Attachment of Acidithiobacillus ferrooxidans onto different solid substrates and fitting through Langmuir and Freundlich equations

Attachments of Acidithiobacillus ferrooxidans ATCC 23270 onto elemental sulfur, quartz and complex chalcopyrite were investigated by analysis of its extracellular polymeric substances as well as applying Langmuir and Freundlich equations. The two equations fitted the adsorption equilibrium data with significant correlation coefficient over 0.9. This indicated that bacterial attachment is complicated and involves Langmuir and Freundlich characterizations. Sulfur-grown cells showed the highest affinity for the three solid substrates. The investigated complex chalcopyrite possessed a higher maximum adsorption capacity for A. ferrooxidans than elemental sulfur or quartz. The Freundlich fitting parameters suggested that quartz had a weaker adsorption capacity and smaller adsorption areas than elemental sulfur or the complex chalcopyrite. It is not the content of total carbohydrates or proteins in EPS but their ratios that determine the affinity differences between cells and substrates.     

Rapid start-up of thermophilic anaerobic digestion with the turf fraction of MSW as inoculum

This study aims to determine suitable start-up conditions and inoculum sources for thermophilic anaerobic digestion. Within days of incubation MSW at 55 °C, methane was produced at a high rate. In an attempt to narrow down which components of typical MSW contained the thermophilic methanogens, vacuum cleaner dust, banana peel, kitchen waste, and garden waste were tested as inoculum for thermophilic methanogenesis with acetate as the substrate. Results singled out grass turf as the key source of thermophilic acetate degrading methanogenic consortia. Within 4 days of anaerobic incubation (55 °C), anaerobically incubated grass turf samples produced methane accompanied by acetate degradation enabling successful start-up of thermophilic anaerobic digestion. Other essential start-up conditions are specified. Stirring of the culture was not conducive for successful start-up as it resulted specifically in propionate accumulation.     

Treatment of dairy industry wastewater with an anaerobic filter

Summary Concentrations of up to 10.2 g COD/L were applied to an horizontal anaerobic filter at 40°C, obtaining efficiencies in COD removal of 85%. The contents of the reactor are kept mixed by recycling and at a pH value of 6.9.The addition of alkali to the influent increases the production of biogas reaching a maximum of 250 L of methane per kg of COD removed.Career Investigator of the Consejo Nacional de Investigaciones Cientificas y Técnicas (R. Argentina).Fellow of the Consejo Nacional de Investigaciones Cientificas y Técnicas (R. Argentina).     

Biomass stabilization in the anaerobic digestion of wastewater sludges

Sludge stabilization processes include both volatile solid destruction and biomass stabilization. Traditionally, both processes have been considered together, in such a way that, when volatile solid destruction is achieved, the biomass is considered stabilized. In this study, volatile solids reduction and biomass stabilization in the anaerobic digestion of primary, secondary and mixed sludges from municipal wastewater treatment plants were researched in batch cultures by measurements of suspended solids and suspended lipid-phosphate. The estimated kinetic constants were higher in all sludge types tested for the biomass stabilization process, indicating that volatile solids destruction and biomass stabilization are not parallel processes, since the latter one is reached before the former.     

The effects of detergents on anaerobic digestion

Summary The anionic detergent sodium dodecylbenzene sulphonate (SDBS) inhibited mesophilic fermentation in anaerobic digesters. Total gas production and methanogenesis from glucose were reduced to half maximal rates at between 20 and 50 ppm SDBS during the initial phase of digestion, and over 20 days the pH declined from 7.4 to 6.0 in inhibited cultures. As well as accentuating the accumulation of propionic, iso-butyric and iso-valeric acids, a most remarkable effect of this anionic detergent observed only at high concentrations (100 ppm) was to divert the pathway of fermentation with transient accumulation of ethanol. Methanogenesis from cellulose was also inhibited. In thermophilic populations degrading glucose, SDBS was less toxic, and ethanol was not produced. Both the non-ionic detergent Tergitol (nonyl phenyl polyethylene glycol ether) and soap were virtually without effect on the mesophilic anaerobic digestion of glucose.     

Hydrolysis,acidification and methanogenesis during low-temperature anaerobic digestion of dilute dairy wastewater in an inverted fluidised bioreactor

The application of low-temperature (10 °C) anaerobic digestion (LtAD) for the treatment of complex dairy-based wastewater in an inverted fluidised bed (IFB) reactor was investigated. Inadequate mixing intensity provoked poor hydrolysis of the substrate (mostly protein), which resulted in low chemical oxygen demand (COD) removal efficiency throughout the trial, averaging ~69 % at the best operational period. Overgrowth of the attached biomass to the support particles (Extendospheres) induced bed stratification by provoking agglutination of the particles and supporting their washout by sedimentation, which contributed to unstable bioprocess performance at the organic loading rates (OLRs) between 0.5 and 5 kg COD m^?3 day^?1. An applied OLR above 2 kg COD m^?3 day^?1 additionally promoted acidification and strongly influenced the microbial composition and dynamics. Hydrogenotrophic methanogens appeared to be the mostly affected group by the Extendospheres particle washout as a decrease in their abundance was observed by quantitative PCR analysis towards the end of the trial, although the specific methanogenic activity and maximum substrate utilisation rate on H₂/CO₂ indicated high metabolic activity and preference towards hydrogenotrophic methanogenesis of the reactor biomass at this stage. The bacterial community in the bioreactor monitored via denaturing gradient gel electrophoresis (DGGE) also suggested an influence of OLR stress on bacterial community structure and population dynamics. The data presented in this work can provide useful information in future optimisation of fluidised reactors intended for digestion of complex industrial wastewaters during LtAD.     

Effect of pre-aeration and inoculum on the start-up of batch thermophilic anaerobic digestion of municipal solid waste

In this study, a short pre-aeration step was investigated as pre-treatment for thermophilic anaerobic digestion of the organic fraction of municipal solid waste (OFMSW). It was found that pre-aeration of 48 h generated enough biological heat to increase the temperature of bulk OFMSW to 60 °C. This was sufficient self-heating of the bulk OFMSW for the start-up of thermophilic anaerobic digestion without the need for an external heat source. Pre-aeration also reduced excess easily degradable organic compounds in OFMSW, which were the common cause of acidification during the start-up of the batch system. Careful consideration however must be taken to avoid over aeration as this consumes substrate, which would otherwise be available to methanogens to produce biogas. To accelerate methane production and volatile solids destruction, the anaerobic digestion in this study was operated as a wet process with the anaerobic liquid recycled through the OFMSW. Appropriate anaerobic liquid inoculum was found to be particularly beneficial. It provided high buffer capacity as well as suitable microbial inoculum. As a result, acidification during start-up was kept to a minimum. With volatile fatty acids (VFAs-acetate in particular) and H₂ accumulation typical of hydrolysis and fermentation of the easily degradable substrates during start-up, inoculum with high numbers of hydrogenotrophic methanogens was critical to not only maximise CH₄ production but also reduce H₂ partial pressure in the system to allow VFAs degradation. In a lab-scale bioreactor, the combined pre-aeration and wet thermophilic anaerobic digestion was able to stabilise the OFMSW within a period of only 12 days. The stabilised inert residual material can be used as a soil amendment product.     

Electrochemical oxidation of the effluent from anaerobic digestion of dairy manure

The electrochemical oxidation of the digested effluent from anaerobic digestion of dairy manure was investigated in this study. The digested effluent sample containing with suspended solids was pretreated by filtration for the electrochemical experiment. The influence of direct anodic oxidation and indirect oxidation was evaluated through the use of dimensionally stable anode (DSA) and Ti/PbO2 as anode. The decreasing rate of chemical oxygen demand (COD) was higher at lead dioxide coated titanium (Ti/PbO2) electrode than at DSA, however the DSA was preferred anode for the decrease of ammonium nitrogen (NH4-N) due to the control of ammonium nitrate (NO3-N) accumulation. The results showed that the filtration of suspended solids as a pretreatment and addition of NaCl could improve the whole removing efficiency of NH4-N in the digested effluent on electrochemical oxidation.     

Simulation of low temperature anaerobic digestion of dairy and swine manure

The data reported by L.M. Safley, P.W. Westerman [Bioresource Technology 47 (2) (1994) 165-171] from the laboratory digestion of dairy and swine manure at psychrophilic temperatures (i.e., 10-23 degrees C) have been used to determine the response of the latest comprehensive dynamic mathematical model of methanogenesis [D.T. Hill, S.A. Cobb, Transactions of the ASAE 39 (2) (1996) 565-573] in this low temperature range. Extensive performance data from digesters using animal waste in this temperature range have been lacking, thus allowing limited validation of the comprehensive model. The results of the comprehensive model simulations were compared with the actual data reported by Safley and Westerman (loc. cit.) and with their empirical regression models. Results indicate that the comprehensive model is as accurate as Safley and Westerman's models for three of the four cases reported, but shows a great dissimilarity for the fourth case.     

Modeling dynamic experiments on the anaerobic degradation of molasses wastewater

The kinetics of anaerobic degradation of a molasses wastewater were measured under constant pH conditions in a laboratory scale packed bed reactor. In continuous and batch experiments the formation and degradation rates of the organic acids (butyric, propionic and acetic) have been followed. The influence of hydrogen gas on the acid degradation rates has been measured and, contrary to the literature and the thermo-dynamic calculations, no inhibition was detected, biofilm diffusional effects may be the reason. Two dynamic simulation models were tested, a heterogeneous model, which considered the biofilm diffusion-reaction phenomena and a quasihomogeneous model with the same kinetics. Except for hydrogen, the diffusion effects were found to be negligible. Otherwise both models gave essentially the same results and the time profiles of acids, hydrogen, carbon dioxide and methane agreed relatively well with dynamic startup experiments. Batch experiments showed the acid concentrations to be highly sensitive to the initial molasses concentration. This aspect was not included in the model but is being investigated further.     

Thermophilic anaerobic digestion of sewage sludge: focus on the influence of the start-up. A review

The thermophilic anaerobic digestion (TAD) of sewage sludge has often been found to be less stable than mesophilic treatment. In comparison to mesophilic digesters, thermophilic reactors treating sludge are generally characterized by relatively high concentrations of volatile fatty acids (VFA) in the effluent along with poor effluent quality, indicating a lower level of process stability. However, reviewing the literature related to the procedure for obtaining a thermophilic inoculum, it seems that most of the problems associated with the instability and the accumulation of organic intermediates are the result of the manner in which the thermophilic sludge has been obtained. In this paper, the different options available for obtaining an anaerobic digester operating at thermophilic temperature (55°C) have been reviewed. In this light, rapid heating to the target temperature followed by the development of thermophilic microorganisms, which can be determined by VFA dropping to ≤500?mg acetic acid L^?1 before increasing the organic loading rate (OLR), has been determined the most suitable means of establishing TAD.     

Citric acid production by recycling its wastewater treated with anaerobic digestion and nanofiltration

We have developed an integrated citric acid-methane fermentation process to solve the problem of wastewater pollution in the citric acid industry. Citric acid wastewater was initially treated by anaerobic digestion. After subsequent ultrafiltration and nanofiltration, the anaerobic digestion effluent (ADE) could be recycled as process water for the next fermentation, maintaining excellent citric acid production efficiency while eliminating wastewater discharge and reducing water consumption. Untreated ADE was not suitable for direct recycling. The effects on citric acid fermentation of components in the ADE were investigated. Production was inhibited when Na⁺ and Mg²⁺ concentrations in recycled ADE were >200 mg/L and >40 mg/L, respectively. This problem was resolved by treating the ADE using ultrafiltration and nanofiltration to reduce Na⁺ and Mg²⁺ concentrations to acceptable levels. Our results prove the technical feasibility of cleaner production in the citric acid industry and provide a strategy for management of wastewater in other submerged fermentation industries.     

Purification of municipal wastewater by subsequent reverse osmosis and anaerobic digestion

Experiments are described in which municipal wastewater is submitted to reverse osmosis. During a test period of two months a tubular apparatus, operated batchwise, maintained its original flux and rejection, the permeate being of good quality as a raw material for drinking water. The wastewater was concentrated 7.7 times. Continuous anaerobic digestion of the brine removed over 90% of the BOD evolving the expected amount of methane. The overall process is considered in its context of environmental and energetic aspects and is compared with a conventional treatment. This reveals clear perspectives for practical application in urban areas.     

Toxic effects of phenolic pollutants on anaerobic benzoate-degrading granules

Summary Phenolic pollutants were toxic to the bioactivity of anaerobic benzoate-degrading granules. Cresols were more toxic than phenol, which in turn was more toxic than dihydroxybenzenes. The toxicity was dependent on the hydrophobicity of the functional group, but not their positions. The granules exhibited mild resistance to the toxicity of phenolic pollutants, probably because of their layered microstructure.     

Two-stage anaerobic treatment of dairy wastewater using HUASB with PUF and PVC carrier

In the present study, an attempt has been made to treat dairy wastewater entirely via anaerobic treatment over a period of 215 days, using two-stage Hybrid Upflow Anaerobic Sludge Blanket (HUASB) reactors, which offer the advantages associated both with fixed film and upflow sludge blanket treatments. A HUASB with polyurethane foam cubes was used for stage I, and a HUASB utilizing PVC-cut rings was used for stage II. The output from stage I was used as the input for stage II. The two-stage reactor was operated at an organic loading rate that varied from 10.7 to 21.4 kg COD m³/d for a period of 215 days, including the start-up period. The ideal organic loading rate for the two-stage reactor was 19.2 kg COD/m³/d. A further 21.4 kg COD m³/d increase in the organic loading rate resulted in the souring of the reactor function in stage I, which consequently reduced the overall reactor performance. Combined COD removal during the stable operation period (10.7 to 19.2 kg COD m³/d) occurred in a range between 97 and 99%. The methane content in the biogas varied from 65 to 70% in stage I, and from 63 to 66% in stage II. The two-stage anaerobic treatment using HUASB with PUF and PVC described in this work is expected to constitute a better alternative for the complete treatment of dairy wastewater than high-rate anaerobic, anaerobic/aerobic, and two-phase anaerobic treatment methods.     

Semi-dry thermophilic anaerobic digestion of the organic fraction of municipal solid waste: focusing on the start-up phase

The paper concerns the results of a pilot-scale study of the simulation of the start-up phase of the thermophilic semi-dry anaerobic digestion of the organic fraction of municipal solid wastes. The aim of the study was to aid and shorten the start-up phase of the full-scale plant (500 t/d) in Verona--Ca' del Bue, where the semi-dry anaerobic digestion process is being used. The substrate used in the experimentation was the mechanically sorted organic fraction of municipal solid waste (MS-OFMSW) enriched with the putrescent fraction from the source sorted OFMSW in order to simulate the substrate which is dealt with in the Verona plant. The results of the pilot scale study agreed with literature data and previous work of the authors: it showed a specific gas production of 0.23 m3/kg TVSfeed and a gas production rate of 2.1 m3/m3 d when operating at a specific organic loading rate of 0.135 kgTVSfeed/kgTVSreacter d. No problems regarding process stability were encountered in the gradual acclimation of the biomass. The design organic loading rate of 9 kg TVSfeed/m3reactor d was reached in about 30 days, during which the total solids content in the feedwas increased. Only a partial comparison with the full scale start-up, which is now in progress, is possible: this shows an initial general concordance with the results found in previous work.     

Influence of substrate concentration on the macroenergetic parameters of anaerobic digestion of black-olive wastewater

Summary The macroenergetic parameters of the anaerobic digestion of black-olive wastewater, i.e. the yield coefficient for the biomass (Y. g VSS/g COD) and the specific rate of substrate uptake for cell maintenance (m, g COD/g VSS-day) decreased 6 limes and increased 5 times. respectively, when the influent substrate concentration increased from 1.1 to 4.4 g COD/l. This was significant at 95% confidence level. The use of the Guiot kinetic model allows a more accurate prediction of growth yield to be made as it relates substrate utilization to product formation.     

16S rDNA characterisation of bacterial and archaeal communities during start-up of anaerobic thermophilic digestion of cattle manure

A laboratory-scale continuously stirred anaerobic thermophilic batch digester was inoculated with cattle manure. Bacterial and archaeal communities, as well as digester performances, were analysed during reactor start-up for about 20 days. Polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) was used for overall detection and for study of the dynamics of microbial populations. Dominant bacteria and archaea 16S rDNAs were sequenced from the sample on day 12. Ten bacteria and 3 archaea OTUs (operational taxonomic units) were identified from the 52 clones sequenced. Sequences corresponding to the dominant bacterial SSCP peak were phylogenetically close to the 16S rDNA sequence of Bacillus thermoterrestris, whereas sequences corresponding to the two dominant archaeal SSCP peaks were phylogenetically close to the 16S rDNA sequence of Methanoculleus thermophilicus and Methanosarcina thermophila.     

The effects of digestion temperature and temperature shock on the biogas yields from the mesophilic anaerobic digestion of swine manure

In order to obtain basic design criteria for anaerobic digesters of swine manure, the effects of different digesting temperatures, temperature shocks and feed loads, on the biogas yields and methane content were evaluated. The digester temperatures were set at 25, 30 and 35 degrees C, with four feed loads of 5%, 10%, 20% and 40% (feed volume/digester volume). At a temperature of 30 degrees C, the methane yield was reduced by only 3% compared to 35 degrees C, while a 17.4% reduction was observed when the digestion was performed at 25 degrees C. Ultimate methane yields of 327, 389 and 403 mL CH(4)/g VS(added) were obtained at 25, 30 and 35 degrees C, respectively; with moderate feed loads from 5% to 20% (V/V). From the elemental analysis of swine manure, the theoretical biogas and methane yields at standard temperature and pressure were 1.12L biogas/g VS(destroyed) and 0.724 L CH(4)/g VS(destroyed), respectively. Also, the methane content increased with increasing digestion temperatures, but only to a small degree. Temperature shocks from 35 to 30 degrees C and again from 30 to 32 degrees C led to a decrease in the biogas production rate, but it rapidly resumed the value of the control reactor. In addition, no lasting damage was observed for the digestion performance, once it had recovered.