Culturing microalgae for nutrients removal from wastewater (review)

Summary

Research works in the field of microalgae culturing with the use of wastewater as substrate have gained ground overseas. In this way the removal of nutrients used for biomass growth as well as of some heavy metals and other pollutants is provided. A description of process flow schemes of wastewater treatment combined with microalgae culturing and basic indicators of wastewater treatment facilities operation is presented. Three options of retrofitting a microalgae culturing plot are considered: at the end of the process flow scheme for enhanced nutrients removal from wastewater and biomass production as a raw material for biofuel; at the beginning of the process flow scheme with possible utilization of both nutrients for microalgae culturing and organic carbon that improves the biomass output; the scheme that provides for feeding only nutrient enriched solution from dewatering aerobically digested sludge are considered. Microalgae can be a valuable raw material for production of biofuel, food supplements, fertilizers, soil conditioners and adsorbents. However, for the implementation of such schemes large production areas are required, therefore their use is expedient for small-scale treatment facilities or facilities located in small towns or rural areas. Beside that a solution for some technological problems is required. The keen interest in the research in this field in different countries shows that the wastewater treatment technology with the use of culturing microalgae is an upcoming trend for experts.

Key words

wastewater , nutrients removal , biomass , microalgae culturing , biodiesel fuel

Development of promising methods of wastewater treatment with energy recuperation in China and India (a review)

Summary

In China, active research is underway for developing a technology for excess activated sludge fermentation to obtain hydrogen. The process of anaerobic fermentation includes three main stages: hydrolysis, formation of hydrogen and acids, and methane generation. At the hydrolysis stage, the formation of low-molecular substances from high-molecular starch, fibers and proteins. At the stage of the hydrogen and acids formation hydrogenogenic and acetogenic bacteria ensure the fermentation of low-molecular substances with the formation of a number of organic acids, hydrogen and carbon dioxide. At the stage of methane generation, methanogenic bacteria metabolize the products formed in the previous stages with the release of methane and carbon dioxide. As a result, hydrogen can be obtained only by inhibiting the activity of methanogenic bacteria eliminating the impact on the activity of hydrogenogenic bacteria. Considering these circumstances methods are being developed to enhance the production of biohydrogen. The main efforts in this area aim at finding strains with high efficiency of anaerobic fermentation. Another direction is choosing a method of activated sludge pre-treatment from among thermal, acid, alkaline, microwave treatment, sterilization and ultrasonic treatment. Significant prospects are associated with the use of a consortium of microorganisms and mixed substrate containing, along with wastewater sludge, food waste, straw or manure. In India, the technologies of processing various types of industrial wastewater with the production of biomass enriched with lipids for the subsequent production of biodiesel have been on the march. The studies have been performed using Rhodococcus opacus bacteria, Rhodosporidium kratochvilovae yeast and Desmodesmus sp microalgae.

Key words

wastewater , surplus active silt , biodiesel fuel , biohydrogen , anaerobic fermentation , hydrogeonogenic bacteria , Rhodococcus opacus bacteria , Rhodosporidium kratochvilovae yeast , Desmodesmus sp. microalgae , intracellular lipid accumulation