Ключевые слова: algae, background, bacteria, biogas, black, bus, chemical, contour, corn, cylinder, digester, energy, fuel, gas, hydrogen, icon, illustration, industrial, ingredient, isolated, laboratory, landfill, line, linear, lined, methane, method, monochrome, natural, outline, plant, reactor, refueling, research, reusing, ship, sign, station, storage, symbol, symbols, tank, transportation, ts, underground,