Monitoring of the impact of the proliferations of cyanobacteria on the characteristics of Natural Organic Matter in a eutrophic water resource: Comparison between 2012-2013 and 2017-2018.

The natural surface waters are widely impacted by the seasonal blooms of phytoplankton and in water rich in nutrients their developments are controlled by the climate. These proliferations modify the global quality of the water resources and the Algal Organic Matter (AOM) produced by the algae and the cyanobacteria impacts the content and the characteristics of the Natural Organic Matter (NOM). However, none study deals with the sustainable influence of the recurrent seasonal blooms of phytoplankton on the chemical quality of the water resources. The physico-chemical, chemical and biological quality of a water resource and more specifically the content and the characteristics of the NOM were thus in situ monitored in a eutrophic pond in 2017-2018 and compared to the characteristics observed in 2012-2013. The blooms of phytoplankton were more important in 2017-2018 and the increase of both the temperature of the air and the radiance promoted the domination of cyanobacteria. None significant evolution of the content in chlorophyll-a, the concentrations in nutrients and the pH was observed between 2012-2013 and 2017-2018. However, the concentrations in DOC increased, more in summer periods than winter, because of the production of AOM by the algae and the cyanobacteria and the NOM presented more hydrophilic and less aromatic characters. These evolutions of the characteristics of the NOM were more important in 2017-2018 than 2012-2013. The recurrent inputs of AOM every year in summer periods seemed thus to sustainably modify the intrinsic characteristics of the NOM.

Impact of agronomic and organic characteristics of waste composts from Togo on Zea mays L. nutrients contents under water stress.

Drought and soils poverty considerably decreased agriculture yields in Togo. In this context, the use of wastes' composts as organic amendments presents the advantages to increase crops' yields and improve the fertility of soils while valorizing wastes. However, the effects of wastes' composts on the growth of plants highly depend on their quality, specifically on their chemical properties and the organic matter maturity. In this study, three different wastes' composts were prepared by mixing household wastes and food wastes with admixtures as natural phosphate and manure. The composts produced were analyzed according to agronomic parameters before applying a leaching test to specially assess the organic matter maturity by considering its hydrophobic and aromatic characters. Whatever the compost, the contents in organic matter and nutrients were comparable to composts usually commercialized in Togo. Their characteristics depended on their initial chemical composition. The higher the food wastes percentage, the higher the organic matter content and the addition of admixtures considerably increased the percentages in nutrients in the final product. Besides, a slightly acidic pH, a high redox potential and a low aromatic and hydrophobic organic matter were recorded for compost of food wastes unlike household wastes and mixed composts and the highest concentrations in trace metals were quantified in compost of household wastes. Agronomic tests were performed on maize (Zea mays L.) under two water regimes to evaluate the impact of the characteristics of composts on both maize's nutrition and adaptation to water stress. The chemical characteristics of composts and the maturity of organic matter highly impacted the absorption of macronutrients by plants. A slightly acidic pH and a high redox potential improved the transfer of nutrients from soils to plants under normal irrigation conditions. On the contrary, a higher aromaticity of organic matter promoted the absorption of nutrients under water stress. Wastes' composts can thus be relevantly used to improve the nutrition of plants in function of the irrigation conditions.

Valorization of extracted organic matter from municipal solid waste leachate: Application to soils from France and Togo.

Hydrophobic like (HPO*) and transphilic like (TPH*) fractions of organic matter (OM) were extracted from municipal solid waste leachate (MSWL) to assess their opportunity of valorization as organic amendments. Two soils with different carbon organic (Corg) content were studied: a soil from Togo (Corg = 0.3% in top horizon) and a soil from France (Corg = 4.2% in top horizon). HPO* and TPH* fractions were characterized by combining elemental analysis, determination of specific ultra-violet absorbance (SUVA) index and distribution of apparent molecular weight (AMW). Comparison to natural organic matter (NOM) fractions from surface water confirmed high similarities in composition except a lower oxygen percentage explained by the different genesis processes. HPO* and TPH* adsorption tests were conducted under batch experiments on each horizon of both soils to evaluate the impact of OM fractions on the physico-chemical characteristics of soils, to determine the carbon adsorption and to calculate their adsorption capacity. Whatever the soil, Corg adsorption did not correlate with clay content but rather with initial Corg content in the horizon. HPO* fraction was better adsorbed than TPH* fraction. Besides, while Corg adsorption percentages on each horizon of soils were higher for French soil, the adsorption capacities, explained as the ratio of organic carbon mass adsorbed on soils on its initial carbon mass, were 2 to 10 times higher for soil from Togo.

Quantification of microcystins in natural waters by HPLC-UV after a pre-concentration step: validation of the analytical performances and study of the interferences.

A method for the determination of microcystins concentrations (MC-LR, MC-RR, MC-YR) in natural water samples was optimized using High Performance Liquid Chromatography with UV/PDA detection after Solid Phase Extraction. Solid Phase Extraction is needed to clean natural sample and concentrate pollutant. The method was validated by evaluation of specificity and repeatability. Average recoveries in ultra-pure grade water were better than 95% with Relative Standard Deviation values lower than 4%. Matrix interferences, as pH, conductivity and organic matter content, were tested. pH must be fixed between 6 and 8 to avoid under-estimation or over-estimation and conductivity did not interfere with the analytical method. Organic Matter content negatively impacted microcystins quantification unlike organic matter characteristics. It over-estimated the concenration by an average of 19%. Then, the developed method was applied to study the occurrence of microcystins in Pigeard pond (France). These results constitute the first report on the concentration levels and seasonal variations of microcystins in this resource water.

Biochemical methane potential of fractions of organic matter extracted from a municipal solid waste leachate: Impact of their hydrophobic character.

Many data on anaerobic digestion (AD) and co-digestion of municipal solid waste leachate (MSWL) are already available in literature. They mainly deal with its performances to decrease the chemical oxygen demand (COD) of MSWL and no information is given on the impact of the specific characteristics of the dissolved organic matter (DOM) in leachate on these performances. DOM in leachate evolves towards more aromatic and hydrophobic compounds during landfilling with increasing specific ultra-violet absorbance index (SUVA) and hydrophobic character. However, according to the humification stages, this DOM would not present the same aptitude for AD. This research thus focused on (i) optimizing a biochemical methane potential (BMP) test applied to MSWL by using the Taguchi method and (ii) evaluating the impact of the hydrophobic character of the DOM in leachate on the BMP of MSWL to finally define the humification degree more suitable for AD. Hydrophobic-like (HPO∗) and transphilic-like (TPH∗) compounds extracted from leachate by a fractionation protocol were tested because of their high content in MSWL during acetogenesis and methanogenesis steps. After 275days of AD, the content in hydrophobic compounds and the SUVA indexes increased in the digestates. Moreover, even if the biogas and methane productions were not significantly different during the whole tests (4072±350mLgDOC-1 and 2370±95mLgDOC-1 respectively), the volume of biogas produced directly correlated with the TPH∗ fraction content in the initial digestates. On the contrary, the methane percentage in biogas was anti-correlated with the hydrophilic-like compounds content. The hydrophobic-like molecules seem thus not to be directly involved in the methanogenic step, however they promote the increase of the methane percent in the biogas.

Assessing Transformations of Algal Organic Matter in the Long-Term: Impacts of Humification-Like Processes.

Algae and cyanobacteria are important contributors to the natural organic matter (NOM) of eutrophic water resources. The objective of this work is to increase knowledge on the modifications of algal organic matter (AOM) properties in the long term to anticipate blooms footprint in such aquatic environments. The production of AOM from an alga (Euglena gracilis) and a cyanobacteria (Microcystis aeruginosa) was followed up and characterized during the stationary phase and after one year and four months of cultivation, in batch experiments. Specific UV absorbance (SUVA) index, organic matter fractionation according to hydrophobicity and apparent molecular weight were combined to assess the evolution of AOM. A comparison between humic substances (HS) mainly derived from allochthonous origins and AOM characteristics was performed to hypothesize impacts of AOM transformation processes on the water quality of eutrophic water resources. Each AOM fraction underwent a specific evolution pattern, depending on its composition. Impacts of humification-like processes were predominant over release of biopolymers due to cells decay and led to an increase in the hydrophobic compounds part and molecular weights over time. However, the hydrophilic fraction remained the major fraction whatever the growth stage. Organic compounds generated by maturation of these precursors corresponded to large and aliphatic structures.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) coupled to XAD fractionation: Method to algal organic matter characterization.

This work is focused on the development of an analytical procedure for the improvement of the Organic Matter structure characterization, particularly the algal matter. Two fractions of algal organic matter from laboratory cultures of algae (Euglena gracilis) and cyanobacteria (Microcystis aeruginosa) were extracted with XAD resins. The fractions were studied using laser desorption ionization (LDI) and Matrix-Assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF). A comparison with the natural organic matter characteristics from commercial humic acids and fulvic acids extracted from Suwannee River was performed. Results show that algal and natural organic matters have unique quasi-polymeric structures. Significant repeating patterns were identified. Different fractions extracted from organic matter with common origin had common structures. Thus, 44, 114 and 169Da peaks separation for fractions from E. gracilis organic matter and 28, 58 and 100Da for M. aeruginosa ones were clearly observed. Using the developed protocol, a structural scheme and organic matter composition were obtained. The range 600-2000Da contained more architectural composition differences than the range 100-600Da, suggesting that organic matter is composed of an assembly of common small molecules. Associated to specific monomers, particular patterns were common to all samples but assembly and resulting structure were unique for each organic matter. Thus, XAD fractionation coupled to mass spectroscopy allowed determining a specific fingerprint for each organic matter.

Organic matter produced by algae and cyanobacteria: quantitative and qualitative characterization.

This work aims at characterizing organic matter produced by an alga Euglena gracilis and a cyanobacteria Microcystis aeruginosa and assessing the evolution of its characteristics during growth. A culture medium was optimized. The species growth phases were monitored using both visible spectrophotometry and flow cytometry cell counting. Organic matter fractionation according to hydrophobicity and specific UV absorbance (SUVA) index were used to specifically characterize the produced algal organic matter (AOM). The AOM characteristics were both growth phase and species dependent. However, a similar evolution was observed. The hydrophilic fraction (HPI) was the major fraction whatever the growth phases and was almost the only one produced during lag and exponential phases. It represented around 75% of AOM during exponential phase and then decreased when the stationary phase appeared. It represented 46% and 60% of the AOM during late decline phase for the cyanobacteria and the alga respectively. The hydrophobic (HPO) and transphilic (TPH) fractions started to appear from the beginning of the stationary phase with more hydrophobic compounds coming from intracellular organic material of dying cells. HPO and TPH percentages still increased during the decline phase probably because of two additional processes: photo-dissolution and leaching of particulate organic matter from cells fragments. A comparison of AOM during late decline phase and natural organic matter (NOM) from Glane River (France) underlined that AOM was more hydrophilic and presented a lower SUVA for each fractions than NOM. However, the difference between NOM and AOM hydrophobicity narrowed during decline phase.

Assessment of the aerobic preparation and bottom ash addition as pretreatment steps before landfilling: impact on methanogenesis kinetics and leachate parameters.

This work focuses on assessing the impact of two types of waste pretreatment: addition of bottom ashes and aerobic pretreatment on both the onset and kinetics of methanogenesis and the evolution of different parameters in the leachate. It also studies the correlation between methane production and the different parameters measured in the leachate produced. A total of six 68-L pilots were thus used with fresh municipal solid waste (MSW) shredded to a 40-mm size. After 14 months of landfilling, the control has produced less than 10 NLkg(-1)DM, which corresponds to around 7% of its biochemical methane potential (BMP). Nevertheless, on one hand for aerobically pretreated waste, the lag phase before the onset of methanogenesis is significantly reduced to 0.9 month compared to more than 1 year for the control. In addition to that, on average 110 NLkg(-1)DM (90% of the BMP) is produced within around 6.5 months. On the other hand, the waste with added bottom ash shows a slight improvement of the lag phase over the control for one of the duplicate: 6.1 months of lag phase. At this stage, on average of 26 NLkg(-1)DM waste are detected (22% of the BMP) no final conclusion concerning the impact of bottom ashes could be made. The data obtained for the leachate parameters agrees with the observations on methane production. Statistical correlation study shows that the two components of the corrected PCA interpret 76% of the variability of the data: SUVA (specific UV absorbance at 254 nm) and HPI(*) (% of hydrophilic compounds) are identified as interesting parameters for following up the biodegradation in landfill conditions.

Influence of organic matter on arsenic removal by continuous flow electrocoagulation treatment of weakly mineralized waters.

The aim of this study is to evaluate and understand the electrocoagulation/flocculation (ECF) process to remove arsenic from both model and natural waters with low mineral content and to compare its performances to the coagulation/flocculation (CF) process already optimized. Experiments were thus conducted with iron electrodes in the same specific treatment conditions (4≤current density (mAcm(-2))≤33) to study the influence of organic matter on arsenic removal in conditions avoiding the oxidation step usually required to improve As(III) removal. The process performance was evaluated by combining quantification of arsenic residual concentrations and speciation and dissolved organic carbon residual concentrations with zeta potential and turbidity measurements. When compared to CF, ECF presented several disadvantages: (i) lower As(V) removal yield because of the ferrous iron dissolved from the anode and the subsequent negative zeta potential of the colloidal suspension, (ii) higher residual DOC concentrations because of the fractionation of high molecular weight compounds during the treatment leading to compounds less prone to coagulate and (iii) higher residual turbidities because of the charge neutralization mechanisms involved. However, during this process, As(III) was oxidized to As(V) improving considerably its removal whatever the matrix conditions. ECF thus allowed to improve As(III) removal without applying an oxidation step that could potentially lead to the formation of toxic oxidation by-products.

Effect of organic matter on arsenic removal during coagulation/flocculation treatment.

The aim of this study is to evaluate the influence of organic matter on arsenic removal by coagulation/flocculation on both a model water with low mineral content and a natural water sample. Ferric chloride was used as coagulant at concentrations avoiding the preoxidation step usually required to oxidize As(III) and increase its removal. Arsenic removal was accomplished by combining evaluation of arsenic residual concentrations and speciation analysis with zeta potential measurements. A preliminary study evaluated the influence of coagulant dose, coagulation pH, and organic matter on As(III) and As(V) removal. The main conclusions were: (i) As(III) removal depended on coagulant dose and on the number of sites available on hydroxide surfaces rather than on coagulation pH; (ii) As(V) removal depended on the zeta potential of colloidal suspension and was more influenced than As(III) by coagulation pH and the presence of organic matter; (iii) organic matter removal followed As(V) removal. This allowed determination of adsorption as the main mechanism occurring during As(V) and organic matter removal and supposing precipitation/coprecipitation as an important As(III) removal mechanism. Adsorption on preformed ferric hydroxide flocs experiments allowed then confirmation of these hypotheses.