Achieving and maintaining of short-cut nitrification in a cyclic activated sludge system.

A lab-scale Cyclic Activated Sludge Technology (CAST) system was operated more than 5 months to evaluate the effects of the operation mode on nitrogen removal performance and investigate a feasible method for achieving short-cut nitrification in the system. Results showed that nitrogen was removed by conventional biological nitrification and denitrification in traditional operation mode (fill/aeration 2 h, settle 1 h, decant 1 h), whereas short-cut nitrification and denitrification was the main nitrogen removal pathway in modified operation mode and the nitrogen removal performance was enhanced. Short-cut nitrification was successfully achieved in CAST system at 17 ± 1 °C by adjusting operation conditions and the average total nitrogen removal efficiency increased by 11.4% compared to traditional mode. It was assumed that low dissolved oxygen (<1.0 mg/L) limitation combined with free ammonia (0.28-0.34 mg/L) inhibition on nitrite-oxidizing bacteria caused nitrite accumulation in modified mode. During maintaining period of short-cut nitrification, preset aeration time enhanced ammonium-oxidizing bacteria dominance. It was also found that low DO could result in overgrowth of filamentous microorganisms and poor sludge settleability. The pH variation could provide effective information for controlling aeration duration in modified mode. However, no evident breakpoint appeared on pH and DO profiles in traditional mode.

Biological nitrogen removal in a step-feed CAST with real-time control treating municipal wastewater.

The performance of a 18 L step-feed cyclic activated sludge technology (CAST) combined with real-time control treating real municipal wastewater was evaluated. The operation strategies employed pH and oxidation reduction potential (ORP) as on-line control parameters, which can control the durations of oxic and anoxic phases flexibly. The obtained results showed that the studied process had achieved advanced and enhanced nitrogen removal by several phases of consecutive oxic/anoxic periods. Total nitrogen in effluent was lower than 2 mg/L and the average TN removal efficiency was higher than 98%, while only requiring small amount of external carbon source. Unexpected characteristic points in pH and ORP profiles denoting the depletion of nitrate were also observed during the last anoxic phase. Denitrification rate was found to be more dependent on the system temperature compared to nitrification rate. Moreover, a stable and efficient phosphorus removal rate above 90% was achieved by using step-feed strategy which enabled the influent carbon source to be fully used and the favourable condition for phosphorus releasing to be created during the anoxic phases.

Composition characterization and transformation mechanism of refractory dissolved organic matter from an ANAMMOX reactor fed with mature landfill leachate.

This study applied combined spectroscopy techniques to assess rDOM compositional characteristic and investigated its transformation mechanisms during the treatment of mature landfill leachate by ANAMMOX process. A novel rDOM metabolism mechanism was proposed in this study for the first time. A stable, high nitrogen removal rate of 5.95 kg N/m3/day and a rDOM conversion efficiency of 51% were achieved in ANAMMOX reactor (AR). In additionally, the initial rDOM removal was closely related to sludge adsorption, with the adsorption force mainly originating from electrostatic interaction and hydrophobicity. As the operating time increased, the removal mechanism of rDOM in the AR changed from adsorption to adsorption-biodegradation and finally stabilized. Furthermore, Anaerolineaceae, associated with the hydrophobic reaction, were the primary degraders for the rDOM and Candidatus Kuenenia dominated the nitrogen consumption. rDOM removal efficiency was suggested to be increased by a moderate enhancement of Anaerolineaceae content in the AR.

Does Puccinelia tenuiflora have the ability of salt exudation?

The leaves surface of Puccinelia tenuiflora seedling under stress of different concentration of Na(2)CO(3) was observed with scanning electron microscopy and X-ray electron probe micro analyzer. All the results indicated that varied salts crystalline distributing in stomatal apparatus on P. tenuiflora leaves surface could be observed by means of frozen-dried sampling. In the case of no stress, these leaves had many kinds of sediments such as Na, K, Ca, Mg, Zn, Cu, Cl, P, S, Si on their surface. When there was stress of Na(2)CO(3), the percentage content of each sediment would have an non-linear relationship to stress. As the concentration of Na(2)CO(3) increased, the percentage contents of Na, Cu, Zn, P, S generally decreased while that of K, Ca, Mg, Si generally increased. The ratio of K/Na also changed the same way as the later. From these results, we concluded, under stress of alkali and salts, P. tenuiflora leaves could exude salts through their stomata or together with wax secretion and these ways might participate many regulation process of P. tenuiflora leaves cells, for example in ion balancing, osmosis regulating and water metabolizing.

Distribution and influence factors of Anammox bacteria in sewage treatment systems / 生物工程学报

Nitrogen removal techniques based on Anammox process are developing rapidly these years. The distribution and diversity of Anammox have become important research directions. A variety of Anammox have been detected till now, of which only Kuenenia and Brocadia are often detected in wastewater treatment systems. In addition, in a single niche there is only one type of Anammox bacteria. However, the distribution mechanism and transformation of Anammox bacteria in different niches are still ambiguous. Therefore, the distribution of Anammox in various conditions was summarized and analyzed in this article. And the key factors influencing the distribution of Anammox were concluded, including substrate concentration and the specific growth rate, sludge properties and microbial niche, the joint action and influence of multiple factors. The engineering significance research on the distribution and influencing factors of Anammox bacteria in the sewage system and proposed research prospects were expounded.

Feedforward-feedback control of dissolved oxygen concentration in a predenitrification system.

As the largest single energy-consuming component in most biological wastewater treatment systems, aeration control is of great interest from the point of view of saving energy and improving wastewater treatment plant efficiency. In this paper, three different strategies, including conventional constant dissolved oxygen (DO) set-point control, cascade DO set-point control, and feedforward-feedback DO set-point control were evaluated using the denitrification layout of the IWA simulation benchmark. Simulation studies showed that the feedforward-feedback DO set-point control strategy was better than the other control strategies at meeting the effluent standards and reducing operational costs. The control strategy works primarily by feedforward control based on an ammonium sensor located at the head of the aerobic process. It has an important advantage over effluent measurements in that there is no (or only a very short) time delay for information; feedforward control was combined with slow feedback control to compensate for model approximations. The feedforward-feedback DO control was implemented in a lab-scale wastewater treatment plant for a period of 60 days. Compared to operation with constant DO concentration, the required airflow could be reduced by up to 8-15% by employing the feedforward-feedback DO-control strategy, and the effluent ammonia concentration could be reduced by up to 15-25%. This control strategy can be expected to be accepted by the operating personnel in wastewater treatment plants.