• Energy Research

Studies have demonstrated that a minute quantity of graphene is sufficient to boost cement characteristics, but the attainment of good dispersion and uniformity of the resultant graphene-cement mixture remains a challenge. To alleviate these challenges, this study proposes a low-energy powder-to-powder homogeniser for dispersing reasonably large quantities of graphene powder into cement powders. Microscopic analysis of graphene dispersion from two samples (1% and 0.02% graphene) at 5x, 10x and 20x objectives revealed that graphene accounts for 1.3% and 0.09% over the cement area respectively, which is relatively uniform across all selected samples. Furthermore, four different dosages of graphene were used to validate the impacts of various proportions of graphene, i.e., 0%, 0.02%, 0.04% and 0.06% (by mass of cement) on two types of cement (i.e., Portland cement CEM I 52.5 N and Portland cement CEM II 42.5 N) which also revealed compressive strength increases up to 25% at 7 and 28 days.

Studies have demonstrated that a minute quantity of graphene is sufficient to boost cement characteristics, but the attainment of good dispersion and uniformity of the resultant graphene-cement mixture remains a challenge. To alleviate these challenges, this study proposes a low-energy powder-to-powder homogeniser for dispersing reasonably large quantities of graphene powder into cement powders. Microscopic analysis of graphene dispersion from two samples (1% and 0.02% graphene) at 5x, 10x and 20x objectives revealed that graphene accounts for 1.3% and 0.09% over the cement area respectively, which is relatively uniform across all selected samples. Furthermore, four different dosages of graphene were used to validate the impacts of various proportions of graphene, i.e., 0%, 0.02%, 0.04% and 0.06% (by mass of cement) on two types of cement (i.e., Portland cement CEM I 52.5 N and Portland cement CEM II 42.5 N) which also revealed compressive strength increases up to 25% at 7 and 28 days.

Abstract Access to sufficient quantities of fresh water is becoming increasingly difficult, especially in dry regions. Moreover, high levels of salinity, arsenic and boron are further limiting the access to quality fresh water in many isolated communities worldwide. This paper evaluates the life cycle environmental impacts of a small multi-effect distillation (MED) plant, treating brackish water with high levels of these metalloids in an isolated location in Northern Chile. The facility currently operates solely with electricity from a diesel generator and heat from a biomass boiler. In order to evaluate the environmental impacts of more sustainable energy options, the implications of the use of solar fields and grid electricity as potential alternatives have been analysed. The results demonstrate that coupling solar fields and grid electricity is the best option, sharply decreasing impact in most categories in comparison to the current operating mode of the plant. This was attributed to the impact savings from reducing/eliminating onsite diesel and biomass combustion, and their associated transportation to the plant. For MED desalination in off-the-grid areas, the use of solar energy is highly recommended as an alternative to complement the use of diesel and biomass, especially if the latter is not nearby the unit. The concentration of arsenic and boron was reduced to below the required standards for irrigation and livestock consumption. The article concludes that the use of solar energy and grid electricity are environmentally beneficial for the production of quality fresh water from brackish water using MED at isolated communities.

Abstract Access to sufficient quantities of fresh water is becoming increasingly difficult, especially in dry regions. Moreover, high levels of salinity, arsenic and boron are further limiting the access to quality fresh water in many isolated communities worldwide. This paper evaluates the life cycle environmental impacts of a small multi-effect distillation (MED) plant, treating brackish water with high levels of these metalloids in an isolated location in Northern Chile. The facility currently operates solely with electricity from a diesel generator and heat from a biomass boiler. In order to evaluate the environmental impacts of more sustainable energy options, the implications of the use of solar fields and grid electricity as potential alternatives have been analysed. The results demonstrate that coupling solar fields and grid electricity is the best option, sharply decreasing impact in most categories in comparison to the current operating mode of the plant. This was attributed to the impact savings from reducing/eliminating onsite diesel and biomass combustion, and their associated transportation to the plant. For MED desalination in off-the-grid areas, the use of solar energy is highly recommended as an alternative to complement the use of diesel and biomass, especially if the latter is not nearby the unit. The concentration of arsenic and boron was reduced to below the required standards for irrigation and livestock consumption. The article concludes that the use of solar energy and grid electricity are environmentally beneficial for the production of quality fresh water from brackish water using MED at isolated communities.

Sewage sludge handling is becoming a concern in Europe due to its increasing amount and the presence of contaminants, such as heavy metals and pharmaceutical and personal care products (PPCPs). Currently, over 70% of sludge in Europe is treated thermally by incineration or used as fertilizer in agriculture. New thermochemical methods are under development and are expected to be implemented in the near future. This paper considers the life cycle environmental impacts of the following five alternatives for sludge handling, taking into account the presence of heavy metals and PPCPs: i) agricultural application of anaerobically digested sludge; ii) agricultural application of composted sludge; iii) incineration; iv) pyrolysis; and v) wet air oxidation. The results suggest that anaerobic digestion with recovery of nutrients and electricity has the lowest environmental impacts in 11 out of 18 categories considered. For the mean to maximum resource recovery, composting is the worst alternative, followed by pyrolysis with lower recovery rates. Agricultural application of anaerobically digested sludge has the highest freshwater ecotoxicity due to heavy metals, unless their concentration is in the lowest range, as found in some European sewage sludge applied on land. Therefore, stricter control of heavy metals in the sludge is needed for this option to limit freshwater ecotoxicity to the levels comparable with the thermal processes. The results also indicate that PPCPs have a negligible contribution to freshwater ecotoxicity when compared to heavy metals in the anaerobically digested sludge. Since thermal processes are currently drawing attention due to their potential benefits, the findings of this work suggest that their adoption is environmentally beneficial only if high resource recovery rates can be achieved.

Sewage sludge handling is becoming a concern in Europe due to its increasing amount and the presence of contaminants, such as heavy metals and pharmaceutical and personal care products (PPCPs). Currently, over 70% of sludge in Europe is treated thermally by incineration or used as fertilizer in agriculture. New thermochemical methods are under development and are expected to be implemented in the near future. This paper considers the life cycle environmental impacts of the following five alternatives for sludge handling, taking into account the presence of heavy metals and PPCPs: i) agricultural application of anaerobically digested sludge; ii) agricultural application of composted sludge; iii) incineration; iv) pyrolysis; and v) wet air oxidation. The results suggest that anaerobic digestion with recovery of nutrients and electricity has the lowest environmental impacts in 11 out of 18 categories considered. For the mean to maximum resource recovery, composting is the worst alternative, followed by pyrolysis with lower recovery rates. Agricultural application of anaerobically digested sludge has the highest freshwater ecotoxicity due to heavy metals, unless their concentration is in the lowest range, as found in some European sewage sludge applied on land. Therefore, stricter control of heavy metals in the sludge is needed for this option to limit freshwater ecotoxicity to the levels comparable with the thermal processes. The results also indicate that PPCPs have a negligible contribution to freshwater ecotoxicity when compared to heavy metals in the anaerobically digested sludge. Since thermal processes are currently drawing attention due to their potential benefits, the findings of this work suggest that their adoption is environmentally beneficial only if high resource recovery rates can be achieved.

Abstract Water treated in advanced wastewater treatment plants (WWTPs) could be reused as potable water to address water shortages. Furthermore, sludge from WWTPs can be used to recover nutrients, energy and chemicals. Thus, the role of WWTPs could change from traditional pollution control facilities to sources of freshwater and other valuable resources. However, the economic viability of advanced wastewater and sludge treatment methods aimed at production of potable water and recovery of other resources is currently unknown. To address this gap and inform their future development, this paper considers life cycle costs of the following four wastewater treatment methods: granular activated carbon, nanofiltration, solar photo-Fenton and ozonation. For recovery of resources from sludge, the following options are examined: agricultural application of anaerobically-digested and composted sludge, incineration, pyrolysis and wet air oxidation. Ozonation has the lowest life cycle costs, averaging £112 per 1000 m3 of water treated, followed by nanofiltration at £134. Solar photo-Fenton is the most expensive option with £238/1000 m3. These costs are significantly lower than water desalination and could be competitive in the future with conventional potable water production. For resource recovery from sludge, anaerobic digestion, pyrolysis and wet air oxidation can operate at a profit with the negative overall life cycle costs (-£65, -£291 and -£26/1000 kg dry matter, respectively) if all their recovered products are fully utilised. The next best option is composting with the total life cycle costs of £35/1000 kg dry matter. Incineration is the least preferred alternative with the cost of nearly £54/1000 kg dry matter. Advanced wastewater and sludge treatment would increase the costs of conventional wastewater treatment by 1.5–2.1 times.

Abstract Water treated in advanced wastewater treatment plants (WWTPs) could be reused as potable water to address water shortages. Furthermore, sludge from WWTPs can be used to recover nutrients, energy and chemicals. Thus, the role of WWTPs could change from traditional pollution control facilities to sources of freshwater and other valuable resources. However, the economic viability of advanced wastewater and sludge treatment methods aimed at production of potable water and recovery of other resources is currently unknown. To address this gap and inform their future development, this paper considers life cycle costs of the following four wastewater treatment methods: granular activated carbon, nanofiltration, solar photo-Fenton and ozonation. For recovery of resources from sludge, the following options are examined: agricultural application of anaerobically-digested and composted sludge, incineration, pyrolysis and wet air oxidation. Ozonation has the lowest life cycle costs, averaging £112 per 1000 m3 of water treated, followed by nanofiltration at £134. Solar photo-Fenton is the most expensive option with £238/1000 m3. These costs are significantly lower than water desalination and could be competitive in the future with conventional potable water production. For resource recovery from sludge, anaerobic digestion, pyrolysis and wet air oxidation can operate at a profit with the negative overall life cycle costs (-£65, -£291 and -£26/1000 kg dry matter, respectively) if all their recovered products are fully utilised. The next best option is composting with the total life cycle costs of £35/1000 kg dry matter. Incineration is the least preferred alternative with the cost of nearly £54/1000 kg dry matter. Advanced wastewater and sludge treatment would increase the costs of conventional wastewater treatment by 1.5–2.1 times.