Reliable method for assessing the COD mass balance of a submerged anaerobic membrane bioreactor (SAMBR) treating sulphate-rich municipal wastewater

The anaerobic treatment of sulphate-rich wastewater causes sulphate reducing bacteria (SRB) and methanogenic archaea (MA) to compete for the available substrate. The outcome is lower methane yield coefficient and, therefore, a reduction in the energy recovery potential of the anaerobic treatment. Moreover, in order to assess the overall chemical oxygen demand (COD) balance, it is necessary to determine how much dissolved CH(4) is lost in the effluent. The aim of this study is to develop a detailed and reliable method for assessing the COD mass balance and, thereby, to establish a more precise methane yield coefficient for anaerobic systems treating sulphate-rich wastewaters. A submerged anaerobic membrane bioreactor (SAMBR) treating sulphate-rich municipal wastewater was operated at 33 °C for an experimental period of 90 d, resulting in a high COD removal (approximately 84%) with a methane-enriched biogas of 54 ± 15% v/v. The novelty of the proposed methodology is to take into account the sulphide oxidation during COD determination, the COD removed only by MA and the dissolved CH(4) lost with the effluent. The obtained biomethanation yield (333 L CH(4) kg(-1) COD(REM MA)) is close to the theoretical value, which confirms the reliability of the proposed method.     

Treatment of high loaded swine slurry in an aerobic granular reactor

Aerobic granular sludge grown in a sequential batch reactor was proposed as an alternative to anaerobic processes for organic matter and nitrogen removal from swine slurry. Aerobic granulation was achieved with this wastewater after few days from start-up. On day 140 of operation, the granular properties were: 5 mm of average diameter, SVI of 32 mL (g VSS)(-1) and density around 55 g VSS (L(granule))(-1). Organic matter removal efficiencies up to 87% and nitrogen removal efficiencies up to 70% were achieved during the treatment of organic and nitrogen loading rates (OLR and NLR) of 4.4 kg COD m(-3) d(-1) and of 0.83 kg N m(-3) d(-1), respectively. However, nitrogen removal processes were negatively affected when applied OLR was 7.0 kg COD m(-3) d(-1) and NLR was 1.26 kg N m(-3) d(-1). The operational cycle of the reactor was modified by reducing the volumetric exchange ratio from 50 to 6% in order to be able to treat the raw slurry without dilution.     

Pretreatment of silk-dyeing industrial wastewater by UASB reactor.

The objective of this study was to investigate the performance of the upflow anaerobic sludge blanket (UASB) reactor as the pretreatment system for silk-dyeing wastewater. Two laboratory-scale UASB reactors, with working volume of 15.59 I, were used during May 1998 to June 1999. The actual wastewater was diluted to reduce ammonium ion toxicity on anaerobic bacteria. The experiments were conducted at the organic loading rates (OLRs) of 0.52, 1.01, 1.04, 1.54 and 2.56 kgCOD/(m3 x d), treating only wastewater generated from the acid-dye process of mixed-species raw silk. It took approximately 4 1/2 months to reach the steady-state conditions. It was found that the COD removal was in the ranges of 74.1-85.3%, except at OLR 2.56 kgCOD/(m3 x d) where efficiency significantly dropped to 55.2%. The apparent color removal was in the similar trend as COD. During the study periods, wastewater input had various color shades while the effluent generally looked pale yellowish. The methane generation rates ranged from 0.18-0.31 m3/kg COD removed, with methane composition 81.0-88.1% in biogas. The average granule size in the sludge bed had slowly increased to 0.73 mm in the last experiment. It can be concluded that the UASB reactor is suitable as a pretreatment system for silk-dyeing wastewater. An OLR of 1 kgCOD/(m3 x d) and an influent concentration diluted to 2,600 mgCOD/l are suggested while COD and apparent color removal efficiency of 80% and 70%, respectively, can be expected.     

Iron and manganese removal from textile effluents in anaerobic attached-growth bioreactor filled with coirfibres.

A laboratory scale study on Fe and Mn removal in upflow anaerobic bioreactor of a working volume of 20 L with coir fibre as the filter medium was investigated for a period of 312 days. The maximum Fe and Mn levels considered were 10 and 5 mg/L respectively, which are the typical average values of textile effluents subsequent to the primary and secondary treatments. Ten sub-experimental runs were conducted with varying HRTs (5 days to 1 day), ratios of COD:SO42- (20 to 3.5), Fe levels (0.005 to 10 mg/L) and Mn levels (0 to 5 mg/L). COD:SO2 of 3.5 was identified as the optimum point at which sulphate reducing bacteria (SRBs) out competed methane producing bacteria (MPBs) and further reduction of this ratio caused total and/or significant inhibition of MPBs, thus building sulphate reducing conditions. The effluent contained Fe and Mn below the permissible levels (1.6 and 1.1 mg/L for Fe and Mn, respectively) stipulated by US National Pollution Discharge Elimination System (NPDES) for inland surface waters at HRTs higher than 3 days. Results of the mass balance showed more Fe accumulation (60%) in sediments whereas 27% in the filter media. An opposite observation was noticed for Mn.     

Continuous hydrogen and methane production in a two-stage cheese whey fermentation system

The feasibility of integrating biological hydrogen and methane production in a two-stage process using mixed cultures and cheese whey powder (CWP) as substrate was studied. The effect of operational parameters such as hydraulic retention time (HRT) and organic loading rate (OLR) on the volumetric hydrogen (VHPR) and methane (VMPR) production rates was assessed. The highest VHPR was 28 L H2/L/d, obtained during stable operation in a CSTR at HRT and OLR of 6 h and 142 g lactose/ L/d, respectively. Moreover, hydrogen (13 L/L/d) was produced even at HRT as low as 3.5 h and OLR of 163 g lactose/L/d, nonetheless, the reactor operation was not stable. Regarding methane production in an UASB reactor, the acidified effluent from the hydrogen-producing bioreactor was efficiently treated obtaining COD removals above 90% at OLR and HRT of 20 g COD/L/d and 6 h, respectively. The two-stage process for continuous production of hydrogen and methane recovered over 70% of the energy present in the substrate. This study demonstrated that hydrogen production can be efficiently coupled to methane production in a two-stage system and that CWP is an adequate substrate for energy production.     

Anaerobic monodigestion of poultry manure: determination of operational parameters for CSTR

In this work the anaerobic monodigestion for the treatment of turkey manure was evaluated, without its codigestion with another substrate. The effect of the organic loading rate (OLR) and the substrate concentration (high total solids (TS) concentration) or product concentration (high volatile fatty acids (VFA) and/or ammonia (NH(3)-N) concentrations) was studied. The results show that for a continuous stirred tank reactor (CSTR) operation, a maximum of 40 g/L of TS and 4.0 g/L of ammonium (NH(4)(+)) was required. In addition, the maximum organic loading rate (OLR) will not exceed 1.5 kg VS/m(3)d. Higher TS and NH(4)(+) concentrations and OLR lead to a reduction on the methane productivity and volatile solids (VS) removal. During the CSTR operation, a high alkalinity concentration (above 10 g/L CaCO(3)) was found; this situation allowed maintaining a constant and appropriate pH (close to 7.8), despite the VFA accumulation. In this sense, the alkalinity ratio (α) is a more appropriate control and monitoring parameter of the reactor operation compared to pH. Additionally, with this parameter a VS removal of 80% with a methane productivity of 0.50 m(3)(CH4)/m(3)(R)d is achieved.     

Anaerobic treatment of a medium strength industrial wastewater at low-temperature and short hydraulic retention time: a pilot-scale experience

The aim of this work was to evaluate the performance of a pilot-scale upflow anaerobic sludge blanket (UASB) reactor during the treatment of cereal-processing industry wastewater under low-temperature conditions (17 degrees C) for more than 300 days. The applied organic loading rate (OLR(appl)) was gradually increased from 4 to 6 and 8 kg COD(sol)/m3d by increasing the influent soluble chemical oxygen demand (COD(sol)), while keeping the hydraulic retention time constant (5.2 h). The removal efficiency was high (82 to 92%) and slightly decreased after increasing the influent COD(sol) and the OLR(appl). The highest removed organic loading rate (OLR(rem)) was reached when the UASB reactor was operated at 8 kg COD(sol)/m3d and it was two times higher than that obtained for an OLR(appl) of 4 kg COD(sol)/m3d. Some disturbances were observed during the experimentation. The formation of biogas pockets in the sludge bed significantly complicated the biogas production quantification, but did not affect the reactor performance. The volatile fatty acids in the effluent were low, but increased as the OLR(appl) increased, which caused an increment of the effluent COD(sol). Anaerobic treatment at low temperature was a good option for the biological pre-treatment of cereal processing industry wastewater.     

Treatment of paper mill effluent using an anaerobic/aerobic hybrid side-stream membrane bioreactor

This paper presents the design and operational performance data of an anaerobic/aerobic hybrid side-stream Membrane Bioreactor (MBR) process for treating paper mill effluent operated over a 6 month period. The paper mill effluent stream was characterized by a chemical oxygen demand (COD) range of between 1,600 and 4,400 mg/L and an average BOD of 2,400 mg/L. Despite large fluctuations in COD feed concentration, stable process performance was achieved. The anaerobic Expanded Granular Sludge Bed (EGSB) pre-treatment step effectively lowered the organic loading by 65 to 85%, thus lowering the MBR COD feed concentration to consistently below 750 mg/L. The overall MBR COD removal was consistent at an average of 96%, regardless of the effluent COD or changes in the hydraulic retention time (HRT) and organic loading rate (OLR). Combining a high-rate anaerobic pre-treatment EGSB with a Modified Ludzack-Ettinger (MLE) MBR process configuration produced a high quality permeate. Preliminary NF and RO results indicated an overall COD removal of around 97 and 98%, respectively.     

Simultaneous removal of ammonium-nitrogen and sulphate from wastewaters with an anaerobic attached-growth bioreactor.

Some industrial wastewaters may contain ammonium-nitrogen and/or sulphate, which need to be removed before their discharge into natural water bodies to eliminate their severe pollution. In this paper, simultaneous removal of ammonium-nitrogen and sulphate with an anaerobic attached-growth bioreactor of 3.8 L incubated with sulphate reducing bacteria (SRB) was investigated. Artificial wastewater containing sodium sulphate as electron acceptor, ammonium chlorine as electron donor and glucose as carbon source for bacteria growth was used as the feed for the bioreactor. The loading rates of ammonium-nitrogen, sulphate and COD were 2.08 gN/m3 x d, 2.38 gS/m3 x d, 104.17 gCOD/m3 x d, respectively, with a N/S ratio of 1:1.14. The results demonstrated that removal rates of ammonium-nitrogen, sulphate and COD could reach 43.35%, 58.74% and 91.34%, respectively. Meanwhile, sulphur production was observed in effluent as well as molecular nitrogen in biogas, whose amounts increased with time substantially, suggesting the occurrence of simultaneous removal of ammonium-nitrogen and sulphate. This novel reaction provided the possibility to eliminate ammonium-nitrogen and sulphate simultaneously with accomplishment of COD removal from wastewater, making wastewater treatment more economical and sustainable.     

Modeling of anaerobic treatment of wastewater in ponds.

A mathematical model to simulate the performance of anaerobic ponds was developed incorporating both settling of particulate components and the biological anaerobic digestion process. The biological activity includes solubilization of particulate organic matter; methanogenesis and the sulphate reduction process. The model considers that an anaerobic pond comprises a series of equal size columns. Each column has three compartments viz. liquid layer, active sediment layer and inert sediment layer. The existence of organic matter and sulphate removal mechanisms both in the bulk as well as sediment layer of the ponds and the exchange of the soluble components between the layers has been included in the model. The model was transferred to a computer program using VisSim Basic software. The model was verified by comparing simulated results with full-scale as well as with laboratory-scale anaerobic pond performance data. A good agreement between the simulated and the observed pond performance was achieved.     

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%.     

Methanogenic and sulphate reducing bacterial population levels in a full-scale anaerobic reactor treating pulp and paper industry wastewater using fluorescence in situ hybridisation.

In this study, specific methanogenic activity (SMA) test and fluorescence in situ hybridisation (FISH) were respectively used to determine acetoclastic methanogenic capacity, and composition and number of methanogenic and sulphate reducing bacterial (SRB) populations within a full scale anaerobic contact reactor treating a pulp and paper industry effluent. The sludge samples were collected from three different heights along the anaerobic reactor having a difficulty of completely stirring. Performance of the anaerobic reactor in terms of COD removal efficiency varied between 47 and 55% at organic loading rates in a range of 1.6-1.8 kg COD m(-3) d(-1) and methane yield varied between 0.18 and 0.20 m3CH4kg CODrem(-1). The anaerobic reactor was not operated for 2 weeks during the monitoring period. According to SMA test results, potential methane production rate was 276 mLCH4 gVSS(-1) d(-1) before the off period of the reactor, however it decreased to 159 mL CH4 gVSS(-1) d(-1) after this period. SMA test and FISH results along the reactor height showed that the acetoclastic methanogenic activity of the sludge samples, the relative abundance of acetoclastic methanogens, hydrogenotrophic methanogens and acetate oxidising SRB decreased as the reactor height increased, however the relative abundance of non-acetate oxidising SRB increased.     

High rate anaerobic thermophilic technologies for distillery wastewater treatment.

In this paper, performance of two high rate technologies, upflow anaerobic fixed-film reactor and fluidized bed laboratory-scale, treating distillery wastewater (wine vinasses) at anaerobic thermophilic conditions have been compared. The results obtained show that the stationary packed bed, with a corrugated plastic support, operated under stable conditions at organic loading rates (OLR0) around 20 kgCOD/m3/d, gives maximal total CODr of 76% at OLR0 of 6.29 kgCOD/m3/d; the fluidized bed reactor, operated on open pore sintered-glass media, gives total CODr of 96% at OLR0 of 5.88 kgCOD/m3/d. The anaerobic fluidized bed technology is more effective than the upflow anaerobic fixed-film technology due, fundamentally, to this technology favouring the transport of microbial cells from the bulk to the surface and enhancing the contact between the microorganism-substrate phases, In this sense, the stationary packed bed technology is adequate for the treatment of easily biodegradable wastewater, or for the cases where elevated percentages of CODr removal are not required, while the fluidized bed technology is especially suitable for treatment of hazardous wastes with recalcitrant compositions.     

Anaerobic fluidized bed reactor application to tropical fruit wine effluent.

The influence of the organic loading rate (OLR), the fluidization level (FL) and the particle diameter of natural zeolite used as support (D(p)), was evaluated at a laboratory scale anaerobic fluidized bed reactor (AFBR), treating tropical fruit wine effluent (vinasse). The experiment was carried out at an OLR from 2-5 kg COD/m3 d, FL of 20 and 40% and D(p) from 0.25 to 0.80 mm. It was demonstrated that OLR and FL had a slight influence on chemical oxygen demand removal and strong influence on the methane production rate. The COD removal was slightly higher for the higher particle diameter used. Additionally using the scanning electron microscope (SEM), it was observed that natural zeolites have excellent physical characteristics as a support medium in AFBR.     

Treatment of low and medium strength sewage in a lab-scale gradual concentric chambers (GCC) reactor.

One of the major challenges of anaerobic technology is its applicability for low strength wastewaters, such as sewage. The lab-scale design and performance of a novel Gradual Concentric Chambers (GCC) reactor treating low (165+/-24 mg COD/L) and medium strength (550 mg COD/L) domestic wastewaters were studied. Experimental data were collected to evaluate the influence of chemical oxygen demand (COD) concentrations in the influent and the hydraulic retention time (HRT) on the performance of the GCC reactor. Two reactors (R1 and R2), integrating anaerobic and aerobic processes, were studied at ambient (26 degrees C) and mesophilic (35 degrees C) temperature, respectively. The highest COD removal efficiency (94%) was obtained when treating medium strength wastewater at an organic loading rate (OLR) of 1.9 g COD/L.d (HRT = 4 h). The COD levels in the final effluent were around 36 mg/L. For the low strength domestic wastewater, a highest removal efficiency of 85% was observed, producing a final effluent with 22 mg COD/L. Changes in the nutrient concentration levels were followed for both reactors.     

Three stages MBR (methanogenic, aerobic biofilm and membrane filtration) for the treatment of low-strength wastewaters

The use of a new three stages MBR process with a first methanogenic UASB stage, a second stage with aerobic biofilm growing on small carrier elements maintained in suspension and third stage with membrane filtration module is presented. The objective of the first methanogenic chamber is to diminish COD of the raw wastewater, producing a biogas rich in methane, and decrease the sludge production. In the second stage, the remaining soluble biodegradable COD is oxidized by heterotrophs. In the third stage, the membrane modules could be operated at higher fluxes than those reported for AnMBR systems, and similar to those obtained in aerobic MBRs. In this sense, the concept of these three stages MBR is to join the advantages of the methanogenic and aerobic membrane bioreactor processes, by reducing energy requirements for aeration, producing biogas with high methane percentage and a permeate with very low COD content. A synthetic wastewater was fed to the three stages MBR. COD in the influent was between 200 and 1,200 mg/L, ammonium ranged from 10 to 35 mg/L and phosphorous concentration was 8 mg/L. OLR in-between 1 and 3 kg COD/(m3 d) and a HRT of 13-21 h were applied. Temperature was between 17.5 and 23.2 degrees C. During the whole operating period the COD removal efficiencies were in the range of 90 and 96% of which in between 40 and 80% was removed in the first methanogenic chamber. Biogas production with methane content between 75 and 80% was observed. With regard to membrane operation, average permeabilities around 150 L/(m2 h bar) were achieved, operating with fluxes of 11-15 L/(m2 h).     

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.     

Effect of the pH influent conditions in fixed-film reactors for anaerobic thermophilic treatment of wine-distillery wastewater.

In anaerobic treatments, the pH conditions affect the efficacy and operation of the process. The main purpose of this research is to compare the effect of the pH influent on the performance of a high rate technology at laboratory scale, upflow anaerobic fixed-film reactor, treating distillery wastewater (wine vinasses) in thermophilic conditions. The results obtained shown that the pH influent influences the performance of the biodegradation process: the depurative efficiency is higher for the operation with alkaline influent. The operation with acid influent allows us to operate at organic loading rates (OLR) around 5.6 kgCOD/m3/d (hydraulic retention time: 1.5 days), maintaining total Chemical Oxygen Demand removals (CODr) of 77.2%; the operation with alkaline influent allows total CODr of 76.8% working at OLR around 10.5 kgCOD/m3/d. The greatest efficiency of substrate removal was 87.5% for OLR 3.2 kgCOD/m3/d and hydraulic retention time of 4.0 days operating with alkaline influent. Therefore, the operation with alkaline influent implicates senior levels of purifying efficiency for similar organic load rate.     

Activity of sulphate reducing bacteria according to COD/SO4(2-) ratio of acrylonitrile wastewater containing high sulphate.

This study was performed to evaluate the biodegradability of acrylonitrile wastewater, microbial inhibition effect of acrylonitrile wastewater on removal efficiency and the activity of sulphate reducing bacteria (SRB) according to COD/sulphate ratio. Acrylonitrile wastewater was hardly biodegradable in a biodegradability test, however, SRB activity was 57% for overall consumption of electron donor and it was relatively high value compared to 17% of reference test with glucose. COD removal of acrylonitrile wastewater was improved to 57% and 61% from 20% as the COD/sulphate ratio were 0.5 and 0.3 by sulphate addition to acrylonitrile wastewater. First order reaction rate constants k on organic removal of acrylonitrile wastewater were 0.001, 0.004 and 0.004 at each COD/sulphate ratio of 0.9, 0.5 and 0.3. Thus it was suggested that the activity of SRB was a significant factor for removing organics and sulphate simultaneously in acrylonitrile wastewater.     

Full scale fluidized bed anaerobic reactor for domestic wastewater treatment: performance, sludge production and biofilm.

This paper describes the performance, sludge production and biofilm characteristics of a full scale fluidized bed anaerobic reactor (32 m3) for domestic wastewater treatment. The reactor was operated with 10.5 m x h(-1) upflow velocity, 3.2 h hydraulic retention time, and recirculation ratio of 0.85 and it presented removal efficiencies of 71+/-8% of COD and 77+/-14% of TSS. During the apparent steady-state period, specific sludge production and sludge age in the reactor were (0.116+/-0.033) kgVSS. kgCOD(-1) and (12+/-5)d, respectively. Biofilm formed in the reactor presented two different patterns: one of them at the beginning of the colonization and the other of mature biofilm. These different colonization patterns are due to bed stratification in the reactor, caused by the difference in local-energy dissipation rates along the reactor's height, and density, shape, etc. of the bioparticles. The biofilm population is formed mainly of syntrophic consortia among sulfate reducing bacteria, methanogenic archaea such as Methanobacterium and Methanosaeta-like cells.