High Carriage of Plasmid-Mediated Quinolone Resistance (PMQR) Genes by Cefotaxime-Resistant Escherichia Coli Recovered from Surface-Leaking Sanitary Sewers

There is a rapid rise in the incident of quinolone resistant bacteria in Nigeria. Most studies in Nigeria have focused on isolates from the clinical settings, with few focusing on isolates of environmental origin. This study aimed to investigate the antibiogram and carriage of plasmid-mediated quinolone resistance (PMQR) genes by quinolone-resistant isolates obtained from a pool of cefotaxime-resistant Escherichia coli (E. coli) recovered from sewage leaking out of some broken sanitary sewers in a University community in Nigeria. Isolation of E. coli from the sewage samples was done on CHROMagar E. coli after enrichment of the samples was done in Brain Heart Infusion amended with 6µg/mL of cefotaxime. Identification of presumptive E. coli was done using molecular methods (detection of uidA gene), while susceptibility to antibiotics was carried out using disc-diffusion method. Detection of PMQR genes (qnrA, qnrB, qnrS, aac(6')-lb-cr, qepA and oqxAB) was done using primer-specific PCR. A total of 32 non-repetitive cefotaxime-resistant E. coli were obtained from the sewage, with 21 being quinolone-resistant. The quinolone-resistant isolates showed varying level of resistance to the tested antibiotics, with imipenem being the only exception with 0% resistance. The PMQR genes: aac(6')-lb-cr, qnrA, qnrB, qnrS and qepA and oqxAB were detected in 90.5%, 61.9%, 47.6%, 38.1%, 4.8% and 0% respectively of the isolates. The findings of this study showed a high level of resistance to antibiotics and carriage of PMQR genes by quinolone-resistant E. coli obtained from the leaking sanitary sewers, suggesting a potential environmental and public health concern.

Determination of Internal Elevation Fluctuation from CCTV Footage of Sanitary Sewers Using Deep Learning

The slope of sewer pipes is a major factor for transporting sewage at designed flow rates. However, the gradient inside the sewer pipe changes locally for various reasons after construction. This causes flow disturbances requiring investigation and appropriate maintenance. This study extracted the internal elevation fluctuation from closed-circuit television investigation footage, which is required for sanitary sewers. The principle that a change in water level in sewer pipes indirectly indicates a change in elevation was applied. The sewage area was detected using a convolutional neural network, a type of deep learning technique, and the water level was calculated using the geometric principles of circles and proportions. The training accuracy was 98%, and the water level accuracy compared to random sampling was 90.4%. Lateral connections, joints, and outliers were removed, and a smoothing method was applied to reduce data fluctuations. Because the target sewer pipes are 2.5 m concrete reinforced pipes, the joint elevation was determined every 2.5 m so that the internal slope of the sewer pipe would consist of 2.5 m linear slopes. The investigative method proposed in this study is effective with high economic feasibility and sufficient accuracy compared to the existing sensor-based methods of internal gradient investigation.

Performance analyses of existing sanitary sewers with the selection of household water-saving schemes

The widespread uptake of household water-saving systems (i.e. appliances, fittings, rainwater harvesting tanks, etc.) usually aims to reduce the gap between water demand and supply without considering the performances of downstream sanitary sewers (SSs). This paper presents an analysis approach that examines the lifespan interaction of water-saving schemes (WSSs) and operation of existing SSs. Examined are three probable ways of using (or not using) these water systems, including the conventional (baseline), full application and optimal selection of efficient WSSs. For optimality, a method that maximises the WSS potential efficiency (overall) and minimises the cost of WSSs including the associated savings across the entire existing SS subject to constraints at the end of the planning horizon has been formulated. The problem is solved using a non-dominated genetic algorithm to obtain optimal solutions. Decision variables include various water use (or saving) capacities of water-saving schemes at different inflow nodes (locations). The method was demonstrated on the subsystem of the Tsholofelo Extension SS. The results indicate impactful and revealing interactions between water use efficiency, instantaneous hydraulic performances and existing SS upgrade requirements due to different applications of WSSs. The impacts and revelations observed would inform decisions during lifespan operations and management of SSs.

Comparative Assessment of Environmental Impacts from Open-Cut Pipeline Replacement and Trenchless Cured-in-Place Pipe Renewal Method for Sanitary Sewers

An environmental impact assessment (EIA) involves the evaluation of information about pipe raw materials, processes, and product manufacturing to obtain the associated emissions and ecological impacts. Open-cut (OC) pipeline replacement involves digging a trench along the length of the proposed pipeline, placing the pipe in the trench on suitable bedding materials, and then embedding and backfilling. The trenchless cured-in-place pipe (CIPP) method involves a liquid thermoset resin saturated material that is inserted into the existing pipeline by hydrostatic or air inversion or by mechanically pulling-in and inflating. The liner material is cured-in-place using hot water or steam or light cured using ultraviolet light, resulting in the CIPP product. The objectives of this paper are: (1) to present a literature review on the progress acquired over the years in understanding the environmental impacts from the OC and CIPP methods, (2) to analyze and compare the environmental impacts for small diameter sanitary sewers (SDSS) using USEPA’s tool for the reduction and assessment of chemical and other environmental impacts (TRACI) methodology from the SimaPro software, and (3) to identify the factors that influence the environment for the OC and CIPP methods. Published papers were identified that reported the environmental impacts from the OC and CIPP methods over a period from 1989 through to 2020. An actual case study based on the City of Pasadena, California, river basin was used to carry out an environmental analysis for small diameter OC and CIPP methods. The literature review suggests that the material production phase consumes a large amount of energy and is a major contributor of environmental impacts. Higher environmental impacts from the OC method are a result of longer project durations and more equipment requirements compared to the CIPP. The assessment results show that, on average, CIPP renewal caused 68% less environmental impact, 75% less impact on human health, and 62% less resource depletion as compared to the OC replacement for SDSS. The liner, felt, and resin influenced the environment the most for CIPP as compared to the OC method, where the power consumption of construction equipment and the pipe material had the greatest environmental impacts. It can be concluded that the comparison of the environmental impacts from pipeline renewal and replacement is an important element when considering a sustainable underground infrastructure development. The pipe material and outside diameter should be considered during the installation phase by OC and CIPP methods to allow a detailed evaluation and comparison of their sustainability impacts. This study can be further developed for analyzing the environmental impacts and associated costs of the OC and CIPP methods for sanitary sewers with different project and site conditions.