Removal and recovery of nutrients from septic tank wastewater using microalgae: Key factors and practical implications

Study on wastewater treatment characteristics and microbial ecosystem of bacteria-algae symbiosis coupling under carbon neutralization background

At present, environmental pollution is becoming more and more serious, the sustainable development of human society is facing severe challenges. As a crucial nexus for pollutant discharge and greenhouse gas emissions, the establishment of carbon-neutral wastewater treatment processes in wastewater treatment plants, aiming to achieve coordinated development of pollution reduction and carbon mitigation, constitutes a pivotal pathway for environmental governance in the new era. The bacteria-algae symbiotic culture system, based on microalgae biological treatment technology, integrates wastewater treatment, carbon fixation, and biomass energy recovery. It represents a green, low-carbon, economical, and sustainable integrated sewage treatment technology, aligning with the requirements of carbon neutrality. This study constructed an algae-assisted sequencing batch photobioreactor (A-SBPBR) and individual microalgal systems to compare the degradation efficiencies of soluble chemical oxygen demand (sCOD), ammonia nitrogen (AN), and total phosphorus (TP) in high-strength food waste anaerobic digestion effluent (ADE), with high-throughput sequencing conducted to analyze bacterial community dynamics and microbial ecological shifts, coupled with carbon accounting model integration to quantify system-specific carbon emission reduction capacities. Experimental results demonstrated that the bacteria-algae symbiotic system achieved removal efficiencies of 58.89 %, 91.94 %, and 78.89 % for sCOD, AN, and TP, respectively, when treating ADE. Notably, the sCOD degradation rate was approximately 8 % higher than that of the pure algal system. At the phylum level, the bacterial community structure within the symbiotic system exhibited greater diversity and balanced phylum distribution. At the class level, the relative abundances of Gammaproteobacteria, Anaerolineae, and Microgenomatia increased by 5-12 %, 11-14 %, and 2-6 %, respectively, compared to the pure algal system. Carbon footprint analysis revealed that treating 1 m3 of ADE with the symbiotic system reduced CO2 emissions by 51.2 g compared to conventional aerobic processes and lowered CH4 emissions (expressed as CO2 equivalents) by 111.94 g relative to anaerobic processes. These findings indicate that the bacteria-algae symbiotic technology synergistically combines high-efficiency pollutant removal with carbon sequestration capabilities, providing a viable solution for wastewater treatment aligned with carbon neutrality objectives.

Feasible cultivation of Verrucodesmus verrucosus on sterile raw wastewater for energy purposes: a case study in Mexico

In this study, wastewater from a sewage treatment plant was used to culture the microalga, Verrucodesmus verrucosus. The ability of microalgae to adapt to adverse environments and produce high lipid concentrations was evaluated using different media, including sterile and non-sterile media and a control medium. The analysis showed that the control medium (distilled water sample enriched with fertilizer) removed 80.35% ammonium, 32.71% phosphate, and 83.86% nitrate. The sterile raw effluent removed 78.91% of ammonium, 83.44% of phosphate, and 98.82% of nitrate. The optimal conditions for biomass production were sterile raw wastewater, which produced 383.3 mg L-1 of biomass, 2.5% of total lipids, and an average lipid production of 9.31 mg L-1. Microalgae can grow and consume inorganic nutrients under adverse environmental conditions such as in raw wastewater, which is of great importance because it is a pollutant that negatively affects the environment and society. However, wastewater may represent a viable alternative substrate, allowing the generation of high-value products, such as lipids. Furthermore, the specificity of microalgal morphotypes must be evaluated, because each has specific metabolic plasticity. Verrucodesmus verrucosus is a microalga that has not been evaluated in bioremediation processes of wastewater with and without the presence of biotic factors. Therefore, the present study provides a viable alternative for this biological process, with the potential to store metabolites of interest in the industry.

Performance, mechanism regulation and resource recycling of bacteria-algae symbiosis system for wastewater treatment: A review

The bacteria-algae synergistic wastewater treatment process not only efficiently eliminates nutrients and absorbs heavy metals, but also utilizes photosynthesis to convert light energy into chemical energy, generating valuable bioresource. The study systematically explores the formation, algal species, and regulatory strategies of the bacterial-algal symbiosis system. It provides a detailed analysis of various interaction mechanisms, with a particular focus on nutrient exchange, signal transduction, and gene transfer. Additionally, the efficacy of the system in removing nitrogen, phosphorus, and heavy metals, as well as its role in CO2 reduction and bioresource recycling, is thoroughly elaborated. Potential future research of bacteria-algae cell factory producing bioenergy production, feed or fertilizers are summarized. This paper clearly presents effective strategies for efficiently removing pollutants, reducing carbon emissions, and promoting resource recycling in the field of wastewater treatment. It also provides recommendations for further research on utilizing microbial-algal symbiotic systems to remove novel pollutants from wastewater and extract value-added products from the resulting biomass.

Effect of bacteria-algae ratio on treatment of anaerobic digested wastewater by symbiotic coupling of bacteria and algae under the background of carbon neutralization

Environmental pollution is a growing concern, particularly the impact of sewage treatment gas on the atmosphere's greenhouse effect. Efficient sewage resource recycling is crucial to achieving carbon neutrality. The bacteria-algae symbiotic sewage treatment system combines wastewater treatment, carbon dioxide fixation, and biomass energy recovery to achieve the goal of carbon neutrality, environmental protection, and the transformation of high-value added products. This paper presents the construction of a sequencing batch photobiological reaction system that utilizes a microbial-algae symbiotic relationship. The system was used to analyze the degradation effects of sCOD, TN, AN, and TP in anaerobic digestion wastewater by varying the microbial-algae ratios. Additionally, changes in the microbial community were analyzed to explore the system's potential for reducing carbon emissions. The study's findings indicate that: 1)When the ratio of bacteria to algae was 2:3, the removal rates of TN, AN, sCOD, and TP were 81.38%, 94.28%, 75.33%, and 96.56%. 2)Changing the ratio of bacteria to algae would affect the bacterial concentration in the mixed system, but not the bacterial community structure. The results indicate that a ratio of 2:3 enhances the removal of pollutants by bacteria and algae symbionts.3) Under the context of carbon neutralization, this paper investigates the reduction of carbon emissions in ADE treated by bacteria-algae symbiosis at the optimal bacteria to algae ratio. The experimental process can reduce 177.03 mg CO2 compared to complete nutrient consumption treatment, which is equivalent to a reduction of 355.08 g CO2 per 1 m3 of ADE. For full anaerobic treatment, this experimental process can reduce 228.35 mg of CO2 equivalent CH4, which translates to a reduction of 456.71 g of CO2 equivalent CH4 per 1 m3 of ADE.

Effect of external acetate added in aquaculture wastewater on mixotrophic cultivation of microalgae, nutrient removal, and membrane contamination in a membrane photobioreactor

The mixotrophic cultivation of microalgae in wastewater has attracted extensive attention due to its many advantages. In this study, acetate, which can be prepared by hydrolysis of aquaculture waste, was used as exogenous organic matter to promote the growth of Chlorella pyrenoidosa cultured in aquaculture wastewater. Microalgae cultivation was carried out in a membrane photobioreactor (MPBR) with continuous inflow and outflow mode. The results showed that exogenous acetate greatly promoted the mixotrophic growth of C. pyrenoidosa. When the dosage of acetate reached 1.0 g L-1, the relative growth rate of microalgae in the logarithmic stage reached 0.31 d-1, which was 4.4 times that of the control. As a result, exogenous acetate also promoted the removal of nutrients from aquaculture wastewater. During the stable operation stage of the MPBR with acetate added in the influent, an average of 87.41%-93.93% nitrogen and 76.34%-88.55% phosphorus was removed from the aquaculture wastewater containing 19.41 mg L-1 total inorganic nitrogen and 1.31 mg L-1 total inorganic phosphorus. However, it was worth noting that adding exogenous acetate also led to an increase in the membrane resistance of the membrane module in the MPBR. Membrane resistance was mainly composed of internal resistance (Ri) and cake resistance (Rc), and with the increase of acetate content in the influent, their proportion in the total resistance gradually increased. Ri contributed the major membrane resistance and was most affected by acetate dosage. Ri reached 32.04 × 1012 m-1 with 1 g L-1 acetate, which accounted for 69.49% of total resistance. Moreover, with the increase of influent acetate concentration of the MPBRs, both the number of insoluble contaminants and dissolved organic contaminants in the membrane modules increased. In addition, the composition of proteins, polysaccharides, and humus in dissolved organic contaminants was close to that in extracellular polymeric substances and soluble microbial products secreted by microalgae. These results suggested that the membrane fouling of membrane modules was closely related to the algal biomass content in the MPBRs. The above results provided a theoretical basis for reducing membrane fouling of MPBR.