Biomedical subjects

W H Rulkens

Publications and source records attributed to W H Rulkens.

15 recordsLinked to original sources

PubMed2006

NH3, N2O and CH4 emissions during passively aerated composting of straw-rich pig manure.

Straw-rich manure from organic pig farming systems was composted in passively aerated static piles to estimate the effect of monthly turning on organic matter degradation and NH(3), N(2)O and CH(4) emissions. Turning enhanced the rate of drying and degradation. The four-month treatment degraded 57+/-3% of the initial organic matter in the turned piles, while only 40+/-5% in the static piles. The turned piles showed low ammonia and N(2)O emissions, 3.9+/-0.2% and 2.5+/-0.1% of total initial nitrogen, respectively. Static piles gave low ammonia (2.4+/-0.1% N(initial)), but high (9.9+/-0.5% N(initial)) N(2)O emissions. Prevalence of anaerobic regions in the static system was supported by the higher CH(4) emissions, 12.6+/-0.6% VS(degraded) for the static vs. 0.4+/-0.0% VS(degraded) for the turned system. It was shown, that straw-rich pig manure with very low C/N ratios could be composted directly without significant NH(3) and N(2)O emissions if turned on a monthly basis.

Air↗

PubMed2004

Sustainable sludge management--what are the challenges for the future?

Sewage sludge is a serious problem due to the high treatment costs and the risks to environment and human health. Future sludge treatment will be progressively focused on an improved efficiency and environmental sustainability of the process. In this context a survey is given of the most relevant sludge treatment options and separate treatment steps. Special attention is paid to those processes that are simultaneously focused on the elimination of the risks for environment and human health and on the recovery or beneficial use of the valuable compounds in the sludge such as organic carbon compounds, inorganic non-toxic substances, phosphorus and nitrogen containing compounds. Also, a brief assessment is given of the specific future technological developments regarding the various treatment steps. Furthermore, it is discussed how to assess the various pathways which can lead to the required developments. In such an assessment the technical and economic feasibility, the environmental sustainability, the societal acceptance and the implementation route are important factors. The optimal approach also strongly depends on the local and regional situation of concern and the relevant current and future boundary conditions.

Carbon↗

PubMed2004

Recovery of energy from sludge--comparison of the various options.

This paper gives a general discussion of existing sludge treatment processes and of innovative treatment options, especially focused on the valuable use of organic carbon compounds as an energy source. Attention is paid both to high and to low temperature processes and to combinations of these processes. Based on an assessment and comparison the most beneficial and sustainable options are identified and a rough indication is given of the possibilities for improvement and future developments.

Conservation of Energy Resources↗

PubMed2003

Innovative developments in the selective removal and reuse of heavy metals from wastewaters.

Sulphide precipitation of heavy metal containing wastewaters results in low effluent concentrations. However, sulphide precipitation is not widely applied in practice because the dosing of sulphide cannot adequately be controlled. A new process was developed where the combination of a sulphide-selective electrode (pS-electrode) and pH electrode controls the sulphide addition. Precipitation experiments were performed on a laboratory-scale in batch and continuous reactor systems with synthetic wastewaters containing Cd, Cu, Ni, Pb or Zn. The response of the pS-electrode during precipitation was unique for each heavy metal and was directly related to the solubility product of the corresponding metal sulphide. The metals were removed to levels < 0.05 mg l(-1) at pH 6.0 by sulphide precipitation while maintaining a total sulphide concentration < 0.02 mg l(-1). By the control of pS at different levels and keeping the pH constant at 6.0, the metals in solutions of both Cu and Zn could be precipitated selectively from solution in a batch and continuous reactors. The use of a membrane reactor in combination with control of pH and pS offers a simple, cheap, efficient and sustainable technique with respect to obtaining very low effluent concentrations and selective removal of metals as pure metal sulphides which can be reused.

Chemical Precipitation↗

PubMed2003

Innovative reactor technology for selective oxidation of toxic organic pollutants in wastewater by ozone.

Ozonation can be a suitable technique for the pre-treatment of wastewater containing low concentrations of toxic or non-biodegradable compounds that cannot be treated with satisfactory results when only the traditional, less expensive biological techniques are applied. In this case, the oxidation process has to be made as efficient as possible, in order to reduce the coats of ozone addition and use. An efficient oxidation process with ozone can be obtained by focusing the oxidation with ozone selectively on the direct oxidation of toxic pollutants and to minimize ozone losses due to the decay of ozone in water. Supported by data of the rate constants of the reactions involved, a mathematical model was developed. It quantifies the ozone consumption by the process, and the share of ozone consumption by undesired side reactions, in several different reactor systems. Results obtained with this model indicate that a plug flow reactor (PFR) will be the most efficient design for the oxidation reactor. As an alternative, the cascaded tank reactor system (CTR), in which the ozone feed may be realized with less practical problems, might be considered. The traditional continuous flow stirred tank reactor (CFSTR) is shown to be the least efficient system.

Conservation of Energy Resources↗

PubMed2002

Heavy metals extraction from anaerobically digested sludge.

This paper reports on the chemical extraction efficiency in the removal of heavy metals from sludge from an activated-sludge system, which receives as influent both industrial and municipal wastewater. Utilizing a series of chemical extractants in a sequential order comprised the first phase of the research, called sequential chemical extraction (SCE). The work started with the well-known Tessier method followed by Veeken and by Sims and Kline SCE schemes. Afterwards, modified versions of Tessier and Veeken schemes were applied. The second phase, named chemical extraction using pH progressive changes, concerns an alternative to the extraction process. Four acids were tested: nitric, hydrochloric, oxalic and citric and the pH values as well as the time were varied. Some conclusions reveal that although modifying Tessier and Veeken schemes provides more consistent results, SCE is still an imperfect method regarding specificity and selectivity. Besides, it is not advisable to apply one SCE scheme developed for one specific situation to another one, once the accurateness of the method depends on several factors such as sort of material and chemicals, contact time, temperature, etc. The extraction efficiency increases using nitric or hydrochloric acids at low pH values, promoting high extraction efficiency level.

Bacteria, Anaerobic↗

PubMed2001

Application of a mechanistic desorption-biodegradation model to describe the behavior of polycyclic aromatic hydrocarbons in peat soil aggregates.

A procedure was developed to obtain three size fractions (2360 < d(p) < 1000, 1000 < d(p) < 710, and 710 < d(p) < 425 microm) of stable aggregates from Koopveen peat soil by application of an intense mixing regime prior to sieving of the soil material. The organic matter content, aggregation structure and the microstructure of these aggregates were determined and the particles were artificially contaminated with naphthalene and phenanthrene via a solvent phase. A nonlinear Freundlich sorption isotherm was determined for the naphthalene contaminated soil aggregates (n = 0.39; K(F) = 1.13 x 10(-2) m(1.17) kg(-0.39)). The applicability of a mathematical model, that describes sorption equilibrium, intraparticle mass-transfer, and nonlinear bacterial degradation kinetics, was tested by fitting results of dynamic desorption and biodegradation experiments, generated in this study and earlier work on the peat soil aggregates. The experimental data were described adequately although strong variations in the values of the fit parameter, the intra-particle porosity (0.30 < epsilon < 0.88), were found. This indicates the necessity of further investigations.

Biodegradation, Environmental↗

PubMed2001

Prediction of complete bioremediation periods for PAH soil pollutants in different physical states by mechanistic models.

Mass-transfer models and biodegradation models were developed for three theoretical physical states of polycyclic aromatic hydrocarbons (PAHs) in soil. These mechanistic models were used to calculate the treatment periods necessary for complete removal of the PAH pollutants from the soil under batch conditions. Results indicate that the bioremediation of PAHs in such systems is mainly mass-transfer limited. The potential for bioremediation as a treatment technique for PAH contaminated soils is therefore mainly determined by the mass-transfer dynamics of PAHs. Under mass-transfer limited conditions simplified mathematical models, based on the assumption of a zero dissolved PAH concentrations, can be used to predict the period of time needed for complete bioremediation.

Biodegradation, Environmental↗

PubMed2001

Phosphate recycling in the phosphorus industry.

The feasibility of phosphate recycling in the white phosphorus production process is discussed. Several types of materials may be recycled, provided they are dry inorganic materials, low in iron, copper and zinc Sewage sludge ash may be used if no iron is used for phosphate precipitation in the treatment plant; using Ca or Al, or bio-P-removal, increases the recycling potential of the ash, but Cu and Zn are still present in problematic concentrations. Side stream P recovery as Ca- or Al-phosphates is a more attractive option and is discussed in detail. Manure ash also has too high levels of Cu and Zn. Recycling phosphates from industrial sources is possible in many cases, depending on the source.

Chemical Industry↗

PubMed2001

Flotation with polyelectrolytes as a first step of a more sustainable wastewater treatment system.

Within the framework of a research programme into more sustainable wastewater treatment systems based on physical-chemical pretreatment the application of dissolved air flotation (DAF) with polyelectrolytes as a primary treatment was investigated. Experiments with municipal wastewater were carried out in 2.5 I flotation batches and in a 100 I DAF pilot reactor. Two cationic polyelectrolytes (PEs) with molecular weights of 4 x 10(6) g/mol and 8 x 10(6) g/mol, were tested. The higher weight PE was more effective in removing turbidity and was used in the pilot experiments for coagulation/flocculation. Within the pilot system experiments the dry solids concentration of the float layer as well as the removal efficiencies of turbidity, CODparticulate, CODdissolved and nutrients, were studied. Typical results were that the obtained dry solids concentration of the floated sludge was 10%, when the float layer was removed after several hours. By using polyelectrolytes it was possible to remove more than 80% of CODparticulate and turbidity at dosages of 7-8 mg/g influent COD (i.e. 5 mg PE/100 NTU). The removal efficiency of CODdissolved was low. There was a proportional relationship between CODparticulate and turbidity. This led to the conclusions that by introducing a dosing control strategy based on continuous turbidity measurements a constant CODparticulate removal efficiency can be obtained.

Air↗

PubMed1999

Enhancement of PAH biodegradation in soil by physicochemical pretreatment.

The effects were studied of short-term heating of contaminated soil and its soaking in an organic solvent on the subsequent biodegradation of PAHs. In a clayey dredged sludge with a high organic-matter content (12%), heating at 120 degrees C for one hour increased the degree of degradation after 21 days of an aged PAH contamination from 9.5 +/- 0.7% to 27 +/- 5%. Lower temperatures resulted in smaller increases. The observed increase in biodegradation is caused by either transfer of PAHs from sorption sites with low desorption rates to those with high ones or transformation of slow-sorption sites into fast-sorption ones. Soaking of the above sludge in a 4:1 (v/v) acetone-water mixture increased the degree of degradation from 9.5 +/- 0.7% to 20.4 +/- 1.4%, probably as a result of dissolution of the PAHs in the pore liquid during soaking. Thermal pretreatment of a contaminated sandy soil with a low organic-matter content showed no significant effect on the degradation of aged PAHs. Soaking of the sandy soil increased the degradation of only PAHs of high molecular weight, namely from 24 +/- 5% to 48 +/- 7%.

Acetone↗

PubMed1998

Effect of nonionic surfactants on naphthalene dissolution and biodegradation.

The effect of six nonionic surfactants, Igepal CA-720, Tergitol NPX, Triton X-100, PLE4, PLE10, and PLE23, on the dissolution rate of solid naphthalene was studied in stirred batch reactors. Results showed increased mass-transfer rates with increased surfactant concentrations up to 10 kg m-3. Dissolution experiments were adequatly described by a mechanistic mass-transfer model. Partitioning of naphthalene into the micelles and the diffusion coefficients of the micelles affected the dissolution rate most significantly. Combined dissolution and biodegradation experiments with Triton X-100 or PLE10 with naphthalene showed that the biomass-formation rate of Pseudomonas 8909N (DSM No. 11634) increased concomitantly with the mass-transfer rate under naphthalene-dissolution limited conditions up to surfactant concentrations of 6 kg m-3.

Biodegradation, Environmental↗

PubMed1998

Influence of hydrodynamic conditions on naphthalene dissolution and subsequent biodegradation.

The influence of hydrodynamic conditions on the dissolution rate of crystalline naphthalene as a model polycyclic aromatic hydrocarbon (PAH) was studied in stirred batch reactors with varying impeller speeds. Mass transfer from naphthalene melts of different surface areas to the aqueous phase was measured and results were modeled according to the film theory. Results were generalized using dimensionless numbers (Reynolds, Schmidt, and Sherwood). In combined mass transfer and biodegradation experiments, the effect of hydrodynamic conditions on the degradation rate of naphthalene by Pseudomonas 8909N was studied. Experimental results were mathematically described using mass-transfer and microbiological models. The experiments allowed determination of mass-transfer and microbiological parameters separately in a single run. The biomass formation rate under mass transfer limited conditions, which is related to the naphthalene biodegradation rate, was correlated to the dimensionless Reynolds number, indicating increased bioavailability at increased mixing in the reactor liquid. The methodology presented in which mass transfer processes are quantified under sterile conditions followed by a biodegradation experiment can also be adapted to more complex and realistic systems, such as particulate, suspended PAH solids or soils with intrapartically sorbed contaminants when the appropriate mass-transfer equations are incorporated.

Biodegradation, Environmental↗

PubMed1995

Influence of nonionic surfactants on bioavailability and biodegradation of polycyclic aromatic hydrocarbons.

The presence of the synthetic nonionic surfactants Triton X-100, Tergitol NPX, Brij 35, and Igepal CA-720 resulted not only in increased apparent solubilities but also in increased maximal rates of dissolution of crystalline naphthalene and phenanthrene. A model based on the assumption that surfactant micelles are formed and act as a separate phase underestimated the dissolution rates; this led to the conclusion that surfactants present at concentrations higher than the critical micelle concentration affect the dissolution process. This conclusion was confirmed by the results of batch growth experiments, which showed that the rates of biodegradation of naphthalene and phenanthrene in the dissolution-limited growth phase were increased by the addition of surfactant, indicating that the dissolution rates were higher than the rates in the absence of surfactant. In activity and growth experiments, no toxic effects of the surfactants at concentrations up to 10 g liter(sup-1) were observed. Substrate present in the micellar phase was shown to be not readily available for degradation by the microorganisms. This finding has important consequences for the application of (bio)surfactants in biological soil remediation.

Journal Article↗

PubMedDate not supplied

Microbiological aspects of surfactant use for biological soil remediation.

Biodegradation of hydrophobic organic compounds in polluted soil is a process involving interactions among soil particles, pollutants, water, and micro-organisms. Surface-active agents or surfactants are compounds that may affect these interactions, and the use of these compounds may be a means of overcoming the problem of limited bioavailability of hydrophobic organic pollutants in biological soil remediation. The effects of surfactants on the physiology of micro-organisms range from inhibition of growth due to surfactant toxicity to stimulation of growth caused by the use of surfactants as a co-substrate. The most important effect of surfactants on the interactions among soil and pollutant is stimulation of mass transport of the pollutant from the soil to the aqueous phase. This can be caused by three different mechanisms: emulsification of liquid pollutant, micellar solubilisation, and facilitated transport. The importance of these mechanisms with respect to the effect of surfactants on bioavailability is reviewed for hydrophobic organic pollutants present in different physical states. The complexity of the effect of surfactants on pollutant bioavailability is reflected by the results in the literature, which range from stimulation to inhibition of desorption and biodegradation of polluting compounds. No general trends can be found in these results. Therefore, more research is necessary to make the application of surfactants a standard tool in biological soil remediation.

Biodegradation, Environmental↗