Andreas Zehnsdorf

Bioavailability of hydrocarbons during microbial remediation of a sandy soil

Abstract The microbial degradation of hydrocarbons was studied in an artificially contaminated sandy soil, using a pilot-scale percolator system. After a short lag period, an intensive degradation occurred, which diminished in time and completely stopped in the end, despite large residual contaminations (residues of 56% diesel fuel, 20% n-hexadecane and 3.5% phenanthrene at the initial loadings of each 3000 mg/kg). The remaining pollutant content was influenced by the kind of hydrocarbon but was nearly independent of its initial loading. According to a model-aided analysis of the carbon dioxide production during remediation, the observed stagnation of degradation was caused by a limited bioavailability of the pollutants. The degradation in the soil-free aqueous phase was more extensive than in the soil, which suggests that the limited bioavailability in the soil can be attributed mainly to matrix-dependent rather than substrate-dependent influences. Generally, fine particles and organic matter are mainly responsible for the adsorption of pollutants to the soil matrix. Our sandy soil also bound hydrocarbons adsorptively although it contained neither silty material nor significant amounts of organic matter. As shown by Brunauer Emmett Teller (BET) analysis, the soil particles were covered by micropores, which enlarged the soil surface by a factor of 120 in comparison with the macroscopic surface area. The microporosity is the reason for the hydrocarbons being more strongly adsorbed to the sandy soil than expected.

Microbial degradation of hydrocarbons in soil during aerobic/anaerobic changes and under purely aerobic conditions

Abstract Microbial hydrocarbon degradation in soil was studied during periodical aerobic/anaerobic switching and under purely aerobic conditions by using a pilot-scale plant with diesel-fuel-contaminated sand. The system worked according to the percolation principle with controlled circulation of process water and aeration. Periodical switching between 4 h of aerobic and 2 h of anaerobic conditions was achieved by repeated saturation of the soil with water. Whatever the cultivation mode, less than 50% of the diesel was degraded after 650 h because the hydrocarbons were adsorbed. Contrary to expectations, aerobic/anaerobic changes neither accelerated the rate of degradation nor reduced the residual hydrocarbon content of the soil. Obviously the pollutant degradation rate was determined mainly by transport phenomena and less by the efficiency of microbial metabolism. The total mass of oxygen consumed and carbon dioxide produced was greater under aerobic/anaerobic changing than under aerobic conditions, although the mass of hydrocarbons degraded was nearly the same. As shown by an overall balance of microbial growth and by a carbon balance, the growth yield coefficient was smaller during aerobic/anaerobic changes than under aerobic conditions.

Foam formation in biogas plants caused by anaerobic digestion of sugar beet

The use of sugar beet in anaerobic digestion (AD) during biogas production can lead to process upsets such as excessive foaming in fermenters. In the present study, foam formation in sugar beet-fed digestates was studied in foaming tests. The increasing disintegration grade of sugar beet was observed to have a promoting effect on foaming in the digestate but did not affect the biogas yield. Chemical analysis of foam and digestate from sugar beet silage AD showed high concentrations of pectin, other carbohydrates and N-containing substances in the foam. Both pectin and sucrose showed little foaming in AD. Nevertheless, sucrose and calcium chloride had a promoting effect on foaming for pectin AD. Salts of divalent ions also enhanced the foam intensity in the case of sugar beet silage AD, whereas ammonium chloride and urea had a lessening effect on sugar beet-based foaming.

Comparative review of foam formation in biogas plants and ruminant bloat

This review gives an overview of the current knowledge concerning the problem of foam formation in the process of anaerobic digestion in biogas plants that utilize renewable resources or biogenic waste material for biogas production. Process upsets in biogas production induced by foam formation can have a negative impact on the efficiency of biogas plants. The foam can block gas pipes and cause severe damage to the bioreactor equipment, ranging from a failure of the feeders to a damage of the roof of the biogas plant. The most common foam removal methods - stirring in the foam, adding anti-foaming agents, diminishing substrate feeding, and altering the biogas reactor management - are not always successful. However, the reasons for the excessive foam formation during the biogas production process have not yet been elucidated in detail. In contrast, foam building in the rumen of ruminants as a cause for bloat has been studied thoroughly. In general, the interaction between proteins, polysaccharides (mucilage), and small plant particles is assumed to be the crucial factor. As the fermentation process in the rumen has many similarities with the biogas production process, the current research results on bloat in ruminants are summarized and compared with the process of foaming in biogas plants.

Repeated fed-batch fermentation using biosensor online control for citric acid production by Yarrowia lipolytica

Biosensor-controlled substrate feeding was used in a citric acid production process with the yeast strain Yarrowia lipolytica H222 with glucose as the carbon source. The application of an online glucose biosensor measurement facilitated the performance of long-time repeated fed-batch process with automated bioprocess control. Ten cycles of repeated fed-batch fermentation were carried out in order to validate both the stability of the microorganism for citric acid production and the robustness of the glucose biosensor in a long-time experiment. In the course of this fermentation with a duration of 553 h, a slight loss of productivity from 1.4 g/(L×h) to 1.1 g/(L×h) and of selectivity for citric acid from 91% to 88% was observed. The glucose biosensor provided 6,227 measurements without any loss of activity.

Conditioning of Heavy Metal-Polluted River Sediments by Helophytes

ABSTRACT Aquatic sediments in industrial regions are often polluted by heavy metals. When removed by dredging, the sediments become an environmental risk. Because of the high costs and the deficient sustainability of landfill disposal, we intend to develop a remediation process for cleaning heavy metal-contaminated sediments by solid-bed bioleaching. Unfortunately, freshly dredged sediments are often impermeable to water. Therefore, they have to be conditioned to improve their hydrodynamic properties and make them suitable for solid-bed leaching. The treatment basin of 5.9 m × 7.5 m of a pilot-scale plant for sediment conditioning was filled with 0.5 m freshly dredged sediment, which originated from a trap in the Weisse Elster River near Leipzig, Germany, and was contaminated with Zn, Cr, Pb, Cu, Ni, and Cd. The sediment was planted with the helophytes Phragmites australis, Phalaris arundinacea, and Agrostis stolonifera. The vegetation evaporated large amounts of water and transported oxygen into the sedi...

Potential uses of Elodea nuttallii-harvested biomass

Elodeanuttallii (PLANCH) St. John, an aquatic plant native to North America, shows invasive traits outside of its area of origin. In Europe, the plant has spread rapidly in water bodies. In Germany, the massive occurrence of E. nuttallii restricts recreational activities on lakes. Massive occurrences of E. nuttallii have been managed up to now by harvesting the plant and disposing of the biomass as organic waste, which results in high maintenance costs for lake administrators. Alternative uses to the disposal of the biomass were investigated. Analyzing the components and elemental composition of E. nuttallii samples from nine lakes in Germany, several potential uses were identified, such as the use of E. nuttallii biomass as a co-substrate with maize silage for biogas generation. Other potential applications, such as biochart production, soil amelioration, and energy recovery of feedstock chars in combustion plants, were identified from a hydrothermal carbonization process. The presence of β-sitosterol in E. nuttallii, which is used in the treatment of enlarged prostates, indicates a pharmaceutical use. Even though the elemental composition of E. nuttallii biomass contains the elements of a complete fertilizer, this particular use is not recommended given its slow decomposition in soil. The most feasible alternative identified was the use of E. nuttallii biomass as a co-substrate for biogas generation in combination with maize silage. The mixing of E. nuttallii with maize silage to facilitate storage and short distances between biogas plants and lakes with massive occurrence of E. nuttallii are important factors for its applicability.

Conditioning of Heavy Metal-Polluted River Sediment by Cannabis sativa L.

ABSTRACT We are currently developing a process for the remediation of heavy metal-polluted sediment by solid-bed bioleaching. Unfortunately, freshly dredged sediment is impermeable to water, unsuitable for solid-bed leaching, and therefore needs preliminary conditioning to improve its structure. A pilot-scale conditioning plant consisting of several basins (each with a base of 6 m2 and a depth of 0.7 m) was filled with freshly dredged, slightly predewatered sediment from the Weisse Elster River. Hemp (Cannabis sativa L.) was chosen for conditioning because it develops quickly from seeds, produces large amounts of biomass, and forms commercially useful fibers. Irrespective of the plant cover, the sediment dried out, was oxidized and turned acidic. However, its structure and permeability only improved when the sediment was covered with plants and not when all the vegetation appearing was removed regularly. Although hemp germinated completely regularly on sediment, 1 week after seeding the leaves became partially discolored, deformed, and dry, and ultimately about 95% of all the hemp plants died. The surviving hemp produced shorter shoots and much lower amounts of biomass than hemp on unpolluted soil. Studies in pots and hydrocultures indicated that the inhibition of hemp growth is caused by the synergistic action of a low pH and several mobile toxic metals. Hemp on sediment incorporated much higher quantities of heavy metals (especially Zn, Cd, and Ni) than hemp on unpolluted soil, which calls the commercial use of the former seriously in question.

Biosensor online control of citric acid production from glucose by Yarrowia lipolytica using semicontinuous fermentation

Our study aimed at the development of an effective method for citric acid production from glucose by use of the yeast Yarrowia lipolytica. The new method included an automated bioprocess control using a glucose biosensor. Several fermentation methodologies including batch, fed‐batch, repeated batch and repeated fed‐batch cultivation were tested. The best results were achieved during repeated fed‐batch cultivation: Within 3 days of cycle duration, approximately 100 g/L citric acid were produced. The yields reached values between 0.51 and 0.65 g/g and the selectivity of the bioprocess for citric acid was as high as 94%. Due to the elongation of the production phase of the bioprocess with growth‐decoupled citric acid production, and by operating the fermentation in cycles, an increase in citric acid production of 32% was achieved compared with simple batch fermentation.

Conditioning of Freshly Dredged Heavy Metal-Polluted Aquatic Sediment with Reed Canary Grass (Phalaris arundinacea L.)

The remediation of heavy metal-polluted sediment by solid-bed bioleaching, using the percolation principle, requires a material well permeable to air and water. Freshly dredged sediment is nearly impermeable, unsuitable for solid-bed leaching, and therefore needs preliminary conditioning. During conditioning, the sediment underwent physicochemical changes such as oxidation and acidification, which were significantly accelerated by the presence of reed canary grass (Phalaris arundinacea L.) in comparison to the processes taking place in sediment without plant cover. P. arundinacea transpired large amounts of water followed by the formation of cavities in the sediment package which were then penetrated by atmospheric oxygen. Furthermore, P. arundinacea actively transported oxygen into the sediment via the roots. Oxygen and root exudates stimulated the growth of microbes, which together with hair roots made mineral sediment particles stick together, forming larger aggregates and changing the sediment structure from muddy-pasty to crumbly and soil-like. The structural changes markedly improved the permeability of the sediment to water by a factor of 5,000. Sediment conditioned with P.arundinacea consisted of larger and more stable particles and therefore it was twice as permeable as unplanted sediment. Comparative solid-bed bioleaching experiments on a pilot scale demonstrated that the removal of heavy metal occurred at nearly the same rate and efficiency with conditioned (for six months with P.arundinacea) and spontaneously ripened (stored for six years in the open) sediment.