Anaerobic treatment of phenol in a two-stage anaerobic reactor

The inhibitory effects of phenol are problematic for the anaerobic treatment of wastewater. The purpose of this study is to demonstrate that a two-stage anaerobic digester (TSAD) can degrade phenol, reducing its toxic effects in the first acidogenic reactor (R1) before going into a methanogenic reactor (R2). The system consisted of two reactors in semi continuous operation. R1 was a Continuous Stirred Tank Reactor at pH 5.5± 0.5; R2 was a packet reactor at pH 8.4± 0.05. Both were operated at a hydraulic retention time (HRT) of 10 days and 35 0 C and fed with a nutritional supplement at organic loading rate (OLR) of 1.8 grams of COD per litre of reactor per day (LR -1 Day -1 ) until steady state conditions. Then one gram of phenol was fed daily over a period of 15 days. The performance of the system was monitored and analysed in terms of degradation of phenol and dissolved chemical oxygen demand (DCOD); concentration of organic acids (OA) and suspended organic carbon (SOC); biogas production and pH evolution. The removal of phenol and DCOD peaked at 99.7% and 70% respectively. The biogas production in the methanogenic reactor reached 0.8195 Lbiogas LR -1 Day -1 . These experiments demonstrate that, given the right conditions, a TSAD can degrade phenol without considerable inhibition

Modeling of the van der Waals forces during the adhesion of capsule-shaped bacteria to flat surfaces

A novel model is developed to evaluate the van der Waals (vdW) interactions between a capsule shaped bacterium (P. putida) and flat minerals plates in different approach profiles: Vertically and horizontally. A comparison of the approaches to the well-developed spherical particle to mineral surface (semi-infinite wall and spherical) approach has been made in this investigation. The van der Waals (vdW) interaction potentials for a capsule-shaped bacterium are found using Hamaker’s microscopic approach of sphere to plate and cylinder to plate either vertically or horizontally to the flat surface. The numerical results show that a horizontal orientated capsule shaped bacterium to mineral surface interaction was more attractive compared to a capsule shaped bacterium approaching vertically. The orientation of the bacterial approaching a surface as well as the type and topology of the mineral influence the adhesion of a bacteria to that surface. Furthermore, the density difference among each type of bacteria shape (capsule, cylinder, and sphere) require different amounts of energy to adhere to hematite and quartz surfaces

Interaction of desulfovibrio desulfuricans biofilms with stainless steel surface and its impact on bacterial metabolism

Aims: To study the influence of some metallic elements of stainless steel 304 (SS 304) on the development and activity of a sulfate-reducing bacterial biofilm, using as comparison a reference nonmetallic material polymethylmethacrylate (PMMA). Methods and Results: Desulfovibrio desulfuricans biofilms were developed on SS 304 and on a reference nonmetallic material, PMMA, in a flow cell system. Steady-state biofilms were metabolically more active on SS 304 than on PMMA. Activity tests with bacteria from both biofilms at steady state also showed that the doubling time was lower for bacteria from SS 304 biofilms. The influence of chromium and nickel, elements of SS 304 composition, was also tested on a cellular suspension of Des. desulfuricans. Nickel decreased the bacterial doubling time, while chromium had no significant effect. Conclusions: The following mechanism is hypothesized: a Des. desulfuricans biofilm grown on a SS 304 surface in anaerobic conditions leads to the weakening of the metal passive layer and to the dissolution in the bulk phase of nickel ions that have a positive influence on the sulfate-reducing bacteria metabolism. This phenomenon may enhance the biocorrosion process. Significance and Impact of the Study: A better understanding of the interactions between metallic surfaces such as stainless steel and bacteria commonly implied in the corrosion phenomena which is primordial to fight biocorrosion.Programme Praxis XXI; University of Santiago de Compostela

Toxicity and biodegradability of caffeic acid in anaerobic digesting sludge

Caffeic acid in waste comes from a variety of industries, and its disposal is likely to increase due to emerging processes such as graphene production and use in healthcare products. The current sustainable option to treat waste caffeic acid and prevent its natural transformation in soil to greenhouse gases, is anaerobic digestion. However, little is known about the toxic and inhibitory effects of caffeic acid on biogas production as well as its ultimate anaerobic biodegradability; or about the reactive-adsorptive processes taking place with caffeic acid in sludge, metabolic intermediates, thermodynamic limitations and the effects on extracellular polymeric substances (EPS). Standard methods revealed that 80% of biogas production (EC80) from a readily digestible biomass was inhibited at 389 mg caffeic acid·g-1 VSS. Up to 52% of caffeic acid was biodegraded. β-oxidation and reductive dehydroxylation were the initial activation reactions transforming caffeic acid into typical polyphenol structural units (protocatechuic acid and 4HBA). Adsorption of caffeic acid (53.3% and 28.6%) to the sludge occurred even at inhibitory concentrations. The EPS structure remained unchanged regardless of the increase in concentration of caffeic acid. Reasonable concentrations of caffeic acid could be co-digested with a similar readily digestible biomass with an expected reduction in biogas production. It is feasible to treat waste caffeic acid by anaerobic digestion and adsorption of its derivates, in order to reduce the contribution to global warming and to protect the environment

Inhibition of biogas production and biodegradability by substituted phenolic compounds in anaerobic sludge

Phenolic compounds are abundant in nature and organic wastes. This biomass may be utilised in biogas generation. Phenolics can inhibit the degradation of readily biodegradable organic fractions and their own biodegradation. In this work, assays were carried out under anaerobic conditions to study the inhibition of both gas production and biodegradability due to seven phenolic compounds and to study their adsorption onto sludge and autoxidation in the aqueous medium. Fifty percent inhibition was in the range of 120 to 594 mg of compound/g VSS. An initial enhancement followed by an inhibition of biogas formation was found. The inhibition by the phenolic compounds was found to be influenced by autoxidation, apolarity, type, size and number of substitutions. Biogas production is influenced by concentration rather than any pH change. The concentration of the phenolic compound was partially biomethanized and the degradation of gallic and caffeic acids by this process is reported here for the first time. The maximum total biodegradation of any phenolic compound was 63.85 ± 2.73%, and remaining non-biodegradable fraction was autoxidized and adsorbed onto the sludge matrix. Inhibition of methanization and partial inhibition of background gas was found at concentrations between 800 and 1600 mg/L organic carbon

Comparison between a two-stage and single-stage digesters when treating a synthetic wastewater contaminated with phenol

Phenol is a pollutant found in many industrial wastewaters, which diminishes biogas formation in anaerobic digesters. In this study, a two-stage (acidogenic and methanogenic) anaerobic digester (TSAD) was compared to a single stage digester (SSD), in treating a synthetic wastewater contaminated with phenol. Both systems were operated in batch-dilution and semi-continuously at 35°C, and were loaded with a synthetic wastewater containing a constant concentration of readily biodegradable organic matter and an increasing concentration of phenol. The TSAD had greater biogas production, and its acidogenic reactor fermented the readily biodegradable matter without inhibition by accumulation of phenol (up to 1 450 mg∙ℓ-1). The acidogenic reactor also prevented inhibition of biogas formation in the second phase (methanogenic), by holding phenol and fast produced organic acids. Batch TSAD is a potential wastewater treatment option to decontaminate streams containing readily biodegradable matter contaminated with phenol. This system enhances biogas production and allows better control of the acidogenic and methanogenic phases

A cost-benefit analysis of methods for the determination of biomass concentration in wastewater treatment

The measurement of biomass concentration is important in biological wastewater treatment. This paper compares the accuracy and costs of the traditional volatile suspended solids (VSS) and the proposed suspended organic carbon (SOC) methods. VSS and SOC values of a dilution system were very well correlated (R² = 0.9995). VSS and SOC of 16 samples were determined, the mean SOC/VSS ratio (0.52,n = 16, o = 001, ) was close to the theoretical value (0.53). For costing analysis, two hypothetical cases were analysed. In case A, it is assumed that 108 samples are analysed annually from two continuous reactors. Case B represents a batch experiment to be carried out in 24 incubated serum bottles. The savings, when using the SOC method, were £11987 for case A and £90 for case B. This study suggests the use of SOC method as a time saving and lower cost biomass concentration measurement

Interpretation of initial adhesion of Pseudomonas Putida on hematite and quartz using surface thermodynamics, DLVO, and XDLVO theories

The initial adhesion behavior of the Pseudomonas (P.) putida bacterium on hematite and quartz was interpreted by the surface thermodynamics, Derjaguin–Landau–Verwey–Overbeek, and extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theories. Physical-chemical analyses revealed that both the bacterium and the minerals are hydrophilic (γ- >28.8 mJ/m2), with hematite being the least hydrophilic (35.06 mJ/m2), followed by P. putida as moderately hydrophilic (54.42 mJ/m2), and then quartz as the most hydrophilic (54.90 mJ/m2). The zeta potential of the hematite-P. putida interaction was more electropositive than that of the quartz interaction, thus there were higher interactions between hematite and P. putida at all pH values. The thermodynamics results indicated a repulsion interaction between the bacterium and the minerals. However, the XDLVO theory effectively predicted the attachment behavior of P. putida on minerals. According to the findings, at a very short distance, interactions between the bacterium and the minerals surfaces were dominated by Lewis acid-base interactions, which constituted most of the total interaction energy. A higher positive value for the total interaction energy for quartz results in a repulsion interaction with the bacterium. Therefore, a more attractive interaction occurs between hematite and P. putida as its interaction energy is less positive. The comparison made between the theoretical results found that the XDLVO theory provides more effective and accurate outcomes for the adhesion behavior prediction between the bacterium and the minerals