Paula Loureiro Paulo

Effect of sulfate on methanol degradation in thermophilic (55°C) methanogenic UASB reactors

A thermophilic (55 degreesC) lab-scale (0.921) methanol-fed upflow anaerobic sludge bed (UASB) reactor (pH 7.0 and hydraulic retention time (HRT) of 7.5 h) was operated at chemical oxygen demand (COD) to sulfate (SO42-) ratios of 10, 5 and 0.5 during 155 days to evaluate the effects of the presence of sulfate on conversion rates, metabolic shifts and possible process disturbances A thermophilic (55 degreesC) lab-scale (0.921) methanol-fed upflow anaerobic sludge bed (UASB) reactor (pH 7.0 and hydraulic retention time (HRT) of 7.5 h) was operated at chemical oxygen demand (COD) to sulfate (SO42-) ratios of 10, 5 and 0.5 during 155 days to evaluate the effects of the presence of sulfate on conversion rates, metabolic shifts and possible process disturbances. Methanol was completely removed when operating at an organic loading rate of 20 g COD l(-1) day(-1) at all COD/SO42- ratios tested. At COD/SO42- ratios of 10 and 5. methanol was converted both via sulfate reduction (up to 13% when operating at a COD/SO42- of 5) and methanogenesis (85%). However, when operating at a COD/sulfate ratio of 0.5 (12 g SO42- l(-1)), the sulfate reduction efficiency strongly deteriorated, due to improper immobilization of sulfate reducing bacteria (SRB) in the sludge bed and the presence of relatively high sodium concentrations (about 6 g Na+ l(-1)) originating from supplying sulfate as its sodium salt. Complete sulfate reduction was achieved when operating at a COD/SO42- ratio of 10 (0.6 g SO42- l(-1)) and 5 (1.2 g SO42- l(-1)), corresponding to sulfate removal rates of 2 and 4 g SO42- l(-1) day(-1), respectively. Activity tests showed that methanol was syntrophically converted via H-2/CO2 by homoacetogenic bacteria, in combination with either sulfate reducing bacteria or methane producing archaea

Enrichment and detection of microorganisms involved in direct and indirect methanogenesis from methanol in an anaerobic thermophilic bioreactor.

To gain insight into the microorganisms involved in direct and indirect methane formation from methanol in a laboratory-scale thermophilic (55°C) methanogenic bioreactor, reactor sludge was disrupted and serial dilutions were incubated in specific growth media containing methanol and possible intermediates of methanol degradation as substrates. With methanol, growth was observed up to a dilution of 108. However, when Methanothermobacter thermoautotrophicus strain Z245 was added for H2 removal, growth was observed up to a 1010-fold dilution. With H2/CO2 and acetate, growth was observed up to dilutions of 109 and 104, respectively. Dominant microorganisms in the different dilutions were identified by 16S rRNA-gene diversity and sequence analysis. Furthermore, dilution polymerase chain reaction (PCR) revealed a similar relative abundance of Archaea and Bacteria in all investigated samples, except in enrichment with acetate, which contained 100 times less archaeal DNA than bacterial DNA. The most abundant bacteria in the culture with methanol and strain Z245 were most closely related to Moorella glycerini. Thermodesulfovibrio relatives were found with high sequence similarity in the H2/CO2 enrichment, but also in the original laboratory-scale bioreactor sludge. Methanothermobacter thermoautotrophicus strains were the most abundant hydrogenotrophic archaea in the H2/CO2 enrichment. The dominant methanol-utilizing methanogen, which was present in the 108-dilution, was most closely related to Methanomethylovorans hollandica. Compared to direct methanogenesis, results of this study indicate that syntrophic, interspecies hydrogen transfer-dependent methanol conversion is equally important in the thermophilic bioreactor, confirming previous findings with labeled substrates and specific inhibitors.

The anaerobic conversion of methanol under thermophilic conditions: pH and bicarbonate dependence

The thermophilic (55 degrees C) anaerobic conversion of methanol was studied in an unbuffered medium (pH 4+/-0.2) and in a phosphate buffered medium (pH 6.4+/-0.1), in both cases without bicarbonate addition. Our cultivated sludge consortium was unable to degrade methanol under acidic conditions. During the 160 d of continuous operation of an up-flow anaerobic sludge blanket (UASB) reactor (R1), at an organic loading rate (ORL) of 6 gCOD/(l.d) and pH around 4, only 5% of the applied methanol load was consumed and no methane (CH4) was detected. However, hydrogenotrophic methanogens were found to be resistant to exposure to such conditions. At the end of the trial, the hydrogenotrophic methanogenic activity of the sludge was 1.23+/-0.16 gCOD/(gVSS.d) at neutral pH. With methanol as the test substrate, the addition of bicarbonate led to acetate accumulation. A second reactor (R2) was operated for 303 d at OLRs ranging from 5.5 to 25.4 gCOD/(l.d) in order to assess the conversion of methanol at neutral pH (phosphate buffered) in a bicarbonate deprived medium. The reactor performance was poor with a methanol-COD removal capacity limited to about 9.5 gCOD/(l.d). The system appeared to be quite susceptible to any type of disturbance, even at low OLR. The fraction of methanol-COD converted to CH4 and acetate was found to be unaffected by the OLR applied. At the end of the trial, the outcome of the competition was about 50% methanogenesis and 50% homoacetogenesis.

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

Abstract. 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 H2/CO2 and acetate. The deprivation of inorganic carbon species [Σ(HCO3−+CO2)] in a phosphate-buffered system reduced the rate of methanol conversion. This suggests that bicarbonate is required as an electron (H2) 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 [1,2-13C]acetate, [1-13C]acetate and [2-13C]acetate were determined. Methanol was preferentially incorporated into the methyl group of acetate, whereas HCO3− was the preferred source of the carboxyl group. A small amount of the added H13CO3− was reduced to form the methyl group of acetate and a small amount of the added 13CH3OH was oxidised and found in the carboxyl group of acetate when 13CH3OH was converted. The recovery of [13C]carboxyl groups in acetate from 13CH3OH was enhanced in bicarbonate-deprived medium. The small amount of label incorporated in the carboxyl group of acetate when 13CH3OH was converted in the presence of bromoethanesulfonic acid indicates that methanol can be oxidised to CO2 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 CO2, with CO2 being incorporated into the carboxyl group of acetate.

Design and configuration criteria for wetland systems treating greywater.

Design and configuration for wetlands treating greywater are usually based on literature data obtained from domestic wastewater operating wetlands. It is very important to determine proper criteria for design and configuration to provide efficiency and minimum maintenance, avoiding bad odour and clogging amongst others, ensuring the acceptance of householders. The aim of this work was to design a wetland system treating greywater for a household and determine whether the chosen criteria were appropriate. Some of the criteria taken into consideration for design and configuration were: quantitative and qualitative characteristics, desired removal of biochemical oxygen demand (BOD) and suspended solids (TSS), substrate and ornamental aspect of the system. The system was composed of a grease trap (kitchen), sedimentation tank, a horizontal flow constructed wetland (HF-CW), intermittent feeding system, and a vertical flow constructed wetland (VF-CW). The results showed that the suggested design and configuration were in accordance with the expected efficiency. Being a compact system, it was susceptible to peak flows, temporarily deteriorating the performance of the HF-CW. The hybrid system, however, showed to cope well with influent fluctuations. The overall performance of the system shows that the removal of turbidity, TSS, COD and BOD were over 88%, reaching 95% removal for both BOD and turbidity.

Application of urea dosing for alkalinity supply during anaerobic digestion of vinasse

Pushed by demand for renewable energy, the ethanol industry in Brazil is expanding. However, production of 1 m(3) of ethanol generates around 13 m(3) of liquid residues (vinasse), so this expansion results in an increasing need for a more adequate destination of these residues. Nowadays the vinasse is dispersed on the sugar cane fields in the practice of fertirrigation, but anaerobic digestion of this residue may be a better solution, additionally offering an alternative source of energy, able to complement hydroelectric power supply in the dry season. However, when trying to digest vinasse at reduced hydraulic retention times, complications arise from its strong tendency toward acidification, upsetting the fragile balance of transformations normally occurring under anaerobic conditions. For successful operation of an anaerobic treatment process with acceptable hydraulic residence times, increasing alkalinity levels inside the reactor is neces-sary. In the present work we show that pH regulation by means of urea dosing, in spite of the risk posed by ammonia toxicity towards methanogenic biomass, can be a viable alternative to avoid vinasse acidification. The ammonia formed in urea conversion remains in solution, rather than escaping to the biogas, and so its use as fertiliser can offset its cost of application in the process.

Optimisation of biogas production from anaerobic digestion of agro-industrial waste streams in Brazil

The important Brazilian agro-industry produces significant amounts of wastewater with high concentrations of biodegradable compounds. A lot can be gained if wastewater treatment would take place using anaerobic reactors instead of the anaerobic lagoons generally used now. Apart from preventing methane emissions to the atmosphere this would permit the use of the biogas as a source of energy. To facilitate implementation of this technology also in small and intermediate sized companies a system requiring only minimal maintenance is needed. The need for maintenance by skilled labour can be reduced using an automated process control system, which is being developed. Cassava (manioc, tapioca) processing wastewater has been treated in a lab scale UASB reactor equipped with an on-line monitoring system, to test a control strategy based mainly on pH control. Good results have been obtained treating not only pre-acidified but also treating raw (diluted) cassava processing wastewater.

The use of microalgae and their culture medium for biogas production in an integrated cycle.

Vinasse is a residue produced in large quantities as a sub-product of ethanol production. Anaerobic digestion of vinasse can yield large amounts of biogas, but often difficulties arise in maintaining stable operation, due to the acidity of the material (which has a pH between 3.5 and 5) and a strong tendency to further acidification. Anaerobically digested vinasse can be used as part of a culture medium for microalgae cultivation, for the production of biodiesel and other compounds, whilst the excess CO2 produced in the ethanol fermentation can be used to stimulate algal growth. During algae cultivation, the pH of the culture medium has a strong tendency to increase; therefore, recycling of the spent culture medium or the concentrated algae suspension to the anaerobic digester treating vinasse was considered an option for pH stabilization there. Batch tests, however, showed that alkalinity of the spent culture broth, in spite of its high pH, is too low (only 350 mgCaCO3L(-1)) to help stabilise the pH of vinasse digestion. Alkalinity of the algae suspension is higher and digestion of a mixture of vinasse and a suspension of algae results in efficient biogas production, but still the alkalinity is insufficient to stabilise the pH in a range suitable for methanogenic microorganisms; hence, the addition of additional alkalinity, for instance as sodium bicarbonate or urea, remains necessary.

Alternative use of Pseudomonas aeruginosa as indicator for greywater disinfection

Greywater presents great potential for reuse; if treated correctly and efficiently, it can be used for several residential uses. The objective of this work was to test advanced oxidation for greywater disinfection through UV/TiO2, UV/TiO2/H2O2, photo-Fenton, UV/H2O2 and photolysis (UV) processes, using Pseudomonas aeruginosa as an alternative indicator. In general, the processes with hydrogen peroxide (150 mg.L-1) mixed in the pretreated greywater and exposed to solar radiation or artificial radiation from UV lamps were the most efficient in the disinfection experiments, with total inactivation of P. aeruginosa. These processes (UV/H2O2 and photo-Fenton) were better fitted to the log-linear/caudal decay model with remaining microorganism for the hydrogen peroxide concentration of 25 mg.L-1. The use of P. aeruginosa as an alternative indicator for the greywater disinfection was very promising due to its high resistance and high natural concentration in the effluent used in the experiments. The treatment applied with the UV/H2O2 process with the hydrogen peroxide concentration at 150 mg.L-1 was the only one that showed acute toxicity, even though it removed a good part of the surfactant concentration from the pre-treated greywater.

Hydraulic and hydrological aspects of an evapotranspiration-constructed wetland combined system for household greywater treatment

ABSTRACT Constructed wetlands systems demand preliminary and primary treatment to remove solids present in greywater (GW) to avoid or reduce clogging processes. The current paper aims to assess hydraulic and hydrological behavior in an improved constructed wetland system, which has a built-in anaerobic digestion chamber (AnC), GW is distributed to the evapotranspiration and treatment tank (CEvaT), combined with a subsurface horizontal flow constructed wetland (SSHF-CW). The results show that both the plants present in the units and the AnC improve hydraulic and volumetric efficiency, decrease short-circuiting and improve mixing conditions in the system. Moreover, the hydraulic conductivity measured on-site indicates that the presence of plants in the system and the flow distribution pattern provided by the AnC might reduce clogging in the SSHF-CW. It is observed that rainfall enables salt elimination, thus increasing evapotranspiration (ET), which promotes effluent reduction and enables the system to have zero discharge when reuse is unfeasible.