Review of biochar role as additive in anaerobic digestion processes

because of the urgent need to provide renewable energy sources and efficiently manage the continuously growing amount of organic waste. Biochar (BC) is an extremely versatile material, which could be produced by carbonization of organic materials, including biomass and wastes, consistently with Circular Economy principles, and “tailor-made” for specific applications. The potential BC role as additive in the control of the many wellknown critical issues of AD processes has been increasingly explored over the past few years. However, a clear and comprehensive understanding of the connections between BC and AD is still missing. This review paper analyses and discusses significant references (review articles, research papers and international databases and reports), mostly published in the last 10 years. This review is aimed at addressing three key issues related to the better understanding of the BC role in AD processes: 1. Investigation of the influence of BC properties on AD performances and of their ability to counteract its main challenges; 2. Assessment of the optimal BC production chain (i.e. feedstock-pyrolysis-activation) to achieve the desired features; 3. Evaluation of the economic and environmental advantages connected to BC use in AD processes, compared to conventional solutions applied to address AD challenges

Slaughterhouse solid residues treatment using anaerobic digestion

Περίληψη: Αντικείμενο της παρούσας μελέτης είναι η αξιολόγηση της χρήσης των υπολειμμάτων σφαγείου ως υποστρώματα για αναερόβια χώνευση με στόχο την παραγωγή μεθανίου. Για τον σκοπό αυτό, αρχικά εκτιμήθηκε το βιοχημικό δυναμικό μεθανίου διαφορετικών υπολειμμάτων σφαγείου, τα οποία σύμφωνα με τον Ευρωπαϊκό Κανονισμό ΕΚ 1069/2009, κατατάσσονται στις Κατηγορίες 2 και 3. Οι παραπάνω δοκιμές, που διήρκησαν 30 ημέρες, διεξήχθησαν υπό μεσόφιλες συνθήκες (35 °C) σε αντιδραστήρες διαλείποντος έργου ονομαστικού όγκου 250 mL και λειτουργικού όγκου 100 mL. Ως εμβόλιο χρησιμοποιήθηκε ιλύς προερχόμενη από αναερόβιο μεσοφιλικό χωνευτήρα Εγκατάστασης Επεξεργασίας Αστικών Λυμάτων. Το εμβόλιο αναμείχθηκε με τα υποστρώματα διατηρώντας σταθερό το λόγο, υπόστρωμα/εμβόλιο (Substrate/Inoculum Rate, SIR) και ίσο με 0,25, βάσει πτητικών στερεών. Οι παραπάνω δοκιμές κατέδειξαν ότι τα δείγματα μαστών και γεννητικών οργάνων (SH3), ουροδόχων κύστεων και εντέρων (SH5) και στομάχων και προστομάχων (SH1) οδήγησαν στην παραγωγή μεγαλύτερων ποσοτήτων μεθανίου με τιμές απόδοσης ίσες με 815, 787 και 759 mLCH4STP/gVS, αντίστοιχα. Στη συνέχεια, μελετήθηκε η δυνατότητα εφαρμογής της αναερόβιας συν-χώνευσης των υπολειμμάτων σφαγείου που κατέδειξαν τα υψηλότερα βιοχημικά δυναμικά μεθανίου με δύο αγροτοβιομηχανικά υπολείμματα, πιο συγκεκριμένα φλούδες πορτοκαλιού και φύλλα ελιάς. Οι δοκιμές αναερόβια συν-χώνευσης διεξήχθησαν σε μεσόφιλες συνθήκες (35 °C) και σε αντιδραστήρες ημι-συνεχούς λειτουργίας. Σκοπός αυτών των δοκιμών ήταν να διερευνηθεί η επίδραση της μεταβολής του ρυθμού οργανικής φόρτισης (Organic Loading Rate, ΟLR) στην απόδοση της παραγωγής μεθανίου. Η πειραματική διαδικασία, συν τοις άλλοις, προέβλεπε τον προσδιορισμό των κύριων χαρακτηριστικών των υπό μελέτη υπολειμμάτων σφαγείου, συμπεριλαμβανομένων των ολικών και πτητικών στερεών, της στοιχειακής ανάλυσης, της θερμογόνου δύναμης, της σύστασης σε μη διαλυτές ίνες και του περιεχομένου σε εξαγώγιμη ύλη με εξάνιο. Σύμφωνα με τα αποτελέσματα των δοκιμών σε ημι-συνεχείς συνθήκες, μέγιστες ειδικές αποδόσεις μεθανίου, μεταξύ 253 - 727 mLCH4/gVSfed ελήφθησαν από τα διάφορα μίγματα αποβλήτων, όταν η τροφοδοσία πραγματοποιούταν με OLR 0,8 gVS/L/d. Επιπλέον, η παραγωγή μεθανίου από τη συν-χώνευση των υπολειμμάτων σφαγείου με φλούδες πορτοκαλιού έδειξε καλύτερα αποτελέσματα από την αντίστοιχη συν-χώνευση με φύλλα ελιάς. Η μόνη περίπτωση στην οποία παρατηρήθηκαν φαινόμενα αναστολής της μεθανιογένεσης λόγω αυξημένης συγκέντρωσης αμμωνίας ήταν η δοκιμή που τροφοδοτούταν με μίγμα δείγματος SH3 και φλουδών πορτοκαλιού, στο μέγιστο ρυθμό τροφοδοσίας. Η αναστολή αυτή αποδόθηκε σε ακατάλληλο λόγο C/N του υποστρώματος.Summarization: The objective of the present study is to evaluate the use of slaughterhouse residues as substrates for anaerobic digestion, aiming at methane production. To this purpose, the biochemical methane potential of slaughterhouse residues of Category 2 and 3, according to European Regulation EC 1069/2009, was initially determined. These assays lasted 30 days and were conducted under mesophilic conditions (35 °C) in batch reactors with nominal volume of 250 mL and working volume of 100 mL. The inoculum used for these assays consisted of anaerobic sludge originating from the anaerobic digesters of the Municipal Wastewater Treatment Plant of Chania. The inoculum was mixed with the substrates, keeping a constant, Substrate/Inoculum Ratio (SIR) equal to 0,25, on volatile solid basis. The above mentioned assays showed that using the sample containing breasts and reproductive organs (SH3), bladders and intestine (SH5) and stomach and rumen (SH1), led to the production of larger methane quantities, yielding 815, 787 and 759 mLCH4STP/gVS, respectively. Subsequently, the applicability of anaerobic co-digestion of the types of slaughterhouse waste which showed higher dynamic biochemical methane potentials, with two agro-residues, particularly orange peel and olive leaves was studied. Anaerobic co-digestion assays were carried out in semi-continuously operated reactors under mesophilic conditions (35°C). The effect of the variation in Organic Loading Rate (OLR) on methane production was investigated. During the experimental procedure, the main characteristics of the collected samples, including total and volatile solids contents, elemental composition, pH, higher calorific value, fiber composition and crude fat content, were also determined. According to the results of the semi-continuous assays, maximum methane yields between 253 - 727 mLCH4/gVSfed were obtained from different waste mixtures, when the feeding took place with an OLR of 0,8 gVS/L/d. Moreover, methane production from the co-digestion of slaughterhouse by-products with orange peels showed better results than the co-digestion with olive leaves. The only case in which methanogenesis inhibition phenomena were observed, due to increased ammonia concentrations, was the assay being fed with a mixture of SH3 and orange peels, at the highest OLR. This inhibition phenomenon was attributed to an inappropriate C/N ratio

Slaughterhouse by-products treatment using anaerobic digestion

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 Managemen

Valorisation of soil contaminated by petroleum hydrocarbons and toxic metals in geopolymer mortar formation

Summarization: Until the complete transition to a renewable energy sources based economy, the potential environmental hazards associated with petroleum refinery industries affecting water, air and soil seek sustainable solutions. In the present study contaminated soil from a refinery is used as an alternative source for producing useful building materials by geopolymerization. To this end, soil remediation by thermal desorption was initially applied. Thermal treatment was performed between 60 and 250 °C for short time intervals (10–30 min) in order to remove organic pollutants (Total Petroleum Hydrocarbons, TPHs and Polycyclic Aromatic Hydrocarbons, PAHs). Physical, chemical analyses, mineral phase composition, as well as thermogravimetric analysis were employed to characterize the sample. Moreover, removal efficiency of TPHs and PAHs was evaluated. Subsequently, the treated soil presenting the maximum elimination of TPH and PAHs was used in geopolymer mortar formation aiming to stabilize the toxic metals (TMs) and produce a possible profitable material. For geopolymer synthesis the substitution of metakaolin (MT) by treated soil at 0, 50, 70 and 100% was tested. The produced specimens were evaluated based on the 28 day compressive strength and metals leaching. Results showed that the geopolymer constructed by 50% MT-50% remediated soil at 250 °C for 30 min, had negligible content of organic pollutants, TMs were immobilized and exhibited increased strength thus giving significant recycling benefits. Valorisation of industrial residues to produce building materials is a promising solution for sustainable waste management.Presented on: Journal of Environmental Managemen