Wastewater treatment decentralization: Is this the right direction for megacities in the Global South?

Economic and environmental benefits of natural treatment systems for sewage treatment: A life cycle perspective

Sewage treatment involves a trade-off of land vs. energy and the location of installing Sewage Treatment Plants (STPs) strongly impacts the decisions regarding treatment technologies. In the wake of rapid urbanization, deteriorating freshwater quality and water scarcity, it is crucial to plan adequate and low-cost sewerage infrastructure that can improve the quality of life in rural and urban areas. The present work involves a novel life cycle analysis through six scenarios generated from a holistic perspective that can aid urban planners and urban local bodies in planning the sewage treatment facilities in their cities, towns or villages. Instead of planning sewerage infrastructure for a long-term period of thirty years, it is suggested to create and operate the STPs only for the upcoming decade. Further, owing to the drawbacks of mechanized and natural treatment systems, adopting a mix of these treatment approaches in planning infrastructure is suggested and the benefits of implementing the same are quantified and discussed. Implementing these strategies results in almost 30 % cost savings and 40 % reduction in greenhouse gas emissions, hence, investing in land for natural treatment systems is suggested instead of incurring heavy electricity bills for mechanized treatment systems. The land cost significantly affects the decision-making regarding treatment technology selection; hence, the variation in the life cycle cost of different sewage treatment approaches is assessed for varying land rates in India.

Toilet effluent separation and brown water treatment: Survey and initial feasibility testing in Mexico

Separation of domestic effluents at the source and the utilization of low-flush toilets offer alternative approaches for developing efficient wastewater treatment systems while promoting energy generation through anaerobic digestion. This study focused on assessing toilet usage in Mexico and exploring the potential of anaerobic co-digestion of brown water (feces) and toilet paper as influential factors in wastewater treatment systems. A survey was conducted on a representative sample of Mexicans to gather information on toilet usage frequency, toilet paper use and disposal practices, as well as the type and quantity of commercial disinfectants and pharmaceutical compounds they use or consume. The survey revealed that per capita toilet paper consumption is 2.9 kg annually, that 58 % of respondents do not dispose used paper in the toilet, and that about 47 % use two to three cleaning and disinfection products. Notably, 97 % of the sampled Mexican population expressed a willingness to transition to more eco-friendly toilet options. Subsequently, in a second step, the anaerobic co-digestion of brown water with toilet paper was evaluated, demonstrating a relatively high production of volatile fatty acids but low methane production. This suggests an efficient hydrolysis/acidogenesis process coupled with restrained methanogenesis, probably due to pH decrease caused by acidogenesis. This study underscores that toilet paper and brown water are potential suitable substrates for anaerobic co-digestion. Furthermore, it sheds light on the behaviors of Mexican society regarding bathroom use and cleaning, contributing to the establishment of foundations for wastewater treatment systems with effluent separation at the source.

Centralization of wastewater treatment in a tourist area: A comparative LCA considering the impact of seasonal changes

Nowadays, environmental protection has become a topic of primary importance, and the interest in wastewater treatment plants (WWTPs) has increased due to the need for a paradigm shift from linear to circular economy. The centralization level of wastewater infrastructure is the basis for a successful system. The aim of this study was to investigate the environmental impacts generated from the centralized treatment of wastewater in a tourist area in central Italy. The combined use of BioWin 6.2 simulation software and life cycle assessment (LCA) methodology was implemented to evaluate the potential connection of a small decentralized WWTP to a medium-size centralized facility. Two different scenarios (decentralized system, corresponding to the current situation, and centralized) were evaluated in two separate periods: high season (HS), corresponding to the main tourist season, and low season (LS), which is the period before the main tourist season. Two sensitivity analyses were conducted, assuming different N2O emission factors, and considering the period at the end of tourist season, respectively. Although with modest advantages (up to -6 % in pollutant emissions), WWTP connection was the best management option in 10 out of 11 indicators in HS, and 6 out of 11 categories in LS. The study showed that wastewater centralization was promoted by scale factors in HS, as the most impactful consumptions decreased as the degree of centralization increased; on the other hand, the decentralized system was less penalized in LS, as small WWTP was less stressed and energy consuming in this period. Sensitivity analysis confirmed the results obtained. Site-specific conditions can lead to conflicting circumstances, as key parameters may have different behaviors depending on seasonal variations, and the degree of centralization in tourist areas should be addressed by distinguishing separate periods, based on changes in tourist flows and pollution loads.

Full-scale application and performance of a new multi-self-reflow decentralized Wastewater treatment device: Impact of hydraulic and pollutant loads

Decentralized treatment of wastewater in rural areas usually has several challenges, which include large fluctuations in pollutant concentration and water quantity, complicated operation and maintenance of conventional biochemical treatment equipment, resulting in poor stability and a low compliance rate of the wastewater treatment process. In order to solve the above problems, a new integration reactor is designed, which uses gravity and aeration tail gas self-reflux technology to realize the reflux of sludge and the nitrification liquid, respectively. The feasibility and operation characteristics of its application for decentralized wastewater treatment in rural areas are explored. The results demonstrated that, under constant influent, the device showed strong tolerance to the shock of pollutant load. The chemical oxygen demand, NH₄⁺-N, total nitrogen and total phosphorus fluctuated in the ranges of 95-715 mg/L, 7.6-38.5 mg/L, 9.32-40.3 mg/L and 0.84-4.9 mg/L, respectively. The corresponding effluent compliance rates were 82.1%, 92.8%, 96.4% and 96.3%, respectively. When the wastewater discharge was non-constant and the maximum single-day Q_max/Q_min reached 5, all indicators of the effluent met the relevant discharge standard. The integrated device also demonstrated high phosphorus enrichment levels in its anaerobic zone; the concentration of phosphorus reached a maximum of 26.9 mg/L, which created a good environment for phosphorus removal. The microbial community analysis showed that sludge digestion, denitrification, and phosphorus-accumulating bacteria all played an important role in pollutant treatment.

A Simple and Efficient Solar Interfacial Evaporation Device Based on Carbonized Cattail and Agarose Hydrogel for Water Evaporation and Purification

One of the main trends in the development of solar interface evaporation technology is the simple, efficient, and environmentally friendly bio-based evaporation device. However, the development of bio-based evaporators with high water evaporation rates and good pollution removal capability is a significant challenge. Here, we present a carbonized cattail-agarose hydrogel (CCAH) membrane with numerous microchannels resembling bamboo knots, exceptional hydrophilicity, outstanding light absorption capability, and potent adsorption. Under one solar irradiation, its evaporation rate and efficiency reached 1.93 kg m^-2 h^-1 and 95.8%, respectively. More importantly, the CCAH membrane produces steam water that is almost totally free of salts (Na⁺, K⁺, Mg²⁺, and Ca²⁺), heavy metal ions (Pb²⁺, Cd²⁺, and Cr²⁺), and organic dyes (Rhodamine B, methylene blue, and methyl orange). The CCAH membrane is highly promising for the use of saltwater desalination and wastewater recovery to help people in impoverished areas with water scarcity problems.

Design and techno-economic analysis of a hybrid system for energy supply in a wastewater treatment plant: A decentralized energy strategy

The crescent urbanization generates large volumes of solid residues and wastewater, more and more geographically concentrated. This worldwide trend has also created new challenges regarding energy generation and consumption. Renewable energy sources can be strategic to keep up with the increasing energy demand, especially for under developing countries whose population is large. This study focuses on designing a hybrid system based on photovoltaic energy, biomass gasifier, and electricity grid to optimize the energy supply and the costs of a wastewater treatment plant (based on activated sludge system with extended aeration, high energy-demanding process). The optimal combination of energy technologies, with and without electric energy generation from biogas combustion derived from anaerobic digestion of sewage sludge, was assessed to define the better cost-effective arrangement. The cost of energy for an off-grid biomass gasifier standing alone is USD 0.0426/kWh. However, in a grid-connected system including photovoltaic energy and biomass gasifier, the cost was reduced to USD 0.0298/kWh with an energy surplus available to supply the whole facility requirement and enough to supply 788,000 residential power consumers. The hybrid combination with biogas combustion can be an alternative for medium-sized wastewater treatment plants, promoting economic and environmental benefits. Moreover, the results of this case study could be applied to other similar facilities towards cleaner and optimized sewage sludge recycling.

The Private Sector as a Partner for SDG 6-Related Issues in Megacities: Opportunities and Challenges in Rio de Janeiro, Brazil

This article reviews recent studies that address water sustainable management opportunities and challenges in megacities around the world, with an emphasis on the case of Rio de Janeiro Metropolitan Region, one of the two megacities in Brazil. With reference to recent debates on water, megacities, and the climate crisis, as well as UN Water and Global Report Initiative documents, we focused on the implementation of the 2030 Agenda Sustainable Development Goal 6: Clean Water and Sanitation for All. The new Brazilian sanitation legal framework regulates public–private partnerships. In this context, the manuscript discusses the main question concerning water, sanitation, and hygiene that arises in the Brazilian case study: is universality possible in profit-oriented models? Through the current technical and academic literature consulted, the paper compares initiatives involving multiple stakeholder governance models that depend on private resources to implement universal access to drinking water, sanitation, and water-related extreme event controls, pointing out alternatives that can help to achieve the targets of SDG. Validation by key informants supports the synthesis of the reviewed documents, and the findings illustrate that concerted public efforts together with market mechanisms can help to overcome challenges and surpass the profit-oriented logics of private companies to achieve access to healthy and safe water, adequate sanitation, and improved hygiene, especially for vulnerable populations. This finding has transferability to other megacities in emerging countries that are facing public–private partnership debates on the provision of clean water and sanitation for all.