• Energy Research

Abstract Offshore cultivation of seaweed provides an innovative feedstock for biobased products supporting blue growth in northern Europe. This paper analyzes two alternative exploitation pathways: energy and protein production. The first pathway is based on anaerobic digestion of seaweed which is converted into biogas, for production of electricity and heat, and digestate, used as fertilizer; the second pathway uses seaweed hydrolysate as a substrate for cultivation of heterotrophic microalgae. As a result the seaweed sugars are consumed while new proteins are produced enhancing the total output. We performed a comparative Life Cycle Assessment of five scenarios identifying the critical features affecting resource efficiency and environmental performance of the systems with the aim of providing decision support for the design of future industrial scale production processes. The results show that all scenarios provide environmental benefits in terms of mitigation of climate change, with biogas production from dried Laminaria digitata being the most favorable scenario, quantified as −18.7*10 2 kg CO 2 eq./ha. This scenario presents also the lowest consumption of total cumulative energy demand, 1.7*10 4 MJ/ha, and even resulting in a net reduction of the fossil energy fraction, −1.9*10 4 MJ/ha compared to a situation without seaweed cultivation. All scenarios provide mitigation of marine eutrophication thanks to bioextraction of nitrogen and phosphorus during seaweed growth. The material consumption for seeded lines has 2–20 times higher impact on human toxicity (cancer) than the reduction achieved by energy and protein substitution. However, minor changes in cultivation design, i.e. use of stones instead of iron as ballast to weight the seeded lines, dramatically reduces human toxicity (cancer). Externalities from the use of digestate as fertilizer affect human toxicity (non-cancer) due to transfer of arsenic from aquatic environment to agricultural soil. However concentration of heavy metals in digestate does not exceed the limit established by Danish regulation. The assessment identifies seaweed productivity as the key parameter to further improve the performance of the production systems which are a promising service provider of environmental restoration and climate change mitigation.

Abstract: In this study the Impact-Pathway Approach methodology was applied for monetary valuation of health impacts due to cadmium emitted to soil as a micro-pollutant present in phosphorus fertilizers. Due to the high persistency of cadmium in soil, and high soil-to-plant transfer rates, humans are exposed to cadmium through their diet causing potential adverse health impacts. Future scenarios for cadmium emissions to soil via agricultural applications of inorganic and organic fertilizers in Denmark were defined. A simplified fate and speciation model allowed the increase in soil cadmium concentration to be calculated for each scenario. Human exposure was determined based on soil-crop bioconcentration factors for cadmium and dietary intake rates of Danish food crops. Updated dose-response functions linking lifetime cadmium intake to the probability of developing cadmium-induced renal disease and osteoporosis were applied. These impacts were converted into monetary values by using the EU standard value of a life-year adjusted for quality of life experience. Annualized cost per unit of phosphorus and cadmium are presented, discounted and undiscounted, for comparison. Application of struvite (magnesium ammonium phosphate) and mineral fertilizer produced the lowest external health costs, followed by the fertilizer products wastewater sludge and pig manure. The external cost estimates produced in this study could be used to design economic policy instruments to encourage use of cleaner fertilizer products.

Abstract The decentralization of waste management argues to support better planning, fair distribution of material and economic resources, and increased citizen participation. This study aims at assessing the environmental and economic performance of a decentralized biowaste management system, using the frameworks of life cycle assessment and net present value analysis. Five scenarios are designed to reflect the transition from an energy-centered biowaste management (scenario 1) towards a novel biorefinery system (scenario 2) and its expansion to a decentralized network (scenarios 3, 4, and 5) of small-scale plants treating urban biowaste. The global warming potential of the energy-centered system is 134 kg CO2 eq, while the biorefinery system offers mitigation of the global warming by -4324 kg CO2 eq t−1 biowaste treated. The decentralized network designed to capture 20% of the urban biowaste generated in Lyon Metropolitan (S5) provides environmental (S5a: -1983 kg CO2 eq, S5b: -1992 kg CO2 eq) and economic (S5a: 491€, S5b: 475€) benefits, especially when collection is performed with electric bikes (S5b) and the bio-products substitute resource and energy intensive equivalents in the market. Collection with electric bikes contributes to a low-carbon economy while significantly increases labor costs. The transition towards a bio-based economy can transform biowaste management into novel cascading biorefineries of multiple high-value products. Resilient and optimized system design can support low carbon economies and increase employment while being economically sustainable.

Wastewater treatment has nowadays multiple functions as produces both clean effluents and sludge, which is increasingly seen as a resource rather than a waste product. Technological as well as management choices influence the performance of wastewater treatment plants (WWTPs) on the multiple functions. In this context, Life Cycle Assessment (LCA) can determine what choices provide the best environmental performance. However, the assessment is not straightforward due to the intrinsic space and time-related variability of the wastewater treatment process. These challenges were addressed in a comparative LCA of four types of WWTPs, representative of mainstream treatment options in Denmark. The four plant types differ regarding size and treatment technology: aerobic versus anaerobic, chemical vs. combined chemical and biological. Trade-offs in their environmental performance was identified considering system expansion to model the avoided impacts achievable in different end-of-life scenarios for sludge: combustion with energy production versus agricultural application. To account for the variability in quality of effluents and sludge, and to address the related uncertainties, Monte Carlo simulation and sensitivity analysis were applied. Uncertainties related to the choice of Life Cycle Impact Assessment (LCIA) method and to the use of different data sources were also discussed. The results showed that, for the climate change and fossil depletion impact categories, recycling phosphorus to agricultural soils appear as a more sustainable alternative compared to the incineration of sludge. However, the uncertainty and sensitivity analysis showed that robust conclusions could not be drawn on the eutrophication and toxicity-related impact categories.

What are the effects, measured as flows of biogenic carbon, plant nutrients, and pollutants, of moving organic waste up the waste hierarchy? We present a case study of Denmark, where most of the organic fraction of household waste (OFHW) is incinerated, with ongoing efforts to increase bio-waste recycling. In this study, one-third of the OFHW produced in North Zealand, Denmark, is diverted away from incineration, according to the Danish Waste Resource Plan 2013–2018. Co-digestion of OFHW, and digestate application on agricultural soil, utilizes biogenic carbon, first for energy conversion, and the remainder for long-term soil sequestration, with additional benefits for plant nutrient composition by increasing the N:P ratio in the digestate. We show a dynamic model of the biogenic carbon flows in a mix of OFHW co-digested with livestock manure and sewage sludge, addressing the contribution of OFHW to long-term carbon sequestration compared to other agricultural residues and bio-wastes over a time span of 100 years. In addition, we trace the associated annual nutrient and cadmium loads to the topsoil. At constant annual input rates and management practices, a diversion of 33% of OFHW would result in an increased organic carbon build-up of approximately 4% over the current amounts applied. The addition of OFHW, moreover, beneficially adjusts the N:P ratio of the digestate mix upwards, albeit without reaching an ideally high ratio by that measure alone. Cd loads from OFHW remain well below regulatory limits.

The circular economy concept offers a number of solutions to increasing amounts of biowaste and resource scarcity by valorising biowaste. However, it is necessary to consistently address the environmental benefits and impacts of circular biowaste management systems (CBWMS). Various decision support tools (DST) for environmental assessment of waste management systems (WMS) exist. This study provides a review of life cycle assessment based WMS-DSTs. Twenty-five WMS-DSTs were identified and analysed through a shortlisting procedure. Eight tools were shortlisted for the assessment of their applicability to deliver sustainability assessment of CBWMS. It was found that six tools model key properties that are necessary for assessing the environmental sustainability of CBWMSs, including waste-specific modelling of gaseous emissions, biogas generation or bioproduct composition. However, only two tools consider both waste-specific heavy metals content in bioproducts and the associated implications when applied on soil. Most of the shortlisted tools are flexible to simulate new technologies involved in CBWMS. Nevertheless, only two tools allow importing directly new background data, which is important when modelling substitution of new bioproducts developed in emerging biowaste refineries.

This review article focuses on recent updates on remediation of industrial wastewater (IWW) through microalgae cultivation. These include how adding additional supplements of nutrient to some specific IWWs lacking adequate nutrients improving the microalgae growth and remediation simultaneously. Various pretreatments strategy recently employed for IWWs treatment other than dealing with microalgae was discussed. Various nutrient-rich IWW could be utilized directly with additional dilution, supplement of nutrients and without any pretreatment. Recent advances in various approaches and new tools used for cultivation of microalgae on IWW such as two-step cultivation, pre-acclimatization, novel microalgal-bioelectrical systems, integrated catalytic intense pulse-light process, sequencing batch reactor, use of old stabilized algal-bacterial consortium, immobilized microalgae cells, microalgal bacterial membrane photobioreactor, low-intensity magnetic field, BIO_ALGAE simulation tool, etc. are discussed. In addition, biorefinery of microalgal biomass grown on IWW and its end-use applications are reviewed.