Search

Rice is an important cereal crop and different types of wastes are produced from it such as; rice straw as a crop residue, rice husk and rice bran as agro-industrial waste and rice waste as a food waste, which are needed to be tested for bio-hydrogen production under similar set of experimental conditions. The bio-hydrogen production potential of these wastes was compared by co-digestion with heat shocked sludge under mesophilic thermophilic temperatures by using an anaerobic bio reactor under no pH control conditions. It was observed that the bio-hydrogen production potential increased with an increase in temperature from 37 °C to 55 °C for all wastes, except for rice waste. Although, the highest experimental yield of 40.04 mL/VS rem was produced from thermophilic rice straw, but the maximum bio-hydrogen production rate of 97.08 mL/h was observed from rice bran after 29.03 h under thermophilic conditions. The bio-hydrogen production period of rice bran was 33–38% smaller than rice straw due to which the highest yield was observed from rice straw. The lignin content of rice husk was 19.34%, which was double than rice straw and hence the rice husk produced the least experimental yield of 23.05 mL/VS rem under mesophilic conditions. Increasing the temperature from mesophilic to thermophilic conditions changed the final pH by 1.79%, −8.33%, 5.17% and 5.41% for rice straw, rice bran, rice husk and rice waste, respectively. The optimum pH range of bio-hydrogen production from rice straw, bran and husk was observed from pH 7 to pH 6. The average yield of wastes produced from rice crop was 30.36 and 33.16 mL/VS rem under mesophilic and thermophilic conditions, respectively. The quadratic modeling found useful in order to explain more than 90% variation caused by incubation time and temperature on cumulative bio-hydrogen production, drop in pH and VFA production. The 3D and 2D plots developed on the basis of quadratic modeling explained the process parameter is in better way as compared to conventional representation of experimental results. As a whole, increasing temperature not only increased bio-hydrogen yield, but also decrease the volatile fatty acid production. [ABSTRACT FROM AUTHOR]

The present study is the first part of research into modeling flocculation processes in a tubular reactor with different width baffles. Computational fluid dynamics numerical simulation methods were used to identify intensive mixing zones and turbulent flow zones. The influence of geometry and baffle width on velocity components of the liquid flow and turbulence parameters was analyzed. The obtained results were represented as vector and contour distribution maps of the determined quantities. Flow visualization was performed to illustrate the structure and size of vortices formed behind baffles. The correctness of the numerical model was experimentally validated based on anemometric measurements using laser Doppler anemometry (LDA) method. [ABSTRACT FROM PUBLISHER]

Polyhydroxyalkanoates (PHAs) are a diverse class of bio-polymers synthesized by bacteria, usually during imbalanced growth conditions. Optimizing PHA productivity is highly dependent on the bioreactor oxygen transfer rate (OTR), which is an important consideration for process performance and economics, particularly with increasing scale. Relatively few in-depth studies are available regarding the effect of OTR and dissolved oxygen content (DOC) on PHA formation, synthesis rates, composition, and characteristics. This review examines past research studies on the effect of low DOC environments on production of short-chain length (scl-) PHAs, synthesized by both pure and mixed cultures, in order to identify opportunities and gaps concerning the effect of DOC on production of medium-chain length (mcl-) PHAs, an area that has not been studied in detail. The literature indicates that production of scl-PHA (a reductive process) acts as an electron sink allowing cells to maintain balanced redox state at low DOC. Conversely, production of mcl-PHA via fatty acid de novo synthesis (also a reductive process) does not occur to any significant extent in low DOC environments, while mcl-PHA synthesis from fatty acids (an oxidative process) can be promoted in low DOC environments. The monomer composition, molecular mass, as well as physical and thermal properties of the polymer can change in response to OTR, but further research in this area is required for both scl- and mcl-PHAs. Process design and management of bioreactor OTR in PHA production might therefore be directed by the final application of the polymer rather than cost considerations. [ABSTRACT FROM AUTHOR]