No (waste-)drop in the ocean
Already in 2014, MIT researchers predicted that by 2050 more than half of the world’s population will live in water-stressed areas.1 In 2020, the World Bank released a report highlighting that 80 percent of the world's wastewater is discharged into the environment without adequate treatment.2 In 2022, Scientific American reported that many US cities are failing to provide clean water to their residents.3
On the back of these manifold issues, water storage, conveyance, and treatment have re-gained attention over the past years. BCC research estimates that the $303Bn global market for water and wastewater treatment technologies will grow at a CAGR of 11.2% for 2028.4
Wastewater treatment works (WWTW), more commonly referred to as sewage works, are facilities designed to treat wastewater from domestic, commercial, and industrial sources before it is released back into the environment. In doing so, they play a crucial role in protecting water quality, public health, and ecosystems.
Flowing slowly
Still, conventional wastewater treatment methods have more or less not changed. The treatment process typically involves four stages and integrates physical, chemical, biological, and combined technologies. First, preliminary treatment is made to remove large objects such as sticks, rags, and debris through screening and grit removal. Then primary treatment is conducted to settle out solid materials in the wastewater through sedimentation, followed by secondary treatment to remove dissolved and suspended organic matter that remains after primary treatment. This is usually done through biological processes, where microorganisms break down organic pollutants into carbon dioxide, water, and biomass. Afterwards, tertiary treatment is used to further polish the effluent and remove any remaining contaminants. This may involve processes such as filtration or disinfection (e.g., using chlorine or ultraviolet light). For microorganisms or leftover sludge, additional processing is sometimes needed.
Figure 1: The technology types that can be used at the different phases of the wastewater treatment process, Water Research Commission 2016.5
Conventional wastewater treatment methods are currently beset by several issues, including increased chemical usage, sludge disposal, and energy and space needs.6 Especially the secondary and tertiary treatment phase show bottlenecks as the biological processes are sensitive to changes in influent quality, temperature, and other factors, and implementing tertiary treatment processes can be complex and costly. Further, to manage ever-changing, non-biodegradable pollution such as perfluoroalkyl and polyfluoroalkyl substances (PFASs) - often called “forever chemicals” because of their persistence in the environment -, advanced methods are essential.
New mix to treat the used
Novel solutions are being developed and commercialized mainly targeted at the secondary and tertiary treatment phase, including approaches such as membrane bioreactors (MBRs), advanced oxidation processes (AOPs) and constructed wetlands as a nature-based solution. Further, enhanced resource recovery of energy and nutrients (e.g., nitrogen; phosphorus) from sludge is explored via approaches such as anaerobic digestion (AD) for biogas production, microbial fuel cell (MFC) technology for electricity production, and struvite precipitation for phosphorus recovery.
Deepsense is the expert network for science and technology.
We have water tech experts from leading institutions. Make better investment and business decisions with technical assessment support in climate tech, healthcare and software.
Diving deeper into the widely explored approaches, membrane bioreactors (MBRs) integrate membrane filtration with biological treatment processes to achieve high-quality effluent in a smaller footprint compared to conventional activated sludge wastewater treatment processes.
Figure 2: Schematic of conventional activated sludge process (top) and external (side stream) membrane bioreactor (bottom).
These systems offer improved solids retention, reduced sludge production, enhanced removal of contaminants, smaller space requirements, and ease of automation which makes them suitable for decentralized applications. However, challenges such as membrane fouling, energy consumption, and high upfront capital and operating costs need to be addressed.
Advanced oxidation processes (AOPs) use chemical reagents or free radicals to break down persistent organic contaminants in wastewater. Techniques such as ozonation, photocatalysis, and electrochemical oxidation are being researched for their effectiveness in treating recalcitrant pollutants and enhancing the removal of emerging contaminants.
Figure 3: Various Advanced oxidation processes (AOPs) and the reactive oxygen species (ROS) involved, retrieved from Bayaroth et al. (2022).
These processes are especially effective for managing chemical compounds that are difficult to treat with conventional methods. However, challenges such as high operating costs due to energy consumption and the use of expensive chemicals or materials, complexity of design and operation, formation of harmful by-products, and scale-up challenges persist currently.7
Sludge on the road?
Based on the recognized urgency, headwinds are on their way. In the US, the Biden-Harris administration recently announced nearly $6 billion for clean drinking water and wastewater infrastructure, bringing the total amount of clean water funding announced from the Bipartisan Infrastructure Law to $22 billion.8 Earlier in 2024, the European Union reached a provisional agreement to update the Urban Wastewater Treatment Directive from 1991, extending the rules to smaller towns, providing targets to cut the sector’s energy use and greenhouse gas emissions, and introducing extended producer responsibility.9
On the private capital side, water treatment and conservation startups, from seed to growth stage, raised $787 million in 2023, more than double the $343 million total funding raised in 2019, with companies such as Gradiant ($225 million Series D) and Allonnia ($30 million Series A) leading the stage.10 In early 2023, Xylem completed a $7.5bn acquisition of US-based water treatment company Evoqua.11
However, dealing with reactive water utilities and governments, and their long sales and infrequent replacement cycles alongside the high upfront capital expenditures, constitutes a persistent challenge for startups. Additionally, in most countries, a WWTW must be authorized across several institutions, leading to lengthy and complex approval processes.12
In line with strict approval processes and regulations, wastewater treatment works are often regarded as a technology type that will be selected as suitable for a particular development rather than as the best technology available, emphasizing that water is hyperlocal with region-by-region variation on water treatment issues and demands. Mostly, analytical parameters such as chemical oxygen demand (COD), biochemical oxygen demand (BOD), and total dissolved solids (TDS) are considered to select treatment technologies and treatment sequences.
Advanced wastewater treatment works could be a much-needed technology leap to address the significant water quality issues we are already facing today. However, industry adoption timelines, government regulations, funding environments, and approval processes are expected to play a key role in widespread industry implementation.