Biotechnological Production of Organic Acids from Renewable Resources.

Biotechnological processes are promising alternatives to petrochemical routes for overcoming the challenges of resource depletion in the future in a sustainable way. The strategies of white biotechnology allow the utilization of inexpensive and renewable resources for the production of a broad range of bio-based compounds. Renewable resources, such as agricultural residues or residues from food production, are produced in large amounts have been shown to be promising carbon and/or nitrogen sources. This chapter focuses on the biotechnological production of lactic acid, acrylic acid, succinic acid, muconic acid, and lactobionic acid from renewable residues, these products being used as monomers for bio-based material and/or as food supplements. These five acids have high economic values and the potential to overcome the "valley of death" between laboratory/pilot scale and commercial/industrial scale. This chapter also provides an overview of the production strategies, including microbial strain development, used to convert renewable resources into value-added products.

Methods of ammonia removal in anaerobic digestion: a review.

The anaerobic digestion of substrates with high ammonia content has always been a bottleneck in the methanisation process of biomasses. Since microbial communities in anaerobic digesters are sensitive to free ammonia at certain conditions, the digestion of nitrogen-rich substrates such as livestock wastes may result in inhibition/toxicity eventually leading to process failures, unless appropriate engineering precautions are taken. There are many different options reported in literature to remove ammonia from anaerobic digesters to achieve a safe and stable process so that along with high methane yields, a good quality of effluents can also be obtained. Conventional techniques to remove ammonia include physical/chemical methods, immobilization and adaptation of microorganisms, while novel methods include ultrasonication, microwave, hollow fiber membranes and microbial fuel cell applications. This paper discusses conventional and novel methods of ammonia removal from anaerobic digesters using nitrogen-rich substrates, with particular focus on recent literature available about this topic.

Leguminose green juice as an efficient nutrient for l(+)-lactic acid production.

Lactic acid is one of the most important building blocks for the production of bioplastic. Many investigations have been conducted to reduce the lactic acid production costs. In this work, the focus was put on the application of legume pressed juice or green juice as nutrient source. The pressed juice was utilized directly without prior pre-treatment and sterilization. Using two different alfalfa green juices and a clover green juice from two different harvest years as sole nutrients, non-sterile fermentations were performed at 52°C and pH 6.0 with a thermotolerant strain Bacillus coagulans AT107. The results showed that alfalfa green juices generally were more suitable for high lactic acid production than clover green juices, presumably due to the higher nitrogen content. A final titer of 98.8g/L after 30h with l(+)-lactic acid purity of >99% was obtained.

Efficient production of 1,3-propanediol from fermentation of crude glycerol with mixed cultures in a simple medium.

The objective of this study was to examine the applicability of mixed cultures for 1,3-propanediol (1,3-PDO) production from crude glycerol. Three different sources of mixed cultures were tested, where the mixed culture from a municipal wastewater treatment plant showed the best results. 1,3-PDO can be produced as the main product in this mixed culture with typical organic acids like acetic and butyric acids as by-products. The yield was in the range of 0.56-0.76 mol 1,3-PDO per mol glycerol consumed depending on the glycerol concentration. A final product concentration as high as 70 g/L was obtained in fed-batch cultivation with a productivity of 2.6 g/L h. 1,3-PDO can be kept in the culture several days after termination of the fermentation without being degraded. Degradation tests showed that 1,3-PDO is degraded much slower than other compounds in the fermentation broth. In comparison to 1,3-PDO production in typical pure cultures, the process developed in this work with a mixed culture achieved the same levels of product titer, yield and productivity, but has the decisive advantage of operation under complete non-sterile conditions. Moreover, a defined fermentation medium without yeast extract can be used and nitrogen gassing can be omitted during cultivation, leading to a strong reduction of investment and production costs.