Rethinking urban water systems – revisiting concepts in urban wastewater collection and treatment to ensure infrastructure sustainability

Abstract

Technology and economic development has led to the growth of megacities and urban centres with populations in the millions. Such population expansion and densification increases the strain on wastewater collection and treatment infrastructure, which has been largely based on an end-of-line centralised model. However, in megacities new challenges arise, because provision of suitable sanitation is expensive and it requires infrastructure expansion through construction of extensive sewer networks and larger capacity wastewater treatment plants, which consume more energy. Alternative disposal techniques for solid and liquid waste generated during the treatment process are required, because disposal solutions are decreasing as landfill costs rise and environmental standards are tightened, the latter reducing opportunities for land reuse. Additionally, mass wastewater discharge can have a detrimental impact on the ecology of water bodies and on the health of downstream populations, and requires suitable treatment before disposal. These challenges have the potential to offset the savings that the economies of scale offered by the traditional wastewater collection and treatment systems can impart. The need for affordable and effective wastewater systems in megacities requires the re-evaluation of traditional systems and the re-engineering of water and wastewater transport and resource concepts. Alternative concepts in wastewater collection and treatment, such as decentralised treatment, allied with innovative solutions using current and new technology could play a role in providing affordable and sustainable solutions to deal with the wastewater issue. This paper investigates the scope that integrated wastewater treatment and localised water reuse (in-line treatment, sewer mining), resource recovery (biogas, biosolids), operational changes (timed discharge of sewers, vacuum sewers) and biotreatment (e.g. vermiculture, faecal coliform removal) can play to guarantee the longevity of wastewater infrastructure in megacities. These alternatives offer increased treatment efficiency, recovery of value-added products, and reduce infrastructure cost, whilst maintaining health standards and reducing environmental discharge.

An Overview of Hybrid Water Supply Systems in the Context of Urban Water Management: Challenges and Opportunities

“…These systems are emerging as an important complement to centralized water services [24,25]. This model of water infrastructure involves small to medium scale systems that utilize locally available sources of water for various indoor and outdoor uses, and facilitate use and reuse of generated wastewater and stormwater runoff locally [22].…”

“…Although these technologies are considered to offer benefits in terms of reducing overall potable water use and decreasing peak demand [33,34], they could have implications on the operational performance of the downstream infrastructures and treatment processes. For instance, as water saving through recycling is encouraged by adopting grey water reuse, dual piping systems and sewer mining, the volume of wastewater may decrease, but this could lead to an increasing in the concentration of key contaminants [24]. Increased concentration of contaminants in wastewater has been known to cause sewer problems, such as sewer blockage, odor and corrosion [35].…”

“…This reduction in wastewater volume increases the potential for septicity, odors, contaminant impacts and corrosion in the assets [24]. Similarly, greywater irrigation (domestic garden irrigation with household wastewater) can cause dry weather pollution (drainage effluent from greywater irrigation) of receiving waters [49].…”

Australian examples of residential Integrated Water Cycle Planning — Accepted current practice and a suggested alternative

“…Blackwater separation would thus represent another barrier within the multiple barrier framework to water reuse. Nutrients in the form of fertilisers can be recovered from blackwater, especially if allied with new technologies, such as membrane filtration, and smaller-scale decentralised systems [15].…”

Production of nutrients for non-edible plants using an anaerobic baffled horizontal wetland system

“…Even though centralized facilities for wastewater have served society well, re-evaluation and re-engineering of conventional system for wastewater collection and treatment are needed in order to develop cheaper and more sustainable approaches for wastewater treatment [5]. Establishment of decentralised systems for areas with low population densities and integration of innovative decentralised treatment into the centralised wastewater treatment system may possibly play a part in the provision of a relatively cheap and sustainable solution to manage the wastewater problem [6]. Decentralised wastewater treatment system is applied to treat comparatively smaller volumes of wastewater, originating from individual or groups of houses and businesses that are situated nearby to each other [7].…”