Anaerobic treatment of wastewater with high concentrations of lipids or sulfate

This thesis describes research on the application of granular sludge bed upflow reactors for anaerobic treatment of wastewaters contaminated with lipids and sulfate, two contaminants that have so far seriously hampered the application of anaerobic treatment in several branches of industry. The Upflow Anaerobic Sludge Bed reactor is the most popular anaerobic treatment system at this moment. However, it is mainly applied to wastewaters with readily biodegradable dissolved contaminants, and hardly to more complex wastewaters.Two problems can occur in anaerobic treatment of lipid containing wastewater, viz. (1) inhibition of anaerobic bacteria by long chain fatty acids, and (2) flotation of the biomass. Sulfate may cause direct and indirect inhibition of methanogenic and acetogenic bacteria.The first part of the thesis deals with the inhibitory effect of long chain fatty acids (LCFA) in anaerobic digestion. Inhibition can occur after overloading, i.e. during the start-up period of the digester, or as a result of a shock load. LCFA affect especially the acetotrophic methanogens, above a critical threshold concentration they exert a bactericidal effect. The methanogens do not adapt to LCFA. The threshold concentration for capric acid - one of the most toxic saturated acids - is approximately 1 kg/m 3. The precise value of the threshold concentration depends upon the mass transfer characteristics of the anaerobic reactor, and upon the particle size and specific activity of the biomass aggregates. Furthermore, the presence of phospholipids may enhance the inhibitory effect of LCFA. Inhibition can be prevented by addition of soluble calcium salts to the wastewater. However, the addition of calcium cannot eliminate the second deleterious effect of a shock load of LCFA, viz. flotation and subsequent wash-out of biomass aggregates.The second part of this thesis describes the anaerobic treatment of solutions of LCFA and emulsions of triglycerides in the Expanded Granular Sludge Bed reactor. With LCFA solutions this modified upflow reactor can achieve a mineralization efficiency of at least 85-90% at space loading rates of ca. 30 kg COD/m 3.day. Modification of the sludge separation system is required to reduce sludge wash-out during treatment of triglyceride emulsions. A novel sieve-drum separator was developed, which allows stable operation. Although the treatment capacity is significantly lower with triglyceride emulsions than with LCFA solutions, the EGSB reactor with sieve-drum separator can accommodate higher organic and hydraulic loading rates than previously described anaerobic filter reactors. Upscaling of the EGSB system and flotation of lipids require further research.The third part of the thesis deals with the inhibitory effect of sulfide and sodium sulfate. From pH 6.4 to 7.2 approximately 250 mg H 2 S per litre causes a 50% decrease of the maximum specific activity of acetotrophic methanogens. The inhibitory effect of a given H 2 S concentration increases significantly when the pH approaches 8. Consequently, an increase of the pH level in the anaerobic digester above ca. 7.2 is not beneficial. Immobilization in biomass aggregates or films may provide protection against H 2 S inhibition. Propionate degradation may be the rate limiting step during treatment of sulfate containing wastewater, because it is affected more severely by sulfide than acetotrophic methanogenesis. At extremely high sulfate concentrations, also inhibition by cations has to be considered. At neutral pH levels, sodium concentrations up to 5 g/l cause no inhibition of acetotrophic methanogens. A sodium concentration of 10 g/l causes a 50% decrease of the maximum specific acetotrophic methanogenic activity, 14 g/l causes complete inhibition. Acetotrophic methanogens do not adapt to high sodium concentrations

Modeling lipid accumulation in oleaginous fungi in chemostat cultures. II: Validation of the chemostat model using yeast culture data from literature

A model that predicts cell growth, lipid accumulation and substrate consumption of oleaginous fungi in chemostat cultures (Meeuwse et al. in Bioproc Biosyst Eng. doi:10.1007/s00449-011-0545-8, 2011) was validated using 12 published data sets for chemostat cultures of oleaginous yeasts and one published data set for a poly-hydroxyalkanoate accumulating bacterial species. The model could describe all data sets well with only minor modifications that do not affect the key assumptions, i.e. (1) oleaginous yeasts and fungi give the highest priority to C-source utilization for maintenance, second priority to growth and third priority to lipid accumulation, and (2) oleaginous yeasts and fungi have a growth rate independent maximum specific lipid production rate. The analysis of all data showed that the maximum specific lipid production rate is in most cases very close to the specific production rate of membrane and other functional lipids for cells growing at their maximum specific growth rate. The limiting factor suggested by Ykema et al. (in Biotechnol Bioeng 34:1268–1276, 1989), i.e. the maximum glucose uptake rate, did not give good predictions of the maximum lipid production rate

Modeling growth, lipid accumulation and lipid turnover in submerged batch cultures of Umbelopsis isabellina

The production of lipids by oleaginous yeast and fungi becomes more important because these lipids can be used for biodiesel production. To understand the process of lipid production better, we developed a model for growth, lipid production and lipid turnover in submerged batch fermentation. This model describes three subsequent phases: exponential growth when both a C-source and an N-source are available, carbohydrate and lipid production when the N-source is exhausted and turnover of accumulated lipids when the C-source is exhausted. The model was validated with submerged batch cultures of the fungus Umbelopsis isabellina (formerly known as Mortierella isabellina) with two different initial C/N-ratios. Comparison with chemostat cultures with the same strain showed a significant difference in lipid production: in batch cultures, the initial specific lipid production rate was almost four times higher than in chemostat cultures but it decreased exponentially in time, while the maximum specific lipid production rate in chemostat cultures was independent of residence time. This indicates that different mechanisms for lipid production are active in batch and chemostat cultures. The model could also describe data for submerged batch cultures from literature well

Methanogens, sulphate and heavy metals: a complex system

Anaerobic digestion (AD) is a well-established technology used for the treatment of wastes and wastewaters with high organic content. During AD organic matter is converted stepwise to methane-containing biogasa renewable energy carrier. Methane production occurs in the last AD step and relies on methanogens, which are rather sensitive to some contaminants commonly found in wastewaters (e.g. heavy metals), or easily outcompeted by other groups of microorganisms (e.g. sulphate reducing bacteria, SRB). This review gives an overview of previous research and pilot-scale studies that shed some light on the effects of sulphate and heavy metals on methanogenesis. Despite the numerous studies on this subject, comparison is not always possible due to differences in the experimental conditions used and parameters explained. An overview of the possible benefits of methanogens and SRB co-habitation is also covered. Small amounts of sulphide produced by SRB can precipitate with metals, neutralising the negative effects of sulphide accumulation and free heavy metals on methanogenesis. Knowledge on how to untangle and balance sulphate reduction and methanogenesis is crucial to take advantage of the potential for the utilisation of biogenic sulphide as a metal detoxification agent with minimal loss in methane production in anaerobic digesters.The research was financially supported by the People Program (Marie Curie Actions) of the European Union's Seventh Framework Programme FP7/2007-2013 under REA agreement 289193

Anaerobic treatment of wastewater with high concentrations of lipids or sulfate

This thesis describes research on the application of granular sludge bed upflow reactors for anaerobic treatment of wastewaters contaminated with lipids and sulfate, two contaminants that have so far seriously hampered the application of anaerobic treatment in several branches of industry. The Upflow Anaerobic Sludge Bed reactor is the most popular anaerobic treatment system at this moment. However, it is mainly applied to wastewaters with readily biodegradable dissolved contaminants, and hardly to more complex wastewaters.Two problems can occur in anaerobic treatment of lipid containing wastewater, viz. (1) inhibition of anaerobic bacteria by long chain fatty acids, and (2) flotation of the biomass. Sulfate may cause direct and indirect inhibition of methanogenic and acetogenic bacteria.The first part of the thesis deals with the inhibitory effect of long chain fatty acids (LCFA) in anaerobic digestion. Inhibition can occur after overloading, i.e. during the start-up period of the digester, or as a result of a shock load. LCFA affect especially the acetotrophic methanogens, above a critical threshold concentration they exert a bactericidal effect. The methanogens do not adapt to LCFA. The threshold concentration for capric acid - one of the most toxic saturated acids - is approximately 1 kg/m 3. The precise value of the threshold concentration depends upon the mass transfer characteristics of the anaerobic reactor, and upon the particle size and specific activity of the biomass aggregates. Furthermore, the presence of phospholipids may enhance the inhibitory effect of LCFA. Inhibition can be prevented by addition of soluble calcium salts to the wastewater. However, the addition of calcium cannot eliminate the second deleterious effect of a shock load of LCFA, viz. flotation and subsequent wash-out of biomass aggregates.The second part of this thesis describes the anaerobic treatment of solutions of LCFA and emulsions of triglycerides in the Expanded Granular Sludge Bed reactor. With LCFA solutions this modified upflow reactor can achieve a mineralization efficiency of at least 85-90% at space loading rates of ca. 30 kg COD/m 3.day. Modification of the sludge separation system is required to reduce sludge wash-out during treatment of triglyceride emulsions. A novel sieve-drum separator was developed, which allows stable operation. Although the treatment capacity is significantly lower with triglyceride emulsions than with LCFA solutions, the EGSB reactor with sieve-drum separator can accommodate higher organic and hydraulic loading rates than previously described anaerobic filter reactors. Upscaling of the EGSB system and flotation of lipids require further research.The third part of the thesis deals with the inhibitory effect of sulfide and sodium sulfate. From pH 6.4 to 7.2 approximately 250 mg H 2 S per litre causes a 50% decrease of the maximum specific activity of acetotrophic methanogens. The inhibitory effect of a given H 2 S concentration increases significantly when the pH approaches 8. Consequently, an increase of the pH level in the anaerobic digester above ca. 7.2 is not beneficial. Immobilization in biomass aggregates or films may provide protection against H 2 S inhibition. Propionate degradation may be the rate limiting step during treatment of sulfate containing wastewater, because it is affected more severely by sulfide than acetotrophic methanogenesis. At extremely high sulfate concentrations, also inhibition by cations has to be considered. At neutral pH levels, sodium concentrations up to 5 g/l cause no inhibition of acetotrophic methanogens. A sodium concentration of 10 g/l causes a 50% decrease of the maximum specific acetotrophic methanogenic activity, 14 g/l causes complete inhibition. Acetotrophic methanogens do not adapt to high sodium concentrations