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Abstract Microorganisms used in syngas fermentation require nutrients to grow and convert syngas (CO, H2 and CO2) into various products. Many of the essential nutrients can be provided by biochar. Poultry litter biochar (PLBC) contains minerals and trace metals and has a high pH buffering capacity, making it suitable as a nutrient supplement. The effects of PLBC loadings from 1 to 20 g L−1 on syngas fermentation were determined in 250 ml bottle assays. Results showed that 10 and 20 g L−1 PLBC significantly increased ethanol production compared to standard yeast extract (YE) medium. Fermentations in a 3L continuous stirred tank reactor (CSTR) with 10 g L−1 PLBC with and without 4-morpholineethanesulfonic acid (MES) showed 64% and 36% more ethanol production, respectively, than standard medium. The acetic acid accumulated at the beginning of fermentation was completely converted to ethanol in all media tested in the CSTR. These results demonstrate the feasibility of using PLBC medium without costly MES in the CSTR to enhance ethanol production from syngas for potential use at commercial scale.

Abstract Small Mediterranean islands are remote, off-grid communities characterized by carbon intensive electricity systems coupled with high energy consuming desalination technologies to produce potable water. The aim of this study is to propose a novel dynamic, multi-objective optimization approach for improving the sustainability of small islands through the introduction of renewable energy sources. The main contributions of our approach include: (i) dynamic modelling of desalination plant operations, (ii) joint optimization of system design and operations, (iii) multi-objective optimization to explore trade-offs between potentially conflicting objectives. We test our approach on the real case study of the Italian Ustica island by means of a comparative analysis with a traditional non-dynamic, least cost optimization approach. Numerical results show the effectiveness of our approach in identifying optimal system configurations, which outperform the traditional design with respect to different sustainability indicators, limiting the structural interventions, the investment costs and the environmental impacts. In particular, the optimal dynamic solutions able to satisfy the whole water demand allow high levels of penetration of renewable energy sources (up to more than 40%) to be reached, reducing the net present cost by about 2–3 M€ and the CO2 emissions by more than 200 tons/y.

This paper investigates thermal mixing caused by the inflow from one or two round, horizontal, buoyant jets in a water storage tank, which is part of a thermal solar installation. A set of experiments was carried out in a rectangular tank with a capacity of 0.3 m3, with one or two constant temperature inflows. As a result, two correlations based on temperature measurements have been developed. One of the correlations predicts the size of a zone of homogenous temperature, referred to herein as the mixing zone, which develops when a single hot inflow impinges on the opposite wall of the tank. The other identifies the degree of mixing resulting from the interaction between a hot inflow and a cold inflow located below the hot one. The correlations are combined with energy balances to predict the amount of hot water available in a tank with open side inlets and the corresponding temperatures of the outflows. Outdoor measurements were also performed in a solar installation, in which a commercial water storage tank with a 1.5 m3 capacity, heated by a solar collector array with a useful surface area of 42.2 m2, drives a LiBr–H2O absorption chiller. Comparison of the predicted and measured outflow temperatures under a variety of weather conditions shows a maximum difference of 3 °C.

Abstract Uninterrupted energy harvest is critical for self-sustained wastewater monitoring in order to achieve efficient and resilient operation of decentralized onsite wastewater treatment facilities. To address this long-standing challenge, an integrated power entity consisting of a miniature microbial fuel cell (volume: 1.5 mL) and a triggered power management system was developed in this study to power the potentiometric millimeter-sized solid-state water sensors for real-time in situ monitoring and uninterrupted transmission of sensor readings (indicating ammonium concentration) under both ammonium shock and toxic shock in wastewater. Specifically, a data trigger including two capacitors, an operation amplifier and a low-power comparator is equipped in the power management system as a switch for turning on power discharge for data transmission once the ammonium shock is captured by the potentiometric sensors, enabling a sufficient recharge duration to store the power needed for high frequency data transmission (16.23 times/min) required under shocks. Furthermore, this power-sensor entity possesses a unique dual-screening capability of capturing the ammonium and toxic shocks, providing an early warning for swift decision making, reducing ~17% of ammonium discharge and saving ~42% of energy consumption in decentralized onsite wastewater treatment facilities.

Abstract Biofuels and the oleochemical industry are highly dependent on plant oils for the generation of renewable product lines. Consequently, production of plant lipids, such as palm and rapeseed oil, for industrial applications competes with agricultural activity and is associated with a negative environmental impact. Additionally, established chemical routes for upgrading bio-lipids to renewable products depend on metal-containing catalysts. Metal leaching during oil processing results in heavy metal contaminated process wastewater. This water is difficult to remediate and leads to the loss of precious metals. Therefore, the biofuels and chemical industry requires sustainable solutions for production and upgrading of bio-lipids. With regard to the former, a promising approach is the fermentative conversion of abundant, low-value biomass into microbial, particularly yeast-based lipids. This study describes the holistic, value-adding conversion of underexploited, macroalgae feedstocks into yeast oil, animal feed and biosorbents for metal-based detoxification of process wastewater. The initial step comprises a selective enzymatic liquefaction step that yields a supernatant containing 62.5% and 59.3% (w/dwbiomass) fermentable sugars from L. digitata and U. lactuca, respectively. By dispensing with chemical pretreatment constraints, we achieved a 95% (w/w) glucose recovery. Therefore, the supernatant was qualified as a cultivation media without any detoxification step or nutrition addition. Additionally, the hydrolysis step provided 27–33% (w/dwbiomass) of a solid residue, which was qualified as a metal biosorbent. Cultivation of the oleaginous yeast C. oleaginosus on the unprocessed hydrolysis supernatant provided 44.8 g L−1 yeast biomass containing 37.1% (w/dwbiomass) lipids. The remaining yeast biomass after lipid extraction is targeted as a performance animal feed additive. Selectivity and capacity of solid macroalgae residues as biosorbents were assessed for removal and recycling of rare and heavy metals, such as Ce+3, Pb+2, Cu+2 and Ni+2 from model wastewater. The biosorption capacity of the macroalgae residues (sorption capacity ∼ 0.7 mmol g−1) exceeds that of relevant commercially available adsorption resins and biosorbents. To facilitate the integration of our technology in existing chemical and biotechnological production environments, we have devised simple, rapid and cost-efficient methods for monitoring both lipogenesis and metal sorption processes. The application of the new optical monitoring tools is essential to determine yeast cell harvesting times and biosorption capacities respectively. For the first time we report on a waste-free bioprocess that combines sustainable, microbial lipid production from low value marine biomass with in-process precious metal recycling options. Our data allowed for a preliminary economic analysis, which indicated that each product could be cost competitive with current market equivalents. Hence, the synaptic nature of the technology platform provides for the economic and ecologic viability of the overall process chain.

Abstract This paper examines the dynamic cell performance of a kW-grade proton exchange membrane fuel cell stack with anode dead-ended mode fuel supply. A self-made kW-grade 40 cells stack with reaction area of 112.85 cm 2 has been used in the experiment. A single-chip (DSPIC30F4011) is utilized for establishing a control circuit to monitor the voltage and current with constant-current loading. The stack temperature is controlled at a low-level temperature rise. To enhance the hydrogen utilization and reduce the water flooding in the fuel cell stack, the dead-ended anode operation is accomplished by controlling the open or close of the anode outlet solenoid valve. As the loading is heavy, the anode outlet solenoid valve is purged frequently to force the water to flow out. While a light load, the anode outlet solenoid valve is shut down for a period time for hydrogen saving. The solenoid valve is controlled to be opened, referred as purge interval, reaching the discharge amount for 1000 C, 1500 C, and 2000 C as parameter, respectively. The open period of solenoid valve, referred as purge duration, is set as 1 s, 3 s, and 5 s for this study. Experimental results indicate an optimal purge interval and duration for water management and cell performance of the fuel cell stack.

Abstract Sustainable design methods focus on reducing or minimizing the demand for ecosystem goods and services, quantified as natural resources and pollutant mitigation. However, the capacity of ecosystems to supply these demands is routinely ignored, leading to decisions that overburden ecological processes and cause environmental damage. This work develops a techno-ecological synergy (TES) design methodology that balances the ecosystem services that can be provided by nature with the ecosystem service demands created by human activities. The methodology includes the design of technological processes that require ecosystem services as well as the ecological processes that supply those services. The TES Design methodology is demonstrated by application to a renewable energy production system that includes both land use activities, such as agriculture and wind turbines, and biomass conversion activities such as corn ethanol and soybean biodiesel. Under TES Design, the system is optimized to balance the demand and supply of ecosystem services, within constraints imposed on energy production and system economics. The system is also optimized under a more conventional approach that reduces ecosystem service demand while neglecting ecosystem service supply and the relevant ecological processes. Results show that only the TES methodology produces system designs in which ecosystem service supply meets or exceeds the demand. TES system designs produce the same amount of energy as conventional designs, have similar system economics, and use land both for energy production and for ecosystem service supply. The additional supply enables the use of intensive agricultural practices with higher ecosystem service demands and higher biomass yields. These results encourage further efforts toward TES Design with additional ecosystem services.

Abstract With impending climate change and ever decreasing supplies of easily extractable fossil fuel, means to produce renewable and sustainable replacement fuels are being sought. Plants or algae appear ideal since they can use sunlight to fix CO2 into usable fuel or fuel feedstocks. However, as the world population approaches the 1010 (10 billion) mark, the use of agricultural land to produce fuel instead of food cannot be justified. Microalgal biofuel production is under intense investigation due to its promise as a sustainable, renewable biofuel that can be produced using non-arable land and brackish or non-potable water. Some species accumulate high levels of TAGs (triacylglycerols) that can be converted to fatty acid esters suitable as replacement diesel fuels. However, there are many technical barriers to the practical application of microalgae for biofuel production and thus a number of significant challenges need to be met before microalgal biodiesel production becomes a practical reality. These include developing cost-effective cultivation strategies, low energy requiring harvesting technologies, and energy efficient and sustainable lipid conversion technologies. The large culture volumes that will be necessary dictate that the necessary nutrients come from wastewaters, such as the effluents from secondary treatment of sewage. Economical and energy sparing harvesting will require the development of novel flocculation or floatation strategies and new methods of oil extraction/catalysis that avoid the extensive use of solvents. Recent advances in these critical areas are reviewed and some of the possible strategies for moving forward are outlined.