Performance of a glucose fed periodic anaerobic baffled reactor under increasing organic loading conditions: 1. Experimental results

The influence of the organic loading rate on the performance of an innovative reactor, the periodic anaerobic baffled reactor (PABR) was examined. A laboratory-scale PABR of four compartments being fed with a glucose based synthetic medium performed with high stability while the feed organic load was doubled from 12.5 to 25 and then to 50 gCOD/l. Finally the feed concentration was increased to 75 gCOD/l. The successive step changes in the feed concentration lasted for 20, 15, and 7 d, respectively. The COD removal efficiency of the PABR was satisfactory in the first two transitions (approximately 97.5 and 96%). In the third transition (OLR=18.75 gCOD/l/d) the reactor failed as the pH dropped to 4. The concentrations of butyric and valeric acids increased as the organic loading was increased and eventually they became greater than the concentration of acetic and propionic acids.     

Design and operation of pulsed anaerobic digesters

The development of a pulse-driven loop reactor (PDLR), a pulsed anaerobic filter (PAF) and a pulsed anaerobic baffled reactor (PABR) is described. In an anaerobic PDLR internal circulation is achieved by a specially designed pulse-nozzle. In a PAF and PABR an oscillation is superimposed onto the liquid content of the fermenters by means of a pulse pump without any moving devices in the reactors. Pulsed digesters faciliate degassing, avoid reactor clogging as well as short-circuiting and allow a variety of packed-bed to fluidized-bed operations. Anaerobic fermentation of acetic acid and distillery slops in pulsed digesters on a laboratory scale shows that hydrodynamic stress caused by pulsation is well compatible to degrading bacteria.List of Symbols PAF Pulsed Anaerobic Filter - PDLR Pulse-Driven Loop Reactor - PABR Pulsed Anaerobic Baffled Reactor     

On the behavior of the periodic anaerobic baffled reactor (PABR) during the transition from carbohydrate to protein-based feedings

The influence of the organic substrate composition in the feed of an innovative reactor, the periodic anaerobic baffled reactor (PABR) is examined. A laboratory-scale PABR fed on a synthetic medium composed of mixtures of glucose (a carbohydrate) and gelatin (a protein) in various ratios performed well. The PABR seemed to be minimally affected during the gradual substitution of glucose by gelatin. In fact, the reactor performance remained at an optimal level (approximately 98%), while operated under an organic loading rate of 3.125 gCOD/l/d.     

Performances of a full-scale novel multiplate anaerobic reactor treating cheese whey effluent

A 450-m(3) multiplate anaerobic reactor (MPAR) has been started-up in April 1992 for treating wastewater (whey permeate and domestic wastewater) at the Nutrinor (Lactel) cheese factory in Chambord (Québec, Canada). The MPAR consists of four superimposed sections. The liquid flows upwards from one section to the next, while the gas is collected below each plate and evacuated through side-outlets. The wastewater is concurrently distributed at the bottom of the first, second, and third sections, as 50%, 33%, and 17% of the total influent stream, respectively. Granular anaerobic sludge at an initial concentration of 30 kg of volatile suspended solids (VSS) per cubic meter of reactor liquid volume was used to inoculate the reactor. Under normal operation of the factory, the chemical oxygen demand (COD) concentration of the influent ranged from 20 to 37 kg COD m(-3). The reactor organic loading rate (OLR) fluctuated between 9 and 14.7 kg COD m(-3) d(-1) for hydraulic retention times (HRT) maintained between 55 and 68 h. At the highest OLR, the MPAR showed an efficiency of 98% and 92% for soluble and total COD removal, respectively, and a methane production rate averaging around 4 m(3) m(-3) d(-1).Biomass-specific activities ranged between 7 and 51, 1.3 and 8.5, 5.3 and 12.2, 60 and 119, and 119 and 211 mmol g(-1) VSS d(-1) for glucose, propionate, acetate, formate, and hydrogen, respectively. Average equivalent-diameter of the granules was around 0.65 mm. The MPAR reactor generally showed a large capacity for solid retention with a biomass content between 32 and 37 kg VSS m(-3). (c) 1995 John Wiley & Sons, Inc.     

Performance of a periodic anaerobic baffled reactor fed on Chinese traditional medicine industrial wastewater

A four-compartment periodic anaerobic baffled reactor (PABR) was run in a 'clockwise sequential' switching manner continuously fed on chinese traditional medicine industrial wastewater under an alkalinity concentration between 1000 and 1500 mg CaCO(3)/L of the feed with average organic load rate (OLR) at about 1, 2, 4 and 6 kg COD/(m(3)d) for 12, 24, 24 and 6d, respectively. Hydraulic residence time was 2d, while switching period was 4d. As the average OLR increased to 6 kg COD/(m(3)d), the time of the sharp fall in pH, chemical oxygen demand (COD) removal, gas production and methane percentage of the biogas of all the compartments and the time of rapid volatile fatty acids accumulation in effluent coincided, hence the PABR became sour. Denaturing gradient gel electrophoresis (DGGE) community fingerprints and their cluster analysis revealed that community structures of each compartment tended to be more closely related if the PABR was not overloaded.     

Anaerobic membrane reactor with phase separation for the treatment of cheese whey

Two-phase anaerobic digestion of cheese whey was investigated in a system consisting of a stirred acidogenic reactor followed by a stirred methanogenic reactor, the latter being coupled to a membrane filtration system to enable removal of soluble effluent whilst retaining solids. The acidogenic reactor was operated at a hydraulic retention time (HRT) of one day, giving maximum acidification of 52.25% with up to 5 g/l volatile fatty acids, of which 63.7% was acetic acid and 24.7% was propionic acid. The methanogenic reactor received an organic load up to 19.78 g COD/ld, corresponding to a HRT of 4 days, at which 79% CODs and 83% BOD(5) removal efficiencies were obtained. Average removals of COD, BOD(5) and TSS in the two-phase anaerobic digestion process were 98.5%, 99% and 100%, respectively. The daily biogas production exceeded 10 times reactor volume and biogas methane content was greater than 70%.     

Mathematical modeling of non-ideal mixing continuous flow reactors for anaerobic digestion of cattle manure

Most conventional digesters used for animal wastewater treatment include continuously stirred-tank reactors. While imperfect mixing patterns are more common than ideal ones in real reactors, anaerobic digestion models often assume complete mixing conditions. Therefore, their applicability appears to be limited. In this study, a mathematical model for anaerobic digestion of cattle manure was developed to describe the dynamic behavior of non-ideal mixing continuous flow reactors. The microbial kinetic model includes an enzymatic hydrolysis step and four microbial growth steps, together with the effects of substrate inhibition, pH and thermodynamic considerations. The biokinetic expressions were linked to a simple two-region liquid mixing model, which considered the reactor volume in two separate sections, the flow-through and the retention regions. Deviations from an ideal completely mixed regime were represented by changing the relative volume of the flow-through region (a) and the ratio of the internal exchange flow rate to the feed flow rate (b). The effects of the hydraulic retention time, the composition of feed, the initial conditions of the reactor and the degree of mixing on process performance can be evaluated by the dynamic model. The simulation results under different conditions showed that deviations from the ideal mixing regime decreased the methane yield and resulted in a reduced performance of the anaerobic reactors. The evaluation of the impact of the characteristic mixing parameters (a) and (b) on the anaerobic digestion of cattle manure showed that both liquid mixing parameters had significant effects on reactor performance.     

Low temperature thermo-chemical pretreatment of dairy waste activated sludge for anaerobic digestion process

An investigation into the influence of low temperature thermo-chemical pretreatment on sludge reduction in a semi-continuous anaerobic reactor was performed. Firstly, effect of sludge pretreatment was evaluated by COD solubilization, suspended solids reduction and biogas production. At optimized condition (60 °C with pH 12), COD solubilization, suspended solids, reduction and biogas production was 23%, 22% and 51% higher than the control, respectively. Secondly, semi-continuous process performance was studied in a lab-scale semi-continuous anaerobic reactor (5 L), with 4 L working volume. With three operated SRTs, the SRT of 15 days was found to be most appropriate for economic operation of the reactor. Combining pretreatment with anaerobic digestion led to 80.5%, 117% and 90.4% of TS, SS and VS reduction respectively, with an improvement of 103% in biogas production. Thus, low temperature thermo-chemical can play an important role in reducing sludge production.     

A Monod-based model of attached-growth anaerobic fermenters

A simple mathematical model of steady-state attached-growth anaerobic fermenter kinetics is described. The model considers a single methanogenic culture following Monod growth kinetics. The model accounts for effects of influent biodegradability and volatile solids concentration, temperature and hydraulic retention time, and predicts volumetric methane productivity and volatile solids reduction. It is distinguished from conventional suspended-growth reactor models by its explicit consideration of bacterial concentration in the reactor system, based on hydraulic flow and influent volatile solids concentration. The model was validated using data from both porous- and solid-media attached-growth fermenters.     

Studies of insufficient mixing in bioreactors: Effects of limiting oxygen concentrations and short term oxygen starvation on Penicillium chrysogenum

The effect of oxygen limitation on the respiration rate of Penicillium chrysogenum was studied. The results show that measurements of critical oxygen tensions within a process that on morphological or on physical grounds exhibits an inhomogenous structure are not likely to resemble the Monod model.In order to study the effects of short term oxygen starvation on the respiratory capacity of Penicillium chrysogenum, a two compartment fermenter was constructed. This fermenter consists of one well mixed aerobic part (CSTR) and one minor anaerobic part (CPFR). In the latter the circulation time as well as the volume can be varied. After passage of the whole cell culture volume through the anaerobic part, irreversible inhibition of the respiration was observed. This was caused by a circulation time of 5 and 10 min in the plug flow reactor and with a volume of 6% of the stirred tank reactor volume. However, circulation times of 1 and 2 min with an anaerobic zone of 1% of the stirred tank reactor volume did not give any irreversible effects on the respiratory capacity.This was compared with the results of the previously established model ln(1 — I _OUR//100)^–1 = kt [1]. The I _OUR is the percentage irreversible inhibition of the respiration, t is the anaerobic circulation time and k is a constant. The two compartment fermenter results agree with the earlier model at circulation times of 5 and 10 min, but not with the shorter times, and this suggests that a lag phase exists in the inactivation kinetics.     

Hydraulics of laboratory and full-scale upflow anaerobic sludge blanket (UASB) reactors

Laboratory-scale upflow anaerobic sludge blanket (UASB) reactors are often used as test platforms to evaluate full-scale applications. However, for a given volume specific hydraulic loading rate and geometry, the gas and liquid flows increase proportionally with the cube root of volume. In this communication, we demonstrate that a laboratory-scale reactor had plug-flow hydraulics, while a full-scale reactor had mixed flow hydraulics. The laboratory-scale reactor could be modeled using an existing biochemical model, and parameters identified, but because of computational speed with plug-flow hydraulics, mixed systems are instead recommended for parameter identification studies. Because of the scaling issues identified, operational data should not be directly projected from laboratory-scale results to the full-scale design.     

High-Rate two-phase process for the anaerobic degradation of cellulose, employing rumen microorganisms for an efficient acidogenesis

A novel two-stage anaerobic process for the microbial conversion of cellulose into biogas has been developed. In the first phase, a mixed population of rumen bacteria and ciliates was used in the hydrolysis and fermentation of cellulose. The volatile fatty acids (VFA) produced in this acidogenic reactor were subsequently converted into biogas in a UASB-type methanogenic reactor.A stepwise increase of the loading rate from 11.9 to 25.8 g volatile solids/L reactor volume/day (g VS/L/day) did not affect the degradation efficiency in the acidogenic reactor, whereas the methanogenic reactor appeared to be overloaded at the highest loading rate. Cellulose digestion was almost complete at all loading rates applied. The two-stage anaerobic process was also tested with a closed fluid circuit. In this instance total methane production was 0.438 L CH(4)g VS added, which is equivalent to 98% of the theoretical value. The application of rumen microorganisms in combination with a high-rate methane reactor is proposed as a means of efficient anaerobic degradation of cellulosic residues to methane. Because this newly developed two-phase system is based on processes and microorganisms from the ruminant, it will be referred to as "Rumen Derived Anaerobic Digestion" (RUDAD-) process.     

Modeling the liquid flow in up-flow anaerobic sludge blanket reactors

By means of stimulus-response experiments an Li(+) tracer, models for the fluid flow in a 30-m(3) UASB reactor, used for the anaerobic treatment of wastewater, were tested. From the model with the best fit it could be derived that both the sludge bed and the sludge blanket can be described as perfectly mixed tank reactors with short-circuiting flows; the settler volume acts like a plug-flow region.Apart from the volumes of the different flow regions, two parameters are necessary and sufficient to describe the fluid flow in a well functioning UASB reactor, i.e., the short-circuiting flow over the sludge bed and the short-circuiting flow over the sludge blanket. The volumes could be measured accurately.The short-circuiting flow over the sludge bed is a linear function of the sludge bed height. When the optimal height of the sludge bed is defined as the height for which the short-circuiting flows are as small as possible, a bed-height of 3.5-4 m is sufficient (for superficial gas velocities between 1 and 1.5 m/h). This is in contradiction to the results of other authors. The short-circuiting flows over the sludge bed and the sludge blanket were also influenced by the superficial gas velocity.     

Comparative evaluation of biogas production from dairy manure and co‐digestion with maize silage by CSTR and new anaerobic hybrid reactor

This study aimed to investigate potential methane production through anaerobic digestion of dairy manure and co‐digestion with maize silage. Two different anaerobic reactor configurations (single‐stage continuously stirred tank reactor [CSTR] and hybrid anaerobic digester) were used and biogas production performances for each reactor were compared. The HR was planned to enable phase separation in order to improve process stability and biogas production under higher total solids loadings (≥4%). The systems were tested under six different organic loading rates increased steadily from 1.1 to 5.4 g VS/L.d. The CSTR exhibited lower system stability and biomass conversion efficiency than the HR. The specific biogas production of the hybrid system was between 440 and 320 mL/gVS with 81–65% volatile solids (VS) destruction. The hybrid system provided 116% increase in specific biogas production and VS destruction improved by more than 14%. When MS was co‐digested together with dairy manure, specific biogas production rates increased about 1.2‐fold. Co‐digestion was more beneficial than mono‐material digestion. The hybrid system allowed for generating methane enriched biogas (>75% methane) by enabling phase separation in the reactor. It was observed that acidogenic conditions prevailed in the first two compartments and the following two segments as methanogenic conditions were observed. The pH of the acidogenic part ranged between 4.7 and 5.5 and the methanogenic part was between 6.8 and 7.2.     

Biodegradation of pentachlorophenol in a continuous anaerobic reactor augmented with Desulfitobacterium frappieri PCP-1.

In this work, a strain of anaerobic pentachlorophenol (PCP) degrader, Desulfitobacterium frappieri PCP-1, was used to augment a mixed bacterial community of an anaerobic upflow sludge bed reactor degrading PCP. To estimate the efficiency of augmentation, the population of PCP-1 in the reactor was enumerated by a competitive PCR technique. The PCP-1 strain appeared to compete well with other microorganisms of the mixed bacterial community, with its population increasing from 10(6) to 10(10) cells/g of volatile suspended solids within a period of 70 days. Proliferation of strain PCP-1 allowed for a substantial increase of the volumetric PCP load from 5 to 80 mg/liter of reaction volume/day. A PCP removal efficiency of 99% and a dechlorination efficiency of not less than 90.5% were observed throughout the experiment, with 3-Cl-phenol and phenol being observable dechlorination intermediates.     

Development of anaerobic sludge bed (ASB) reactor technologies for domestic wastewater treatment: motives and perspectives

During the treatment of raw domestic wastewater in the upflow anaerobic sludge blanket (UASB) reactor, the suspended solids (SS) present in the wastewater tend to influence negatively the methanogenic activity and the chemical oxygen demand (COD) conversion efficiency. These problems led to the emergence of various anaerobic sludge bed systems such as the expanded granular sludge bed (EGSB), the upflow anaerobic sludge blanket (UASB)-septic tank, the hydrolysis upflow sludge bed (HUSB), the two-stage reactor and the anaerobic hybrid (AH) reactor. However, these systems have, like the UASB reactor, limited performance with regard to complete treatment (e.g., removal of pathogens). In this respect, a new integrated approach for the anaerobic treatment of domestic wastewater is suggested. This approach combines a UASB reactor and a conventional completely stirred tank reactor (CSTR) for the treatment of the wastewater low in SS and sedimented primary sludge, respectively. The principal advantages of the proposed system are energy recovery from organic waste in an environmentally friendly way; lowering the negative effect of suspended solids in the UASB reactor; production of a high quality effluent for irrigation; and prevention of odour problems.     

Anaerobic digestion of processed municipal solid waste using a novel high solids reactor: Maximum solids levels and mixing requirements

Summary Novel, laboratory-scale, high solids reactors operated under mesophilic conditions were used to study the anaerobic fermentation of processed municipal solid waste (MSW) to methane. The anaerobic digestion consortium was introduced to high solids levels through gradual adaptation. The maximum sludge solids level for stable anaerobic fermentation performance was identified as approximately 36% wt/wt. Recovery of the anaerobic consortium, following dilution of inhibitory high solids levels, was swift. Reactor mixing requirements were also studied. No significant difference in fermentation performance was observed between agitator speeds of 1 and 25 rpm. Preliminary fermentation performance tests showed that solids loading rates as high as 9.5 g VS (volatile solids) feed/L sludge^.d, at 32% solids within the reactor, were possible. Under these conditions, operation was stable with an average pH of 7.8–8.0, total volatile fatty acid pools of <20 mM, and a biogas composition of 55%–60% methane.     

Methane production using whole and screened dairy manure in conventional and fixed-film reactors

The technical feasibility of adopting the fixed-film reactor concept for biogas production from screened dairy manure was investigated. The methane production capability of laboratory-scale 4-L anaerobic reactors (conventional and fixed-film) receiving screened dairy manure and operated at 35 degrees C was compared. Dairy manure filtrate with 4.4% total solids (TS) and 3.4% volatile solids (VS) (average value) was prepared from 1:1 manure-water slurry. The feed material was added intermittently at loading rates ranging from 2.34 to 25 and 2.25 to 785 g VS/L d, respectively, for the conventional and fixed-film reactors. Maximum methane production rate (L CH(4)/L d) for the conventional reactor was 0.63 L CH(4)/L d achieved at a 6-day hydraulic retention time (HRT). For the fixed-film reactor the maximum production rate was 3.53 L CH(4)/L d when operated at a loading rate of 262 g VS/L d (3 h HRT). The fixed-film reactor was capable of sustaining a loading of 785 g VS/L d (1 h HRT). The fixed-film reactor performed much better than the conventional reactors. These results indicate that a large reduction of required reactor volume is possible through application of a fixed-film concept combined with a liquid-solid separation pretreatment of dairy manure.     

Microbial biomass and community structure of a phase-separated methanogenic reactor determined by lipid analysis

Summary An anaerobic phase-separation biomass reactor was established on cellulose with the hydrolysis and fermentation steps occurring in the first stage, and acetogenesis and methanogenesis in the second stage. Based upon lipid biomarker analysis, eubacterial and eukaryotic cells accounted for approximately 6% of the volatile solids of the first stage and 17% of the second, while methanogens were approximately 1% of the volatile solids in the first stage and 9% of the second. Clustering the polar lipid fatty acids into groups based upon their distributions between the two stages of the reactor clarified the differences in community structure caused by phase-separated operation. Although inoculated from the same source, the two stages maintained very different microbial communities. Signature fatty acids known as indicators of unbalanced growth in eubacteria were significantly higher in the first stage of the reactor.     

Two-phase anaerobic digestion for production of hydrogen-methane mixtures

An anaerobic digestion process to produce hydrogen and methane in two sequential stages was investigated, using two bioreactors of 2 and 15 L working volume, respectively. This relative volume ratio (and shorter retention time in the second, CH(4)-producing reactor) was selected, in part, to test the assumption that separation of phase can enhance metabolism in the second methane producing reactor. The reactor system was seeded with conventional anaerobic digester sludge, fed with a glucose-yeast extract--peptone medium and operated under conditions of relatively low mixing, to simulate full scale operation. A total of nine steady states were investigated, spanning a range of feed concentrations, dilution rates, feed carbon to nitrogen ratios and degree of integration of the two stages. The performance of this two-stage process and potential practical applications for the production of clean-burning hydrogen-methane mixtures are discussed.