A laboratory-scale study by Nguyen Thi Minh, Do Thi Thuy, and Le Minh Nguyet of Vietnam National University of Agriculture (VNUA) found that combining selected bacterial strains with microalgae improved domestic wastewater treatment efficiency. After 14 days, the combined system achieved a chemical oxygen demand (COD) removal efficiency of 96.67%, while substantially reducing organic pollutants, nutrients, and microbial indicators of contamination.
Selecting indigenous bacteria for wastewater treatment
Domestic wastewater contains readily biodegradable organic matter, nutrients such as nitrogen and phosphorus, and diverse groups of microorganisms. Harnessing the metabolic capabilities of microorganisms to transform pollutants is therefore an important research direction for improving water quality and developing biological treatment technologies.
In their study, "Research on domestic wastewater treatment using a mixed system of bacteria and microalgae", the authors focused on selecting indigenous bacterial strains with suitable biological characteristics for use in combination with microalgae. From five wastewater samples collected around VNUA in Hanoi, the researchers isolated 28 bacterial strains. Following assessments of enzyme activity and adaptability to different environmental conditions, four strains were selected for further wastewater treatment experiments.
The selected strains were Bacillus sp. A1, Pseudomonas sp. A2, Bacillus sp. A3, and Bacillus sp. C2. All four produced three extracellular enzymes: amylase, protease, and carboxymethyl cellulase (CMCase), which are involved in the breakdown of different substrates, including starch, proteins, and cellulose derivatives. These enzyme-producing capabilities were among the key characteristics used to screen bacterial strains for wastewater treatment.
The selected strains could grow across a pH range of 4–8, tolerate temperatures of approximately 30–50°C, and utilize various carbon and nitrogen sources. Compatibility tests also showed no antagonistic interactions among the four strains, supporting their potential use together in a treatment system.
The selection of bacterial strains with suitable biological activity and a relatively broad range of environmental tolerance provided a basis for evaluating their performance in wastewater treatment, both as a bacterial consortium and in combination with microalgae.
Combined treatment improves pollutant removal
The experiments were conducted at the laboratory scale using four treatment configurations: an untreated control, a bacterial consortium, a microalgal consortium, and a combined bacterial–microalgal system. Water quality was assessed after 14 days to compare their pollutant removal performance.
The combined system achieved the highest treatment efficiency among the configurations tested. The initial COD concentration of 465 mg/L decreased to 15.48 mg/L, corresponding to a removal efficiency of 96.67%. Five-day biochemical oxygen demand (BOD₅), an indicator of the oxygen required for the biodegradation of organic matter, decreased from 289 mg/L to 16.67 mg/L, representing a removal efficiency of 94.23%.
The system also reduced other water quality parameters. After 14 days, total suspended solids (TSS) decreased by 97.35%, total nitrogen by 94.25%, total phosphorus by 96.99%, and ammonium by 98.02%. These results indicate that the combined system reduced not only the organic pollutant load but also nutrient concentrations in the wastewater.
Another important finding was the reduction in microbial indicators of contamination. The total coliform count decreased by 99.99%, reaching 2,432 most probable number (MPN)/100 mL after treatment. This value was within the limit specified in Vietnam’s National Technical Regulation QCVN 14:2008/BTNMT, Column A, which the study used as its reference. According to the study’s results, all measured parameters in the combined-treatment configuration were within the corresponding limits of this regulation.
Although the bacterial and microalgal consortia also achieved substantial removal efficiencies when used separately, their combination produced better results across the principal parameters assessed. The findings therefore highlight the potential benefits of integrating complementary microbial groups for domestic wastewater treatment.
Potential for resource recovery and circular wastewater management
The significance of the study lies not only in the treatment efficiencies achieved but also in its approach of combining indigenous bacteria with microalgae. Isolating bacterial strains from wastewater, characterizing their biological properties, and incorporating selected strains into a combined treatment system provide an initial scientific basis for further research into environmental biotechnology.
The findings also suggest opportunities to explore the use of nutrients present in wastewater to support microalgal biomass production, an approach relevant to research on circular systems in agriculture. However, the study focused on assessing water quality after treatment. The recovery and subsequent use of microalgal biomass require separate evaluations of its composition and safety before suitable applications can be determined.
Further work is needed to assess the system at larger scales, using wastewater sources with different characteristics and under longer operating periods. Evaluating microbial community stability, treatment performance under real-world conditions, and the feasibility of biomass recovery would help establish the technology’s potential applications.
The study by Nguyen Thi Minh, Do Thi Thuy, and Le Minh Nguyet provides promising preliminary evidence for the use of bacterial–microalgal systems in domestic wastewater treatment. Further research could help determine how this approach can contribute to effective biological treatment and appropriate resource recovery within more sustainable wastewater management systems.
Sources: This article is based on the study “Research on domestic wastewater treatment using a mixed system of bacteria and microalgae” by Nguyen Thi Minh, Do Thi Thuy, and Le Minh Nguyet, published in the Science Journal of Agriculture and Environment, Issue 1, July 2026.
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