Biomedical subjects

G Lettinga

Publications and source records attributed to G Lettinga.

At least 19 recordsLinked to original sources

PubMed2006

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.

Anaerobiosis↗

PubMed2006

Stability and activity of anaerobic sludge from UASB reactors treating sewage in subtropical regions.

The production of small amounts of well-stabilized biological sludge is one of the main advantages of upflow anaerobic sludge bed (UASB) reactors over aerobic wastewater treatment systems. In this work, sludge produced in three pilot-scale UASB reactors used to treat sewage under subtropical conditions was assessed for both stability and specific methanogenic activity. Stability of primary sludge from settling tanks and digested sludge from conventional sludge digesters was also measured for comparison purposes. Kinetic parameters like the hydrolysis rate constant and the decay rate constant were calculated. High stability was observed in sludge from UASB reactors. Methanogenic activity in anaerobic sludges was relatively low, probably due to the low organic matter concentration in influent sewage. Knowledge on sludge growth rate, stability, and activity might be very useful to optimize sludge management activities in full-scale UASB reactors.

Anaerobiosis↗

PubMed2006

A good life environment for all through conceptual, technological and social innovations.

In conventional environmental protection the parallel development of advanced technical solutions alongside ever more stringent environmental standards increasingly conflicts with the moral and practical imperatives to ensure sustainability and drastically improve the life conditions of the world's poor. Such priorities are far better tackled by technological and social innovations based on relatively simple and highly sustainable concepts: e.g., applying Natural Biological Mineralization Routes (NBMR) for wastewater and waste treatment, implementing Decentralized Sanitation and Resource Recovery and Reuse (DESAR3) where transport of waste(water)s is kept to an optimum level and pollutants valorized, etc. With developing countries now taking a lead in applying these concepts in public sanitation, the more prosperous countries will gradually abandon the expensive, vulnerable and non-sustainable conventional approaches to wastes treatment and environmental protection.

Environmental Health↗

PubMed2005

Treatment of strong domestic sewage in a 96 m3 UASB reactor operated at ambient temperatures: two-stage versus single-stage reactor.

A 96 m3 UASB reactor was operated for 2.5 years under different conditions to assess the feasibility of treating strong sewage (COD(tot) = 1531 mg/l) at ambient temperatures with averages of 18 and 25 degrees C for winter and summer respectively. During the first year, the reactor was operated as a two-stage system at OLRs in the range of 3.6-5.0 kg COD/m3 d for the first stage and 2.9-4.6 kg COD/m3 d for the second stage. The results of the first stage showed average removals of 51% and 60% for COD(tot) and COD(ss) respectively without significant effect of temperature. The second stage reactor was unstable. The temperature affected sludge stabilization. During the second year, the first stage was operated as a single-stage UASB reactor at half of the previous loading rates. The results showed an average removal efficiency of 62% for COD(tot) during summer, while it dropped to 51% during wintertime. However, the effluent suspended solids were stabilized with VSS/TSS ratio around 0.50 all over the year. The sludge in the single-stage reactor was well-stabilized and exerted an excellent settlability. During the last three months of research, sludge was discharged regularly from the single-stage UASB reactor. The results showed no significant improvement in the performance in terms of COD(tot). Based on the results of the experiment, a single-stage UASB reactor operated at relatively long HRT is preferred above two-stage system at the Jordanian conditions.

Bacteria, Anaerobic↗

PubMed2005

Bioflocculation of mesophilic and thermophilic activated sludge.

Thermophilic activated sludge treatment is often hampered by a turbid effluent. Reasons for this phenomenon are so far unknown. Here, the hypothesis of the temperature dependency of the hydrophobic interaction as a possible cause for diminished thermophilic activated sludge bioflocculation was tested. Adsorption of wastewater colloidal particles was monitored on different flat surfaces as a function of temperature. Adsorption on a hydrophobic surface varied with temperature between 20 and 60 degrees C and no upward or downward trend could be observed. This makes the hydrophobic interaction hypothesis unlikely in explaining the differences in mesophilic and thermophilic activated sludge bioflocculation. Both mesophilic and thermophilic biomass did not flocculate with wastewater colloidal particles under anaerobic conditions. Only in the presence of oxygen, with biologically active bacteria, the differences in bioflocculation behavior became evident. Bioflocculation was shown only to occur with the combination of wastewater and viable mesophilic biomass at 30 degrees C, in the presence of oxygen. Bioflocculation did not occur in case the biomass was inactivated or when oxygen was absent. Thermophilic activated sludge hardly showed any bioflocculation, also under mesophilic conditions. Despite the differences in bioflocculation behavior, sludge hydrophobicity and sludge zetapotentials were almost similar. Theoretical calculations using the DLVO (Derjaguin, Landau, Verweij and Overbeek) theory showed that flocculation is unlikely in all cases due to long-range electrostatic forces. These calculations, combined with the fact that bioflocculation actually did occur at 30 degrees C and the unlikelyness of the hydrophobic interaction, point in the direction of bacterial exo-polymers governing bridging flocculation. Polymer interactions are not included in the DLVO theory and may vary as a function of temperature.

Adsorption↗

PubMed2005

Effect of SRT and temperature on biological conversions and the related scum-forming potential.

Sludge flotation was reported to cause several operational problems in anaerobic systems including UASB reactors treating both strong domestic sewage and some industrial wastewater. This research is to investigate the effect of anaerobic digestion on scum-forming potential (SFP) of sludge and other physical-chemical properties. A simple test was developed to measure and compare the tendency of different sludge to form a scum layer. Results showed that anaerobic digestion affects chemical composition of sludge flocs and consequently, SFP, which was found to be inversely proportional to the degree of digestion (both SRT and temperature). It was suggested that higher protein concentration at elevated SRT and 25 degrees C increased the negative surface charge of sludge flocs and ,consequently, reduced the ability of sludge to attach to gas bubbles and float. Floc average size increased with increasing SRT and temperature, especially for sludge with 75d SRT at 25 degrees C. On the other hand, settling properties of sludge were negatively affected by increasing SRT to 75d at 25 degrees C. Filterability had a strong positive correlation with average floc size, but also polymeric constituents correlated positively with filterability at 25 degrees C.

Anaerobiosis↗

PubMed2005

The anaerobic treatment approach towards a more sustainable and robust environmental protection.

Anaerobic biological degradation processes (AnDe), when properly integrated with complementary biological and physical methods, constitute the ideal route to a sustainable protection of the life environment. However unfortunately for a smooth implementation of AnDe-processes drastic conceptual innovations are urgently needed in the field of environment protection; the present highly centralized approach in the public sanitation sector (CENSA) need to be substituted by a concept that focuses on optimal decentralization, problem prevention, self-sufficiency, resource recovery and reuse, with coupling to agriculture practices at or nearby the location (DESAR). Although a variety of excellent DESAR-based systems already are available and anaerobic digestion and treatment methods have found successful full-scale application for waste and wastewater treatment, there still is potential to improve these systems. Interesting questions to be elucidated are the effect of trace elements and macro-nutrients, the sludge immobilization phenomenon and the effect of environmental factors like temperature, pressure, mixing. Therefore tentatively a lot of challenging interdisciplinary research is waiting to attain further profitable innovations.

Agriculture↗

PubMed2005

A dispersion based model for anaerobic digestion of solid cattle wastes in a stratified thermophilic accumulation system.

A dynamic model has been developed to describe the anaerobic digestion of solid cattle waste in an accumulation system (AC). To calibrate the model an experiment was carried out at a lab-scale AC at 50 degrees C. The predicted methane production shows a very good agreement (i.e. R2 = 0.998) with the experimental data. However less agreement is evident for the intermediates. After model validation the model was applied to study the effect of different aspect ratios on the system performance. An optimum aspect ratio of 2-3 could be determined.

Animals↗

PubMed2005

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.

Bacteria, Anaerobic↗

PubMed2005

Phosphate inhibition on thermophilic acetoclastic methanogens: a warning.

The inhibitory effect of phosphate on acetoclastic-methanogens was investigated for three different thermophilic (55 degrees C) anaerobic consortia. When 70 mM of phosphate was tested, acetoclastic methanogens was completely inhibited in "Eerbeek" sludge which is dominated by Methanosaeta-like methanogens. For the "Hoogezand" sludge the specific methanogenic activity dropped by 79%, indicating that any of the acetate-consuming methanogens present in the sludge was more resistant to the phosphate applied. The results demonstrated that the inhibitory effect of phosphate may affect both methane production rate and final methane concentration and might also be time dependent. This study indicates that the degree of inhibition is species-dependent, and even more resistant species may be affected during long-term experiments. Such inhibition is a matter of concern for researchers since misleading conclusions might be taken from growth and specific methanogenic activity tests when considerable concentrations of phosphate buffer are used and no interference is expected.

Acetates↗

PubMed2004

Quinone-respiration improves dechlorination of carbon tetrachloride by anaerobic sludge.

The impact of humic acids and the humic model compound, anthraquinone-2,6-disulfonate (AQDS), on the biodegradation of carbon tetrachloride (CT) by anaerobic granular sludge was studied. Addition of both humic acids and AQDS at sub-stoichiometric levels increased the first-order rate of conversion of CT up to 6-fold, leading to an increased production of inorganic chloride, which accounted for 40-50% of the CT initially added. Considerably less dechlorination occurred in sludge incubations lacking humic substances. By comparison, very limited dechlorination occurred in sterile controls with autoclaved sludge. Accumulation of chloroform (1-10%) and dichloromethane (traces) also accounted for the CT converted. The accumulation of a chlorinated ethene, perchloroethylene (up to 9% of added CT), is also reported for the first time as an end-product of CT degradation. A humus-respiring enrichment culture (composed primarily of a Geobacter sp.) derived from the granular sludge also dechlorinated CT, yielding products similar to the AQDS-supplemented granular sludge consortium. The dechlorination of CT by the Geobacter enrichment was dependent on the presence of AQDS or humic acids, which were reduced during the assays. The reduced form of AQDS, anthrahydroquinone-2,6-disulfonate, was shown to cause the chemical reduction of CT when incubated in sterile medium. The results taken as a whole indicate that the formation of reduced humic substances by quinone-respiring microorganisms can contribute to the reductive dechlorination of CT.

Alkanesulfonic Acids↗

PubMed2004

Anaerobic sludge granulation.

This paper reviews different theories on anaerobic sludge granulation in UASB-reactors that have been proposed during the past two decades. The initial stages of the formation of anaerobic granules follow the same principles as biofilm formation of bacteria on solid surfaces. There exist strong evidence that inert carriers play an important positive role in granulation. Most researchers conclude that Methanosaeta concilii is a key organism in granulation. Only the Cape Town Hypothesis presumes that an autotrophic hydrogenotrophic organism, i.e., Methanobacterium strain AZ, growing under conditions of high H(2)-pressures, is the key organism in granulation. Many authors focus on the initial stage of granulation, and only a few contributions discuss the latter stages in granulation: granule maturation and multiplication. Granule enhancing factors in the latter stages predominantly rely on manipulation of the selection pressure, through which selectively heavier sludge particles are retained in the UASB reactor.

Bacteria, Anaerobic↗

PubMed2003

Effect of carbon monoxide, hydrogen and sulfate on thermophilic (55 degrees C) hydrogenogenic carbon monoxide conversion in two anaerobic bioreactor sludges.

The conversion routes of carbon monoxide (CO) at 55 degrees C by full-scale grown anaerobic sludges treating paper mill and distillery wastewater were elucidated. Inhibition experiments with 2-bromoethanesulfonate (BES) and vancomycin showed that CO conversion was performed by a hydrogenogenic population and that its products, i.e. hydrogen and CO2, were subsequently used by methanogens, homo-acetogens or sulfate reducers depending on the sludge source and inhibitors supplied. Direct methanogenic CO conversion occurred only at low CO concentrations [partial pressure of CO (PCO) <0.5 bar (1 bar=10(5) Pa)] with the paper mill sludge. The presence of hydrogen decreased the CO conversion rates, but did not prevent the depletion of CO to undetectable levels (<400 ppm). Both sludges showed interesting potential for hydrogen production from CO, especially since after 30 min exposure to 95 degrees C, the production of CH4 at 55 degrees C was negligible. The paper mill sludge was capable of sulfate reduction with hydrogen, tolerating and using high CO concentrations (PCO>1.6 bar), indicating that CO-rich synthesis gas can be used efficiently as an electron donor for biological sulfate reduction.

Acetates↗

PubMed2003

Long-term adaptation of methanol-fed thermophilic (55 degrees C) sulfate-reducing reactors to NaCl.

A laboratory-scale upflow anaerobic sludge bed (UASB) reactor was operated during 273 days at increasing NaCl concentrations (0.5-12.5 g NaCl l(-1)) to assess whether the stepwise addition of the salt NaCl results in the acclimation of that sludge. The 6.5-l thermophilic (55 degrees C), sulfidogenic [a chemical oxygen demand (COD) to SO4(2-) ratio of 0.5] UASB reactor operated at an organic loading rate of 5 g COD l(-1) day(-1), a hydraulic retention time of 10 h and was fed with methanol as the sole electron donor. The results show that the adaptation of the thermophilic, sulfidogenic methanol-degrading biomass to a high osmolarity environment is unlikely to occur. Sulfide was the main mineralization product from methanol degradation, regardless of the NaCl concentration added to the influent. However, sulfide production in the reactor steadily decreased after the addition of 7.5 g NaCl l(-1), whereas acetate production was stimulated at that influent NaCl concentration. Batch tests performed with sludge harvested from the UASB reactor when operating at different influent salinities confirmed that acetate is the main metabolic product at NaCl concentrations higher than 12.5 g l(-1). The apparent order of NaCl toxicity towards the different trophic groups was found to be: sulfate-reducing bacteria > methane-producing archaea > acetogenic bacteria.

Archaea↗

PubMed2003

Pathways of methanol conversion in a thermophilic anaerobic (55 degrees C) sludge consortium.

The pathway of methanol conversion by a thermophilic anaerobic consortium was elucidated by recording the fate of carbon in the presence and absence of bicarbonate and specific inhibitors. Results indicated that about 50% of methanol was directly converted to methane by the methylotrophic methanogens and 50% via the intermediates H(2)/CO(2) and acetate. The deprivation of inorganic carbon species [Sigma(HCO(3)(-)+CO(2))] in a phosphate-buffered system reduced the rate of methanol conversion. This suggests that bicarbonate is required as an electron (H(2)) sink and as a co-substrate for the efficient and complete removal of the chemical oxygen demand. Nuclear magnetic resonance spectroscopy was used to investigate the route of methanol conversion to acetate in bicarbonate-sufficient and bicarbonate-depleted environments. The proportions of [1,2-(13)C]acetate, [1-(13)C]acetate and [2-(13)C]acetate were determined. Methanol was preferentially incorporated into the methyl group of acetate, whereas HCO(3)(-) was the preferred source of the carboxyl group. A small amount of the added H(13)CO(3)(-) was reduced to form the methyl group of acetate and a small amount of the added (13)CH(3)OH was oxidised and found in the carboxyl group of acetate when (13)CH(3)OH was converted. The recovery of [(13)C]carboxyl groups in acetate from (13)CH(3)OH was enhanced in bicarbonate-deprived medium. The small amount of label incorporated in the carboxyl group of acetate when (13)CH(3)OH was converted in the presence of bromoethanesulfonic acid indicates that methanol can be oxidised to CO(2 )prior to acetate formation. These results indicate that methanol is converted through a common pathway (acetyl-CoA), being on the one hand reduced to the methyl group of acetate and on the other hand oxidised to CO(2), with CO(2) being incorporated into the carboxyl group of acetate.

Anaerobiosis↗

PubMed2003

Effect of specific gas loading rate on thermophilic (55 degrees C) acidifying (pH 6) and sulfate reducing granular sludge reactors.

The effect of the specific gas loading rate on the acidifying, sulfate reducing and sulfur removal capacity of thermophilic (55 degrees C; pH 6.0) granular sludge bed reactors treating partly acidified wastewater was investigated. A comparison was made between a regular UASB reactor and a UASB reactor continuously sparged with N(2) at a specific gas loading rate of 30 m(3)m(-2)d(-1). Both UASB reactors (upflow velocity 1.0 mh(-1), hydraulic retention time about 5h) were fed a synthetic wastewater containing starch, sucrose, lactate, propionate and acetate and a low sulfate concentration (COD/SO(4)(2-) ratio of 10) at volumetric organic loading rates (OLR) ranging from 4.0 to 49.8 gCODl(-1) reactord(-1). Immediately after imposing an OLR of 25 gCODl(-1) reactord(-1), the acidification and sulfate reduction efficiency dropped to 80% and 30%, respectively, in the UASB reactor. Both efficiencies recovered slowly to 100% during the course of the experiment. In the N(2) sparged reactor, both the acidification and sulfate reduction efficiency remained 100% following the OLR increase to 25 gCODl(-1) reactord(-1). However, the sulfate reduction efficiency gradually decreased to about 20% at the end of the experiment. The biogas (CO(2) and CH(4)) production rate in the UASB was very low, i.e. <3l biogasl(-1) reactorday(-1), resulting in negligible amounts (<20%) of H(2)S stripped from the reactor liquid. The total H(2)S concentration of the N(2) sparged UASB reactor effluent was always below 25 mgl(-1), but incomplete sulfate reduction kept the maximal H(2)S stripping efficiency below 70%.

Air Pollutants↗

PubMed2003

Effect of NaCl on thermophilic (55 degrees C) methanol degradation in sulfate reducing granular sludge reactors.

The effect of NaCl on thermophilic (55 degrees C) methanol conversion in the presence of excess of sulfate (COD/SO(4)(2-)=0.5) was investigated in two 6.5L lab-scale upflow anaerobic sludge bed reactors inoculated with granular sludge previously not adapted to NaCl. Methanol was almost completely used for sulfate reduction in the absence of NaCl when operating at an organic loading rate of 5 g CODL(-1)day(-1) and a hydraulic retention time of 10h. The almost fully sulfidogenic sludge consisted of both granules and flocs developed after approximately 100 days in both reactors. Sulfate reducing bacteria (SRB) outcompeted methane producing archaea (MPA) for methanol, but acetate represented a side-product, accounting for maximal 25% of the total COD converted. Either MPA or SRB did not use acetate as substrate in activity tests. High NaCl concentrations (25 gL(-1)) completely inhibited methanol degradation, whereas low salt concentrations (2.5 g NaClL(-1)) provoked considerable changes in the metabolic fate of methanol. The MPA were most sensitive towards the NaCl shock (25 gL(-1)). In contrast, the addition of 2.5 gL(-1) of NaCl stimulated MPA and homoacetogenic bacteria.

Biodegradation, Environmental↗

PubMed2003

Use of sulfate reducing cell suspension bioreactors for the treatment of SO2 rich flue gases.

This paper describes a novel bioscrubber concept for biological flue gas desulfurization, based on the recycling of a cell suspension of sulfite/sulfate reducing bacteria between a scrubber and a sulfite/sulfate reducing hydrogen fed bioreactor. Hydrogen metabolism in sulfite/sulfate reducing cell suspensions was investigated using batch activity tests and by operating a completely stirred tank reactor (CSTR). The maximum specific hydrogenotrophic sulfite/sulfate reduction rate increased with 10% and 300%, respectively, by crushing granular inoculum sludge and by cultivation of this sludge as cell suspension in a CSTR. Operation of a sulfite fed CSTR (hydraulic retention time 4 days; pH 7.0; sulfite loading rate 0.5-1.5 g SO3(2-) l(-1) d(-1)) with hydrogen as electron donor showed that high (up to 1.6 g l(-1)) H2S concentrations can be obtained within 10 days of operation. H2S inhibition, however, limited the sulfite reducing capacity of the CSTR. Methane production by the cell suspension disappeared within 20 days reactor operation. The outcompetition of methanogens in excess of H2 can be attributed to CO2 limitation and/or to sulfite or sulfide toxicity. The use of cell suspensions opens perspectives for monolith or packed bed reactor configurations, which have a much lower pressure drop compared to air lift reactors, to supply H2 to sulfite/sulfate reducing bioreactors.

Bioreactors↗