Ibrahim Saadi

Publications of Ibrahim Saadi

• Original and Residual Phytotoxicity of Olive Mill Wastewater Revealed by Fractionations before and after Incubation with Pleurotus ostreatus.

  Authors: Ido Aviani, Michael Raviv, Yitzhak Hadar, Ibrahim Saadi, Yael Laor

  Journal of agricultural and food chemistry. 11/2009;

  Concentrations of dissolved organic carbon (DOC) and total phenols (TP), and the phytotoxicity to cress (Lepidium sativum L.) were determined for three molecular-sized fractions of olive millConcentrations of dissolved organic carbon (DOC) and total phenols (TP), and the phytotoxicity to cress (Lepidium sativum L.) were determined for three molecular-sized fractions of olive mill wastewater (OMW), <1000, 1000-5000, and >5000 Da, before and after incubation with Pleurotus ostreatus. The <1000-Da fraction contained 82% of the total DOC and 48% of the TP, and was the most phytotoxic. Ethyl acetate separation of aqueous and solvent fractions showed that the aqueous fraction contained 93% of the total DOC, 83% of the TP, and was most phytotoxic, indicating low importance of monomeric phenols. Incubation of whole OMW and of the separate size fractions with P. ostreatus mycelia reduced TP by factors of 4.3-5.3, but exerted diverse impact on phytotoxicity; overall, P. ostreatus efficacy in organic load removal and OMW detoxification was limited. Additional size fractionation of the incubated fractions revealed that most residual phytotoxicity was associated with low-molecular weight (MW) compounds originated from the <1000 Da fraction and not with low-MW byproducts from the degradation of higher-MW fractions and that polymerized metabolites were nonphytotoxic. Total phenols should not be used as sole indicators of the successful remediation of OMW.

• Methodological aspects of microcalorimetry used to assess the dynamics of microbial activity during composting.

  Authors: Shlomit Medina, Michael Raviv, Ibrahim Saadi, Yael Laor

  Bioresource technology. 07/2009;

  Isothermal microcalorimetry is a sensitive non-invasive analytical tool that can become useful in research on compost and other biosolids. The aim of the present study was to address severalIsothermal microcalorimetry is a sensitive non-invasive analytical tool that can become useful in research on compost and other biosolids. The aim of the present study was to address several methodological aspects that are critical to the use of microcalorimetry to assess the dynamics of microbial activity in such systems. The results show that: (1) The calorimetric baseline is strongly influenced by the run temperature in the range relevant to composting systems (20-60 degrees C), and is also affected by addition of the water that is required to maintain or optimize microbial activity, presumably because some water evaporates through ampoule gaskets. (2) Amending mature compost with readily available substrates requires additional careful baseline treatment. (3) Sample heterogeneity can be successfully minimized by passing through a 2-mm sieve. Additional size separation can be useful to enable focusing on the more active fractions. (4) Oxygen depletion is a key feature in batch calorimetric analysis; for samples of highly active composts or manure, the total amount of heat released relative to the oxygen available in the ampoule may indicate the co-existence of anaerobic and aerobic metabolic pathways. Finally, practical recommendations for microcalorimetry analyses of pre-mature and mature composts are outlined.

• Land spreading of olive mill wastewater: effects on soil microbial activity and potential phytotoxicity.

  Authors: Ibrahim Saadi, Yael Laor, Michael Raviv, Shlomit Medina

  Chemosphere. 02/2007; 66(1):75-83.

  Extremely high organic load and the toxic nature of olive mill wastewater (OMW) prevent their direct discharge into domestic wastewater treatment systems. In addition to the various treatment schemesExtremely high organic load and the toxic nature of olive mill wastewater (OMW) prevent their direct discharge into domestic wastewater treatment systems. In addition to the various treatment schemes designed for such wastewater, controlled land spreading of untreated OMW has been suggested as an alternative mean of disposal. A field study was conducted between October 2004 and September 2005 to assess possible effects of OMW on soil microbial activity and potential phytotoxicity. The experiment was carried out in an organic orchard located on a Vertisol-type soil (Jezre'el Valley, Israel) and included two application levels of OMW (36 and 72m(3)ha(-1)). Total microbial counts, and to less extent the hydrolytic activity and soil respiration were increased following the high OMW application level. A bench-scale lab experiment showed that the rate of OMW mineralization was mainly dependent on the general status of soil activity and was not related to previous acclimatization of the soil microflora to OMW. Soil phytotoxicity (% germination and root elongation) was assessed in soil extracts of samples collected before and after each OMW application, using germinating cress (Lepidium sativum L.) seeds. We found direct short-term effect of OMW application on soil phytotoxicity. However, the soil was partly or completely recovered between successive applications. No further phytotoxicity was observed in treated soils as compared with control soil, 3 months after OMW application. Such short-term phytotoxicity was not in correlation with measured EC and total polyphenols in the soil extracts. Overall, the results of this study further support a safe controlled OMW spreading on lands that are not associated with sensitive aquifers.

• Fluorescence-based evidence for adsorptive binding of pyrene to effluent dissolved organic matter.

  Authors: Mikhail Borisover, Yael Laor, Nadezhda Bukhanovsky, Ibrahim Saadi

  Chemosphere. 01/2007; 65(11):1925-34.

  Using fluorescence intensity measurements, pyrene interactions with different types of effluent dissolved organic matter (EDOM) originated from treated municipal wastewater are examined. MultipleUsing fluorescence intensity measurements, pyrene interactions with different types of effluent dissolved organic matter (EDOM) originated from treated municipal wastewater are examined. Multiple observations show that fluorescence intensity of pyrene-EDOM solutions is non-linearly related to pyrene concentration, with distinct concave-up dependence. Testing the effect of pyrene concentration on fluorescence intensity of pyrene-EDOM solutions provides a tool to examine whether binding of an organic compound to EDOM follows linear or non-linear isotherm. Possible coupling between static and dynamic quenching effects was addressed while analyzing fluorescence data. Limited number of EDOM binding sites results in a non-linear binding isotherm such that the concept of pyrene "partitioning" between aqueous phase and "bulky" EDOM organic phase is hardly relevant. Maximal EDOM capacity for pyrene binding is estimated approximately as 0.1% ww(-1). Examination of the differences between the total fluorescence intensity of pyrene-EDOM solution and the fluorescence intensities of separated constituents (pyrene and EDOM) was used to illustrate the accumulation of pyrene-EDOM complexes and saturation of some EDOM binding sites. Strong interactions between pyrene and EDOM binding sites may result in pyrene distribution coefficients differing at least by a factor 3.5-7 at varying pyrene concentrations.

• Monitoring of effluent DOM biodegradation using fluorescence, UV and DOC measurements.

  Authors: Ibrahim Saadi, Mikhail Borisover, Robert Armon, Yael Laor

  Chemosphere. 05/2006; 63(3):530-9.

  The potential of effluent DOM to undergo microbial degradation was assessed in batch experiments. Effluent samples from Haifa wastewater treatment plant and Qishon reservoir (Greater Haifa wastewaterThe potential of effluent DOM to undergo microbial degradation was assessed in batch experiments. Effluent samples from Haifa wastewater treatment plant and Qishon reservoir (Greater Haifa wastewater reclamation complex, Israel) were incubated either with effluent or soil microorganisms for a period of 2-4 months and were characterized by dissolved organic carbon contents (DOC), UV(254) absorbance and by fluorescence excitation-emission matrices. Three main fluorescence peaks were identified that can be attributed to humic/fulvic components and "protein-like" structures. During biodegradation, specific fluorescences (F/DOC) of the three peaks were increased at various extents, suggesting selective degradation of non-fluorescing constituents. In some cases increase in the effluent fluorescence (F) was observed thus proposing (i) the formation of new fluorescing material associated with DOM biodegradation and/or (ii) degradation of certain organic components capable of quenching DOM fluorescence. Based on the ratio between fluorescence intensity and UV(254), different biodegradation dynamics for fluorescent DOM constituents as compared with other UV-absorbing molecules was delineated. Overall, about 50% of the total DOM was found to be readily degradable such that residual resistant DOC levels were between 8 and 10 mg l(-1). Enhanced levels of residual DOM in effluent-irrigated soils may contribute to the DOM pool capable of carrying pollutants to groundwater.

• Methodological aspects of microcalorimetry used to assess the dynamics of microbial activity during composting

  Authors: Shlomit Medina, Michael Raviv, Ibrahim Saadi, Yael Laor

  Bioresource Technology.

  Isothermal microcalorimetry is a sensitive non-invasive analytical tool that can become useful in research on compost and other biosolids. The aim of the present study was to address severalIsothermal microcalorimetry is a sensitive non-invasive analytical tool that can become useful in research on compost and other biosolids. The aim of the present study was to address several methodological aspects that are critical to the use of microcalorimetry to assess the dynamics of microbial activity in such systems. The results show that: (1) The calorimetric baseline is strongly influenced by the run temperature in the range relevant to composting systems (20–60 °C), and is also affected by addition of the water that is required to maintain or optimize microbial activity, presumably because some water evaporates through ampoule gaskets. (2) Amending mature compost with readily available substrates requires additional careful baseline treatment. (3) Sample heterogeneity can be successfully minimized by passing through a 2-mm sieve. Additional size separation can be useful to enable focusing on the more active fractions. (4) Oxygen depletion is a key feature in batch calorimetric analysis; for samples of highly active composts or manure, the total amount of heat released relative to the oxygen available in the ampoule may indicate the co-existence of anaerobic and aerobic metabolic pathways. Finally, practical recommendations for microcalorimetry analyses of pre-mature and mature composts are outlined.

• Compost suppressiveness against Fusarium oxysporum was not reduced after one-year storage under various moisture and temperature conditions

  Authors: Ibrahim Saadi, Yael Laor, Shlomit Medina, Arkady Krassnovsky, Michael Raviv

  Soil Biology and Biochemistry.

  The effect of storage conditions on compost suppressiveness against fusarium wilt of melon, caused by Fusarium oxysporum f. sp. melonis (FOM) was studied in relation to the dynamics of compostThe effect of storage conditions on compost suppressiveness against fusarium wilt of melon, caused by Fusarium oxysporum f. sp. melonis (FOM) was studied in relation to the dynamics of compost microbial activity and biodegradability. For this purpose, mature suppressive compost, prepared from tomato plants and separated cow manure, was divided into four portions and stored for one year under cool/warm (12 or 28 °C) or dry/wet (15–35 or 55–65% moisture content) conditions, in four different combinations: cool-dry, warm-dry, cool-wet and warm-wet. All composts retained and even enhanced their suppressive capacity during storage, with no significant differences among them by the end of the storage period. However, significant differences were found in the dynamics of some of the measured chemical and microbial properties. The microbial activity of composts stored under wet conditions was higher than that of those stored under dry condition, which resulted in a substantial decrease in dissolved organic matter content (expressed as dissolved organic carbon; DOC) and increase in its recalcitrance to biological degradation, decrease in basal heat emission, slower response to added glucose or citric acid, and higher NO3 concentration, indicating increased nitrification under wet conditions. The DOC significantly correlated with several microbial properties as well as with compost suppressiveness of fusarium wilt of melon seedlings, and may be regarded as a most suitable general index for compost maturity. A best-subset multiple linear regression analysis revealed that the three best predictors, namely dissolved organic carbon (DOC), basal heat, and mesophilic bacterial counts, could explain as much as 83% of the total variance in compost suppressiveness. The generally agreed association between compost maturity and suppressiveness was verified in this case. It appears that compost microbial populations might compete and interfere with the saprophytic stage of FOM conidia, between germination and host invasion. In conclusion, it was demonstrated that compost suppressiveness against fusarium wilt of melon can be maintained for at least one year under a wide range of storage conditions, without any loss of suppressive capacity. This fact has positive logistical implications for the use of suppressive composts against FOM.

• Fluorescence-based evidence for adsorptive binding of pyrene to effluent dissolved organic matter

  Authors: Mikhail Borisover, Yael Laor, Nadezhda Bukhanovsky, Ibrahim Saadi

  Chemosphere.

  Using fluorescence intensity measurements, pyrene interactions with different types of effluent dissolved organic matter (EDOM) originated from treated municipal wastewater are examined. MultipleUsing fluorescence intensity measurements, pyrene interactions with different types of effluent dissolved organic matter (EDOM) originated from treated municipal wastewater are examined. Multiple observations show that fluorescence intensity of pyrene–EDOM solutions is non-linearly related to pyrene concentration, with distinct concave-up dependence. Testing the effect of pyrene concentration on fluorescence intensity of pyrene–EDOM solutions provides a tool to examine whether binding of an organic compound to EDOM follows linear or non-linear isotherm. Possible coupling between static and dynamic quenching effects was addressed while analyzing fluorescence data. Limited number of EDOM binding sites results in a non-linear binding isotherm such that the concept of pyrene “partitioning” between aqueous phase and “bulky” EDOM organic phase is hardly relevant. Maximal EDOM capacity for pyrene binding is estimated approximately as 0.1% w w−1. Examination of the differences between the total fluorescence intensity of pyrene–EDOM solution and the fluorescence intensities of separated constituents (pyrene and EDOM) was used to illustrate the accumulation of pyrene–EDOM complexes and saturation of some EDOM binding sites. Strong interactions between pyrene and EDOM binding sites may result in pyrene distribution coefficients differing at least by a factor 3.5–7 at varying pyrene concentrations.