Production and harvesting of microalgae for wastewater treatment, biofuels, and bioproducts

Among different conversion processes for biomass, biological anaerobic digestion is one of the most economic ways to produce biogas from various biomass substrates In addition to hydrolysis of polymeric substances, the activity and performance of the methanogenic bacteria is of paramount importance during methanogenesis The aim of this paper is primarily to review the recent literature about the occurrence of both acetotrophic and hydrogenotrophic methanogens during anaerobic conversion of particulate biomass to methane (not wastewater treatment), while this review does not cover the activity of the acetate oxidizing bacteria Both acetotrophic and hydrogenotrophic methanogens are essential for the last step of methanogenesis, but the reports about their roles during this phase of the process are very limited Despite, some conclusions can still be drawn At low concentrations of acetate, normally filamentous Methanosaeta species dominate, eg, often observed in sewage sludge Apparently, high concentrations of toxic ionic agents, like ammonia, hydrogen sulfide (H2S) and volatile fatty acids (VFA), inhibit preferably Methanosaetaceae and especially allow the growth of Methanosarcina species consisting of irregular cell clumps, eg, in cattle manure Thermophilic conditions can favour rod like or coccoid hydrogenotrophic methanogens Thermophilic Methanosarcina species were also observed, but not thermophilic Methanosaetae Other environmental factors could favour hydrogentrophic bacteria, eg, short or low retention times in a biomass reactor However, no general rules regarding process parameters could be derivated at the moment, which favours hydrogenotrophic methanogens Presumably, it depends only on the hydrogen concentration, which is generally not mentioned in the literature

The roles of acetotrophic and hydrogenotrophic methanogens during anaerobic conversion of biomass to methane: a review

The aim of this paper is to present a comprehensive review on renewable methane fuel production through the biological route of biomethanation process from major lignocellulosic agricultural crop waste biomass (maize, wheat, rice and sugarcane). Global annual approximate production of major agriculture based lignocellulosic biomass has been explored. Fundamental requirements of biomethanation process have been discussed in details for optimum production of methane. The essential properties of biomass (proximate, ultimate and compositional) conscientious for quality of derived fuel have also been presented along with the pretreatment requirements for lignocellulosic biomass. Methane generation potential of the major lignocellulosic agricultural crop biomass has been explored and presented. Furthermore, the methane production potential and its energetic analysis have also been compared with the bio-ethanol productions. The overall parametric analysis involved in anaerobic digestion and alcoholic fermentation explore that methane generation from lignocellulosic agricultural crop waste biomass is more economical and environmentally beneficial way of biomass utilization in a sustainable way of energy production.

Methane production from lignocellulosic agricultural crop wastes: A review in context to second generation of biofuel production

The methane productivity of manure in terms of volatile solids (VS), volume and livestock production was determined. The theoretical methane productivity is higher in pig (516 l kg −1 VS ) and sow (530 l kg −1 VS ) manure than in dairy cattle manure (469 l kg −1 VS ) , while the ultimate methane yield in terms of VS is considerably higher in pig (356 l kg −1 VS ) and sow manure (275 l kg −1 VS ) than in dairy cattle manure (148 l kg −1 VS ) . Methane productivity based on livestock units (LU) shows the lowest methane productivity for sows (165 m 3 CH 4 LU −1 ) , while the other animal categories are in the same range (282– 301 m 3 CH 4 LU −1 ). Pre-treatment of manure by separation is a way of making fractions of the manure that have a higher gas potential per volume. Theoretical methane potential and biodegradability of three types of fractions deriving from manure separation were tested. The volumetric methane yield of straw was found to be higher than the yield from total manure and the solid fractions of manure, due to the higher VS content, and hence the use of straw as bedding material will increase the volumetric as well as the livestock-based methane productivity.

Methane productivity of manure, straw and solid fractions of manure

Use of algae as biofuel sources.

Biological conversion of biomass to methane has received increasing attention in recent years. Hand- and mechanically-sorted municipal solid waste and nearly 100 genera of fruit and vegetable solid wastes, leaves, grasses, woods, weeds, marine and freshwater biomass have been explored for their anaerobic digestion potential to methane. In this review, the extensive literature data have been tabulated and ranked under various categories and the influence of several parameters on the methane potential of the feedstocks are presented. Almost all the land- and water-based species examined to date either have good digestion characteristics or can be pre-treated to promote digestion. This review emphasizes the urgent need for evaluating the inumerable unexplored genera of plants as potential sources for methane production.

V N Gunaseelan

Papers

Anaerobic digestion of biomass for methane production: A review