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Redensification of the housing stock is also creating challenges for the drainage of wastewater and rainwater in existing sewer systems, particularly in growing cities. One alternative here is the evaporation of rainwater, which reduces hydraulic loads on sewers. Rainwater evapotranspiration using helophyte mats on building roofs is a possible approach. Helophytes are able to transpire considerably more rainwater than extensively planted green roofs. Other than conventional green roofs helophyte mats in the form of wetland roofs require a permanent water supply on a daily basis. Greywater application can be an additional advantage in terms of nutrient supply of the wetland roof after being treated microbiologically within the plant carrier mat. The treatment of greywater using a helophyte-planted roof can help to meet the water and nutrient requirements of the helophytes even during rain-free periods. However, it must be ensured that the root mat treats the greywater to a sufficient extent. It was shown under practical conditions that a 0.1 m-thick helophyte mat is suitable for treating typical domestic greywater at loads of up to 15 L m−2 d−1.

Aquatic macrophytes are important components of aquatic habitats. However, the overgrowth of aquatic plants can cause severe problems for the management of bodies of water. As a result, these plants must be removed and disposed of as waste. However, the usage of this biomass as a substrate in biogas plants would appear to be more beneficial. The present study shows the advantages and barriers to the use of harvested aquatic biomass for energy production in Germany. The results cover several aspects of this issue, such as the question of biomass potential, the quality of the harvested aquatic plants, and ensiling for the purpose of conservation for anaerobic digestion. In addition, the social aspects of the de‐weeding in bodies of water are discussed.

The effect of ensiling fermentation and mechanical pretreatment on the methane yield of lignocellulosic biomass was investigated in order to determine the optimum pretreatment conditions for biogas production. Wheat straw was treated using the following techniques: mechanical disintegration by chopping and extruder-grinding to particle sizes of 2.0 and 0.2 cm, respectively, and ensiling by 30% and 45% total solids with addition of enzymatic, chemical and biological silage additives individually and in combination. The total and volatile solid content, biochemical methane potential and products of silage fermentation of 32 variants were tested. The results indicate that the methane potential increased by 26% (from 179 to 244 mL CH4 g−1 VS) by reducing particle size. The maximum methane potential of 275 mL CH4 g−1 VS was obtained from silage with 30% total solids and extruder grinding. However, the effect of the addition of silage additives on the methane potential was limited.

The total amount of sealed surfaces is increasing in many urban areas, which presents a challenge for sewerage systems and wastewater treatment plants when extreme rainfall events occur. One promising solution approach is the application of decentralized eco-technologies for water management such as green roofs and constructed wetlands, which also have the potential to improve urban biodiversity. We review the effects of these two eco-technologies on species richness, abundance and other facets of biodiversity (e.g., functional diversity). We find that while green roofs support fewer species than ground-level habitats and thus are not a substitute for the latter, the increase in green roof structural diversity supports species richness. Species abundance benefits from improved roof conditions (e.g., increased substrate depth). Few studies have investigated the functional diversity of green roofs so far, but the typical traits of green roof species have been identified. The biodiversity of animals in constructed wetlands can be improved by applying animal-aided design rather than by solely considering engineering requirements. For example, flat and barrier-free shore areas, diverse vegetation, and heterogeneous surroundings increase the attractiveness of constructed wetlands for a range of animals. We suggest that by combining and making increasing use of these two eco-technologies in urban areas, biodiversity will benefit.

The reactor systems used for microbial electrosynthesis, i.e. bioelectrochemical systems for achieving bioproduction so far reported in literature are relatively small in scale and highly diverse in their architecture and modes of operation. The often diverging requirements of the electrochemical and the biological processes and the interdisciplinarity of the field make the engineering of these systems a special challenge. This has led to multiple, differently optimized approaches of reactor vessels, designs and operating conditions making standardization and normalization or even a systematic engineering almost impossible. Overcoming this lack of standardization, scalability and knowledge‐driven engineering is the driving force for this work introducing an upgrade kit for bioreactors transforming these reversibly to bioelectroreactors. The prototypes of the bioreactor upgrade kit were integrated with commercial bioreactor (fermentor) systems and performances compared to a classic, small‐scale bioelectrochemical glass cell system. The use of the upgrade kit allowed interfacing with the existing infrastructure of the conventional bioreactors for growing electroactive microorganisms in pure culture conditions, with the added electrochemical control and further process monitoring. The results of growing Shewanella oneidensis MR‐1 clearly show that these systems can be used to control, monitor, and scale microbial bioelectrochemical processes, providing better resolution of the data for the tested experimental conditions.

The environmentally benign disposal of acid mine drainage (AMD) is still a technical challenge. In the present study, artificial AMD was treated in a laboratory-scale floating hydroponic root mat of soft rush, Juncus effusus. This ecotechnological system was operated with hydrogen injection and water recirculation but without an external carbon supply. It achieved a mean increase of ΔpH = 3.3 up to pH ≈ 8.2, high sulfate removal of up to 87%, and efficient removal of iron (100%), aluminum (99.8%), manganese (97.4%), and zinc (99.6%). Sulfide was not detected in the outflow. Treatment performance correlated with the amount of hydrogen loading. Daily oscillations of the redox potential up to amplitudes of ΔEh ≈ 450 mV in a mean range of Eh ≈ −150 to +300 mV indicated a correlation of plant physiology and removal processes. Apparently, sulfate and metal removal were the result of chemolithotrophic microbial sulfate reduction supported by the externally provided H2 and chemoorganotrophic sulfate reduction driven by rhizodeposits. Bicarbonate generated in the microbial transformation of such plant-derived organic carbon contributed to pH neutralization. The effluent's pH increase was governed further by recirculation of the treated AMD. The flow regime and the injection of hydrogen at the ground of the root mat caused concentration gradients where the most efficient removal occurred in the deepest zone of the root mat. Further investigations should target long-term stability, plant growth dynamics, load variations, balances of carbon and sulfur, the removal of H2S and metal precipitates from the system as well as efficient hydrogen supply.

Die dezentrale Behandlung von Grauwasser findet weltweit immer grosere Beachtung. Da in der Regel ebenerdige Flachen kostenintensiv sind, kann alternativ die Grauwasserbehandlung mithilfe von Sumpfpflanzenmatten auf Gebaudedachern erfolgen. Neben der Wasserbehandlung wirkt sich dieses Vorgehen positiv auf die Gebaudeklimatisierung aus. In einem Test unter Praxisbedingungen konnte gezeigt werden, dass eine Sumpfpflanzenmatte mit 0,1 m Wurzelschichthohe bei hydraulischen Flachenbelastungen bis 15 L m−2d−1 fur die Behandlung von typischem Grauwasser eines Wohnhauses geeignet ist. There is increasing interest worldwide in the decentralized treatment of gray water. Since ground-level areas are generally costly, gray-water treatment can also be carried out using helophyte mats on the roofs of buildings as an alternative. Alongside the water treatment itself, this process also has a positive effect on the indoor climate in the building. In a test carried out under realistic conditions, it was shown that a helophyte mat with a root-layer depth of 0.1 m and with hydraulic loads per unit up to 15 L m−2d−1 is suitable for treating typical gray water from a residential building.

Many non-native species have been introduced because they provide one or more ecosystem service. As some of these species also cause disservices, case-by-case approaches are required to assess risks vs. opportunities related to their spread.

The application of spent yeast for biogas production has been studied only in the context of breweries so far. This study is focused on the anaerobic digestion of concentrated yeast biomass (CYB), being a by‐product of citric acid biosynthesis. Two experimental set‐ups were used in order to test CYB as a mono‐substrate and co‐substrate for closing the loop in accordance with the ‘bioeconomy’ approach. The results show that CYB allows for obtaining a high biogas yield, with a maximum of 1.45 m(3) (N)/kg(VS) produced when CYB was used as a mono‐substrate. The average methane concentration was 66 ± 4%. However, anaerobic digestion of CYB alone was difficult to perform because of a tendency for over‐acidification, meaning that the maximum possible organic loading rate was 1 kg/(m(3)*d). Repeated clogging of tubes with coagulated biomass also disturbed continuous feeding. In contrast, the co‐digestion of CYB with waste frying fat at a ratio of 1:20 showed stable operation during a 70‐day fermentation period. The biogas yield using the substrate mixture was 1.42 m(3)/kg(VS) at an organic loading rate of 2 kg/(m(3)*d). The methane concentration reached 67 ± 4% and the acetate concentration did not exceed 30 mg/L during the entire fermentation.

Many anaerobic digestion plants have problems with excessive foam formation. The causes remain mostly unclear. By means of foaming tests, it is demonstrated that the substrate disintegration grade plays a crucial role in the process of foaming. Mixing of coarse grain with soybean oil turned out to be an effective instrument for foam suppression.

Mit dem Ziel, die Materialeigenschaften zu verbessern und die Schwermetallgehalte von belasteten Gewassersedimenten soweit zu reduzieren, dass eine Verwertung moglich ist, wurde ein kombiniertes Konditionierungs- und Bioleaching-Verfahren in den Praxismasstab uberfuhrt. Am Beispiel eines schwermetallbelasteten Teichsedimentes konnte die Praxistauglichkeit des Verfahrens gezeigt werden. Aus zwei Chargen des Gewassersedimentes wurden Zink und Cadmium entfernt. Das Sediment wurde erfolgreich bei der Renaturierung von Bergbauhalden verwendet. Der bei der Prozesswasseraufbereitung anfallende Fallungsschlamm konnte als Quelle fur strategische Elemente genutzt werden. Water sediment contaminated with heavy metals is a problem worldwide. The presented ecological conditioning and bioleaching process was demonstrated on a practical scale with the aim to improve material properties and to reduce the heavy metal content so that the sediment can be reused. The bioleaching part of the process was performed in two trials, resulting in the removal of zinc and cadmium. After the treatment the sediment was suitable to be reused for recultivation of mining dumps, while the precipitation sludge may possibly be used as a source for strategic elements.

The invasive aquatic plant Elodea nuttallii was subjected to hydrothermal carbonization at 200 °C and 240 °C to produce biochar. About 58% w/w of the organic carbon of the pristine plant was translocated into the solid biochar irrespectively of the operating temperature. The process water rich in dissolved organic matter proved a good substrate for biogas production. The E. nuttallii plants showed a high capability of incorporating metals into the biomass. This large inorganic fraction which was mainly transferred into the biochar (except sodium and potassium) may hamper the prospective application of biochar as soil amendment. The high ash content in biochar (∼ 40% w/w) along with its relatively low content of organic carbon (∼ 36% w/w) is associated with low higher heating values. Fatty acids were completely hydrolyzed from lipids due to hydrothermal treatment. Low molecular-weight carboxylic acids (acetic and lactic acid), phenols and phenolic acids turned out major organic breakdown products.

Excessive foaming in anaerobic digestion occurs at many biogas plants and can cause problems including plugged gas pipes. Unfortunately, the majority of biogas plant operators are unable to identify the causes of foaming in their biogas reactor. The occurrence of foaming is often related to the chemical composition of substrates fed to the reactor. The consistency of the digestate itself is also a crucial part of the foam formation process. Thus, no specific recommendations concerning substrates can be given in order to prevent foam formation in biogas plants. The safest way to avoid foaming is to test the foaming tendency of substrates on-site. A possible solution is offered by an innovative foaming test. With the help of this tool, biogas plant operators can evaluate the foaming disposition of new substrates prior to use in order to adjust the composition of substrate mixes.

Elodea nuttallii and Elodea canadensis, two invasive submerged and rooted aquatic macrophyte species, are receiving increasing attention for their rapid and lasting invasion of many freshwater habitats throughout Europe, Asia and Australia. This review summarizes the present scientific knowledge about means of controlling E. nuttallii and E. canadensis within of aquatic weed management programs. Both species exhibit high growth rates with a high tolerance to wide ranges of environmental conditions, low vulnerability to grazing and other stress factors, high distribution and reproduction potential, and relatively high resistance to common conventional aquatic weed management procedures. Possibilities for the further use of harvested Elodea biomass are presented and novel approaches to the improvement of the monitoring and management of Elodea plagues are discussed.

Anaerobic digestion (AD) of biogenic materials is a core contributor to biogas production and thus an important component of bioenergy supply. However, AD process instabilities can threaten the economic viability of AD plants. One of these process upsets is the uncontrollable formation of foam. Foam generally causes the blocking of gas pipes in anaerobic digesters, and the produced biogas then escapes through the pressure safety device into the atmosphere. In addition, foam can cause technical problems with pumps, feeders, and measuring sensors. Foam formation in AD is a very complex phenomenon that can have various causes that are not always easy to identify. In this chapter, the current research on AD foaming is summarized. After a general literature review of foam in biotechnological processes, the development of methods for investigations of foam formation and stabilization is described. The causes of foaming and countermeasures that have been developed so far are presented. Surveys of AD plant operators are also introduced in a separate section. Although there has been comprehensive research in the last decade on identifying the causes of foaming, many issues remain unclear. Recommendations for further research are given in the last section.

Green Infrastructure can be defined as a network of natural and engineered areas that are designed and managed to provide an increased breadth and depth of ecosystem services in both urban and rural areas. It is based on the concept that a specific area of land that has healthy ecosystems can actively mitigate challenges such as urban growth and climate change. Green Infrastructure offers a myriad of environmental, economic, and social benefits, as well as valuable ecosystem goods and services. This chapter addresses resource efficiency as it relates to water, and specifically to resilience and quality of life in urban areas.

While constructed wetlands have become established for the decentralized treatment of wastewater and rainwater, wetland roofs have only been built in isolated cases up to now. The historical development of wetland roofs is described here on the basis of a survey of literature and patents, and the increasing interest in this ecotechnology around the world is presented. In particular, this article describes the potential for using wetland roofs and examines experience with applications in decentralized water management in urban environments and for climate regulation in buildings. Wetland roofs are suitable as a green-blue technology for the future—particularly in cities with an acute shortage of unoccupied ground-level sites—for the decentralized treatment of wastewater streams of various origins. Positive “side effects” such as nearly complete stormwater retention and the improvement of climates in buildings and their surroundings, coupled with an increase in biodiversity, make wetland roofs an ideal multi-functional technology for urban areas.

A bioremediation process for sediments contaminated with heavy metals has been developed based on two core stages: (1) conditioning of dredged sludge using plants; and (2) solid-bed bioleaching of heavy metals from the resulting soil-like material using microbially produced sulfuric acid. In laboratory and pilot-scale tests, reed canary grass (Phalaris arundinacea) was found to be best suited for the conditioning process. To demonstrate the feasibility of conditioning in practice, a study on a larger scale was performed. The sediment originated from a detritus basin of the Weisse Elster River in Leipzig (Saxony, Germany) and was polluted with heavy metals, especially with zinc and cadmium. The dredged sludge was a muddy-pasty, anoxic, and had a high organic matter content. The experimental basin (base area of 50 × 23 m) was filled with 1,400 m3 of sludge to a height of 1.2 m. Conditioning was carried out in five segments that were planted with pre-cultivated Phalaris plants at two plant densities, sowed with Phalaris seeds using two different seeding devices, and grown over by vegetation. Plant development and changing sediment characteristics were analyzed during two vegetation periods by harvesting plant biomass every 4 weeks and sampling sediment material at two different depths every 2 weeks over a total duration of 475 days. At the end of the second vegetation period, the pre-cultivated Phalaris plants had reached a height of 2 m, compared to 1.8 m for the sowed Phalaris seeds. Regarding root penetration and the degree of sediment conditioning, the less expensive sowing techniques yielded similar results to planting pre-cultivated plants. The content of heavy metals in the Phalaris plants was below the permissible limits for Germany. The vegetation evapotranspirated large amounts of water from the sediment and transported oxygen into the anoxic sludge. The water content was reduced from 68 to 37 %. The muddy-pasty sludge turned into a soil-like oxic material with a high permeability to water. The oxidation of sediment-borne compounds lowered the pH from 7.3 to 6.0. Due to the high total precipitation in Saxony in the summer of 2010, a maximum of 65 % of the sediment was conditioned. The feasibility of the first core stage of the bioremediation process for sediments was demonstrated in practice by conditioning 1,400 m3 of dredged sludge using reed canary grass. To establish the proposed sediment treatment in practice, the applicability of the central core stage–solid-bed bioleaching of conditioned soil-like sediment–will also be tested at a larger scale.

The genetically modified yeast strain Yarrowia lipolytica H222-S4(p67ICL1)T5 is able to utilize sucrose as a carbon source and to produce citric and isocitric acids in a more advantageous ratio as compared to its wild-type equivalent. In this study, the effect of pH of the fermentation broth (pH 6.0 and 7.0) and proteose-peptone addition on citric acid production by the recombinant yeast strain were investigated. It was found that the highest citric acid production occurred at pH 7.0 without any addition of proteose-peptone. Furthermore, two process strategies (fed-batch and repeated fed-batch) were tested for their applicability for use in citric acid production from sucrose by Y. lipolytica. Repeated fed-batch cultivation was found to be the most effective process strategy: in 3 days of cycle duration, approximately 80 g/L citric acid was produced, the yield was at least 0.57 g/g and the productivity was as much as 1.1 g/Lh. The selectivity of the bioprocess for citric acid was always higher than 90% from the very beginning of the fermentation due to the genetic modification, reaching values of up to 96.4% after 5 days of cycle duration.

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.

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.

Premise of the Study To enhance the understanding of the recent invasion process of the clonal waterweed Elodea nuttallii (Hydrocharitaceae), analyses of population structure and genotypic diversity need to be undertaken, for which genetic markers are needed. Methods and Results High‐throughput sequencing of DNA enriched for microsatellites was used to develop 24 loci that were characterized in E. nuttallii, 21 of which were polymorphic, with the number of alleles ranging from two to 10. In two populations, expected heterozygosity ranged among loci between zero and 0.796. In the congener E. canadensis, all markers yielded PCR products, 19 of which were polymorphic, with two to nine alleles and expected heterozygosity ranging from zero to 0.690 in two populations. Conclusions The markers described should be useful for future studies of population structure and clonal diversity of E. nuttallii as well as E. canadensis in their native and invasive range.

Citric acid (CA) is mainly produced in a biotechnological process using Aspergillus niger. In this process, large amounts of wastes have to be removed. Since the use of Yarrowia lipolytica for CA production is an environmental compatible alternative method, the CA production was optimized in regard to growth temperature and pH as well as substrate and product inhibition. The highest value of the maximum specific growth rate at pH 6.5 was found to be μ max = 0.192 h -1 , whereas the largest amount of CA of 24.91 g/L as well as the highest selectivity of the bioprocess (89.9 % CA) and the maximum yield (0.22 g CA /g Glucose ) were obtained at pH 6.0. During the growth phase, the temperature optimum was found to be in the range of 30-34°C (μ max = 0.132 h -1 ). Nevertheless, the highest concentration of CA during the production phase was obtained at 30°C (41 g/L CA, 93.1 % CA, 0.55 g CA /g glucose ). In studying the substrate inhibition of the process, a clear tendency of decrease in the maximum specific growth rate was detected when the initial glucose concentration was increased from 50 g/L μ max = 0.17 h -1 ) to 200 g/L (μ max = 0.055 h -1 ). The addition of 120 g/L CA to the culture broth at the start of the production phase reduced the production of CA from 32.1 g/L to 7.4 g/L.

A remediation process for heavy metal polluted sediment has previously been developed, in which the heavy metals are removed from the sediment by solid-bed bioleaching using sulfuric acid as a leaching agent arising from added elemental sulfur (S 0 ). This process has been engineered with WeiBe Elster River sediment (dredged near Leipzig, Germany), as an example. Here, six heavy metal polluted sediments originating from various bodies of water in Germany were subjected to bioleaching to evaluate the applicability of the developed process on sediment of different nature: each sediment was mixed with 2 % S 0 , suspended in water and then leached under identical conditions. The buffer characteristics of each sediment were mainly governed by its carbonate and Ca content, i.e., by its geological background, the redox potential and oxidation state depended on its pre-treatment (e.g., on land disposal), while the pH value was influenced by both. The added 5° was quickly oxidized by the indigenous microbes even in slightly alkaline sediment. The microbially generated H 2 SO 4 accumulated in the aqueous phase and was in part precipitated as gypsum. Significant acidification and heavy metal solubilization only occurred with sediment poor in buffer substances. With the exception of one sediment, the behavior in bioleaching correlated well with the behavior in titration with H 2 SO 4 . Since the content in carbonate seemed to be the most important factor deciding on the leachability of a sediment, oxic WeiBe Elster River sediment was mixed with 2 % S 0 and 0 to 100 g/kg of ground limestone to simulate various buffer capacities, suspended in water and then leached. The lime did not inhibit microbial S° oxidation but generated a delay in acidification due to neutralization of formed H 2 SO 4 , where the pH only started to decrease when the lime was completely consumed. The more lime the sediment contained, the longer this lag period lasted, and the higher the pH and the lower the fraction of the solubilized heavy metals finally was. Since Cu requires stronger acidic conditions for its solubilization, it responded more sensitively to lime addition than Zn, Ni, and Cd. Heavy metal polluted sediment containing large amounts of carbonate may, in principle, also be remediated by bioleaching, but metal solubilization requires excessive amounts of the leaching agent and is thus uneconomical.

Remediation of heavy metal polluted sediment through bioleaching using elemental sulfur (S 0 ) as the leaching agent can be regarded as a two-step process: firstly, the microbial oxidation of the added S 0 to sulfuric acid and, secondly, the reaction of the produced acid with the sediment. Here, both subprocesses were studied in detail independently: oxidized river sediment was either suspended in sulfuric acid of various strengths, or mixed with various amounts of finely ground S 0 powder (diameter of the S° particles between 1 and 175 μm with a Rosin-Rammler-Sperling-Bennet (RRSB) distribution and an average diameter of 35 μm) and suspended in water. The leaching process was observed by repeated analysis of the suspension concerning pH, soluble sulfate and metals, and remaining S°. In the case of abiotic leaching with H 2 SO 4 , the reaction between the acid and the sediment resulted in a gradual increase in pH and a solubilization of sediment-borne heavy metals which required some time; 80 % of the finally solubilized heavy metals was dissolved after 1 h, 90 % after 10 h, and 100 % after 100 h. In the case of bioleaching, the rate of S 0 oxidation was maximal at the beginning, gradually diminished with time, and was proportional to the initial amount of S 0 . Due to its very low solubility in water, S 0 is oxidized in a surface reaction catalyzed by attached bacteria. The oxidation let the particles shrink, their surface became smaller and, thus, the S 0 oxidation rate gradually decreased. The shrinking rate was time-invariant and, at 30 °C, amounted to 0.5 μm/day (or 100 μg/cm 2 /day). Within 21 days, 90 % of the applied S 0 was oxidized. Three models with a different degree of complexity have been developed that describe this So oxidation, assuming S 0 particles of uniform size (I), using a measured particle size distribution (II), or applying an adapted RRSB distribution (III). Model I deviated slightly from the measured data but was easy to handle, Model II fitted the measured data best but its simulation was complicated, and Model III was intermediate. The amount of soluble sulfate was smaller than the amount of H 2 SO 4 added or microbially generated as the H 2 SO 4 reacted with the sediment to form in part poorly soluble sulfates. A model has been developed that describes the pH and the soluble sulfate and metals at equilibrium, depending on the amount of H 2 SO 4 applied or microbially generated, and that is based on the condition of electrical neutrality, a global metal/proton exchange reaction, and a sulfate-fixation reaction. In suspension, bioleaching with S 0 required considerably more time than abiotic leaching with H 2 SO 4 , but the final pH and metal solubilization were identical when equimolar amounts of leaching agents were applied.

The strain Pseudomonas putida DOT-T1E was tested for its ability to tolerate second phases of different alkanols for their use as solvents in two-liquid-phase biotransformations. Although 1-decanol showed an about 10-fold higher toxicity to the cells than 1-octanol, the cells were able to adapt completely to 1-decanol only and could not be adapted in order to grow stably in the presence of a second phase of 1-octanol. The main explanation for this observation can be seen in the higher water and membrane solubility of 1-octanol. The hydrophobicity (log P) of a substance correlates with a certain partitioning of that compound into the membrane. Combining the log P value with the water solubility, the maximum membrane concentration of a compound can be calculated. With this simple calculation, it is possible to predict the property of an organic chemical for its potential applicability as a solvent for two-liquid-phase biotransformations with solvent-tolerant P. putida strains. Only compounds that show a maximum membrane concentration of less than 400 mM, such as 1-decanol, seem to be tolerated by these bacterial strains when applied in supersaturating concentrations to the medium. Taking into consideration that a solvent for a two-liquid-phase system should possess partitioning properties for potential substrates and products of a fine chemical synthesis, it can be seen that 1-decanol is a suitable solvent for such biotransformation processes. This was also demonstrated in shake cultures, where increasing amounts of a second phase of 1-decanol led to bacteria tolerating higher concentrations of the model substrate 3-nitrotoluene. Transferring this example to a 5-liter-scale bioreactor with 10% (vol/vol) 1-decanol, the amount of 3-nitrotoluene tolerated by the cells is up to 200-fold higher than in pure aqueous medium. The system demonstrates the usefulness of two-phase biotransformations utilizing solvent-tolerant bacteria.

The remediation of heavy metal-polluted aquatic sediment by solid-bed bioleaching requires a material well permeable to air and water. Freshly dredged sediment is nearly impermeable and needs previous conditioning to make it suitable for solid-bed leaching. This conditioning – in practice carried out by planting sediment packages with helophytes – comprises water removal by evapotranspiration, abiotic and microbial oxidation of sediment-borne reduced compounds, acidification, as well as structural changes improving the sediment permeability. The rate of this process seems to be limited by the transport of oxygen into the sediment bed. For a better understanding of the physicochemical processes occurring during conditioning, sediment oxidation was studied in a stirred suspension to minimize transport limitations. Freshly dredged, silty, anoxic, heavy metal-polluted sediment from the Weisse Elster River (Germany) was suspended in water and then continuously stirred and aerated at 20 °C. Aerobic conditions appeared within a few hours. The redox potential increased from – 400 to + 220 mV, at first very quickly and later more slowly. Sediment-borne inorganic sulfur compounds were oxidized to sulfate (S0 mainly within two days and sulfide within ten days), which reduced the pH from 7.2 to 5.9. A successive oxidation of FeS to Fe(II) sulfate, the oxidation of Fe(II) to Fe(III) followed by Fe(III) oxyhydrate formation caused the dissolved Fe to sharply increase and thereafter rapidly decrease. Ammonium was completely oxidized in a nitrification process to form nitrate, further decreasing the pH to 5.5. The acidification increased the solubility of Mn, Zn, Mg, Ca, and K. The increase in dissolved Mn rules out any oxidation of Mn(II) to Mn(IV) since Mn(IV) would have been insoluble under the prevailing pH and redox conditions. Sediment oxidation did not proceed in a well-defined, redox-potential-directed order, but individual (partly microbially) oxidation processes superimposed each other. Physicochemical conditioning of suspended sediment was completed after 20 days while conditioning in a solid bed would require months or even years. These different rates result from transport limitations in the solid bed. Sediment conditioning in a solid bed could therefore possibly be accelerated by prior sediment aeration.

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.

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 part...

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.

Weisse Elster River sediment from the Leipzig Lowlands region (Saxony, Germany) is anthropogenically polluted by heavy metals. Sediment dredged from a trap to the south of Leipzig was characterized in detail. When freshly dredged sediment contacts air, the material turns acidic because of oxidation processes, the heavy metals become soluble and the sediment poses an environmental risk. We are therefore developing a sediment-treatment process based on heavy metal removal by bioleaching. Leaching experiments were carried out in suspension and in the solid bed. The heavy metals were solubilized to nearly the same extent by H2SO4 dosage (pure chemical extraction) and addition of elemental sulphur (microbial oxidation of S0 to H2SO4). With increasing dosage of the leaching agent, Zn, Cd, Ni, Cu and Cr were more and more solubilized, whereas Pb was only dissolved in small amounts. The addition of 2% S0 is considered an optimum dosage. When 5% S0 was added to the sediment, the pH dropped to 1.76 and large amounts of undesirable compounds such as Ca, Al and Fe were solubilized. The higher the temperature, the faster the metals were solubilized in both suspension and the solid bed. The temperature optimum for activating the indigenous S0-oxidizing microbes of the sediment lies between 30 and 40 °C. Conditioning of freshly dredged sediment with plants makes it suitable for solid-bed leaching; the kinetics of heavy metal solubilization from sediment conditioned for 6 months with Phragmites australis was the same as from long-term stored sediment.

During the microbial treatment of a sandy model soil artificially contaminated with polycyclic aromatic hydrocarbons (PAHs), a large residual pollution was found. The remaining PAHs were sorbed into the micropores of the soil and were therefore not bioavailable. Using a lab-scale percolator, the microbially pretreated soil was subjected to aftertreatment with surfactants with the aim of further degradation of its pollution. Two commercial nonionic surfactants of the polyethoxylate type, Prawozell F1214/5 N and Sapogenat T-300, were used. The surfactants differ both in their physicochemical properties (CMC value, PAH solubilization capacity, adsorption onto soil) and in their microbial degradability. During aftertreatment under permanently aerobic conditions, only a weak PAH accumulation in the liquid phase was observed, which was due to a low solubilization rate as well as to simultaneous microbial degradation of the dissolved PAHs. Temporary anaerobiosis successfully suppressed the microbial degradation of both the surfactant and the solubilized PAHs, resulting in a more intensive PAH accumulation. But the PAH content of the soil - the essential criterion for evaluating the efficiency of surfactant application - was not decreased to a larger extent with surfactants than without them. To find out why the surfactants failed to act, the surfactant and hydrocarbon distribution among the liquid and solid phases was studied in mixtures of phenanthrene-spiked soils and Prawozell-containing liquids; at heavy phenanthrene loading, the aqueous phase was saturated with PAH; at weak loading, it was unsaturated. Model-aided data analysis showed that the soil may contain PAH in two fractions: strongly sorbed into soil pores and, in the case of heavy loading, also weakly attached to the soil surface. The latter is easily extractable, resulting in a PAH-saturated liquid, while strongly adsorbed PAH is only partially dissolved due to competition between the micelles and the soil pores for the PAH. The microbially pretreated soil contains only strongly bound PAHs, which are as difficult to extract by surfactants as they are poorly accessible for microbes.

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...

Standardized bioreactors allowing systematic process engineering are established. The field of bioelectrotechnology, which combines the microbial or enzymatic conversion with electrical current flow, is still in its infancy. Thus, bioelectrochemical reactor systems are diverse, poorly characterized and not standardized. Here we present a reversible upgrade kit for existing bioreactor systems to perform bioelectrochemical syntheses–allowing a systematic process characterization and development.

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.

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.

We report the study of the dynamics of substrate utilization by the genetic modified strain Yarrowia lipolytica H222-S4(p67ICL1) T5. In contrast to its wild-type equivalent, this recombinant strain is able to excrete the sucrose cleaving enzyme invertase. Both the sucrose degradation rate and the glucose and fructose consumption rate have been investigated. In all experiments, satisfied amounts of invertase were produced so that all sucrose was cleaved into its monomers. While glucose and fructose as sole carbon sources were consumed with the same uptake rate, a clear preference for glucose uptake was detected in cultivations with sucrose as sole carbon source or mixed substrates when compared with fructose. Nevertheless, no real diauxie could be observed because of partly simultaneous consumption of both monosaccharides. Fructose being present in the cultivation medium at the beginning of the fermentation led to the retardation of glucose uptake. This effect was observed for various fructose starting concentrations in the range of 5–85 g/l.

Remediation of heavy metal polluted sediment by extracting the metals with sulfuric acid can be performed as follows: abiotic suspension leaching, microbial suspension leaching, abiotic solid-bed leaching, and microbial solid-bed leaching. Abiotic leaching means that the acid is directly added, while microbial leaching means that the acid is generated from sulfur by microbes (bioleaching). These four principles were compared to each other with special emphasis on the effectiveness of metal solubilization and metal removal by subsequent washing. Abiotic suspension leaching was fastest, but suspending the solids exhibits some disadvantages (low solid content, costly reactors, permanent input of energy, high water consumption, special equipment required for solid separation, large amounts of waste water, sediment properties hinder reuse), which prevent suspension leaching in practice. Abiotic solid-bed leaching implies the supply of acid by percolating water which proceeds slowly due to a limited bed permeability. Microbial solid-bed leaching means the generation of acid within the bed and has been proven to be the only principle applicable to practice. Metal removal from leached sediment requires washing with water. Washing of solid beds was much more effective than washing of suspended sediment. The kinetics of metal removal from solid beds 0.3, 0.6 or 1.2m in height were similar; when using a percolation flow of 20lm(-2)h(-1), the removal of 98% of the mobile metals lasted 57-61h and required 8.5, 4.2 or 2.3lkg(-1) water. This means, the higher the solid bed, the lower the sediment-mass-specific demand for time and water.

Basic research on remediation of polluted sediment by leaching has, to date, been carried out exclusively with suspended material. For economic reasons, only solid-bed leaching is applicable to large-scale processes. Abiotic and microbial solid-bed leaching were comparatively studied in a percolator system using ripened and therefore permeable heavy metal polluted river sediment. In the case of abiotic leaching, sulfuric acid was supplied to the sediment by circulating water; the lower the pH of the percolating water, the higher the percolation flow, and the lower the solid-bed height was, the faster the heavy metals were solubilized. However, the pH and percolation flow are subjected to restrictions: strongly acidic conditions result in dissolution of mineral components, and the percolation flow must not exceed the bed permeability. And a high solid bed is an economic requirement. In the case of bioleaching, elemental sulfur added to the sediment was oxidized to sulfuric acid within the package which, in turn, solubilized the heavy metals. Here, the percolation flow and the solid-bed height did not affect the rate of metal solubilization. Solid-bed leaching on a larger scale will thus be much more efficient applying bioleaching with sulfur as the leaching agent than abiotic leaching with sulfuric acid.

The core stages of a sediment remediation process--the conditioning of dredged sludge by plants and the solid-bed leaching of heavy metals using microbially produced sulfuric acid--were tested on a pilot scale using a highly polluted river sediment. Conditioning was performed in 50 m3 basins at sludge depths of 1.8 m. During one vegetation period the anoxic sludge turned into a soil-like oxic material and became very permeable to water. Reed canary grass (Phalaris arundinacea) was found to be best suited for conditioning. Bioleaching was carried out in an aerated solid-bed reactor of 2000 L working volume using oxic soil-like sediment supplemented with 2% sulfur. When applying conditioned sediment, the oxidation of easily degradable organic matter by heterotrophic microbes increased the temperature up to 50 degrees C in the early leaching phase, which in turn temporarily inhibited the sulfur-oxidizing bacteria. Nevertheless, most of the metal contaminants were leached within 21 days. Zn, Cd, Mn, Co, and Ni were removed by 61-81%, Cu was reduced by 21%, while Cr and Pb were nearly immobile. A cost-effectiveness assessment of the remediation process indicates it to be a suitable treatment for restoring polluted sediments for beneficial use.