Activated sludge

Abstract

PROCESS MODELING AND KINETICSMechanistic approaches. A procedure was developed to obtain stoichiometric and kinetic parameters for heterotrophic growth and hydrolysis of slowly degradable organic matter in the activated sludge process. I The procedure was based on oxygen-uptake measurements to distinguish between organic fractions in domestic wastewater. The influence ofparticle size on biological treatability of particulate matter and on treatment process kinetics was investigated," Pretreatment to modify particle-size distribution was discussed in relation to its effect on process performance. Hydrolysis of particulate organic substrate was found to be highly influenced by the electron donor available. 3 Using raw municipal wastewater as a substrate, the hydrolysis rate was high under aerobic conditions, medium under anaerobic conditions, and low under anoxic conditions. Hydrolysis ofa( 1-4) glucan bonds in macromolecular carbohydrates found in municipal wastewater was seen to be controlled by concentrations ofoxygen and/or alternate electron acceptors and was suppressed in the presence of high concentrations of soluble substrate." The extracellular enzymes responsible for carbohydrate hydrolysis were associated with the particulate fraction. Under denitrifying conditions, slowly biodegradable chemical oxygen demand (COD) was hydrolyzed more rapidly in biological phosphorusremoval systems incorporating nitrification and denitrification than in conventional nitrification/denitrification systems." The increased rate of hydrolysis in the biological phosphorus-removal system was proposed to result from the presence ofan anaerobic reactor. Measurement of dehydrogenase activity indicated that activated sludge microorganisms metabolized adsorbed substrate in the absence of significant oxygen uptake."Sykes" formulated a product-maintenance model of the activated sludge process. A cited advantage to this approach was that empirical observations were described better than with conventional kinetic models. Formation of soluble microbial products in batch reactors was studied using radiolabeled phenol and glucose." Zero-and first-order kinetic expressions adequately described the disappearance ofinitial substrate and net formation of soluble microbial products. For organisms subjected to anaerobic conditions before substrate and oxygen supply in batch systems, the observed biomass yield decreased as initial substrate to biomass concentration (So/X o) increased." A proposed explanation for this phenomenon was that the organisms needed to rebuild energy reserves at the expense of growth. In a study using synthetic wastewater, the existence ofsynchronized cell division was reported to occur in laboratory-activated sludge systems. 10 Synchronization was related to starvation ofthe organisms under anaerobic conditions in batch culture and occurred at So/X o greater than two. A model was proposed to describe the rate and extent of cometabolic transformation of halogenated aliphatic compounds by resting microbial cells.II The mod...

The application of composting materials to degrade polycyclic aromatic hydrocarbon on oil field drill cuttings

“…The addition of organic waste is essential to promote the development of a diverse microbial community capable of breaking down complex contaminants (Aitken et al, 1992;Jorgensen et al, 2000;Ma et al, 2016). A case study on Mushroom compost-assisted remediation of soil contaminated with PAHs from a manufactured gas plant was conducted in a thermally insulated composting chamber.…”