Heiko Feitkenhauer

Degradation of polycyclic aromatic hydrocarbons and long chain alkanes at 6070 °C by Thermus and Bacillus spp

Although polycyclic aromatic hydrocarbons (PAH) and alkanesare biodegradable at ambient temperature, in some cases low bioavailabilities are thereason for slow biodegradation. Considerably higher mass transfer rates and PAH solubilities and hence bioavailabilities can be obtained at higher temperatures. Mixed and pure cultures of aerobic, extreme thermophilic microorganisms (Bacillus spp., Thermus sp.) were used to degrade PAH compounds and PAH/alkane mixtures at 65 °C. The microorganismsused grew on hydrocarbons as sole carbon and energy source. Optimal growthtemperatures were in the range of 60–70 °C at pH values of 6–7. The conversion of PAH with 3–5 rings (acenaphthene, fluoranthene, pyrene, benzo[e]pyrene) was demonstrated. Efficient PAH biodegradation required a second, degradable liquid phase. Thermus brockii Hamburg metabolized up to 40 mg (l h)-1 pyrene and 1000 mg(1 h)-1 hexadecane at 70 °C. Specific growth rates of 0.43 h-1 were measured for this strain with hexadecane/pyrene mixtures as the sole carbon and energy source in a 2-liter stirred bioreactor. About 0.7 g cell dry weight were formed from 1 g hydrocarbon. The experiments demonstrate the feasibility and efficiency of extreme thermophilic PAH and alkane biodegradation.

On-line titration of volatile fatty acids for the process control of anaerobic digestion plants

The on-line titration of volatile fatty acids (VFA) was found to be a reliable method to measure the substrate (metabolite) concentration without the use of expensive analytical devices. A measurement cell was designed that ensures stable long-term operation, high throughputs and copes with both very low and very high VFA concentrations. Using synthetic textile wastewater, a recalibration of the pH probe was necessary only twice a week. A good reproducibility of the VFA concentrations was determined and standard deviations were below +/- 1% of the measured concentration. Changing salt concentrations of the wastewater in the range of 2.5-150 gl(-1) NaCl did not influence the determined VFA concentration significantly. The method was suitable to control the hydraulic retention time in an acidic phase reactor and to determine the acidification rates of wastewater compounds in batch experiments.

New approach to control the methanogenic reactor of a two-phase anaerobic digestion system.

A new control strategy for the methanogenic reactor of a two-phase anaerobic digestion system has been developed and successfully tested on the laboratory scale. The control strategy serves the purpose to detect inhibitory effects and to achieve good conversion. The concept is based on the idea that volatile fatty acids (VFA) can be measured in the influent of the methanogenic reactor by means of titration. Thus, information on the output (methane production) and input of the methanogenic reactor is available, and a (carbon) mass balance can be obtained. The control algorithm comprises a proportional/integral structure with the ratio of (a) the methane production rate measured online and (b) a maximum methane production rate expected (derived from the stoichiometry) as a control variable. The manipulated variable is the volumetric feed rate. Results are shown for an experiment with VFA (feed) concentration ramps and for experiments with sodium chloride as inhibitor.

Integration of biotechnological wastewater treatment units in textile finishing factories: from end of the pipe solutions to combined production and wastewater treatment units

Increasing costs for water, wastewater and energy put pressure on textile finishing plants to increase the efficiency of wet processing. An improved water management can decrease the use of these resources and is a prerequisite for the integration of an efficient, anaerobic on-site pretreatment of effluents that will further cut wastewater costs. A two-phase anaerobic treatment is proposed, and successful laboratory experiments with model effluents from the cotton finishing industry are reported. The chemical oxygen demand of this wastewater was reduced by over 88% at retention times of 1 day or longer. The next step to boost the efficiency is to combine the production and wastewater treatment. The example of cotton fabric desizing (removing size from the fabric) illustrates how this final step of integration uses the acidic phase bioreactor as a part of the production and allows to close the water cycle of the system.

Software sensors based on titrimetric techniques for the monitoring and control of aerobic and anaerobic bioreactors

Abstract Microbial activity influences the vicinity of a microbial cell in a way that changes the pH value of the surrounding medium. Key processes are the production or degradation of charged substances (e.g. volatile fatty acids) and the production of carbon dioxide (or hydrogen carbonate). In a technical system, the shift of the pH value may be prevented by a pH control system. It is proposed in this paper that the resulting base (or acid) consumption rates can be used as input for “software sensors” for substrate and biomass concentrations. This titrimetric technique was successfully applied to extreme thermophilic, aerobic bioprocesses (growth substrates phenol, aliphatic hydrocarbons) for the estimation of biomass and substrate concentrations (formation/degradation rates). In anaerobic experiments, the formation of volatile fatty acids (VFA) was monitored and the reduction of the VFA formation rate in the presence of an inhibitory compound investigated. The results show the versatility of software sensors based on titrimetric techniques and demonstrate the potential for process control in applications in which more sophisticated sensors are not available or affordable.

Microbial Desizing Using Starch as Model Compound: Enzyme Properties and Desizing Efficiency

A film of sizing agents protects yarn during weaving. Its removal in a subsequent washing process causes 50% of the organic effluent load of textile finishing processes and requires large amounts of auxiliary chemicals (e.g., surfactants). Microbial desizing is a new bioprocess that uses the acidifying culture of a two‐phase anaerobic digestion plant for the removal and partial degradation (acidification) of the sizing agent. Soluble starch is used in this study to characterize the enzymatic properties in the supernatant of the desizing culture and to link them to desizing efficiencies. The supernatant of the culture (grown at 37 °C, pH 5.5) displayed the highest enzymatic activity between pH 4 and 5 and in a broad temperature range (20–80 °C). Highest metabolization rates were determined with the substrate amylose. Short chain dextrins (average of 5 and 10 glucose units) and amylopectin were converted significantly more slowly. At 37 °C the half‐life time of the enzymatic activity in the supernatant was 45 h. In a desizing test a decisive reduction of the chain length was found already after 1 h (allowing starch solubilization). A microbial desizing experiment with dyed, native maize starch demonstrated the efficiency of the proposed bioprocess.

Anaerobic Microbial Cultures in Cotton Desizang: Efficient Combination of Fabric and Wastewater Treatment

The aim of our proposed microbial desizing process is to combine production (cotton desizing) and wastewater treatment in one process and to replace auxiliary chemicals with a mixed microbial culture. Cotton fabric desizing is integrated in the acidic phase bioreactor of a wastewater treatment system. The mixed culture removes the size from tht fabric and converts it into volatile fatty acids, which are eliminated in a second (biogas) reactor. The effluent of this reactor is recycled to the desizing reactor to close the water cycle. A starch-based product is selected as a model compound for polysaccharide sizing agents. Experiments demonstrate the high potential of this biotechnology to replace problematic auxiliaries. High activities of important enzymes (α-amylase) during fabric treatment are detected. Data on the efficiency of microbial desizing at different temperatures and a mass balance for size degradation are presented, as well as details on intermediates accumulation.