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Summarization: This study focused on the valorization of different types of waste biomass through biochar production at two pyrolysis temperatures (400 and 600°C). The different feedstocks being used included three materials of municipal origin, specifically two types of sewage sludge and the organic fraction of municipal solid waste, and three materials of agroindustrial origin, specifically grape pomace, rice husks and exhausted olive pomace. The scope of the research was to characterize the resulting materials, in order to evaluate their possible uses in agronomic and environmental applications. Biochar characterization included the determination of several physical and chemical parameters, while germination assays were also carried out. Under the investigated conditions, both pyrolysis temperature and feedstock type appeared to significantly affect biochar characteristics, leading to the production of versatile materials, with many different possible uses. Specifically, results implied that biochars of both municipal and agroindustrial origin have the potential to effectively be used in applications including the improvement of soil characteristics, carbon sequestration, the removal of organic and inorganic contaminants from aqueous media, and the remediation of contaminated soil, with the degree of suitability of each material to each specific use being estimated to differ depending on its particular characteristics. For this reason, with these characteristics in mind, before proceeding to larger scale applications a cautious selection of materials should be conducted. Παρουσιάστηκε στο: Detritus

In the last years, global focus has been directing towards the circular economy model. In this framework materials that had so far been regarded as waste, are now considered as valuable resources for both energy and added-value materials recovery. In this context, more and more valorization methods and technologies are being developed for waste valorization, with biomass materials of municipal and agroindustrial origin constituting ideal options, due to both composition and availability.Biochar generation from waste biomass is a method with high potential for effectively valorizing such residual resources, by providing not only a waste management option, but also multiple agronomic and environmental benefits. In fact, biochar materials are characterized by high versatility as far as their applications are concerned. Due to their wide variety of properties, biochars can be used in various applications, such the use as an adsorbent for contaminant removal from water or wastewater, or the use as an amendment for improving soil characteristics and remediating contaminated sites.In the present study, six different waste biomass feedstocks, specifically three of municipal origin, namely two types of sewage sludge and the organic fraction of municipal solid waste, and three of agroindustrial origin, namely grape pomace, rice husks and exhausted olive pomace, were used to generate biochar through pyrolysis at two different temperatures, i.e. 400 and 600 °C. The resulting carbonaceous materials were then characterized through a series of analyses. Based on both physical and chemical biochar properties, it was able to evaluate their potential use in different applications, for agronomic or environmental purposes.

This study focuses on the use of microwave heating as a pretreatment for lignocellulosic agroindustrial waste prior to anaerobic digestion for methane production. Four materials were investigated, namely winery waste, cotton gin waste, olive pomace and juice industry waste. Results showed different effects of microwave heating on the solubilization and methane potential of the studied substrates. The variations were attributed to the specific characteristics of each substrate combined with the pretreatment conditions. In the cases of winery waste and juice industry waste, microwave pretreatment resulted in relatively high solubilization levels for both materials. Nevertheless, the portion retained on the solid fraction after pretreatment was larger and less biodegradable for winery waste, while for juice industry waste it was smaller but with a higher biodegradability degree. As far as cotton gin waste and olive pomace are concerned, microwave pretreatment seems not to cause high organic matter solubilization, while it most likely induced structural changes in the materials matrices. This resulted in methane production levels that indicate the presence of recalcitrant or/and inhibitory compounds on the pretreated samples. Moreover, the increased moisture and hydrogen contents for pretreated samples suggested that additional changes were made to the substrates. Ultimately, although microwave pretreatment did not improve methane production, results indicated that at temperatures between 125 and 150 °C, such a process could eventually provide samples which are more suitable for methane production. Moreover, an improved energy balance could be obtained by combining these temperatures with lower exposure times and higher solid to liquid ratios.

Summarization: The scope of this study is to evaluate the use of laboratory-scale landfill-bioreactors, operated consecutively under anaerobic and aerobic conditions, for the combined treatment of the organic fraction of municipal solid waste (OFMSW) with two different co-substrates of lignocellulosic nature, namely green waste (GW) and dried olive pomace (DOP). According to the results such a system would represent a promising option for eventual larger scale applications. Similar variation patterns among bioreactors indicate a relatively defined sequence of processes. Initially operating the systems under anaerobic conditions would allow energetic exploitation of the substrates, while the implementation of a leachate treatment system ultimately aiming at nutrient recovery, especially during the anaerobic phase, could be a profitable option for the whole system, due to the high organic load that characterizes this effluent. In order to improve the overall effectiveness of such a system, measures towards enhancing methane contents of produced biogas, such as substrate pretreatment, should be investigated. Moreover, the subsequent aerobic phase should have the goal of stabilizing the residual materials and finally obtain an end material eventually suitable for other purposes. Presented on: Waste Management

This study focuses on evaluating the influence of different substrate to inoculum ratios (SIR) and inoculum types on the methane potential of four solid agroindustrial waste, namely winery waste (WW), cotton gin waste (CGW), olive pomace (OP) and juice industry waste (JW). To this purpose, Biochemical Methane Potential (BMP) assays were conducted, in which four SIR, i.e. 0.25, 0.5, 1 and 2 (on a volatile solids (VS) basis) were tested and three different inocula, namely anaerobic sludge, landfill leachate and thickened anaerobic sludge, were compared. All four materials were proved viable substrates for anaerobic digestion. Furthermore, anaerobic sludge was found the most adequate inoculum among tested samples, and due to its high availability it may be considered a manageable choice in real-scale applications. Contrarily, using landfill leachate and thickened anaerobic sludge for the same purpose showed lower efficiencies. The optimum SIR for determining the methane potential of the studied substrates were of 0.5 for WW and JW, yielding 446.23 and 445.97 NmLCH4/gVSsubstrate, respectively, and of 0.25 for CGW and OP, yielding 267.96 and 258.65 NmLCH4/gVSsubstrate, respectively. Higher SIR delayed methane production, indicating process inhibition. Experimental methane potentials were lower than theoretical, suggesting that eventual pretreatments prior to anaerobic digestion might be worth investigating. The association of different SIR with 2- and 3-parameter kinetic models manifested the complexity of the anaerobic digestion of the studied substrates. Moreover, a different modeling approach, assuming the occurrence of multiple-stages, appeared to be more suitable for describing the behavior of the experimental data.

This study aims to evaluate dried olive pomace derived biochar as a potential soil amendment for cadmium and nickel immobilization. Biochar was produced through pyrolysis under oxygen-limited conditions, at 400 °C (BC400) and 700 °C (BC700). Batch sorption/desorption experiments were conducted, investigating different agitation times (30–1440 min), initial metal concentration in the solution (100–3000 μM) and desorption pH (2–7). Results showed that by amending soil with biochar at increasing rates, enhanced sorption and decreased desorption of both metals were observed. In fact, biochar addition resulted in increased soil pH, possibly enhancing not only metal adsorption on soil surfaces (minerals or oxides), but also metal precipitation. Modeling results concerning sorption equilibrium corroborated this statement. Amended samples showed higher metal retention even at low pH values. Both biochars enhanced the ability of soil to immobilize cadmium and nickel, however in most cases BC700 was proven to be more efficient.

The present study aimed at investigating the anaerobic digestion of four agroindustrial waste, namely cotton gin waste, winery waste, olive pomace and juice industry waste, in semi-continuous mode, conducting mono-digestion and co-digestion assays, using an artificial organic fraction sample as co-substrate. These assays were divided into two groups, in which different conditions were applied. Group I investigated the variation in two operational parameters, i.e. the organic loading rate (OLR) and the hydraulic retention time (HRT), while in Group II, the assays were fed with different substrates in a sequential order. Results showed more elevated specific methane yields for co-digestion assays compared with mono-digestion assays. Maximum yields were achieved at an OLR of 1.0gVS/(L·d) and a HRT reduced to half of the initial. Further reduction of the HRT coupled to an increase of the OLR generally caused a significant decrease of specific methane yields, as well as one case of severe overloading, i.e. the mono-digestion of juice industry waste, which resulted in instability and ultimately system failure. Sequential feeding with different substrates led to a more equilibrated operation, especially for co-digestion systems, with higher specific methane yields being observed during the phases corresponding to winery waste and juice industry waste substrates. Overall more positive results were obtained in the cases in which the latter substrates were fed to the reactors at process startup.

Summarization: The objective of the present study is to evaluate the use of animal by-products (ABP) as substrates for anaerobic digestion, aiming at methane production. Specifically, four ABP of Category 2 and 3, namely (i) stomach and rumen, (ii) stomach contents, (iii) breasts and reproductive organs and (iv) bladders and intestines with their contents, were selected. The methane potential of each ABP was initially determined, while the feasibility of anaerobic co-digestion of ABP with two agroindustrial waste, i.e. orange peels and olive leaves was also studied. To this purpose, Biochemical Methane Potential (BMP), as well as semi-continuous assays were respectively conducted. In the latter, the effect of the variation in the organic loading rate (OLR) on methane production was investigated. Results obtained from BMP assays showed that the samples containing breasts and reproductive organs, bladders and intestine, and stomach and rumen, had higher methane potentials of 815, 787 and 759 mLCH4,STP/gVS, respectively. Moreover, according to the results of the semi-continuous assays, maximum methane yields between 253 and 727 mLCH4/gVSfed were obtained at an OLR of 0.8 gVS/L/d. The only case in which methanogenesis inhibition phenomena, due to increased ammonia concentrations, were observed, was the assay being fed with a mixture of breasts and reproductive organs and orange peels, at the highest OLR. This inhibition phenomenon was attributed to an inappropriate C/N ratio. Παρουσιάστηκε στο: Waste Management

Summarization: The present study evaluates the influence of alkaline (NaOH) pretreatment on anaerobic digestion of olive pomace. Batch hydrolysis experiments with different NaOH dosages, process durations and temperatures were conducted, in which the variation of olive pomace solubilization in the liquid phase was investigated. The effect of pretreatment on anaerobic digestion was studied through biochemical methane potential assays. The results demonstrated the effectiveness of the NaOH pretreatment in improving olive pomace solubilization as well as its biodegradability. Maximum specific methane yields were achieved at different NaOH dosages depending on the pretreatment temperature. Consequently, it was concluded that the two operating parameters of the pretreatment stage (NaOH dosage and temperature) may exert a joint effect on substrate biodegradability and methane yields. The highest methane yield (242 NmL CH4/gVS) was obtained for the material pretreated at 90 °C, at a dosage of 1 mmol/gVS (4% of VS). Presented on: Waste Management

Summarization: In this study, the adsorption of Cu(II) from aqueous solutions by agricultural by-products, such as rice husks, olive pomace and orange waste, as well as compost, was evaluated. The aim was to obtain sorbent materials (biochars) through hydrothermal treatment (300 °C) and pyrolysis (300 °C and 600 °C). The effect of adsorbent dose, pH, contact time and initial Cu(II) concentration in batch-mode experiments was investigated. The optimum Cu(II) adsorption conditions was found to occur at 5-12 g/L adsorbent dose, initial pH 5-6, and reaction time 2-4 h. Furthermore, the adsorption kinetics were best described by the pseudo-second order model for all the tested materials, while the adsorption equilibrium best fitted by the linear and Freundlich isotherms. Comparing rice husks and olive pomace, the higher adsorption capacity resulted after pyrolysis at 300 °C. With respect to the orange waste and compost, the highest adsorption capacity was observed using biochars obtained after hydrothermal treatment and pyrolysis at 300 °C. Presented on: Journal of Environmental Management

Summarization: The objective of this study was to demonstrate biochar’s effectiveness on Ni(II) removal from aqueous solutions by adsorption on three different biochars. Three different waste feedstocks, namely sewage sludge, exhausted olive pomace and the organic fraction of municipal solid waste, were used to produce biochar through pyrolysis at 300 °C, under inert conditions. The obtained biochars were characterized regarding their main properties and then evaluated as potential Ni(II) adsorbents. All investigated materials showed high adsorption efficiency in the range of 78–97%, with the biochar derived from SS exhibiting the best results, possibly because of its higher cation exchange capacity. Ni(II) removal rates were higher when the adsorption experiments were conducted at natural pH, while the removal efficiency under adjusted pH (acidic or alkaline) was slightly lower. The pseudo-second-order kinetic model adequately described the adsorption kinetics depicting high correlation coefficients, while the Freundlich adsorption isotherm model was successful in simulating equilibrium of adsorption. Presented on: Water, Air, & Soil Pollution

Summarization: This study investigates the effect of different chemical pretreatments on the solubilization and the degradability of different solid agroindustrial waste, namely winery waste, cotton gin waste, olive pomace and juice industry waste. Eight different reagents were investigated, i.e. sodium hydroxide (NaOH), sodium bicarbonate (NaHCO3), sodium chloride (NaCl), citric acid (H3Cit), acetic acid (AcOH), hydrogen peroxide (H2O2), acetone (Me2CO) and ethanol (EtOH), under three condition sets resulting in treatments of varying intensity, depending on process duration, reagent dosage and temperature. Results indicated that chemical pretreatment under more severe conditions is more effective on the solubilization of lignocellulosic substrates, such as those of the present study and among the investigated reagents, H3Cit, H2O2 and EtOH appeared to be the most effective to this regard. At the same time, although chemical pretreatment in general did not improve the methane potential of the substrates, moderate to high severity conditions were found to generally be the most satisfactory in terms of methane production from pretreated materials. In fact, moderate severity treatments using EtOH for winery waste, H3Cit for olive pomace and H2O2 for juice industry waste and a high severity treatment with EtOH for cotton gin waste, resulted in maximum specific methane yield values. Ultimately, the impact of pretreatment parameters on the different substrates seems to be dependent on their characteristics, in combination with the specific mode of action of each reagent. The overall energy balance of such a system could probably be improved by using lower operating powers and higher solid to liquid ratios. Παρουσιάστηκε στο: Waste Management