Treatment of chemical-pharmaceutical wastewater in packed bed anaerobic reactors.

Biological degradation in packed bed anaerobic mesophilic reactors with five different support materials was studied for the treatment of chemical-pharmaceutical wastewater with high COD (23-31 g/L), which contains toxic organic compounds. Experimental up-flow bio-filters were operated at different organic loads for a two-year period. Removals of 80-98% were obtained in the reactors with sand, anthracite and black tezontle, but at relatively low organic loads, less than 3.6 kg m(-3)d(-1). The reactor with granular activated carbon (GAC) had a better performance; efficiencies higher than 95% were obtained at loads up to 17 kg m(-3)d(-1) and higher than 80% with loads up to 26 kg m(-3)d(-1). Second in performance was the reactor with red tezontle which allows COD removals higher than 80% with loads up to 6 kg m(-3)d(-1). The use of GAC as support material allows greater biodegradation rates than the rest of the materials and it makes the process more resistant to organic load increases, inhibition effects and toxicity. Methanogenic activity was inhibited at loads higher than 21.9 kg m(-3)d(-1) in the GAC-reactor and at loads higher than 3.6 kg m(-3)d(-1) in the rest of the reactors. At loads lower than the previously mentioned, high methane production yield was obtained, 0.32-0.35 m3CH4/kg CODremoved.     

Treatment of organic synthesis wastewater using anaerobic packed bed and aerobic suspended growth bioreactors.

The performance of an anaerobic mesophilic packed bed reactor, with a mixture of GAC and tezontle, followed by an aerobic suspended growth system was studied for the treatment of organic chemical wastewater with a high COD concentration (22-29 g/L). The testing of the anaerobic-aerobic system was conducted in an experimental set-up for almost 2.5 years. Different operational conditions were evaluated. The anaerobic reactor showed performance stability and COD removals higher than 80% were obtained with loads up to 16.6 kg x m(-3) x d(-1). The acclimation of the aerobic biomass to the substrate in the anaerobic effluent was very quick and COD removals higher than 94% were obtained even at high organic loads. The combined anaerobic-aerobic system allowed total COD removals higher than 99.5% and the accomplishment of the discharge requirements of 200 mgCOD/L when the anaerobic reactor was operated with loads of 8-11 kg x m(-3)x d(-1) and the aerobic reactor with 0.33 kg x kg(-1) x d(-1), being the total HRT of 4.4. The average TKN removal in the anaerobic-aerobic system was 97%, the average for the anaerobic reactor being 52% and that one for the aerobic system being 94%.     

Anaerobic treatment of organic chemical wastewater using packed bed reactors.

The studied organic chemical wastewater had a high COD, 20-45g/L, and low TSS, less than 200 mg/L, making anaerobic bio-filtration a suitable treatment method. The organic matter consisted of alcohols, amines, ketones and aromatic compounds, such as toluene and phenol. Granulated activated carbon (GAC) and a porous stone called tezontle, widely available in Mexico, were used as a bio-film support. Once inoculated, the mesophilic reactors with granulated activated carbon (GAC-BFs) reached stability with 80% COD removal in 40 days, while the reactors with tezontle material (tezontle-BF) required 145 days. Biodegradation of more than 95% was obtained with both support media: at organic loads less than 1.7 kg m(-3) d (-1) in tezontle-BF and with loads of up to 13.3 kg m(-3) d(-1) in GAC-BFs. The bio-filters with GAC allowed COD removal efficiency of 80% at a load as high as 26.3 kg m (-3) d(-1), while the same efficiency with tezontle was obtained at loads up to 4.45 kgm (-3d) (-1). The use of GAC as support material allows greater biodegradation rates than tezontle and it makes the bio-filters more resistant to organic increases, inhibition effects and toxicity. Methanogenic activity was inhibited at loads higher than 1.7 kg m(-3) d(-1) in bio-filters with tezontle and 22.8 kg m(-3) d(-1 ) in bio-filters with GAC. At loads lower than the previously mentioned, high methane production yield was obtained, 0.32-0.35 m(3) CH4/kg COD removed. The biomass growth rates were low in the bio-filters with both kinds of material; however, a sufficiently high biomass holdup was obtained.     

Biological nitrogen removal with three different SBBR.

In order to compare the performance of biofilms growing on different support media, three reactors were fed with municipal wastewater from the city of Garching, Germany, and operated under the sequencing batch procedure. The support media tested have the commercial names of Kaldnes, polyethylene special support for moving bed reactors with approximate diameter of 12 mm; Liapor, ceramic spheres with diameters between 4 and 6 mm; Linpor, plastic foam cut in cubes of 15 mm. The bench-top reactors were tested for COD, TSS and ammonia nitrogen removal. During 452 days runs with organic loads between 0.5 and 8.0 gCOD/m2 x d were tested. Thin biofilms (Kaldnes and Liapor) perform better for COD and ammonia removal under lower organic loading values (< 2.5 gCOD/m2 x d). For organic loads over 3.0 gCOD/m2 x d, the reactor packed with Linpor (thick biofilm) showed a better COD and ammonia nitrogen removal than the other two. Linpor achieved the highest NOx-N production reaching values between 15 and 20 mg/l. For low organic loading rates Linpor and Liapor present similar average NOx-N concentrations. Kaldnes shows the lowest concentrations throughout the whole experimental period. The difference between ammonia nitrogen removal and NOx-N generation is simultaneous denitrification inside the deep biofilms. The average mean cellular retention times were 5.4 days for Liapor, 10.0 days for Kaldnes and 22.9 days for Linpor. This is the reason why Linpor achieved complete nitrification even with higher organic loads.     

Simultaneous nitrification and de-nitrification in MBR.

Experiments have been carried out to get an understanding of the effect of DO, C/N ratio and pH on the performance of a bench scale membrane bioreactor (MBR) in simultaneous nitrification and denitrification. It was found that under the conditions of MLSS in the range of 8000-9000 mg/L and temperature of water in the MBR of 24 degrees C, influent COD and NH3-N in the range of 523-700 mg/L and 17.24-24 mg/L respectively, the removals of COD, NH3-N and TN were 98%, 99% and 60%; 96.5%, 0,98% and 75%; 96%, 95% and 92%; 90%,70% and 60% respectively at DO of 6, 3, 1 and 0.5 mg/L. It was also found that the changes in C/N ratio and pH in a certain range have a slight effect on COD removal but have significant influence on the removal of NH3-N and TN. The results showed that only under the conditions that each ecological factor was maintained relatively steadily, simultaneous nitrification and de-nitrification proceeded smoothly. It was found that when C/N ratio was 30, the influent pH 7.2, the temperature of water in MBR 24 degrees C and DO 1 mg/L, as optimum conditions, the removals of COD, NH3-N and TN were 96%, 95% and 92% respectively. In addition, mechanism research on simultaneous nitrification and de-nitrification in MBR has been conducted as well.     

垂直流人工湿地中污染物昼夜及沿程变化规律

利用垂直潜流人工湿地单元模型探讨COD、TN和NH4+-N质量浓度在一昼夜之中随时间及深度的变化规律。结果表明:垂直潜流人工湿地中污染物去除率的变化呈一定的周期性,昼夜差距较大。COD、NH4+-N和TN的去除率在15:00达到最大,夜间最小。COD和NH4+-N质量浓度在表层(距湿地底部60～90cm段)迅速降低,底部变化幅度较小。TN浓度沿程的降低趋势很明显。湿地中COD、NH4+-N和TN质量浓度的变化趋势与DO显著相关,DO质量浓度越高,越有利于有机物和氮的去除。     

Nutrients removal in hybrid fluidised bed bioreactors operated with aeration cycles.

Abstract Two hybrid fluidised bed reactors filled with sepiolite and granular activated carbon (GAC) were operated with short cycled aeration for removing organic matter, total nitrogen and phosphorous, respectively. Both reactors were continuously operated with synthetic and/or industrial wastewater containing 350-500 mg COD/L, 110-130 mg NKT/L, 90-100 mg NH3-N/L and 12-15 mg P/L for 8 months. The reactor filled with sepiolite, treating only synthetic wastewater, removed COD, ammonia, total nitrogen and phosphorous up to 88, 91, 55 and 80% with a hydraulic retention time (HRT) of 10 h, respectively. These efficiencies correspond to removal rates of 0.95 kgCODm(-3)d(-1) and 0.16 kg total N m(-3)d(-1).The reactor filled with GAC was operated for 4 months with synthetic wastewater and 4 months with industrial wastewater, removing 98% of COD, 96% of ammonia, and 66% of total nitrogen, with an HRT of 13.6 h. No significant phosphorous removing activity was observed in this reactor. Microbial communities growing with both reactors were followed using polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) techniques. The microbial fingerprints, i.e. DGGE profiles, indicated that biological communities in both reactors were stable along the operational period even when the operating conditions were changed.     

DO对短程同步硝化反硝化除磷工艺的影响

针对碳源偏低的城市污水,采用序批式活性污泥法研究D0对短程同步硝化反硝化除磷工艺的影响,同时对短程同步硝化反硝化和反硝化除磷的机理进行探讨。试验表明：控制DO浓度可在同一个反应器内既实现短程同步硝化反硝化反应又达到反硝化除磷的效果。综合考虑COD、NHg—N、TN、TP的出水浓度达到一级A排放标准,得出最佳的D0控制范围。当D0浓度在0．5～1．0mg／LU时．COD的去除率达到93％～94％,Nil,＋一N的去除率为97％～98％,TN的去除率达到85％一96％,TP的去除率为91％～93％。     

Pumped flow biofilm reactors (PFBR) for treating municipal wastewater

A novel laboratory bench-scale sequencing batch biofilm reactor (SBBR) system was developed for the treatment of synthetic domestic strength wastewater, comprising two side-by-side 18 l reactor tanks, each containing a plastic biofilm media module. Aerobic and anoxic conditions in the biofilms were effected by intermittent alternate pumping of wastewater between the two reactors. With a media surface area loading rate of 4.2 g chemical oxygen demand (COD)/m2.d, the average influent COD, total nitrogen (TN) and ammonium-nitrogen (NH4-N) concentrations of 1021 mg/l, 97 mg/l and 54 mg/l, respectively, reduced to average effluent concentrations of 72 mg COD/l, 17.8 mg TN/l, and 5.5 mg NH4-N /l. Using a similar alternating biofilm exposure arrangement, a 16 person equivalent pilot (PE) plant was constructed at a local village treatment works to remove organic carbon from highly variable settled municipal wastewater and comprised two reactors, one positioned above the other, each containing a module of cross-flow plastic media with a surface area of 100 m2. Two different pumping sequences (PS) in the aerobic phase were examined where the average influent COD concentrations were 220 and 237 mg/l for PS1 and PS2, respectively, and the final average effluent COD was consistently less than 125 mg/l--the European Urban Wastewater Treatment Directive limit--with the best performance occurring in PS1. Nitrification was evident during both PS1 and PS2 studies. A 300 PE package treatment plant was designed based on the bench-scale and pilot-scale studies, located at a local wastewater treatment works and treated municipal influent with average COD, suspended solids (SS) and TN concentrations of 295, 183 and 15 mg/l, respectively resulting in average effluent concentrations of 67 mg COD/l, 17 mg SS/l and 9 mg TN/l. The SBBR systems performed well, and were simple to construct and operate.     

The effects of hydraulic and organic shock loads on the robustness of upflow anaerobic sludge blanket reactors treating sewage.

In this investigation, the robustness and stability of UASB reactors was evaluated on the basis of four indicators: (i) COD removal efficiency; (ii) effluent variability; (iii) pH stability; and (iv) recovery time. The experiments were carried out using six pilot-scale UASB reactors fed with domestic sewage and operated under different operational conditions. After establishment of a "steady-state", organic and hydraulic shock loads (six times the loading rate during six hours) were imposed. The results show that the UASB reactors are robust systems with regards to COD removal efficiency and pH stability when exposed to shock loads. However, this reactor cannot attenuate the imposed fluctuation in the influent COD. A secondary treatment unit is needed to retain the expelled sludge occurring as a result of a hydraulic shock load, or prior to the shock, a sufficient amount of sludge needs to be discharged from the reactor.     

Performance of UASB and DAEB reactors in the anaerobic digestion of synthetic wastewater containing sodium oleate and sodium stereate.

This study aimed at evaluating the performance of five laboratory-scale reactors, three UASB and two downflow anaerobic expanded bed (DAEB), fed with saccharose and long chain fatty acids (LCFA) for 410 days. Reactors operated at a temperature of 35 degrees C. The organic load rates were changed between 3.45 and 6.38 kg COD.m3.d(-1). During period I the substrate was saccharose and in periods II, III and IV it was saccharose plus sodium oleate, stereate and a mixture of sodium oleate and stereate. The UASB and DAEB reactors showed a similar performance. In UASB reactors specific methanogenic activity decreased in the periods II, III and IV. COD removal, biogas production and CH4 concentration in biogas decreased in all reactors at the end of the study. A washout occurred in UASB 2 and 3 when sodium stereate exceeded 500 mg.L(-1). In DAEB reactors the main problem was adsorption of LCFA particles onto the solid support.     

Microphyte and macrophyte-based lagooning in tropical regions.

A 720 m2 plant made of 8 ponds in series, set in Yaounde (Cameroon), was successively operated as a macrophyte-based system (type M) from November 1997 to October 98, a microphyte-based system (type m) from October 1999 to September 2000 and a combination of macrophyte and microphyte ponds (type M + m) from May to July 2001. Average applied loads varied over the years; from 420 kg. BOD5 ha(-1)d(-1) on the year 1997/98, the loads reached 510 kg BOD5 ha(-1)d(-1) in 1999/2000 and 500 in 2001. Though the system became more and more overloaded and sludge accumulated rapidly in the first ponds, it provided average removals of SS, BOD5 and COD that were always higher than 90% whatever the type of lagooning. Performances in the removal of SS, organic matter and the abatement of N-NH4+ and PO4(3-) did not significantly differ according to the type of lagooning and the applied load. Macrophyte lagooning did not show any definitive superiority as to nutrient removal when compared to microphyte lagooning. Microphyte lagooning was the most effective process in faecal indicators removal.     

Microbial sulphate reduction during anaerobic digestion: EGSB process performance and potential for nitrite suppression of SRB activity.

The present study investigated mesophilic anaerobic treatment of sulphate-containing wastewater in EGSB reactors and assessed the inclusion of nitrite in the reactor influent as a method for control of biological sulphate reduction. Two EGSB reactors, R1 and R2, were operated for a period of 581 days at varying volumetric loading rates, COD/SO4(2-) ratios and influent nitrite concentrations (R2 only). COD removal efficiencies of > 93% were achieved in both reactors at influent sulphate concentrations of up to 3,000 mg l(-1). A two-fold increase in the influent sulphate concentration, giving an influent COD/SO4(2-) ratio of 2, resulted in a reduction in reactor COD removal efficiency to 84% and 89%, in R1 and R2, respectively. Despite inclusion of nitrite in the R2 influent at concentrations up to 500 mg NO2-N l(-1), sulphate reduction proceeded similarly in R2 and R1, suggesting the ineffectiveness of nitrite as a potential inhibitor of SRB     

Granular biofilm-based anaerobic digestion: molecular biomonitoring and high-rate psychrophilic treatment of phenolic wastewater.

Two pairs of expanded granular sludge bed (EGSB) bioreactors, R1/R2 and R3/R4, were designed. R1/R2 were used for mesophilic (37 degrees C) treatment of synthetic wastewater over a 100-day trial. A successful start-up was achieved by R1 and R2, with COD removal over 90%. Both reactors were operated under identical parameters; however, increased organic loading induced a reduction in COD removal by R1, while R2 maintained satisfactory performance throughout the experiment. R3/R4 were operated at 15 degrees C throughout a 422-day trial and were used for the stabilisation of volatile fatty acid-based wastewater. Phenol was introduced to R4 at an applied loading rate of 1 kg phenol m(-3)d(-1), which was increased to 2 kg phenol m(-3)d(-1). No phenol was supplied to R3. Efficient COD conversion was recorded in both R3 and R4, thus demonstrating the feasibility of high-rate phenol degradation under psychrophilic conditions. Terminal restriction fragment length polymorphism analysis was applied to the characterisation of microbial community dynamics within each of the reactors. The results indicated a microbiological basis for the deviation, in terms of operational performance, of R1 and R2. TRFLP analyses indicated stable microbial communities in R3 and R4, but detected changes in the abundance of specific ribotypes in response to phenol mineralisation.     

Influence of operating conditions on ceramic ultrafiltration membrane performance when treating textile effluents

This work studies the performance of three commercial ceramic ultrafiltration membranes (ZrO(2)-TiO(2)) treating raw effluent from a textile industry. The effect of crossflow velocity at 3, 4 and 5 m s(-1) as well as membrane characteristics, such as molecular weight cut-off (30, 50 and 150 kDa), on process performance were studied. Experiments were carried out in concentration mode in order to observe the effect of volume reduction factor simultaneously. Results showed a combined influence of both crossflow velocity and molecular weight cut-off on flux performance. TOC and COD removals up to 70% and 84% respectively were reached. On the other hand, almost complete color (>97%) and turbidity (>99%) removals were achieved for all the membranes and operating conditions.     

The effect of operational conditions on the performance of UASB reactors for domestic wastewater treatment.

In this investigation, the performance of Upflow Anaerobic Sludge Blanket (UASB) reactors treating municipal wastewater was evaluated on the basis of: (i) COD removal efficiency, (ii) effluent variability, and (iii) pH stability. The experiments were performed using 8 pilot-scale UASB reactors (120 L) from which some of them were operated with different influent COD (CODInf ranging from 92 to 816 mg/L) and some at different hydraulic retention time (HRT ranging from 1 to 6 h). The results show that decreasing the CODInf, or lowering the HRT, leads to decreased efficiencies and increased effluent variability. During this experiment, the reactors could treat efficiently sewage with concentration as low as 200 mg COD/L. They could also be operated satisfactorily at an HRT as low as 2 hours, without problems of operational stability. The maximum COD removal efficiency can be achieved at CODInf exceeding 300 mg/L and HRT of 6h.     

The performance of a nitrogen-fixing SBR.

A laboratory study has successfully demonstrated that a nitrogen deficient thermomechanical pulping wastewater can be effectively treated in a sequencing batch reactor (SBR) operated under conditions of biological nitrogen fixation (the N-ViroTech process). In comparison to continuous stirred tank reactor activated sludge (CSTR-AS) configurations operated under either nitrogen fixing or nitrogen supplemented conditions, slightly lower removals of dissolved organic material were observed in the SBR. However, this was largely offset by significantly better suspended solids removal in the SBR, which contributes to the overall COD discharge. The settleability and dewaterability of sludge produced by the SBR was significantly better than that obtained from the nitrogen fixing CSTR-AS reactors, and comparable to that of a nitrogen supplemented system. Consistently low total and dissolved nitrogen discharges from the N-ViroTech systems demonstrated the advantage of this system over ones requiring nitrogen supplementation. The feast-famine regime of an SBR-type configuration has significant potential for the application of this technology in the treatment of nitrogen deficient waste streams, particularly those in which conventional single-stage systems may be susceptible to sludge bulking problems.     

Optimization of subsurface vertical flow constructed wetlands for wastewater treatment.

Constructed wetlands (CWs) use the same processes that occur in natural wetlands to improve water quality and are used worldwide to treat different qualities of water. This paper shows the results of an Austrian research project having the main goals to optimize vertical flow beds in terms of surface area requirement and nutrient removal, respectively. It could be shown that a subsurface vertical flow constructed wetland (SSVFCW) operated with an organic load of 20 g COD x m(-2) x d(-1) (corresponding to a specific surface area demand of 4 m2 per person) can fulfil the requirements of the Austrian standard regarding effluent concentrations and removal efficiencies. During the warmer months (May - October), when the temperature of the effluent is higher than 12 degrees C, the specific surface area might be further reduced. Even 2 m2 per person have been proven to be adequate. Enhanced nitrogen removal of 58% could be achieved with a two-stage system (first stage: grain size for main layer 1-4 mm, saturated drainage layer; and second stage: grain size for main layer 0.06-4 mm, free drainage) that was operated with an organic load of 80 g COD x m(-2) x d(-1) for the first stage (1 m2 per person), i.e. 40 g COD x m(-2) x d(-1) for the two-stage system (2 m2 per person). Although the two-stage system was operated with higher organic loads a higher effluent quality compared to a single-stage SSVFCW (grain size for main layer 0.06-4 mm, free drainage, organic load 20 g COD x m(-2) x d(-1)) could be reached.     

UASB reactor for domestic wastewater treatment at low temperatures: a comparison between a classical UASB and hybrid UASB-filter reactor.

The performance of an upflow anaerobic sludge blanket (UASB) reactor and a hybrid UASB-filter reactor was investigated and compared for the treatment of domestic wastewater at different operational temperatures (28, 20, 14 and 10 degrees C) and loading rates. For each temperature studied a constant CODt removal was observed as long as the upflow velocity was lower than 0.35 m/h. At these upflow velocities similar removals were observed for both reactor types at 28 and 20 degrees C, 82 and 72% respectively. However, at 14 and 10 degrees C the UASB reactor showed a better COD removal (70% and 48%, respectively) than the hybrid reactor (60% and 38%). COD removal resulted from biological degradation and solids accumulation in the reactors. At 28 degrees C, a constant 200 g sludge mass was observed in both reactors and COD removal was attributed to biological degradation only. At lower temperatures, solids accumulation was observed in addition to biological degradation with an increase in reactor sludge as the temperature decreased. The decrease in biological degradation at lower temperatures was offset by solids accumulation and explains the similar overall COD removal efficiency observed at 28 degrees C, 20 degrees C and 14 degrees C. The decrease in temperature was also followed by an increase in the effluent TSS concentration in both reactors. At 14 and 10 degrees C a lower effluent TSS concentration and better performance was observed in the UASB reactor.     

Low-temperature post-treatment of anaerobically treated-sewage in anaerobic filter with cationic-polymer addition.

The post-treatment of domestic sewage pretreated in a 6 m3 UASB was investigated in two high-rate anaerobic filter (AF) reactors operated in parallel. The difference between the two AF reactors was only the addition of cationic polymer to the second reactor (AF + P). The reactors were operated at low temperatures, ranged between 13 and 20 degrees C. The media in each AF reactor consisted of vertical sheets of reticulated-polyurethane foam (RPF) with knobs. The results demonstrated that the AF + P reactor (HRT = 3 h) with cationic polymer addition (2 mg/L) was an efficient system for post-treatment. The removal efficiencies for total, suspended, colloidal and dissolved COD were, respectively, 41, 86 and 76 and 12% in the AF + P reactor and they were, respectively, 80, 97, 77 and 66% in the UASB + (AF + P) system. The removal of total, suspended and colloidal COD in the UASB + (AF + P) system were significantly higher than those achieved in the UASB + AF system. As hardly any nutrient was removed in the UASB + (AF + P) system, the effluent after pathogen removal is a valuable product for irrigation and fertilisation to close the water and nutrients cycle.