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Fermentative hydrogen production is a novel aspect of anaerobic digestion. The main advantage of hydrogen is that it is a clean and renewable energy source/carrier with high specifi c heat of combustion and no contribution to the Greenhouse effect, and can be used in many industrial applications. This review discusses fermentative hydrogen production from various points of view. First, the theoretical principles of the biological processes taking place in hydrogen production, as well as the organisms responsible for this process, are described. Second, practical aspects of fermentative hydrogen production are overviewed. Suitable conditions for the hydrogen-producers (pH and temperature), suitable substrates for hydrogen production and applicable reactor designs are discussed.Finally, the challenges faced by fermentative hydrogen production are discussed. Current research directions are listed together with the most important problems currently constraining full-scale application.

Nitrogen removal from wastewater with high nitrogen concentration and low COD/N ratio via nitrite is advantageous. The specific character of the sludge liquor enables the application of such a method. The factors affecting process efficiency were studied. From the factors followed pH, NH4+/NH3 and NO2-/HNO2 concentration and distribution seem to be most important, using sequencing batch reactor technology and treating wastewater with high NH4+ concentration (above 1 g/l). The efficient oxidation of N-NH4+ to nitrite was achieved at a minimal nitrate production. Primary sludge was used as an internal source of substrate for the denitritation because of the organic substrate deficiency of the sludge liquor. The denitritation can be controlled by dosing of the primary sludge and can be complete. There are two operational alternatives of sludge liquor pretreatment: without pH control--lower operational costs and N-removal up to 65% and with pH control--higher operational costs and N-removal close to complete.

The thermophilic anaerobic process brings an acceleration of biochemical reactions and higher efficiency in the degradation of organic matter in comparison with the mesophilic process. The methanogenic activity of the thermophilic and mesophilic digested sludge was examined during the adaptation of full-scale digesters to an increasing temperature from 38 to 55°C. The results proved a higher activity of the thermophilic sludge after the addition of glucose, acetate and propionate in comparison with the mesophilic sludge; the maximum methane production rates and the methane yield of the raw sludge were always higher under thermophilic conditions; the stability of the degradation process at an increased substrate load was also better. After the adaptation of anaerobic biomass to the temperature of 55°C, the responses of this culture to addition of simple substrates substantially changed, especially in favor of acetate and propionate degradation rates.