Preservation methods for the storage of anaerobic sludges

Different preservation methods were evaluated for the storage of anaerobic sludges: room temperature, refrigeration at 4 °C, freezing at –20 °C and freeze-drying. Specific methanogenic activity for glucose and acetate were used as indicators of the subsequent recovery of the anaerobic sludge. Storage at room temperature and refrigeration resulted in a better conservation of the methanogenic activity than freezing and freeze-drying.     

Influence of physico-chemical properties of porous microcarriers on the adhesion of an anaerobic consortium

The ability for biomass colonization of four porous mineral microcarriers (sepiolite, clay, pozzolana and foam glass-Poraver), was studied and related to their surface properties. The surface hydrophobicity of the mineral carriers was a more important factor influencing colonization by the anaerobic consortium than was surface charge. It was possible to correlate linearly the degree of hydrophobicity with the biomass retention capacity. Although the thermodynamic theory did not explain adhesion, an increase in cell attachment was directly related to the decrease of the positive values of the free energy of adhesion. Surface roughness, porosity and the amount of surface Mg²⁺, were also determinant factors in bacterial immobilization. However a great biomass accumulation can originate a decrease in biological activity due to mass transfer limitations. Journal of Industrial Microbiology & Biotechnology (2000) 24, 181–186. Received 09 August 1999/ Accepted in revised form 01 December 1999     

Cultivation of low-temperature (15°C), anaerobic, wastewater treatment granules

Aims: Anaerobic sludge granules underpin high‐rate waste‐to‐energy bioreactors. Granulation is a microbiological phenomenon involving the self‐immobilization of several trophic groups. Low‐temperature anaerobic digestion of wastes is of intense interest because of the economic advantages of unheated bioenergy production technologies. However, low‐temperature granulation of anaerobic sludge has not yet been demonstrated. The aims of this study were to (i) investigate the feasibility of anaerobic sludge granulation in cold (15°C) bioreactors and (ii) observe the development of methanogenic activity and microbial community structure in developing cold granules. Methods and Results: One mesophilic (R1; 37°C) and two low‐temperature (R2 and R3, 15°C) laboratory‐scale, expanded granular sludge bed bioreactors were seeded with crushed (diameter <0·4 mm) granules and were fed a glucose‐based wastewater for 194 days. Bioreactor performance was assessed by chemical oxygen demand removal, biogas production, granule growth and temporal methanogenic activity. Granulation was observed in R2 and R3 (up to 33% of the sludge). Elevated hydrogenotrophic methanogenesis was observed in psychrophilically cultivated biomass, but acetoclastic methanogenic activity was also retained. Denaturing gradient gel electrophoresis of archaeal 16S rRNA gene fragments indicated that a distinct community was associated with developing and mature granules in the low‐temperature (LT) bioreactors. Conclusions: Granulation was observed at 15°C in anaerobic bioreactors and was associated with H₂/CO₂‐mediated methanogenesis and distinct community structure development. Significance and Impact of the Study: Granulation underpins high‐rate anaerobic waste treatment bioreactors. Most LT bioreactor trials have employed mesophilic seed sludge, and granulation <20°C was not previously documented.     

Temperature dependent (37-15°C) anaerobic digestion of a trichloroethylene-contaminated wastewater

The impact of a trichloroethylene (TCE) contaminated wastewater on the microbial community structure of an anaerobic granular biomass at 15 °C compared to 37 °C was investigated. Four expanded granular sludge bed (EGSB) bioreactors (R1-R4) were employed in pairs at 37 and 15 °C. The influents of one of each pair were supplemented with increasing concentrations of TCE (max. 60 mg l⁻¹). At 37 °C, stable operation was maintained with 88% COD removal and >99% TCE removal at maximum influent TCE concentrations. R3 performance decreased at influent TCE concentration of 60 mg l⁻¹, although TCE removal rates of >97% were recorded. Archaeal community analysis via clone library and quantitative polymerase chain reaction (qPCR) analysis, and bacterial community analysis via denaturing gradient gel electrophoresis (DGGE), indicated that temperature resulted in a greater change in community structure than the presence of TCE, and clones related to cold adaptation of biomass were identified at 15 °C.     

The effect of calcium on the treatment of fresh leachate in an expanded granular sludge bed bioreactor

This research investigated the calcium effect on the anaerobic treatment of fresh leachate in an expanded granular sludge bed (EGSB) bioreactor under mesophilic conditions. The observations show that the bioreactor, inoculated with anaerobic granular sludge, can be started up only in about 40 days for the treatment of calcium-containing fresh leachate with chemical oxygen demand (COD) removal efficiency above 90% and organic loading rate up to 72.84 kg COD/m³ day. The calcium accumulation onto the granules was monotonically related to the calcium concentration, accounting for 17-18 wt.% of Ca in the suspended solid in the form of calcium carbonate, phosphates/phosphonates and carboxylates. The mineral formation significantly increased the granule settling velocity (by ∼50%) and the suspended solid concentration (by ∼100%). However, the effect of calcium precipitation on the specific methanogenic activity and the CH₄ production rate was complex, first positive during the start-up but later on negative.     

pH、温度和癸酸对厌氧颗粒污泥产甲烷毒性关系的研究

在间歇培养中研究了癸酸对UASB反应器厌氧颗粒污泥的产甲烷毒性,并考察了pH、温度和癸酸抑制的关系。结果表明,癸酸对厌氧颗粒污泥产甲烷活性有强烈的抑制,对厌氧颗粒污泥比产甲烷活性产生50％抑制的浓度为1．9mmol/L。pH影响癸酸在液相中的存在形式,pH越低,游离癸酸比例越大,对厌氧颗粒污泥的抑制越严重。高温条件下癸酸使厌氧颗粒污泥的结构变得松散,对厌氧颗粒污泥产甲烷毒性较中温和低温条件下严重。     

Co-digestion of different waste mixtures from agro-industrial activities: kinetic evaluation and synergetic effects

Several wastes from agro-industrial activities were mixed in different ratios to evaluate the co-digestion process. Methane yield (Y_CH4), specific methanogenic activity (SMA) and a kinetic parameter (k₀) were determined. A second feeding was also performed to examine the recovery of bacterial activity after exhaustion.Mixture ratios of 1:1:1:1 and 1:3:4:0.5 (w/w) showed the best performance, with Y_CH4 of 664; 582 NmL CH₄/gVS_substrate, as well as SMA of 0.12; 0.13 gCOD_NmLCH4/gVS_inoculum/d, respectively, during the digestion of the first feed. It was possible to relate synergetic effects with enhancement in Y_CH4 by up to 43%, compared with values calculated from Y_CH4 of the individual substrates. All batches started up the biogas production after an exhaustion period, when a second feed was added. However, long lag phases (up to 21 days) were observed due to stressed conditions caused by the substrate limitation prior to the second feed.     

Methanogenic bacteria in mangrove sediments

The occurrence of methanogenic bacteria in the Kodiakkarai (10° 18 N; 79° 52 E) mangrove sediments, whereAvicennia spp are predominant, was studied. Trimethylamine under N₂:CO₂ (80:20% v/v) was used as the substrate. Most Probable Number (MPN) of methanogenic bacteria was determined for a period of one year from July 1987 to June 1988 with monthly sampling. The methanogenic bacterial populations were found to be at the maximum of 1.1 × 10⁵ MPN gm^–1 of wet sediment during August 1987 and from February to June 1988. The bacterial numbers were found to decrease during October to December 1987 with a minimal value of 3.6 × 10² MPN gm^–1 during December 1987. Environmental factors were correlated with the methanogenic bacterial population.     

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.     

Ecophysiology of syntrophic communities that degrade saturated and unsaturated long-chain fatty acids

Syntrophic relationships are the key for biodegradation in methanogenic environments. We review the ecological and physiological features of syntrophic communities involved in the degradation of saturated and unsaturated long-chain fatty acids (LCFA), as well as their potential application to convert lipids/fats containing waste to biogas. Presently, about 14 species have been described with the ability to grow on fatty acids in syntrophy with methanogens, all belonging to the families Syntrophomonadaceae and Syntrophaceae . The principle pathway of LCFA degradation is through β-oxidation, but the initial steps in the conversion of unsaturated LCFA are unclear. Communities enriched on unsaturated LCFA also degrade saturated LCFA, but the opposite generally is not the case. For efficient methane formation, the physical and inhibitory effects of LCFA on methanogenesis need to be considered. LCFA adsorbs strongly to biomass, which causes encapsulation of active syntrophic communities and hampers diffusion of substrate and products in and out of the biomass. Quantification of archaea by real-time PCR analysis suggests that potential LCFA inhibitory effect towards methanogens might be reversible. Rather, the conversion of adsorbed LCFA in batch assays was shown to result in a significant increase of archaeal cell numbers in anaerobic sludge samples.     

Molecular assessment of complex microbial communities degrading long chain fatty acids in methanogenic bioreactors

Microbial diversity of anaerobic sludge after extended contact with long chain fatty acids (LCFA) was studied using molecular approaches. Samples containing high amounts of accumulated LCFA were obtained after continuous loading of two bioreactors with oleate or with palmitate. These sludge samples were then incubated in batch assays to allow degradation of the biomass-associated LCFA. In addition, sludge used as inoculum for the reactors was also characterized. Predominant phylotypes of the different samples were monitored using denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA gene fragments. Fingerprinting analysis showed changes in bacterial and archaeal communities during LCFA accumulation and degradation. Full-length 16S rRNA gene sequences of 22 clones, representing the predominant bacteria and archaea, were determined. Most bacterial clones (80%) clustered within the Clostridiaceae. Two major groups of methanogens were identified: hydrogen- and formate-utilizing organisms, closely related to Methanobacterium, and acetoclastic organisms closely related to Methanosaeta and Methanosarcina. Quantification by FISH and real-time PCR showed that the relative abundance of archaea increased during degradation of biomass-accumulated LCFA. These results provide insight into the importance and dynamics of balanced communities of bacteria and methanogens in LCFA-accumulation/degradation cycles.