Effectiveness of communal wastewater treatment plant in peri-urban Yogyakarta, Indonesia, for Escherichia coli removal

Yogyakarta Special Region, one of Indonesia’s provinces, has many communal wastewater treatment plants (CWWTPs). However, less than 40% of the province’s CWWTPs are operationally viable. Based on data from the Environmental Agency of Sleman Regency, the physical and chemical parameters of approximately 163 CWWTPs were evaluated. Their biological characteristics, however, still need to be understood. This study aimed to investigate the efficacy of CWWTPs in terms of biological parameters, specifically total Coliform and Escherichia coli (E. coli) concentrations in the observed CWWTPs. Five CWWTPs were used as study sites, namely IPAL Manunggal Pringgodani Sejati, IPAL Bakti Warga, IPAL Tambakrejo Bersih, IPAL Nologaten Bersih, and IPAL Andum Roso, which were classified as extremely high and high sanitation risk areas. The total Coliform and E. coli concentrations were determined using MPN techniques based on APHA 9221 (2017). The study found that the E. coli removal effectiveness of the CWWTPs in the very-high sanitation risk areas, namely IPAL Manunggal Pringgodani Sejati, IPAL Bakti Warga, and IPAL Tambakrejo Bersih, was 49%, 18%, and 83%, respectively. Furthermore, in high sanitation risk regions, such as IPAL Nologaten Bersih and IPAL Andum Roso, the CWWTPS were 17% and 73%, respectively. Total Coliform concentrations at all CWWTPs were below the standard limit set by Permen LHK No 68 and the EPA. The findings of this study will help to improve understanding of the WWTP process for E. coli elimination, which will, in turn, help to improve CWWTP performance.


Introduction
Communal WWTPs use biological treatment as their primary treatment, where microorganisms are the primary agents aiding in decomposing organic matter in wastewater [1].There are numerous varieties of microorganisms in wastewater treatment, including bacteria, fungi, viruses, and protozoa; some of these microorganisms have the potential to be pathogenic.[2].The final product of refuse treatment at the Communal WWTP will be discharged into water bodies, but the effluent must conform to government-established quality standards [3].If the quantity of microorganisms in the effluent discharge exceeds the quality standard, they can harm human health [4].
According to the Central Statistics Agency (BPS) of Sleman Regency, the population of Sleman Regency in 2021 will be 1,088,109, up from 1,082,754 in 2020, indicating an increase in population.This increase may impact the purity of the wastewater that flows to the WWTP, particularly the bacteria found in domestic wastewater.Domestic effluent typically contains beneficial bacteria, such as those that degrade organic matter, as well as a small number of pathogenic bacteria [5].
Pathogenic bacteria, viruses, and protozoa in water due to faecal contamination continue to contribute to waterborne diseases significantly.These microorganisms can endure in contaminated water for extended periods, eventually developing infections [6,7].The primary method for evaluating faecal contamination in water involves using faecal indicator bacteria, such as Escherichia coli and Enterococci [8].The assessment of water quality is of utmost importance as it enables investigations into the origins of pollution and helps prevent potential waterborne illnesses.This assessment provides valuable evidence regarding the dangers associated with human exposure to water for various purposes [9,10].
In response to the potential health risks associated with microbiological contaminants in water sources, wastewater treatment plants (WWTPs) were established as centralized facilities to mitigate pollutant levels to acceptable thresholds before releasing the resulting effluent into receiving bodies of water.Identifying disease-causing microorganisms in wastewater treatment plant effluents is a matter of concern, particularly for individuals involved in public health and water management [11].Individuals residing and employed near wastewater treatment plants (WWTPs) are regularly subjected to a diverse array of microbial pathogens [12,13].
The Environmental Service of Sleman Regency reports 163 Communal WWTPs in all sub-districts, majority of which run properly.Then, the Environmental Agency of the Special Region of Yogyakarta examined 41 Communal WWTPs for effluent quality, including some in Sleman Regency.This test only uses physical and chemical factors and is rarely tested for biological parameters.Therefore, this study was conducted to investigate the efficacy of CWWTPs in terms of biological parameters, specifically total Coliform and Escherichia coli (E.coli) concentrations in the observed CWWTPs.The results of this investigation will contribute to a better understanding of the WWTP process for E. coli elimination, thereby improving CWWTP performance.

2.1.Communal wastewater treatment plant classification
Communal wastewater recorded in Sleman Regency will be classified, and its function to minimize wastewater area will be studied.The classification of Communal WWTPs is based on previous research.The classification is based on four criteria obtained after a survey and searching for data from practical guidebooks for implementing Environmental Health Risk Assessment (EHRA) and WWTP processing engineering planning guidelines.The four criteria are as follows: 1. Population density of more than 25 people/ha 2. WWTPs have a service coverage ratio of more than 75 families 3. WWTPs peak discharge of more than 50 m3/day 4. WWTPs are more than eight years old Further, the Communal WWTP will be divided into four class levels.The first level is a WWTP with a low-risk level that meets one of the four criteria mentioned above.The second level is WWTP, that have met two of the four criteria above and is referred to as WWTP with moderate sanitation risk.The third level is WWTP, with high sanitation risk because they meet three criteria.The fourth level is WWTP, with very high sanitation risks because it meets the four criteria.According to the classification carried out by WWTPs with level two, 55 WWTPs were found from 163 Communal WWTPs in Sleman Regency.This study will investigate the third and fourth level WWTP-very high and high sanitation risk WWTP, namely IPAL Manunggal Pringgodani Sejati, IPAL Bakti Warga, IPAL Tambakrejo Bersih, IPAL Nologaten Bersih, and IPAL Andum Roso.

Study sites and sampling location
The Communal WWTPs used as the sampling location is in Sleman Regency, Yogyakarta, which is spread over several sub-districts.In 2021, the area of Sleman Regency is 574.82 km2sq.kmwith 17 subdistricts and a population of 1,087,339 people.Sleman Regency is directly adjacent to Boyolali Regency in the North, Klaten Regency in the East, Bantul Regency in the South and Kulonprogo Regency in the West.After the distribution of the Communal WWTPs classification was carried out, there were six Communal WWTPs selected, namely IPAL Manunggal Pringgodani Sejati, IPAL Bakti Warga, IPAL Tambakrejo Bersih, IPAL Nologaten Bersih, and IPAL Andum Roso.

Sample collection
Samples were taken from Communal WWTPs with very-high sanitation risk, namely IPAL Manunggal Pringgodani Sejati, IPAL Bakti Warga, and IPAL Tambakrejo Bersih and CWWTPs with high sanitation risk in Sleman Regency, Yogyakarta namely IPAL Nologaten Bersih, IPAL Andum Roso using aseptic grab sampling method.Samples were taken from 3 points in each WWTP: Inlet, Process and Outlet.

Total Coliform and Escherichia coli testing
Total Coliform and E. coli testing was carried out with reference to APHA 9221 (2017) [14], by growing the bacteria in a liquid medium, and the calculation was carried out based on the number of positive tubes after incubation at a specific temperature and time.The results of calculating the number of positive tubes in the media are then adjusted to the Most Probable Number (MPN) table.

Data analysis
For Total Coliform testing, in principle, the MPN method consists of a presumptive test and a confirmed test, using liquid media in test tubes, and is carried out based on the number of positive tubes.Positive tube observation can be seen by the emergence of gas and acid in the Durham tube.For testing E. coli, the test is carried out with a presumptive test, a confirmed test, and a completed test using liquid media in test tubes and is carried out based on the number of negative tubes (indicated by the absence of gas and acid) in the estimator test and proceed to the following observation until the tube is positive.Then, it was transferred into the EC MUG liquid medium until bubbles and a bright blue glow were on the media under a UV lamp.The positive results were then transferred to the Eosin Methylene Blue medium, which, if the sample were positive for E. coli, would change colour to metallic green.

Results and Discussions
It has been observed that the concentration of Escherichia coli (E.coli) bacteria varies significantly across the inlets of the Communal WWTP (CWWTP) under study.This is likely due to the different waste conditions at each inlet.The quantity of E. coli bacteria correlates with the number of human faeces that enter the WWTP inlet community because E. coli bacteria are intestinal bacteria that reside in the human digestive tract and exit with human faeces [15].As in the Manunggal Pringgodani Sejati CWWTP, the concentration of E. coli bacteria in the CWWTP was the highest, namely 36 MPN/100 ml, because based on observations when taking wastewater samples, there were faecal sludge solids that were quite thick.While at the Tambakrejo Bersih CWWTP, the inlet condition is very different from the inlet at the Manunggal Pringgodani Sejati CWWTP.In the Tambakrejo Bersih CWWTP, there is no solid faecal sludge at the inlet, so the concentration of E. coli bacteria in the CWWTP is the lowest, namely 6 MPN/100 ml.At the Nologaten Bersih WWTP, E. coli was reduced by 17%.Similarly, WWTP Andum Roso saw a 73% decrease in E. coli presence (Figure 1.).

Figure 1.
The concentration of E. coli in the inlet and outlet of all tested CWWTPs and its removal efficiency.The number of E. coli bacteria that enter the inlet at various stages of the process affects the variation in the concentrations of E. coli bacteria at the outlet.In the Manunggal Pringgodani Sejati CWWTP and Tambakrejo Bersih CWWTP, the wastewater treatment technology used is the same, namely Anaerobic Baffled Reactor (ABR).Anaerobic Baffled Reactor technology must effectively reduce wastewater's nutrient content [17].Despite using the same technology, the efficiency of bacteria removal can due to differences in processing loads and unit conditions.These conditions may differ depending on the age and maintenance of the technology unit, which can impact its performance at each CWWTP.
Inadequate disinfection methods or suboptimal operation can lead to the survival or proliferation of diverse microorganisms within treated wastewater effluents [18], facilitating their release into the surrounding environment.The presence of harmful microorganisms in ambient waters is a persistent issue of great concern to public health officials and individuals involved in water management globally.The primary source of enteric pathogens found in ambient surface waterways is effluent release from sewage treatment plants (STPs).Currently, the microbial quality of water is monitored by enumerating the levels of faecal indicator bacteria (e.g., thermotolerant Escherichia coli and Enterococci) to determine levels of faecal input and the possible presence of pathogens [14].In this study, All CWWTPs were found to have total Coliform concentration levels that fall below the standard limit set by the Ministry of Environment and Forestry of the Republic of Indonesia No. P.68/Menlhk-Setjen/2016 [20] and the Environmental Protection Agency (EPA).However, concentrations of E. coli in some IPALs exceed the standard limit.Previous studies have supported this research's findings, highlighting the limitations of using anaerobic baffled reactors (ABRs) for treating household wastewater.The eradication of pathogenic bacteria, including total Coliform and E. coli, was deemed unattainable [21].Identifying a drawback associated with ABR could serve as a valuable indicator for developing an alternative approach to mitigate microbial contamination in CWWTPs.According to some studies, using an active sludge system and membrane bioreactor [22] might be a good option for testing in treating municipal wastewater at a treatment plant (CWWTP).Moreover, a crucial aspect to consider is the incorporation of a disinfection unit prior to the release of effluent into water bodies or infiltration tanks.Nevertheless, the successful implementation of this strategy demands more than just the willingness of CWWTP management.It also requires the active involvement of the government and users.

Conclusions
CWWTPs' efficacy varies greatly in high-risk sanitation areas.IPAL Tambakrejo Bersih has an impressive 83% success rate in eliminating Escherichia coli.Moreover, in areas with high sanitation risks, like IPAL Nologaten Bersih and IPAL Andum Roso, the compliance rates of CWWTPS were 17% and 73%, respectively.All CWWTPs were found to have Total Coliform concentration levels that fall below the standard limit set by the Ministry of Environment and Forestry of the Republic of Indonesia No. P.68/Menlhk-Setjen/2016 and the Environmental Protection Agency (EPA).The results of this study will enhance our comprehension of the WWTP process for eliminating Escherichia coli.This will ultimately lead to better performance for the CWWTP.