When does infrastructure hybridisation outperform centralised infrastructure paradigms? - Exploring economic and hydraulic impacts of decentralised urban wastewater system expansion

We explore the dynamics of centralised and decentralised wastewater infrastructure across various scenarios and introduce novel insights into their performance regarding structural vulnerability, hydraulic capacity, and costs. This study determines circumstances under which infrastructure hybridisation outperforms traditional centralised infrastructure paradigms. We combined system analysis to map out the modelling problem with the model-based exploration of the transition space using the novel TURN-Sewers model. System diagramming was used to identify the parameters or combinations of parameters that significantly influence the performance indicators being assessed. This allowed the creation of relevant simulation scenarios to identify circumstances where a decentralised sewer system could outperform a centralised one. TURN-Sewers was applied to model the infrastructure maintenance and generation of new infrastructure over 20 years for a municipality on the Swiss Plateau, considering a population growth rate of 0.03 a-1. Results show that decentralisation in expansion areas with higher densification can outperform the hydraulic performance and structural vulnerability of expanding centralised sanitary wastewater infrastructure. Decentralised systems can also offer economic advantages when capital expenditure costs for small-scale wastewater treatment plants are significantly reduced compared to current costs, particularly at higher discount rates, e.g. reaping effects of economies of scale. The findings of this study emphasise the potential of transition pathways towards decentralisation in urban water infrastructures and the value of models that allow the exploration of this transition space.

Tracing the origins of plastics in biosolids: The role of sewerage pipe materials and trade waste

Plastics are ubiquitous in virtually every environment on earth. While the specific sources of plastics entering wastewater are not well known, growing evidence suggests sewage sludge (biosolids) can be a sink for plastics. One potential source could be the sewerage pipe materials used to transport sewage between premises and wastewater treatment plants (WWTPs). To evaluate the significance of sewerage piping as a source of biosolids plastics concentrations, we compared the proportion of the total network (by length and surface area) of polyethylene (PE), polyvinylchloride (PVC), and polypropylene (PP) pipes from 10 WWTPs against their biosolids mass concentrations (mg plastic/g biosolid). Among the 10 catchments, the percentage of the network consisting of PP piping ranged from 0 to 1 %, with 0.8-21 % for PE, and 8-73 % for PVC. Biosolids plastics concentrations ranged from 0.09 to 8.62 mg/g (mg plastic/g biosolid) for PP and PE, respectively. For all three plastics, there was no significant Pearson correlation (r < 0.4) between the biosolids concentration (dry weight mg/g) and the proportion of the network material of the sewerage piping as plastic (either length or surface area). A comparison of trade waste entering a subset of 6 WWTP showed the highest biosolid principal components analysis (PCA) associations between loads of plastics (g/day) and automotive wash bays, general manufacturing, hospitals, laboratories, food manufacturing, laundry and dry cleaning, and cooling towers. A stepwise regression analysis indicated pipe length and surface area, as well as automotive wash bays and food manufacturing may be significant. While our data gave mixed results on the attribution of the sources of plastics entering WWTPs, it suggests that sewerage infrastructure and trade waste may play some role. Future studies should investigate the leachability of sewerage infrastructure and contributions from specific trade waste categories to determine their significance in plastics entering WWTPs.

Implementing wastewater monitoring on American Indian reservations to assess community health indicators

Healthcare access and health-related information for American Indian/Alaska Native (AIAN) communities is often limited. A potential solution to acquire additional population level health data is through wastewater-derived measurements, a method termed wastewater-based epidemiology (WBE), however, due to often remote locations with rudimentary wastewater infrastructure, the feasibility of implementing WBE on an AIAN reservation is unclear. In this study, we i) performed a preliminary assessment of percent connectivity of the top 10 most populous tribal reservations using available wastewater treatment facility information from the Environmental Protection Agency Enforcement and Compliance History Online database and satellite imagery, and ii) performed a sampling campaign on a select tribal reservation to measure common WBE indicators of health and behavior. Results indicate that, on average, approximately 81 ± 23% of tribal residents are connected to some form of aggregated wastewater collection system. On the sampled reservation, 6 communities comprising 7500 people were sampled across 160 km of reservation land using active samplers successfully deployed within the sewer network upstream of terminal lagoon systems. Results showed detectable levels of 7 opioids, 1 opioid maintenance medication, 5 stimulants, 1 hallucinogen, and chemical indicators of alcohol, nicotine, caffeine, and an over-the-counter cough suppressant. These results illustrated the feasibility in implementing WBE in rural and remote communities where information on community health may be lacking.

Opportunities and limits of wastewater-based epidemiology for tracking global health and attainment of UN sustainable development goals

Wastewater-based epidemiology (WBE) emerged as a powerful, actionable health management tool during the COVID-19 pandemic. Hypothesizing future uses, we explored its potential for real-time, tracking of progress in attaining United Nations Sustainable Development Goals (SDGs) globally as a non-expensive method using existing infrastructure. We inventoried (i) literature-documented sewerage infrastructure, (ii) demographics of populations served, and (iii) WBE markers informative of 9 SDGs. Among the 17 different sustainable development goals listed by the UN 2030 agenda, more than half of these may be monitored by using WBE monitoring at centralized treatment infrastructure as tabulated in this study. Driven mainly by COVID-19, WBE currently is practiced in at least 55 countries, reaching about 300 million people. Expansion of WBE to 109,000 + treatment plants inventoried in 129 countries would increase global coverage 9-fold to 34.7% or 2.7 billion, leaving out 5 billion people not served by centralized sewerage systems. Associations between population demographics and present-day infrastructure are explored, and geospatial regions particularly vulnerable to infectious disease outbreaks are identified. The results suggest that difference in the differential outcomes in well-being is an outcome of the sanitation infrastructure inequalities and lack of sanitation infrastructure creates doubly disadvantaged populations at risk of poor hygiene and cut off from the early-warning benefits of conventional WBE. This is the first study to explore the feasibility and potential barriers to the use of WBE for tracking the attainment of SDGs globally with at least 9 out of 17 SDGs.

A Simplified Sanitary Sewer System Generator for Exploratory Modelling at City-Scale

Future climatic, demographic, technological, urban and socio-economic challenges call for more flexible and sustainable wastewater infrastructure systems. Exploratory modelling can help to investigate the consequences of these developments on the infrastructure. In order to explore large numbers of adaptation strategies, we need to re-balance the degree of realism of sewer network and ability to reflect key performance characteristics against the model's parsimony and computational efficiency. We present a spatially explicit algorithm for creating sanitary sewer networks that realistically represent key characteristics of a real system. Basic topographic, demographic and urban characteristics are abstracted into a squared grid of 'Blocks' which are the foundation for the sewer network's topology delineation. We compare three different pipe dimensioning approaches and found a good balance between detail and computational efficiency. With a basic hydraulic performance assessment, we demonstrate that we attain a computationally efficient and high-fidelity wastewater sewer network with adequate hydraulic performance. A spatial resolution of 250 m Block size in combination with a sequential Pipe-by-Pipe (PBP) design algorithm provides a sound trade-off between computational time and fidelity of relevant structural and hydraulic properties for exploratory modelling. We can generate a simplified sewer network (both topology and hydraulic design) in 18 s using PBP, versus 36 min using a highly detailed model or 1 s using a highly abstract model. Moreover, this simplification can cut up to 1/10th to 1/50th the computational time for the hydraulic simulations depending on the routing method implemented. We anticipate our model to be a starting point for sophisticated exploratory modelling into possible infrastructure adaptation measures of topological and loading changes of sewer systems for long-term planning.

Comparison of wastewater-associated contaminants in the bed sediment of Hempstead Bay, New York, before and after Hurricane Sandy

Changes in bed sediment chemistry of Hempstead Bay (HB) have been evaluated in the wake of Hurricane Sandy, which resulted in the release of billions of liters of poorly-treated sewage into tributaries and channels throughout the bay. Surficial grab samples (top 5cm) collected before and (or) after Hurricane Sandy from sixteen sites in HB were analyzed for 74 wastewater tracers and steroid hormones, and total organic carbon. Data from pre- and post-storm comparisons of the most frequently detected wastewater tracers and ratios of steroid hormone and of polycyclic aromatic hydrocarbon concentrations indicate an increased sewage signal near outfalls and downstream of where raw sewage was discharged. Median concentration of wastewater tracers decreased after the storm at sites further from outfalls. Overall, changes in sediment quality probably resulted from a combination of additional sewage inputs, sediment redistribution, and stormwater runoff in the days to weeks following Hurricane Sandy.

To connect or not to connect? Modelling the optimal degree of centralisation for wastewater infrastructures

The strong reliance of most utility services on centralised network infrastructures is becoming increasingly challenged by new technological advances in decentralised alternatives. However, not enough effort has been made to develop planning tools designed to address the implications of these new opportunities and to determine the optimal degree of centralisation of these infrastructures. We introduce a planning tool for sustainable network infrastructure planning (SNIP), a two-step techno-economic heuristic modelling approach based on shortest path-finding and hierarchical-agglomerative clustering algorithms to determine the optimal degree of centralisation in the field of wastewater management. This SNIP model optimises the distribution of wastewater treatment plants and the sewer network outlay relative to several cost and sewer-design parameters. Moreover, it allows us to construct alternative optimal wastewater system designs taking into account topography, economies of scale as well as the full size range of wastewater treatment plants. We quantify and confirm that the optimal degree of centralisation decreases with increasing terrain complexity and settlement dispersion while showing that the effect of the latter exceeds that of topography. Case study results for a Swiss community indicate that the calculated optimal degree of centralisation is substantially lower than the current level.