A Comparative Analysis of Environmental Impacts of Operational Phases of Three Selected Microalgal Cultivation Systems

In recent years, microalgal biomass cultivation has been growing in importance, not only related to the production of alternative foods and nutritional supplements but also for its usage for energy purposes or as a natural solution for wastewater treatment. Regarding these cases, the practical potential associated with the circular economy is evident. However, this is not an option for microalgal food and supplements due to strict hygiene requirements for microalgae cultivation used for these purposes. Currently, the most common cultivation options for microalgae include phototrophic cascades, photobioreactors, and heterotrophic fermenters. Generally, the higher requirements for the purity of the resulting biomass, the higher the consumption of energy and nutrients needed. These are the main operational parameters that significantly shape the total environmental and economic performance of microalgae cultivation processes. The comparative Life Cycle Assessment (LCA) of environmental aspects in the operational phases of three selected cultivation systems, located in the Czech Republic and used for pure microalgae biomass production, confirmed that the impacts of these systems in the assessed categories are fundamentally dependent on the amount of electricity needed and nutrient consumption, as well as their sources. For this reason, the heterotrophic fermenter was evaluated as being the most damaging in the comparison of the three cultivation systems, while the phototrophic cascade showed a lower total environmental impact by 15% and the flat photobioreactor was lower still, by 95%, mainly due to energy production from biomass. The major impact categories observed were climate change, depletion of fossil fuels, human toxicity, and freshwater and marine ecotoxicity. The environmental impacts of microalgae cultivation systems could be further reduced if cycling practices, such as process water recycling and reprocessing of generated sewage sludge, were addressed

Agroforestry systems as new strategy for bioenergy — Case example of Czech Republic

The paper deals with the analysis of economic efficiency of innovative agroforestry systems (AFS) using coppiced tree belts (CTB), which combine the advantages of traditional alley cropping with the short rotation coppice (dense plantation of fast-growing trees for biomass — SRC) on an agricultural field. We have analyzed and compared such innovative agroforestry system (AFS-CTB) with conventional food crops production in conventional 4 crop year rotation (winter barley, winter wheat, rapeseed and corn). The minimum price of production, (based on net present value criterion), was performed to enable simultaneous assessment of annual and perennial crops over time in order to obtain also economic evaluation and comparison. Our results show that AFS-CTB generate similar income and profits as from conventional annual crops when cultivating on suitable sites and adhering to good farming principles

Waste Feathers Processing to Liquid Fertilizers for Sustainable Agriculture—LCA, Economic Evaluation, and Case Study

The poultry meat industry generates about 60 million tons of waste annually. However, such waste can serve as a cheap material source for sustainable liquid fertilizers or biostimulant production. Moreover, its practical potential associated with the circular economy is evident. One of the options for waste feather reprocessing is to use a hydrolysis process, whose operating parameters vary depending on the waste material used. The better the quality of the waste feathers, the less energy is needed; moreover, a higher yield of amino acids and peptides can be achieved. These are the main operational parameters that influence the overall environmental and economic performance of the hydrolysis process. The assessment of process operational environmental aspects confirmed that the environmental impacts of hydrolysate production are highly dependent on the amount of electricity required and its sources. This fact influences the midpoint and the endpoint impacts on the observed environmental impact categories. It also minimizes the pressure associated with fossil resource scarcity and the related impact on climate change. During an economic evaluation of the process, it was found that the option of processing more fine waste, such as CGF, provided a 5% saving in energy costs related to the reduction in the cost per liter of hydrolysate of 4.5%. Finally, a case study experiment confirmed the fertilizing effect of the hydrolysate on pepper plants (biometric parameters, yield). Thus, the hydrolysate produced from the waste feathers can serve as a substitute for nitrate fertilizing, which is commonly drawn from raw fossil materials

Techno-Economic Analysis of Fluidized Bed Combustion of a Mixed Fuel from Sewage and Paper Mill Sludge

The treatment and disposal of sewage sludge is one of the most important and critical issues of wastewater treatment plants. One option for sludge liquidation is the production of fuel in the form of pellets from mixed sewage and paper mill sludge. This study presents the results of the combustion of pelletized fuels, namely sewage and paper mill sludge, and their 2:1 and 4:1 blends in a fluidized bed combustor. The flue gas was analysed after reaching a steady state at bed temperatures of 700–800 °C. Commonly used flue gas cleaning is still necessary, especially for SO2; therefore, it is worth mentioning that the addition of paper mill sludge reduced the mercury concentration in the flue gas to limits acceptable in most EU countries. The analysis of ash after combustion showed that magnesium, potassium, calcium, chromium, copper, zinc, arsenic, and lead remained mostly in the ash after combustion, while all cadmium from all fuels used was transferred into the flue gas together with a substantial part of chlorine and mercury. The pellets containing both sewage and paper mill sludge can be used as an environmentally friendly alternative fuel for fluidised bed combustion. The levelized cost of this alternative fuel is at the same current price level as lignite