The Severity of Global Water Scarcity and Water Pollution Management Issues

Figure 1. Wastewater treatment is highly interlinked with the SDG 6 targets

The global water crisis is deteriorating at an unprecedented rate. According to a UNESCO 2025 report, approximately half of the global population experiences severe water scarcity for at least part of the year. As of 2021, about 10% of the global population (roughly 720 million people) resided in countries facing high or extremely high water stress. More critically, by 2025, up to two-thirds of the global population could be living under water-scarce conditions, and by 2030, severe water scarcity could displace up to 700 million people.

Industrial wastewater pollution is a significant factor exacerbating the water crisis. Data from UN-Water in August 2024 indicates that, among 22 countries reporting on industrial wastewater treatment, only 38% of such wastewater received treatment, with a mere 27% being safely treated. This signifies that vast quantities of untreated industrial effluent are discharged directly into the environment, severely contaminating the limited freshwater resources.

Figure 2. Estimated volumes of water consumption, wastewater generated, wastewater treated, wastewater discharged and wastewater untreated from the 150 industrial and urban facilities, in million m3 per year.

In 2024, the global industrial wastewater treatment market reached a scale of USD 18.3 billion and is projected to grow to USD 34.11 billion by 2034. This rapid growth reflects the urgency of the demand for industrial wastewater treatment. The Asia-Pacific region accounted for 40.53% of the global market share in 2021, with China expected to become the most attractive market due to its accelerating industrialization .

The Prospects of Engineered Bacteria in Wastewater Treatment and the Challenge of Their Easy Loss

Given the severity of global water pollution, considerable attention has been focused on developing innovative remediation technologies. Among these, microbial remediation stands out as a revolutionary approach. This technique utilizes microorganisms(e.g., bacteria, fungi, algae, and yeast) to offer long-term, eco-friendly solutions. Specifically, engineered bacteria demonstrate significant potential for industrial wastewater treatment, with proven capabilities to degrade various contaminants, including synthetic dyes, heavy metals, petroleum hydrocarbons, polychlorinated biphenyls (PCBs), benzalkonium chloride, and agrochemicals (Liu et al., 2019).

However, a major obstacle limiting the large-scale application of engineered bacteria is their significant loss in practical scenarios. Wastewater treatment plants commonly face the "washout" phenomenon, where a high hydraulic load flushes microorganisms out of the treatment tanks at a rate exceeding their replication. This occurs most frequently during peak flow periods or rainfall events. A relatively short hydraulic retention time (HRT) can lead to the washout of active microbial biomass from the reactor before sufficient contact with organic pollutants is achieved, consequently resulting in failed degradation.

In summary, the intensifying global water scarcity, exacerbated industrial wastewater pollution, and the inherent limitation of microbial washout in conventional treatment systems collectively present multifaceted challenges for current wastewater management. There is a critical need to develop novel biological treatment platforms capable of immobilizing engineered bacteria stably and enriching heavy metal contaminants continuously and efficiently. Grounded in this context, our TasAnchor project aims to engineer biofilm proteins to enhance bacterial adhesion to solid substrates, thereby constructing a stable and highly efficient system for bacterial immobilization. This initiative is designed to provide a sustainable solution for industrial wastewater treatment.

Our Project — TasAnchor

Specific Application Scenario: Polystyrene-Based Biological Aerated Filters

The Biological Aerated Filter (BAF) is a widely used, novel biofilm-based process in biological oxidation treatment. It primarily relies on the adsorption and filtration effects of biofilm and filter media to achieve rapid wastewater purification. The system features a relatively compact structure and ease of operation (Jin et al., 2019). Within BAFs, the filter media plays a critical role in microbial immobilization, growth, and colonization. Polystyrene foam media is a common lightweight material favored for its excellent mechanical properties, low wear rate, low density, and high impact resistance. However, the low hydrophilicity of this material compromises its biocompatibility, leading to slow initial microbial adhesion and proliferation on the media surface. This results in prolonged reactor start-up times and, during normal operation, the formation of less dense biofilms, which ultimately limits its effectiveness in biofilm systems (Wang et al., 2016).

To address the challenge of poor bacterial adhesion to polystyrene media, our project focuses on engineering the TasA protein on the surface of Bacillus subtilis. This approach aims to significantly enhance the adhesion of engineered bacteria to polystyrene foam filter media.

Fig. 3 Polystyrene-Based Biological Aerated Filter

Specific Application Scenario: Cadmium Ion (Cd²⁺) Pollution

Among various industrial pollutants, heavy metal contamination poses a significant global challenge for environmental governance due to its persistence, bioaccumulation, and high toxicity. Cadmium (Cd) pollution is particularly severe. Recognized as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC), cadmium is highly hazardous to human health, characterized by a long half-life and difficulty of excretion. Long-term exposure to cadmium is associated with a 31% increased risk of lung cancer and can lead to severe conditions such as osteoporosis.

As one of the world's largest industrial producers, China faces substantial challenges from cadmium contamination. Research data indicate that cadmium contamination affects 7.75% of China's farmland soils—the highest contamination rate among all heavy metals—accounting for 47.87% of the highest contamination rates found across 389 heavy metal contamination records (Zhang et al., 2015). The average cadmium concentration in farmland across five major grain-producing regions is 0.86 mg/kg, which already exceeds China's risk screening value of 0.6 mg/kg for agricultural soil. More alarmingly, monitoring data from 2010 to 2021 show an increasing trend of cadmium contamination across all major agricultural zones. Cadmium is not only the most frequently detected metal but also exhibits the highest upward trend (Wen et al., 2022).

In addressing heavy metal pollution, engineered bacteria have emerged as a promising solution with significant potential. Given the urgency of cadmium ion pollution, we have chosen to optimize the engineered bacterial solution for cadmium remediation using the TasAnchor platform.

Fig. 4 Heavy metal pollution rates from different sources

Fig. 5 Overview of TasAnchor

References

• UN-Habitat and EPA Ghana. (2023). Technical report: Volumes of wastewater and pollutant loads discharged by industrial and municipal facilities in Ghana, in line with the global monitoring of SDG Indicator 6.3.1. United Nations Human Settlements Programme (UN-Habitat) and Environmental Protection Agency (EPA) Ghana.
• Hou, D., Jia, X., Wang, L., McGrath, S. P., Zhu, Y.-G., Hu, Q., Zhao, F.-J., Bank, M. S., O'Connor, D., & Nriagu, J. (2025). Global soil pollution by toxic metals threatens agriculture and human health. Science, 388(6744), 316-321. https://doi.org/10.1126/science.adr5214
• Qureshi, N., Annous, B. A., Ezeji, T. C., Karcher, P., & Maddox, I. S. (2005). Biofilm reactors for industrial bioconversion processes: Employing potential of enhanced reaction rates. Microbial Cell Factories, 4(1), 24. https://doi.org/10.1186/1475-2859-4-24
• Su, C., Cui, H., Wang, W., Liu, Y., Cheng, Z., Wang, C., Yang, M., Qu, L., Li, Y., Cai, Y., He, S., Zheng, J., Zhao, P., Xu, P., Dai, J., & Tang, H. (2025). Bioremediation of complex organic pollutants by engineered vibrio natriegens. Nature, 642(8069), 1024-1033. https://doi.org/10.1038/s41586-025-08947-7
• Wen, M., Ma, Z., Gingerich, D. B., Zhao, X., & Zhao, D. (2022). Heavy metals in agricultural soil in China: A systematic review and meta-analysis. Eco-Environment & Health, 1(4), 219-228. https://doi.org/10.1016/j.eehl.2022.10.004
• Zhang, X., Zhong, T., Liu, L., & Ouyang, X. (2015). Impact of soil heavy metal pollution on food safety in China. PLOS ONE, 10(8), e0135182. https://doi.org/10.1371/journal.pone.0135182
• Liu L ,Bilal M ,Duan X , et al.(2019).Mitigation of environmental pollution by genetically engineered bacteria — Current challenges and future perspectives. Science of the Total Environment, 667444-454.DOI:10.1016/j.scitotenv.2019.02.390.
• Jin, X., Li, M., Xie, P., et al. (2019). Research Progress on Treatment Technologies for Micro-Polluted Source Water. Environmental Science and Management, 44(1), 119-123.
• Wang Zheng,Fei Xiang,He Shengbing,Huang Jungchen & Zhou Weili.(2016).Application of light-weight filtration media in an anoxic biofilter for nitrate removal from micro-polluted surface water..Water science and technology : a journal of the International Association on Water Pollution Research,74(4),1016-24.https://doi.org/10.2166/wst.2016.299.
• Wang, L., Tan, F., Shao, J., et al. (2016). Current Status and Prospects of Polystyrene Filter Media Application in Water Treatment. Water Purification Technology, 35(3), 31-37.