Conventional Sewer Systems Research Articles

Sustainability of Simplified Sewer systems

The universal access to safely managed sanitation remains one of the challenges to achieving the UN SDG target 6.2 in unplanned urban settlements including the Vingunguti area in Dar es Salaam City which is high-density populated. In an attempt to address this challenge, a simplified sewer system was piloted as an option for achieving safely managed sanitation in this particular area. The objective of this study was to assess the sustainability of the piloted simplified sewer system for its potentiality to up-scale and replication in areas with similar sanitation challenges in the country. Methodology involved collection of data on performance of different components of the sanitation service chain in the study area; and determination of sustainability index using a set of indicators. Data collection techniques included literature reviews, household questionnaires, expert surveys, and physical observations. Data analysis utilized the analytical hierarchy process (AHP) to assign weights to sustainability indicators, while the urban sanitation status index (USSI) was used to evaluate the status of the sanitation service chain, and the sanitation sustainability index (SSI) determined the level of sustainability of the sewerage system. Results showed that the emptying and transport component of the sanitation service chain performed better, with a USSI value of 0.905. However, the system performed poorly on the complementary services (stormwater, greywater, and solid waste management), which had a USSI value of 0.552, probably due to fewer investments in these services. On the other hand, the sustainability of the simplified sewer system was found to be high, with an SSI score of 76.5%. Hence, the study concludes that, simplified sewer system is an appropriate option for addressing safely managed sanitation in unplanned urban settlements where connection to conventional sewer systems is challenging. Thus, the system in Vingunguti area can be up-scaled and replicated elsewhere with similar conditions in the country.

A tale of two communities: Comparing user perceptions of condominial and conventional sewer systems in Salvador, Brazil

Problems of access and quality of sanitary sewage disproportionately impact the health of populations in urban peripheries of low-and middle-income countries. The condominial sewer system is a practical, low-cost, effective, and simplified engineering approach compared to conventional sewer systems. In support of meeting the sanitation needs in highly populated urban settings, there is a need to understand the residents’ perceptions regarding the advantages and disadvantages of this sanitation model compared to conventional sewer systems. We conducted a cross-sectional study from September to December 2021 in two urban communities of Salvador, Bahia, Brazil, where condominial and conventional sewer systems had been implemented in the last five years. Of the 203 residents we interviewed, 50.7% lived in a site served by a condominial sewer system. Residents in the condominial sewer site reported not connecting to public sewage network (23.7% vs. 11.2%; p = 0.022) more often than in the conventional site. They reported more collective action to solve urban sanitation problems (69.9% vs. 54.0%; p = 0.020), such as manhole cleaning and unclogging efforts to fix plumbing. Despite these challenges, these residents expressed that the current service quality is better than it was in the previous two years. Our results suggest that even within urban periphery communities of a large Brazilian city, disparities exist in access to and quality of sanitation services that may be linked to sewage system implementation. Implementing simplified sewer systems is important to meet the growing sanitation demands of urban areas. However, these systems should also play a role in reducing sanitation disparities and the adoption of participatory approaches to meet the needs of populations in the most disadvantaged conditions. Despite challenging conditions, there is the potential for community engagement and active participation in sanitation-related matters, which could enhance the implementation and long-term sustainability of these systems.

English

In areas where conventional sewer systems are not possible, innovative and low-cost methods are needed to get rid of pathogens in human urine. Treatment through acidification is a reliable method. In this study, the effect of fresh cabbage waste, potato peel, and teff flour water as substrate for lactic acid treatment of source-separated urine was investigated. Laboratory scale batch experiments were conducted to compare the substrates for pH 4 and high distribution of lactic acid bacteria (LAB), important for urine hygienization and urea stabilization. It was found that with the addition of 10% molasses as a sugar supplement, fermentation of fresh cabbage waste could establish the desired effect for lactic acid treatment of source-separated urine. The final pH in the urine mixed with lactic acid in the ratio of 1:1 and 1:2 (lactic acid: urine) was 4.12 and 4.26, respectively. While the final pH in the 1:4 and control reactors was 8.3 and 9.2, respectively. Escherichia coli count was below the detection limit in both 1:1 and 1:2 reactors after 5 days, whereas the number of E. coli in the samples collected from 1:4 and control reactors showed only slight reduction until the final day of the treatment process. Urea decomposition improved in 1:1 and 1:2 reactors, while it kept increasing in 1:4 and control reactors. The results revealed that food waste produced lactic acid enhances pathogen inactivation, urea stabilization and reduce odors in human urine. Key words: Lactic acid, odor control, pathogen inactivation, urea stabilization

Multi-Criteria Framework for Selection of City-Wide Sanitation Solutions in Coastal Towns in Northern Angola

In this paper, an expedited multi-criteria decision analysis framework, capable of tackling several dimensions for the choice of sanitation services, at an early planning stage is presented. The approach combines geographic information systems aided analysis for onsite solutions, with a multi-criteria decision analysis tool capable of suggesting and ranking several viable offsite treatment alternatives, according to the desired criteria. The framework was applied to four coastal cities in Northern Angola, one of the sub-Saharan countries of the west coast of Africa, thus obtaining an indication for city-wide solutions, as an aid to achieve the goal of ensuring full sanitation coverage in those four locations. It included possible onsite collection and storage interfaces, namely Ventilated Improved Pit latrines, fossa alterna, septic tanks or conventional sewer systems. The study also contributed to an informed decision regarding optimal offsite treatment facility type, namely based on dedicated or combined wastewater and faecal sludge treatment (co-treatment), as well as different options for locations and sanitation technologies. Alternatives were compared and ranked according to ten main criteria concerning social, economic, technological and environmental aspects. This work helped demonstrate the usefulness of decision-aiding tools in the multi-stakeholder and complex context of sanitation in a developing country.

Conventional Sewer Systems Are Too Time-Consuming, Costly and Inflexible to Meet the Challenges of the 21st Century

There is an urgent need for innovation in the sanitation sector because the conventional model (toilet-to-sewer-to-treatment) is too time-consuming and costly, and alternatives are lacking. We estimate the challenge ahead by developing scenarios for 60 of the fastest-growing urban conglomerates in the World. We find that the majority would need to build out their sewer systems at a rate that is ten to 50 times higher than the highest rate for any project in the World Bank’s database, which is unrealistic. We also carry out a case study of Lagos, Nigeria, which suggests that, in any given year, 14–37% of Lagos State’s budget would need to be invested to provide sanitation to the presently underserviced population while keeping up with population growth, which also is unrealistic. Our study provides clear evidence that the conventional model for sanitation is unworkable for rapidly growing urban areas. We conclude there is an urgent need to encourage and fund projects that promote innovations that can tackle the three core challenges: can be built sufficiently quickly, are flexible, and affordable. This is not likely to happen unless the future generation is systematically trained and educated to creatively support innovation in sustainable sanitation.

Field-Scale Co-fermentation of Solid Waste From Urine-Diverting Dry Toilets (UDDT-SW) and Banana Waste to Produce Undissociated Carboxylic Acids to Inactivate Ascaris Eggs

Innovative, low-cost methods for inactivating pathogens in human fecal material (HFM) are needed, particularly in expanding urban areas where conventional sewer systems and centralized wastewater treatment plants are not feasible. To address this challenge, we have developed a bioprocess that utilizes open cultures of anaerobic bacteria (i.e., microbiomes) to produce carboxylic acids using HFM as substrate. When the pH is sufficiently low, the carboxylic acids exist in the undissociated form and inactivate pathogens. Here, we used real sanitation waste collected from container-based, urine-diverting dry toilets (UDDT-SW) in Nairobi, Kenya to conduct lab-scale and field-scale trials. Through these trials, we investigated operating conditions required to use carboxylic acid fermentation in sanitation waste treatment processes. We tested three different inoculum treatments and determined that the microbiome in UDDT-SW is well suited to produce carboxylic acids without the need for an external inoculum. We also tested co-fermentation of UDDT-SW with carbohydrate-rich food waste as a means of reducing the pH. We found that when food waste was incorporated in a way that maintained the pH between 4.8 and 5.2, then the food waste was quickly converted to carboxylic acids, and the low pH created high concentrations of undissociated carboxylic acids. The resulting concentrations of undissociated carboxylic acids resulted in Ascaris inactivation within 15 days. However, we found that a temperature ≥30°C is required for carboxylic acid production to occur.

Transformative Approaches for Sustainable Water Management in the Urban Century

Sustainable Urban Water Management (SUWM) approaches highlighted in this special issue have the potential to contribute to the transformation of urban water systems. The aim of the transformation is to accommodate population and economic growth and at the same time enable a system which is environmentally sustainable and resilient to future challenges such as climate change. These approaches have increasingly entered mainstream dialogue over the last ten years as knowledge on the approaches has developed, and there is an acceptance that there needs to be a change to how urban water systems are designed and operated. However, there are still a range of aspects of these approaches that are maturing and require further research to realize the objectives of SUWM. The issue explored supply-side interventions, such as rainwater harvesting and stormwater harvesting, demand-side interventions, and water storage solutions that have the potential to enable a range of recycling technologies. The issue also highlighted a novel method for better managing the integrity of a conventional sewer system. Furthermore, there are articles that explore methods for integrated assessments, integrated decision making and an exploration of what factors may promote community adoption of technology.

Study of the spatiotemporal correlation between sediment-related blockage events in the sewer system in Bogotá (Colombia).

The planning and scheduling of maintenance operations of large conventional sewer systems generate a complex decision-making environment due to the difficulty in the collection and analysis of the spatiotemporal information about the operational and structural condition of their components (e.g. pipes, gully pots and manholes). As such, water utilities generally carry out these operations following a corrective approach. This paper studies the impact of the spatiotemporal correlation between these failure events using Log-Gaussian Cox Process (LGCP) models. In addition, the association of failure events to physical and environmental covariates was assessed. The proposed methods were applied to analyze sediment-related blockages in the sewer system of an operative zone in Bogotá (Colombia). The results of this research allowed the identification of significant covariates that were further used to model spatiotemporal clusters with high sediment-related failure risk in sewer systems. The LGCP model proved to be more accurate in comparison to those models that build upon a fundamental assumption that a failure is equally likely to occur at any time regardless of the state of the system and the system's history of failures (i.e. a homogeneous Poisson process model).

Design of water reuse storage facilities in Sustainable Urban Drainage Systems from a volumetric water balance perspective

This paper presents a methodology for designing water reuse storage facilities as part of Sustainable Urban Drainage Systems (SUDS) in urban catchments. The method analyzes the whole water balance of the catchment. The contributions to the balance are irrigation and precipitation; the outlets are evapotranspiration, seepage and discharge to the conventional sewage system. The internal system variations are the volume of water to be locally reutilized and the soil water content variation. A cost function that includes the costs of irrigation, discharge to the conventional sewer system and reuse of water locally is proposed to estimate the optimum volume of water to be reused. This approach for SUDS design goes beyond traditional events-based perspectives oriented to damage prevention. This method conceives stormwater as a resource and seeks its optimal use through the design of SUDS. Several types of urban catchments were studied, and the results show that the proposed methodology can be applied either for simulating SUDS behavior in urban catchments or for estimating the optimum volume of water to be locally reused.

The effect of successive low-impact development rainwater systems on peak flow reduction in residential areas of Shizhuang, China

Against a background of frequent urban flooding and the construction of new so-called “sponge cities” in China, this paper proposes a scheme for Successive Low-Impact Development Rainwater Systems (SLIDRS) in residential areas. The Shizhuang community in China is used as a case study site for a simulated SLIDRS infrastructure based on a stormwater management model (SWMM). Peak flows, peak delay times, infiltration, and water conservation were simulated and analyzed under three different scenarios: pre-development conditions, residential development with the use of a conventional sewer system, and residential development with the use of SLIDRS. The differing effects of development under the following four rainfall conditions were evaluated: 1-year, 2-year, 5-year, and 10-year return periods. Results showed that SLIDRS can decrease peak flows and total runoff volume effectively. Moreover, peak flow times were delayed compared with those resulting from the conventional technology. Therefore, SLIDRS may represent a viable strategy towards solving local urban flooding problems.

The cost of urban sanitation solutions: a literature review

Abstract The main objective of this paper is to review the literature on and compare the lifecycle costs of full sanitation chain systems in developing cities of Africa and Asia. Overall, financial cost reporting methodologies have been inconsistent and many studies only focus on capital costs or do not report cost data on desludging, transport and treatment. In addition, a comparative analysis of raw cost data across cities and countries would be of low utility, owing to the numerous determinants of costs (e.g. density, level of service) and their high sensitivity to local contexts. To circumvent this, this paper compares the cost ratios between different sanitation systems analysed in a same study. It concludes that conventional sewer systems are in most cases the most expensive sanitation options, followed, in order of cost, by sanitation systems comprising septic tanks, ventilated improved pit latrines (VIP), urine diversion dry toilets and pour-flush pit latrines. The cost of simplified sewer systems is found to be lower than both conventional sewer systems and septic tank-based systems, but lack of data prevented further comparisons with other types of sanitation solutions.

Green infrastructure for flood-risk management in Dar es Salaam and Copenhagen: exploring the potential for transitions towards sustainable urban water management

The risk of flooding in urban areas could be better approached by complementing conventional sewer systems with sustainable urban drainage systems (SUDS) for storm-water management. This may be the case for developing world cities like Dar es Salaam with incomplete sewer services, as well as cities like Copenhagen with fully developed sewer systems. This paper explores some theories relevant to understanding how the implementation of SUDS may be one option for supporting a transition towards sustainable urban water management (SUWM). Using interviews, document analysis and observation, a comparison of the opportunities and barriers to the implementation of SUDS in Dar es Salaam and Copenhagen is presented. The results indicate that a bottom-up approach in Dar es Salaam is important, with the community level taking the lead, while in Copenhagen the top-down approach currently employed is promising. The ability of the institutional frameworks of both cities to support the implementation of SUDS is also discussed.

Model Evaluation of Potential Impacts of On‐Site Wastewater Systems on Phosphorus in Turkey Creek Watershed

Nutrient loading to surface water systems has traditionally been associated with agricultural sources. Sources such as on-site wastewater systems (OWS) may be of concern especially in rural, nonagricultural watersheds. The impact of various point and nonpoint sources including OWS in Turkey Creek Watershed was evaluated using the Watershed Analysis Risk Management Framework, which was calibrated using 10 yr of observed stream flow and total P concentrations. Doubling the population in the watershed or OWS septic tank effluent P concentration increased mean stream total P concentration by a factor of 1.05. Converting all the OWS to a conventional sewer system with a removal efficiency of 93% at the wastewater treatment plant increased the mean total P concentration at the watershed outlet by a factor of 1.26. Reducing the soil adsorption capacity by 50% increased the mean stream total P concentration by a factor of 3.2. Doubling the initial P concentration increased the mean stream total P concentration by a factor of 1.96. Stream flow and sediment transport also substantially affected stream P concentration. The results suggest that OWS contribution to stream P in this watershed is minimal compared with other factors within the simulated time frame of 10 yr.

On-site stormwater management as an alternative to conventional sewer systems: a new concept spreading in Germany

In Germany a new stormwater management system is spreading across the country – the so called “Mulden-Rigolen-System” (MR-System), which may be translated as the ‘Swale-Infiltration Trench System’. The overall applicable system consists of on-site located swale-trench-elements which are connected by throttled sewers to a decentralized stormwater management system. The elements are designed and dimensioned in order to allow the highest possible infiltration of stormwater runoff. This is obtained by a short-term storage in the grassed swale and a long-term storage provided by the trench. The latter is formed by highly porous material such as gravel or lava granules, wrapped in geotextile. By infiltration through the active soil layer along the swale bottom, stormwater quality is enhanced up to the quality of drinking water. The MR-System has been applied in many German projects, not only in new developments, but also as a retrofit measure in the existing urban developments.

On-site stormwater management as an alternative to conventional sewer systems: A new concept spreading in Germany

In Germany a new stormwater management system is spreading across the country – the so called “Mulden-Rigolen-System” (MR-System), which may be translated as the ‘Swale-Infiltration Trench System’. The overall applicable system consists of on-site located swale-trench-elements which are connected by throttled sewers to a decentralized stormwater management system. The elements are designed and dimensioned in order to allow the highest possible infiltration of stormwater runoff. This is obtained by a short-term storage in the grassed swale and a long-term storage provided by the trench. The latter is formed by highly porous material such as gravel or lava granules, wrapped in geotextile. By infiltration through the active soil layer along the swale bottom, stormwater quality is enhanced up to the quality of drinking water. The MR-System has been applied in many German projects, not only in new developments, but also as a retrofit measure in the existing urban developments.