Water reclamation and sludge recycling scenarios for sustainable resource management in a wastewater treatment plant in Kinmen islands, Taiwan

Highlights

• Sustainable management strategies for the developing small islands are proposed.

• Use of heavy-oil based electricity contribute to the increase of overall impacts.

• Reuse of tertiary treated wastewater shows little environmental benefits.

• Incineration of sludge reduces overall energy demand and global warming impact.

Abstract

Sustainable resource management in small islands is very challenging. To address the challenges, four water and waste management strategies were proposed for a wastewater treatment plant in the Kinmen islands, Taiwan. Life cycle assessment was employed for evaluation of the environmental impacts and benefits (i.e., avoidance of impacts) associated with the resource management strategies at the plant. The results showed that the energy requirements (mainly electricity consumption) for water and sludge treatments in the wastewater treatment plant had the most remarkable impact as high as 98.6%. Significant environmental advantages could be achieved by reusing the reclaimed wastewater for agricultural applications (27.8% reduction in eutrophication potential), reusing the sludge for land applications (157% reduction in global warming potential), and generating energy from incineration of recycled sludge (impacts were neutralized). Impacts from addition of tertiary treatment for wastewater reclamation could be offset by preventing discharge of nutrients (i.e. N and P) into the environment. The reclamation also reduced the demand from groundwater pumping and associated impacts. Reuse of sludge for energy generation was more favorable than for land applications. This was mainly because eutrophication impact could not be avoided when the sludge was applied to soil (excess in nutrients), and, relatively higher reduction in global warming potential was observed for energy generation (−197 kg CO₂ eq/m³) than for land applications (−18.8 kg CO₂ eq/m³).

Introduction

Small islands are vulnerable to natural disasters and human activities (Kurniawan et al., 2016). Development expansion, such as population growth, increased tourism and poor infrastructure management, makes sustainable management in small islands very challenging from water resource and solid waste management perspectives. The challenges of freshwater and waste management generally come from its limited land size, resource availability and physical characteristics (Mohee et al., 2015). For instance, water sources in small islands are extremely vulnerable, as most of the surface water flows quickly into the sea instead of into catchment areas (Máñez et al., 2012). Contamination of the freshwater by seawater intrusion is also a major concern for water management (Polido et al., 2014a, Polido et al., 2014b). On the other hand, the solid waste in small islands is usually poorly managed by inappropriate disposal (UNEP, 2012). Despite the fact that the challenges are obvious and well-recognized, solutions or strategies (e.g., sustainable management practices) to address these challenges were seldom investigated in small islands.

Domestic wastewater is now being seen as a resource than as a waste. It offers opportunities to recover water, energy and fertilizing nutrients in a wastewater treatment plant (WWTP) (McCarty et al., 2011). An Amsterdam based study quantified the organic matter and phosphorus in wastewater using material flow analysis and sketched out strategies for recovering the resources (van der Hoek et al., 2016). Reclamation of wastewater is also regarded as an important and attractive approach for effective and sustainable management of water resource (Chang et al., 2017). Opher and Friedler (2016) further compared four urban wastewater management approaches and pointed out that decentralized systems (i.e. onsite treatment systems) are generally perferrabler than centralized ones.

Through wastewater reuse, energy can be indirectly conserved from production of potable water and treatment of wastewater. Moreover, it reduces the need for exploring energy-intensive water sources, such as desalination, and the impacts associated with freshwater use (Lyons et al., 2009). Reducing of freshwater abstraction by pumping was found to be the key contributor to the reduction in Freshwater Ecosystem impact for water reclamation (Amores et al., 2013). Addition of tertiary treatment in existing wastewater treatment system for wastewater reclamation showed little increment in most of the environmental impacts but a notable net saving of freshwater (Meneses et al., 2010). Reuse of the reclaimed water for agricultural applications was viewed as the most environmentally friendly approach (Meneses et al., 2010), and its environmental benefit (avoidance of the acidification and eutrophication impacts) was proportional to the amount of treated wastewater (Renzoni and Germain, 2007).

Similarly, reuse of waste sludge is proposed for advanced management of sludge. Combining the applications of sludge as fertilizer, fuel and raw material replacements was found to be the most environmental option for the final destination of the sludge (Pasqualino et al., 2009). Productive use of sludge such as agricultural application (i.e., serves as fertilizers) was reported to improve the environmental performance and offered the greatest environmental offsets in eutrophication and acidification impacts of WWTPs (Murray et al., 2008). The impact from presence of emerging micropollutants such as pharmaceuticals and personal care products in the sludge was found to be minimal (Hospido et al., 2010). Economic benefits from recycling of sludge for agricultural applications also made it an attractive option for sludge management (Kleemann and Morse, 2015).

Moreover, recycling of sludge for electricity or heat generation could potentially reduce use of natural resources, occupation of land, energy consumption and generation of end products, and consequently avoid environment impacts associated with sludge treatment. Thermal processes such as incineration or pyrolysis presented opportunities for energy recovery with little nutrient loss (Hospido et al., 2005). Bravo and Ferrer (2011) suggested that increase in biogas production through anaerobic digestion of sewage sludge could enhance the environment performance of the WWTPs due to the recovery of energy and nutrient. The sludge could be potentially utilized as substitution for fossil fuels in co-incineration in power plants or cement kilns (Remy et al., 2013), or acted as an alternative fuel in industrial processes (Valderrama et al., 2013). A considerably low carbon footprint (−11.6 kg CO₂ equivalent per population equivalent chemical oxygen demand) was reported in a study of co-incineration of sludge in cement kilns (Remy et al., 2013). The co-incineration also presented high economic benefits than environmental benefits (Hong et al., 2013). All of these management strategies were seldom reported for developing areas such as small islands.

Kinmen islands is one of the small islands in Taiwan that faces difficulties in sustainable management of their resources. As the government in the islands are putting efforts to find sustainable solutions in addressing the issues, their associated environmental benefits is therefore need to be quantified, particularly for policy making purpose. This study aims to evaluate the environmental performances of four sustainable resource management scenarios for Jincheng WWTP, the largest WWTP in Kinmen islands, including reclamation of wastewater for agricultural and urban uses and recycling of waste sludge for agricultural use and energy production from incineration. The studied scenarios are specially designed for the islands, considering the economic activities and geographical constraints in the area. Improvements in future electricity mix of the islands is also considered in this study. Environmental performances for the studied scenarios are quantified using life cycle assessment approach. This study could provide a useful demonstration for making of more environmentally sustainable wastewater treatment plant for developing areas.