Evaluation of high rate ponds operational and design strategies for algal biomass production and domestic wastewater treatment

Enhancing environmental performance in biogas production from wastewater-grown microalgae: A life cycle assessment perspective

The production of biogas from microalgae has gained attention due to their rapid growth, CO2 sequestration, and minimal land use. This study uses life cycle assessment to assess the environmental impacts of biogas production from wastewater-grown microalgae through anaerobic digestion within an optimized microalgae-based system. Using SimaPro® 9 software, 3 scenarios were modeled considering the ReCiPe v1.13 midpoint and endpoint methods for environmental impact assessment in different categories. In the baseline scenario (S1), a hypothetical system for biogas production was considered, consisting of a high rate algal pond (HRAP), a settling, an anaerobic digester, and a biogas upgrading unit. The second scenario (S2) included strategies to enhance biogas yield, namely co-digestion and thermal pre-treatment. The third scenario (S3), besides considering the strategies of S2, proposed the biogas upgrading in the HRAP and the digestate recovery as a biofertilizer. After normalization, human carcinogenic toxicity was the most positively affected category due to water use in the cultivation step, accounted as avoided product. However, this category was also the most negatively affected by the impacts of the digester heating energy. Anaerobic digestion was the most impactful step, constituting on average 60.37% of total impacts. Scenario S3 performed better environmentally, primarily due to the integration of biogas upgrading within the cultivation reactor and digestate use as a biofertilizer. Sensitivity analysis highlighted methane yield's importance, showing potential for an 11.28% reduction in ionizing radiation impacts with a 10% increase. Comparing S3 biogas with natural gas, the resource scarcity impact was reduced sixfold, but the human health impact was 23 times higher in S3.

Biocompounds from wastewater-grown microalgae: a review of emerging cultivation and harvesting technologies

Microalgae biomass has attracted attention as a feedstock to produce biofuels, biofertilizers, and pigments. However, the high production cost associated with cultivation and separation stages is a challenge for the microalgae biotechnology application on a large scale. A promising approach to overcome the technical-economic limitations of microalgae production is using wastewater as a nutrient and water source for cultivation. This strategy reduces cultivation costs and contributes to valorizing sanitation resources. Therefore, this article presents a comprehensive literature review on the status of microalgae biomass cultivation in wastewater, focusing on production strategies and the accumulation of valuable compounds such as lipids, carbohydrates, proteins, fatty acids, and pigments. This review also covers emerging techniques for harvesting microalgae biomass cultivated in wastewater, discussing the advantages and limitations of the process, as well as pointing out the main research opportunities. The novelty of the study lies in providing a detailed analysis of state-of-the-art and potential advances in the cultivation and harvesting of microalgae, with a special focus on the use of wastewater and implementing innovative strategies to enhance productivity and the accumulation of compounds. In this context, the work aims to guide future research concerning emerging technologies in the field, emphasizing the importance of innovative approaches in cultivating and harvesting microalgae for advancing knowledge and practical applications in this area.

Emerging revolving algae biofilm system for algal biomass production and nutrient recovery from wastewater

Toward the direction of zero‑carbon emission and green technologies for wastewater treatment, algae-based technologies are considered promising candidates to deal with the current situation of pollution and climate change. Recent developments of algae-based technologies have been introduced in previous studies in which their performances were optimized for wastewater treatment and biomass production. Among these, revolving algae biofilm (RAB) reactors have been proven to have a great potential in high biomass productivity, simple harvesting method, great CO2 transfer rate, high light-use efficiency, heavy metal capture, nutrient removal, and acid mine drainage treatment in previous studies. However, there were few articles detailing RAB performance, which concealed its enormous potential and diminished interest in the model. Hence, this review aims to reveal the major benefit of RAB reactors in simultaneous wastewater treatment and biomass cultivation. However, there is still a lack of research on aspects to upgrade this technology which requires further investigations to improve performance or fulfill the concept of circular economy.

Characteristics and risks of microplastic contamination in aquaculture ponds near the Yangtze Estuary, China

Microplastic pollution has been frequently reported in natural water environments, but studies on the occurrence and characteristics of microplastic in aquaculture environments especially in pond production system are relatively scarce. Herein, we investigated the abundance and characteristics of microplastic pollution in aquaculture ponds that farm different species (fish, prawn and crab) near the Yangtze Estuary, China. The average abundance of microplastic in pond water and sediment was 36.25 ± 6.79 items/L and 271.65 ± 164.83 items/kg, respectively. Compared to fish ponds (208.43 ± 57.82 items/kg), microplastic abundance was significantly higher in sediment of crab and prawn ponds (312.02 ± 38.76 and 248.87 ± 36.51 items/kg respectively). Across all ponds, transparent, white and black microplastic were the common colors. Fiber was the most common type, accounting for 40.9% and 58.6% in pond water and sediment, respectively. The size of microplastic was mainly distributed between 300 and 1000 μm. For microplastic polymer composition, polyethylene (PE) was predominant in pond water, accounting for 55%, followed by polyamide with 15%. The predominant polymer in sediment was PE with 34%, followed by polypropylene with 18%. As for the ecological risk assessment of microplastic, the pollution load index was 7.6 (risk level I) and 8.9 (risk level I) for pond water and sediment, respectively. The polymer hazard index was 85.3 (risk level II) and 12.1 (risk level II) for pond water and sediment, respectively. Taken together, the pollution risk index was rated as high and very high for pond sediment and water, respectively. These results provide a basis for the comprehensive evaluation and developing practical approaches to deal with microplastic in aquaculture pond, which is of great significance to the healthy development of pond aquaculture.

Microalgae-based domestic wastewater treatment: a review of biological aspects, bioremediation potential, and biomass production with biotechnological high-value

This review aims to perform an updated bibliographical survey on the cultivation of microalgae in domestic wastewater with a focus on biotechnological aspects. It was verified that the largest number of researches developed was about cultures in microalgae-bacteria consortium and mixed cultures of microalgae, followed by researches referring to the species Chlorella vulgaris and to the family Scenedesmaceae. According to published studies, these microorganisms are efficient in the biological treatment of domestic wastewater, as well as in the production of high value-added biomass, as they are capable of biosorbing the organic and inorganic compounds present in the culture medium, thus generating cells with high levels of lipids, proteins, and carbohydrates. These compounds are of great importance for different industry sectors, such as pharmaceuticals, food, and also for agriculture and aquaculture. In addition, biomolecules produced by microalgae can be extracted for several biotechnological applications; however, most studies focus on the production of biofuels, with biodiesel being the main one. There are also other emerging applications that still require more in-depth research, such as the use of biomass as a biofertilizer and biostimulant in the production of bioplastic. Therefore, it is concluded that the cultivation of microalgae in domestic wastewater is a sustainable way to promote effluent bioremediation and produce valuable biomass for the biobased industry, contributing to the development of technology for the green economy.

Sustainable treatment of primary and secondary effluent by algal-bacterial flocculent biomass in raceway ponds

Two 5.5-L raceway open ponds were used to evaluate the removal of organic material and nutrients from wastewater. Algal-bacterial flocs were placed in the ponds to treat primary and secondary effluent. The organic loading rate ranged from 29 to 95 and 9 to 38 g sCOD m^-3 d^-1 for the reactor fed with primary and secondary effluent, respectively. The hydraulic retention time (HRT) gradually decreased in both reactors from 5.5 to 2.2 d during a period of 21 days, and after that, both reactors operated at an HRT of 1.1 d. A high biomass concentration of around 2.2 g L^-1 was sustained using primary and secondary effluent after 130 days. The biomass, developed with both substrates was very active and completely removed organic material and nutrients in less than 12 h. The algal-bacteria biomass had excellent settling properties and could settle in less than 10 min.

Multi-kingdom microbiota and functions changes associated with culture mode in genetically improved farmed tilapia (Oreochromis niloticus)

Genetically improved farmed tilapia (GIFT, Oreochromis niloticus) are intensively farmed in China, where most of the yield derives from the pond culture system (PCS). The in-pond raceway system (IPRS) is a new type of highly efficient aquaculture mode, and has been recommended as a novel system for GIFT farming. To determine the effects of these culture modes on the gut microbiome of GIFT, we conducted a 90-days experiment in IPRS and PCS units. A 16S rRNA gene profile analysis showed that the composition of gut microbiota in GIFT under IPRS and PCS conditions gradually separated as rearing progressed, with divergent responses by the midgut and hindgut bacteria. The α-diversity in hindgut decreased significantly by day 90, as compared with on day 7 (p < 0.05), with a significantly greater decrease in PCS-reared fish than in IPRS fish (p < 0.05). The α-diversity of microbiota in midgut remained stable (p > 0.05). The overall dominant gut bacteria were Bacteroidetes, Proteobacteria, and Firmicutes. Rearing mode affected the taxonomic profile of the gut bacteria; in midgut, IPRS samples had more Firmicutes and Fusobacteria compared with PCS samples, but less Proteobacteria, Verrucomicrobia, and Actinobacteria. Firmicutes was enriched in IPRS hindgut, and Fusobacteria was enriched in PCS hindgut. Using random-forest models and LEfSe, we also screened core taxa that could discriminate between the gut microbial communities under IPRS and PCS conditions. The genus Cetobacterium (of family Fusobacteriaceae) was significantly enriched in midgut in IPRS fish, and enriched in hindgut in PCS fish. The genus Clostridium sensu stricto (of family Clostridiaceae 1) was significantly enriched in both IPRS midgut and hindgut. Analysis with PICRUSt2 software revealed that the culture modes were similar in their effects on the gut microbial metabolic functions. The predicted pathways were significantly enriched in the metabolism class (level 1). Further, the relative abundance of functions related to amino acid metabolic, carbohydrate metabolic, energy metabolic, and metabolic of cofactors and vitamins were high at hierarchy level 2, as the metabolic activity of intestinal bacteria is especially active. Overall, this study enhances our understanding of the characteristics of gut microbiota in GIFT under IPRS and PCS culture modes. Moreover, our findings provide insights into the microecological balance in IPRS units, and a theoretical reference for further development of this culture system.

Advanced biokinetic and hydrodynamic modelling to support and optimize the design of full-scale high rate algal ponds

High rate algal ponds (HRAP) are known for their suitability to treat wastewater and to produce microalgal biomass, which can be converted into bioproducts. However, full-scale application of HRAP is still limited to few cases, and design procedures are not consolidated or standardized. In this study, a demonstrative-scale HRAP system for secondary wastewater treatment to be implemented in India (treatment capacity of 50 m3·d-1) has been designed combining conventional dimensioning techniques and advanced modelling tools. The objective of the study was to assist, verify and optimize the conventional dimensioning of the secondary HRAP by means of simulations predicting the behaviour of the system in the specific local conditions under different configurations and operational strategies. Biokinetic modelling and hydrodynamic analysis using Computational Fluid Dynamics (CFD) were carried out. The simulations performed with the biokinetic model showed that the optimal hydraulic retention time to enhance nutrient removal and biomass production is 4 days. For the hydrodynamic modelling, a 3D model of the HRAP was built to simulate the hydrodynamic behaviour of 36 different designs. Simulations allowed quantifying the presence of low velocity zones as well as the land use efficiency of the different designs in terms of the useful area vs. the total occupied area. Two baffles and tear-shapes with a diameter equal to ¼ of the channel width was the most efficient configuration. Moreover, a technical-economic assessment of the system was carried out, resulting in an investment cost of 483 € per population equivalent and an operational cost of 0.19 € per m3 of treated wastewater.

Dual-purpose high-efficiency air filter paper loaded with reactive zirconium hydroxide for the filtration aerosols and degradation of chemical warfare agents

Traditional air filter papers can only filter toxic aerosols without the function of decontamination. If the poison stagnating in the paper is desorbed, it may pose a secondary threat to personnel and make it more difficult to dispose of the scrapped paper. Using an alkali-free glass fiber as the base material and zirconium hydroxide as the decontaminant, a self-decontaminating air filter paper that can degrade HD and VX simultaneously was successfully prepared by an intra-pulp addition method, with high filtration efficiency, low pressure drop and moderate tensile strength. The physicochemical properties were characterized by FE-SEM, EDX, XRD and TGA, and the results indicated that Zr(OH)₄ was dispersed uniformly in the paper and filled in the interstices of the glass fiber. The preparation of the composite material had no impact on the structure of fibers and Zr(OH)₄. The preparation technology of the self-decontaminating air filter paper was optimized. It was found that the paper with a fiber grammage of 50 g m⁻², the adhesive of 2% and a Zr(OH)₄ retention rate of 175.0 wt% could completely degrade HD and VX, whose conversion rate exceeded 99.0%, and had a tensile strength of 0.1193 kN m⁻¹, a filtration efficiency of 99.995%, and a pressure drop of 313.6 Pa. Using GC-MS to detect the decontamination products, it was speculated that HD mainly underwent hydrolysis and elimination reactions, VX mainly underwent hydrolysis and polymerization reactions, and their products were non-toxic or low-toxic. The reaction kinetics of HD and VX on the paper was investigated and the half-lives were 2.6 h and 16.2 min, respectively, which demonstrated an outstanding degradation performance. This work manifested for the first time that the air filter paper can be optimized as an efficient self-decontaminating material, which will open up new possibilities for the design and manufacture of multifunctional protective materials.

Dual-functional air filter paper with addition of Zr(OH)₄ was prepared by an intra-pulp addition method, whose filtration performance is maintained while the decontamination performance is added for HD and VX.