Lead removal from aqueous solutions by olive mill wastes derived biochar: Batch experiments and geochemical modelling.

In this study, lead removal from aqueous solutions using biochar derived from olive mill solid and liquid wastes has been investigated by applying batch experiments and geochemical modelling. The batch adsorption experiments included the assessment of several key parameters such as the contact time (kinetic), initial concentration (isotherm), pH, adsorbent dose, and the presence of competitive cations, whilst the geochemical modelling focused on the involved adsorption mechanisms using the PHREEQC code. The kinetic studies showed that lead adsorption is a relatively fast process, where intraparticle diffusion is the rate-limiting step. Biochar dose, solution pH and the presence of competitive ions significantly affected the Pb adsorption effectiveness by the biochar. Especially the higher Pb removal percentages were observed in mono-elemental solutions with high biochar dose at mildly acidic solution pH values. The maximum Pb adsorption capacity of biochar was estimated as 40.8 mg g-1 which is higher than various biochars derived from sludge, lignocellulosic and animal biomasses. On the other hand, the geochemical modelling employing the PHREEQC code showed that ion exchange and Pb precipitation are the main reactions controlling its removal from aqueous solutions, whilst surface complexation is insignificant, mainly due to the low surface functional groups on the used biochar.

Olive mill wastewater: From a pollutant to green fuels, agricultural and water source and bio-fertilizer - Hydrothermal carbonization.

Hydrothermal carbonization (HTC) is considered as a promising technique for wastes conversion into carbon rich materials for various energetic, environmental and agricultural applications. In this work, the HTC of olive mill wastewater (OMWW) was investigated at different temperatures (180-220 °C) and both, the solid (i.e., hydrochars) and the final process liquid derived from the thermal conversion process were deeply analyzed. Results showed that the solid yield was affected by the temperature, i.e., decrease from 57% to 25% for temperatures of 180 °C and 220 °C, respectively. Furthermore, the hydrochars presented an increasing fixed carbon percentage with the increase of the carbonization temperature, suggesting that decarboxylation is the main reaction driving the HTC process. The decrease in the O/C ratio promoted an increase of the high heating value (HHV) by 32% for hydrochar prepared at 220 °C. The process liquids were sampled and their organic contents were analyzed using GC-MS technique. Acids, alcohols, phenols and sugar derivatives were detected and their concentrations varied with carbonization temperatures. The assessment of the physico-chemical properties of the generated HTC by-products suggested the possible application of the hydrochars for energetic insights while the liquid fraction could be practical for in agricultural field.

A modelling approach to assess the environmental/radiological impact of C-14 release from radioactive waste repositories.

Assessments of the environmental impact of C-14 disposal often assume that C-14 is converted into gases that are able to migrate to the surface, where they pose a radiological risk. However, uncertainties, associated with the long-term release of C-14 from graphite and the evolution in the post-closure environment of a geological disposal facility (GDF), exist. In this paper, an integrated modelling framework has been developed to investigate these uncertainties. The modelling framework consists of a biogeochemical near field model which interfaces with a geosphere/biosphere model and it is verified by comparing the results to those obtained from other models. A sensitivity analysis discloses that a faster mid chain scission rate of stopped cellulose about four orders of magnitude assesses a twice higher effective dose. In another scenario, which is related to the control of microbial activity by pH and the availability of carbon dioxide to microbes, the effective dose is two orders of magnitude higher compared with a reference scenario. This modelling work illustrates also the importance of far field parameters, such as the rock permeability and the release area of gas pathway, to the assessment of effective dose.

Anoxic Biodegradation of Isosaccharinic Acids at Alkaline pH by Natural Microbial Communities.

One design concept for the long-term management of the UK's intermediate level radioactive wastes (ILW) is disposal to a cementitious geological disposal facility (GDF). Under the alkaline (10.013.0) anoxic conditions expected within a GDF, cellulosic wastes will undergo chemical hydrolysis. The resulting cellulose degradation products (CDP) are dominated by α- and ß-isosaccharinic acids (ISA), which present an organic carbon source that may enable subsequent microbial colonisation of a GDF. Microcosms established from neutral, near-surface sediments demonstrated complete ISA degradation under methanogenic conditions up to pH 10.0. Degradation decreased as pH increased, with ß-ISA fermentation more heavily influenced than α-ISA. This reduction in degradation rate was accompanied by a shift in microbial population away from organisms related to Clostridium sporosphaeroides to a more diverse Clostridial community. The increase in pH to 10.0 saw an increase in detection of Alcaligenes aquatilis and a dominance of hydrogenotrophic methanogens within the Archaeal population. Methane was generated up to pH 10.0 with acetate accumulation at higher pH values reflecting a reduced detection of acetoclastic methanogens. An increase in pH to 11.0 resulted in the accumulation of ISA, the absence of methanogenesis and the loss of biomass from the system. This study is the first to demonstrate methanogenesis from ISA by near surface microbial communities not previously exposed to these compounds up to and including pH 10.0.

Ecosystem approach to water resources management using the MIKE 11 modeling system in the Strymonas River and Lake Kerkini.

The ability to apply an ecosystem approach to the Strymonas River catchment was investigated using the MIKE 11 modeling system for the simulation of surface water. The Strymonas River catchment is shared mainly between Bulgaria and Greece. The river feeds the artificial Lake Kerkini, a significant wetland ecosystem, and further downstream it outflows to the Gulf of Strymonikos, whose estuary ecosystem is very important for fisheries, biodiversity and tourism. MIKE 11-NAM was used for the simulation of rainfall-runoff process in the Strymonas River catchment and MIKE 11-HD was used to simulate the unsteady flow of the Strymonas River and to apply management rules based on the water level of Lake Kerkini. Two water level management scenarios were investigated. The first scenario referred to the mean daily-observed water level of Lake Kerkini between 1986 and 2006, and the second scenario represented adjustments necessary to fulfill the lake's ecosystem requirements. Under the current water level management practices (Scenario 1), the Strymonas River-Lake Kerkini system has enough water to fulfill its Irrigation Water Requirements (IWR) in normal and wet years while a slight deficit is appeared in dry years; however, both Lake Kerkini and the Strymonas River estuary ecosystems are subject to pressures, since reduction of the forest area has been recorded. Applying the ecosystem approach (Scenario 2), the protection of the riparian forest of Lake Kerkini is achieved while in normal and wet years the IWR are fulfilled and the deficit of the IWR is increased in dry years. Compared to Scenario 1, the pressure of the Strymonas River estuary ecosystem is slightly increased.