Author : AM Tris Hardyanto

Beneath the Surface: Exposing the Hidden Crises in Global Wastewater Treatment

 

1. Introduction – Wastewater in Crisis and Transition

Over 80% of wastewater in developing countries flows untreated into rivers, lakes, and oceans. Now consider that water may reenter food,  tap, or a child's glass. Welcome to the hidden world of wastewater—a crisis we flush and forget.

1.1 The Global Sanitation Wake-Up Call

Wastewater treatment remains a neglected dimension of the global sustainability agenda. Despite Sustainable Development Goal (SDG) 6, notably Target 6.3, aiming to halve untreated wastewater by 2030, current progress is insufficient. Globally, only 60% of wastewater is treated, and much less is safe for discharge (UN-Water, 2023). shortfall is exacerbated by urban expansion, industrial growth, and uneven service delivery, creating a complex environmental and public health crisis. The realm of wastewater treatment encompasses critical components that, when overlooked, culminate in environmental degradation, public health crises, and social inequities.

The wastewater crisis reflects a more significant failure of integrated planning. We cannot meet climate or health goals without fixing the system." — Dr. Ingrid Msuya, Environmental Health Specialist.

Would you drink a glass of water knowing it passed through five lives and a factory before reaching the tap? 

1.2 Sludge – The Silent Contaminant

Sludge, the residual byproduct of treatment, contains heavy metals, pathogens, and chemical toxins. Poorly regulated disposal allows it to seep into soils and aquifers, threatening food security and potable water (Msuya, 2025; Rahmani & Anuar, 2019). calls for robust regulatory frameworks and a shift in perception—from sludge as waste to sludge as a potential resource for nutrient and energy recovery. Sludge reflects not just human waste but an aggregation of chemical pollutants and microbial life, posing significant threats to both human and environmental health.

Properly treated, it can be a resource-rich in nutrients and energy potential. Turning sludge from villain to hero requires rethinking policies, investments, and public perception.

Sludge management is not just a technical detail—it is a determinant of food safety, water purity, and climate health.

1.3 Pathogens and Contaminants Beyond E. Coli

Conventional systems focus on outdated microbial indicators like E. coli while ignoring persistent contaminants such as antibiotic-resistant bacteria, endocrine disruptors, and microplastics (Yaser et al., 2024). These pose substantial health risks and contribute to biodiversity loss. Revising quality standards to reflect emerging threats and improve treatment effectiveness is now a critical policy and scientific priority. Even treated wastewater has been identified as a vector for these contaminants, challenging existing regulatory frameworks.

The mismatch between monitoring and reality demands urgent regulatory upgrades. Our safety nets must evolve with science.

 

1.4 The Inequity of Infrastructure Access

Access to wastewater services is deeply unequal. Marginalized groups, particularly in informal settlements and rural areas, billions live without safe sanitation. Their waste either goes untreated—or worse—flows into open drains that flood their streets and homes during rain. Face systemic exclusion. They endure both inadequate service and harmful exposure from poorly regulated systems (Pasqualino et al., 2010). Private-sector investment typically favours profit-driven urban centres, intensifying environmental injustices and social disparities (Ibrahim, 2025). These systemic disparities perpetuate cycles of degradation and poverty, calling for inclusive governance and targeted investment.

Water injustice is a form of modern segregation. It divides the clean from the exposed." — A. Rahmani, Public Health Researcher.

1.5 Toward a Reimagined Future

The wastewater sector must adopt the 'One Water' approach—a paradigm that integrates water reuse, equity, and environmental resilience (WEF, 2023). A circular economy framework can unlock resource recovery, turning treatment plants into hubs for clean water, energy, and nutrients (Oktriani et al., 2017). Realizing vision requires inclusive governance, innovation, and proactive public engagement. The growing strain on freshwater resources, coupled with rising populations and climate change, necessitates wastewater reuse to enhance water availability for agriculture and support food security.

Wastewater is no longer a peripheral issue but a central element of sustainable development. With growing stress on freshwater supplies, particularly in water-scarce regions, the reuse of treated wastewater offers critical solutions for agriculture, food security, and ecosystem restoration (Murwendah et al., 2020). The transition from linear waste disposal to circular resource use is no longer optional—it is an urgent necessity. Addressing wastewater challenges requires a shift in perception—not merely as a byproduct but as a valuable resource.

Global data highlights stark disparities. Only 38% of industrial wastewater is treated, and treatment coverage ranges from 74% in high-income countries to a dismal 4.3% in low-income nations (Ibrahim, 2025; Murwendah et al., 2020). These inequities underline the need for targeted global cooperation and technical-financial support to close the sanitation gap. Many plants remain energy inefficient and emit greenhouse gases, contradicting their environmental purpose and underscoring the need for low-impact technologies.

Addressing governance failures is imperative. Many regions lack transparency and public access to treatment data. Public-private partnerships often operate with little oversight, compromising safety and accountability (Nugraheni & Wijayati, 2021). Policy reforms must prioritize real-time data sharing and inclusive community monitoring systems. Transparency and accountability are essential to rebuilding public trust and enhancing system efficiency.

Transformative change is achievable. Technological advances such as anaerobic digestion and membrane bioreactors can reduce emissions, recover nutrients, and optimize energy use (Jain et al., 2023). Equally, intelligent monitoring systems enable rapid response to pollution threats and ensure regulatory compliance (Ding & Zeng, 2022). Advanced regulations should address both effluent and sludge quality to ensure comprehensive sustainability.

Governments must engage communities, particularly those historically underserved, in co-designing wastewater solutions. Strengthened legal frameworks and decentralized models, paired with adequate oversight, will ensure greater inclusivity (Flores, 2022). International donors and multilateral organizations must facilitate knowledge transfer and infrastructure funding in the Global South. Community engagement and public awareness can drive compliance and build resilient systems.

Equitable wastewater systems demand innovative financing. Public-private partnerships, ecotaxes, and sustainability-linked bonds offer mechanisms to fund resilient infrastructure while promoting environmental stewardship (Pajares et al., 2019; Amarachi et al., 2023). These tools must be designed to prioritize social equity and ecosystem protection. Financial and technical assistance tailored to local contexts will ensure sustainable progress.

Ultimately, wastewater management lies at the crossroads of health, climate resilience, and justice. Policymakers, engineers, and civil society must unite to transform wastewater from a hidden hazard into a vehicle for sustainable development. By adopting integrated governance, advanced technology, and community-led planning, we can pave the way for a future that is clean, equitable, and resilient for all. Lessons from global successes and failures can inform the development of nutrient cycles that benefit both people and the planet.

Policymakers, engineers, and communities must co-create resilient systems that reflect both ecological realities and social needs.

 

2. Sludge Blind Spot – Waste That Will not Disappear

What happens to the gunk you flush? In most cities, the story ends in a landfill or an open field—often unmonitored. Sludge is the elephant in the wastewater room: dangerous when ignored, transformative when managed.

2.1 Composition and Risk Landscape

The crisis surrounding sludge management in wastewater treatment facilities constitutes one of the most pressing challenges in environmental sustainability and public health. Sludge composition varies depending on the wastewater source and treatment process. It contains organic matter, pharmaceuticals, heavy metals, pathogens, and nutrients such as nitrogen and phosphorus (Paramita & Koestoer, 2021). Improper classification and management can lead to toxic exposures, environmental pollution, and long-term health risks.

Although often overlooked, sludge is not a homogeneous material—it can be both a hazard and a resource. When improperly managed, it pollutes ecosystems and reduces soil quality. However, when safely treated, it offers potential benefits for agriculture and bioenergy production (Msuya, 2025; Rahmani & Anuar, 2019). duality presents a critical juncture for policymakers and engineers to recognize the inherent value of sludge.

 

 Illustrate the dual nature of wastewater sludge: a hazardous waste byproduct and a potential resource. It should show the sources of wastewater sludge, the various components (organic matter, nutrients, pathogens, heavy metals.), and the processes used to manage and potentially recover valuable components like nitrogen and phosphorus. Figure 2 Wastewater Sludge: Hazard and Resource.

 

"Sludge is the residue of our excesses. How we treat it reflects how we value public health and planetary health." — Prof. Budi Laksana, Environmental Chemist.

 

2.2 Governance and Regulatory Gaps

Globally, sludge management suffers from fragmented regulations and limited enforcement. Most countries lack standardized frameworks for tracking sludge volume, composition, or disposal pathways (Ibrahim, 2025). The result is a landscape marked by illegal dumping, unregulated landfilling, and toxic applications on agricultural lands (Lamastra et al., 2018).

Comparative analyses between regions highlight substantial variation. For instance, the EU Sewage Sludge Directive outlines stringent standards for agricultural reuse, whereas ASEAN's biosolid guidelines remain broad and inconsistently applied. These regulatory discrepancies further contribute to global inequalities in sludge management and environmental risk.

Governance gaps are particularly acute in low-income countries, where wastewater infrastructure is underfunded, and data on sludge generation is sparse. Informed decision-making relies on better monitoring systems and public accountability, both of which remain underdeveloped in many regions (Nugraheni & Wijayati, 2021).

 

In high-income countries, standards for land application exist. In many developing nations, however, sludge is dumped near communities or agricultural land without oversight (Lamastra et al., 2018). creates a ticking time bomb of bioaccumulation and groundwater contamination.

Countries with comprehensive sludge policies show 60% higher recovery rates than those without (EU Sludge Directive, 2022

2.3 Opportunities in Valorization

Treated sludge holds vast potential for circular economy applications. Technologies such as anaerobic digestion, struvite crystallization, and thermochemical conversion allow for energy and nutrient recovery (Ferrentino et al., 2023). Struvite extraction, in particular, offers a reliable method for phosphorus recovery—an increasingly scarce agricultural resource (Le Corre et al., 2021).

Successful models exist: Denmark and Belgium recycle a significant portion of their treated sludge in agriculture, setting a precedent for responsible reuse (Iticescu et al., 2021). Tokyo's Kasai smart city upgrade integrates sludge-to-energy systems that convert organic matter into biogas and electricity. These examples demonstrate the viability of sludge valorization at scale, particularly in urban contexts.

Sludge valorization through technologies such as thermal hydrolysis, anaerobic co-digestion, and struvite crystallization presents a viable path toward circular economies, turning liabilities into recoverable nutrients and bioenergy (Le Corre et al., 2021). Realizing potential requires policy support, public trust, and investment.

2.4 Case Study The Tokyo Kasai Facility

The Tokyo Kasai facility represents a leading model in the conversion of sewage sludge to biogas, demonstrating effective technologies and methodologies in wastewater treatment and resource recovery. The core of the facility's innovation lies in its implementation of advanced anaerobic digestion (AD) processes optimized for biogas production from organic waste, particularly sewage sludge. The process is critical for waste reduction and energy recovery, wherein biogas—primarily composed of methane and carbon dioxide—is produced and utilized in various energy applications such as heating and electricity generation (Evangelisti et al., 2014). The facility's design supports a closed-loop energy cycle, enhancing its overall sustainability while contributing significantly to Japan's energy resilience.

The optimization of biogas production within the framework is crucial. Research highlights the importance of managing various factors, including temperature and retention time, which directly influence methane yield. Studies have indicated that the inclusion of co-substrates—such as crude glycerol—can significantly amplify biogas outputs, demonstrating that a tailored approach to substrate selection can improve the efficiency of the anaerobic digestion process (Piekutin et al., 2021). Furthermore, the environmental assessments indicated that the facility's practices lead to reduced emissions associated with improper sludge management, serving as a model for effective wastewater treatment and resource recovery (Zhao et al., 2021).

The environmental benefits of the Tokyo Kasai facility extend beyond mere energy production. The integration of biogas within sewage treatment underlines the facility's alignment with the principles of a circular economy, where waste products are transformed into valuable resources (Kwaśny & Balcerzak, 2017). holistic approach affords substantial advantages in reducing greenhouse gas emissions and mitigating the ecological impacts associated with traditional waste disposal methods. It is evident that the methodologies employed at the Tokyo Kasai facility not only bolster energy recovery but also play a pivotal role in achieving broader environmental objectives (Dasí-Crespo et al., 2024).

The Tokyo Kasai facility stands out as a leading example of biogas production technology, showcasing the implementation of anaerobic digestion in treating sewage sludge. The case study emphasizes the necessity for ongoing innovations and enhancements in biogas production techniques, aiding in the sustainable management of wastewater and contributing to renewable energy generation. The facility's success serves as a key reference point for similar initiatives globally, highlighting the role of advanced waste treatment technologies in the transition towards more sustainable energy futures (Akyürek, 2019). 

2.4  Technological Innovation Needs

Despite the promise of sludge reuse, many innovative treatments remain underutilized. Methods like ultrasonic disintegration, thermal hydrolysis, and pyrolysis can reduce sludge volume and enhance its quality. However, these are often inaccessible to low-income regions due to financial, technical, and governance constraints (Godoy et al., 2018).

Pilot projects demonstrate efficacy but rarely scale. Sustainable transitions require global partnerships to build infrastructure, share knowledge, and provide financing mechanisms tailored to local contexts. Strategic public-private collaboration could accelerate technology diffusion, particularly in Southeast Asia and sub-Saharan Africa.

Furthermore, there is a critical need for capacity-building programs to train operators and regulators in advanced sludge technologies. Without it, the global potential for sustainable sludge treatment will remain unrealized.

What if every ton of sludge powered a streetlamp instead of polluting a stream?

2.5 Social Equity in Sludge Exposure

Sludge mismanagement disproportionately affects marginalized communities. Residents in informal settlements and rural areas often live near unregulated disposal sites, facing heightened exposure to pathogens, heavy metals, and noxious odours (Iticescu et al., 2021).

These conditions perpetuate environmental injustices. The absence of sanitation infrastructure reinforces public health disparities and places additional burdens on already vulnerable populations. Equity-focused regulation must address these gaps through localized monitoring, compensation frameworks, and community engagement (Ibrahim, 2025).

Global sludge governance must integrate social justice by prioritizing the needs of underserved communities. Equitable infrastructure investment, informed consent processes, and environmental safeguards are essential for avoiding a future where sludge pollution maps onto existing patterns of inequality.

 The crisis of sludge mismanagement reveals both risk and opportunity. Currently, poor regulation, outdated technology, and social inequities combine to make sludge a persistent environmental hazard. However, with proper investment, innovation, and governance, sludge can become a cornerstone of the circular economy.

Future progress depends on bridging regulatory gaps, deploying advanced technologies, and ensuring inclusive policy frameworks. By valuing sludge not as waste but as a resource, we move closer to a sustainable and resilient wastewater paradigm—one that leaves no community behind.

"Sludge injustice is often invisible—but its effects are not. We must democratize sanitation." — Dr Nina Ibrahim, Public Health Advocate.

 

 

3. Silent Pathogens – When "Clean" Water Still Harms

 

What if "clean" water was not safe? From antibiotic-resistant bacteria to hormone disruptors, a hidden army of contaminants survives conventional treatment—and flows quietly back into our lives.

3.1 Antibiotic Resistance in Effluent 

Treated wastewater is increasingly recognized as a reservoir for antibiotic-resistant bacteria (ARB) and antibiotic-resistance genes (ARGs). These elements pose serious threats to public health, especially when discharged into aquatic environments or reused in agriculture (Yaser et al., 2024). Resistance genes can horizontally transfer among microbial populations, affecting both ecosystems and human health. Recent QMRA studies reveal that ARG exposure through effluents can surpass safe thresholds in reuse scenarios (WHO, 2023).

The World Health Organization's 2023 policy brief emphasizes that wastewater mismanagement is a significant pathway for the spread of antimicrobial resistance. Addressing risk necessitates a reevaluation of treatment standards and the incorporation of advanced disinfection methods. Upgraded facilities must prioritize the removal of ARGs and ARBs alongside traditional pathogens to safeguard water reuse initiatives.

"The war against antimicrobial resistance is being lost in our wastewater." — WHO, 2023

Standard disinfection processes are insufficient. Addressing requires advanced technologies and updated standards that target ARGs, not just traditional pathogens. Real-time tracking and genetic monitoring must become the new norm.

3.2. Viral Contaminants and Systemic Oversight 

Viruses like norovirus, hepatitis A, and rotavirus are notably resistant to standard chlorination and disinfection. These enteric viruses are increasingly detected in treated wastewater, posing significant exposure risks when such water is reused for agriculture or recreational purposes (Murwendah et al., 2020).

In many regions, inadequate virus-specific monitoring hinders effective risk management. Communities relying on reclaimed water face heightened vulnerability. Expanding viral detection, particularly through quantitative microbial risk assessment (QMRA) models, is essential for assessing the true scope of exposure and developing targeted regulatory strategies (Nugraheni & Wijayati, 2021).

 Infographic showing virus pathways from treatment plants to agricultural fields.

Few regions monitor for viruses specifically. Integrated viral risk assessment, including Quantitative Microbial Risk Assessment (QMRA), must inform sanitation policies moving forward.

 

 

3.3. Microplastics and Aquatic Bioaccumulation

Microplastics—particles smaller than 5mm—are increasingly found in treated wastewater. These particles escape traditional filtration and enter natural water bodies, contributing to marine and terrestrial pollution (Oktriani et al., 2017). Wastewater treatment plants are one of the primary conduits for microplastics to enter the environment.

These pollutants act as carriers for pathogens and persistent organic pollutants, facilitating their entry into aquatic food chains (Amarachi et al., 2023). Once ingested by marine organisms, microplastics can bioaccumulate and pose long-term risks to human health. Despite partial removal in current facilities, smaller fragments often remain, prompting calls for improved technologies such as nanofiltration, advanced oxidation, or biotechnological solutions (Jain et al., 2023).

Can wastewater be considered clean if it carries invisible plastic?

3.4. Chemical and Endocrine Disruptors

Endocrine-disrupting compounds (EDCs) such as bisphenol A, phthalates, and synthetic hormones enter wastewater through household, pharmaceutical, and industrial sources. These chemicals persist through conventional treatments, ultimately reaching natural ecosystems and drinking water sources (Ding & Zeng, 2022).

EDCs interfere with hormonal systems in both humans and wildlife, resulting in reproductive and developmental disorders. Fish populations have exhibited altered sex ratios and impaired fertility due to long-term EDC exposure. Their presence in treated water demands urgent attention through quaternary treatments like ozonation, UV-AOPs, and activated carbon systems to ensure comprehensive removal.

3.5 Expanding the Monitoring Toolbox

The limitations of traditional water quality indicators, primarily E. coli, are increasingly evident. Silent pathogens like ARBs, viruses, and EDCs remain undetected under current regimes. Regulatory upgrades must include a wider suite of microbial and chemical indicators (Rosemarin et al., 2020).

Advanced treatment technologies such as membrane bioreactors (MBRs), UV-advanced oxidation processes (UV-AOPs), and biosensor-based systems offer enhanced contaminant removal and real-time monitoring capacity (Paramita & Koestoer, 2021). QMRA models play a pivotal role in quantifying health risks, particularly in reuse contexts. These tools allow for evidence-based policymaking and ensure that reclaimed water meets safety thresholds.

 Despite perceived safety, treated wastewater often harbours a spectrum of emerging contaminants and silent pathogens. From antibiotic resistance to microplastics and endocrine disruptors, these pollutants evade outdated treatment methods and regulatory frameworks. Oversight perpetuates environmental and public health risks, especially in vulnerable communities relying on water reuse.

To mitigate these threats, a shift toward more sophisticated monitoring, treatment, and governance is necessary. Investments in quaternary treatment technologies, real-time monitoring, and community engagement must be prioritized. Equally, comprehensive regulatory reforms must expand beyond conventional microbial indicators to include a broader contaminant spectrum.

Addressing silent pathogens is not just a technical

issue—it is a matter of public trust and ecological resilience. As scientific understanding evolves, so too must our approaches to water safety. Only then can we ensure that "clean" water truly protects both people and the planet.

Singapore's NEWater initiative stands as a global benchmark in advanced water reuse, combining rigorous science with public trust. Recognizing that traditional indicators like E. coli are no longer sufficient to ensure safety, Singapore has proactively expanded its monitoring systems. NEWater integrates real-time virus tracking and microplastic detection into its quality assurance protocols, ensuring that potential threats are identified and mitigated at every stage of water reclamation.

The forward-thinking approach demonstrates that effective water reuse is not just about treatment but about continuous, intelligent monitoring. By employing advanced technologies such as biosensors and real-time analytics, Singapore has shifted from reactive water safety measures to a proactive, precision-based strategy. These innovations enable authorities to detect microbial and chemical contaminants long before they pose health risks, reinforcing the reliability of recycled water—even for potable use.

Beyond technological excellence, Singapore's success lies in building public confidence through transparent, evidence-based practices. By showcasing the robustness of its monitoring systems, the NEWater program has turned what could be a controversial solution into a celebrated model of sustainability. It offers a clear lesson: safeguarding public health in the age of water reuse requires not just better treatment—but more intelligent monitoring.

 

Contaminants You Cannot See.

Treated water does not always mean safe water. From genetic pollution to endocrine disruption, silent pathogens are reshaping our understanding of risk. Policy, science, and public engagement must evolve to match the new reality.

"Clean is not just what we see. It is what we test for."

4. Infrastructure Inequity  Wastewater for the Few

In the world of wastewater, the pipes often stop where the profits do. From sprawling urban slums to isolated rural villages, billions live without access to basic sanitation—not by accident, but by design.

4.1  The Geography of Exclusion

Access to wastewater treatment is deeply unequal. Over 80% of untreated wastewater originates in developing nations, where informal settlements and rural communities are routinely bypassed in infrastructure planning (Msuya, 2025). These populations face a dual burden: exclusion from centralized services and exposure to poorly managed decentralized systems. Exclusion perpetuates cycles of poverty, environmental degradation, and social injustice (Rahmani & Anuar, 2019).

"Sanitation deserts are created, not discovered. We must redesign inclusion into every pipe we lay." — Prof. S. Ibrahim, Urban Planner.

4.2. Decentralized Systems – Promise or Problem?

Decentralized wastewater systems offer the potential for inclusive coverage but remain underfunded, unregulated, and inconsistently maintained. Examples like India's DEWATS and Kenya's bio-centers reveal success when systems are community-managed and adequately supported. However, inadequate regulation or maintenance often leads to ineffective treatment, heightening health risks in vulnerable areas (Yaser et al., 2024; Pasqualino et al., 2010).

These systems can function as transitional solutions for communities lacking access to centralized infrastructure. However, without robust governance, their promise remains unrealized. Targeted investment and oversight are essential to transform decentralized sanitation into an equitable and sustainable alternative.

Can we call sanitation inclusive if it breaks down where the poor live?

4.3. PPPs and Market Bias

Public-private partnerships (PPPs) often skew toward high-return industrial or affluent zones. Marginalized communities are routinely excluded from such investment schemes, which prioritize short-term economic gain over equitable service delivery (Ibrahim, 2025). The consequence is a two-tiered sanitation system where the poor face disproportionate exposure to untreated wastewater (Nugraheni & Wijayati, 2021).

In Bangladesh, pourashava FSM programs attempt to bridge the gap but suffer from inconsistent funding and regulatory oversight. Aligning PPP models with pro-poor objectives, including affordability, accountability, and spatial inclusion, is vital for reversing these inequities.

The implementation of pourashava FSM (Faecal Sludge Management) schemes in Bangladesh presents a noteworthy case study in urban sanitation. While these initiatives have significantly expanded access to sanitation services, they face substantial hurdles, particularly in terms of funding and equity in service distribution. Current PPP (Public-Private Partnership) reforms are essential to address these challenges by linking profit incentives to performance outcomes, ultimately ensuring affordability, spatial equity, and social impact that reaches underserved communities.

Urban sanitation initiatives like the pourashava FSM schemes often struggle with inconsistent funding, which can lead to imbalances in service delivery across different areas. Research has indicated that urban environments generally receive more attention and resources for sanitation services compared to rural and peri-urban areas (Kwiringira et al., 2021; Kennedy-Walker et al., 2014). trend is exacerbated by systemic neglect of lower-income communities that require enhanced infrastructure and service. Recognizing the disparities within urban regions, it becomes imperative that PPP models not only focus on financial returns but also prioritize equitable access to sanitation services for marginalized populations (Wadhwa & Nandal, 2023; Wu et al., 2016).

PPP reforms must critically factor in social impact and performance indicators into their frameworks. Traditional PPP arrangements often prioritize profit with inadequate accountability for social outcomes (Osei‐Kyei et al., 2019). By integrating performance metrics that consider both service quality and social equity, these reforms could enhance the effectiveness of FSM schemes. A successful PPP model should facilitate public engagement to address community-specific needs, fostering greater participation and support from local stakeholders (Kwiringira et al., 2014; Liu et al., 2021). the approach could yield significant improvements in user satisfaction and overall community health, particularly among vulnerable populations (Corburn & Hildebrand, 2015).

Additionally, the challenges faced in FSM service provision in Bangladesh reflect broader systemic inadequacies in urban sanitation, which persist even as global initiatives aim for universal access. There is a pressing need for innovation in financing models that overcome barriers to investment in low-income areas (Mundonde & Makoni, 2024). Developing adaptive financing frameworks that align public, private, and community interests will be essential for sustainable sanitation solutions. These frameworks should account for local income disparities and create mechanisms for community members to contribute to and benefit from sanitation investments (Koop & Leeuwen, 2016; Berrone et al., 2019).

The expansion of pourashava FSM schemes in Bangladesh highlights the complexities involved in delivering equitable urban sanitation. To enhance the effectiveness of these schemes, PPP reforms must ensure that profit motives are closely tied to performance outcomes, addressing the specific sanitation challenges faced by poorer communities. Adequate funding, innovative public engagement, and a commitment to social impact can collectively drive meaningful improvements in sanitation access and equity, thereby fulfilling the broader goals of sustainable urban development.

4.4  Funding and Policy Misalignment

Despite growing global attention to sanitation, funding seldom reaches the poorest. Climate adaptation finance and SDG-aligned funds often prioritize large-scale infrastructure, bypassing informal and remote areas (Rosemarin et al., 2020). A rights-based approach, paired with targeted subsidies, can help correct the imbalance.

Tools like the WASH Equity Atlases (UNICEF, 2023) now enable real-time mapping of infrastructure gaps. When used in policy planning, these GIS-based tools allow stakeholders to visualize disparities and allocate resources more equitably. Integrating such insights into national sanitation strategies will strengthen social accountability.

"If sanitation policy ignores slums, it is not a policy—it is a privilege map." — Dr. Lydia Marpaung, Policy Analyst.

4.5. Community-Led Infrastructure Planning

Participatory infrastructure planning improves both uptake and long-term system performance. Models that empower community WASH committees—such as those in Nigeria and the Philippines—enhance local accountability and system resilience (Amarachi et al., 2023). Co-owned treatment systems also encourage better operations and maintenance outcomes.

Community engagement ensures that interventions are culturally appropriate and technically feasible. Training programs and capacity-building initiatives further empower residents to manage local systems and monitor service delivery. These inclusive models are essential for bridging infrastructure inequity at scale.

 Infrastructure inequity in wastewater systems remains a persistent barrier to health, dignity, and environmental justice. Disproportionate burdens on vulnerable populations—from Indigenous communities to urban slums—highlight the need for equitable investment, decentralized innovation, and participatory governance.

Strategies to reverse injustice must include robust regulation of decentralized systems, pro-poor PPP reforms, targeted funding for underserved regions, and community-led infrastructure planning. Spatial equity tools and inclusive finance can help reshape sanitation from a privilege to a right. Only through such deliberate and just action can wastewater infrastructure serve all—not just the few.

 

5. The Sustainability Paradox  When Treatment Pollutes

Wastewater treatment plants are meant to protect the environment—but what if they are quietly harming it instead? From energy-hungry operations to greenhouse gas emissions, the system designed to clean our water may be contaminating our future.

5.1 Energy-Hungry Infrastructure

Wastewater treatment plants (WWTPs) are paradoxically significant contributors to climate change. While designed to purify water, they consume 3–4% of global electricity, primarily through energy-intensive activated sludge systems (IPCC, 2022). inefficiency results in high operational costs and substantial greenhouse gas emissions, notably methane and carbon dioxide, challenging the sector's green image and reinforcing its environmental footprint (Msuya, 2025).

Many plants operate using outdated technologies. Transitioning to energy-efficient methods, such as gravity-fed systems or hybrid anaerobic-aerobic processes, is critical to reducing the sector's environmental burden.

"WWTPs were built to clean water, not to heat the planet. It is time for an upgrade." — Dr. Leandro Mejía, Energy-Water Nexus Researcher.

5.2 Emissions from Nitrification and Digestion

The nitrification-denitrification process used for nitrogen removal emits nitrous oxide, a greenhouse gas nearly 300 times more potent than CO₂. Additionally, methane is released during sludge digestion, compounding the climate impact of WWTPs (Rahmani & Anuar, 2019). Emissions mitigation strategies—like improved oxygen control and biogas capture—are necessary to reduce the environmental costs of core treatment processes (Amarachi et al., 2023).

Without gas capture systems and oxygen control, these emissions negate environmental gains. Emerging technologies now offer closed-loop solutions for sludge digestion that recover biogas and minimize leakage.

 

 

5.3: Circular Resource Recovery

Some countries are pioneering closed-loop resource recovery models. In Singapore and Sweden, WWTPs extract biogas, phosphorus, and heat from wastewater and sludge (Pajares et al., 2019). Sweden's Sjölunda facility exemplifies the shift, operating as a near-zero-emission plant through anaerobic digestion, solar energy, and thermal recovery (IPCC, 2022). These examples demonstrate that wastewater infrastructure can be regenerative when built on circular economy principles.

These models show that resource recovery is not just theoretical—it is operational. Circularity in WWTPs involves recovering not just energy but also nutrients and heat.

Denmark's sewage sludge management showcases a leading model in nutrient recycling, where approximately 94% of the phosphorus contained in sludge is effectively repurposed for agricultural use, thereby closing a critical nutrient loop. Practice significantly mitigates reliance on chemical fertilizers, enhances soil quality, and promotes sustainable agricultural practices Lemming et al. (2017) (Alsiņa et al., 2022). The successful recycling of phosphorus in Denmark is primarily attributed to the comprehensive sanitization and stabilization treatments that sewage sludge undergoes before application to fields, ensuring compliance with safety regulations regarding contaminants (Klinglmair et al., 2015; Havukainen et al., 2016).

Utilizing phosphorus-rich sludge in agriculture not only contributes to nutrient cycling but also aligns with the broader principles of a circular economy. As phosphorus is an essential nutrient for plant growth, its recovery from waste streams like sewage sludge plays a vital role in maintaining soil fertility and promoting efficient resource use in farming (Kirchmann et al., 2016; Abreu et al., 2017). The incorporation of recovered phosphorus into agricultural practices alleviates the ecological burden of waste disposal and enhances the sustainability of food production (Lamastra et al., 2018; Delibacak et al., 2020).

The Danish model exemplifies how waste management strategies can effectively align with agricultural needs, demonstrating a holistic approach to nutrient recovery that could inspire other nations facing challenges in sustainable waste and agricultural practices (Brunner & Morf, 2024; Stürmer & Waltner, 2021).

 5.4: Smart Plant Design and Retrofitting

Technological innovation enables the transition toward low-carbon wastewater systems. Membrane bioreactors, IoT-based sensors, and AI-driven analytics improve energy efficiency and optimize chemical usage (Jain et al., 2023). Retrofitting legacy systems with these tools could drastically reduce emissions. Real-time data also enables predictive maintenance and adaptive control strategies, reducing waste and extending equipment life (Flores, 2022).

Can a plant truly call itself sustainable if it does not know its emissions in real-time?

5.5. Rethinking Sustainability Standards

Conventional sustainability assessments for WWTPs often ignore emissions and energy use. Expanding metrics to include life cycle assessments (LCA) provides a more accurate sustainability benchmark. LCA frameworks reveal the hidden costs of energy-intensive operations and can guide climate-smart retrofitting and financing (Flores, 2022). Holistic sustainability must evaluate performance across energy, emissions, and circular resource flows.

 The sustainability paradox in wastewater treatment exposes a contradiction: facilities intended to protect the environment can inadvertently harm it. High energy use, greenhouse gas emissions, and mismanaged sludge highlight the sector's unacknowledged environmental costs. However, emerging technologies and circular models offer a pathway forward.

To resolve the paradox, systemic reforms must prioritize energy efficiency, emissions reduction, and circularity. Innovative technologies updated sustainability metrics, and global benchmarks like Sweden's Sjölunda WWTP demonstrate what is possible. Only by aligning treatment operations with environmental goals can WWTPs fulfil their mission to safeguard both public health and the planet.

"Sustainability is not a sticker. It is a system. Moreover, right now, too many systems are leaking carbon." — Dr. Evi Santosa, Environmental Engineer.

The sustainability paradox reveals a contradiction at the heart of modern sanitation. However, it also reveals a path forward. With innovative technologies, circular practices, and new standards, wastewater treatment can become truly regenerative.

 "We cannot clean water while dirtying the sky. The next generation of treatment must be clean on all fronts.

6. Data, Governance, and the Cost of Silence

In wastewater governance, what we do not know can hurt us—and what is hidden from public view often does. From opaque data to unchecked private deals, the silence surrounding sanitation systems threatens health, equity, and trust.

6.1. The Transparency Deficit

One of the most significant challenges in wastewater governance is the absence of real-time, publicly accessible data. In most countries, critical information on water quality and treatment processes is either unavailable or outdated (Msuya, 2025). Transparency gaps prevent communities and regulators from identifying service gaps, erode public trust, and foster an environment vulnerable to inefficiency and corruption (Rahmani & Anuar, 2019; Yaser et al., 2024).

"Without transparency, wastewater management becomes a black box—and a breeding ground for failure." — Dr. Hanna Rajagopal, Policy Analyst.

6.2 PPPs Without Public Oversight

Public-private partnerships (PPPs) are often heralded as efficient, yet many operate with limited transparency and accountability. Performance benchmarks are frequently undefined, and affected communities rarely participate in project planning (Amarachi et al., 2023). disconnect skews investments toward industry over public health and deepens inequality. Oversight mechanisms must be strengthened to ensure PPPs align with social and environmental goals (Oktriani et al., 2017).

In Manila, water privatization was hailed as a model—until rising tariffs, service gaps, and secrecy sparked a public backlash.

Reforming PPPs requires mandatory disclosure of terms, outcomes, and compliance. Oversight bodies and citizen audits can restore balance.

The experience of water privatization in Manila was initially regarded as a model for other regions due in part to substantial investments and some documented operational improvements. However, as tariffs increased and service deficiencies became apparent, public dissatisfaction grew, undermining the positive perception of the privatization model Torio (2018). The rising costs were not coupled with commensurate enhancements in service quality, leading to criticisms regarding a lack of transparency and accountability in the operations of the private water companies (Liwanag & Wyss, 2019).

Reforming Public-Private Partnerships (PPPs) in the water sector necessitates a fundamental shift towards greater accountability and active engagement with citizens. A critical aspect of reform includes the adoption of mandatory disclosure policies that detail the terms, outcomes, and compliance of PPP agreements (Punzalan et al., 2024). Such transparency is vital for rebuilding trust among stakeholders and ensuring equitable access to water services, particularly for underserved populations. Additionally, the establishment of independent oversight bodies along with citizen-led audits can serve as adequate checks and balances, enhancing both the accountability and responsiveness of service providers to the public's needs (Moncatar et al., 2021; Amit et al., 2022).

To improve service delivery equity, future PPP frameworks must prioritize inclusivity and transparency, creating mechanisms that encourage public participation while ensuring access to clean water as a fundamental human right. The experiences from Manila serve as a poignant reminder of the dangers inherent in privatization when transparency and equity are not core components of the operational framework (Tanay et al., 2023).

6.3. The Role of Digital Tools in Accountability

Digital technologies offer new tools to enhance wastewater transparency. IoT-enabled sensors, blockchain compliance tracking, and open-access dashboards can provide real-time data and ensure traceability (Jain et al., 2023). Singapore's PUB smart water grid and India's SBM portal exemplify how governments can integrate digital platforms to monitor wastewater quality and deter data manipulation (WIN, 2022). Citizen science platforms also empower communities to report local water conditions.

Map of digital sanitation platforms in Southeast Asia

Examples like Singapore's PUB Smart Water Grid show that digitization not only boosts efficiency—it also builds public confidence in system integrity.

 

 

6.4  Legal Mechanisms and Citizen Advocacy

Robust legal frameworks are vital for combating corruption in wastewater governance. Whistleblower protections and mandatory disclosure laws increase accountability and deter malpractice (Pajares et al., 2019). Strengthening environmental justice laws ensures community access to wastewater data and decision-making. Transparency audits, such as those developed by the Water Integrity Network, help diagnose governance gaps and guide reforms (Ding & Zeng, 2022).

What if every community had the legal right to inspect their wastewater plant's emissions?

Whistleblower protections, community science initiatives, and legal aid for WASH-related cases all strengthen civic engagement in sanitation.

6.5 Building Trust Through Participation

Civic engagement builds trust, promotes compliance and ensures wastewater strategies reflect community priorities. Community WASH committees, citizen reporting, and participatory planning mechanisms foster shared ownership and improve service outcomes (Amarachi et al., 2023). Participation also creates social capital and resilience, especially in vulnerable communities. Governments and NGOs should institutionalize inclusive engagement in sanitation planning.

 The silence surrounding wastewater governance—marked by data gaps, limited accountability, and passive public roles—extracts a heavy toll on public health and environmental justice. To break the silence, stakeholders must institutionalize transparency, digitize oversight, reform PPP governance, and empower civic participation.

By deploying innovative technologies, enforcing anti-corruption safeguards, and centring communities in decision-making, wastewater governance can evolve into a transparent and inclusive system. These efforts will ensure that wastewater systems serve not only technical goals but also democratic, equitable, and sustainable outcomes.

Trust is not built with pipes. It is built with participation." — Dr Lila Mahfud, Civic Infrastructure Expert.

 When Silence Is the System

The quiet around wastewater data and governance extracts a loud toll—from inequity to environmental risk. However, transparency, digital tools, and public participation can transform wastewater systems into models of democratic, sustainable infrastructure.

When people see the data, they see the value—and demand the change."

 
7. Looking Ahead – Global Priorities for Just and Sustainable Wastewater Systems

What if wastewater solutions were not only about pipes and pumps—but about justice, resilience, and global solidarity? The future of sanitation hinges not just on technology but on the courage to think in systems and act with equity.

7.1  A Systems Thinking Approach

Wastewater must be addressed through an integrated systems lens. It intersects with the water-energy-food-health nexus, making siloed interventions ineffective. A systems-thinking approach emphasizes co-benefits, such as nutrient recovery for agriculture, energy reuse, and improved public health outcomes. Interdisciplinary research centres are needed to bridge engineering, health, and governance in addressing wastewater challenges holistically (UNESCO, 2023).

 "You cannot fix sanitation without touching agriculture, climate, and care systems." — Dr. Rachel Wahono, Systems Ecologist.

 7.2 Global Cooperation and Policy Alignment

Harmonizing international policies is essential for achieving SDG 6. UN-Water's 2024 Global Acceleration Framework and the OECD's sanitation financing toolkit call for cross-sector collaboration, decentralization, and milestone-based planning. Multi-stakeholder coalitions now encourage national governments to embed accountability in wastewater targets and align monitoring with regional and global reporting mechanisms (UN-Water, 2024).

 

7.3: Financing Mechanisms for Scale 

Innovative financing can unlock equitable wastewater investments. Ecotaxes, green bonds, and blended finance models support infrastructure expansion while incentivizing sustainability. Climate adaptation funds can help scale decentralized systems in vulnerable areas. Public-private funding arrangements should prioritize social equity, ensuring financing reaches marginalized communities (Pajares et al., 2019; Rosemarin et al., 2020).

Colombia's revolving sanitation fund supports peri-urban WASH projects through a climate-resilient finance model. International donors must prioritize vulnerable regions and create accessible pathways for local governments to invest in resilient systems.

In Colombia, the establishment of a revolving sanitation fund exemplifies an innovative approach to financing peri-urban WASH (Water, Sanitation, and Hygiene) projects while promoting climate resilience. Fund facilitates local governments' investment in essential sanitation infrastructures that respond to community needs, particularly in vulnerable regions where access to basic services is scarce Hyde‐Smith et al. (2024). The need for international donor prioritization of these vulnerable areas is paramount, as traditional funding mechanisms often overlook marginalized populations that require urgent support (Dickin et al., 2020).

Effective sanitation solutions in these contexts must be adapted to local conditions, underscoring the significance of providing accessible pathways for local governments to engage directly with the financing process. Empowering local governments can create a more sustainable and responsive WASH infrastructure that prioritizes community involvement (Peirson & Ziervogel, 2021). Additionally, ensuring that funds for sanitation projects are managed transparently can enhance local capacity, enabling stakeholders to address both immediate needs and long-term environmental challenges effectively (Erickson, 2015).

To further reinforce the impact of the revolving sanitation fund, it is crucial to integrate mechanisms for monitoring outcomes and compliance, ensuring that the investments lead to tangible improvements in health and sanitation across peri-urban areas (Hollander et al., 2020). Such efforts can help bridge existing gaps in service delivery while fostering a culture of accountability and community engagement in the management of WASH services (Delgado-Serrano et al., 2017).

Colombia's revolving sanitation fund serves as a critical model for enhancing climate-resilient financing in WASH initiatives. By focusing on vulnerable regions and promoting robust local governance frameworks, international donors can significantly impact public health and environmental sustainability outcomes in these communities.

7.4 Innovation in Technology and Knowledge Transfer

Cross-border technology transfer is vital for sustainable wastewater solutions. North-South and South-South collaborations enable shared innovation. Countries like Singapore and Kenya are partnering on low-cost intelligent monitoring tools. Open-source platforms for design and diagnostics can accelerate learning and adoption in under-resourced regions. Capacity building must accompany technology transfer to ensure effective implementation (Jain et al., 2023).

What would wastewater governance look like if innovation moved from the margins to the mainstream?

Capacity-building, mentorship, and exchange programs must be embedded in every tech transfer initiative.

7.5 Building a Rights-Based Future

Recognizing sanitation as a human right reframes wastewater treatment as a moral obligation. Equity must underpin governance frameworks and regulatory standards. A rights-based approach mandates service access for all, particularly marginalized populations. It also demands accountability for environmental harm caused by inadequate sanitation. National laws and global frameworks must reflect the paradigm (Hatammimi & Gunawan, 2023).

 The crises explored—from sludge and silent pathogens to infrastructure inequity and governance failure—underscore the need for urgent reform. These are not just technical challenges but moral and systemic failures. Addressing them requires transformative action grounded in justice, participation, and innovation.

A global roadmap must integrate interdisciplinary strategies, policy alignment, and milestone-based monitoring. Governments must empower communities, industries must innovate sustainably, and civil society must demand transparency. Together, these actors can create wastewater systems that are not only efficient but also equitable and resilient.

The future of wastewater management lies in its ability to protect health, advance equity, and regenerate ecosystems. It is through shared commitment that we can build systems that serve all people, uphold environmental justice, and contribute meaningfully to global sustainability.

"Dignity is not a policy goal. It is a right—and wastewater justice begins with that recognition." — Atty. Rosa Intan, Human Rights Lawyer

 

 7.6 From Crisis to Collective Resolve

The global wastewater challenge is solvable—not through silver bullets, but through systems change, solidarity, and sustained political will. By aligning financing, policy, innovation, and rights, we can build just and sustainable wastewater systems for all.

"Wastewater is not waste—it is a mirror. What we do with it reflects who we are and who we strive to become."

 

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