Biological treatment of acid dyeing wastewater using a sequential anaerobic/aerobic reactor system

The treatment of the wastewater taken from a wool dyeing processing in a wool manufacturing plant was investigated using an anaerobic/aerobic sequential system. The process units consisted of an anaerobic UASB reactor and an aerobic CSTR reactor. Glucose, alkalinity and azo dyes were added to the raw acid dyeing wastewater in order to simulate the dye industry wastewater since the raw wastewater contained low levels of carbon, NaHCO₃ and color through anaerobic/aerobic sequential treatment. The UASB reactor gave COD and color removals of 51–84% and 81–96%, respectively, at a HRT of 17 h. The COD and color removal efficiencies of the UASB/CSTR sequential reactor system were 97–83% and 87–80%, respectively, at a hydraulic retention time (HRTs) of 3.3 days. The aromatic amines (TAA) formed in the anaerobic stage were effectively removed in the aerobic stage.     

Effect of nitrate on anaerobic azo dye reduction

The aim of the study was to investigate the effect of nitrate on anaerobic color removal efficiencies. For this aim, anaerobic–aerobic sequencing batch reactor (SBR) fed with a simulated textile effluent including Remazol Brilliant Violet 5R azo dye was operated with a total cycle time of 12 h, including anaerobic (6 h) and aerobic cycles (6 h). Microorganism grown under anaerobic phase of the reactor was exposed to different amounts of competitive electron acceptor (nitrate) and performance of the system was determined by monitoring color removal efficiency, nitrate removal, nitrite formation and removal, oxidation reduction potential, color removal rate, chemical oxygen demand (COD), specific anaerobic enzyme (azo reductase) and aerobic enzyme (catechol 1,2 dioxygenase), and formation and removal of aromatic amines. Variations of population dynamics of microorganisms exposed to various amount of nitrate were identified by denaturing gradient gel electrophoresis (DGGE). It was found that nitrate has adverse effect on anaerobic color removal efficiency and color removal was achieved after denitrification process was completed. It was found that nitrate stimulates the COD removal efficiency and accelerates the COD removal in the first hour of anaerobic phase. About 90 % total COD removal efficiencies were achieved in which microorganism exposed to increasing amount of nitrate. Population dynamics of microorganisms exposed to various amount of nitrate were changed and diversity was increased.     

Integrated biological process for olive mill wastewater treatment

The biological process for OMW treatment is based on an aerobic detoxification step followed by methanization step and aerobic post-treatment.The first aerobic detoxification step of OMW supplemented with sulfate and ammonium was carried out by the growth of Aspergillus niger in a bubble column. This step decreased OMW toxicity and increased its biodegradability because of phenolic compounds degradation. Growth of A. niger resulted in 58% COD removal, with production of biomass containing 30% proteins (w/w). Filtration of OMW was enhanced by this fermentation because the suspended solids were trapped in the mycelium. The filtrate liquid was then methanized using an anaerobic filter packed with flocoor. This reactor showed a short start up and a good stability. COD removal was around 60% and the methane yield (1 CH₄/g COD removed) was close to the theoretical yield.The anaerobic filter effluent was treated in an activated sludge fluidized reactor containing olive husk as a packing material. Husks were maintained in fluidization state by the aeration. This step induces COD removal at 45% and sludge (up to 2 g/dm³).The entire process allowed a global COD reduction up to 90%; however, the black colour due to polyphenolic compounds with high molecular weight persisted.     

The effect of biological sulfate reduction on anaerobic color removal in anaerobic–aerobic sequencing batch reactors

Combination of anaerobic–aerobic sequencing processes result in both anaerobic color removal and aerobic aromatic amine removal during the treatment of dye-containing wastewaters. The aim of the present study was to gain more insight into the competitive biochemical reactions between sulfate and azo dye in the presence of glucose as electron donor source. For this aim, anaerobic–aerobic sequencing batch reactor fed with a simulated textile effluent including Remazol Brilliant Violet 5R (RBV 5R) azo dye was operated with a total cycle time of 12 h including anaerobic (6 h) and aerobic cycles (6 h). Microorganism grown under anaerobic phase of the reactor was exposed to different amounts of competitive electron acceptor (sulfate). Performance of the anaerobic phase was determined by monitoring color removal efficiency, oxidation reduction potential, color removal rate, chemical oxygen demand (COD), color, specific anaerobic enzyme (azo reductase) and aerobic enzyme (catechol 1,2-dioxygenase), and formation of aromatic amines. The presence of sulfate was not found to significantly affect dye decolorization. Sulfate and azo dye reductions took place simultaneously in all operational conditions and increase in the sulfate concentration generally stimulated the reduction of RBV 5R. However, sulfate accumulation under anaerobic conditions was observed proportional to increasing sulfate concentration.     

Two-stage anaerobic treatment of dairy wastewater using HUASB with PUF and PVC carrier

In the present study, an attempt has been made to treat dairy wastewater entirely via anaerobic treatment over a period of 215 days, using two-stage Hybrid Upflow Anaerobic Sludge Blanket (HUASB) reactors, which offer the advantages associated both with fixed film and upflow sludge blanket treatments. A HUASB with polyurethane foam cubes was used for stage I, and a HUASB utilizing PVC-cut rings was used for stage II. The output from stage I was used as the input for stage II. The two-stage reactor was operated at an organic loading rate that varied from 10.7 to 21.4 kg COD m³/d for a period of 215 days, including the start-up period. The ideal organic loading rate for the two-stage reactor was 19.2 kg COD/m³/d. A further 21.4 kg COD m³/d increase in the organic loading rate resulted in the souring of the reactor function in stage I, which consequently reduced the overall reactor performance. Combined COD removal during the stable operation period (10.7 to 19.2 kg COD m³/d) occurred in a range between 97 and 99%. The methane content in the biogas varied from 65 to 70% in stage I, and from 63 to 66% in stage II. The two-stage anaerobic treatment using HUASB with PUF and PVC described in this work is expected to constitute a better alternative for the complete treatment of dairy wastewater than high-rate anaerobic, anaerobic/aerobic, and two-phase anaerobic treatment methods.     

Decolorization and mineralization of Amaranth dye using multiple zoned aerobic and anaerobic baffled constructed wetland

The objective of this study is to determine the reduction efficiency of Chemical Oxygen Demand (COD) as well as the removal of color and Amaranth dye metabolites by the Aerobic–anaerobic Baffled Constructed Wetland Reactor (ABCW). The ABCW reactor was planted with common reed (Phragmite australis) where the hydraulic retention time (HRT) was set to 1 day and was fed with synthetic wastewater with the addition of Amaranth dye. Supplementary aeration was supplied in designated compartments of the ABCW reactor to control the aerobic and anaerobic zones. After Amaranth dye addition the COD reduction efficiency dropped from 98 to 91% while the color removal efficiency was 100%. Degradation of azo bond in Amaranth dye is shown by the UV–Vis spectrum analysis which demonstrates partial degradation of Amaranth dye metabolites. The performance of the baffled unit is due to the longer pathway as there is the up-flow and down-flow condition sequentially, thus allowing more contact of the wastewater with the rhizomes and micro-aerobic zones.     

Performances and microbial features of an aerobic packed-bed biofilm reactor developed to post-treat an olive mill effluent from an anaerobic GAC reactor

Background  

Olive mill wastewater (OMW) is the aqueous effluent of olive oil producing processes. Given its high COD and content of phenols, it has to be decontaminated before being discharged. Anaerobic digestion is one of the most promising treatment process for such an effluent, as it combines high decontamination efficiency with methane production. The large scale anaerobic digestion of OMWs is normally conducted in dispersed-growth reactors, where however are generally achieved unsatisfactory COD removal and methane production yields. The possibility of intensifying the performance of the process using a packed bed biofilm reactor, as anaerobic treatment alternative, was demonstrated. Even in this case, however, a post-treatment step is required to further reduce the COD. In this work, a biological post-treatment, consisting of an aerobic biological "Manville" silica bead-packed bed aerobic reactor, was developed, tested for its ability to complete COD removal from the anaerobic digestion effluents, and characterized biologically through molecular tools.     

The effect of cyclic anaerobic–aerobic conditions on biodegradation of azo dyes

The effect of cyclic anaerobic–aerobic conditions on the biodegradative capability of the mixed microbial culture for the azo dye Remazol Brilliant Violet 5R (RBV-5R) was investigated in the sequencing batch reactor (SBR) fed with a synthetic textile wastewater. The SBR had a 12-h cycle time with anaerobic–aerobic periods of 3/9, 6/6 and 9/3 h. General SBR performance was assessed by measurement of catabolic enzymes (catechol 2,3-dioxygenase, azo reductase), chemical oxygen demand (COD), color and amount of aromatic amines. In this study, under steady-state conditions, the anaerobic period of the cyclic SBR was found to allow the reductive decolorization of azo dye. Longer anaerobic periods resulted in higher color removal efficiencies, approximately 71% for the 3-h, 87% for 6-h and 92% for the 9-h duration. Total COD removal efficiencies were over 84% under each of the cyclic conditions and increased as the length of the anaerobic period was increased; however, the highest color removal rate was attained for the cycle with the shortest anaerobic period of 3 h. During the decolorization of RBV-5R, two sulfonated aromatic amines (benzene based and naphthalene based) were formed. Additionally, anaerobic azo reductase enzyme was found to be positively affected with the increasing duration of the anaerobic period; however; it was vice versa for the aerobic catechol 2,3-dioxygenase (C23DO) enzyme.     

Pilot study on the upgrading configuration of UASB-MBBR with two carriers: Treatment effect,sludge reduction and functional microbial identification

Two kinds of biocarriers were adopted and a combined process of “AMC (Anaerobic microorganism carrier)-UASB and PBG (Porous bio-gel)-MBBR” was operated at the pilot scale for the treatment of real textile wastewater. The influence mechanism of the two carriers on the start-up, pollutant removal and sludge reduction were investigated within 118 days of operation. The dominant functional bacteria in anaerobic and aerobic systems were identified by high-throughput sequencing, and the possible ways and related mechanisms of nutrient removal and sludge reduction were analyzed based on the data. 37.0 ± 7.5 % and 53 ± 12.7 % of COD removal efficiencies were achieved in anaerobic system and aerobic system, respectively. Ammonia nitrogen concentration decreased from 20 to 45 to 3.49 ± 0.54 mg/L after treatment. An anaerobe was found to be closely related to color removal, which existed in both anaerobic and aerobic systems, achieving 84.0 % of color removal. With the operation of the system, the sludge yield decreased gradually. The sludge yields of anaerobic and aerobic systems were calculated individually and compared with similar studies. Aging biofilms were characterized to explore the factors associated with biofilm renewal.     

The development of simultaneous partial nitrification, ANAMMOX and denitrification (SNAD) process in a single reactor for nitrogen removal

The simultaneous partial nitrification, ANAMMOX and denitrification (SNAD) process was validated to potentially remove ammonium and COD from wastewater in a single, oxygen-limited, non-woven rotating biological contactor (NRBC) reactor. An ammonium conversion efficiency of 79%, TN removal efficiency of 70% and COD removal efficiency of 94% were obtained with the nitrogen and COD loading rate of 0.69 kgN/m(3)d and 0.34 kg/m(3)d, respectively. Scanning electron microscopy (SEM) observation and fluorescence in situ hybridizations (FISH) analysis revealed the existence of the dominant groups of bacteria. As a result, the aerobic ammonia-oxidizing bacteria (AOB), with a spot of aerobic heterotrophic bacteria were mainly distributed in the aerobic outer part of the biofilm. However, ANAMMOX bacteria with denitrifying bacteria were present and active in the anaerobic inner part of the SNAD biofilm. These bacteria were found to exist in a dynamic equilibrium to achieve simultaneous nitrogen and COD removal in NRBC system.     

Modeling and experimental study on the anaerobic/aerobic/anoxic process for simultaneous nitrogen and phosphorus removal: The effect of acetate addition

A mathematical model based on the simulation software AQUASIM was developed to validate an anaerobic/aerobic/anoxic (AOA) process that enables simultaneous nitrogen and phosphorus removal in a single reactor by adding external organic carbon to preclude excess aerobic phosphate uptake by polyphosphate-accumulating organisms (PAOs) and provide phosphate for denitrifying PAOs (DNPAOs). Aerobic batch tests after anaerobic phosphate release with different chemical oxygen demand (COD) concentrations indicated that the effect of COD concentration on the phosphate uptake preclusion could be expressed by a simple formula. The reduction factor reflecting the formula, which retards the aerobic phosphate uptake in the presence of COD, was added to the process rates of aerobic polyphosphate storage and PAOs growth in the model. The improved model, which included the reduction factor, reasonably matched the experimental result regarding aerobic phosphate uptake behavior whereas the model without it did not; thus, the former precisely predicts the AOA process behavior.     

A novel UASB–MFC–BAF integrated system for high strength molasses wastewater treatment and bioelectricity generation

An up-flow anaerobic sludge blanket reactor–microbial fuel cell–biological aerated filter (UASB–MFC–BAF) system was developed for simultaneous bioelectricity generation and molasses wastewater treatment in this study. The maximum power density of 1410.2 mW/m² was obtained with a current density of 4947.9 mA/m² when the high strength molasses wastewater with chemical oxygen demand (COD) of 127,500 mg/l was employed as the influent. The total COD, sulfate and color removal efficiencies of the proposed system were achieved of 53.2%, 52.7% and 41.1%, respectively. Each unit of this system had respective function and performed well when integrated together. The UASB reactor unit was mainly responsible for COD removal and sulfate reduction, while the MFC unit was used for the oxidation of generated sulfide with electricity generation. The BAF unit dominated color removal and phenol derivatives degradation. This study is a beneficial attempt to combine MFC technology with conventional anaerobic–aerobic processes for actual wastewater treatment.     

Distribution and change of microbial activity in combined UASB and AFB reactors for wastewater treatment

A thermophilic upflow anaerobic sludge blanket (UASB) reactor was combined with a mesophilic aerobic fluidized bed (AFB) reactor for treatment of a medium strength wastewater with 2,700?mg COD?l^?1. The COD removal efficiency reached 75% with a removal rate of 0.2 g COD?l^?1 h^?1 at an overall hydraulic retention time 14 hours. The distribution of microbial activity and its change with hydraulic retention time in the two reactors were investigated by measuring ATP concentration in the reactors and specific ATP content of the biomass. In the UASB reactor, the difference in specific ATP was significant between the sludge bed and blanket solution (0.02?mg ATP g VS^?1 versus 0.85?mg ATP g VS^?1) even though the ATP concentrations in these two zones were similar. A great pH gradient up to 4 was developed along the UASB reactor. Since a high ATP or biological activity in the blanket solution could only be maintained in a narrow pH range from 6.5 to 7.5, the sludge granules showed a high pH tolerance and buffering capacity up to pH 11. The suspended biomass in AFB reactor had a higher specific ATP than the biomass fixed in polyurethane carriers (1.6?mg ATP g VS^?1 versus 1.1?mg ATP g VS^?1), which implies a starvation status of the immobilized cells due to mass transfer limitation. The aerobes had to work under starvation conditions in this polishing reactor. The anaerobic biomass brought into AFB reactor contributed to an increase in suspended solids, but not the COD removal because of its fast deactivation under aerobic conditions. A second order kinetic model was proposed for ATP decline of the anaerobes. The results on distribution of microbial activity in the two reactors as well as its change with hydraulic retention time lead to further performance improvement of the combined anaerobic/aerobic reactor system.     

Sequential anaerobic/aerobic digestion of waste activated sludge: analysis of the process performance and kinetic study

Sequential anaerobic-aerobic digestion was applied to waste activated sludge (WAS) of a full scale wastewater treatment plant. The study was performed with the objective of testing the sequential digestion process on WAS, which is characterized by worse digestibility in comparison with the mixed sludge. Process performance was evaluated in terms of biogas production, volatile solids (VS) and COD reduction, and patterns of biopolymers (proteins and polysaccharides) in the subsequent digestion stages. VS removal efficiency of 40%, in the anaerobic phase, and an additional removal of 26%, in the aerobic one, were observed. For total COD removal efficiencies of 35% and 25% for anaerobic and aerobic stage respectively, were obtained. Kinetics of VS degradation process was analyzed by assuming a first order equation with respect to VS concentration. Evaluated kinetic parameters were 0.44 ± 0.20 d(-1) and 0.25 ± 0.15 d(-1) for the anaerobic stage and aerobic stage, respectively. With regard to biopolymers, in the anaerobic phase the content of proteins and polysaccharides increased to 50% and 69%, respectively, whereas in the subsequent aerobic phase, a decrease of 71% for proteins and 67% for polysaccharides was observed. The average specific biogas production 0.74 m(3)/(kg VS destroyed), was in the range of values reported in the specialized literature for conventional anaerobic mesophilic WAS digestion.     

Thermophilic anaerobic digestion of Lurgi coal gasification wastewater in a UASB reactor

Lurgi coal gasification wastewater (LCGW) is a refractory wastewater, whose anaerobic treatment has been a severe problem due to its toxicity and poor biodegradability. Using a mesophilic (35 ± 2 °C) reactor as a control, thermophilic anaerobic digestion (55 ± 2 °C) of LCGW was investigated in a UASB reactor. After 120 days of operation, the removal of COD and total phenols by the thermophilic reactor could reach 50-55% and 50-60% respectively, at an organic loading rate of 2.5 kg COD/(m³ d) and HRT of 24 h; the corresponding efficiencies were both only 20-30% in the mesophilic reactor. After thermophilic digestion, the wastewater concentrations of the aerobic effluent COD could reach below 200 mg/L compared with around 294 mg/L if mesophilic digestion was done and around 375 mg/L if sole aerobic pretreatment was done. The results suggested that thermophilic anaerobic digestion improved significantly both anaerobic and aerobic biodegradation of LCGW.     

Effects of nitrobenzene concentration and hydraulic retention time on the treatment of nitrobenzene in sequential anaerobic baffled reactor (ABR)/continuously stirred tank reactor (CSTR) system

The effects of increasing nitrobenzene (NB) concentrations and hydraulic retention times (HRT) on the treatment of NB were investigated in a sequential anaerobic baffled reactor (ABR)/aerobic completely stirred tank reactor (CSTR) system. In the first step of the study, the maximum COD removal efficiencies were found as 88% and 92% at NB concentrations varying between 30 mg L^?1 and 210 mg L^?1 in ABR. The minimum COD removal efficiency was 79% at a NB concentration of 700 mg L^?1. The removal efficiency of NB was nearly 100% for all NB concentrations in the ABR reactor. The methane gas production and the methane gas percentage remained stable (1500 mL day^?1 and 48–50%, respectively) as the NB concentration was increased from 30 to 210 mg L^?1. In the second step of the study it was found that as the HRT decreased from 10.38 days to 2.5 days the COD removal efficiencies decreased slightly from 94% to 92% in the ABR. For maximum COD and NB removal efficiencies the optimum HRT was found as 2.5 days in the ABR. The total COD removal efficiency was 95% in sequential anaerobic (ABR)/aerobic (CSTR) reactor system at a minimum HRT of 1 day. When the HRT was decreased from 10.38 days to 1 day, the methane percentage decreased from 42% to 29% in an ABR reactor treating 100 mg L^?1 NB. Nitrobenzene was reduced to aniline under anaerobic conditions while aniline was mineralized to catechol with meta cleavage under aerobic conditions.     

The influence of anaerobic pretreatment on the nitrogen removal from biosynthetic pharmaceutical wastewaters

The C:N ratio of the pharmaceutical wastewaters is usually suitable for a combination of the anaerobic pretreatment with the high COD removal and aerobic posttreatment with the efficient biological N removal. This kind of anaerobic-aerobic process was tested in semipilot scale by using a UASB reactor and an activated sludge system with a predenitrification (total volume 100 1). It was found that at a total HRT of 2.3 days an average of 97.5% of COD and 73.5% of total N was removed. The UASB reactor was operated at 30°C with a volumetric loading rate of 8.7 kg.m^-3.d^-1, the efficiency of COD removal was 92.2%. The processes, which take part in the biological removal of nitrogen, especially the nitrification, were running with lower rates than usually observed in aerobic treatment systems.Abbreviations AAO anaerobic anoxic oxic configuration - AOO anaerobic oxic oxic configuration - B _V volumetric organic loading rate (kg COD.m^-3. d^-1) - dB _x specific COD removal rate (mg COD. g^-1 VSS. d^-1) - DNR denitrification rate (mg N–NO₃. g^-1 VSS. h^-1) - E_COD efficiency of COD removal (%) - HRT hydraulic retention time (d) - NR nitrification rate (mg N–NO₃. g^-1 VSS. h^-1) - R recirculation ratio (%) - SBP specific biogas production (m³.kg^-1 removed COD) - SRT solids retention time; sludge age (d) - SS suspended solids (g.1^-1) - UASB upflow anaerobic sludge blanket reactor - VSS volatile suspended solids (g.1^-1)     

Challenge of psychrophilic anaerobic wastewater treatment

Psychrophilic anaerobic treatment is an attractive option for wastewaters that are discharged at moderate to low temperature. The expanded granular sludge bed (EGSB) reactor has been shown to be a feasible system for anaerobic treatment of mainly soluble and pre-acidified wastewater at temperatures of 5--10 degrees C. An organic loading rate (OLR) of 10--12 kg chemical oxygen demand (COD) per cubic meter reactor per day can be achieved at 10--12 degrees C with a removal efficiency of 90%. Further improvement might be obtained by a two-module system in series. Stabile methanogenesis was observed at temperatures as low as 4--5 degrees C. The specific activity of the mesophilic granular sludge was improved under psychrophilic conditions, which indicates that there was growth and enrichment of methanogens and acetogens in the anaerobic system. Anaerobic sewage treatment is a real challenge in moderate climates because sewage belongs to the 'complex' wastewater category and contains a high fraction of particulate COD. A two-step system consisting of either an anaerobic up-flow sludge bed (UASB) reactor combined with an EGSB reactor or an anaerobic filter (AF) combined with an anaerobic hybrid reactor (AH) is successful for anaerobic treatment of sewage at 13 degrees C with a total COD removal efficiency of 50% and 70%, respectively.     

An analysis of the factors that influence biological phosphorous removal (BPR) in a sequencing batch anaerobic/aerobic reactor

A sequencing batch anaerobic/aerobic reactor was operated in such a manner as to simulate typical variations in loading and influent feed composition as might be encountered in an urban wastewater treatment plant. The impact of these variations on biological phosphorous removal (BPR) was assayed using a number of statistical techniques including simple regression, multiple regression, ANOVA and factorial analysis. The results demonstrate the importance of biomass loading on efficiency and relate this to the level of mixed liquor suspended solids retained within the system. The ratio of COD:P in the influent wastewater had no significant impact on removal. Multiple regression analysis of factors associated with the release of phosphorous in the anaerobic phase revealed a strong correlation of these factors with subsequent phosphorous uptake efficiency in the aerobic phase. On the basis of the coefficients derived from the analysis an equation was proposed which showed a good fit to experimental data on BPR.     

Anthracene Removal using Activated Soil Reactors

The aim of this study was to evaluate anthracene removal using activated soil reactors, previously inoculated, under both aerobic and anaerobic conditions. In the reactors, the soil was maintained at 60% moisture (weight basis), room temperature, in the dark, and under constant agitation at 100 rpm. Two experiments were run during and after acclimatization to evaluate anthracene removal under both aerobic and anaerobic conditions. The first one took place during inoculum acclimatization using three different concentrations of anthracene (50, 100, and 500 mg anthracene/L per day) during 90 days. The second experiment took place after acclimatization (during 132 days). The results of anthracene removal were compared with controls in which no additional inoculum was added. During the two experiments, the behavior of pH, chemical oxygen demand (COD), and biogas production was evaluated. Results indicate that the bacterial community adapted for removal of anthracene became enriched through the acclimatization process. Anthracene biodegradation occurred in the soil model with both types of reactors (aerobic and anaerobic), but the rates and extent of biodegradation in the aerobic reactor were higher (95%) than those in anaerobic conditions (74%). Microbial activity also contributed to enhancing bioremediation in the soil by reducing anthracene sorption.