Bench-scale Sequencing Batch Reactors Research Articles

Evaporation–condensation of olive mill wastewater: Evaluation of condensate treatability through SBR and constructed Wetlands

In this study, a novel strategy for olive mill wastewater (OMW) treatment, which combines an evaporation–condensation step followed by the biological treatment of the condensate, was evaluated. Different solutions were evaluated as biological step, through a experimental tests, by operating for three weeks: two bench scale sequencing batch reactor (SBR), with and without media for attached growth, and two pilot scale constructed wetlands, a vertical (VF) and a horizontal (HF) submerged flow beds. When treating an influent OMW with a COD concentration in the range from 130 to 150gL−1, the evaporation/condensation process allowed to achieve up to 98.7% of COD removal (2.4gCODL−1 in average in the condensate); moreover, the condensate showed a large biodegradable fraction, allowing the further treatment of the residual COD by simple biological reactors like SBRs or constructed wetlands (CWs). The CWs, either in HF or VF configuration, showed more stable and barely higher performances in comparison with the SBR, especially during the first week of operation and allowed to obtain an effluent with a pH close to neutrality without alkalinity dosing. The overall COD removal was about 99.8% and less than two weeks were needed for the start-up of the biological system, which is of pivotal importance given the olive mill process cycle. The evaporation process also generated a concentrate containing a high concentration of valuable chemicals, including polyphenols.

The stability of aerobic granular sludge treating municipal sludge deep dewatering filtrate in a bench scale sequencing batch reactor

Inoculated with mature aerobic granular sludge in a sequencing batch reactor, gradually increasing the proportion of municipal sludge deep dewatering filtrate in influent, aerobic granular sludge was domesticated after 84days and maintained its structure during the operation. The domesticated AGS was yellowish-brown, dense and irregular spherical shape, average size was 1.49mm, water content and specific density were 98.13% and 1.0114, the SVI and settling velocity were 40ml/g and 46.5m/h. After 38days, NO3−-N accumulated obviously in the reactor as lack of carbon sources. When adding 1–3g solid CH3COONa at 4.5 and 5.5h of each cycle from the 57th day, the removal rate of TN rose to above 90% after 20days, where effective COD removal and denitrification were realized in a single bioreactor. Finally, the removal rates of COD, TP, TN and NH4+-N were higher than 95%, 88%, 96% and 99%.

Production of nitrous oxide from anaerobic digester centrate and its use as a co-oxidant of biogas to enhance energy recovery.

Coupled Aerobic-anoxic Nitrous Decomposition Operation (CANDO) is a new process for wastewater treatment that removes nitrogen from wastewater and recovers energy from the nitrogen in three steps: (1) NH4(+) oxidation to NO2(-); (2) NO2(-) reduction to N2O gas; and (3) N2O conversion to N2 with energy production. In this work, we optimize Steps 1 and 2 for anaerobic digester centrate, and we evaluate Step 3 for a full-scale biogas-fed internal combustion engine. Using a continuous stirred reactor coupled to a bench-scale sequencing batch reactor, we observed sustained partial oxidation of NH4(+) to NO2(-) and sustained (3 months) partial reduction of NO2(-) to N2O (75-80% conversion, mass basis), with >95% nitrogen removal (Step 2). Alternating pulses of acetate and NO2(-) selected for Comamonas (38%), Ciceribacter (16%), and Clostridium (11%). Some species stored polyhydroxybutyrate (PHB) and coupled oxidation of PHB to reduction of NO2(-) to N2O. Some species also stored phosphorus as polyphosphate granules. Injections of N2O into a biogas-fed engine at flow rates simulating a full-scale system increased power output by 5.7-7.3%. The results underscore the need for more detailed assessment of bioreactor community ecology and justify pilot- and full-scale testing.

Fate of malathion and a phosphonic acid in activated sludge with varying solids retention times

This study examined the ability of activated sludge (AS) to sorb and biodegrade ethylmethylphosphonic acid (EMPA) and malathion, a degradation product and surrogate, respectively, for an organophosphate chemical warfare agent. Sorption equilibrium isotherm experiments indicate that sorption of EMPA and malathion to AS is negligible. EMPA at a concentration of 1 mg L−1 degraded by approximately 30% with apparent first-order kinetics, possibly via co-metabolism from nitrification. Heterotrophic bacteria and abiotic mechanisms, however, are largely responsible for malathion degradation also with apparent first-order kinetics. EMPA did not inhibit chemical oxygen demand (COD) oxidation or nitrification activity, although malathion did appear to induce a stress response resulting in inhibition of COD oxidation. The study also included a 30-day experiment in which malathion, at a concentration of 5 mg L−1, was repeatedly fed to AS in bench-scale sequencing batch reactors (SBRs) operating at different solids retention times (SRTs). Peak malathion concentrations occurred at day 4.5, with the longer SRTs yielding greater peak malathion concentrations. The AS reduced the malathion concentrations to nearly zero by day 10 for all SRTs, even when the malathion concentration in the influent increased to 20.8 mg L−1. The data suggest a biodegradation pathway for malathion involving an oxygenase. Phylogenetic analyses revealed that all samples had an abundance of Zoogloea, though there was greater bacterial diversity in the SBR with the SRT of 50 days. The SBR with an SRT of 9.5 days had an apparent reduction in the diversity of the bacterial community.

Ammonium reduction from piggery wastewater using immobilized ammonium-reducing bacteria with a full-scale sequencing batch reactor on farm

This work aims to evaluate the efficiency of ammonium removal from piggery wastewater by an intermittent aeration (IA) sequencing batch reactor (SBR) with immobilized NH4(+)-reducing bacteria under mesophilic conditions. When a 20-L bench-scale SBR with 11% (v/v) of alginate beads containing NH4(+)-reducing bacteria was used, removal efficiency of NH4(+) was 63% after 240 h. When a full-scale SBR system (available volume = 83 m(3)) with 0.1% (v/v) of alginate-coated light-expanded clay aggregates beads containing NH4(+)-reducing bacteria was used, removal efficiency of NH4(+) by the full-scale intermittent aeration SBR (IA-SBR) was significantly different from both traditional intermittent aeration SBR (T-SBR) and the continuous aeration SBR with AL beads containing NH4(+)-reducing bacteria (P < 0.05). In summary, the IA-SBR with AL beads can significantly promote removal efficiency of NH4(+) on farm.

Applicability of industrial wastewater as carbon source for denitrification of a sludge dewatering liquor

The applicability of four industrial waste streams from potato processing, canola processing and oil refining, biodiesel production (glycerol), and glycol as substitutes to methanol and ethanol in denitrification of anaerobically digested sludge dewatering liquor (centrate) was evaluated in bench-scale sequencing batch reactors. It was found that glycerol was the best substitute with the specific denitrification rate (SDNR) of 13 mg NO 3-N/(g VSS·h) followed by potato processing wastewater at 12 mg NO 3-N/(g VSS·h ). Both substrates produced faster SDNR than methanol's 10 mg NO 3-N/(g VSS·h ); however, they were inferior to ethanol's 17 mg NO 3-N/(g VSS·h ). Glycol had SDNR of 8 mg NO 3-N/(g VSS·h ) and demonstrated a very fast acclimation rate, i.e. the response in increased denitrification rate was visible in three days following glycol addition. Canola processing and oil refining wastewater was considered an inappropriate carbon source due to a low SDNR of 5 mg NO 3-N/(g VSS·h ) and apparent inhibitory effect on nitrification.

Mixed-culture polyhydroxyalkanoate production from olive oil mill pomace

Polyhydroxyalkanoate (PHA) was produced in bench-scale sequencing batch reactors (SBRs) fed olive pomace fermentate containing a mixed microbial consortium. Initial anaerobic fermentation in a sequencing batch fermentor (SBF) produced soluble carbon compounds, mainly organic acids. SBF effluent was centrifuged, removing solids, and fed into a SBR where intracellular PHA was produced. Buffer pre-treatment of diluted olive pomace increased organic acid production 75% in SBF fermentate over no pre-treatment. Hydraulic retention time (HRT), solids retention time (SRT), pomace concentration/dilution, and aerobic operation vs. anoxic/oxic cycling were studied to improve PHA formation. Maximum %PHA achieved was 39% (on a dry-weight cell basis), and the highest volumetric productivity was 0.042g PHA/L-day under fully aerobic conditions. The highest PHA conversion yield was 0.3625g PHA/L fermentate.

The role of the microbial stringent response in excess intracellular accumulation of phosphorous in mixed consortia fed synthetic wastewater

Four bench-scale sequencing batch reactors (SBRs) seeded with activated sludge were operated under either fully oxic or anoxic/oxic conditions and fed synthetic wastewater containing either peptone or acetate. The function of each reactor was assessed through the measure of (i) soluble chemical oxygen demand, orthophosphate, ammonia, and nitrate; and (ii) biomass concentrations of phosphorus, polyhydroxyalkanoate, guanosine tetraphosphate, adenosine monophosphate, adenosine diphosphate, and adenosine triphosphate. In all four reactors, the biomass concentration of phosphorous was correlated statistically with the biomass concentration of ppGpp. The microbial consortia in all four reactors removed an appreciable quantity of phosphorous from solution (67–99%), and the net quantity of phosphorous removed from solution corresponded to the net increase in the biomass concentration of phosphorous. Hence, the microbial stringent response (MSR) was associated with excess intracellular accumulation of phosphorous in mixed microbial consortia fed synthetic wastewater. With recognition of the potential role of the MSR in the removal of soluble phosphorous from wastewater, additional research may lead to further optimization of treatment technologies and the development of new treatment systems for the biological removal of phosphorus from wastewater.

Influence of water characteristics on partial nitrification in a sequencing batch reactor

Due to the potential benefits on energy/cost savings from partial nitrification, this studycarried a series of laboratory tests to study the combined influence from water temperature, organic carbon and dissolved oxygen (DO) on partial nitrification. The purpose of this study was to obtain a general direction to operate activated sludge systems for partial nitrification under changing environment conditions and wastewater strengths. The time profiles of the mixed liquor NO2-N and NO3-N during a 11 h aeration phase were monitored in a 6 L bench scale sequencing batch reactor (SBR) under varying water temperatures (20 to 30°C), organic carbon abundances(initial mixed liquor COD/N ratio ranged 2.8 to 14), and DO levels (0.4 to 4.0 mg L-1). Results showed that organic carbon abundance should be firstly lowered to below a certain threshold level (14 in this study) in order to allow nitrification to occur. Then, water temperature should be kept at relatively higher levels (at least 30°C) and DO should be controlled at relatively lower levels (depending on aeration duration). However, the adverse effect on partial nitrification from low water temperatures can be compensated by a low DO, while the favoring effect on partial nitrification from high water temperatures can be reversed by a high DO and/or excess aeration. Although it was not the focus of this study, simultaneous nitrification and denitrificaiton (SND) was also indicated viable when organic carbon abundance was kept at relatively higher levels but still below the inhibitory level for nitrification. Successive study is recommended to further quantify the interactions between these influential factors on partial nitrification and to improve and better understand the reliability and sensitivity of activated sludge systems in achieving partial nitrification under normally always changing reaction conditions. The overall conclusion is that partial nitrification is under normally always changing reaction conditions. Key words: Best management practice, bioreactor operation, nitrogen removal, wastewater, water temperatures, organic carbon abundances, dissolved oxygen (DO).

Modeling the decay of ammonium oxidizing bacteria

A bench-scale sequencing batch reactor was used to study factors affecting the endogenous decay of the ammonium oxidizing biomass (AOB) in different operating conditions. AOB decay was very sensitive to oxygen concentration, and increased up to 0.4 d−1 for oxygen concentration of 7 mg O2 L−1. The decay in anaerobic conditions was shown to be very low (0.03 d−1) when compared to literature data.The effect of nitrite and nitrate on AOB decay was also studied. The correlation was quite weak suggesting that both nitrate and nitrite absence had little impact on decay which is contrary to what is typically assumed in some of the existing process models. A simple expression for the decay of AOB was proposed, calibrated and validated using the results of batch kinetic tests and of the continuous sequencing batch reactor monitoring.

Artificial intelligence control of a sequencing batch reactor for nitrogen removal via nitrite from landfill leachate

Leachate generated in old landfills is a high-strength wastewater, which is particularly difficult to treat owing to its low biochemical oxygen demand/total Kjeldahl nitrogen ratio. This paper seeks to demonstrate that reliable leachate treatment by means of sequencing batch reactors (SBRs) is indeed possible by means of the application of a smart control system. This study assesses the results of a computer-controlled bench-scale SBR treating raw sanitary landfill leachate to achieve nitrogen removal through the nitrite shortcut. Significant improvements have been obtained by introducing a fuzzy inferential system based on simple process measurements (i.e. dissolved oxygen, oxidation-reduction potential and pH). The paper analyzes the results of a test period of over 280 consecutive days of operation, during which the fuzzy control system correctly recognized over 97% of the SBR phase transitions and provided smart adjustments of the process operating conditions in terms of phase length and external COD addition. In spite of time-varying process conditions, the application of fuzzy logic provided stable nitrogen removal via nitrite through continuous adjustments of the main process parameters and resulted in a decreased hydraulic retention time, an increased loading rate, a saving in the external COD addition and considerable aeration energy conservation.

Dissolved oxygen as a key parameter to aerobic granule formation

Much research has asserted that high shear forces are necessary for the formation of aerobic granular sludge in Sequencing Batch Reactors (SBRs). In order to distinguish the role of shear and dissolved oxygen on granule formation, two separate experiments were conducted with three bench-scale SBRs. In the first experiment, an SBR was operated with five sequentially decreasing superficial upflow gas velocities ranging from 1.2 to 0.4 cm s(-1). When less than 1 cm s(-1) shear was applied to the reactor, aerobic granules disintegrated into flocs, with corresponding increases in SVI and effluent suspended solids. However, the dissolved oxygen also decreased from 8 mg L(-1) to 5 mg L(-1), affecting the Feast/Famine regime in the SBR and the substrate removal kinetics. A second experiment operated two SBRs with an identical shear force of 1.2 cm s(-1), but two dissolved oxygen concentrations. Even when supplied a high shear force, aerobic granules could not form at a dissolved oxygen less than 5 mg L(-1), with a Static Fill. These results indicate that the substrate removal kinetics and dissolved oxygen are more significant to granule formation than shear force.

Enhanced Biological Phosphorus Removal with P seudomonas putida GM6 from Activated Sludge

The enhanced biological phosphorus removal (EBPR) method is widely adopted for phosphorus removal from waste-water, yet little is known about its microbiological and molecular mechanisms. Therefore, it is difficult to predict and control the deterioration of the EBPR process in a large-scale municipal sewage treatment plant. This study used a novel strain isolated in the laboratory, Pseudomonas putida GM6, which had a high phosphate accumulating ability and could recover rapidly from the deteriorated system and enhance the capability of phosphorus removal in activated sludge. Strain GM6 marked with gfp gene, which was called GMTR, was delivered into a bench-scale sequencing batch reactor (SBR) of low efficiency, to investigate the colonization of GMTR and removal of phosphorus. After 21 days, the proportion of GMTR in the total bacteria of the sludge reached 9.2%, whereas the phosphorus removal rate was 96%, with an effluent concentration of about 0.2 mg L −1. In the reactor with the addition of GMTR, phosphorus was removed quickly, in 1 h under anaerobic conditions, and in 2 h under aerobic conditions. These evidences were characteristic of EBPR processes. Field testing was conducted at a hospital sewage treatment facility with low phosphorus removal capability. Twenty- one days after Pseudomonas putida GM6 was added, effluent phosphorus concentration remained around 0.3 mg L −1, corresponding to a removal rate of 96.8%. It was therefore demonstrated that Pseudomonas putida GM6couldbeused for a quick startup and enhancement of wastewater biological phosphorus removal, which provided a scientific basis for potential large-scale engineering application.

Combined chemical biological treatment of bleached eucalypt kraft pulp mill effluent

Effectiveness of ozonation before and after biological treatment for removal of recalcitrant organic matter in bleached kraft pulp effluents was compared. Two industrial ECF bleached eucalypt kraft pulp effluents (E1 and E2) were pretreated with 100 mg O3/L. Raw and pretreated effluents were treated biologically in bench-scale sequencing batch reactors, under constant conditions. Following biological treatment, effluents were post-treated with 100 and 200 mg O3/L. Effluent pretreatment increased effluent biodegradability by 10% in E1 and 24% in E2. Combined O3-biological treated led to small but significant increases in COD, BOD and lignin removal over biological treatment alone, but pretreatment had no significant effect on effluent colour and carbohydrate removal. Ozone pretreatment did not affect biological activity during treatment of effluent E1 but resulted in a 38% lower specific oxygen uptake rate in effluent E2. At an equivalent dose of 100 mg/L, pre-ozonation produced better quality effluent than post-ozonation, especially with regard to COD and colour. Likewise, when an equivalent dose of 200 mg/L was applied, splitting the dose equally between pre- and post-treatments was more efficient than applying the entire dose in the post-treatment. The potential for combined chemical-biological treatment to improve effluent quality has been confirmed in this study.

An aerobic sequencing batch reactor for 2,4,6‐trinitrophenol (picric acid) biodegradation

A bench scale sequencing batch reactor (SBR) was designed and tested for degradation of 2,4,6-trinitrophenol (TNP) or picric acid-contaminated wastewater or groundwater. Under varying temperatures (25, 15 and 10 degrees C) and influent concentrations (40-200 mg/L TNP) a stable biomass was developed that was consistently capable of degrading the explosive compound to below regulatory drinking water limits (0.057 mg/L). The reactor was initially seeded with a nitroaromatic and nitramine degrading isolate Rhodococcus opacus strain JW01. Kinetic growth modeling was conducted revealing micro(max) values at 25, 15 and 10 degrees C of 0.14, 0.08 and 0.04 d(-1), while the modeled K(s) values were 0.68, 1.11 and 1.24 mg/L, respectively. Overall TNP removal efficiency in the SBR was on average > 99.9% over the 2000 hours of operation. Removal of TNP to below drinking water standards, with low residual dissolved carbon and significant release of nitrogen from the parent compound was accomplished.

Monitoring of sequencing batch reactor for nitrogen and phosphorus removal using neural networks

The information of nutrient dynamics is essential for the precise control of effluent quality discharged from biological wastewater treatment processes. However, these variables can usually be determined with a significant time delay. Although the final effluent quality can be analyzed after this delay, it is often too late to make proper adjustments. In this paper, a neural network approach, a software sensor, was proposed for the real-time estimation of nutrient concentrations and overcoming the problem of delayed measurements. In order to improve the neural network performance, a split network structure applied separately for anaerobic and aerobic conditions was employed with dynamic modeling methods such as auto-regressive with exogenous inputs. The proposed methodology was applied to a bench-scale sequencing batch reactor (SBR) for biological nutrient removal. The extrapolation problem of neural networks was possible to be partially overcome with the aid of multiway principal component analysis because of its ability of detecting of abnormal situations which could generate extrapolation. Real-time estimation of PO 4 3−, NO 3 − and NH 4 + concentrations based on neural network was successfully carried out with the simple on-line information of the SBR system only.

Potential for Enhancement of Aerobic Biological Removal of Recalcitrant Organic Matter in Bleached Pulp Mill Effluents

Increasingly stringent effluent quality limits for bleached kraft pulp mills pose a great challenge to mill wastewater system managers since these limits can require levels of chemical oxygen demand (COD) removal efficiency rarely reported for biological treatment of these types of effluents. The present study was therefore undertaken to better understand the nature of recalcitrant COD in bleached kraft pulp effluents that persists through the biological treatment system. Bleaching effluents from a Brazilian eucalypt bleached kraft pulp mill were collected and treated in a bench-scale sequencing batch reactor. Organic matter in raw and treated effluents was characterized before and after separation into low and high molecular mass fractions. Biological treatment removed 71% of the COD, with 83% removal of the low molecular mass COD but only 36% removal of the high molecular mass COD. Microorganisms capable of degrading the recalcitrant COD were isolated from enrichment cultures of the original activated sludge fed on fractions of the bleaching effluent that presented low biodegradabilities. Use of a microbial consortium composed of ten of these isolates to treat the biologically treated effluent removed a further 12% of the effluent COD, all from the high molecular mass fraction. Results of this research indicate that microorganisms with potential for degrading recalcitrant COD are present in activated sludge, but that these are not metabolically active during normal activated sludge treatment of mill effluents. The use of biological selectors in the treatment system to promote growth of such microorganisms may enhance removal of recalcitrant organic matter.

Activated sludge morphology characterization through an image analysis procedure

This work deals with the development of a digital image analysis procedure to characterize microbial flocs obtained in three different WWTP: a bench-scale Sequencing Batch Reactor (SBR) dealing with phenol and nitrogen biological removal, a municipal treatment unit (Ilha do Governador, Rio de Janeiro, Brazil) and an industrial wastewater treatment plant (Ciba - Estrada do Colégio, Rio de Janeiro, Brazil). The developed procedure permits to obtain its morphological parameters like equivalent diameter, compactness, roundness and porosity properties as well as the fractal dimension. This procedure was validated and lead to identify the major relationships between the analysed morphological parameters. A minimum of 300 flocs should be included in the image analysis and a significant influence of the sample dilution step on the mean size of the flocs was verified. The porosity parameter positively correlated with the fractal dimension of microbial aggregates indicating the that highly porous flocs are very irregular.

Activated Sludge Diffusion for Odour Removal - Effects of H2S on the Biomass

The removal of odours from wastewater treatment plants through diffusion of odour-containing air volumes into the aerated basins was investigated in a bench scale experimental campaign which lasted more than 200 days. Hydrogen sulphide was selected as a model odorous compound and its removal efficiencies were experimentally evaluated along with its effects on the biomass and on the main biochemical processes. Two bench scale sequencing batch reactors were fed in parallel on real primary sewage and monitored for chemical oxygen demand removal, nitrification and denitrification. The balance of H2S was also monitored after adding to one of them a Na2S liquid solution of 17 mgS lreactor −1 d−1, corresponding to a gas-phase concentration of 240 mgS (Nm3)−1. Results showed an average sulphide removal of 94% in the reactor supplied with Na2S. Moreover, microbial composition did not show relevant variations after the addition of sulphide, and the good features of activated sludge flocs were maintained also in terms of sludge settleability. No relevant effects of sulphide were detected on carbon and nitrogen metabolism and chemical oxygen demand removal, nitrification and denitrification efficiencies were always above 75%, 95%, and 50% respectively, and comparable across the two reactors.

A two-step fed SBR for treating swine manure

Specially designed sequencing batch reactors (SBR) may be a solution to disposal of massive pig manure, rich in nitrogen (N) and phosphorus (P), produced by concentrated swine operations. In this study, the technical feasibility of simultaneous N and P removals for swine manure was investigated through a bench-scale SBR system operated in a cyclic fashion of anaerobic–anoxic–anoxic/anaerobic–anoxic/aerobic using low-intensity aeration (1.0 L/(m 3 s)), coupled with two-step influent feeding. The risks of emission of greenhouse gases (i.e., CH 4, N 2O and CO 2) were also investigated during the critical periods of operation. 97.5% of the total nitrogen (TN) in the treated manure was removed with only 15 mg N/L of the oxidized N (NO 3–N) left in the effluent. The reductions of total P (TP), chemical oxygen demand (COD), 5-day biochemical oxygen demand (BOD 5), and turbidity reached 95, 96, 100, and 95%, respectively. The changes of nutrients as well as soluble COD over time in a complete cycle demonstrated that the SBR system could accomplish multiple processes featuring simultaneous nitrification–denitrification and P removal under aeration with undetectable dissolved oxygen (DO) in the liquid. The unique features of DO, oxidation–reduction potential (ORP) and pH tracked throughout the SBR operation reflected biological changes associated with the nutrients and organic matter in the manure. The primary influent feeding in 75% of the total amount, accompanied by a rapid drop in ORP, stimulated CH 4 emission in a range from 990 to 1200 ppm; however, the secondary influent feeding in 25% of the total amount at the end of the first aeration, with combination of the previously accumulated NO 2–N, resulted in N 2O emission up to 13.9 ppm.