Alternative routes of the Russian section of the Nord Stream 2 gas pipeline were studied using environmental criteria. The planned anthropogenic impact was assessed making use of a complex of biotic and abiotic parameters of marine ecosystems allocated in the zones of influence. On land the water protection zones and coastal protective strips of water bodies, specifically protected natural areas, cultural heritage sites, settlements' infrastructure and land transport routes were allocated. The offshore zone of the pipeline includes the navigable routes, anchorages, areas of dangerous navigation and limited access due to the Navy activities, areas of intersection with the existing marine infrastructure (cables and pipelines), fishing areas, areas of dangerous exogenous geological processes and hydrological phenomena (degassing of gas-saturated deposits, ice plowing of the bottom, erosion activity of bottom currents, slope and coastal processes). The results of environmental risk assessment for alternative versions of the Nord Stream 2 route (Russian section) in standard mode and in case of potential accidents are presented.

Ability of plants to degrade waste water pollutants was studied in model experiment. The following aquatic macrophytes were used: Eichhornia crassipes, Cyperus alternifolius, Elodea densa and a mix of plants. Industrial and municipal waste water diluted by tap water to content 10% and 20% were used as a growth media for plants. Concentration of TOC, TN, chlorides and sulfates was measured in water during 7 days of incubation. The best results were obtained for Eichhornia crassipes which was able to decrease TOC and TN in water in 3 days of incubation: for TOC (in mg/l) from 47 to 24 (20% industrial waste water) and from 25 to 10 (20% municipal waste water); for TN (in mg/l) from 5,6 to 1,2 (20% industrial waste water) and from 2,5 to 0,35 (20% municipal waste water). Other plants also demonstrated improvement of water quality but were less effective. Concentration of chlorides remained close to initial level. Concentration of sulfates in several cases increased due to oxidation of sulfides.

The article presents the research results of anaerobic digestion processes in bioreactors of composite mixtures based on initial and residual biomass of Lemna minor duckweed and additives: inoculum (manure), food waste, and spent sorbents to determine biogas potential (biogas volume, methane content). Duckweed Lemna minor, which is widespread in freshwater reservoirs, is one of the promising aquatic vegetation species for energy use. Residual biomass is obtained by chemically extracting valuable components from the primary product. The purpose of the research was to evaluate the possibility of the energy potential of residual biomass of Lemna minor to reduce the consumption of fossil fuels and reduce greenhouse gas emissions. This is in line with the International Energy Agency (IEA) scenarios for the reduction of environmental impact. The obtained results confirm the feasibility of using this type of waste for biogas/biomethane production. The recommendations on the optimal composition of the mixture based on the residual biomass of Lemna minor, which will allow for an increase in biogas production, are given. The obtained data can be used in the design of bioreactors.