Elvira E. Ziganshina

Uneaten feed and feces are major sources of waste in aquaculture systems, which lead to the eutrophication of water bodies. This study proposes a multidisciplinary approach to the valorization of two types of aquaculture waste. The first component of the strategy is the cultivation of microalgae in raw wastewater. The wastewater from a recirculation aquaculture system (RAS) for sturgeon was tested as an alternative growth medium for eight microalgae species. The highest biomass concentration was achieved when cultivating Tetradesmus obliquus, reaching 1.34 ± 0.04 g L^–1. Anaerobic digestion (AD) of sludge from the RAS and mixed algal biomass harvested from wastewater treatment was proposed as a secondary component of a waste valorization strategy. Granular activated carbon (GAC) was selected as the conductive material to enhance methane production from tested substrates. The specific methane production (SMP) during AD of the sludge ranged from 94 to 99 NmL g^–1_{VS (volatile solids)}. In contrast, the SMP for treatments containing algae reached 321–327 NmL g^–1_VS. The addition of GAC to the anaerobic reactors was an effective method for enhancing methane formation from algal biomass. Finally, this study combines aquaculture water treatment and sludge management with the production of valuable algal biomass and biofuel.

Today, waste is viewed as a renewable energy source and a potential supplier of new bioproducts. Microalgae are essential in wastewater treatment, and the anaerobic digestion (AD) of the harvested biomass leads to the production of biomethane. However, the process of producing methane from algae requires energy-intensive pretreatment steps. This study investigates the potential of carbon nanotubes (CNTs) and granular activated carbon (GAC) to enhance methane production through AD of untreated Chlorella sorokiniana and Tetradesmus obliquus biomass. Indicators of process stability included organic acid, total ammonia nitrogen concentrations, methane production data, and microbial community structure and dynamics. The results suggest that adding CNTs (2.0 and 4.0 g L^–1) and GAC (4.0 g L^–1) following the acclimatization stage is an effective strategy to enhance the utilization of produced organic acids and promote long-term methane production from the tested biomass. Additionally, the significance of the bacterial genus Ruminofilibacter in biomass hydrolysis has been emphasized. Among methanogens, there was a decrease in the relative abundance of Methanosarcina, while the relative abundances of Methanothrix and Methanoculleus increased by day 12 in CNTs/GAC-added experiments, during which substantial differences in methane production were observed. This proposed approach has the potential to promote environmentally sound waste management and enhance the production of renewable energy.

Microbially induced corrosion is a common problem in the petroleum industry. In this study, weight loss and surface analysis of grade 20 carbon steel corrosion witness samples were used to evaluate biocorrosion in produced fluids from different wells (Romashkino oilfield, Republic of Tatarstan, Russia). The structure of the resulting microbial communities in the systems with high corrosion indicators was elucidated. The addition of acetate/lactate, yeast extract, and sulfate was found to promote the growth of individual microorganisms in the designed systems and to increase the corrosion rate in several samples (to an average of 0.12 mm year⁻¹). The results of 16S rRNA gene sequence analysis showed that water from different wells from the Romashkino oilfield had distinct microbial compositions. The main genera in the analyzed waters were Oleidesulfovibrio, Halanaerobium, Proteiniphilum, Acetobacterium, Fusibacter, and Methanocrinis, but their relative abundances depended on the water itself and the type of stimulation. Acetogenic bacteria of the genera Fusibacter, Proteiniphilum, Acetobacterium, and acetoclastic methanogenic archaea Methanocrinis became dominant in the microbial community structure in the acetate-enriched systems in water from one of the studied wells. Electron donors, generated by various bacteria and artificially introduced ones, facilitated active dissimilatory sulfate reduction by Oleidesulfovibrio, Desulfotignum, Desulfocurvus, and Pseudodesulfovibrio in water from another production well. The obtained results are important for identifying the causes of premature failures of oilfield equipment, particularly in areas where microbial enhanced oil recovery is used.

Microalgae are emerging as a key biological platform for the production of important metabolites, environmental monitoring, and water treatment. However, despite their significant potential for a variety of industrial applications, several challenges associated with the efficiency of their cultivation hinder their widespread use. Here, focus was placed on the freshwater organism, Micractinium inermum strain EE-M2, to study the growth and accumulation of pigments, proteins, lipids, and starch under various strategies of increased inorganic carbon supply and ammonium nutrition conditions. NaOH and NaHCO₃ were tested as pH control agents. Combinations of constant sparging with atmospheric air enriched with CO₂ (finally 2.0% CO₂, v/v) and NaHCO₃ addition showed a slight increase in algal biomass productivity, but the metabolic profiles were indistinguishable from those obtained with pH regulation using NaOH. Decreasing the CO₂ concentration from 2.0% to 0.5% significantly reduced the final biomass yield and productivity of this strain (in a batch process). Also, the present study showed the feasibility of continuous cultivation of M. inermum to produce marketable biomass and metabolites. Under two cultivation strategies, batch and continuous, the alga effectively accumulated pigments (up to 2.7% of dry weight), proteins (up to 37.3%), lipids (up to 23.3%), and starch (up to 22.5%), indicating its biotechnological value. Overall, the obtained results demonstrate that M. inermum strain EE-M2 is a robust and fast-growing microalgal strain suitable for both laboratory and industrial cultivation.

Incorporating microalgae into integrated biotechnologies facilitates rational resource management. Cultivation of microalgae in various types of wastewater offers a number of advantages: safe disposal of liquid waste, restoration of water resources, and the production of valuable products. This study presents a comparative analysis of the growth and biomass productivity of various algal strains in an unsterilized fish processing plant wastewater. Desmodesmus sp. EE-M8 demonstrated the most efficient growth, with a biomass yield of 2.21 ± 0.09 g L⁻¹. The average biomass yield obtained during the growth of Chlorella vulgaris SB-M4, Chlorella sp. EE-P5, Micractinium inermum EE-M2, and Tetradesmus obliquus EZ-B11 ranged from 1.42 to 1.96 g L⁻¹. Ammonium, phosphate, and sulfate ions were completely utilized from the wastewater during algal growth. In addition, the bacterial community structure of wastewater was found to change drastically toward the dominance of Alphaproteobacteria during the microalgal growth. The algal strains (in combination with bacterial partners) used to determine their biostimulant potential demonstrated a positive effect on the germination of garden cress seeds. These findings demonstrate that incorporating algae into the wastewater purification process will reduce the negative impact on the environment and produce valuable biomass for various purposes.

Poultry slaughterhouse wastewater (PSW) affects environmental and economic issues, and the introduction of modern treatment technologies, including microalgae-based ones, is strictly necessary. In this study, bioremediation of unsterilized PSW by several algal representatives of the genera Chlorella, Tetradesmus, Desmodesmus, and Neochloris was investigated. All microalgae grew in original wastewater, and the elevated N, P, and S levels in PSW allowed the microalgae to increase the biomass yield (from 2.44–3.15 to 2.73–4.42 g L⁻¹). Modification of PSW for cultivation of microalgae made it possible to obtain biomass with a high content of valuable metabolites. The highest protein content was observed in cells of cultures of Chlorella sorokiniana and Neochloris sp. (26% and 33% of the final dry weight, respectively). At the same time, starch and lipids were also accumulated in the algal cells at substantial levels in both original and modified PSW. With the growth of algae, a decrease in the relative abundance of members of Arcobacteraceae and Clostridium, which include pathogens, was also observed. At the same time, PSW contained a variety of bacteria capable of stimulating the growth of microalgae. Thus, integrating microalgae into the treatment of PSW will reduce the negative impact of such wastewaters on the environment and improve the sanitary indicators.

The study of microalgae has led to significant progress in recent decades. The current microalgal biomass yield is unsatisfactory, except for certain species that are cultivated for the nutraceutical and pharmaceutical industries. In this study, the growth efficiency and biochemical composition of Tetradesmus obliquus at high levels of nutrients were characterized. Increasing the NH₄⁺-N content in the medium to 164 mg L⁻¹ allowed the algae to steadily accumulate biomass (6.14 ± 0.28 g L⁻¹) with a moderate content of starch. Optimizing the levels of N, P, and S allowed the biomass productivity to increase from the average 0.45 to 0.88 g L⁻¹ day⁻¹. A further increase of NH₄⁺-N to 410 mg L⁻¹ and other nutrients’ concentration allowed the algae to accumulate biomass (7.50 ± 0.28 g L⁻¹), enriched with protein and pigments. The algae cultivated with the high load of nutrients reached 100%, 84%, and 96% removal of N, P, and S, respectively. Adding the NaHCO₃ to the photobioreactor for pH adjustment (instead of NaOH) did not significantly improve the growth parameters or affect the composition of the algal cells. In general, our study will improve the comprehensive understanding of culture-based approaches to study the perspective use of the alga T. obliquus.

Today, studying the diversity of microbial communities associated with samples of highly mineralized oil industry waters is expanding our knowledge of the ecology of polyextremophilic microorganisms. During this work, samples of produced water and wastewater from the oil industry were thoroughly analyzed. The analyzed waters were characterized by very high concentrations of Na+, Ca2+, Mg2+, and Cl– ions. Furthermore, enriched and pure bacterial cultures from oilfield waters were obtained. Additionally, enriched cultures were analyzed using high-throughput sequencing of the bacterial 16S rRNA gene on the Illumina platform. Among the representatives of the studied bacterial communities, members of the genera Halomonas, Marinobacter, Modicisalibacter, Bacillus, Clostridium, Prauserella, and Rubrobacter were identified. They can be considered for various biotechnological applications.

A variety of microorganisms grow in oil reservoirs, where they participate in the biodegradation of oil and lead to changes in oil quality. Today, our knowledge about microbial processes in oil reservoirs is largely limited, and among the urgent tasks for the oil industry, monitoring and controlling microbial activity (including the activity of microbes responsible for biocorrosion) are important. In this work, we aimed to characterize the bacterial community structure of the produced waters from oilfields in the south of the Republic of Tatarstan (Russian Federation) using cultural and molecular methods of analysis. Bacteria from produced water samples from various oil wells were enriched, and 16S rRNA gene amplicon sequencing was used to assess the phylogenetic diversity of the bacterial communities. Thus, analysis of the bacterial communities revealed the presence of various members within the genera Desulfotomaculum, Clostridium, Acetobacterium, Desulfovibrio, Dethiosulfovibrio, Desulfomicrobium, Fusibacter, Dethiosulfatibacter, Thermovirga, Sphaerochaeta, and Desulfoplanes, but in different produced water samples. The role of the bacterial associations in biocorrosion was separately assessed in experiments on monitoring and stimulating biocorrosion. The bacterial community receiving additional nutrition was shown to have a higher corrosion potential, and scanning electron microscopy analysis confirmed changes in the surface of the metal coupons during immersion testing. The practical value of this research lies in identifying the potential contribution of microbial communities to oil pipeline corrosion.

Improving methods for landless production of bioproducts is considered an important stage in the development of the modern bioeconomy. In this context, microalgal biomass is one of the most promising sources of valuable substances due to its rich biochemical composition. Despite the high adaptability of microalgae to various environmental factors, the effectiveness of cultivation systems depends on precisely selected parameters. Both the light conditions and the supply of inorganic carbon sources are key in determining the efficiency of photoautotrophic cultivation. In this work, the effect of a high daily photosynthetic photon flux density (PPFD) ranging from 37.44 to 112.32 mol m⁻² day⁻¹ on the growth and productivity of a novel Scenedesmaceae alga, strain EZ-B1, was assessed. The next stage of cultivation consisted of selecting the optimal CO₂ concentration. Improved performance of microalga during cultivation in a photobioreactor was achieved at 112.32 mol m⁻² day⁻¹ (24 h photoperiod) and by supplying 2% CO₂, as evidenced by the high biomass productivity (0.69 g L⁻¹ day⁻¹), total biomass yield (5.23 g L⁻¹), and ammonium nitrogen consumption rate. The data obtained suggest that a higher level of PPFD led to the highest growth rate of the novel strain and the highest biomass productivity, which, in practice, will increase production capacity.