Photoreactivity of humic substances: relationship between fluorescence and singlet oxygen production

Humic substances are natural compounds abundantly present in the environment. They play a significant role in the natural attenuation of pollution in surface water due to their capacity to generate reactive species upon solar light excitation. Finding physico chemical parameters related to this property would be of a great help in the prediction studies of the organic pollutants fate. In this work, we investigated relationships between the ability of the humic substances to produce singlet oxygen and their fluorescence properties. For this, a series of sixteen humic acids, fulvic acids, and water-extractable organic matter from soils were studied. The steady-state singlet oxygen concentrations in the irradiated humic substances solutions were measured by monitoring the loss of furfuryl alcohol added as a singlet oxygen scavenger. The emission spectra of the sixteen samples were also recorded. Values of the steady-state singlet oxygen concentrations and the emission intensities showed significant variations among the humic samples and a parallel increase. Thus, here we demonstrate that the rate of singlet oxygen production and the emission intensity of the humic samples are correlated, the best correlation being obtained for emission wavelengths between 500 and 580 nm. This correlation which was never reported until now can be used to estimate the singlet oxygen-production capacity of the humic substances based on their fluorescent properties.     

The evaluation of stability during the composting of different starting materials: comparison of chemical and biological parameters

Three blends formed by: (i) food processing waste (CP(FP)), (ii) waste water sewage sludge (CP(WW)), and (iii) their mixture (CP(FP+WW)), blended with tree pruning as bulking agent, were composted over 3 months. During composting the blends were monitored for the main physical-chemical characteristics: temperature, oxygen saturation level (O(2)%), pH, total and volatile solids, total organic carbon, and organic nitrogen (N(org)). In addition to the main parameters, the dissolved organic carbon (DOC), the inorganic nitrogen and the Oxygen Uptake Rate (OUR) were monitored. All the mixtures easily reached a peak temperature around 70°C, related to the lowest O(2)%. After 90 d, CP(FP), CP(FP+WW), and CP(WW) showed an organic matter mineralization of 43%, 35% and 33%, respectively; CP(FP) fitted an exponential model while both CP(FP+WW), and CP(WW) fitted a logistic model. During composting an OUR reduction of 79%, 78% and 73% was registered in CP(FP), CP(FP+WW), and CP(WW), respectively; the OUR successfully fitted the adopted exponential model and well reflected the stabilization process in time. The N(org) recovery at the end of the process was positive only in CP(WW) (11.6%). The DOC significantly decreased during the composting process but did not successfully fit any model. The mineral nitrogen did not follow the typical pattern with NH(4)(+) disappearance and NO(3)(-) accumulation. Strong NO(3)(-) losses were evident in all blends, while NH(4)(+) accumulations were detectable only in CP(FP), and CP(FP+WW). The NH(4)(+)/NO(3)(-) ratio did not satisfactorily reflect the composting process over time. The comparison of the first order (exponential) and logistic (sigmoidal) models applied to the OUR and OM course highlights the role of mineral nitrogen as limiting factor during composting of the more stabilized sludge.     

A multivariate approach to the study of the composting process by means of analytical electrofocusing

Three blends formed by: agro-industrial waste, wastewater sewage sludge, and their mixture, blended with tree pruning as bulking agent, were composted over a 3-month period. During the composting process the blends were monitored for the main physical and chemical characteristics. Electrofocusing (EF) was carried out on the extracted organic matter. The EF profiles were analyzed by principal component analysis (PCA) in order to assess the suitability of EF to evaluate the stabilisation level during the composting process. Throughout the process, the blends showed a general shifting of focused bands, from low to high pH, even though the compost origin affected the EF profiles. If the EF profile is analyzed by dividing it into pH regions, the interpretation of the results can be affected by the origin of compost. A good clustering of compost samples depending on the process time was obtained by analyzing the whole profile by PCA. Analysis of EF results with PCA represents a useful analytical technique to study the evolution and the stabilisation of composted organic matter.     

Conservation and development in Amazonian extractive reserves: the case of Alto Juruá

Extractive reserves constitute an innovative approach to match conservation and development objectives, which were originally envisaged as part of a land struggle by forest dwellers in Brazil. In spite of the idea's popularity and the attempts to apply the concept to different tropical regions, there has been little analysis of the combined conservation and development performance of extractive reserve programs. We present a detailed analysis of deforestation and demographic and socioeconomic changes in Alto Juruá, the first extractive reserve created in Brazil in 1990. Forest cover has remained fairly stable. Population has declined slightly, with some internal displacements. The cash economy base has shifted from the original rubber production to a diversified portfolio of agriculture and livestock, and there has been a dramatic rise in nonagrarian income. We conclude that the Reserve represents a very dynamic setting with positive conservation and development outcomes during its first decade.     

The seasonal distribution of dissolved inorganic nitrogen and phosphorous in the lagoon of Venice: a numerical analysis

This paper investigates the seasonal evolution of the spatial distributions of dissolved inorganic nitrogen and phosphorus, in relation to the estimation of the N and P loads, which were obtained in the framework of the DRAIN project. Such investigation is carried out by using a 3D reaction-diffusion model which has been calibrated against salinity data and then used for obtaining the most likely scenario of the spatial and seasonal distribution of DIN and DIP. The consequences of different management policies are also discussed, in relation to the current Italian legislation, which sets quality standards for both DIN and DIP in the lagoon of Venice.     

The Extended Kalman Filter (EKF) as a tool for the assimilation of high frequency water quality data

The Extended Kalman Filter (EKF) was applied to the analysis of high frequency field measurements of dissolved oxygen (DO), water temperature, salinity, collected by multiparametric sensors in the lagoon of Venice. This paper focuses on the practical aspects of the implementation of the EKF as a data assimilation technique and does not deal with the problems associated with the identification of the model. In this regard, the EKF has proved to be a useful tool for the updating of the estimates of the parameters of a simple DO-chlorophyll model, which can be used for linking the high frequency data to meteorological forcings, such as solar radiation and wind, and to other low frequency measurements of water quality parameters, such as the concentrations of Chlorophyll a and nutrients. The model can subsequently be used as a tool for checking the consistency of all this data, and may also be employed for controlling the quality of the data collected by the multiparametric sensors.     

Rates of production of hydroxyl radicals and singlet oxygen from irradiated compost

The use of organic matter from compost to promote the catalytic photodegradation of micropollutants by solar light appears to be environmentally promising. However, quantitative evaluation of the photodegradation potential of the compost is needed. Our goal was to measure the formation rate of hydroxyl radicals and singlet oxygen, two strongly oxidant species, from irradiated compost organic matter. These two reactive species were photogenerated in all of our extracts regardless of the origin of the compost or the extraction procedure; however, their formation rates increased with composting time. Two herbicides and a fungicide were successfully photodegraded when irradiated with simulated or natural solar light in the presence of the compost organic matter or compost suspensions. For reasons of simplification and ease, the use of the latter is recommended in practice.     

Humic-like substances extracted from composts can promote the photodegradation of Irgarol 1051 in solar light

Humic-like substances (HLS) were extracted from a mixture of sewage sludges and trimmings (70-30%, w/w) after different times of composting (0, 70 days and 130 days). HLS were analyzed by elemental analysis, UV-visible and fluorescence spectroscopy and also tested for their ability to photosensitize the degradation of Irgarol. The rate of Irgarol photodegradation in artificial solar light was found to be 2.5- to 4.3-fold higher in the presence of HLS than in buffered Milli-Q water. These results were confirmed by experiments in solar light that evidenced the photodegrading properties of HLS in a more striking way. Using 2-propanol as hydroxyl radical scavenger, we could show that hydroxyl radicals contributed to the photosensitized Irgarol degradation for about 25%. The photodegrading activity of HLS, their absorbance and their emissive properties were all found to increase between 0 and 70 days of composting and to remain quite constant between 70 and 130 days. The degree of humification varied in the same way, linking all these properties to the humification process.