Life Cycle Assessment of wastewater treatment systems for small communities: Activated sludge, constructed wetlands and high rate algal ponds

Abstract

The aim of this study was to assess the environmental impact of three alternatives for wastewater treatment in small communities. To this end, a Life Cycle Assessment (LCA) was carried out comparing a conventional wastewater treatment plant (i.e. activated sludge system) with two nature-based technologies (i.e. hybrid constructed wetland and high rate algal pond systems). Moreover, an economic evaluation was also addressed. All systems served a population equivalent of 1,500 p.e. The functional unit was 1 m 3 of water. System boundaries comprised input and output flows of material and energy resources for system construction and operation. The LCA was performed with the software SimaPro ® 8, using the ReCiPe midpoint method. The results showed that the nature-based solutions were the most environmentally friendly alternatives, while the conventional wastewater treatment plant presented the worst results due to the high electricity and chemicals consumption. Specifically, the potential environmental impact of the conventional wastewater treatment plant was between 2 and 5 times higher than that generated by the nature-based systems depending on the impact category. Even though constructed wetland and high rate algal pond systems presented similar results in terms of environmental impact, the latter showed to be the less expensive alternative. Nevertheless, the constructed wetland system should be preferred when land occupation is of major concern, since it has a smaller footprint compared to the high rate algal pond alternative.

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“…Over the WWTP's life cycle the greatest environmental impacts contributing were as follows: the final effluent, operation and, to a lesser extent, the construction. The most relevant impact for the operation phase confirms those of other LCA studies on wastewater treatment (Lopsik, 2013;Paéz et al, 2017;Garfí et al, 2017;Sabeen et al, 2018). Some researchers have exempted the construction phase, arguing that this phase has little impact compared to the impact of the whole lifecycle WWTP (Hospido et al, 2007).…”

Life cycle assessment of high rate algal ponds for wastewater treatment and resource recovery

“…activated sludge system) (around 0.02 kWh m-3 of water vs. 1 kWh m-3 of water, respectively) Passos et al, 2017). Moreover, HRAPs are less expensive and require little maintenance compared to conventional systems (Cragg et al, 2014;Garfí et al, 2017;Molinos-Senante et al, 2014). Due to their low cost and low energy consumption, HRAP systems could have a wide range of applications in Mediterranean regions, which present suitable climatic conditions for microalgae growth (e.g.…”

Algal Cultivation for Treating Wastewater in African Developing Countries: A Review

“…However, these technologies have their own impact on the environment through the consumption of natural resources utilized for construction and operation. [ 88 ] Hence, the selection of suitable technology for wastewater treatment must not only be based on technical and economic considerations but also on environmental aspect. In this context, Garfi et al.…”

“…However, these technologies have their own impact on the environment through the consumption of natural resources utilized for construction and operation. [88] Hence, the selection of suitable technology for wastewater treatment must not only be based on technical and economic considerations but also on environmental aspect. In this context, Garfi et al [88] studied a life-cycle assessment (LCA) of conventional wastewater treatment plant (activated sludge), constructed wetland and HRAP technologies treating wastewater in small communities.…”

“…[88] Hence, the selection of suitable technology for wastewater treatment must not only be based on technical and economic considerations but also on environmental aspect. In this context, Garfi et al [88] studied a life-cycle assessment (LCA) of conventional wastewater treatment plant (activated sludge), constructed wetland and HRAP technologies treating wastewater in small communities. The impact categories assessed were fossil depletion, climate change, ozone depletion, terrestrial acidification, freshwater eutrophication, marine eutrophication, and metal depletion.…”