Assessing the impact of industrial wastewater reuse as a demand-side management strategy for potable water deficit in Selangor, Malaysia.

Abstract

Policy makers are now re-aligning their thinking towards demand-side management (DSM), where for the industrial sector specifically, strategies have been emphasising water consumption reduction through conservation, increased efficiency, and wastewater recycling. Although DSM-based strategies have been seen as a viable option to delay the need for large capital investment and to avoid irreversible environmental impact, their implementation at a large scale have been largely unknown as is implementation has generally been reported at a small-scale. As such, this research attempts to assess the effectiveness of implementation of decentralised wastewater reuse facilities in industrial parks as a DSM-based strategy targeted at the manufacturing sector. The research first assessed the vulnerability of three reservoirs in Selangor – namely Semenyih, Klang Gates, and Langat dam – against water deficiency events using a modelling approach to analyse their: i) reliability, via the use of an inflow-demand reliability index, and ii) resilience, through a water supply resilience index. Total potential potable water savings were then estimated for all industrial parks in the area served by each reservoir and subsequent potable water treatment plant. The impact of the potential water savings through reuse of wastewater in industrial parks within an overall water supply system was then evaluated. The feasibility of this DSM-based strategy was assessed in terms of its technical, economics, and environmental impact. Four treatment trains corresponding to the two cases of i) potable and ii) non-potable reuse were assessed in terms of their removal efficiencies necessary to comply with the current potable and non-potable water quality standards. The financial cost of each treatment train was determined for both capital and operational costs, while the environmental assessment was assessed using a Life Cycle Assessment (LCA) approach based on several environmental impact categories. Findings for the three dams indicated varying level of vulnerability, with Klang Gates dam being the most vulnerable, while Semenyih the least. For Klang Gates and Langat dams, the resultant IDR and WSR indexes achieved similar conclusions; both indices resulted in almost constant negative values for both dams, suggesting that an effective DSM-based strategy could possibly delay the need for implementation of an SSM strategy. For Semenyih dam, it was observed that the system is approaching system vulnerability, where lower IDR and WSR values were observed in the later years as compared to historical scenarios. Here, it can be hypothesised that a well-planned DSM-based strategy might eliminate the need for a SSM strategy. It was found that there was minimal number of industrial parks within the Klang Gates water supply area, further reducing the feasibility of wastewater reuse to reduce the vulnerability of this WSS. Conversely, it was estimated that, for Langat and Semenyih WSS, approximately 308,903 and 430,281 m3/month of water consumed by the premises within the identified IPs. This translates to approximately 266,430 and 374,009 m3/month of water savings if 90% of the total demand was discarded as effluent, and treated at 95% recovery rate. The savings calculated for this reuse option could contribute to a savings of 5.5% (8.8 MLD) and 12.2% (12.47 MLD) for the Langat and Semenyih dam respectively. These accumulated savings had a different impact on each dam’s vulnerability. For the Langat dam, recalculation of the IDR and WSR values with the savings indicated little change to the system’s overall vulnerability. In contrast, recalculations for the Semenyih dam resulted in positive changes for the WSR specifically, indicating reduced vulnerability of the system. The feasibility of four treatment trains corresponding to both reuse options for their technical, financial, and environmental dimensions were considered. The general findings in all three dimensions reinforced the option of non-potable reuse, specifically the NP-1 treatment train, which resulted in the lowest cost while providing the highest technical capability to remove contaminants from the industrial wastewater to meet both non-potable and potable water reuse standards. Additionally, from the environmental perspective, the resultant water for reuse had a lower human toxicity impact without an additional blending requirement, though this produced a higher terrestrial eco-toxicity impact due to the contaminants removal to landfill. On the other hand, it was also illustrated via this research that the additional financial resources, institutional reconfiguration of existing water service industry, as well as current awareness of the industrial players itself will limit the effective implementation of the identified strategy. As such, it was concluded that, although the use of industrial wastewater for manufacturing sector is technical, financial, and environmental feasible, its deployment however, is improbable against the current organizational structure and current awareness of the users.