Anaerobic Degradation Process Research Articles

Fungal survival during anaerobic digestion of organic household waste

Anaerobic digestion of organic waste yields energy rich biogas and retains nutrients (N, P, K, S, etc.) in a stabilised residue. For the residue to be used as a soil fertiliser, it must be free from pollutants and harmful microorganisms. Fungal survival during sanitation and anaerobic treatment of source-separated organic household waste and during aerobic storage of the residue obtained was investigated. Decimal reduction times were determined for inoculated fungi ( Aspergillus flavus and Aspergillus fumigatus, Penicillium roqueforti, Rhizomucor pusillus, Thermoascus crustaceus and Thermomyces lanuginosus). Several different fungal species were found after waste sanitation treatment (70 °C, 1 h), with Aspergillus species dominating in non-inoculated waste. Anaerobic waste degradation decreased the diversity of fungal species for processes run at both 37 and 55 °C, but not total fungal colony forming units. Fungi surviving the mesophilic anaerobic digestion were mainly thermotolerant Talaromyces and Paecilomyces species. T. crustaceus and T. lanuginosus were the only inoculated fungi to survive the thermophilic anaerobic degradation process. Aerobic storage of both types of anaerobic residues for one month significantly decreased fungal counts.

Microbial community analysis of mesophilic anaerobic protein degradation process using bovine serum albumin (BSA)-fed continuous cultivation

Two mesophilic anaerobic chemostats, one without added Ni2+ and Co2+ (chemostat 1) and the other with added Ni2+ and Co2+ (chemostat 2), were supplied with synthetic wastewater containing bovine serum albumin (BSA) as the sole carbon and energy source in order to study the capacity of protein degradation, microbial community structure and the effects of the addition of trace metals. Volatile fatty acids and ammonia were the main products of chemostat 1, while methane, CO2 and ammonia were the main products of chemostat 2, and critical dilution rates of 0.15 d-1 and 0.08 d-1 were obtained, respectively. Fluorescence in situ hybridization (FISH) with archaeal and bacterial domain-specific probes showed that archaeal cells were very limited in chemostat 1 while large populations of several types of archaeal cells were present in chemostat 2. Phylogenetic analyses based on 16S rRNA gene clonal sequences, DGGE, and quantitative real-time polymerase chain reaction (PCR) showed that, within the domain Archaea, methanogens affiliated with the genera Methanosaeta and Methanoculleus were predominant in chemostat 2. Within the domain Bacteria, rRNA genes obtained from chemostat 1 were affiliated with the three phyla; Firmicutes (43%), Bacteroidetes (50%) and Proteobacteria (7%). A total of 56% of rRNA genes obtained from chemostat 2 was affiliated with the three phyla, Firmicutes (32%), Bacteroidetes (11%) and Proteobacteria (13%) while 44% of rRNA genes remained unclassified. Phylogenetically distinct clones were obtained in these two chemostats, suggesting that different protein degradation pathways were dominant in the two chemostats: coupled degradation of amino acids via the Stickland reaction in chemostat 1 and uncoupled degradation of amino acids via syntrophic association of amino acid degraders and hydrogenotrophic methanogens in chemostat 2.

Anaerobic 2-propanol degradation in anoxic paddy soil and the possible role of methanogens in its degradation.

The anaerobic degradation of 2-propanol in anoxic paddy soil was studied with soil cultures and a 2-propanol-utilizing methanogen. Acetone was the first and the major intermediate involved in the methanogenic degradation of 2-propanol. Analyses with a methanogenesis inhibitor, bacteria antibiotics, and the addition of H2 to the gas phase revealed that 2-propanol oxidation to acetone directly occurred using 2-propanol-utilizing methanogens, but not with H2-producing syntrophic bacteria, for which the removal of acetone is required for complete 2-propanol oxidation. The 2-propanol-utilizing strain IIE1, which is phylogenetically closely related to Methanoculleus palmolei, was isolated from paddy soil, and the potential role of the strain in 2-propanol degradation was investigated. 2-Propanol is one of the representative fermentation intermediates in anaerobic environments. This is the first report on the anaerobic 2-propanol degradation process.

Effect of intermediate soil cover on municipal solid waste decomposition

A complex series of chemical and microbiological reactions is initiated with the burial of refuse in a sanitary landfill. At the end of each labour day, the municipal solid wastes (MSW) are covered with native soil (or an alternative material). To investigate interaction between the intermediate cover and the MSW, five sets of columns were set up, one packed with refuse only, and four with a soil-refuse mixture (a clay loam, an organic-rich peaty soil, a well limed sandy soil and a chalky soil). The anaerobic degradation over 6 months was followed in terms of leachate volatile fatty acids, chemical oxygen demand, pH and ammoniacal-N performance. Results suggest that the organic-rich peaty soil may accelerate the end of the acidogenic phase. Clay appeared not to have a significant effect on the anaerobic degradation process.

Control of microbial methane production in wetland rice fields

Methane emission rates are a function of production, transport and oxidation of CH4 in the rice field. Production of CH4 is the prerequisite for any flux. The most important variables that control CH4 production include soil type, rice variety, temperature, soil redox potential, water management and fertilization with organic carbon or nitrogen. The effects of these variables have empirically been assessed on a macroscopic scale. However, the actual mechanisms by which these variables affect the microbial CH4 production on a microscopic scale are little understood. The purpose of the present contribution is to review existing knowledge of microbiological data and microscopic processes that are relevant for the control of CH4 production. These include the flow of carbon and electrons during the anaerobic degradation process, thermodynamic constraints of reactions in-situ and changes in the composition of the microbial community.

Anaerobic digestion of alcohol sulfate (anionic surfactant) rich wastewater – batch experiments. Part II: influence of the hydrophobic chain length

High-strength wastewater of some industries contains high concentrations of surfactants and readily biodegradable compounds like starch and other carbohydrates. Wastewater of this type is found in the textile wet-processing industry (e.g., cotton desizing). The anaerobic degradation process in such wastewater is inhibited due to the high surfactant content. Alcohol sulfate (AS) of increasing hydrophobic chain length (C 8 to C 18, surfactant) and soluble starch (size) were used as model compounds in a series of batch experiments with high loadings of the biomass (65 g AS/kg cell dry weight; 910 g starch/kg cell dry weight). The strongest inhibition of the hydrolysis, acidogenesis and acetogenesis was found in reactors containing medium chain ASs like dodecyl sulfate. Starch hydrolyzation rates decreased by nearly 90% in the presence of dodecyl sulfate. Decyl sulfate caused the strongest inhibition of the methanogenesis and a decrease of the methane evolution by 75% within 87 days experimental time. It was found that short as well as long chain ASs caused only minor inhibition phenomena. The presented data can be used as a basis for the selection of suitable surfactants that do not (or not seriously) inhibit the anaerobic digestion of industrial effluents.

Disintegration as a key-step in sewage sludge treatment

Fields of application of the mechanical sewage sludge disintegration are presented. Various methods of mechanical cell disintegration are described and the obtained results are compared. All methods are able to break up the flocs, but only some of them provide enough energy for the disruption of micro-organisms. The possible improvement of the anaerobic degradation process using raw sludge, excess sludge and digested sludge is shown. Excesssludge proves to be the most suitable. The use of disintegrated sludge as a carbon source for the denitrification is explained as a second field of application. External carbon sources can be substituted and the amount of sewage sludge to be disposed of is reduced at the same time. Foamingin digesters caused by filamentous micro-organisms can be reduced by disintegration of these sludges. Adsorbed gas bubbles are released and the settling properties of the sludge are improved. Another field of application is the solution of organic components of the sludge solids. The increased concentration of nitrogen and phosphorous in the supernatant causes recovery processes to be operated at a higher cost efficiency. A comparison of effort and advantages shows that disintegration is especially useful if there are problems in the sludge treatment process of the WTP.

Full scale experience of two stage thermophilic/mesophilic sludge digestion

The general goals of anaerobic sludge stabilisation are degradation of organic substances, reduction of solids, decrease of pathogenic bacterias, improvement of dewatering capabilities and production of biogas. The anaerobic degradation process can be divided in several steps with different optimum operational conditions. This gives the possibility to design treatment plants as a two-stage process, optimizing the process conditions in each step and thereby leading to an overall increase in process efficiency. Research results in lab scale and pilot scale have shown that a two-stage digestion process with a high loaded first thermophilic (50-55°C) stage and a second stage under mesophilic (35-37°C) conditions with sufficient retention time will lead to the best results. After giving a short summary of the development of the two-stage thermophilic/mesophilic digestion process the paper will present full scale experiences with this system in Germany.

Full scale experience of two stage thermophilicimesophilic sludge digestion

The general goals of anaerobic sludge stabilisation are degradation of organic substances, reduction of solids, decrease of pathogenic bacterias, improvement of dewatering capabilities and production of biogas. The anaerobic degradation process can be divided in several steps with different optimum operational conditions. This gives the possibility to design treatment plants as a two-stage process, optimizing the process conditions in each step and thereby leading to an overall increase in process efficiency. Research results in lab scale and pilot scale have shown that a two-stage digestion process with a high loaded first thermophilic (50–55°C) stage and a second stage under mesophilic (35–37°C) conditions with sufficient retention time will lead to the best results. After giving a short summary of the developement of the two-stage thermophilic/mesophilic digestion process the paper will present full scale experiences with this system in Germany.

Surface charge and extracellular polymer of sludge in the anaerobic degradation process

Changes of surface charge and extracellular polymer (ECP) content were investigated in batch experiments for three anaerobic sludges, each of which had been enriched at 35°C and pH 639-7.3 for more than 40 batches using propionate, butyrate and glucose, individually, as the sole substrate. Results showed that both ECP and the negative surface charge were dependent on the growth phase of microorganisms. They increased at the beginning of all batches when the microorganisms were in the prolific-growth phase, having high substrate concentration and food-to-microorganisms ratio. Both later gradually returned to their initial levels when the microorganisms were in the declined-growth phase, as the substrate became depleted. The negative surface charge increased linearly with the total-ECP content in all series with slopes of 0.0187, 0.0212 and 0.0157 meq/mg-total-ECP for sludge degrading propionate, butyrate and glucose, respectively. The change of surface charge for the first two sludges was mainly due to the increase of proteinaceous fraction of ECP; but, for glucose-degrading sludge, that could be due to the increases of both proteinaceous and carbohydrate fractions of ECP. The negative-charged nature of anaerobic sludge implies that cations should be able to promote granulation of anaerobic sludge.

Comprehensive monitoring of a fluidised bed reactor for anaerobic treatment of high strength wastewater

Attempts at validation of models of the anaerobic degradation process in high-rate reactors have generally been inconclusive as a result of the lack of sufficiently comprehensive sets of reported experimental data. In most cases, the data have not been self-verifying, as a result of insufficient analysis of all the components in the biogas, no comparison of the total carbon in the volatile fatty acids with measured total organic carbon, or failure to measure all the components in the carbon and nitrogen balances. This paper reports a study of a pilot-scale reactor treating a glucose substrate, in which these shortcomings were largely overcome. Daily samples of biogas were taken for immediate determination of hydrogen, methane, carbon dioxide and nitrogen. Approximately daily samples of the effluent were analysed for nine volatile fatty acids, total organic carbon, biochemical oxygen demand, suspended solids, sugars and protein content, in addition to the physical variables of temperature, pH and redox potential. The height of the fluidised bed and the head loss through it were also measured daily, as were the effluent flow, the recycle flow and the flow rate of the biogas. The duration of the run was 41 days. The paper reports on the relative consistency of these measurements and their use in calculating the carbon and nitrogen balances on a daily basis. These balances lead to estimates of the rate of increase of biomass within the fluidised bed, which can then be used to estimate mean bioparticle diameter and variations in pore space.

Surface charge and extracellular polymer of sludge in the anaerobic degradation process

Changes of surface charge and extracellular polymer (ECP) content were investigated in batch experiments for three anaerobic sludges, each of which had been enriched at 35°C and pH 6.9–7.3 for more than 40 batches using propionate, butyrate and glucose, individually, as the sole substrate. Results showed that both ECP and the negative surface charge were dependent on the growth phase of microorganisms. They increased at the beginning of all batches when the microorganisms were in the prolific-growth phase, having high substrate concentration and food-to-microorganisms ratio. Both later gradually returned to their initial levels when the microorganisms were in the declined-growth phase, as the substrate became depleted. The negative surface charge increased linearly with the total-ECP content in all series with slopes of 0.0187, 0.0212 and 0.0157 meq/mg-total-ECP for sludge degrading propionate, butyrate and glucose, respectively. The change of surface charge for the first two sludges was mainly due to the increase of proteinaceous fraction of ECP; but, for glucose-degrading sludge, that could be due to the increases of both proteinaceous and carbohydrate fractions of ECP. The negative-charged nature of anaerobic sludge implies that cations should be able to promote granulation of anaerobic sludge.

Treatment of seafood‐processing wastewaters in mesophilic and thermophilic anaerobic filters

Wastewaters from fish‐canning industries have a high concentration of organic polluting substances (10–50 g chemical oxygen demand L−1 [COD]) and, in some cases, a high content of sea salts (Cl−: 8–19 g L−1, Na+: 5–12 g L−1, SO2−4: 0.6–2.7 g L−1). The presence of high sodium ion concentrations in wastewaters with high organic content traditionally is considered as a very negative factor for their anaerobic treatment. In fact, both the presence of Na+ and SO2−4, transformed into H2S during the anaerobic degradation process, may cause toxicity and inhibition on the methanogenic process. This work deals with the operation and treatment efficiency of two lab‐scale mesophilic and thermophilic anaerobic filters (MAF and TAF, respectively). So that the adaptation of anaerobic sludge to high saline concentrations is attained, a prolonged start‐up period of about nine months was necessary. After this, a stable operation and similar treatment efficiencies were reached, even when organic loading rate (OLR) as high as 9 kg COD m−3 d−1 (TAF) or 24 kg COD m−3 d−1 (MAF) were applied at chloride concentration of 13 g L−1. At these conditions, the COD removal reached 73% (TAF) and 64% (MAF), and the COD methanized reached 69% (TAF) and 66% (MAF). The sulphate in the influent was removed practically completely, leading to a H2S concentration in the biogas between 3–4%. In spite of the lower specific activity of sludge from MAF (0.21 g COD g−1 volatile suspended solids [VSS] d−1) than from TAF (0.66), the MAF reached a higher OLR than TAF. This fact can be explained because of the higher retention of sludge into MAF (72 g VSS L−1) than TAF (10 g VSS L−1). Two practical conclusions may be derived from this work: the thermophilic operation needs the use of a packing material with a higher capacity to retain biomass and the mesophilic operation requires a more frequent detachment of biomass from the support in order to avoid clogging problems.

Dynamic modelling of a single-stage high-rate anaerobic reactor—II. Model verification

A structured model of the anaerobic degradation process, incorporating dynamic equations for the description of a single-stage high-rate anaerobic reactor was validated by comparing its predictions with previously reported experimental data. This data came from two different laboratory-scale reactors and a pilot-scale reactor. With the manipulation of key model parameters, significant improvements in the fit of the model to the experimental data were possible. This study was able to show that the production and consumption of lactic acid, and the moderate hydrogen inhibition and regulation of the acidic products of the acidogenic bacteria, can be successfully modelled. Insufficient experimental data were available to draw conclusions as to the importance of product inhibition in anaerobic reactors, while the need to use deterministic models to account for pH inhibition highlighted the need to develop mechanistic models able to reflect the pH inhibited behaviour of the major anaerobic groups present in the ecosystem.

Microbial acetate conversion to methane: kinetics, yields and pathways in a two-step digestion process

Organic waste is converted in a two-stage process to methane and carbon dioxide by mixed cultures of microorganisms. Acetate, a product of acidogenic and acetogenic bacteria and the main substrate for methanogenic bacteria, is an important intermediate of the anaerobic degradation process, which results in the generation of methane. It was shown by labelling experiments using (U-14C) acetate that as much as 65%–96% of the total methane produced came from the acetate. The first order utilization rate for acetate in the methanogenic stages of a two-stage digestion process was between 0.17 h-1 and 0.5 h-1. The kinetics as well as the mass flow and yields of acetate and the methyl group of acetate were determined by pulse-labelling experiments with (U-14C) acetate and (2-14C) acetate without a significant rise of the total concentrations. Up to 58% of the acetate carbon was transformed to methane, and about 30% to carbon dioxide; only 4%–15% was incorporated into the biomass. There are at least two parallel degradation mechanisms in the metabolic transformation of acetate to methane: acetate is cleaved either to form methane and carbon dioxide or to form hydrogen and carbon dioxide, which can be transformed by an additional reaction to methane. Labelling experiments with (2-14C) acetate show that both mechanisms took place at similar order.