Manual of PEARLNEQ v4

This document describes a PEARLNEQ-PEST combination, which can be used to estimate the parameters for long-term sorption kinetics in the PEARL model on the basis of an incubation experiment for a certain soil and a certain pesticide. The combination provides also the transformation half-life at reference temperature (when long-term sorption kinetics are included in PEARL, the definition of this half-life changes so it has to be recalculate

Anaerobic degradation of methanethiol in a process for Liquefied Petroleum Gas (LPG) biodesulfurization

Due to increasingly stringent environmental legislation car fuels have to be desulfurized to levels below 10 ppm in order to minimize negative effects on the environment as sulfur-containing emissions contribute to acid deposition (‘acid rain’) and to reduce the amount of particulates formed during the burning of the fuel. Moreover, low sulfur specifications are also needed to lengthen the lifetime of car exhaust catalysts. The research presented in this thesis focuses on the biological desulfurization of Liquefied Petrol Gas (LPG). Currently, LPG is mainly desulfurized by physical-chemical methods that absorb volatile sulfur compounds present (mainly hydrogen sulfide and thiols) into a strong caustic solution, whereafter the thiols are partially oxidized to disulfides whilst the dissolved hydrogen sulfide is discharged as a ‘spent sulfidic caustic’. Disadvantages of this physical-chemical method are the relatively high energy and caustic consumption and the production of a hazardous waste stream. As an alternative, a new three-step biotechnological LPG desulfurization technology has been studied, that produces elemental sulfur as an end-product from the bio-conversion of hydrogen sulfide (H2S) and methanethiol (MT). The new process involves: (i) extraction of the sulfur compounds from the LPG phase into a (bi)carbonate-containing solution; (ii) anaerobic degradation of MT to H2S, CO2 and CH4 and (iii) partial oxidation of H2S to elemental sulfur. The formed sulfur particles are removed from the system whilst the sulfur-free alkaline process water is re-used in the extraction process. The sulfur can be used for the production of sulfuric acid and hydrogen sulfide or for agricultural applications. In this research attention is paid to the feasibility of the second process step, i.e. the anaerobic treatment step as the first and third process step are already well described. Anaerobic degradation of MT appeared to be possible with a variety of anaerobic (reactor) sludges and sediments, both under methanogenic and sulfate-reducing conditions. The related compounds dimethyl disulfide and dimethyl sulfide were degraded as well, in contrast to ethanethiol and propanethiol, which were not degraded anaerobically. In the new LPG biodesulfurization process higher thiols are converted to their corresponding oily disulfides that have to be skimmed off from the reactor solution and can be sent for disposal, e.g. to an incinerator. The fifty percent inhibition concentration of MT, ethanethiol and propanethiol for methanogenic activity of anaerobic granular sludge on methanol and acetate was found between 6 and 10 mM (pH 7.2, 30°C). Hydrogen sulfide inhibited anaerobic MT degradation at concentrations below 10 mM, depending on the pH and the source of the inoculum. Dimethyl disulfide inhibited MT degradation already at concentrations below 2 mM. In a lab-scale upflow anaerobic sludge blanket (UASB) reactor that was inoculated with anaerobic granular sludge originating from a full-scale reactor treating paper mill wastewater, MT degradation was possible up to a volumetric loading rate of 17 mmol MT∙L-1∙day-1 (pH 7.0-7.5, 30°C, < 0.03 M total salts). MT degradation with this inoculum was inhibited by sodium concentrations exceeding 0.2 M. Initially, MT-degrading methanogenic archaea related to the genus Methanolobus were enriched in the reactor. Later, they were outcompeted by methanogens belonging to the genus Methanomethylovorans, which were mainly present in small aggregates (10-100 μm) in between larger particles. Estuarine sediment from the Wadden Sea was used to inoculate an anaerobic reactor operated at Na+ concentrations of 0.5 M. The maximum volumetric degradation rate achieved amounted to 37 mmol MT∙L-1∙day-1 at pH 8.2-8.4 and 22 mmol MT∙L-1∙day-1 at pH 8.9-9.1 (30°C). MT degradation at pH 10 was not possible with this inoculum. In activity tests, no inhibition of MT degradation was observed till 0.8 M Na+. Initially, Methanosarcina mazei was the dominant MT-degrading methanogen, but after about 1.5 years of continuous reactor operation, methanogens related to Methanolobus taylorii became dominant, probably due to the pH shift to pH 9.0 in the reactor. In a UASB reactor inoculated with a mixture of estuarine and salt lake sediments from the Soap Lake (USA) and the Kalunda Steppe (Russia) it was possible to degrade MT at pH 10, at a maximum volumetric loading rate of 13 mmol MT∙L-1∙day-1 (30°C, 0.8 M Na+) in the presence of methanol as a co-substrate. The methanogenic archaea responsible for the degradation of MT were related to Methanolobus oregonensis. Thiols that are not degraded in the anaerobic reactor of the novel LPG desulfurization process are directed to the third process step, i.e. the aerobic bioreactor. Our research shows that here MT will react with biologically produced sulfur (both 1-16 mM; pH 8.7 and 10.3; 30-60ºC) to form poly-sulfur compounds, i.e. polysulfide ions and dimethyl polysulfides. The first reaction step is a S8 ring opening by nucleophilic attack to form CH3S9-. The reaction rate depends on the MT and bio-sulfur concentrations, pH and temperature. The activation energy of this reaction was determined to be 70 kJ·mol-1 at pH 8.7 and 16 kJ·mol-1 at pH 10.3. The CH3S9- ion is unstable and leads to shorter-chain sulfur compounds. The main end-products formed are polysulfides (S32-, S42-, S52-), dimethyl polysulfides [(CH3)2S2, (CH3)2S3] and H2S. Also long-chain dimethyl polysulfides [(CH3)2S4-7] are formed in trace amounts (μM level). Excess MT results in complete methylation of the initially formed inorganic polysulfides. An increased molar MT/S ratio results in the formation of relatively more (CH3)2S2 over (CH3)2S3. Flowsheet simulations of the new LPG desulfurization process reveal that for an acceptable degree of desulfurization (i.e. less than 10 ppm in the treated LPG product) the pH in the recycle stream to the extractor column must be higher than 9. This means that the used inocula (estuarine and salt lake sediments) provide good opportunities to be applied in the process

The effect of the runoff size on the pesticide concentration in runoff water and in FOCUS streams simulated by PRZM and TOXSWA

Within the European Union the exposure of aquatic organisms to pesticides is assessed by simulations with the so-called FOCUS Surface Water Scenarios. Runoff plays an important role in these scenarios. As little is known about the effect of runoff size on the exposure, we investigated the effect of runoff size on the concentration in the runoff water and in streams simulated with the PRZM and TOXSWA models for two FOCUS runoff scenarios.For weakly sorbing pesticides (K F,oc -1) the pesticide concentration in the runoff water decreased exponentially with increasing daily runoff size. The runoff size hardly affected the pesticide concentration in the runoff water of strongly sorbing pesticides (K F,oc ≥1000Lkg-1).For weakly sorbing pesticides the concentration in the FOCUS stream reached a maximum at runoff sizes of about 0.3 to 1. mm. The concentration increased rapidly when the runoff size increased from 0 to 0.1. mm and gradually decreased when runoff exceeded 1. mm. For strongly sorbing pesticides the occurrence of the maximum concentration in the stream is clearly less pronounced and lies approximately between 1 and 20. mm runoff. So, this work indicates that preventing small runoff events (e.g. by vegetated buffer strips) reduces exposure concentrations strongly for weakly sorbing pesticides.A simple metamodel was developed for the ratio between the concentrations in the stream and in the runoff water. This model predicted the ratios simulated by TOXSWA very well and it demonstrated that (in addition to runoff size and concentration in runoff) the size of the pesticide-free base flow and pesticide treatment ratio of the catchment determine the stream concentration to a large extent

Reactions between Methanethiol and Biologically Produced Sulfur

Recently, new biotechnological processes have been developed to enable the sustainable removal of organic and inorganic sulfur compounds from liquid and gaseous hydrocarbon streams. In comparison to existing technologies (e.g., caustic scrubbing or iron based redox technologies) far less chemicals are consumed, while reusable elemental sulfur is formed as the main end-product. This research shows that in these processes a number of consecutive reactions occur between methanethiol (MT) from the hydrocarbon stream and the formed biosulfur particles, leading to the formation of (dimethyl) polysulfides. This is an important feature of this family of new bioprocesses as it improves the MT removal efficiency. The reaction kinetics depend on the MT and biosulfur concentration, temperature, and the nature of the biosulfur particles. The first reaction step involves a S(8) ring-opening by nucleophilic attack of MT molecules to form CH(3)S(9)(-). This work shows that CH(3)S(9)(-) reacts to polysulfides (S(3)(2-), S(4)(2-), S(5)(2-)), dimethyl polysulfides [(CH(3))(2)S(2), (CH(3))(2)S(3)], and dissociated H(2)S, while also some longer-chain dimethyl polysulfides [(CH(3))(2)S(4)-(7)] are formed at µM levels. Control experiments using orthorhombic sulfur flower (S(8)) did not reveal these reactions

DROPLET to calculate concentrations at drinking water abstraction points : user manual for evaluation of agricultural use of plant protection products for drinking water production from surface waters in the Netherlands

The user-friendly shell DROPLET, acronym for DRinkwater uit OPpervlaktewater- Landbouwkundig gebruik Evaluatie Tool, assists the Dutch Board for the Authorisation of Plant Protection Products and Biocides (Ctgb) in evaluating whether pesticides may exceed the 0.1 μg/L standard in one of the Dutch surface water abstraction points for drinking water production. It operationalises the methodology developed by a Dutch expert group described in Adriaanse et al (2008). This manual explains how to use (i) SWASH to enter compound properties and application pattern, (ii) to run MACRO to calculate the drainage fluxes, (iii) to enter the deposition according to the Dutch Drift Table in TOXSWA, next (iv) to run TOXSWA to obtain an edge-of-field concentration in the FOCUS D3 ditch and finally (v) to run DROPLET to obtain the concentrations in the nine Dutch abstraction points plus the Bommelerwaard. DROPLET maintains a central database (in addition to the SWASH database) and combines the peak concentration of the FOCUS D3 ditch with intake area and compound specific factors, such as crop areas and compound degradation to calculate concentrations in the abstraction points

Anaerobic methanethiol degradation in upflow anaerobic sludge bed reactors at high salinity (> 0.5 M Na+)

The feasibility of anaerobic methanethiol (MT) degradation at elevated sodium concentrations was investigated in a mesophilic (30°C) lab-scale upflow anaerobic sludge bed (UASB) reactor, inoculated with estuarine sediment originating from the Wadden Sea (The Netherlands). MT was almost completely degraded (>95%) to sulfide, methane and carbon dioxide at volumetric loading rates up to 37 mmol MT·L-1·day-1, 0.5 M sodium (NaCl or NaHCO3) and between pH 7.3 and 8.4. Batch experiments revealed that inhibition of MT degradation started at sodium (both NaCl and NaHCO3) concentrations exceeding 0.8 M. Sulfide inhibited MT degradation already around 3 mM (pH 8.3)