Tomonori Matsuo

Activated Sludge Model No.2d, ASM2D

The Activated Sludge Model No. 2d (ASM2d) presents a model for biological phosphorus removal with simultaneous nitrification-denitrification in activated sludge systems. ASM2d is based on ASM2 and is expanded to include the denitrifying activity of the phosphorus accumulating organisms (PAOs). This extension of ASM2 allows for improved modeling of the processes, especially with respect to the dynamics of nitrate and phosphate.

Nitrous oxide production in high-loading biological nitrogen removal process under low COD/N ratio condition

Effects of influent COD/N ratio on N2O emission from a biological nitrogen removal process with intermittent aeration, supplied with high-strength wastewater, were investigated with laboratory-scale bioreactors. Furthermore, the mechanism of N2O production in the bioreactor supplied with low COD/N ratio wastewater was studied using 15N tracer method, measuring of reduction rates in denitrification pathway, and conducting batch experiments under denitrifying condition. In steady-state operation, 20-30% of influent nitrogen was emitted as N2O in the bioreactors with influent COD/N ratio less than 3.5. A 15N tracer study showed that this N2O originated from denitrification in anoxic phase. However, N2O reduction capacity of denitrifiers was always larger than NO3(-)-N or NO2(-)-N reduction capacity. It was suggested that a high N2O emission rate under low COD/N ratio operations was mainly due to endogenous denitrification with NO2(-)-N in the later part of anoxic phase. This NO2(-)-N build-up was attributed to the difference between NO3(-)-N and NO2(-)-N reduction capacities, which was the feature observed only in low COD/N ratio operations.

EFFECT OF PHOSPHORUS ACCUMULATION ON ACETATE METABOLISM IN THE BIOLOGICAL PHOSPHORUS REMOVAL PROCESS

An experimental study was carried out to investigate the metabolic pathway of acetic acid and the relationship between the phosphorus accumulation in the sludge and the metabolism of organic substrates in the anaerobic aerobic biological phosphorus removal process. Two laboratory-scale anaerobic aerobic processes were operated continuously with different phosphorus loadings and batch experiments were conducted with the sludges obtained from the continuous systems. The metabolic pathway of acetate was postulated, in which NADH2 required for PHB synthesis is supplied from the consumption of intracellular carbohydrate through the EMP pathway. The ability of the sludge to uptake acetate anaerobically was limited by the amount of polyphosphate stored in the cell, so long as the phosphorus content of sludge was below 35 mgP/gVSS. From energy balance consideration, the energy required for the accumulation of polyphosphate is found to be very little compared with the total energy produced and the sludge can maintain the yield coefficient at a required level even when a large amount of polyphosphate is accumulated.

Enzyme activities under anaerobic and aerobic conditions in activated sludge sequencing batch reactor

Abstract An experimental study was performed to observe the effect of electron acceptor conditions on the enzyme activities in an anaerobic–aerobic activated sludge sequencing batch reactor (SBR). Four types of extra-cellular enzymes, i.e. alkaline phosphatase, acid phosphatase, α -glucosidase and protease were selected for the study. In addition to these enzymes, dehydrogenase, an intracellular enzyme, was also assayed. A lab scale anaerobic–aerobic SBR was operated and used for the experimental work. It was observed that the specific enzyme activities did not change significantly during anaerobic and aerobic phase of SBR. The enzymatic behavior of sludge observed under anaerobic and aerobic conditions was explained by considering three important factors: (1) enzyme synthesis under aerobic and anaerobic conditions, (2) location of enzymes, and (3) stability of enzymes in activated sludge. Based on the experimental results, it was established that, even though synthesis of the enzyme is to some extent affected depending on the anaerobic and aerobic incubation, it is the stable and the floc bound nature of these extra-cellular enzymes which results in no significant difference in enzyme activity under anaerobic and aerobic phase of a steady state operated single sludge anaerobic–aerobic system.

Internal energy-based competition between polyphosphate- and glycogen-accumulating bacteria in biological phosphorus removal reactors—Effect of PC feeding ratio

Abstract In acetate-fed, anaerobic-aerobic alternated bioreactors, the P C feeding ratio (wt/wt) was found to be a key factor influencing an “internal energy-based” competition between polyphosphate-accumulating bacteria (PAB) that mediate biological phosphorus removal and glycogen-accumulating bacteria (GAP) that do not. Both groups were previously known to use internally stored polyphosphate and glycogen, respectively, as energy sources for storing acetate as polyhydroxyalkanoate in the anaerobic stage, and to use the reserved material for growth in the aerobic stage. When excessive P was provided ( P C feeding ratio = 20 100 ), PAB could accumulate a high content of polyphosphate, and with a higher and faster acetate uptake ability, successfully out-competed GAB. In contrast, reduction of the P C ratio to 2/100 caused the depletion of the polyphosphate content in PAB, eventually leading to a replacement by GAB as the majority. Stable coexistence of both groups occurred under operation with a median P C ratio, because the stored energy pool of PAB was not enough for the complete uptake of acetate under anaerobic conditions. Thus, GAB could share what acetate remained, coexisting with PAB. These competitive outcomes were strongly supported by results on the anaerobic metabolism of acetate, and by microscopic observations in this study.

Glycogen accumulating population and its anaerobic substrate uptake in anaerobic-aerobic activated sludge without biological phosphorus removal

Abstract The presence of a glycogen accumulating population and its abilities of substrate uptake and storage in anaerobic-aerobic activated sludge fed with mainly acetate were investigated. Because a low phosphorus/carbon feeding ratio (2/100, wt/wt) was used to suppress the growth of polyphosphate-accumulating bacteria, the sludge exhibited no biological phosphorus removal activity. Still, under anaerobic conditions, acetate, propionate, butyrate, valerate, pyruvate, lactate, most key intermediates in the tricarboxylic acid cycle, and gluconate were taken up and stored as polyhydroxyalkanoate (PHA); and glucose, fructose, maltose, sucrose, trehalose, and raffinose as cellular glycogen and PHA. The energy and reducing equivalents required for the carbon uptake and storage were generated from the glycolysis of either cellular glycogen or a sugar taken up. Results of substrate uptake further suggested that the sludge preferred to utilize glucose instead of cellular glycogen as an energy source during acids uptake. Different morphological types of bacteria with deposits of cellular PHA granules after substrate uptake were observed as the majority in the sludge, suggesting that they could assimilate or possibly scavenge most of the dissolved substrate of the waste water and dominate in the deteriorated biological phosphorus removal processes.

Role of glycogen in acetate uptake and polyhydroxyalkanoate synthesis in anaerobic-aerobic activated sludge with a minimized polyphosphate content

Abstract The role of glycogen in the uptake of acetate in anaerobic-aerobic activated sludge without enhanced biological phosphorus removal were investigated. Although the polyphosphate content of the sludge was minimized by lowering the phosphorus feeding concentration, significant acetate uptake and accumulation of polyhydroxyalkanoates (PHAs) were observed in proportion to glycogen consumption under anaerobic conditions. The results of anaerobic inhibition studies, which showed suppressive effects on acetate uptake by a glycolysis inhibitor (iodoacetate) but not by a membrane ATPase inhibitor (N,N′-dicyclohexyl carbodiimide), supported an assumption that glycogen degradation through glycolysis supplies the required ATP and reducing power for PHA synthesis from acetate and consumed glycogen. Under subsequent aerobic conditions, the accumulated PHAs were depleted and the consumed glycogen recovered to the same level as that at the start of the anaerobic phase. Iodoacetate also inhibited the recovery of glycogen under aerobic conditions, suggesting that nearly 50% of the PHAs depleted was used for glycogen synthesis through reversed glycolysis.

Biological mechanism of acetate uptake mediated by carbohydrate consumption in excess phosphorus removal systems

The basic mechanism of substrate utilization has yet to be conclusively identified in the anaerobic-aerobic activated sludge process for enhanced phosphorus removal. Various researchers have reported PHB production and accumulation by the cell when fed with acetate under anaerobic conditions. Acetate is converted to acetyl-CoA, and the energy required for this conversion is supplied by the hydrolysis of intracellular polyphosphates. Synthesis of PHB from acetyl-CoA does not require ATP, but reducing power as NADH is essential. Some researchers have suggested that circulating some acetyl-CoA through the tri-carbonic acid (TCA) cycle would produce the requisite reducing power, but the TCA cycle is generally believed to accomplish complete oxidation of acetyl-CoA by transport of electrons to terminal electron acceptors like oxygen or nitrates. Therefore, investigation for alternate sources of NADH was undertaken. Four anaerobic batch experiments were conducted with anaerobic-aerobic acclimatized sludge fed with acetate. Samples were analyzed for COD and acetate uptake, P release, CO2 production and for intracellular carbohydrate, protein and PHB content. PHB was synthesized by the sludge corresponding to acetate and COD uptake, along with orthophosphate release. Protein synthesis was not observed but intracellular carbohydrates were consumed. From the results, it is concluded that intracellular carbohydrates are consumed via the Embden-Meyerhoff-Paranas pathway and converted to acetyl-CoA, which provides NADH required for PHB synthesis. As observed carbohydrate consumption is greater than theoretical requirement for PHB synthesis, the consequent excess NADH available makes the possibility of some acetyl-CoA being circulated through the TCA cycle very remote.

Modelling glycogen storage and denitrification capability of microorganisms in enhanced biological phosphate removal processes

Some important aspects in the modelling of enhanced biological phosphate removal processes which are not considered in IAWQ Activated Sludge Model No. 2 are discussed and three submodels are proposed. When denitrification by polyphosphate accumulating organisms (PAOs) is introduced to the model, anoxic uptake of soluble orthophosphate, which is sometimes observed in the real world can be expressed. Appropriate values of stoichiometric and kinetic coefficients remain to be determined. Glycogen storage capability is another essential character of PAOs. By incorporating biochemical information obtained so far, the processes relating to glycogen storage can be modelled. The model implies very delicate kinetic characteristics of PAOs. A group of organisms, which can cause deterioration of phosphate removal and has been referred to as “G bacterium”, is characterized as glycogen accumulating non-poly-P organisms (GAOs). A preliminary model for GAO metabolism is proposed.

Polychlorinated dibenzo-p-dioxins and dibenzofurans in sediment, soil, fish, shellfish and crab samples from Tokyo Bay area, Japan

Concentrations of tetra- to octa-chlorinated dibenzo-p-dioxins and dibenzofurans in samples collected in or near Tokyo Bay, Japan, with a densely inhabited catchment area, were congener-specifically determined and discussed. Analyzed in this study were samples of surface sediment covering the whole bay area, reference soil representing atmospheric impact, and fish, shellfish and crab commonly consumed as food. The range of concentrations were comparable to or higher than those in other parts of Japan. The origins of these compounds in the catchment area of the bay were investigated in terms of homolog and isomeric compositions in the sediment samples. Biota-sediment accumulation factors for benthic species declined as the degree of chlorination increased.