Nitrogen behavior during sludge ozonation: a long-term observation by pilot experiments.

Sludge ozonation is a promising technology for dealing with the increasing challenge of excess sludge treatment and disposal. However, nitrogen behavior during sludge ozonation and subsequent biological removal remains unclear. To clarify the feasibility and stability of oxidizing organic nitrogen (released during sludge ozonation) in the bioreactor (but not during ozonation), and the best operational conditions for sludge ozonation, nitrogen behavior was investigated by a long-term observation. The results showed that when inlet ozone concentration increased from 30 to 80 mg O3/L, and ozonation time decreased from 29 to 11 h, less soluble organic nitrogen was oxidized to ammonia (from 66.1 to 18.7% of soluble total nitrogen). This can reduce the operational costs of sludge ozonation. Furthermore, it is feasible to convert organic nitrogen to nitrate by biological processes because full nitrification was restored in three weeks after shock loading of organic nitrogen owing to the change in ozonation conditions. After combining sludge ozonation with the anaerobic/oxic process, the mass balance for nitrogen showed that nitrogen in the excess sludge decreased with increasing sludge reduction rate. The decreased nitrogen in the excess sludge was mainly transformed to nitrogen gas by denitrification, whereas nitrogen in the effluent did not increase noticeably

Prediction of calcium phosphate generation and behaviors of metals during phosphorus recovery using a modified thermodynamic model

In this study, behaviors of metals and their effects on phosphorus recovery by calcium phosphate were investigated by the laboratory and pilot experiments as well as by the modified thermodynamic model. Batch experimental results indicated that the efficiency of phosphorus recovery decreased with the increase in metal content and more than 80% phosphorus can be recovered with a Ca/P molar ratio of 3.0 and a pH of 9.0 for the supernatant of an anaerobic tank in the A/O process with the influent containing a high metal level. The mixture of amorphous calcium phosphate (ACP) and dicalcium phosphate dihydrate (DCPD) was assumed to be the precipitated product with an experimental time of 30 min. A modified thermodynamic model was developed using ACP and DCPD as the precipitated products, and the correction equations were incorporated to simulate the short-term precipitation of calcium phosphate based on the experimental results. From the perspective of maximizing both the efficiency of phosphorus recovery and the quality or purity of the recovered product, the simulation results showed that a pH of 9.0 and a Ca/P molar ratio of 3.0 were the optimized operational condition for phosphorus recovery by calcium phosphate when the influent metal content was at the level of actual municipal sewage. HIGHLIGHTS With a short reaction time, the main recovery product obtained was not HAP but DCPD and ACP.; Modified thermodynamic model to simulate the inhibition effect of metals and carbonate.; Co-precipitation of other metals either pH or molar Ca/P increased.; Optimized operational conditions: molar Ca/P = 3.0 and pH = 9.0.; More than 80% of P was recovered for the anaerobic supernatant containing metals under optimized conditions.

Modelling basin-scale distribution of fish occurrence probability for assessment of flow and habitat conditions in rivers

<div><p></p><p>Flow regimes play an important role in sustaining biodiversity in river ecosystems. However, the effects of flow regimes on riverine fish have not been clearly described. Therefore, we propose a new methodology to quantitatively link habitat conditions (such as flow indices and physical habitat conditions) to the occurrence probability (OP) of fish species. We developed a basin-scale fish distribution model by integrating the concept of habitat suitability assessment with a distributed hydrological model in order to estimate the OP of fish, with particular attention to flow regime. A generalized linear model was used to evaluate the relationship between the probabilities of fish occurrence and major environmental factors in river sections. A geomorphology-based hydrological model was adopted to simulate river discharge, which was used to calculate 10 flow indices. The occurrence probabilities of 50 fish species in the Sagami River in Japan were modelled. For the prediction accuracy, field survey results that included at least five observations of both the presence and the absence of each species were required to obtain relatively reliable prediction (accuracy > 60%). Using the developed model, important habitat conditions for each species were identified, which showed the importance of low-flow events for more than 10 species, including <i>Hypomesus nipponensis</i> and <i>Rhinogobius fluviatilis</i>. The model also confirmed the positive effects of natural flow and the negative effect of river-crossing structures, such as dams and weirs, on the OP of most species. The suggested approach enables us to evaluate and project the ecological consequences of water resource management policy. The results demonstrate the applicability of the fish distribution model to provide quantitative information on the flow required to maintain fish communities. </p><p></p><p><b>Editor</b> Z.W. Kundzewicz; <b>Guest editor</b> M. Acreman</p><p><b>Citation</b> Sui, P., Iwasaki, A., Saavedra, V.O.C., and Yoshimura, C., 2013. Modelling basin-scale distribution of fish occurrence probability for assessment of flow and habitat conditions in rivers. <i>Hydrological Sciences Journal</i>, 59 (3–4), 618–628.</p><p></p><p></p></div