A two-stage thermophilic anaerobic process for the treatment of source sorted household solid waste

Summary Hydrolysis and acidification of source sorted household solid waste (SSHSW) at 70°C was studied using continuous stirred tank reactor (CSTR). The soluble COD/total initial COD-ratio of the SSHSW increased from 25 to 35% during the CSTR treatment. A thermophilic (55°C) upflow anaerobic sludge blanket (UASB) reactor removed up to 80% of the COD in the liquid fraction of the SSHSW treated at 70°C.     

Interpreting the effect of increasing COD loading rates on the performance of a pre-anoxic MBBR system: implications on the attached and suspended biomass dynamics and nitrification–denitrification activity

A pre-anoxic MBBR system was subjected to increasing organic loading rates up to 18 gCOD/(m² day). At 3 gCOD/(m² day), most of the incoming organic matter was removed via denitrification. However, at higher loads, anoxic COD removal became limited by the nitrite/nitrate supply from the aerobic reactor, which assumed an important role in this conversion. Despite the application of low dissolved oxygen (DO) levels (<2 mg/L) in this tank, nitrification was observed to be nearly complete until 8 gCOD/(m² day). As the organic input was increased, the maximum specific nitrifying activity gradually declined. Activity tests suggested that an oxygen-limited environment was established in the biofilm. At lower loads [3–8 gCOD/(m² day)], the nitrification product obtained was affected by the DO concentration, whereas from 16 to 21 gCOD/(m² day), nitrite/nitrate profiles were likely associated with microbial stratification in the biofilm. The results also indicated that the role of the suspended biomass in the overall nitrification and denitrification can be very significant in high loaded MBBRs and should not be neglected, even at low HRTs.     

Effect of metals on the regulation of acidogenic metabolism enhancing biohydrogen and carboxylic acids production from brewery spent grains: Microbial dynamics and biochemical analysis

The present study reports the mixed culture acidogenic production of biohydrogen and carboxylic acids (CA) from brewery spent grains (BSG) in the presence of high concentrations of cobalt, iron, nickel, and zinc. The metals enhanced biohydrogen output by 2.39 times along with CA biosynthesis by 1.73 times. Cobalt and iron promoted the acetate and butyrate pathways, leading to the accumulation of 5.14 gCOD/L of acetic and 11.36 gCOD/L of butyric acid. The production of solvents (ethanol + butanol) was higher with zinc (4.68 gCOD/L) and cobalt (4.45 gCOD/L). A combination of all four metals further enhanced CA accumulation to 42.98 gCOD/L, thus surpassing the benefits accrued from supplementation with individual metals. Additionally, 0.36 and 0.31 mol green ammonium were obtained from protein‐rich brewery spent grain upon supplementation with iron and cobalt, respectively. Metagenomic analysis revealed the high relative abundance of Firmicutes (>90%), of which 85.02% were Clostridium, in mixed metal‐containing reactors. Finally, a significant correlation of dehydrogenase activity with CA and biohydrogen evolution was observed upon metal addition.     

Performance characteristics of a two-stage dark fermentative system producing hydrogen and methane continuously

The performance of a mesophilic two-stage system generating hydrogen and methane continuously from sucrose (10-30 g/L) was investigated. A hydrogen-generating CSTR followed by an upflow anaerobic filter were both inoculated with anaerobically digested sewage sludge, and ORP, pH, gas output, %H(2), %CH(4) and %CO(2) monitored. pH was controlled with NaOH, KOH or Ca(OH)(2). Using NaOH as alkali with 10 g/L sucrose, yields of 1.62 +/- 0.2 mol H(2)/mol hexose added and 323 mL CH(4)/gCOD added to the hydrogen and methane reactors respectively were achieved. The overall chemical oxygen demand (COD) reduction was 92.6% with 0.90 +/- 0.1 g/L sodium and 316 +/- 40 mg/L residual acetate in the methane reactor. Operation at 20 g/L sucrose and NaOH as alkali led to impaired volatile fatty acid (VFA) degradation in the methane reactor with 2.23 +/- 0.2 g/L sodium, 1,885 mg/L residual acetate, a hydrogen yield of 1.47 +/- 0.1 mol/mol hexose added, a methane yield of 294 mL/gCOD added and an overall COD reduction of 83%. Using Ca(OH)(2) as alkali with 20 g/L sucrose gave a hydrogen yield of 1.29 +/- 0.3 mol/mol hexose added, a methane yield of 337 mL/gCOD added and improved the overall COD reduction to 91% with residual acetate concentrations of 522 +/- 87 mg/L. Operation at 30 g/L sucrose with Ca(OH)(2) gave poorer overall COD reduction (68%), a hydrogen yield of 1.47 +/- 0.2 mol/mol hexose added, a methane yield of 138 mL/gCOD added and residual acetate 7,343 +/- 715 mg/L. It was shown that sodium toxicity and overloading are important issues for successful anaerobic digestion of effluent from biohydrogen reactors in high rate systems.     

Effect of high nitrate concentration on PHB storage in sequencing batch reactor under anoxic conditions

The study investigated effect of high influent nitrate concentration on poly-beta-hydroxybutyrate, (PHB), storage in a sequencing batch reactor, (SBR), under anoxic conditions. Acetate was fed as pulse during anoxic phase, sustained with external nitrate feeding. SBR operation involved three runs at steady state with COD/N ratios of 3.84, 2.93 and 1.54 gCOD/gN, where external nitrate concentrations gradually increased from 50 mg N/l to 114 mg N/l and 226 mg N/l, in 1st, 2nd and 3rd runs, respectively. In 1st run, acetate was fully converted into PHB with the storage yield value of 0.57-0.59 gCOD/gCOD, calculated both in terms of PHB formation and NO(X) utilization, confirming storage was the sole substrate utilization mechanism. In the following runs, PHB formation was reduced and the storage yield based on PHB dropped down to 0.40 and 0.33 gCOD/gCOD with increasing influent nitrate concentrations, indicating that higher portions of acetate were diverted to simultaneous direct growth. The observations suggested that nitrite accumulation detected at low COD/N ratios was responsible for inhibition of PHB storage.     

Repeated batch and continuous operations for phosphatidylglycerol synthesis from phosphatidylcholine with immobilized phospholipase D

Summary The repeated batch and continuous operations for transphosphatidylation reaction were carried out for phosphatidylglycerol (PG) synthesis from phosphatidylcholine (PC) with the help of immobilized cabbage phospholipase D (PLD) in the presence of glycerol. The biphasic reaction system was used which included the aqueous phase containing immobilized PLD along with high concentrations of glycerol (30%–50%) and buffer, whereas the main part of substrate (PC) and products (mainly PG) formed were in the organic phase (diethyl ether).Octyl-Sepharose CL-4B having a hydrophobic octyl group was chosen for the PLD immobilization. Both immobilization yield and activity yield of immobilized enzyme were 100%. The effects of solvents, temperature and glycerol concentrations on the immobilized PLD were examined. Repeated batch conversion of PC (15 g/l) to PG was examined with the immobilized PLD in 30% glycerol. In all five batch cycles examined, 100% selectivity was obtained and there was no significant decrease in the fractional conversion of PC to PG (98%–99%) in the first three batch cycles. In the cases of a packed-bed reactor (PBR) and a continuous stirred-tank reactor (CSTR) used for continuous synthesis of PG with the immobilized PLD, the operational stabilities of the immobilized enzyme were almost the same (half life=14 h at 30°C) when purified PC was used, while in the case of partially purified PC in CSTR the half life increased more than five times.Abbreviations used PC phosphatidylcholine - PG phosphatidylglycerol - PA phosphatidic acid - PLD phospholipase D - PBR packed bed reactor - CSTR continuous stirred tank reactor Studies on enzymatic conversion of phospholipids (III)     

Performance of a glucose fed periodic anaerobic baffled reactor under increasing organic loading conditions: 1. Experimental results

The influence of the organic loading rate on the performance of an innovative reactor, the periodic anaerobic baffled reactor (PABR) was examined. A laboratory-scale PABR of four compartments being fed with a glucose based synthetic medium performed with high stability while the feed organic load was doubled from 12.5 to 25 and then to 50 gCOD/l. Finally the feed concentration was increased to 75 gCOD/l. The successive step changes in the feed concentration lasted for 20, 15, and 7 d, respectively. The COD removal efficiency of the PABR was satisfactory in the first two transitions (approximately 97.5 and 96%). In the third transition (OLR=18.75 gCOD/l/d) the reactor failed as the pH dropped to 4. The concentrations of butyric and valeric acids increased as the organic loading was increased and eventually they became greater than the concentration of acetic and propionic acids.     

Sludge exchange process on two serial CSTRs anaerobic digestions: process failure and recovery

The sludge exchange process using two anaerobic digesters (CSTRs) in series was investigated under the mesophilic condition (36-38 °C). At first, the digesting sludge of the CSTRs in series with different TVFA/alkalinity ratios was tested in the laboratory by mixing the digesting sludge of two CSTRs from 6.5% to 50% based on volume. The sludge exchange test was then performed using the same CSTRs under batch and continuous processes. The change in the TVFA/alkalinity ratio was found to be linear with the digesting sludge exchange volume. The CSTR of TVFA/alkalinity ratio 1.970 recovered completely failed within 11 days for the batch process and the CSTR of TVFA/alkalinity ratio 1.514 within 3 weeks for the continuous feeding process at a sludge exchange volume of 13%. The reactor operation was stable when the TVFA/alkalinity ratio was less than 1.0 and when the TVFA concentration was lower than 10,000 mg L⁻¹.     

Influence of substrate concentration and moisture content on the specific methanogenic activity of dry mesophilic municipal solid waste digestate spiked with propionate

The objective of this study was to evaluate the influence of substrate concentration and moisture content on the specific methanogenic activity (SMA) of a fresh dry mesophilic digestate from a municipal solid waste digester plant. For this purpose, SMA tests were performed under mesophilic conditions into glass bottles of 500 mL volume used as batch reactors, during a period of 20-25 days. Propionate was used as substrate at concentrations ranging from 1 to 10 gCOD/kg. Four moisture contents were studied: 65%, 75%, 80% and 82%. Experimental results showed that propionate concentration and moisture content strongly influenced the SMA. The highest SMA was observed at a substrate concentration of 10 gCOD/kg (11.3 mgCOD gVS⁻¹ d⁻¹ for the second dose of propionate) and at a moisture content of 82% (7.8 mgCOD gVS⁻¹ d⁻¹ for the second dose of propionate, at a concentration of 5 gCOD/kg). SMA was found to decrease linearly when decreasing the moisture content.     

Differential bacterial growth kinetic and nitrification of fisheries wastewaters containing high ammonium and organic matter concentration by using pure oxygen

Nitrification with pure O of fisheries wastewaters high in N-NH4+ (0.2-1g/l) and in organic matter (1-2gCOD/l) gave specific growth rates for the bacteria degrading organic matter of 0.24h and for nitrifying bacteria of 0.15h. Average organic matter abatement was 75% whereas N-NH (0.7g/l as initial concentration) oxidation to nitrite and nitrate was 20%.     

Thermophilic anaerobic treatment of sulphur rich forest industry wastewater

Thermophilic anaerobic treatment of sulphur-rich paper mill wastewater (0.8-3.1 gCOD/l, 340–850 mgSO₄/l; COD:SO₄ 3.4-5.3) was studied in three laboratory-scale, upflow anaerobic sludge blanket (UASB) reactors and in bioassays. The reactors were inoculated with non-adapted thermophilic granular sludge. In the bioassays, no inhibition of the inoculum was detected and about 62% COD removal (sulphide stripped) was obtained. About 70 to 80% of the removed COD was methanised. In the reactors, up to 60–74% COD removal (effluent sulphide stripped) was obtained at loading rates up to 10–30 kgCOD/m³d and hydraulic retention times down to 6 to 2 hours. The effluent total sulphide was up to 150–250 mg/l. Sulphide inhibition could not be confirmed from the reactor performances. The results from bioassays suggested that both the inoculum and sludge from the UASB reactor used acetate mainly for methane production, while sulphide was produced from hydrogen or its precursors.     

The effect of temperature,pH, and initial glucose concentration on the kinetics of ethanol production by Zymomonas mobilis in batch fermentation

Summary Zymomonas mobilis, strain ATCC 10988, was used to evaluate the effects of pH (5.0 to 8.0), temperature (30°C to 40°C), and initial glucose concentration (75 g/l to 150 g/l) on the kinetics of ethanol production from glucose using batch fermentation. Specific ethanol production rate was maximum and nearly constant over a pH range of 6.0 to 7.5. End-of-batch ethanol yield and specific growth rate were insensitive to pH in the range of 5.0 to 7.5. End-of-batch ethanol yield was maximum and nearly constant between 30°C and 37°C but decreased by 24% between 37°C and 40°C. All other kinetic parameters are greatest at 34°C. End-of-batch ethanol yield is maximum at an initial glucose concentration of 100 g/l. Specific growth rate reaches a maximum at 75 g/l, but specific ethanol production rate decreases throughout the range. The optimum initial glucose concentration of 100 g/l gives the highest ethanol yield at a specific ethanol production rate less than 10% below the maximum observed.     

Anaerobic granule development for removal of pentachlorophenol in an upflow anaerobic sludge blanket (UASB) reactor

The granulation process using synthetic wastewater containing pentachlorophenol (PCP) in four 1.1 l laboratory scale upflow anaerobic sludge blanket (UASB) reactors was studied, and the anaerobic biotransformation of PCP during the granulation process investigated. After 110 days granular sludge was developed and up to 160 and 180 mg/l of PCP was added into the reactors R1 and R2, respectively, when they were inoculated with acclimated anaerobic sludge from an anaerobic digester of a citric acid plant. The inoculum was predominately composed of bacilli and filamentous bacteria. Granulation did not occur in reactors R3 and R4 which were inoculated with acclimated anaerobic sludge from aerobic sludge of the municipal sewage treatment plant which consisted mainly of cocci. Despite similar bacilli in the granule, the filamentous bacteria from reactor R1 were thicker than those of reactor R2. The granular sludge had a maximum diameter of 2.5 and 2.2 mm, and SMA of 1.44 and 1.32 gCOD/gTVS per day for reactors R1 and R2, respectively. Over 98% chemical oxygen demand (COD) removal rate and 99% of PCP removal rate were achieved when reactors R1 and R2 were operated at PCP and COD loading rates of 150 and 7.5 g/l per day, respectively. H₂-producing acetogens were the dominant anaerobes in the granular sludge.     

Evolution of microorganisms in thermophilic-dry anaerobic digestion

Microbial population dynamics were studied during the start-up and stabilization periods in thermophilic-dry anaerobic digestion at lab-scale. The experimental protocol was defined to quantify Eubacteria and Archaea using Fluorescent in situ hybridization (FISH) in a continuously stirred tank reactor (CSTR), without recycling solids. The reactor was subjected to a programme of steady-state operation over a range of the retention times from 40 to 25 days, with an organic loading rate between 4.42 and 7.50 kg volatile solid/m3/day. Changes in microbial concentrations were linked to traditional performance parameters such as biogas production and VS removal. The relations of Eubacteria:Archaea and H2-utilising methanogens:acetate-utilising methanogens were 88:12 and 11:1, respectively, during start-up stage. Hydrogenotrophic methanogens, although important in the initial phase of the reactor start-up, were displaced by acetoclastic methanogens at steady-state, thus their relation were 7:32, respectively. The methane yield coefficient, the methane content in the biogas and VS removal were stabilized around 0.30 LCH4/gCOD, 50% and 80%, respectively. Methanogenic population correlated well with performance measurements.     

Gravitational force modulates muscle activity during mechanical oscillation of the tibia in humans

Mechanical oscillation (vibration) is an osteogenic stimulus for bone in animal models and may hold promise as an anti-osteoporosis measure in humans with spinal cord injury (SCI). However, the level of reflex induced muscle contractions associated with various loads (g force) during limb segment oscillation is uncertain. The purpose of this study was to determine whether certain gravitational loads (g forces) at a fixed oscillation frequency (30 Hz) increases muscle reflex activity in individuals with and without SCI. Nine healthy subjects and two individuals with SCI sat with their hip and knee joints at 90° and the foot secured on an oscillation platform. Vertical mechanical oscillations were introduced at 0.3, 0.6, 1.2, 3 and 5g force for 20 s at 30 Hz. Non-SCI subjects received the oscillation with and without a 5% MVC background contraction. Peak soleus and tibialis anterior (TA) EMG were normalized to M-max. Soleus and TA EMG were <2.5% of M-max in both SCI and non-SCI subjects. The greatest EMG occurred at the highest acceleration (5g). Low magnitude mechanical oscillation, shown to enhance bone anabolism in animal models, did not elicit high levels of reflex muscle activity in individuals with and without SCI. These findings support the g force modulated background muscle activity during fixed frequency vibration. The magnitude of muscle activity was low and likely does not influence the load during fixed frequency oscillation of the tibia.     

Thermophilic downflow stationary fixed film reactors for methane production from bean blanching waste

Summary Active thermophilic (55°C) biofilms developed in downflow stationary fixed film (DSFF) reactors (needle punched polyester or red draintile clay support material) within 8 weeks. Maximum steady state methane production rates were similar to those for mesophilic reactors.     

Thermal stability characteristics of cellulase enzymes produced by Sporotrichum thermophile

Summary The thermal stability characteristics of the cellulase enzymes present in culture filtrates of the thermophilic fungus Sporotrichum thermophile were investigated at different temperatures and at different times of exposure. Maximum enzymic activities under assay conditions were found at 68°C for the filter paper activity (FPA) and the Cx activity (carboxymethylcellulose), while the maxima for the C₁ activity (cotton) and -glucosidase activity (cellobiose) were found to be at 55°C and 72°C respectively. Culture filtrates were exposed to a given constant temperature for varying lengths of time to a maximum of 48 hrs. and then analyzed for residual enzymic activities under assay conditions. The exposure temperatures studied were 50°C, 60°C and 65°C. After 48 hrs. exposure time at 50°C the residual activities for the FPA, Cx and -glucosidase were found to be 88%, 98% and 93% of the original activities respectively.     

High productivity continuous ethanol fermentation with a flocculating mutant strain of Zymomonas mobilis

High fermenter (volumetric) ethanol productivities (80 g/lh^–1) were attained in a simple single-stage continuous-stirred-tank-reactor (CSTR) employing a flocculent mutant of Zymomonas mobilis with a feed containing 100g/l glucose. Under these conditions a final ethanol concentration of 47.6 g/l was obtained, representing a maximum conversion efficiency of 97% of theoretical.Nomenclature SR = Medium glucose concentration (g/l)X Biomass concentration (g/l) - P Ethanol concentration (g/l) - VP Volumetric productivity (g ethanol/l/h) - Yp/s Product yield coefficient (g ethanol/g glucose consumed) - Qp Specific rate of ethanol formation (g ethanol/g cells/h) - D Dilution rate (h^–1) - Dmax Maximum dilution rate: ie., highest dilution rate at which the effluent glucose concentration 4g/l (h^–1)     

Comparative study of reactor performance for the resolution of d,l-amino acids

The racemic resolution of l-valine and l-serine by fungal aminoacylase has been evaluated by comparing the performance of various reactor configurations including an anion exchange nylon tangential flow membrane reactor, a tubular reactor with aminoacylase adsorbed onto DEAE-Sephadex as support and a continuous stirred tank reactor with enzyme recycling using a flat ultrafiltration module (CSTR/UF). Among the substrates tested, the N-chloroacetyl-d,l-amino acids were the preferred substrates, showing the highest catalytic efficiency (V_m/K_m).Optimum reactor operational conditions obtained in discontinuous assays were selected to study the behaviour of the reactors in a continuous mode. DEAE-Sephadex loaded six-fold more enzyme than anion exchange nylon (60 and 10 gE/litre, respectively, related to reactor volume), whereas enzyme concentration within the CSTR/UF reactor was limited only by enzyme solubility.The tangential flow membrane reactor configuration with a 10 g/litre enzyme concentration produced higher productivity values (0·35 kg l-valine/litre per day, and 80% conversion degree) and operational stability (t = 161 days) than the CSTR/UF reactor (0·24 kg l-valine/litre per day, and 80% conversion degree) performing with the same enzyme concentration. The tubular reactor with the enzyme adsorbed onto DEAE-Sephadex (60 g/litre enzyme load) showed higher productivity values (1·9 kg l-valine/litre per day, and 80% conversion degree) and operational stability (t = 70 days) than the CSTR/UF reactor (1·05 kg l-valine/litre per day, and 80% conversion degree). However, the CSTR/UF reactor was the preferred configuration, as it had the highest enzyme load and productivity (1·95 kg l-valine/litre per day of reactor volume, and 80% conversion degree), a half-life of 55 days at 50°C, and the possibility of easy continuous enzyme addition.     

The influence of ionic concentration on population parameters,development time,activity, and respiration rate of Arctodiaptomus spinosus (Daday) (Calanoida,Copepoda)

Summary For A. spinosus, significant correlations were found between population parameters and the ecological parameters of alkalinity and temperature. For the birth rate, 43.33% of variance is explained by alkalinity and 56.33% by alkalinity and temperature. Alkalinity, and alkalinity and temperature combined account for 48.22% and 70.23% respectively of the observed variances in nauplii hatching. It was demonstrated that, provided sufficient time for adaptation is allowed, the activity of individuals is not affected by differences in the alkalinity of the medium within the normal range of concentration. Embryonic development does not appear to be influenced by the ionic concentration, but significant increases in time of development of the nauplii (at alkalinity 100 meq/l: 8.8 days/20°C) and of the copepodites (at alkalinity 100 meq/l: 12.6 days/20°C) were recorded at both low and high ionic concentrations. The lowest respiration rates (3.7 nl O₂·h^-1·g dw^-1/20°C) occurred at an alkalinity of 100 meq/l. Rates increased at lower (10 meq/l: 5.7 nl) and at higher (400 meq/l: 11.9 nl) alkalinities.