Elsevier

Science of The Total Environment

Volume 660, 10 April 2019, Pages 57-68
Science of The Total Environment

Environmental and cost life cycle assessment of different alternatives for improvement of wastewater treatment plants in developing countries

https://doi.org/10.1016/j.scitotenv.2018.12.386Get rights and content

Highlights

  • Environmental impacts of four different scenarios to improve WWTPs were studied.

  • Energy consumption in WWTPs has a great influence on the environmental impacts.

  • Tertiary treatment was beneficial to all impact categories due to water reuse.

  • Merging anaerobic digestion and tertiary treatment attained maximum benefits.

Abstract

Most of wastewater treatment plants (WWTPs) in developing countries comprised primary and secondary treatment without including any tertiary treatment or sludge processing. Decision makers think that additional treatment is costly and the gained environmental benefits are limited. This study aims to investigate the environmental and economic benefits of improving current conventional WWTPs in developing countries by adding tertiary treatment and/or anaerobic digestion of sludge. For this purpose, life cycle assessment (LCA) for four different scenarios was studied for a wastewater plant located in Gamasa, Egypt. The 1st scenario is the plant in its current state. The 2nd scenario is the addition of anaerobic digestion of sludge. The 3rd scenario is the addition of a tertiary treatment stage. The 4th scenario is the addition of anaerobic digestion of sludge and tertiary treatment stage. CML 2000 method was used for assessing the environmental impacts of the four scenarios. The 4th scenario attained maximum environmental benefits for all categories due to the energy saving and the prospect of water reuse. The application of the 4th scenario achieved environmental benefits in some important categories such as ozone layer depletion. According to the economic evaluation, the addition of tertiary treatment leads to gain financial profits due to the value of the reusable produced water. This study underlines the importance of considering LCA in development of WWTPs in developing countries.

Introduction

Disposal of domestic wastewater without sufficient treatment is increasingly concerned in developing countries. The improper design and operating of wastewater treatment plants (WWTPs) may cause severe environmental problems on local and global scales (Sabeen et al., 2018; Xiong et al., 2018a). Moreover, many developing countries are not totally served by wastewater treatment plants. Primitive methods are still used to mitigate the direct impacts of untreated wastewater on human health, but many environmental and health impacts are unbeatable. In addition, most of wastewater treatment plants in developing countries only include primary (physical treatment) and secondary (biological treatment) stages without tertiary treatment or advanced sludge processing. Decisions about wastewater projects in developing countries are primarily influenced by direct capital and operating costs as long as the design is meeting the local standards, while life-cycle cost and life-cycle environmental impacts are rarely considered.

Achievement of integrated sustainability in wastewater treatment projects requires the consideration of life cycle perspective, which is not only limited to water remediation benefits (Song et al., 2017; Zang et al., 2015). Accordingly, many recent studies reported the significance of life cycle assessment (LCA) in the evaluation of wastewater treatment facilities (Benetto et al., 2009; Corbella et al., 2017; Liu et al., 2013; Muñoz et al., 2009). LCA is a standardized, integrated, and complicated tool to compile and evaluate the environmental impacts for a product including all inputs and outputs from cradle to grave (Finkbeiner et al., 2006; Tang et al., 2018). This assessment is mainly carried out by assembling an inventory of the most related inputs and outputs to the system and determining the possible impacts related to the inventory (inputs and outputs). The outcomes of the inventory analysis and impact assessment stages are then interpreted relative to the purposes of the study (Foteinis et al., 2018). There are mainly two types of life cycle assessment procedures: the first one gives emphasis to energy and materials flow in a manufacturing process and is called the conventional process-based life cycle assessment and the second type highlights environmental data in a manufacturing process and is called the input-output life cycle assessment (Zhang et al., 2010). Input-output life cycle assessment is mostly used for evaluation of environmental impacts in the studies emphasizing on sustainable development like energy and water production (Chen et al., 2012; Lorenzo-Toja et al., 2016).

Development of wastewater treatment technologies is recently considered an important role to achieve upcoming water security in a world that has an increase in water stress (Gar Alalm et al., 2016; Xiong et al., 2018b). Wastewater treatment plants are considered as units aiming the effective removal of nutrients and organic matter from contaminated wastewaters to avoid the accumulation of these pollutants in the environment. Although these benefits, WWTPs have been found to consume a great portion of energy, resulting in increasing of greenhouse gases emissions and other impacts on the environment (Yoshida et al., 2014; Zou et al., 2018). More than 50% of the energy consumption in WWTPs is caused by mechanical aeration (Au et al., 2013; Gar Alalm et al., 2018). Therefore, it is necessary to study the improvement of WWTPs from the life cycle perspective to maximize the environmental benefits and minimize the undesired impacts, especially for the WWTPs that have been constructed without taking the sustainability requirements into account.

This study aims to study the environmental performance of different scenarios for the improvement of existing WWTPs in developing countries. Complete input-output LCA study is carried out for suggested scenarios to develop an existing WWTP located in Gamasa, Egypt. CML 2000 method was used for the determination of seven different impact categories for all scenarios.

Section snippets

Goal and scope

The goal of this study is to determine the environmental impacts for improvement of a conventional municipal wastewater treatment plant in developing countries. A conventional wastewater treatment plant in Gamasa city, Egypt was taken as a case study. The information and data of the plant were collected from the official documents of the Egyptian Company of Water and Wastewater. The plant was put into operation in 2010. The plant consists of two grit removal chambers, four primary settling

Environmental impacts of conventional activated sludge system (scenario 1)

Gamasa wastewater treatment plant in its current state (scenario 1) causes considerable effects in all analyzed impact categories as shown in Fig. 3(a). In the conventional system, the high electricity consumption and the effluent of secondary treatment in operation stage were the main contributors to environmental impacts. On the other hand, the impacts of the construction stage were relatively small as they were assigned to the functional unit of 1 m3 of treated water. This finding was also

Conclusions

Four different scenarios of Gamasa wastewater plant were environmentally evaluated by LCA technique based on CML 2000 baseline method. The LCA showed that the influence associated with the operational activities is more important than the influence of construction materials and activities. In addition, the results show that the gaseous emissions and energy consumption have the greatest effects on environmental impacts. The conventional activated sludge system with anaerobic digestion of sludge

Acknowledgment

The authors gratefully acknowledge the support from the Science and Technology Development Fund (STDF), Egypt through the project No 262279.

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