Showing papers on "Hydraulic retention time published in 1988"

Anaerobic acidogenesis of a complex wastewater: I. The influence of operational parameters on reactor performance

Abstract: The influence of operational, parameters, such as hydraulic retention time, organic loading rate, influent substrate concentration, pH, and temperature, on the performance of the first phase of anaerobic digestion has been investigated. A complex substrate based on beef extract was used, and six series of experimental runs were conducted, each one showing the effect of one operational variable. The predominant fermentation products were always acetic and propionic acid, independent of the values of the operational parameters. For initial COD concentrations and hydraulic retention times above the critical values identified as 3 g/L and 6 h, respectively, the degree of acidification achieved was between 30 and 60%. The degree of acidification was found to increase with the hydraulic retention time and decrease with the influent substrate concentration and organic loading rate, while the opposite held true for the rate of product formation. Furthermore, it has been demonstrated that acidification is primarily determined by the hydraulic retention time and the rate of product formation by the influent substrate concentration. The concentration of the acetic acid produced was found to depend on the operational parameters. However, the concentration of propionic acid produced depended only on the substrate availability with a consistent proportion of 8% initial COD converted to it. The optimum pH and temperature were 7 and 40 degrees C, respectively. The percentage of acetic acid as a proportion of the total volatile fatty acids produced was found to increase with increasing pH and temperature, while the percentage of propionic acid seemed to decrease accordingly. Finally the effect of the temperature on the rate of acidification followed an Arrhenius type equation with an activation energy equal to 4739 cal/mol.

Fast Kinetics of Fe2+ Oxidation in Packed-Bed Reactors

Abstract: Thiobacillus ferrooxidans was used in fixed-film bioreactors to oxidize ferrous sulfate to ferric sulfate. Glass beads, ion-exchange resin, and activated-carbon particles were tested as support matrix materials. Activated carbon was tested in both a packed-bed bioreactor and a fluidized-bed bioreactor; the other matrix materials were used in packed-bed reactors. Activated carbon displayed the most suitable characteristics for use as a support matrix of T. ferrooxidans fixed-film formation. The reactors were operated within a pH range of 1.35 to 1.5, which effectively reduced the amount of ferric iron precipitation and eliminated diffusion control of mass transfer due to precipitation. The activated-carbon packed-bed reactor displayed the most favorable biomass holdup and kinetic performance related to ferrous sulfate oxidation. The fastest kinetic performance achieved with the activated-carbon packed-bed bioreactor was 78 g of Fe2+ oxidized per liter per h (1,400 mmol of Fe2+ oxidized per liter per h) at a true dilution rate of 40/h, which represents a hydraulic retention time of 1.5 min.

Anaerobic treatment of leachate using fixed film and sludge bed systems

Abstract: Pretreated landfill leachate was successfully treated in anaerobic upflow blanket filter (UBF) and downflow stationary film (DSF) reactors. The DSF reactor achieved 94% chemical oxygen demand (COD) removal at a loading rate of 14.7 kg COD/ m3 d and corresponding hydraulic retention time (HRT) of 1.5 days. The UBF reactor, operated similarly, maintained 97% COD removal. An inorganic heavy metal precipitate formed in both reactors; the precipitate coated the biofilm support in the DSF reactor while in the UBF reactor the precipitate was concentrated in the reactor sludge bed and filter media. Biofilm and sludge granules in both reactors were about 80% fixed solids. Raw un treated leachate, saturated with acclimated biomass, was treated in a UBF at loading rates up to 44 kg COD/m3 d and HRT down to 10 hours. COD removal was in excess of 88%. The maximum specific removal rate of the biomass for this wastewater and reactor configuration was 1.2 kg COD/kg VSS-d (VSS = volatile sus pended solids). J. Water Pollut. Control Fed., 60, 1675 (1988).

Sulphate removal in acidogenic phase anaerobic digestion

Abstract: The acidogenic phase of a two stage anaerobic digestion process using distillery molasses slops effluent with high sulfate concentrations (4.2–5.1 gl‐1) was investigated. Sulfate removal was studied at pH 5.4, 5.8, 6.2, 6.6 and in a stirred reactor (CSTR) and in an upflow fixed film fixed bed reactor operated at 22 h, 1.2 days retention time. The biological sulfate removal increased with pH and so did the acetic acid production from the fermentative and sulfate reducing bacteria. For the same pH and hydraulic retention time more efficient sulfate removal was obtained in the fixed film reactor than in the CSTR.

Carbon-to-nitrogen ratio and hydraulic retention time effect on the anaerobic digestion of cheese whey.

Abstract: SIXTEEN 1-L digesters were used to test four carbon-to-nitrogen ratios of 8.4, 13.9, 22.2 and 27.6 and four hydraulic retention times of 12, 18, 24 and 30 days on the efficiency of digester operation. Percent methane in the biogas and methane production were dependent on both carbon-to-nitrogen ratio and hydraulic retention times. Percent chemical oxygen demand reduction, volatile solids removal, total volatile acids concentrations, digester pH and amount of sodium hydroxide solution needed to control digester pH were dependent on hydraulic retention time only.

Effect of hydraulic residence time on microbial sulfide production in an upflow sludge blanket denitrification reactor fed with methanol

Abstract: In the combined ion exchange/biological denitrification process for nitrate removal from ground water anion exchange resins are regenerated in a closed circuit by way of an upflow sludge blanket denitrification reactor. The regenerant (a concentrated sodium bicarbonate solution) is recirculated through the ion exchanger in the r generation mode and the denitrification reactor. In the closed system sulfate accumulates to very high concentrations. For that reason it was examined under what process conditions sulfate reduction occurs in an upflow sludge blanket denitrification reactor, when the influent contains high sulfate concentrations (5.45 g SO42-/l) and high sodium bicarbonate concentrations (19.8 g NaHCO3/l) in addition to nitrate and methanol. It appeared that at a hydraulic residence time of 5 h sulfide production started, when the nitrate loading rate was 20% of the denitrification reactor capacity and methanol was added in excess. The excess of methanol was converted into acetate after nitrate was depleted. Conversion of methanol into acetate was a function of the hydraulic residence time. At hydraulic residence times above 8 h this conversion was complete. Also in batch experiments it was observed that excess of methanol was converted into acetate, and that sulfate reduction started when nitrate was depleted. From all experiments it is clear that, provided that methanol is added in good relation to the quantity of nitrate that has to be denitrified, acetate will not be produced and sulfate reduction will not occur in the denitrification reactor, even in the presence of very high sulfate concentrations.

Stability of a downflow anaerobic fixed-film reactor to feed change

Abstract: A stepped-loading start-up regime utilising volatile fatty acids as carbon and energy sources was applied to a downflow anaerobic fixed-film reactor operated at 37°C. A steadystate was attained with over 90% COD reduction at an organic loading rate of 6.1 Kg COD/m3·day. A complex wastewater coming from a citrus processing plant was then used to test the feasibility of feeding changes as well as the stability of the reactor performance. A final COD reduction of 60% was achieved with hydraulic retention times down to 1.5 days.

The potential of bacteriophage to act as tracers of water movement

Abstract: Bacteriophage to the bacteria Serratia marcescens and Enterobacter cloaceae were used to trace the movement of water in a number of environments: surface waters, activated sludge reactors and waste stabilisation ponds. In addition a number of factors thought to influence their survival characteristics were assessed. The die-off rate of these bacteriophage in aquatic environments was a function of temperature and sunlight, and the die-off increased dramatically with increased temperature. Bacteriophage proved excellent for time of travel studies on rivers. Also for activated sludge reactors with short hydraulic retention times, they proved useful for the determination of the degree of reactor short circuiting. They did not suffer from the problem of sludge binding, but their high die-off meant they could not be used to estimate dispersion numbers in reactors with a hydraulic retention time >6h. In waste stabilisation ponds the elevated temperatures resulted in a one log reduction of bacteriophage/d. Again this meant they were of little use for the determination of dispersion number but could be exploited to provide a good qualitative indication of the degree of short-circuiting occurring within the ponds.