Promoting Sustainability: Wastewater Treatment Plants as a Source of Biomethane in Regions Far from a High-Pressure Grid. A Real Portuguese Case Study

A mini-review of biomethane valorization: Managerial and policy implications for a circular resource

The green transition requires renewable energy resources, especially the role of biomass is very crucial as it promotes resource circularity if sustainable substrates are used. This mini-review focuses on green gas derived from biomass called biomethane, which appears to be strategic in the face of soaring energy costs. Hence, combined Strengths, Weaknesses, Opportunities and Threats-Analytic Hierarchy Process analysis is used to compare and evaluate the critical factors. The results provide not only methodological insights through the application of the local-global priority method, but also managerial insights that see biomethane as a winning element for the green transition, fighting climate change and reducing dependence on external energy sources. Subsidies have played a key role in pursuing economic sustainability; however, their use should be reduced over time and measured to the actual contribution related to environmental and social improvement. The results of this work highlight that biomethane development is important to tackle climate change and to be self-sufficient from an energy perspective. This development plan, based on circularity of resources, includes subsidies for small-scale plants, substrates from neighbouring territories, citizen involvement in decision-making processes, valorization of suitable waste from an environmental perspective and stability of political choices.

Economic Assessment of Energy Consumption in Wastewater Treatment Plants: Applicability of Alternative Nature-Based Technologies in Portugal

Understanding how to address today’s global challenges is critical to improving corporate performance in terms of economic and environmental sustainability. In wastewater treatment systems, such an approach implies integrating efficient treatment technologies with aspects of the circular economy. In this business field, energy costs represent a large share of operating costs. This work discusses technological and management aspects leading to greater energy savings in Portuguese wastewater treatment companies. A mixed methodology, involving qualitative and quantitative aspects, for collecting and analysing data from wastewater treatment plants was used. The qualitative aspects consisted of a narrative analysis of the information available on reports and websites for 11 wastewater management companies in Portugal (e.g., technologies, treated wastewater volumes and operating costs) followed by a review of several international studies. The quantitative approach involved calculating the specific energy consumption (kWh/m3), energy operating costs (EUR/m3) and energy operating costs per population equivalent (EUR/inhabitants) using data from the literature and from Portuguese companies collected from the SABI database. The results suggested that the most environmentally and economically sustainable solution is algae-based technology which might allow a reduction in energy operating costs between 0.05–0.41 EUR/m3 and 15.4–180.8 EUR/inhabitants compared to activated sludge and other conventional methods. This technology, in addition to being financially advantageous, provides the ability to eliminate the carbon footprint and the valorisation of algae biomass, suggesting that this biotechnology is starting to position itself as a mandatory future solution in the wastewater treatment sector.

Biomethane Community: A Research Agenda towards Sustainability

The bioeconomy is an effective solution to align with the sustainability agenda and to meet the pressing calls for action from Cop26 on a global scale. The topic of the circular bioeconomy has gained a key role in the literature, while the theme of energy community is a basic form of social aggregation among stakeholders. This work focuses on biomethane and proposes a framework based on several criteria that are evaluated using a hybrid Analytic Hierarchy Process (AHP) and 10-point scale methodology. The results show that regulation and energy community are considered the two most relevant categories. The overall ranking of criteria sees the stakeholders’ engagement as the most important, followed by more significant subsidies for small- and medium-sized plants and the principle of self-sufficiency applied at the inter-regional level. Subsequently, the Italian Adriatic corridor composed of four MMAP (Marche, Molise, Abruzzo, and Puglia) regions is considered as a case study in order to evaluate the possible environmental (854 thousand tons CO2eqyear) and economic (from 49 million EUR to 405 million EUR in function of plant size) benefits associated with potential biomethane production of 681.6 million m3. It is found that the biomethane community is an enabler of sustainability and this strategy can be used for sharing different natural resources.

Tree Resin, a Macroergic Source of Energy, a Possible Tool to Lower the Rise in Atmospheric CO2 Levels

Tree resin is a macroergic component that has not yet been used for energy purposes. The main goal of this work is to determine the energy content of the resin of spruce, pine, and larch and of wood components—pulp and turpentine. The combustion heat of resin from each timber was determined calorimetrically. Approximately 1.0 g of liquid samples was applied in an adiabatic calorimeter. The energy values of the tree resin (>38.0 MJ·kg−1) were 2.2 and 2.4 times higher than that of bleached and unbleached cellulose, and the highest value was recorded for turpentine (>39.0 MJ·kg−1). Due to the high heating values of the resin, it is necessary to develop approaches to the technological processing of the resin for energy use. The best method of resin tapping is the American method, providing 5 kg of resin ha−1 yr−1. The tapped resin quantity can be raised by least 3 times by applying a stimulant. Its production cost compared to other feedstocks was the lowest. Tree resin can be applied as a means of mitigating global warming and consequently dampening climate change by reducing the CO2 content in the atmosphere. One tonne of tree resin burned instead of coal spares the atmosphere 5.0 Mt CO2.

Biogas upgrading to biomethane as a local source of renewable energy to power light marine transport: Profitability analysis for the county of Cornwall

In this work, the use of biomethane produced from local biogas plants is proposed as renewable fuel for light marine transport. A profitability analysis is performed for three real biogas production plants located in Cornwall (United Kingdom), considering a total of 66 different scenarios where critical parameters such as distance from production point to gas grid, subsidies, etcetera, were evaluated. Even though the idea is promising to decarbonize the marine transport sector, under the current conditions, the approach is not profitable. The results show that profitability depends on the size of the biogas plant. The largest biogas plant studied can be profitable if feed-in tariffs subsidies between 36.6 and 45.7 €/MWh are reached, while for the smallest plant, subsidies should range between 65 and 82.7 €/MWh. The tax to be paid per ton of CO₂ emitted by the shipping owner, was also examined given its impact in this green route profitability. Values seven times greater than current taxes are needed to reach profitability, revealing the lack of competitiveness of renewable fuels vs traditional fuels in this application. Subsidies to make up a percentage of the investment are also proposed, revealing that even at 100% of investment subsidized, this green approach is still not profitable. The results highlight the need for further ambitious political actions in the pursuit of sustainable societies.

Bioeconomy of Sustainability: Drivers, Opportunities and Policy Implications

Sustainability is characterized by a growing trend in the number of papers published in the last years, for an increasing impact factor and because today a large number of experts and researchers dealing with this issue have published in this journal [...]

Hydropower Technology for Sustainable Energy Generation in Wastewater Systems: Learning from the Experience

Hydropower is a well-known technology, applied worldwide for electricity generation from renewable sources. Within the current framework, some studies have started to consider its application to existing urban water systems, to harness an excess of energy that otherwise would be wasted. This research sought to determine a methodology to assess the potential of hydropower application to wastewater treatment plants (WWTPs), regarding different aspects of sustainability. Firstly, previously developed methodologies for potential assessment in this sector at a country level were analyzed. Secondly, data from existing real case studies were gathered from publicly available documents and a theoretical analysis of their actual performance was conducted to validate assumptions made in the previous methodologies. As a result, the proposed new approach suggests adapting methodologies for potential assessment at a lower level, considering possible driving factors, other than economic feasibility. To define the study area, the management model scope should be considered. The power to determine the cut-off point for a WWTP to be considered as a potential site, is proposed to be lowered according to technical feasibility. Additionally, bearing in mind the sustainability concept, social or environmental factors should also be introduced in the methodology, tailored to the region being assessed. This novel perspective could provide a closer approach to the most likely decision-making level for these kinds of strategies in the wastewater industry.

Synthesis, Characterization, and Synergistic Effects of Modified Biochar in Combination with α-Fe2O3 NPs on Biogas Production from Red Algae Pterocladia capillacea

This study is the first work that evaluated the effectiveness of unmodified (SD) and modified biochar with ammonium hydroxide (SD-NH2) derived from sawdust waste biomass as an additive for biogas production from red algae Pterocladia capillacea either individually or in combination with hematite α-Fe2O3 NPs. Brunauer, Emmett, and Teller, Fourier transform infrared, thermal gravimetric analysis, X-ray diffraction, transmission electron microscopy, Raman, and a particle size analyzer were used to characterize the generated biochars and the synthesized α-Fe2O3. Fourier transform infrared (FTIR) measurements confirmed the formation of amino groups on the modified biochar surface. The kinetic research demonstrated that both the modified Gompertz and logistic function models fit the experimental data satisfactorily except for 150 SD-NH2 alone or in combination with α-Fe2O3 at a concentration of 10 mg/L. The data suggested that adding unmodified biochar at doses of 50 and 100 mg significantly increased biogas yield compared to untreated algae. The maximum biogas generation (219 mL/g VS) was obtained when 100 mg of unmodified biochar was mixed with 10 mg of α-Fe2O3 in the inoculum.