The challenge of realigning the present path of development on a sustainable trajectory concerns all sectors of society, including engineering. To move towards a sustainable practice of engineering, the design process needs to be modified in order for engineers to efficiently tackle the related issues. Such 'sustainable design processes' (SDPs) are proposed in the literature. By reviewing the conventional design process and SDP, this paper aims to identify the differences between both approaches. The potential contribution of recent design theories, methods and techniques to sustainable engineering is also briefly discussed. Tasks from existing SDPs are combined with crucial complements into a novel integrated sustainable engineering design process. Instead of representing conventional and sustainable engineering as a dichotomy, this paper places both paradigms on a continuum along which the engineer can position himself and assess his progress. The proposed procedure reveals shades of sustainability along six dimensions: (1) the structure of the design process, (2) the scope of sustainability issues covered, (3) the relevance of the indicators considered, (4) the accuracy of the tools used for evaluation, (5) the potential improvements expected from the alternatives assessed and (6) decision-making.
The mineralization of 14C-labelled naphthalene was studied in pristine and oil-contaminated soil slurry (30% solids) under denitrifying conditions using a range of concentrations from below to above the aqueous phase saturation level. Results from sorption-desorption experiments indicated that naphthalene desorption was highly irreversible and decreased with an increase in the soil organic content, thus influencing the availability for microbial consumption. Under denitrifying conditions, the mineralization of naphthalene to CO2 occurred in parallel with the consumption of nitrate and an increase in pH from 7.0 to 8.6. When the initial substrate concentration was 50 ppm (i.e. close to the aqueous phase saturation level), about 90% of the total naphthalene was mineralized within 50 days, and a maximum mineralization rate of 1.3 ppm day-1 was achieved after a lag period of approx. 18 days. When added at concentrations higher than the aqueous phase saturation level (200 and 500 ppm), similar mineralization rates (1.8 ppm day-1) occurred until about 50 ppm of the naphthalene was mineralized. After that the mineralization rates decreased logarithmically to a minimum of 0.24 ppm day-1 for the rest of the 160 days of the experiments. For both of these higher concentrations, the reaction kinetics were independent of the concentration, indicating that desorption of the substrate governs the mineralization rate. Other results indicated that pre-exposure of soil to oil contamination did not improve the degradation rates nor reduce the lag periods. This study clearly shows the potential of denitrifying conditions for the biodegradation of low molecular weight PAHs.
This paper aims to provide engineers and the engineering community with a conceptual framework setting out the connections between engineering projects and the sustainable development of environmental and social systems. The main principles of sustainable development on the one hand and of sustainable engineering on the other hand are first reviewed and summarized. Particular attention is paid to the principles put forward by international and national engineering organizations. Second, concepts and models originating in natural and social sciences are outlined to shed more light on the ways the various aspects of sustainability are related. The conceptual framework we propose combines the reviewed principles, concepts and models in a relevant manner for engineering projects. Engineering and physical or social systems prove to be related in manifold ways. While the most common relations are exposed in the sustainability framework, others have to be further elaborated in order to fully take into account the specificities of the various fields of engineering. Finally, applications of the sustainability framework in engineering practice and engineering education are discussed.
Most industries in the world treat their wastewaters with a conventional coagulation-flocculation process using alum as coagulant, polyacrylamide (PAM) as flocculant and lime as coagulant aid. To reduce the use of chemical products in the process, experiments were conducted to substitute the PAM with cactus juice (CJ) as flocculant. From the obtained data, it was concluded that the substitution of PAM with CJ in the coagulation-flocculation process was very effective, compared with PAM. Depending on the wastewater's origin, the bioflocculant showed removal efficiencies of 83.3-88.7% for suspended solids (SS) and 59.1-69.1% for chemical oxygen demand (COD). Lime addition enhanced the coagulation-flocculation process in the presence of CJ similarly to the PAM with efficiencies greater than 90% for both SS and COD. The CJ powder's infrared (IR) spectrum showed the main functional groups present in PAM. It was concluded that CJ as a flocculant fits well with the definition of sustainability and it is appropriate for countries that have regions where cactuses grow naturally.
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