Effect of Increasing Nitrobenzene Loading Rates on the Performance of AMBR and Sequential AMBR/CSTR Reactor System

A laboratory scale sequential anaerobic migrating blanket reactor (AMBR)/aerobic completely stirred tank reactor (CSTR) system was operated to investigate the effect of increasing nitrobenzene (NB) concentrations on the performance of AMBR/CSTR reactor system. The reactor system was operated at increasing NB loading rates from 1.93?to?38.54?g?NB?m?3?day?1 and at a constant hydraulic retention time of 10.38?days. In this study, chemical oxygen demand (COD) and NB removal efficiencies, variations of bicarbonate alkalinity (Bic.Alk.), total volatile fatty acid (TVFA), and total methane gases were monitored. COD removal efficiencies were 93–94% until a NB loading rate of 5.78?g?m?3?day?1 in the AMBR reactor. For maximum COD removal, the optimum NB loading rate and NB concentration were found to be 5.78?g?m?3?day?1 and 60?mg?L?1, respectively. COD removal efficiencies decreased from 94 to 87% and to 85% at NB loading rates of 1.93–28.90 and 38.54?g?m?3?day?1, respectively. COD was mainly removed in the first compartment. NB removal efficiencies also were approximately 100% at all NB loading rates in the effluent of the AMBR reactor. The maximum total gas and methane gas productions were found to be 2.8?L?day?1 and 1.3?mL?day?1, respectively, at a NB loading rate of 5.78?g?m?3?day?1. The TVFA concentration in the effluent of AMBR was low (17?mg?L?1) at a NB loading rate as high as 38.54?g?m?3?day?1. Overall COD removal efficiencies were found to be 99 and 96% at NB loading rates of 1.93 and 38.54?g?m?3?day?1, respectively, in a sequential AMBR/CSTR reactor system. In this study, NB was reduced to aniline under anaerobic conditions. Aniline removal efficiencies were 100% until a NB loading rate of 17.34?g?m?3?day?1 in aerobic CSTR reactor while aniline removal efficiency decreased to 90% at a NB loading rate of 38.54?g?m?3?day?1 in an aerobic reactor. In the aerobic step, aniline was mineralized to catechol. The contribution of aerobic step is not only the degradation of aniline, it may also increase the COD removals from 85 to 99% at a NB loading rate as high as 38.54?g?m?3?day?1.     

Acidification of Lactose in Wastewater

Acidification of lactose in wastewater was conducted in four series of experiments in an upflow reactor to investigate individual effects of hydraulic retention time (HRT) (2–24 h), lactose concentration in wastewater (2–30 g COD∕L), pH (4.0–6.5), and temperature (20°–60°C). Optimum acidification was found at pH 5.5 and 55°C. Acidification increased with HRT, but with the decrease of lactose concentration in wastewater. Degradation of lactose followed the Michaelis-Menten model with a maximum specific degradation rate of 4.39 g∕g VSS?day and a half-rate concentration of 1.97 g∕L. Production of volatile fatty acids, in general, favored lower lactose concentrations and higher pH, but was not sensitive to HRT and temperature. Distribution of individual volatile fatty acids∕alcohols was dependent on lactose concentration, pH, and temperature, but less sensitive to HRT. Under most conditions acetate, propionate, and ethanol were the predominant products. Biogas produced under all test conditions was composed of mostly hydrogen and carbon dioxide, but no detectable methane. Sludge yield was estimated as 0.230 ± 0.021 g VSS∕g COD.     

Treatment of High-Strength Pharmaceutical Wastewater and Removal of Antibiotics in Anaerobic and Aerobic Biological Treatment Processes

Anaerobic and aerobic treatment of high-strength pharmaceutical wastewater was evaluated in this study. A batch test was performed to study the biodegradability of the wastewater, and the result indicated that a combination anaerobic-aerobic treatment system was effective in removing organic matter from the high-strength pharmaceutical wastewater. Based on the batch test, a pilot-scale system composed of an anaerobic baffled reactor followed by a biofilm airlift suspension reactor was designed. At a stable operational period, effluent chemical oxygen demand (COD) from the anaerobic baffled reactor ranged from 1,432 to 2,397?mg/L at a hydraulic retention time (HRT) of 1.25 day, and 979 to 1,749?mg/L at an HRT of 2.5 day, respectively, when influent COD ranged from 9,736 to 19,862?mg/L. As a result, effluent COD of the biofilm airlift suspension reactor varied between 256 and 355?mg/L at HRTs of from 5.0 to 12.5 h. The antibiotics ampicillin and aureomycin, with influent concentrations of 3.2 and 1.0?mg/L, respectively, could be partially degraded in the anaerobic baffled reactor: ampicillin and aureomycin removal efficiencies were 16.4 and 25.9% with an HRT of 1.25 day, and 42.1 and 31.3% with HRT of 2.5 day, respectively. Although effective in COD removal, the biofilm airlift suspension reactor did not display significant antibiotic removal, and the removal efficiencies of the two antibiotics were less than 10%.     

Combined Removal of Carbon and Nitrogen in an Integrated UASB-Jet Loop Reactor Bioreactor System

An innovative anaerobic–aerobic integrated bioreactor system consisting of an upflow anaerobic sludge blanket (UASB) and a jet loop reactor was developed to investigate the feasibility of combined removal of carbon and nitrogen for a low-strength wastewater at different hydraulic retention times (HRTs) and recycle ratios. Total chemical oxygen demand (COD) removal of the integrated system increased from 87 to 92%, at a combined system HRT of 44?h, when the recycle ratio was increased from 100 to 400%, respectively. Denitrification efficiency of the integrated system increased from 49 to 86%, at all HRTs, when the recycle ratio was increased from 100 to 400%. The integrated system, on average, achieved more than 78% of total nitrogen at all HRTs. Nitrogen content of the biogas produced from the UASB reactor increased with increase in recycle ratios while the methane content exhibited a reverse trend, irrespective of the HRTs. Sludge volume index of the UASB reactor increased from 15?to?42?mL/g total suspended solids at the end of the study. Specific methanogenic activity of the granular sludge decreased from 1.3 to 0.8 g CH4–COD/g volatile suspended solids per day at the end of the study. Nitrogen and COD mass balance of the integrated system indicated that a substantial amount of influent nitrogen and COD was lost in the effluent as dissolved form.     

Biodegradation of Phenol with Wastewater as a Cosubstrate in Upflow Anaerobic Sludge Blanket

Anaerobic degradation of phenol mixed with a readily degradable synthetic wastewater (DSWW) as a cosubstrate was studied in a 12?L upflow anaerobic sludge blanket reactor at 30±2°C over a period of 632?days. DSWW was prepared by diluting sugar cane based molasses. The biomass was acclimatized to high phenol concentration by gradually decreasing the DSWW chemical oxygen demand (COD) of 4,000?mg/L. Feed made up of phenol COD and DSWW COD in the ratio of 7:3 (phenol concentration = 1,176?mg/L) was successfully treated at a hydraulic retention time (HRT) of 12?h and organic loading rate (OLR) of 8?g?COD/L?day. Phenol removal ranged from 99.9 to 84% at phenol COD varying from 10 to 70% in the feed. During the entire operation, COD removal varied from about 74 to 91.3%. The influent COD was distributed into CH4–COD ( ～ 72%), effluent COD ( ～ 17%), and sludge and unaccounted COD ( ～ 11%). The process failure occurred at 4:1 phenol COD: DSWW COD. Specific methanogenic activity of granular sludge exhibited uniform activity up to phenol COD of 70%. The performance of the reactor could not be maintained beyond 70% phenol COD even by reducing the sludge loading rate, increasing HRT, or decreasing OLR.     

Activated Carbon Addition to a Submerged Anaerobic Membrane Bioreactor: Effect on Performance, Transmembrane Pressure, and Flux

This study examined the effect of the addition of activated carbon to three, 3 L submerged anaerobic membrane bioreactors (SAMBRs) in terms of chemical oxygen demand (COD) removal, flux, and transmembrane pressure (TMP). The feed was a synthetic substrate with a COD of 460?mg?L?1, with one reactor run as a control, one with 1.7?g?L?1 of powdered activated carbon (PAC), and the third with 1.7?g?L?1 of granular activated carbon (GAC). While COD removal was high in all reactors (>90%), in comparison to the control (SAMBR1), the average COD removal in SAMBR2 (PAC) increased by 22.4%, while SAMBR3 with GAC was not significantly better. Because PAC has a significantly greater surface area per mass than GAC, it is probable that this difference was primarily due to the greater absorbance of fine colloidal particles and high molecular weight organics onto the carbon surface. These effects manifested themselves by SAMBR2 having lower TMPs and higher fluxes than both SAMBR3 and SAMBR1. Volatile fatty acids in the effluent from all three SAMBRs were extremely low (<18?mg?L?1), even during step changes in hydraulic retention tune, and most of the soluble COD in the effluent was soluble microbial products. Biochemical methane potential assays showed that biomass in the SAMBRs was less active than the seed sludge, and it appears that the addition of activated carbon to Reactors SAMBR2 and SAMBR3 provided a solid support for growth, and hence reduced floc breakage.     

2,4,6 Tri-Chlorophenol Containing Wastewater Treatment Using a Hybrid-Loop Bioreactor System

A hybrid-loop bioreactor system consisting of a packed column biofilm and an aerated tank bioreactor with an effluent recycle was used for biological treatment of 2,4,6 tri-chlorophenol (TCP) containing synthetic wastewater. The effects of sludge age (solids retention time) on chemical oxygen demand (COD), TCP, and toxicity removal performance of the system were investigated for sludge ages between 5 and 30?days, while the feed COD (2600±100?mg?L?1), TCP (370±10?mg?L?1), and the hydraulic residence time (25?h) were constant. Percent TCP, COD, and toxicity removals increased with increasing sludge age resulting in nearly complete COD, TCP, and toxicity removal at sludge ages above 20?days. Biomass concentrations in the packed column and in the aeration tank increased with increasing sludge age resulting in low reactor TCP concentrations, and therefore, high TCP, COD, and toxicity removals. More than 95% of COD, TCP, and toxicity removal took place in the packed column reactor. Volumetric rates of TCP and COD removal increased due to increasing biomass and decreasing effluent TCP and COD concentrations with increasing sludge age. The specific rate of TCP removal was maximum (120?mg?TCP?gX?1?day?1) at a sludge age of 20?days. TCP inhibition was eliminated by operation of the system at sludge age above 20?days to obtain nearly complete COD, TCP, and toxicity removal.     

Biotransformation of Carbon Tetrachloride and Anaerobic Granulation in a Upflow Anaerobic Sludge Blanket Reactor

Carbon tetrachloride (CT) in a synthetic wastewater was effectively degraded in a 2?l upflow anaerobic sludge blanket reactor during the granulation process by increasing the chemical oxygen demand (COD) and CT loadings. The effect of operational parameters such as influent CT concentrations, COD, CT loading, food to mass (F/M) ratio, and specific methanogenic activity (SMA) were also detected during granulation. Over 97% of CT was removed at 37°C, at a COD loading rate of 10?g/L?day. Chemical oxygen demand and CT removal efficiencies of 92 and 88% were achieved when the reactor was operating at CT and COD loading rates of 17.5?mg/L?day and 12.5?g/L?day, respectively. This corresponds to an hydraulic retention time of 0.28?day and an F/M ratio of 0.57?g?COD/g?volatile?suspended?solids?(VSS)?day. In 4?weeks, the seed sludge developed the CT degrading capability that was not very sensitive to shocks. The granular sludge cultivated had a maximum diameter of 2.5?mm and SMA of 1.64?g?COD/g?VSS?day. Glucose biodegradation by CT acclimated anaerobic granules was expressed with competitive inhibition. However the competitive inhibition was not significant since the competitive inhibition coefficient (Ki) was as high as 18.72?mg/L. Kinetic coefficients of k (maximum specific substrate utilization rate), Ks (half velocity coefficient), Y (growth yield coefficient), and b (decay coefficient) were determined as 0.6/day, 1.1?mg/L, 0.23?g?VSS/g glucose-COD, and 0.01/day, respectively, based on growth substrate glucose–COD during CT biotransformation. The CT was treated via biodegradation and this contributed to 89% of the total removal. The removal contributions from biomass adsorption, abiotic transformation, and volatilization were negligible. Adsorption and volatilization accounted for only 0.8 and 0.5% of the total removal, respectively.     

Treatment of Landfill Leachate by a Combined Anaerobic Fluidized Bed and Zeolite Column System

The use of a combined anaerobic fluidized bed and zeolite fixed bed system in sanitary landfill leachate treatment was investigated. Anaerobic treatability studies were successfully performed in the anaerobic fluidized bed reactor. The chemical oxygen demand (COD) removal was attained up to 90% with increasing organic loading rates as high as 18?g?COD/L?day after 80?days of operation. Good biogas production yield (Ygas) of 0.53?L biogas per gram removed COD with methane (CH4) content of 75% was obtained. The attached biomass concentration increased along the column height from bottom to top, and its mean value was found 6,065?mg/L after 100?days of operation. The anaerobically treated landfill leachate was further treated by a zeolite fixed bed reactor. While excellent ammonia removal (>90%) was obtained with the untreated zeolite, the regenerated zeolites showed higher performance. Consequently, this combined anaerobic and adsorption system is an effective tool to remove high COD and high ammonia in landfill leachate.     

Improved Anaerobic Degradation of Phenol with Supplemental Glucose

In this study, phenol degradation was investigated, with and without glucose as a cosubstrate, in batch and continuous studies. The two 2-L lab upflow anaerobic sludge blanket reactors were operated at a constant hydraulic retention time of 12 h with a gradual stepwise increase in phenol concentration from 105 to 1,260 mg∕L. Batch studies showed that a 1,000-mg∕L glucose supplement provided the fastest phenol removal and sludge acclimation. The effect of the glucose supplement was assessed based on microbial acclimation and granulation, phenol degradation, and resistance to shock loading. The reactor with the 1,000-mg∕L glucose supplement had a shorter start-up and granulation period (4 months, compared to 7 months for the reactor without glucose supplement), larger granule size (2.76 mm, compared to 1.77 mm), and higher phenol removal efficiency under steady-state operation at 6-kg phenol-COD∕L?day (98% compared to 88%). The reactor with the glucose supplement also exhibited a higher resistance to shock load or temperature change and faster recovery than the reactor without a glucose supplement.     

Treatment of Dilute Wastewaters Using a Novel Submerged Anaerobic Membrane Bioreactor

Three 3?L laboratory scale submerged anaerobic membrane bioreactors (SAMBRs) with in situ membrane cleaning due to the bubbling of recycled biogas underneath them were studied for their ability to treat dilute wastewaters. Both Mitsubishi Rayon hollow-fiber and Kubota flat sheet membranes made of polyethylene with a pore size of 0.4?μm were used in this study, and the effect of different substrates (460?mg/L of glucose or synthetic) on chemical oxygen demand (COD) performance in the SAMBR was investigated. It was found that both membranes resulted in similar COD removals (>90% soluble COD at a hydraulic retention time of 3?h), but that the transmembrane pressure across the hollow fiber membranes was higher under similar conditions. Molecular weight analysis of the feed, reactor contents, effluent, and extracellular polymers using high pressure liquid chromatography showed that the membrane filtered out most of the high MW soluble organics, resulting in high COD removals. The experimental results from the SAMBR show the potential benefits of using this novel reactor design in a biological wastewater treatment process to minimize energy use and sludge production.     

Automatic Start-Up of UASB Reactors

A control system to automate the start-up of anaerobic wastewater treatment reactors is presented. The system controls the feedflow rate, using the biogas production or the biogas flow rate as the only on-line variable. Furthermore, other off-line parameters, such as methane content in the biogas and COD of influent are also necessary to calculate the COD balance in the reactor. Two different start-up strategies were applied: fed batch and continuous operation. In the fed-batch operation the frequency of feeding is automatically set depending on the efficiency in COD removal. The residual organic load fraction (the fraction of influent COD not degraded to methane), is the key parameter enabling the controller the modification of feeding frequency. In order to improve reliability of the system, a second parameter k representing the gas flow rate, was introduced. By using this strategy, starting from an organic loading rate (OLR) lower than 0.5 kg COD∕(m3?day), a load higher than 8 kg COD∕(m3?day) was achieved in only 33 days, with an efficiency, in terms of COD removal, higher than 90%. When the system was operated in continuous mode, the key parameter applied is again the residual organic loading rate fraction, expressed as the percentage of COD that remained undegraded in methane. Two extreme values—“minimum” and “maximum”—have to be defined. Once the system reaches the minimum, the controller increases the feeding pump speed automatically, and when it attains the maximum value, the feeding flow is decreased proportionally. In order to ensure stable operation, a further parameter, the waiting time between the moment at which the threshold value is reached and the modification of the feeding flow rate, was introduced. 24 h has proven to be an excellent value for this purpose. By means of this strategy, starting from an influent OLR lower than 0.5 kg COD∕(m3?day), an OLR of 9–12 kg COD∕(m3?day) was achieved in 40 days, with COD removal efficiency higher than 95%.     

Granular Bed Baffled Reactor (Grabbr): Solution to a Two-Phase Anaerobic Digestion System

A single unit anaerobic granular bed baffled reactor (GRABBR) is proposed as an alternative to a separately operated two-phase anaerobic digestion system. This overcomes the problems related to wastewater treatment at high loading rates which usually results in accumulation of intermediate acid products, and consequently inhibits methanogenesis. This study was carried out to evaluate the stability of a five compartment GRABBR system when treating synthetic glucose wastewater at various operational conditions. The reactor was started with volumetric organic loading rate (OLR) of 1 kg chemical oxygen demand (COD)/m3?day, equivalent to 120 h hydraulic retention time (HRT), and loading rates were gradually increased at suitable intervals to up to 20 kg COD/m3?day (6 h HRT). At steady state, the overall soluble COD (SCOD) removal was over 95% under all applied loading conditions. At lower loadings, the reactor operated as a completely mixed system, and most of the treatment was achieved in the first compartment. At higher loadings, the entire system transformed into different phases, acidogenesis being dominant near the influent point, whilst methanogenesis was the main activity in the compartments near the effluent point. Granule breaking and flotation was observed in the acidogenic zone, whilst the methanogenic zone retained its original granular form. High assimilation rate of influent nitrogen was observed in the first compartment with the formation of nongranular biomass, identified as Klebsiella pneumoniae. The success of GRABBR as a single unit two-phase anaerobic digestion system could save the cost of an extra unit traditionally employed to achieve similar goals in treatment of high strength wastewaters.     

Simultaneous Removal of Carbon and Nitrogen from Swine Wastewater Using an Immobilized-Cell Reactor

A single-stage phosphorylated polyvinyl alcohol immobilized-cell reactor with three operation modes was employed to investigate the efficiency of simultaneous carbon/nitrogen removal from raw swine wastewater. In continuous aeration mode, the removal efficiency of chemical oxygen demand (COD) and total nitrogen (T-N) exceeded 70 and 8%, respectively, at hydraulic retention time of 10?days. In intermittent aeration (IA) mode, the removal efficiency of COD and T-N was more than 85 and 46%, respectively, when the reactor was set at 50% aeration duration to cycle time to operate at three aerobic-anoxic cycles per day. When oxidation-reduction-potential control was adopted to control the duration of the anoxic period in the real-time controlled (RTC) IA mode for a 4?h aeration period, the total cycle time was reduced by about 20% with a slight increase in removal efficiency of COD (87%) and T-N (47%). The system with no extra chambers required is efficient in simultaneous carbon/nitrogen removal.     

Comparative Study between a Hybrid System and a Biofilm System for the Treatment of Ammonia and Organic Matter in Wastewaters

The efficiency of two similar gas-lift bioreactors, a biofilm reactor and a hybrid circulating floating bed reactor (CFBR), were studied and compared. In the biofilm CFBR the biomass grew preferably adhered on a plastic granular support, whereas in the hybrid CFBR both suspended biomass and biofilms were allowed to grow in the reactor. COD/NH4+ ratio (COD=chemical oxygen demand) was manipulated between 0.0 and 8.0?g/g, maintaining the ammonia influent concentration around 50?mg N–NH4+/L, the ammonia loading rate at 0.9?kg N–NH4+/m3?day and the hydraulic retention time at 1.36?h. At low COD/NH4+ ratio (0 and 0.5?g/g) both systems behaved similarly, achieving ammonia removal percentages higher than 95%. In the biofilm CFBR a reduction of the nitrification percentage from 95 to 20% was observed when a COD/N–NH4+ ratio up to 8?g/g was applied in the influent. However, at the same operational conditions, the nitrification process in the hybrid CFBR was slightly affected. In the hybrid-CFBR reactor heterotrophs growing in suspension consumed the COD source faster than those growing in biofilms as was monitored. The growth of heterotrophic microorganism in suspension had a beneficial effect for the nitrifying population growing in the biofilm of the hybrid CFBR. Nitrifying activity of the biofilm was not limited by the presence of heterotrophs consuming dissolved oxygen, displacing the nitrifying bacteria or creating mass transfer resistance as was observed in the biofilm CFBR.     

Granulation Enhancement in Anaerobic Sequencing Batch Reactor Operation

Two laboratory-scale anaerobic sequencing batch reactors (anSBRs) were used to investigate the effectiveness of polymer addition for enhancing granulation. Mixed liquor volatile suspended solids (MLVSS) concentrations in R1 (with a polymer supplement) and R2 (control) were maintained at approximately 5 g/L. Granule development was measured by determination of the average bioparticle diameter of biosolids from the anSBRs. Addition of cationic polymer to R1 started on the 47th day after reactor start-up at a dosage of 1 ppm (on reactor volume) once per every two cycles. The cationic polymer had a beneficial effect on granulation. Compared to the control, it shortened the granulation process by approximately four months. Within the range investigated, food-to-microorganism (F/M) ratios at 0.5–0.6 g COD/g VSS?d were also beneficial to granulation. After 300 days operation (at F/M ratio 0.5 g COD/g VSS?d), the average bioparticle diameter of R1 was 0.78 mm, while R2 was only 0.39 mm. R1, aside from having a larger granule size, also had a higher methane production and lower soluble COD in effluent at F/M ratio 0.6 g COD/g VSS?d compared to R2.     

Organic Removal of Anaerobically Treated Leachate by Fenton Coagulation

The leachate from a Hong Kong landfill, containing 15,700 mg∕L of chemical oxygen demand (COD) and 2,260 mg∕L of ammonia nitrogen (NH3–N), was first treated in a UASB (upflow anaerobic sludge blanket) reactor at 37°C. The process on average removed 90.4% of COD with 6.6 days of hydraulic retention at an organic loading rate of 2.37 g of COD∕L?day. The UASB effluent was further treated by the Fenton coagulation process using H2O2 and Fe2+. Under the optimal condition of 200 mg of H2O2∕L and 300 mg of Fe2+∕L and an initial pH of 6.0, 70% of residual COD in the UASB effluent was removed, of which 56% was removed by coagulation∕precipitation and only 14% by free radical oxidation. It is obvious that H2O2 and Fe2+ had a strong synergistic effect on coagulation. The average COD in the final effluent was 447 mg∕L. Removing each gram of COD required 0.28 g of Fe2+ and 0.18 g of H2O2.     

Effect of Carbon Source on PCE Dehalogenation

A laboratory study using the upflow anaerobic sludge blanket reactor for treating high-strength wastewater containing tetrachloroethene (PCE) was carried out to study the effect of carbon source, recycle, and shock loading on dehalogenation of PCE and process performance. The PCE was dehalogenated to trichloroethylene, cis-1,2-dichloroethylene, vinyl chloride, and ethylene. During the study on the effect of carbon source, the PCE and COD removal up to 97% and biogas production of 0.518–0.47 m3∕kg CODrem with methane content up to 66% were achieved under steady-state operating conditions. An increase in the influent COD from 2,000 to 4,000 mg∕L did not show any improvement in the PCE removal. Recycling of effluent at 50% showed the decrease in COD removal and increase in the effluent concentration of dichloroethylene and vinyl chlorides. Around 1–3.5% of influent PCE stripping to biogas was observed. It was observed that methanol has the stimulatory effect on the dehalogenation of PCE. A shock loading study showed that the upflow anaerobic sludge blanket reactor could assimilate 1.5–2 times the original PCE concentration (50 mg∕L) without much effect on the process performance.     

Sodium Inhibition of Thermophilic Methanogens

This study investigated the sodium inhibition of methanogens using two thermophilic (55°C) anaerobic sequencing batch reactors (ASBRs). The ASBRs were operated at a chemical oxygen demand (COD) loading of 4 g/L/day and a hydraulic retention time of 3 days. To evaluate the chronic toxicity of sodium to methanogens, the biomass in one of the ASBRs was acclimated to increasing sodium concentrations of 4.1, 7.1, and 12.0 g/L while the feed to the second ASBR was not supplemented with any additional sodium. The methanogenic activity (mL CH4/g volatile suspended solids/day) decreased by nearly 44% at an acclimation concentration of 12.0 g Na+/L, but the COD removal efficiency and methane production did not vary appreciably at the different acclimation concentrations studied. The acute toxicity of sodium to methanogens was determined by a series of batch anaerobic toxicity assays (ATAs). The biomass acclimated to different concentrations of sodium was collected from the ASBRs and used as inocula for the batch tests, and the sodium concentration was varied up to 17.7 g/L. The methanogens in the biomass acclimated to 0, 4.1, 7.1, and 12.0 g Na+/L were completely inhibited (100% inhibition) at predicted sodium concentrations of 10.6, 12.7, 18.0, and 22.8 g/L, respectively. To simulate the results of batch ATA in the ASBR, 7-day feeding with sodium concentrations in the influent measuring 6.2, 10.6, and 16.0 g/L were introduced into the reactor. Among each feeding, the reactor was operated with no additional sodium in the feed with 2–3 week intervals. Even though the methanogenic activity was not significantly affected at 6.2 and 10.6 g/L of sodium, there was a deterioration in methanogenic activity at 16.0 g/L dosage of sodium.     

Metal Stimulation and Municipal Digester Thermophilic/Mesophilic Activity

Biomass from thermophilic and mesophilic digesters (four temperature-phased anaerobic digesters and one phased thermophilic digester) was assayed for potential methane production rate increases resulting from nutrient (Ni, Co, and Fe) addition. Furthermore, digester operations and biomass activities were compared. The majority (77%) of biomass samples benefited from nutrients, with propionate and acetate utilization rates increasing as much as 50 and 35%, respectively, after nutrient addition. Propionate utilization rates were more frequently stimulated by nutrient addition, demonstrating increased methane production rates of from 14 to 50% upon nutrient amendment. Others have observed difficulty achieving low propionate concentrations in municipal thermophilic digesters, especially at lower retention times. Trace nutrient supplementation is one method to increase propionate and acetate utilization in some municipal thermophilic as well as mesophilic digesters.