Wastewater Treatment Enters the "Carbon-Negative" Era: CAS Bioelectrochemical Cascade Process Published in Nature Communications, Achieving Grade III Surface Water Effluent and 80% Sludge Reduction

[TIANYI TECH News] The "electron-flow-regulated hybrid bioelectrochemical cascade process" proposed by a Chinese Academy of Sciences research team was recently published online in the authoritative international journal Nature Communications and publicly reported via the Beijing Municipal Science and Technology Commission and other channels on August 7. The process integrates wastewater purification, energy recovery and plant cultivation into a single system, simultaneously achieving full resource recovery of carbon, nitrogen and phosphorus. It compresses the hydraulic retention time (HRT) to 6 hours, cuts sludge yield by more than 80%, delivers effluent that stably meets the Grade III surface water standard, and achieves "carbon-negative emissions" at the system level. This offers a disruptive technical vision for the energy-intensive, high-carbon conventional wastewater treatment route.

1. Background: The "Carbon Burden" of Wastewater Treatment Must Be Addressed

Wastewater treatment has long been viewed as environmental infrastructure, yet it is also an undeniable consumer of energy and emitter of carbon. Industry estimates show that the direct electricity consumption of urban wastewater treatment in China accounts for about 1% of total social electricity use, while non-CO2 greenhouse gases such as methane and nitrous oxide released during biological treatment have global warming potentials dozens of times and nearly 300 times that of CO2 respectively. At the same time, for every 10,000 tonnes of wastewater treated, the conventional activated sludge process produces several tonnes of excess sludge with extremely high moisture content, and the subsequent dewatering, transport, incineration or landfill stages add another round of energy consumption and carbon emissions.

Under the twin goals of the "dual carbon" strategy and wastewater resource recovery, the industry has formed three mainstream carbon-reduction pathways. The first is energy conservation and consumption reduction, represented by AI precision aeration, which dynamically optimizes dissolved oxygen and blower frequency to achieve aeration energy savings of 20%–40% and plant-wide electricity reductions of 15%–25%. The second is short-process and low-chemical-consumption routes, represented by gradient-pore ultrafiltration membranes combined with a high-load MBR short process, cutting cleaning chemicals by about 50%, compressing membrane tank footprint by more than 60%, and reducing water production energy consumption by about 30%. The third is resource recovery, offsetting part of the emissions through phosphorus recovery, biogas power generation and waste-heat utilization.

However, all three pathways are essentially "subtraction" — reducing energy consumption and emissions within the existing process framework, whose theoretical floor is still "near-zero carbon." To truly cross the zero point and achieve "carbon-negative," the process must be re-engineered at the principle level.

2. Core Breakthrough: One System Completing "Purification – Energy Production – Cultivation"

The innovation of this published result lies precisely in re-engineering at the principle level. Taking "electron-flow regulation" as the core concept, the research team built a hybrid bioelectrochemical cascade module that treats the chemical energy contained in wastewater as a dispatchable electron resource. By directing the electron flow, the same system performs three tasks in parallel:

First, deep purification. The bioelectrochemical process enhances organic matter degradation and nitrogen and phosphorus removal, enabling the effluent to stably meet the Grade III surface water standard. This water quality far exceeds the conventional Grade 1A discharge standard and can be used directly for ecological replenishment, landscape water bodies and even some industrial reuse scenarios, without the need for additional conventional advanced treatment units.

Second, energy recovery. The system partially recovers the energy contained in wastewater in the form of electricity, replacing the external power input required by conventional aeration. This is the key that makes "carbon-negative" possible — the treatment process shifts from net energy consumption to partial energy production.

Third, full utilization of carbon, nitrogen and phosphorus coupled with cultivation. The system directs the nitrogen and phosphorus nutrients in wastewater into plant cultivation, where biomass carbon sequestration completes the final carbon-sink loop. Carbon is fixed into biomass, while nitrogen and phosphorus become plant nutrients, realizing a complete "pollutant-to-resource" conversion rather than simple end-of-pipe removal.

In terms of engineering performance, two indicators stand out: HRT compressed to 6 hours, meaning the structure volume can be greatly reduced at the same treatment scale, with significant reductions in land and civil works investment; and sludge yield reduced by more than 80%, meaning the sludge disposal costs and secondary pollution risks that have long plagued the industry are substantially reduced. For operators, these two are precisely the most flexible parts of the whole-lifecycle cost.

3. Industry Significance: A Technical Anchor for "Carbon-Negative Plants"

It should be objectively noted that this result is still at the principle-verification and pilot stage. Moving from the laboratory to large-scale engineering application still requires thorough validation of system stability, electrode material lifespan and cost, robustness under extreme influent shock, and the operational complexity of the cultivation stage. Nevertheless, its industry significance is already quite clear:

First, it redefines the value boundary of wastewater treatment. When a wastewater plant is no longer just an "energy-consuming pollution-control cost center" but can become a "resource factory" producing water, energy, fertilizer and carbon sinks, the industry's business model and valuation logic will be rewritten.

Second, it provides a technical direction for low-carbon benchmark plants. In recent years, demonstration projects such as semi-underground reclaimed water plants and green low-carbon benchmark plants have continued to emerge, with some already achieving more than 50% tail-water reuse. The emergence of carbon-negative processes raises the technical ceiling for the next generation of demonstration projects.

Third, it resonates with the institutional side. In the same period, the reclaimed water marketization mechanism is accelerating — Shenzhen has issued the Reclaimed Water Supply Management Guide as a group standard, pioneering negotiated pricing for reclaimed water and a tiered "by-use, quality-based pricing" system. When high-quality reclaimed water can be sold at a price matching its cost, the Grade III surface water produced by carbon-negative processes gains clear economic value support. The dual drive of technology and institutions is jointly raising the industry ceiling for wastewater resource recovery.

4. Industry Perspective and TIANYI TECH's Technical Reserves

TIANYI TECH Co., Ltd. has long focused on industrial wastewater treatment and water reuse. Our attention on this result centers on three transferable directions:

• The economic value of sludge reduction. In industrial-park wastewater treatment projects, sludge disposal often accounts for a considerable share of operating costs. If an 80%+ sludge reduction can be reproduced at engineering scale, it will significantly improve project whole-lifecycle economics — a key area we continue to track.

• The significance of short HRT for footprint. Land scarcity is common in industrial parks. The structure compression brought by a 6-hour HRT aligns with the footprint optimization of short-process membrane technologies and holds real appeal for park retrofit and expansion projects.

• High-quality effluent linking to reuse. Grade III surface water effluent has natural synergy with our technical accumulation in dual-membrane, fluoride removal and salt separation advanced treatment, enabling us to design more flexible graded water-quality reuse solutions for clients.

TIANYI TECH will continue to track the engineering progress of bioelectrochemical, AI intelligent control and short-process membrane technologies, proactively building low-carbon and carbon-negative technology reserves while ensuring stable and compliant operation of existing projects. We believe that in the next decade of the wastewater treatment industry, the competitive focus will shift from "compliance discharge" to "resource output and carbon performance." For water-intensive, high-emission industrial enterprises, planning ahead for resource recovery and low-carbon pathways is both a compliance requirement and a tangible cost opportunity.

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*Source: Nature Communications (published online 2026-07-29); Beijing Municipal Science and Technology Commission and other public reports (2026-08-07); industry energy and process data compiled from public sources.*

*TIANYI TECH Co., Ltd. · News Center*