Protein degradation in anaerobic digestion: influence of volatile fatty acids and carbohydrates on hydrolysis and acidogenic fermentation of gelatin

Performance of an Innovative Two-Stage Process Converting Food Waste to Hydrogen and Methane

“…A heat-shock treatment is conducted to inhibit hydrogenotrophic bacteria and to harvest anaerobic 15 It was reported that cellulose degradation increased at high retention time 16 and protein degradation increased at both high retention time and neutral pH. 17 H 2 fermentation of 6 days is reasonable considering operation time and efficiency, 15 which is followed by post-treatment. Fifteen L/min of air is injected through the bottom of the reactor for 45 hr after dewatering in the same reactor for 3 hr.…”

“…Because of the various components of food waste, it is important to adjust the fermentation conditions 16 and protein degradation increased at both high retention time and neutral pH. 17 The production of VFA and H 2 was dramatically enhanced by reducing D from 4.5 to 2.3 days Ϫ1 . The pH increased gradually to neutral values and the second VFA peak (2990 mg COD/L) and H 2 peak (27.4 L/day) appeared on day 3.…”

Anaerobic Treatment of Milk Processing Wastewater

“…Some suggestions about this problem were given by Lettinga et al (37) and by Verstraete and Vandevivere (79) -As was mentioned above, the precipitation of milk proteins (casein) will lead to the formation of aggregates of solid material that are difficult to degrade (80). Protein denaturation (loss of tertiary structure) is a main mechanism of hindering their decomposition -Several authors have reported that the presence of easily degradable substrates (sugars and hydrocarbons) will hinder the degradation of more complex substrates like proteins and fats (71). This result was observed even with bacterial populations previously adapted to protein degradation…”

“…So, due to the conjugation of the high concentration of easily degradable sugars and the presence of proteins and fats, the effluents from milk processing have a high content of solids that may cause problems in their anaerobic degradation because, as it is well known, the lower the degree of substrate solubilization the lower its biological degradation rate. Furthermore, according to some authors (39,(67)(68)(69)(70)(71), the production of enzymes capable of degrading complex substrates, e.g., proteinaceous and/or fatty matter, may be hindered by the presence of easily degradable substrates such as glucose, amino-acids, or lactose. Contrary to these verifications, Hwu (48) referred that the degradation of oleic acid (the most common LCFA in milk effluents) was significantly enhanced by the addition of an easily degradable cosubstrate, e.g., butyrate or glucose.…”

Simulating the Degradation of Odor Precursors in Primary and Waste-Activated Sludge During Anaerobic Digestion

“…In a pioneering work, Breure et al [7] studied degradation of a model protein, gelatin, in controlled anaerobic digestion, and observed that it was converted at high rates and to a substantial extent to volatile fatty acids. Since proteins, carbohydrates, and lipid are almost always present simultaneously in biosolids, complete degradation of protein in the presence of carbohydrates may not be achieved as glucose and other easily fermentable substrates can repress the synthesis of exoproteases (a necessary enzyme) in pure cultures of bacteria [7], and the degradation of gelatin was retarded by increasing concentrations of carbohydrates present in the feed as a second substrate.…”