The most common strategy for handling paper mill solid waste is typically disposal in landfills. However, several drawbacks are associated with this type of solid waste management, such as increasing costs due to oil price rise, governmental restrictions on land use, and environmental concerns such as leaching of disposed contaminants into groundwater, as well as methane generation of and release to the atmosphere, thus contributing to global warming. An alternative to reduce solids prior to disposal and to recover methane as a renewable fuel is anaerobic digestion, but it is not yet clear whether such an approach is feasible in paper mills. In this study, the anaerobic digestion of paper mill waste streams was evaluated for a paper plant located in Belen, Costa Rica, to investigate up to what extent certain waste streams can be anaerobically digested, to what extent energy can be produced in the form of methane for implementation in a wastewater treatment plant and to evaluate the conditions that will favor methane generation from select waste streams. Batch assays were performed to evaluate the biodegradability of single and combined waste samples under ideal, laboratory conditions. Samples were obtained from the manufacturing plant as well as the wastewater treatment plant at the paper mill under study. The ultimate biodegradability ranged 25 to 85% in terms of volatile solids destruction, corresponding to the waste activated sludge (WAS) and Flotation Cell rejects, respectively. The COD destruction of single samples ranged from 45 to 63%, corresponding to WAS and wastewater treatment plant (WWTP) dissolved air flotation (DAF) skimmings, respectively. Methane generation ranged from 80 to 190 ml at 35oC/g COD added for all single samples (excluding underflows). In combination Feed 1 was reduced by 46 and 52% and Feed 2 by 27 and 38%, respectively. Two combinations of two single samples each (Feed 1 and 2), formulated according to plant operational data, and their solids and COD destruction as well as methane generation in semicontinuous flow anaerobic digesters were evaluated at different solids retention times (30, 20, 15, and 7 days). Nutrients (N, and P) availability as well as alkalinity in the plant waste streams were evaluated and minimum supplements were used to support an efficient anaerobic digestion process. The reactors reached stable operation at all retention times evaluated. Methanogenesis was the predominant, terminal metabolic process under anaerobic, mesophilic conditions, but the overall process rate was determined by the hydrolysis of the particulate substrate. Reactors fed with Feed 1 achieved the highest level of destruction, which amounted to 85% of phosphorus that is typically present in paper mill wastes. Alkalinity addition to the feed (3.5 mg NaHCO3/L) was necessary to maintain the reactors pH above 6.9.

<p>Possibilities for energy recovery from sludge at Chişinȃu wastewater treatment plant have been investigated and evaluated. One way of recovering energy from sludge is to produce biogas through anaerobic digestion. Which method of biogas usage that is to prefer in Chişinȃu has been evaluated from a cost-efficiency point of view. There is a possibility that a new waste incineration plant will be built next to the wastewater treatment plant, and therefore solutions that benefit from a co-operation have been discussed. The results show that biogas production would be suitable and profitable in a long time perspective if the gas is used for combined heat and power production. Though, the rather high, economical interest rates in Moldova are an obstacle for profitability.</p>

Bioenergy has the potential to reduce the world's dependence on fossil fuels, and to decrease the CO2 emissions due to fossil combustion. Lignocellulosic and algae biomass have been presented as promising feedstocks for bioenergy production. In this study, a comparative Life Cycle Assessment (LCA) has been developed to evaluate the environmental impacts associated with different energy products via different routes across the whole life of algal and lignocellulosic bioenergy. Results were compared per energy basis, the production of 1 million BTU of energy products. For the development of the comparative algae biomass conversion LCA, algal biomass was converted to liquid biofuels via a thermochemical gasification and Fisher-Tropsch Synthesis (FTS) process; and to electricity and heat via anaerobic digestion and combined heat and power (CHP) process. Overall results from the algae biomass conversion LCA showed that the process that converts algae biomass through anaerobic digestion and CHP process to electricity and heat had the highest overall environmental impact. Results also showed that the impact categories that appear to contribute the most to the overall impacts are ecotoxicity, human health non-cancer, and human health cancer. For the development of the comparative lignocellulosic biomass conversion LCA, lignocellulosic biomass was converted to ethanol and higher alcohols through thermochemical gasification and alcohol synthesis process, to liquid biofuels via thermochemical gasification and FTS process, and to liquid biofuels via a thermochemical gasification and FTS process that uses methane. Overall results from the lignocellulosic biomass conversion LCA showed that the process that converts lignocellulosic biomass into alcohols has the highest overall environmental impact. Results also showed that the impact categories that appear to contribute the most to the overall impacts are ecotoxicity, human health non-cancer, human health cancer, and global warming. This study determined that cultivated algae biomass feedstock has much higher environmental impacts compared with lignocellulosic biomass feedstock from forestation and agriculture byproducts. It was also concluded that thermochemical gasification and FTS process showed higher efficiency when converting biomass to bioenergy. In addition, the five biomass to bioenergy conversion pathways used in the development of this LCA study were compared. Results showed that the pathway with lignocellulosic biomass (feedstock), thermochemical gasification and alcohol synthesis process (conversion process), and ethanol and higher alcohols (energy products) has the largest environmental impact.

Three continuously stirred tank reactors (CSTR) were operated in semi continuous mode treating swine waste using anaerobic digestion. The reactors were used to test the effect of solid retention time (SRT) on CH4 yield, total ammonia nitrogen (TAN) concentrations, % volatile solids (VS), chemical oxygen demand (COD) and volatile fatty acids (VFA) removal, readily biodegradable COD concentration and the denitrification potential for the effluent in a biological nutrient removal (BNR) system. During Phase I of the study, the three reactors were operated at the same 28 day SRT for 16 weeks. SRTs were then changed during the 12 week Phase II period. The SRTs studied were 14, 21 and 28 days, with the same organic loading rate (OLR) of 1.88 ± 0.2 kg VS/ m3-day. The reactor with the lowest SRT (14 days) had the highest VS and VFA removal at 73.6 and 67.6% and lowest TAN concentration at 0.78 g NH4+-N/L, followed by the 21 day and 28 day reactors. This was likely due to the fast microbial growth rates and substrate utilization rates in this reactor compared with the other two. The 14 day reactor had the highest CH4 yield at 0.33 m3CH4/kg VS added and readily biodegradable COD concentration at 0.93 COD/L. The variations in CH4 yield and readily biodegradable COD concentrations between the three reactors were not statistically significant. Denitrification potential for the reactors was 1.20, 0.73 and 0.56 g COD/g N for 14, 21 and 28 day reactors, respectively, and the differences were statistically significant. None of the reactors achieved a denitrification potential of 5 g COD/g N, the amount required to use effluent of anaerobically digested swine waste as an internal carbon source in a BNR. This was attributed to operating conditions such as freezing and thawing of the raw swine waste that maximized CH4 yield and lowered the readily biodegradable COD concentration. In addition the 14 day reactor had low TAN concentrations thus increasing the denitrification potential of the centrate from that reactor.

Fat, oil, and grease residues, food particles, solids and some kitchen wastewaters are collected in grease traps which are separate from the municipal wastewater stream. Grease traps are emptied periodically and grease trap waste (GTW) is hauled for treatment. This dissertation focuses on anaerobic co-digestion of un-dewatered (raw) GTW with municipal wastewater treatment sludge (MWS) at wastewater treatment plants. In particular, this research focuses on the biochemical methane potential of un-dewatered GTW as well as the stability and performance of anaerobic co-digestion of MWS and un-dewatered GTW. A set of modified biochemical methane potential tests was performed to determine the methane potential of un-dewatered GTW under mesophilic conditions (35 °C). Methane potential of un-dewatered GTW in this study was 606 mL CH₄/g VS [subscript added] which is less than previously reported methane potentials of 845 - 1050 mL CH₄/g VS [subscript added] for concentrated/dewatered GTW. However, the methane potential of un-dewatered GTW (606 mL CH₄/g VS [subscript added]) was more than two times greater than the 223 mL CH₄/g VS [subscript added] reported for MWS digestion alone. A comprehensive study was performed to determine the stability and performance of anaerobic co-digestion of MWS with un-dewatered GTW as a function of increasing GTW feed ratios. The performance of two semi-continuously fed anaerobic digesters at 35 °C was evaluated as a function of increasing GTW feed ratios. Anaerobic co-digestion of MWS with un-dewatered GTW at a 46% GTW feed ratio (on a volatile solids basis) resulted in a 67% increase in methane production and a 26% increase in volatile solids reduction compared to anaerobic digestion of MWS alone. On the other hand, anaerobic co-digestion of un-dewatered GTW resulted in a higher inhibition threshold (46% on VS basis) than that of dewatered GTW. These results indicate that using un-dewatered GTW instead of dewatered GTW can reduce the inhibition risk of anaerobic co-digestion of MWS and GTW. Recovery of the anaerobic digesters following upset conditions was also evaluated and semi-continuous feed of digester effluent into upset digesters yielded of the biogas production level of the undisrupted digestion. Finally, a mathematical model was used to describe the relationship between methane potential and GTW feed ratio on a VS basis. The results of this research can be used to predict methane production and identify suitable GTW feeding ratios for successful co-digestion of un-dewatered GTW and MWS. / text

The MP-AES 4200 using microwave plasma and an atomic emission spectroscopy detector provide a new and improved instrument to the analytical field. In this project will the performance of the equipment be evaluated in controlled NaCl-heavy matrices for selected metals (Cu, Zn, Li) and the result from this will be used to optimize a method for specific samples. These samples consist of combustion ashes from the incineration of hazardous waste and are provided by the company SAKAB AB. The sample preparation consisted of several cycles of L/S 10 followed by microwave assisted dissolution with concentrated HNO3, aqua regia or 18.2 MΩ. An extended amount of metals were quantified for these samples (Al, As, Ba, Ca, Cd, Cr, Cu, Fe, K, Li, Mn, Na, Ni, Pb, V, Zn) and most (not Ca, Li, K or Na) were compared with an ICP-MS instrument equipped with a collision cell used for the elements As, Fe and V. A final experiment was made on an L/S 10 of the samples to attempt to separate the metals from the salt with ion exchange, something that would make it possible to recycle this otherwise unused waste. The detection limits were all in the low μg L-1 except for Cd, Mn and Zn, which were between 2-4 μg L-1. The MP-AES was found to be able to handle matrices up to 5 g L-1 NaCl without a significant loss of response and provided near identical results to the ICP-MS for the elements that could be compared, this did not included the elements not quantified with the ICP-MS or V which was the only element under the limit of detection for the MP-AES. The experiment where an attempt was made to separate the metals from the salt was proven successful after treatment of bark compost and another type of waste ash as cation exchangers.

published_or_final_version / Civil and Structural Engineering / Master / Master of Philosophy

Τα υγρά απόβλητα των ελαιοτριβείων είναι το παραπροϊόν της παραγωγικής διαδικασίας του ελαιολάδου. Η γεωργική αυτή δραστηριότητα έχει ιδιαίτερη κοινωνική και οικονομική σημασία για το πληθυσμό των ελαιοπαραγωγικών χωρών, που βρίσκονται κυρίως στη περιοχή της Μεσογείου, όπου παράγεται και το 80% περίπου της παγκόσμιας παραγωγής. Τεράστιες ποσότητες αποβλήτων παράγονται κάθε ελαιοκομική περίοδο και σε συνδυασμό με τα χαρακτηριστικά τους (υψηλή συγκέντρωση σε οργανικό φορτίο και φαινολικές ενώσεις), καθιστούν τα υγρά απόβλητα ελαιοτριβείου ένα δυσεπίλυτο πρόβλημα καθώς είναι επικίνδυνα για την απευθείας διάθεσής τους στο περιβάλλον. Μια από τις πιο αποτελεσματικές και πολλά υποσχόμενες μεθόδους επεξεργασίας υγρών αποβήτων ελαιοτριβείου (ΥΑΕ) είναι η αναερόβια χώνευση. Το ενδιαφέρον της έρευνας για την επεξεργασία των ΥΑΕ εστιάζεται στην ανάπτυξη αναερόβιων μεθόδων και βιοαντιδραστήρων που μπορούν να απομακρύνουν αποτελεσματικά υψηλά οργανικά φορτία. Ανάμεσα στις ταχύρρυθμες διεργασίες που έχουν αναπτυχθεί τα τελευταία χρόνια, οι αναερόβιοι αντιδραστήρες ανοδικής ροής που σχηματίζουν ‘κουβέρτα’ ιλύος (UASB) είναι οι πιο επιτυχημένοι. Μέσα σε ένα UASB αντιδραστήρα, οι μικροοργανισμοί προσκολλώνται μεταξύ τους σχηματίζοντας συσσωματώματα, γνωστά ως granules, τα οποία έχουν υψηλή βιοδραστηριότητα και εξαιρετική δυνατότητα καθίζησης. Στόχος αυτής της μελέτης ήταν να εκτιμηθεί η απόδοση τριών ταχύρρυθμων αναερόβιων συστημάτων, δύο αναερόβιων αντιδραστήρων με ανοδική ροή που σχηματίζουν ‘κουβέρτα’ ιλύος (UASB) και ενός υβριδικού UASB, κάτω από μεσοφιλικές συνθήκες (37oC) λειτουργίας για την επεξεργασία φυγοκεντριμένων υγρών αποβλήτων προερχόμενων από τριφασικό ελαιοτριβείο. Ο εμβολιασμός του ενός UASB πραγματοποιήθηκε με αναερόβια κροκιδωμένη λάσπη (UASB-F), ενώ στο δεύτερο και στον υβριδικό αντιδραστήρα (UASB-G και HUASB-G αντίστοιχα) χρησιμοποιήθηκε αναερόβια λάσπη που περιείχε ήδη σχηματισμένα συσσωματώματα τύπου granules. Η τροφοδοσία όλων των συστημάτων γινόταν με φυγοκεντριμένα ΥΑΕ αραιωμένα κατάλληλα με 3D-H2O, προκειμένου να αποφευχθεί παρεμπόδιση λόγω φαινολών στο σύστημα. Και οι τρεις αντιδραστήρες λειτούργησαν κάτω από όμοιες οργανικές φορτίσεις και πραγματοποιήθηκε σύγκριση της απόδοσης των συστημάτων μεταξύ τους. Πιο συγκεκριμένα στον UASB-F αντιδραστήρα επετεύχθη σταθερή λειτουργία σε υψηλότερους ρυθμούς οργανικής φόρτισης συγκριτικά με τους HUΑSB-G και UASB-G αντιδραστήρες και γενικά παρουσίασε τη μεγαλύτερη απόδοση (1.15 LCH4/Lαντμέρα-1) σε σχέση με τους άλλους δύο. Ως προς την αποδόμηση ΧΑΟ, ο UASB-F αντιδραστήρας παρουσίασε μεγαλύτερη του 50%, ενώ οι άλλοι δύο αντιδραστήρες μικρότερη του 45-50%. Ο UASB-F αντιδραστήρας λειτούργησε για 500 ημέρες και σε αυτό το διάστημα δεν παρατηρήθηκε ο σχηματισμός granules (οπτική παρατήρηση). Από την άλλη πλευρά, τα καλοσχηματισμένα granules με τα οποία εμβολιάστηκαν οι HUΑSB-G και UASB-G αντιδραστήρες έχασαν τη δομή τους (οπτική παρατήρηση) και η απόδοση των αντιδραστήρων παρέμεινε σε χαμηλά επίπεδα. / Olive Mill Wastewaters, OMW, are the byproduct of the olive oil production. The olive oil production has an economic and social impact on people of countries who produce olive oil, which are mainly located in the Mediterranean region, where 80% of the global production is produced. Large quantities of OMW are produced every year and in combination with their characteristics, they make OMW a serious problem to be solved as they are dangerous if they are disposed directly to the environment. One of the most effective and very promising method of treatment of OMW is anaerobic digestion. The interest of the research on treatment of OMW is focused on the development of anaerobic methods and biological reactors which can reduce sufficiently high organic loading rates. Among the high-rate processes that have been developed the recent years, Upflow Anaerobic Sludge Blanket, UASB, reactors are the most successful. The microorganisms form aggregates into UASB, known as granules, which have great biological activity and extraordinary sedimentation ability. The aim of this study was to estimate the production efficiency of three high-rate anaerobic systems, two UASB reactors and one hybrid UASB, under mesophilic conditions( 37oC) for the treatment of centrifuged OMW from a three-phase olive mill. One UASB inoculated with anaerobic flocculant sludge, UASB-F, while the other two, UASB-G and HUASB-G, inoculated with granulated sludge. All reactors feed consisted of centrifuged and diluted with 3D-H2O OMW in order to avoid phenols obstruction. All three reactors worked under similar organic loading rates and their production efficiency was compared. More specifically, UASB-F reactor was stable for higher loading rates compared with HUASB-G and UASB-G reactors and the higher efficiency, 1.15 LCH4/Lreactor/d, was achieved in this system. Concerning COD reduction, more than 50% was achieved in UASB-F reactor, while the percentage was lower than that in the other two reactors. UASB-F reactor worked for 500 days and granules were not formed (optical observation). on the other hand, the initial granules in UASB-G and HUASB-G reactors lost their structure (optical observation) and the efficiency of these systems was kept in low levels.

Η αναερόβια χώνευση αποτελεί στις μέρες μας μια σημαντική βιολογική διεργασία απομάκρυνσης του οργανικού φορτίου των αποβλήτων με ταυτόχρονη παραγωγή ενέργειας υπό μορφή βιοαερίου (μίγμα μεθανίου και διοξειδίου του άνθρακα). Η χρήση υποστρωμάτων φυτικής προέλευσης (βιομάζα) και κυρίως ενεργειακών φυτών έχει αποδειχθεί ότι μπορεί να δώσει υψηλές αποδόσεις σε βιοαέριο. Στη διδακτορική αυτή διατριβή μελετήθηκε η αναερόβια επεξεργασία του στερεού/υγρού αποβλήτου που προέρχεται από την αλκοολική ζύμωση του γλυκού σόργου, αλλά και η χρήση του αυτού καθ’ αυτού γλυκού σόργου, προκειμένου να εξεταστούν ο ρυθμός υδρόλυσης και αποδόμησης της οργανικής ύλης και η ικανότητα των αναερόβιων συστημάτων να επεξεργάζονται τέτοιου είδους υποστρώματα και να παράγουν ενέργεια υπό μορφή βιοαερίου. Στόχος της παρούσης εργασίας ήταν η ανάπτυξη ενός καινοτόμου διβάθμιου συστήματος αναερόβιας χώνευσης στερεών αποβλήτων και βιομάζας, όπου τα στάδια της υδρόλυσης και της μεθανογένεσης διαχωρίζονται, προκειμένου να μελετηθεί χωριστά για κάθε στάδιο η βελτιστοποίηση των συνθηκών λειτουργίας του και οι επιμέρους παράμετροι που επηρέαζαν τη διεργασία της αναερόβιας χώνευσης, με απώτερο σκοπό τη μεγιστοποίηση της παραγωγή του βιοαερίου. Τα υπολείμματα του αποβλήτου της αλκοολικής ζύμωσης του γλυκού σόργου μετά και από την απομάκρυνση της αιθανόλης με απόσταξη, αποτελούνταν από ένα δύσκολα βιοαποδομήσιμο στερεό/υγρό μίγμα υψηλής συγκέντρωσης στερεών (9% TS) και υψηλής συγκέντρωσης χημικά απαιτούμενου οξυγόνου ΧΑΟ (~115 g/l). Αρχικά, εξετάσθηκε η πιθανότητα η υδρόλυση και η χώνευση του αποβλήτου της αλκοολικής ζύμωσης του γλυκού σόργου να γίνει σε σύστημα ενός σταδίου. Οι βέλτιστες συνθήκες της αναερόβιας χώνευσης του αποβλήτου αυτού προσδιορίστηκαν χρησιμοποιώντας διαφορετικές οργανικές φορτίσεις, καταλήγοντας στο συμπέρασμα ότι η υδρόλυση των στερεών ήταν το περιοριστικό βήμα της διεργασίας. Έτσι, το απόβλητο διαχωρίστηκε σε δύο φάσεις, στερεή και υγρή, όπου μελετήθηκε χωριστά το στάδιο της υδρόλυσης και της χώνευσης, αντίστοιχα. Τα αποτελέσματα των πειραμάτων αυτών οδήγησαν στο συμπέρασμα ότι μια αποδοτική επεξεργασία του αποβλήτου απαιτεί το διαχωρισμό της στερεής από την υγρή φάση, ώστε να βελτιστοποιηθούν οι συνθήκες της αναερόβιας χώνευσης για κάθε φάση χωριστά, μεγιστοποιώντας τους διαφορετικούς ρυθμούς υδρόλυσης και αποδόμησης της στερεής και της υγρής φάσης, καταλήγοντας σε μια περισσότερο αποδοτική διάταξη αναερόβιας χώνευσης. Έτσι δημιουργήθηκε ένα σύστημα αναερόβιας χώνευσης δύο σταδίων αποτελούμενο από έναν θερμόφιλο υδρολυτικό και έναν μεσόφιλο ταχύρυθμο μεθανογόνο χωνευτήρα, όπου εξετάστηκε η απόδοση του συστήματος σε μεθάνιο. Ο ρυθμός παραγωγής μεθανίου του συστήματος έφτασε τα 16 l CH4/l αποβλήτου με συνολικό υδραυλικό χρόνο παραμονής 19d. Στη συνέχεια, το διβάθμιο αναερόβιο σύστημα που αναπτύχθηκε, χρησιμοποιήθηκε και σε πειράματα αναερόβιας χώνευσης με υπόστρωμα το γλυκό σόργο. Το ενεργειακό αυτό φυτό βιβλιογραφικά θεωρείται ως μια πολλά υποσχόμενη ανανεώσιμη πηγή ενέργειας, το οποίο κάτω από συγκεκριμένες βιολογικές διεργασίες μπορεί να δώσει υψηλές αποδόσεις ενέργειας, υπό μορφή βιοαερίου. Ένα μεγάλο μέρος του γλυκού σόργου αποτελείται από εύκολα διαλυτούς υδατάνθρακες. Έτσι πριν την αναερόβια επεξεργασία του, εφαρμόστηκε ένα στάδιο υδατικής εκχύλισης. Το εκχυλισμένο υγρό κλάσμα πλούσιο σε ΧΑΟ (14-34 g/l) και το στερεό υπόλειμμα της εκχύλισης με 20% ολικά στερεά και υψηλό ΧΑΟ (~1,2 g/g VS) τροφοδοτήθηκαν στο καινοτόμο διβάθμιο αναερόβιο σύστημα, επιτυγχάνοντας 70-80% υδρόλυση των στερεών, με ταυτόχρονα υψηλή παραγωγή μεθανίου της τάξεως του 0,63 l/l αντιδραστήρα/d και υδραυλικό χρόνο παραμονής του συστήματος 22d. Συμπερασματικά, το διβάθμιο σύστημα αναερόβιας χώνευσης λειτούργησε το ίδιο αποτελεσματικά και με τα δύο υποστρώματα, με ικανοποιητικές αποδόσεις όσον αφορά την υδρόλυση των στερεών και την παραγωγή βιοαερίου, αποδεικνύοντας έτσι και την ευρύτερη εφαρμογή του στο τομέα της παραγωγής ενέργειας από βιομάζα (ενεργειακά φυτά). Προτείνεται η μελέτη διαφόρων μαγιών, όπως είναι η αγελαδοκοπριά, η χρήση της οποίας φέρει ιδιαίτερα χαρακτηριστικά και ιδιότητες τα οποία βελτιώνουν τις αποδόσεις ως προς τη διεργασία της αναερόβιας χώνευσης του στερεού γλυκού σόργου. / In our days anaerobic digestion has received an increasing interest, as it is an effective method for the biological treatment of a variety of organic wastes, by degrading the organic matter and converting it into energy in the form of biogas (a mixture of methane and carbon dioxide). The use of biomass, especially energetic plants, as substrate has been proved that could yield a high biogas production. In this research work, the anaerobic treatment of the solid/liquid wastes from alcohol fermentation of sweet sorghum, but also the use of the cultivated sweet sorghum as substrate was investigated, in order to study the hydrolysis and degradation rates of organic matter and the ability of anaerobic systems to produce energy in the form of biogas using such solids substrates. The main aim of this work was the development of an innovative two-stage anaerobic digestion system for solid wastes and biomass, in which hydrolysis and methanogenesis was taking place in two different bioreactors (a hydrolyser and a methanizer) respectively. Hence, it was possible to investigate for each separate stage the optimal operating conditions and parameters that affect the anaerobic digestion process with the intention to maximize the biogas production. The sweet sorghum residues stream, originating from the alcoholic fermentation of sweet sorghum and the subsequent distillation step, contained high concentration of solid matter (9% TS) and thus could be characterized as a semi-solid, not easily biodegradable wastewater with high COD (115 g/l). At first, the possibility of direct hydrolysis and digestion of bioethanol process sludge (sweet sorghum residues) in a single-stage system was examined. Optimal conditions for the anaerobic digestion of this particular waste were determined using different organic loadings, concluding that solids hydrolysis was the process limiting step. Thus, in order to optimize the process performance, it was suggested to separate the solid and liquid phases of the wastewater and to treat the two streams under different operating conditions. Hence, a novel two-stage anaerobic bioreactor system consisted of a thermophilic hydrolyser and a mesophilic high-rate methaniser was made. The application of the proposed two-stage configuration achieved a methane production of 16 l/l wastewater under a hydraulic retention time of 19 days. Energetic plants such as sweet sorghum are a promising renewable energy resource. The energy contained in the chemical bonds of carbohydrates could be converted to fuels such as methane through anaerobic digestion. The anaerobic conversion of sweet sorghum to biogas was studied using the novel two-stage bioreactor system. Since a large portion of carbohydrates in sorghum were easily extractable, a water extraction step was preceded. The extracted liquid portion of sweet sorghum, rich in COD (14-34 g/l) and the remaining solid portion with 20% total solids and high COD (~1,20 g/g VS), were treated successfully in a two-stage anaerobic digestion system achieving a solids hydrolysis of 70-80% with a high simultaneous methane production on the order of 0,63 l/l reactor/d under a hydraulic retention time of 22 days. It could be concluded that using a two-stage anaerobic digestion system in treatment of organic materials with high solids concentration, performs efficiently in hydrolysis of solids and production of biogas and could be employed for energy production from biomass (such as energetic plants). Finally, a study over the use of other microbial biomasses, such as cow manure, which seems that has particular properties that improve the anaerobic digestion yields during processing of lingocellulosic materials, is proposed.

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