 0.74㎥/kg COD treated. The COD removal efficient was about 80-95% depending on the hydraulic retention time. ii ) Crossflow ultrafiltration as post treatment to anaerobic filter. The effluent from anaerobic filter, which had a total COD in the range of 4,500-5,200 mg/L was treated by crossflow ultrafiltration units. The study conducted with different membrane pore size indicated that membrace with 1,000,000 molecular weight cut-off size gave a higher COD removal efficiency in the range of 83-87% while giving a study flux of .h. A study was conducted to see the long term clogging effect of membrane also.