Showing papers on "Hydraulic retention time published in 1995"

Subsurface flow wetlands : a performance evaluation

Abstract: This paper evaluates data collected by the authors as well as other individuals and agencies at operational subsurface flow constructed wetlands. The purpose of the evaluation was to identify the influence of hydraulic loading, organic loading, hydraulic residence time (HRT) on removal performance for biochemical oxygen demand (BOD), total suspended solids (TSS), nitrogen and phosphorus. The results indicate that BOD and TSS removal can be very effective at a relatively short HRT and that BOD removal exhibits a linear relationship with organic loading. Effective nitrogen removal requires a longer HRT and appears to be limited by the low oxygen availability in these systems. Phosphorus removal is also somewhat limited and ranges from 30 to 60 percent. Design models for these parameters are available or under development

Pilot- and full-scale two-phase anaerobic digestion of municipal sludge

Abstract: Two-phase anaerobic digestion tests were conducted at DuPage County, Ill., to ascertain if this process configuration would alleviate severe foaming and overloading conditions experienced by the existing high-rate digestion system. Pilot-scale two-phase digestion of activated sludge exhibited aggregated carbohydrate-protein-lipid and volatile solids (VS) reductions of more than 70%, and gas yield and gas production rate of 0.29 m 3 /kg VS.d and 2.2 volume per culture volume per day, respectively, at an hydraulic retention time 12 days and a loading rate of 4.7 kg VS/m 3 .d without any evidence of digester foaming; this performance was considerably better than that of high-rate digestion. Acid- and methane-phase digester culture development was completed in approximately a month. The acid-digester gases contained 67% CO 2 , 30% CH 4 , 2% nitrogen, 1% H 2 S compared with 30% CO 2 , 69% CH 4 , 0% N 2 , and 0.1% H 2 S in the methane-digester gases. The methane digester generated 90 volume percent to 95 volume percent of the system methane production. An enrichment culture of fermentative acidogens was established in the acid-phase digester, whereas the methane digester harbored a dominant population of methanogenic organisms. The, existing high-rate digestion system was converted to a two-phase digestion process

UASB treatment of wastewater containing concentrated benzoate

Abstract: The upflow anaerobic sludge blanket (UASB) process removed 9799% of soluble chemical oxygen demand (COD) from wastewater containing concentrated benzoate at 37C, pH 7.5, a hydraulic retention time ...

Microbial response to environmental changes in an Anaerobic Baffled Reactor (ABR)

Abstract: Two 10 litre Anaerobic Baffled Reactors (ABR), with 8 separate compartments, were used to examine the effect of Hydraulic Retention Time (HRT), effluent recycle and temperature changes on the trophic groups in anaerobic digestion. A synthetic carbohydrate (sucrose)-protein substrate was used, and the reactors run at 20 h HRT, and 35 °C. Changing the HRT from 40 to 20 hours doubled the organic loading which caused accumulation of reduced intermediates. The pattern of Volatile Fatty Acids (VFA) at steady state due to an increase in recycle ratios led to the breakage of microbial flocs, and a reduced overall microbial activity. However, the quantity of reduced intermediates was substantially reduced. Decreasing the temperature to 25 °C had differing degrees of influence on reactors I I that is the slower growing microorganisms were more affected by the temperature drop. It was found that the unique structure of the ABR brings about the partial separation of acidogenesis and methanogenesis.

Anaerobic Treatment of Eucalyptus Fiberboard Manufacturing Wastewater by a Hybrid USBF Lab-Scale Reactor

Abstract: A hybrid upflow sludge bed-filter anaerobic reactor (USBF) at lab-scale was used for the treatment of eucalyptus fiberboard manufacturing wastewater at 37oC. A physical-chemical pre - treatment adding a neutral polyelectrolyte was applied to remove inert solids present in the wastewater that may accumulate in the reactor. Chemical Oxygen Demand (COD) removals around 94% were obtained at an organic loading rate (OLR) of 14.8 kg COD m−3 d−1, corresponding to a hydraulic retention time (HRT) of 3 days. About 70% of COD was converted to methane, giving a volumetric yield of 2.6 m3 CH4 m−3 reactor d−1 and about 7.8 m3 CH4 m−3 wastewater. The biogas methane content was approximately 53%.

Anaerobic treatment of a synthetic dairy effluent using a hybrid digester

Abstract: A mesophylic laboratory-scale hybrid anaerobic digester, combining an upflow sludge blanket and a fixed-bed design, was evaluated for the anaerobic treatment of a synthetic dairy effluent. In the first experimental study, the chemical oxygen demand of the dairy effluent was increased stepwise from 3 700 to 10 300 mg.t -1 . In the second experimental study the chemical oxygen demand (COD) of the synthetic dairy effluent was kept constant at 10 000 mgt -1 and the hydraulic retention time (HRT) was shortened stepwise from 4.1 to 1.7 d. A COD removal of between 90 and 97% was achieved at organic loading rates of between 0.82 and 6. 1 kg COD.m -3I .d -1 . At an HRT of 1.7 d, the digester achieved a methane yield of 0.354 m 3 CH 4 per kg COD removed . The best results in terms of methane yield were achieved at an HRT of 1.9 d. The data also showed that the maximum operational potential of the digester had been reached, as indicated by the drop in methane yield observed at the end of the second experimental study. The results clearly show that this particular type of digester would be suitable for the anaerobic treatment of dairy effluents. An important consequence of the data from this study is that a two-phase set-up will be required to protect the methanogens in the digester from inhibitively low pH values and high concentrations of volatile fatty acids (VFAs) produced during the acidogenic phase. The two-phase system will allow pH control in the acidogenic phase, should it be needed at a full-scale or pilot-scale treatment plant.

Continuous operations of a fluidized bed bioreactor for anaerobic digestion : Residence time effect on degradation kinetics

Abstract: A fluidized bed fermentor is used for anaerobic digestion. The influence of Hydraulic Retention Time, inlet concentration and degree of colonization is investigated. The degradation kinetics seems to depend on the ratio between outlet and inlet concentration. Different kinetic regimes are identified, showing that mass transfer in the biofilms may play an important role on the degradation kinetics.

Use of ferrous sulphate to reduce the redox potential and allow the start-up of UASB reactors treating slowly biodegradable compounds : application to a wastewater containing 4-methylbenzoic acid

Abstract: During the anaerobic treatment of slowly biodegradable wastewaters containing dissolved oxygen, the natural communities of aerobic and anaerobic facultative bacteria present in reactors' sludges may not succeed in lowering the redox potential of their environment to a level compatible with methanogenesis. In order to allow reactor start-up, it is proposed to add a single initial dose of FeSO4 directly to the reactor liquor, together with an inexpensive easily biodegradable compound (i. e. carbohydrates, agroindustrial wastes...). Under the action of sulphate reducing bacteria, FeSO4 is reduced to FeS which in turn lowers redox potential. This method was tested on an Upflow Anaerobic Sludge Bed (UASB) reactor fed at an hydraulic retention time of 5.3 ± 0.3 days with an aerobic synthetic wastewater (dissolved O2, 5 mg.l-1; redox potential referred to the standard hydrogen electrode (Eh ), +119 to +250 mV; pH 7 to 7.4; 6°C) containing p-toluic acid (4-methylbenzoic acid) as sole carbon and energy source. During the first 37 days of reactor operation, sludge Eh was high (+118 to +161 mV; pH 7.2 to 7.4; 30 to 35°C) and no COD (Chemical Oxygen Demand) removal occured. Soon after the addition of FeSO4 (0.15 g FeSO4. 7H2O per g of Volatile Suspended Solids [VSS]) and glucose (0.38 g per g VSS), sludge Eh decreased to -95 mV (pH 7.3; 33°C) while COD removal increased to 51.3%. An economical way to implement this method at full scale is suggested.

Anaerobic digestion of sewage sludge in an anaerobic fixed bed digester

Abstract: The anaerobic digestion of sewage sludge in conventional reactors requires a hydraulic retention time of around 20 days. By using a fixed bed reactor the hydraulic retention time was reduced to 3–7 days. Recirculation increased the removal of organic matter in this system.

Wastewater treatment in a pilot scale inverse fluidized-bed biofilm reactor

Abstract: A 400 L pilot-scale inverse fluidized-bed biofilm reactor(IFBBR) was used to treat synthetic wastewater. The removal efficiency of the soluble chemical oxygen demand(SCOD) was more than 90% at a hydraulic retention time(HRT) of 5 h. The IFBBR could be operated successfully for 5 months without any significant problems.

Microbial process for treatment of phenol bearing dye ‐ industry effluent in a fixed film bioreactor

Abstract: Microbial process developed to treat waste effluent arising from a dye‐industry manufacturing methyl violet, rhodamine B, nigrosine and chrysoidine was evaluated at site of the factory in a fixed film bioreactor. A culture of Pseudomonas alcaligenes, isolated from cattle dung by adaptation to the waste effluent was immobilized on rock media packed in a rectangular steel tank of 1.93 m capacity. The waste effluent was treated by recycling it for 24 h in the form of a shower through rock media at a 7 day Hydraulic Retention Time (HRT) at an influent loading rate of 0.055 m3/m2 stone bed area per day. The phenol and COD loading rates were 0.035 kg phenol/m2/day and 0.305 kg COD/m2/day respectively. The microbial treatment resulted in the removal of 51% COD, 82% BOD, 74% TOC (Total Organic Carbon), 76% phenol, 67% acetic acid and 60% colour in terms of methyl violet. The pH of the waste effluent remained stable at 8.02. Thus, using a culture of Pseudomonas sp., phenol bearing effluent from a dye‐indu...

Anaerobic digestion of ice-cream wastewater: a comparison of single and two-phase reactor systems.

Abstract: The anaerobic digestion of ice-cream wastewater, a complex substrate which includes milk proteins, carbohydrates, and lipids, has received little attention. Work using an aerobic contact system showed that at a 7.5-d hydraulic retention time (HRT), with an organic loading rate of 1.7 g COD/Ld and influent TSS (total suspended solids) of 5870 mg/L, the effluent COD was 628 mg/L, BOD was 91 mg/L and TSS was 674. Anaerobic filters have also been used at organic loadings of 6 kg COD/m{sup 3}d applied at a HRT of 0.42 day, with COD removals of 80%. Goodwing showed that this waste was capable of being treated by the UASB process with granulation commencing after 60-70 days, and gas production ranging between 0.73 and 0.93 L CH{sub 4}/g COD removed with loading rates between 0.7 and 3.0 g TOC/Ld. Two-phase anaerobic digestion is an innovative fermentation mode that has recently received increased attention. The kinetically dissimilar fermentation phases, hydrolysis-acidification and acetogenesis-methanation are operated in two separate reactors; the first of which is maintained at a very short HRT. The effluent from the first, acid-forming, phase is used as the substrate for the methane-phase reactor which has a longer HRT or cell immobilization. The aimmore » of this work was to compare the methane production capability and performance of a single-phase upflow fixed bed reactor with a two-phase digestion system. The two-phase digestion system consists of a completely mixed reactor for the acidogenic reaction and an upflow fixed bed reactor for the methanogenic reaction. Because of the high lipid content and COD of ice cream wastewater off site disposal has proved to be both expensive and poses problems to the receiving effluent treatment plant. For this reason the potential for a rapid anaerobic stabilization of the waste, with energy recovery in the form of methane gas, has been investigated in an attempt to minimize plant size and maximize gas production. 9 refs., 2 tabs.« less