Laboratory analyses for assessing the potential for biogas production of various agricultural residues in Greece

Received: February 23rd, 2021 ; Accepted: May 27th, 2021 ; Published: June 8th, 2021 ; Correspondence: [email protected], [email protected] produces significant amounts of agricultural and livestock waste. For the needs of this study, Greece was divided into a Northern and a Southern part and relevant proposals were made for residues that can be used for energy production, through anaerobic digestion. For Northern Greece, this study concluded that the most abundant residues and potential substrates for anaerobic digestion valorisation are those of maize, inedible vegetables (including greenhouse vegetables), cattle manure, as well as the residues of beer and wine industry. For Southern Greece, the corresponding substrates are those of maize, inedible vegetables, sheep/goat manure and residues of wine, tomato, orange and olive processing, respectively. Based on the physicochemical characterization of individual feedstocks, corn silage, tomato husks, watermelon, malt, cattle manure, orange, and olive processing residues (olive pomace) were considered as the most suitable feedstocks for anaerobic digestion. Biochemical Methane Potential (BMP) assays for Northern Greece were also performed, testing the most abundant and appropriate residues for anaerobic digestion (of this area), namely corn silage, cattle manure and malt, in order to define their BMP yield as well as their prospective optimum mixtures. It was concluded that the BMP of the mono-substrates is in accordance with literature, while there were no statistically significant differences in the methane yield of all tested mixtures. The residual biomass originating from the three main categories of the agricultural sector (crop residues, agro-industrial residues, and animal manure) in Northern Greece can be efficiently valorised via anaerobic co-digestion, without observing, though, any synergistic effects on methane production

New techniques in olive mill wastewater treatment (OMW)

A new cost-effective system for complete exploitation of OMW is suggested, offering a viable solution to the problem of OMW disposal. Use of the proposed separation techniques prefiltration (PF), Ultrafiltration [UF], nanofiltration [NF], and reverse osmosis [RO]) produce byproducts that might include additional benefits. A pilot plant was developed in an olive mill operating in Achaia (Patras, Greece) during an olive harvesting season. Large volumes of OMW produced daily were treated systematically in a semibatch procedure to identify problems relevant to long-term behavior and reliability. The study showed that a fraction of pure water up to 75% can be recovered. Also fractions are isolated that contained concentrate nutritious and polyphenol content which can be further exploited in order to reduce the, indeed, high cost of the suggested treatment process. Finally, a feasibility-exploitation study was done to estimate if depreciation of the (indeed) expensive investment may occur in a short period of time. Together with the proposed method a synopis of commercially available techniques for the effective treatment of OMW is given. These techhnologies are based on biological, advanced oxidation, physicochemical and separation processes (composting, trickling filters, evaporation, oxidation, hydrolysis, co-digestion in a sewage treatment plant, production of solid fuels, etc)

Carbonation-Related Microstructural Changesin Long-Term Durability Concrete

This paper discusses the effects of carbonation on the microstructure of Portland cement concrete for long-term durability applications. A class C40 concrete (characteristic compression strength between 40 MPa and 44 MPa on the 28th day, according to Brazilian standard NBR 8953) was chosen for the experimental study of the carbonation effects, from which test samples were molded for accelerated test under a 100%-CO2 atmosphere after physical and mechanical characterization. It was observed that carbonation provoked a reduction of 5% to 12% of the concrete open porosity accessible to water. Flexural strength values obtained after the carbonation tests revealed a decrease of 12% and 25% in relation to the values obtained before tests on the 28th and 91st days, respectively