The paper describes the construction of a mechanistic energy balance model for the production of ... more The paper describes the construction of a mechanistic energy balance model for the production of biogas from anaerobic digestion of micro-algal biomass grown in raceways, based on simple principles and taking into account growth, harvesting and energy extraction. The model compares operational energy inputs with the calorific value of the output biomass in terms of the energy return on operational energy invested (EROOI). Initial results indicate that production of microalgal biogas will require: a) Favourable climatic conditions. The production of microalgal biofuel in UK would be energetically challenging at best. b) Achievement of ‘reasonable yields’ equivalent to ~3% photosynthetic efficiency (25 g m-2 day-1) c) Low or no cost and embodied energy sources of CO2 and nutrients from flue gas and wastewater d) Mesophilic rather than thermophilic digestion e) Adequate conversion of the organic carbon to biogas (≥ 60%) The model itself provides a powerful assessment tool both for comparison of alternative options and potentially for benchmarking real schemes.
Anaerobic digestion of autoclaved (160°C, 6.2 bar) and untreated source segregated food waste (FW... more Anaerobic digestion of autoclaved (160°C, 6.2 bar) and untreated source segregated food waste (FW) was compared over 473 days in semi-continuously fed mesophilic reactors with trace elements supplementation, at organic loading rates (OLRs) of 2, 3, 4 and 6 kg volatile solids(VS)/m(3)d. Methane yields at all OLR were 5-10% higher for untreated FW (maximum 0.483±0.013 m(3) CH4/kg VS at 3 kg VS/m(3) d) than autoclaved FW (maximum 0.439±0.020 m(3) CH4/kg VS at 4 kg VS/m(3) d). The residual methane potential of both digestates at all OLRs was less than 0.110 m(3) CH4/kg VS, indicating efficient methanation in all cases. Use of acclimated inoculum allowed very rapid increases in OLR. Reactors fed on autoclaved FW showed lower ammonium and hydrogen sulphide concentrations, probably due to reduced protein hydrolysis as a result of formation of Maillard compounds. In the current study this reduced biodegradability appears to outweigh any benefit due to thermal hydrolysis of ligno-cellulosic ...
Household bulky waste includes large and heavy items such as furniture and electrical appliances.... more Household bulky waste includes large and heavy items such as furniture and electrical appliances. Local authorities in England provide two options for disposing of these items: a special collection service, often involving a collection charge, and Household Waste Recycling Centres (HWRCs), where residents can take their waste free of charge. Local private companies and community or charitable organisations may also collect certain bulky items.In this study, 1450 householders in 3 cities across England were surveyed about a range of issues relating to the disposal of bulky items. Questionnaires were hand delivered to households pre-selected using the national Index of Multiple Deprivation in order to compare how disposal of bulky items differs with level of affluence.Sixty-five percent of householders had discarded bulky items in the 12 months prior to the survey. The principal disposal route was found to be the HWRC, with almost 60% of residents who had discarded items using this method. Only 19% of the householders had used the special collection services. In low-affluence areas, lower car ownership made residents more reliant on council collections of bulky items, and HWRCs were used less frequently. Householders were found to be satisfied with the collection service they had received.The study demonstrates that there is significant capacity for reuse and recycling of bulky items at a national level. Using the Waste Hierarchy, these management options are environmentally preferable to landfill, which is the widely-used disposal method at present. Where items are reused there are also social benefits for the community or charity groups involved, volunteers employed, and recipients of the items. Only the current bulky waste handlers – local authorities, can implement the logistical, and in some cases financial, solutions that are required to increase recovery in this waste stream.
This research explored the possible application of pressurised carbon dioxide (P CO(2)), a promis... more This research explored the possible application of pressurised carbon dioxide (P CO(2)), a promising non-thermal sterilisation technique, for the treatment of sewage sludge (SS) before anaerobic digestion to inactivate pathogenic microorganisms. Escherichia coli was selected as the test organism and was isolated from SS and maintained in pure culture. The growth curve of the isolated strain was determined by measuring the optical density (OD) in liquid culture medium and relating this information to the spread plate count so that a culture of known cell density could be grown for optimisation experiments. Inactivation of E. coli was enhanced by increase in pressure (1,500, 2,000 and 2,800 kPa) and treatment time (from 0.75 to 24 h). A short exposure time at high pressure was sufficient to provide a degree of inactivation which could also be achieved by longer exposure at lower pressure. Complete inactivation (8 log(10) reduction) was possible at all three pressures. scanning (SEM) and transmission (TEM) electron microscopy studies of E. coli treated with P CO(2) revealed that the cell walls were ruptured, and the cytoplasm was unevenly distributed and had lost its density, indicating the possible leakage of intracellular substances.
The River Nura in Central Kazakhstan has been heavily polluted by mercury originating from an ace... more The River Nura in Central Kazakhstan has been heavily polluted by mercury originating from an acetaldehyde plant. Mercury in the riverbed is mainly associated with power station fly ash, forming a new type of technogenic deposit. A systematic survey of the bed was carried out to establish the location, extent and nature of the contaminated sediments, and to evaluate the potential for sediment transport. The bed sediments were found to contain very high concentrations of mercury, particularly in the first 15 km downstream of the source of the pollution. Average total mercury concentrations in this section of the river are typically between 150 and 240 mg/kg, falling rapidly with increasing distance downstream. The estimated total volume of silts in the riverbed between Temirtau, the origin of the pollution, and Intumak Reservoir, located 75 km downstream, has been calculated as 463500 m3, containing an estimated 9.4 tonnes mercury. Forty-six percent of the total volume of contaminated silts containing almost 95% of the mercury are located in the upper 25 km of the river, however. The data clearly support the hypothesis that large quantities of polluted sediment are not transported long distances downstream but are removed from the aquatic environment in times of flood and deposited on the low-lying lands adjacent to the river. This process, however, does not stop mercury moving further downstream in the water column.
Completely mixed batch reactors were used to compare the methane production from maize at inoculu... more Completely mixed batch reactors were used to compare the methane production from maize at inoculum to substrate volatile solids ratios (r I/S ) of 3, 2, 1.5 and 1. The tests were carried out at 35 8C and run against a control of inoculum without substrate. The stability and progress of the reaction from solid substrate to gaseous end product was monitored by measuring the pH, soluble chemical oxygen demand (CODs), total alkalinity (TA), volatile fatty acids (VFA) and gas composition on a daily basis. The results showed that the yield coefficient showed little variation over the range used, with an average value of 211 AE 6 ml CH 4 at standard temperature and pressure (STP) conditions g VS À1 added . The methane production curves were further analysed to give values for the maximum specific methane production rate, ranging from 10 ml CH 4 g VSS À1 day À1 for a r I/S of 3-23 ml CH 4 g VSS À1 day À1 for a r I/S of 1. The initial buffering capacity of the system was enhanced by addition of NaHCO 3 to 9100 mg CaCO 3 l À1 which allowed digestion to proceed within the pH range 7.2-8.0 and at TVFA to TA ratio below the critical limit of 0.4. The largest proportion of the CODs was in the form of VFA and the reactor with the highest VS loading showed an accumulation of longer chain acids. #
Landfill avoidance for organic wastes is now a high priority worldwide. Two fractions of the muni... more Landfill avoidance for organic wastes is now a high priority worldwide. Two fractions of the municipal waste stream were considered with respect to their potential for diversion through controlled anaerobic digestion. The physical and chemical properties of source segregated domestic food waste (ss-FW) and of the mechanically-recovered organic fraction of municipal solid waste (mr-OFMSW) were analysed, and their methane yields determined in both batch and semi-continuous digestion. Methane potentials were compared with predicted values based on biochemical composition, elemental analysis and carbon mass balance, and the differences explained by compositional analysis of feedstocks and digestates.
ABSTRACT The biphasic production of the energy gases hydrogen and methane was possible in a fed b... more ABSTRACT The biphasic production of the energy gases hydrogen and methane was possible in a fed batch culture resulting in a volumetric mix of approximately 20% H2 and 80% CH4 and an energy conversion efficiency of 95%, based on the measured Chemical Oxygen Demand and theoretical calculations assuming that the substrate (a dairy waste permeate) was lactose. Gas production showed a rapid initial phase over 0–20h in which the composition was up to 50% hydrogen with the balance mainly carbon dioxide. This was accompanied by the accumulation of volatile fatty acids (VFA) in which butyric was predominant. A slower second phase of gas production produced a mixture of methane and carbon dioxide with a reduction in the accumulated acids. The duration of this second phase depended on the initial load applied to the reactor, and in the experiments carried out lasted between 6 and 12 days. Where the applied initial load led to an acid accumulation such that the pH fell below 5.5, the second phase of gas production was inhibited. Where pH control was exerted to prevent the pH dropping below 6.5, ethanol accumulated alongside VFA as a first phase product, with the gas comprised entirely of carbon dioxide. Despite the excellent energy conversion and the production of biogas fuel elements matching those for hythane (a mixture of hydrogen and methane, with improved combustion characteristics), the overall process loading was considered too low for efficient volumetric conversion of the feedstock to energy. The concept could be further developed based on high rate reactor systems with granular or immobilised biomass either as a single tank biphasic system or in a split tank two phase production process.
The research aimed to improve the overall conversion efficiency of the CTec® family of enzymes by... more The research aimed to improve the overall conversion efficiency of the CTec® family of enzymes by identifying factors that lead to inhibition and seeking methods to overcome these through process modification and manipulation. The starting material was pulp derived from municipal solid waste and processed in an industrial-scale washing plant.
Anaerobic co-digestion of residues from the cold pressing and trans-esterification of oilseed rap... more Anaerobic co-digestion of residues from the cold pressing and trans-esterification of oilseed rape (OSR) with other farm wastes was considered as a means of enhancing the sustainability of on-farm biodiesel production. The study verified the process energy yields using biochemical methane potential (BMP) tests and semi-continuous digestion trials. The results indicated that high proportions of OSR cake in the feedstock led to a decrease in volatile solids destruction and instability of the digestion process. Co-digestion with cattle slurry or with vegetable waste led to acceptable specific and volumetric methane productions, and a digestate low in potentially toxic elements (PTE). The results were used to evaluate energy balances and greenhouse gas emissions of the integrated process compared with biodiesel production alone. Co-digestion was shown to provide energy self-sufficiency and security of supply to farms, with sufficient surplus for export as fuel and electricity.
A two-phase system composed by a leach bed and a methanogenic reactor was modified for the first ... more A two-phase system composed by a leach bed and a methanogenic reactor was modified for the first time to improve volumetric substrate degradation and methane yields from a complex substrate (maize; Zea mays). The system, which was operated for consecutive feed cycles of different durations for 120 days, was highly flexible and its performance improved by altering operational conditions. Daily substrate degradation was higher the shorter the feed cycle, reaching 8.5 g TS destroyed d À1 (7-day feed cycle) but the overall substrate degradation was higher by up to 55% when longer feed cycles (14 and 28 days) were applied. The same occurred with volumetric methane yields, reaching 0.839 m 3 (m 3 ) À1 d À1 . The system performed better than others on specific methane yields, reaching 0.434 m 3 kg À1 TS added , in the 14-day and 28-day systems. The UASB and AF designs performed similarly as second stage reactors on methane yields, SCOD and VFA removal efficiencies.
Corrigendum to ''Biochemical methane potential of winter wheat (Triticum aestivum L.): Influence ... more Corrigendum to ''Biochemical methane potential of winter wheat (Triticum aestivum L.): Influence of growth stage and storage practice"
An anaerobic digester receiving food waste collected mainly from domestic kitchens was monitored ... more An anaerobic digester receiving food waste collected mainly from domestic kitchens was monitored over a period of 426 days. During this time information was gathered on the waste input material, the biogas production, and the digestate characteristics. A mass balance accounted for over 90% of the material entering the plant leaving as gaseous or digestate products. A comprehensive energy balance for the same period showed that for each tonne of input material the potential recoverable energy was 405 kWh. Biogas production in the digester was stable at 642 m3 tonne(-1) VS added with a methane content of around 62%. The nitrogen in the food waste input was on average 8.9 kg tonne(-1). This led to a high ammonia concentration in the digester which may have been responsible for the accumulation of volatile fatty acids that was also observed.
Cattle slurry and card packaging were used to improve the operational stability of food waste dig... more Cattle slurry and card packaging were used to improve the operational stability of food waste digestion, with the aim of reducing digestate total ammoniacal nitrogen concentrations compared to food waste only. Use of cattle slurry could have major environmental benefits through reducing greenhouse gas emissions associated with current management practices; whilst card packaging is closely linked to food waste and could be co-collected as a source segregated material. Both options increase the renewable energy potential whilst retaining organic matter and nutrients for soil replenishment. Co-digestion allowed higher organic loadings and gave a more stable process. A high ammonia inoculum acclimated more readily to cattle slurry than card packaging, probably through supplementation by trace elements and micro-organisms. Long-term operation at a 75-litre scale showed a characteristic pattern of volatile fatty acid accumulation in mono-digestion of food waste, and allowed performance parameters to be determined for the co-digestion substrates.
Abstract: A previously-developed mechanistic energy balance model for production of biogas from t... more Abstract: A previously-developed mechanistic energy balance model for production of biogas from the anaerobic digestion of microalgal biomass grown in open raceway systems was used to consider the energetic viability of a number of scenarios, and to explore some of the most critical parameters affecting net energy production. The output demonstrated that no single harvesting method of those considered (centrifugation, settlement or flocculation) produced an energy output sufficiently greater than operational energy inputs to make microalgal biogas production energetically viable. Combinations of harvesting methods could produce energy outputs 2.3–3.4 times greater than the operational energy inputs. Electrical energy to power pumps, mixers and harvesting systems was 5–8 times greater than the heating energy requirement. If the energy to power the plant is generated locally in a combined heat and power unit, a considerable amount of “low grade” heat will be available that is not required by the process, and for the system to show a net operational energy return this must be exploited. It is concluded that the production of microalgal biogas may be energetically viable, but it is dependent on the effective use of the heat generated by the combustion of biogas in combined heat and power units to show an operational energy return.
The paper describes the construction of a mechanistic energy balance model for the production of ... more The paper describes the construction of a mechanistic energy balance model for the production of biogas from anaerobic digestion of micro-algal biomass grown in raceways, based on simple principles and taking into account growth, harvesting and energy extraction. The model compares operational energy inputs with the calorific value of the output biomass in terms of the energy return on operational energy invested (EROOI). Initial results indicate that production of microalgal biogas will require: a) Favourable climatic conditions. The production of microalgal biofuel in UK would be energetically challenging at best. b) Achievement of ‘reasonable yields’ equivalent to ~3% photosynthetic efficiency (25 g m-2 day-1) c) Low or no cost and embodied energy sources of CO2 and nutrients from flue gas and wastewater d) Mesophilic rather than thermophilic digestion e) Adequate conversion of the organic carbon to biogas (≥ 60%) The model itself provides a powerful assessment tool both for comparison of alternative options and potentially for benchmarking real schemes.
Anaerobic digestion of autoclaved (160°C, 6.2 bar) and untreated source segregated food waste (FW... more Anaerobic digestion of autoclaved (160°C, 6.2 bar) and untreated source segregated food waste (FW) was compared over 473 days in semi-continuously fed mesophilic reactors with trace elements supplementation, at organic loading rates (OLRs) of 2, 3, 4 and 6 kg volatile solids(VS)/m(3)d. Methane yields at all OLR were 5-10% higher for untreated FW (maximum 0.483±0.013 m(3) CH4/kg VS at 3 kg VS/m(3) d) than autoclaved FW (maximum 0.439±0.020 m(3) CH4/kg VS at 4 kg VS/m(3) d). The residual methane potential of both digestates at all OLRs was less than 0.110 m(3) CH4/kg VS, indicating efficient methanation in all cases. Use of acclimated inoculum allowed very rapid increases in OLR. Reactors fed on autoclaved FW showed lower ammonium and hydrogen sulphide concentrations, probably due to reduced protein hydrolysis as a result of formation of Maillard compounds. In the current study this reduced biodegradability appears to outweigh any benefit due to thermal hydrolysis of ligno-cellulosic ...
Household bulky waste includes large and heavy items such as furniture and electrical appliances.... more Household bulky waste includes large and heavy items such as furniture and electrical appliances. Local authorities in England provide two options for disposing of these items: a special collection service, often involving a collection charge, and Household Waste Recycling Centres (HWRCs), where residents can take their waste free of charge. Local private companies and community or charitable organisations may also collect certain bulky items.In this study, 1450 householders in 3 cities across England were surveyed about a range of issues relating to the disposal of bulky items. Questionnaires were hand delivered to households pre-selected using the national Index of Multiple Deprivation in order to compare how disposal of bulky items differs with level of affluence.Sixty-five percent of householders had discarded bulky items in the 12 months prior to the survey. The principal disposal route was found to be the HWRC, with almost 60% of residents who had discarded items using this method. Only 19% of the householders had used the special collection services. In low-affluence areas, lower car ownership made residents more reliant on council collections of bulky items, and HWRCs were used less frequently. Householders were found to be satisfied with the collection service they had received.The study demonstrates that there is significant capacity for reuse and recycling of bulky items at a national level. Using the Waste Hierarchy, these management options are environmentally preferable to landfill, which is the widely-used disposal method at present. Where items are reused there are also social benefits for the community or charity groups involved, volunteers employed, and recipients of the items. Only the current bulky waste handlers – local authorities, can implement the logistical, and in some cases financial, solutions that are required to increase recovery in this waste stream.
This research explored the possible application of pressurised carbon dioxide (P CO(2)), a promis... more This research explored the possible application of pressurised carbon dioxide (P CO(2)), a promising non-thermal sterilisation technique, for the treatment of sewage sludge (SS) before anaerobic digestion to inactivate pathogenic microorganisms. Escherichia coli was selected as the test organism and was isolated from SS and maintained in pure culture. The growth curve of the isolated strain was determined by measuring the optical density (OD) in liquid culture medium and relating this information to the spread plate count so that a culture of known cell density could be grown for optimisation experiments. Inactivation of E. coli was enhanced by increase in pressure (1,500, 2,000 and 2,800 kPa) and treatment time (from 0.75 to 24 h). A short exposure time at high pressure was sufficient to provide a degree of inactivation which could also be achieved by longer exposure at lower pressure. Complete inactivation (8 log(10) reduction) was possible at all three pressures. scanning (SEM) and transmission (TEM) electron microscopy studies of E. coli treated with P CO(2) revealed that the cell walls were ruptured, and the cytoplasm was unevenly distributed and had lost its density, indicating the possible leakage of intracellular substances.
The River Nura in Central Kazakhstan has been heavily polluted by mercury originating from an ace... more The River Nura in Central Kazakhstan has been heavily polluted by mercury originating from an acetaldehyde plant. Mercury in the riverbed is mainly associated with power station fly ash, forming a new type of technogenic deposit. A systematic survey of the bed was carried out to establish the location, extent and nature of the contaminated sediments, and to evaluate the potential for sediment transport. The bed sediments were found to contain very high concentrations of mercury, particularly in the first 15 km downstream of the source of the pollution. Average total mercury concentrations in this section of the river are typically between 150 and 240 mg/kg, falling rapidly with increasing distance downstream. The estimated total volume of silts in the riverbed between Temirtau, the origin of the pollution, and Intumak Reservoir, located 75 km downstream, has been calculated as 463500 m3, containing an estimated 9.4 tonnes mercury. Forty-six percent of the total volume of contaminated silts containing almost 95% of the mercury are located in the upper 25 km of the river, however. The data clearly support the hypothesis that large quantities of polluted sediment are not transported long distances downstream but are removed from the aquatic environment in times of flood and deposited on the low-lying lands adjacent to the river. This process, however, does not stop mercury moving further downstream in the water column.
Completely mixed batch reactors were used to compare the methane production from maize at inoculu... more Completely mixed batch reactors were used to compare the methane production from maize at inoculum to substrate volatile solids ratios (r I/S ) of 3, 2, 1.5 and 1. The tests were carried out at 35 8C and run against a control of inoculum without substrate. The stability and progress of the reaction from solid substrate to gaseous end product was monitored by measuring the pH, soluble chemical oxygen demand (CODs), total alkalinity (TA), volatile fatty acids (VFA) and gas composition on a daily basis. The results showed that the yield coefficient showed little variation over the range used, with an average value of 211 AE 6 ml CH 4 at standard temperature and pressure (STP) conditions g VS À1 added . The methane production curves were further analysed to give values for the maximum specific methane production rate, ranging from 10 ml CH 4 g VSS À1 day À1 for a r I/S of 3-23 ml CH 4 g VSS À1 day À1 for a r I/S of 1. The initial buffering capacity of the system was enhanced by addition of NaHCO 3 to 9100 mg CaCO 3 l À1 which allowed digestion to proceed within the pH range 7.2-8.0 and at TVFA to TA ratio below the critical limit of 0.4. The largest proportion of the CODs was in the form of VFA and the reactor with the highest VS loading showed an accumulation of longer chain acids. #
Landfill avoidance for organic wastes is now a high priority worldwide. Two fractions of the muni... more Landfill avoidance for organic wastes is now a high priority worldwide. Two fractions of the municipal waste stream were considered with respect to their potential for diversion through controlled anaerobic digestion. The physical and chemical properties of source segregated domestic food waste (ss-FW) and of the mechanically-recovered organic fraction of municipal solid waste (mr-OFMSW) were analysed, and their methane yields determined in both batch and semi-continuous digestion. Methane potentials were compared with predicted values based on biochemical composition, elemental analysis and carbon mass balance, and the differences explained by compositional analysis of feedstocks and digestates.
ABSTRACT The biphasic production of the energy gases hydrogen and methane was possible in a fed b... more ABSTRACT The biphasic production of the energy gases hydrogen and methane was possible in a fed batch culture resulting in a volumetric mix of approximately 20% H2 and 80% CH4 and an energy conversion efficiency of 95%, based on the measured Chemical Oxygen Demand and theoretical calculations assuming that the substrate (a dairy waste permeate) was lactose. Gas production showed a rapid initial phase over 0–20h in which the composition was up to 50% hydrogen with the balance mainly carbon dioxide. This was accompanied by the accumulation of volatile fatty acids (VFA) in which butyric was predominant. A slower second phase of gas production produced a mixture of methane and carbon dioxide with a reduction in the accumulated acids. The duration of this second phase depended on the initial load applied to the reactor, and in the experiments carried out lasted between 6 and 12 days. Where the applied initial load led to an acid accumulation such that the pH fell below 5.5, the second phase of gas production was inhibited. Where pH control was exerted to prevent the pH dropping below 6.5, ethanol accumulated alongside VFA as a first phase product, with the gas comprised entirely of carbon dioxide. Despite the excellent energy conversion and the production of biogas fuel elements matching those for hythane (a mixture of hydrogen and methane, with improved combustion characteristics), the overall process loading was considered too low for efficient volumetric conversion of the feedstock to energy. The concept could be further developed based on high rate reactor systems with granular or immobilised biomass either as a single tank biphasic system or in a split tank two phase production process.
The research aimed to improve the overall conversion efficiency of the CTec® family of enzymes by... more The research aimed to improve the overall conversion efficiency of the CTec® family of enzymes by identifying factors that lead to inhibition and seeking methods to overcome these through process modification and manipulation. The starting material was pulp derived from municipal solid waste and processed in an industrial-scale washing plant.
Anaerobic co-digestion of residues from the cold pressing and trans-esterification of oilseed rap... more Anaerobic co-digestion of residues from the cold pressing and trans-esterification of oilseed rape (OSR) with other farm wastes was considered as a means of enhancing the sustainability of on-farm biodiesel production. The study verified the process energy yields using biochemical methane potential (BMP) tests and semi-continuous digestion trials. The results indicated that high proportions of OSR cake in the feedstock led to a decrease in volatile solids destruction and instability of the digestion process. Co-digestion with cattle slurry or with vegetable waste led to acceptable specific and volumetric methane productions, and a digestate low in potentially toxic elements (PTE). The results were used to evaluate energy balances and greenhouse gas emissions of the integrated process compared with biodiesel production alone. Co-digestion was shown to provide energy self-sufficiency and security of supply to farms, with sufficient surplus for export as fuel and electricity.
A two-phase system composed by a leach bed and a methanogenic reactor was modified for the first ... more A two-phase system composed by a leach bed and a methanogenic reactor was modified for the first time to improve volumetric substrate degradation and methane yields from a complex substrate (maize; Zea mays). The system, which was operated for consecutive feed cycles of different durations for 120 days, was highly flexible and its performance improved by altering operational conditions. Daily substrate degradation was higher the shorter the feed cycle, reaching 8.5 g TS destroyed d À1 (7-day feed cycle) but the overall substrate degradation was higher by up to 55% when longer feed cycles (14 and 28 days) were applied. The same occurred with volumetric methane yields, reaching 0.839 m 3 (m 3 ) À1 d À1 . The system performed better than others on specific methane yields, reaching 0.434 m 3 kg À1 TS added , in the 14-day and 28-day systems. The UASB and AF designs performed similarly as second stage reactors on methane yields, SCOD and VFA removal efficiencies.
Corrigendum to ''Biochemical methane potential of winter wheat (Triticum aestivum L.): Influence ... more Corrigendum to ''Biochemical methane potential of winter wheat (Triticum aestivum L.): Influence of growth stage and storage practice"
An anaerobic digester receiving food waste collected mainly from domestic kitchens was monitored ... more An anaerobic digester receiving food waste collected mainly from domestic kitchens was monitored over a period of 426 days. During this time information was gathered on the waste input material, the biogas production, and the digestate characteristics. A mass balance accounted for over 90% of the material entering the plant leaving as gaseous or digestate products. A comprehensive energy balance for the same period showed that for each tonne of input material the potential recoverable energy was 405 kWh. Biogas production in the digester was stable at 642 m3 tonne(-1) VS added with a methane content of around 62%. The nitrogen in the food waste input was on average 8.9 kg tonne(-1). This led to a high ammonia concentration in the digester which may have been responsible for the accumulation of volatile fatty acids that was also observed.
Cattle slurry and card packaging were used to improve the operational stability of food waste dig... more Cattle slurry and card packaging were used to improve the operational stability of food waste digestion, with the aim of reducing digestate total ammoniacal nitrogen concentrations compared to food waste only. Use of cattle slurry could have major environmental benefits through reducing greenhouse gas emissions associated with current management practices; whilst card packaging is closely linked to food waste and could be co-collected as a source segregated material. Both options increase the renewable energy potential whilst retaining organic matter and nutrients for soil replenishment. Co-digestion allowed higher organic loadings and gave a more stable process. A high ammonia inoculum acclimated more readily to cattle slurry than card packaging, probably through supplementation by trace elements and micro-organisms. Long-term operation at a 75-litre scale showed a characteristic pattern of volatile fatty acid accumulation in mono-digestion of food waste, and allowed performance parameters to be determined for the co-digestion substrates.
Abstract: A previously-developed mechanistic energy balance model for production of biogas from t... more Abstract: A previously-developed mechanistic energy balance model for production of biogas from the anaerobic digestion of microalgal biomass grown in open raceway systems was used to consider the energetic viability of a number of scenarios, and to explore some of the most critical parameters affecting net energy production. The output demonstrated that no single harvesting method of those considered (centrifugation, settlement or flocculation) produced an energy output sufficiently greater than operational energy inputs to make microalgal biogas production energetically viable. Combinations of harvesting methods could produce energy outputs 2.3–3.4 times greater than the operational energy inputs. Electrical energy to power pumps, mixers and harvesting systems was 5–8 times greater than the heating energy requirement. If the energy to power the plant is generated locally in a combined heat and power unit, a considerable amount of “low grade” heat will be available that is not required by the process, and for the system to show a net operational energy return this must be exploited. It is concluded that the production of microalgal biogas may be energetically viable, but it is dependent on the effective use of the heat generated by the combustion of biogas in combined heat and power units to show an operational energy return.
Uploads
Papers by Sonia Heaven
a) Favourable climatic conditions. The production of microalgal biofuel in UK would be energetically challenging at best.
b) Achievement of ‘reasonable yields’ equivalent to ~3% photosynthetic efficiency (25 g m-2 day-1)
c) Low or no cost and embodied energy sources of CO2 and nutrients from flue gas and wastewater
d) Mesophilic rather than thermophilic digestion
e) Adequate conversion of the organic carbon to biogas (≥ 60%)
The model itself provides a powerful assessment tool both for comparison of alternative options and potentially for benchmarking real schemes.
the energetic viability of a number of scenarios, and to explore some of the most critical parameters affecting net energy production. The output demonstrated that no single harvesting method of
those considered (centrifugation, settlement or flocculation) produced an energy output sufficiently greater than operational energy inputs to make microalgal biogas production energetically viable.
Combinations of harvesting methods could produce energy outputs 2.3–3.4 times greater than the operational energy inputs. Electrical energy to power pumps, mixers and harvesting systems was 5–8 times greater than the heating energy requirement. If the energy to power the plant is generated locally in a combined heat and power unit, a considerable amount of “low grade” heat will be available that is not required by the process, and for the system to show a net operational energy
return this must be exploited. It is concluded that the production of microalgal biogas may be energetically viable, but it is dependent on the effective use of the heat generated by the combustion
of biogas in combined heat and power units to show an operational energy return.
a) Favourable climatic conditions. The production of microalgal biofuel in UK would be energetically challenging at best.
b) Achievement of ‘reasonable yields’ equivalent to ~3% photosynthetic efficiency (25 g m-2 day-1)
c) Low or no cost and embodied energy sources of CO2 and nutrients from flue gas and wastewater
d) Mesophilic rather than thermophilic digestion
e) Adequate conversion of the organic carbon to biogas (≥ 60%)
The model itself provides a powerful assessment tool both for comparison of alternative options and potentially for benchmarking real schemes.
the energetic viability of a number of scenarios, and to explore some of the most critical parameters affecting net energy production. The output demonstrated that no single harvesting method of
those considered (centrifugation, settlement or flocculation) produced an energy output sufficiently greater than operational energy inputs to make microalgal biogas production energetically viable.
Combinations of harvesting methods could produce energy outputs 2.3–3.4 times greater than the operational energy inputs. Electrical energy to power pumps, mixers and harvesting systems was 5–8 times greater than the heating energy requirement. If the energy to power the plant is generated locally in a combined heat and power unit, a considerable amount of “low grade” heat will be available that is not required by the process, and for the system to show a net operational energy
return this must be exploited. It is concluded that the production of microalgal biogas may be energetically viable, but it is dependent on the effective use of the heat generated by the combustion
of biogas in combined heat and power units to show an operational energy return.