Sustainability assessment of community-based wastewater treatment plant: case study of Semarang District, Indonesia

Current sanitation initiatives in Indonesia focus on community-based sanitation to promotes ownership and understanding of sanitation systems. However, the community has faced numerous challenges in maintaining the socio-economic and technical aspects of the community-based wastewater treatment system (CWWTP) in operation. This study aimed to identify and analyse the sustainability dimensions of CWWTP in Indonesia. In this study, a set of sustainability index (SSI) tools was proposed to evaluate the sustainability of CWWTP, which included environmental, social, economic, technological, and institutional aspects of the sanitation system. Rapid appraisal for fisheries (RAPFISH) method was adapted to evaluate the multidimensional scaling (MDS) approach within the proposed SSI. The applicability of developed SSI was demonstrated by evaluating the implementation of three CWWTP in Semarang district. Data was collected through direct observation, questionnaires, interviews, CWWTP design evaluation, and water quality analysis. Major findings indicated that Tegalsari CWWTP have higher sustainability index, while Pedalangan and Podorejo need to enhance technical efficiency, institutional structure, and community engagement. The leverage analysis identifies key performance drivers in the CWWTP management including operation & maintenance, user acceptance, O&M expenses, community involvement, and effluent water quality. This paper highlights adequate tools for sustainability assessments of CWWTP in Semarang district. Methodology and dissemination of the obtained results can be applied to other rural communities in Indonesia.


Introduction
Indonesia as developed nation still facing a significant challenge in managing its wastewater effectively.The national coverage for sewerage and sanitation services is less than 10% [1], predominantly in urban areas, leaving a vast majority of the population without access to proper sanitation facilities.The situation is exacerbated in rural areas, where the need for sustainable, community-based wastewater treatment solutions is particularly urgent.
Community-based sanitation systems, specifically community-wastewater treatment plant (CWWTP), have been promoted in Indonesia as an approach to increase sanitation coverage in both urban and rural areas [2].These systems are touted for their ability to manage local conditions, reduce the need for extensive sewer networks, and foster community engagement [3].However, with the rapid expansion of these systems, there is a crucial need for a comprehensive understanding of their sustainability.Sustainability in the context of wastewater treatment is a complex issue encompassing environmental, economic, technical, and social dimensions [4].While CWWTP offer potential benefits, the actual sustainability performance of these systems has not been systematically evaluated [2].Several studies have discussed the general sustainability of wastewater treatment systems [3][4].However, these studies typically focus on centralized systems in urban settings and might not fully capture the unique challenges and opportunities associated with community-based systems in countries like Indonesia, where geographical and socioeconomic conditions vary significantly.Moreover, even though some initial steps have been taken to assess the performance of CWWTP in Indonesia [5], there is a clear gap in understanding their holistic sustainability, which includes not only technical and economic aspects but also environmental and social dimensions [6].A rigorous sustainability assessment of CWWTP could provide essential insights into the strengths and weaknesses of these systems, informing policy making, system design, and operational practices for future implementation.
Given these considerations, the objective of this paper is to explore the sustainability of communitybased wastewater treatment plant in the Indonesian context.We propose to develop a comprehensive assessment framework that captures all dimensions of sustainability and can be applied to CWWTP in various geographical and socio-economic contexts across Indonesia.

Methods
To identify relevant sustainability indicator, a systematic literature search was performed in the Scopus database using key words 'sustainability', 'criteria', 'indicator' and 'wastewater treatment plants'.The contextualization of sustainability indicators identified from the literature was conducted by elimination of unmatched criteria.Finally, a set of sustainability index (SSI) tools for CWWTP was proposed.
Sustainability assessment using developed SSI was conducted in three CWWTP in Semarang district namely Tegalsari, Pedalangan, and Podorejo through in-depth interviews and field observation.A set of questionnaires was distributed to residents of all ages in the area.A random sample of 20 households was chosen for each CWWTP, and one person from each household was chosen and interviewed.While field observation of the CWWTP was conducted to evaluate the physical condition and technical aspect of CWWTP.Water quality analysis also conducted to investigate the treatment performance.The effluent of each CWWTP were taken and analyzed according to the Indonesia wastewater standard.
Data analysis in this study using Multi-dimensional Scaling (MDS) with Approach on sustainability has been modified from RAPFISH (Rapid Assessment Technique for Fisheries) [7].The classification of the sustainability index of the CWWTP is divided into four categories: the sustainability index value < 25% shows a very poor condition of CWWTP; the sustainability index value ranging from 25,00 to 49,99% indicates a poor condition of CWWTP; the sustainability index value from 50 to 74,99% shows a good condition of CWWTP, and the sustainability index value ≥ 75% demonstrates a very good condition of CWWTP.The leverage analysis was used to determine the attributes that affect the sustainability index.The attributes with high values indicate a strong influence on the improvement of the sustainability index.

Development of sustainability index
Several sustainability indicators were identified through the literature review and organised into five dimensions: environment, society, economy, technology, and institutions with defined scale (Table 1).

Evaluation of selected CWWTP
As shown in Table 2, the selected CWWTP used identical anaerobic process.In overall, the number of houses connected to the CWWTP remains below the maximum design capacity, whereas the actual treatment capacity in Podorejo is 2,3 times higher than the design capacity.The wastewater quality parameters were determined in all CWWTP effluent and compared to the Indonesian domestic wastewater standard (Table 4).Tegalsari CWWTP's water quality appears to be superior to the other two sites.However, the high Total Coliform count at all three sites is a serious concern that must be addressed.Podorejo CWWTP appears to have the poorest water quality of the three sites, exceeding all parameter within the Indonesia wastewater standard.24) have low institutional indices, indicating significant institutional weaknesses.This may imply a lack of effective coordination in wastewater management, which may impede their sustainability efforts [12].Tegalsari (54), on the other hand, indicates a relatively better institutional setup.The cost-effectiveness and financial feasibility of wastewater treatment systems are examined in the economic dimension.Podorejo (82) and Tegalsari (81) have high economic indices, indicating efficient financial management and appropriate tariffs, which can significantly contribute to the sustainability of wastewater treatment.Pedalangan, on the other hand, has a lower score (61), implying that improved economic strategies are required [13].

Sustainability index of CWWTP
Finally, in the social dimension of sustainability, the impact on the community and stakeholders is assessed, which includes public acceptance, community engagement, and health impact.The Tegalsari plant receives the highest score of 86, indicating a high level of social acceptance and strong engagement with the local community.Pedalangan and Podorejo, on the other hand, have lower scores of 52 and 59, indicating potential social challenges such as a lack of community engagement or social conflicts [14].

Influence of the attributes within the SSI
This study also utilised the root-mean-square value of the leverage analysis to evaluate the influential attributes.The greater the value of root means square, the greater the impact of the attributes on the status of the sustainability index.Figure 2 present the results of the leverage analysis regarding the root mean square.
According to our findings, the most significant factor influencing the social dimension of the CWWTP's sustainability assessment (Figure 2) is the social dimension itself.A variety of factors, including perceptions of system effectiveness, impacts on local environments, and cultural beliefs and practises, can all influence acceptance [2].According to studies, CWWTPs have a relatively high level of user acceptance in Indonesia, particularly when systems are perceived to be effective and beneficial to local communities [15].The social dimension is critical for long-term viability because it has a direct impact on community engagement and system usage.While operational and maintenance expenses (O&M Expenses) are the most critical sustainability aspect in the economy dimension.O&M expenses are recurring costs that have an impact on the long-term economic sustainability of these systems.These costs include energy, personnel, and maintenance materials, as well as potential costs for replacing parts or entire systems [2].Meanwhile, the capital costs of CWWTP can be significant, potentially impeding their adoption, particularly in rural areas or among low-income populations [1].However, it has been suggested that CWWTP can be more cost-effective in the long run than centralised systems due to lower operational and maintenance costs [3]. Figure 2 also highlighted the importance of community involvement in CWWTP sustainability.According to research [5] higher levels of community participation result in improved system performance and maintenance.However, due to constraints such as limited technical knowledge, financial resources, and institutional support, local governments and communities continue to face challenges in managing these systems [15].
The main consideration of wastewater treatment in terms of the environmental dimension is the reduction of pollution load in receiving water bodies.The operation of the CWWTP has resulted in a significant reduction in organic and nutrient loads [16].Variability in system performance due to differences in design, operation, and local conditions, on the other hand, suggests the need for more comprehensive evaluations of pollution reduction across different settings [2].In line with this, our research in Figure 2 shows that the most important attribute in the environmental dimension is effluent quality.Whereas leverage analysis in Figure 2 revealed operation maintenance to be an important aspect of the technical dimension.Inadequate maintenance can lead to system failures and decreased performance over time due to a lack of local technical skills or resources [15].Thus, capacity building at the local level is critical for the long-term viability of CWWTP.

Conclusion
Through technical, environmental, social, economic, and institutional assessments, our study proposed a set of sustainability indexes as tools for CWWTP management.The case study's CWWTP sustainability assessment revealed that Tegalsari outperforms in all domains; however, it is critical to recognise the limitations and areas for improvement for the Pedalangan and Podorejo plants.The sustainability index indicates a clear need for these plants to improve their technical efficiency, institutional setup, and community engagement strategies.The leverage analysis emphasises critical sustainability factors such as the social aspect, operational and maintenance costs, community involvement, effluent quality, and maintenance.The social dimension, which is critical for community engagement, can ensure economic sustainability, along with careful management of operational and maintenance costs.Encouraging community participation improves system performance and maintenance.While effluent quality determines environmental impact, operation maintenance is critical for the technical aspect.Addressing these factors through local capacity building ensures the long-term viability and performance of wastewater treatment systems.

Figure 2
depicts the sustainability index values for each CWWTP.In the technical dimension, which refers to the facilities functional efficiency in treating and managing wastewater.Tegalsari CWWTP has a high technical index of 72 indicating that the plant is effective in wastewater treatment.The Pedalangan and Podorejo plants on the other hand have indexes of 58 and 41, indicating a lower level of technical efficiency.This implies an inefficient treactment process and a lack of maintenance affecting their ability to effectively treat wastewater[11].

Table 2 .
General information of selected CWWTP.

Table 3 )
reveals that Tegalsari and Pedalangan CWWTP have significantly longer hydraulic residence times (HRT) than Podorejo.A lower HRT in both ABR and AF unit in Podorejo suggests that the treatment process was overload.These phenomena can result in inefficient wastewater treatment and require flow rate adjustments to meet HRT standards.Regular desludging at all sites, particularly Pedalangan and Podorejo, is necessary to overcome a potential buildup of solid waste, possibly leading to decreased efficiency and potential mechanical or structural issues within the reactor.

Table 3 .
Technical information of selected CWWTP.

Table 4 .
Effluent water quality of selected CWWTP.