Wastewater - Turning Problem to Solution

Table 3.1: Different processes for black wastewater treatment and associated products.

Recovered resource

Process

Liquid

Solid

Gas

Energy

Aerobic composting Anaerobic co-digestion Membrane distillation Membrane bioreactors Upflow anaerobic sludge blankets Electrochemical Microwave Constructed wetlands Microbial fuel cell Microbial electrolysis cell

Compost Biogas residue

Digestate Reusable water Water to discharge Digestate Reusable water Pathogen-free water Irrigation water

Biogas

Biogas

Biogas residue

Biogas

Biogas

Plant biomass

Electricity Hydrogen

Hydrogen

Struvite Microalgae biomass

Struvite precipitation Microalgae treatment

Note: Adapted from Zhang et al. 2023.

Centralized systems for resource recovery

The projected expansion requirements present a significant challenge in terms of financial, institutional and human capacity. In 2015, the United States Environmental Protection Agency estimated that US$ 600 billion needs to be spent on national water infrastructure improvements over the next 20 years, in large part due to existing infrastructure reaching its end of life (National Science Foundation et al. 2015). This however has been identified as an opportunity to ensure investment is made in infrastructure with economic, social and environmental benefits. The Billund Biorefinery in Denmark and the Hamburg Wasser wastewater treatment plant in Germany are examples of conventional wastewater treatment plants that have been converted for resource recovery. While expenditure on infrastructure improvements can be very high, a World Bank report (Rodriguez et al. 2020) gives several examples where a relatively small investment has provided significant economic and environmental gains. For example, in a Chilean town, a US$ 2.7 million retrofit of a wastewater plant enabled the production of biogas, which generated an annual net profit of US$ 1 million. Decentralized systems for resource recovery and reuse There are many cases where centralized systems are not appropriate, for example in rural areas as well as in low and middle income countries where there are no

Centralized wastewater systems are dedicated networks connecting homes, business, services and some industries that collect wastewater and treat it off-site. Such systems are suitable for treating large volumes of wastewater and are typically developed in highly populated urban areas to take advantage of the economies of scale (Pasciucco, Pecorini and Iannelli 2020). While conventional wastewater treatment has been designed to collect wastewater and treat it centrally and discharge (Thompson Rivers University 2020), the focus here is on the application of treatment for resource recovery and reuse. Pasciucco, Pecorini and Iannelli (2020) suggest that centralized wastewater systems are suited to producing reclaimed resources that require higher-quality standards, such as potable water. Between 2015 and 2020 China invested US$ 81.6 billion in municipal wastewater systems to accelerate capacity in wastewater treatment. In the United Kingdom, a 10-year, £5 billion project started in 2015 to update the 150-year-old London sewer system focusing on improving collection capacity to reduce leakage of untreated wastewater. In India, Delhi, there are ambitious plans under way to expand wastewater treatment alongside work to connect unsewered areas in the city by 2031.

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