[Mainland China] Tianjin University team uses 3D-printed "living materials" to integrate Anaerobic Ammonium Oxidation and Denitrification: spatial confinement shortens startup time by 71.43%, achieving 100% Total Nitrogen removal without external organic

Tianjin University Professor Zhao Yingxin's team constructed a double-network hydrogel bioink from sodium alginate and cellulose, and used 3D bioprinting to fabricate anaerobic ammonium oxidation microbial communities into Engineered Living Materials (ELMs). Spatial confinement not only brought functional microbial communities closer together but also retained public metabolites such as amino acids, polysaccharides, and cofactors, enabling the two to form stable cross-feeding. The results were a 71.43% reduction in system startup time, achieving 100% Total Nitrogen removal without additional organic carbon source supplementation, and validated in real wastewater. The findings were published in Nature Sustainability.

Most people who have encountered Anaerobic Ammonium Oxidation technology have heard the same complaint: the principle is well understood, but startup is just too slow.

Anammox bacteria can directly use nitrite as an electron acceptor to convert ammonium into nitrogen gas, without requiring an organic carbon source throughout the process—compared with conventional Nitrification and Denitrification, it is regarded as one of the most disruptive low-carbon nitrogen removal pathways in the field of wastewater treatment. But it has an unavoidable "tail": the reaction process produces nitrate as a byproduct, theoretically equivalent to about 11% of the influent Total Nitrogen.

To remove this portion of nitrate, Anammox bacteria must effectively "cooperate" with Denitrifying bacteria. The trouble is that microorganisms are too far apart and metabolites easily diffuse and are lost, making such cooperation difficult to establish stably.

The solution proposed by Professor Zhao Yingxin's team at Tianjin University is quite distinctive: rather than allowing microorganisms to aggregate randomly, they "print" them.

From Random Aggregation to Spatial Printing

According to paper information disclosed by 2026 年 9 月 8 日, the team's approach was to print Anammox microbial communities into Engineered Living Materials (ELMs), using spatial confinement to simultaneously solve two problems:

• The physical distance problem—bringing key microbial communities closer together, so that material exchange between functional bacteria no longer depends on long-distance diffusion;
• The metabolite loss problem—retaining "public metabolites" such as amino acids, polysaccharides, and cofactors produced by the microbial communities in the local space, truly forming efficient cross-feeding between Anammox bacteria and Denitrifying bacteria.

The ingenuity of this approach lies in transforming the long-standing challenge of Anammox engineering—"unstable microbial community relationships"—from a biological problem into a material geometry design problem. Distance is no longer determined by the microorganisms themselves, but by the path of the print head.

Bioink: How the Double-Network Hydrogel Was Formed

To "print" bacteria and keep them alive and working, the first step is to find a suitable carrier. The team chose a sodium alginate + cellulose system.

• Ratio—when the ratio of the two is 1:1, a good balance is achieved among printing performance, cell activity, and mass transfer;
• Network formation mechanism—sodium alginate and cellulose form a network through hydrogen bonding, and then further crosslink via Ca²⁺ coordination with carboxyl groups, yielding a stable double-network hydrogel;
• Structural verification—XRD, FTIR, and XPS results collectively confirmed the formation of this network structure and Ca²⁺ coordination;
• Low-carbon attributes—this system is mainly composed of natural, renewable polymers, and compared with conventional petroleum-based carriers, it better aligns with the material logic of low-carbon wastewater treatment.

Microscopic structure further revealed that microorganisms were not simply "buried" in the gel, but formed a controllable distribution pattern within the confined space—this is precisely where "living materials" differ from ordinary immobilized carriers.

Key Results: Two Numbers

The two most noteworthy quantitative results of this study are:

• System startup time reduced by 71.43%;
• Achieving 100% Total Nitrogen / TN removal without additional organic carbon source supplementation, and the related effects were validated in real wastewater.

The paper was published in Nature Sustainability under the title "3D-printed living materials for anammox–denitrification coupling in wastewater treatment," with Yinuo Liu as the first author.

The combination of "zero external carbon source + 100% Total Nitrogen / TN removal" is a landmark threshold in the field of low-carbon denitrification. Traditional processes often have to dose external carbon sources such as methanol and sodium acetate to completely denitrify nitrate—this not only increases operating costs but also sends back the carbon emissions originally saved. The cross-feeding mechanism design essentially allows the metabolic byproducts of one type of bacteria to become the food source of another, achieving carbon self-sufficiency within the community.

Why it matters in the broader industry context

Anaerobic Ammonium Oxidation / Anammox has never lacked advantages; what it lacks is engineering economics. The recently released "China Water Treatment Industry Sustainable Development Strategy Industry Research Report (2026–2030)" points out that compared with traditional Nitrification and Denitrification processes, Anaerobic Ammonium Oxidation / Anammox can save approximately 60% of aeration energy consumption and 100% of organic carbon source demand, making it one of the most disruptive low-carbon technologies in the wastewater treatment field.

But in reality, three hurdles to the promotion of Anaerobic Ammonium Oxidation / Anammox have always existed:

• Long startup period—functional bacteria have long doubling times and are difficult to enrich; a project often takes months from inoculation to compliance, during which the owner bears the risk of non-compliant effluent and capacity loss;
• Poor stability—significantly affected by temperature, load shocks, and inhibitors; once the bacterial community is lost, it is difficult to recover;
• Nitrate residue—that is, the approximately 11% byproduct nitrate mentioned above, which requires coupling with Denitrification to be completely resolved.

If these three problems were ranked, the startup period is often the first reason owners give up: under the schedule constraints of upgrading and retrofitting, waiting for enrichment itself means it is practically infeasible.

This is precisely where the value of this research lies—it uses spatial printing to compress the largest cost item, "startup time," by more than 70%. If it can be scaled up to the engineering level, the distance for Anaerobic Ammonium Oxidation / Anammox to move from "an empirical product of a few demonstration plants" to a "standard process package" will be significantly shortened.

Of course, from the laboratory to engineering application, several questions remain to be answered: the mass production cost and batch consistency of 3D-printed ELMs, the mechanical strength and swelling behavior during long-term operation in real wastewater, the evolution of microbial community structure under complex water quality conditions, and the most critical point—whether it can be adapted to continuous-flow reactors rather than small pilot-scale test devices. These are the key variables that determine whether a beautiful result can reach frontline wastewater treatment plants.

What it means for us: TIANYI TECH's judgment

TIANYI TECH has long served municipal and Industrial Park wastewater treatment and Reclaimed Water Reuse clients. We have always followed the engineering progress of low-carbon denitrification routes. Based on this result, our judgment is: the commercialization bottleneck of Anaerobic Ammonium Oxidation / Anammox is shifting from "whether it can be enriched" to "how long it takes to start up, and how long after startup it will disperse." Along this direction, we recommend focusing on two types of practical entry points—first, for projects that have already adopted Anaerobic Ammonium Oxidation / Anammox or are conducting upgrading feasibility studies, make "startup period assurance" an explicit indicator in process package selection rather than a risk accepted by default; second, for high-ammonia nitrogen wastewater limited by temperature and carbon-to-nitrogen ratio (livestock biogas slurry, Landfill Leachate, some Industrial Wastewater), prioritize evaluating bacterial dosing schemes with spatially structured communities, rather than relying solely on extending sludge age.

It should be noted that the laboratory indicators of new materials must be recalculated under on-site water quality and real operating conditions. From "printed out" to "running," what lies in between is not only time, but also engineering validation.

About TIANYI LIMITED: TIANYI LIMITED is deeply engaged in the fields of wastewater treatment and Reclaimed Water Reuse, committed to providing efficient, low-carbon, and sustainable water treatment solutions for municipal and industrial clients.