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This study characterized the nitrification in a reclaimed water distribution system (DS) and the population size of ammonium-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) distributed along the flow course by a series of mixed reactors. The series reactors were initially adopted to study the DS of the reclaimed water and can be used as a feasible method for a similar investigation. This method was easy to model, control, and sample the biofilm formed in the DS. The series reactors were assembled in the Qingyuan Wastewater Treatment and Reuse Company of Xi'an, where the finished water was drawn directly. A mean of 85.0% NH4+-N removal was obtained during a continuous operation of 239 days, when the influent concentration of NH4+-N was 5.21 mg/L on average. The measurement of inorganic nitrogen and nitrification rate along the flow course indicated high activities of the nitrifiers that mainly existed at the initial segment of DS, whereas the pH value and dissolved oxygen concentration decreased. The analysis of the fluorescence in situ hybridization exhibited that the population of the nitrifiers was the highest (an average of 14.33-41.75%) of all bacteria in the biofilm. The dominating species of AOB were Nitrosospira, which presented an increasing trend along the DS course. The dominant shift of NOB, from Nitrobacter to Nitrospira, along the DS may be attributed to the variance of the nutrient condition. This shift confirmed the K/r hypothesis. [ABSTRACT FROM AUTHOR]

This study aims to investigate the diagnosis of acidification and efficient recovery of a laboratory-scale anaerobic sequencing batch reactor (ASBR) which treats synthetic glucose wastewater under mesophilic conditions (35°C). The diagnosis of the ASBR showed that acidification occurred on the seventh day after adding 20 mmol/L of sodium 2-bromoethanesulfonate into the reactor. A three-step recovery strategy was employed to recover the acidified reactor efficiently and to study its restoration process. Results indicated that the acidified ASBR can be revived in approximately 50 d. The specific methanogenic activities of the sludge, which were based on the substrate of acetate, propionate, and butyrate, were restored at 0.85, 0.67, and 0.51 (gCOD-CH4)/(gVSS∙d), respectively. The fluorescent observation images revealed large amounts of Methanosarcina-like and rod-shaped methanogens distributed in the sludge flocs after reactor restoration, thus ensuring that the fermentative, acidogenic, and methanogenic processes proceeded effectively in the anaerobic system. [ABSTRACT FROM AUTHOR]

The uncontrolled release of nutrients from waste sludge results in nitrogen and phosphorus overloading in wastewater treatment plants when supernatant is returned to the inlet. A controlled release, recovery and removal of nutrient from the waste sludge of a Biological Nutrient Removal system (BNR) are investigated. Results showed that the supernatant was of high mineral salt, high electrical conductivity and poor biodegradability, in addition to high nitrogen and phosphorus concentrations after the waste sludge was hydrolysed through sodium dodecyl sulphate addition. Subsequently, over 91.8% of phosphorus and 10.5% of nitrogen in the supernatants were extracted by the crystallization method under the conditions of 9.5 pH and 400 rpm. The precipitate was mainly struvite according to X-ray diffraction and morphological examination. A multistage anoxic–oxic Moving Bed Biofilm Reactor (MBBR) was then adopted to remove the residual carbon, nitrogen and phosphorus in the supernatant. The MBBR exhibited good performance in simultaneously removing carbon, nitrogen and phosphorus under a short aeration time, which accounted for 31.25% of a cycle. Fluorescencein situhybridization analysis demonstrated that nitrifiers presented mainly in floc, although higher extracellular polymeric substance content, especially DNA, appeared in the biofilm. Thus, a combination of hydrolysis and precipitation, followed by the MBBR, can complete the nutrient release from the waste sludge of a BNR system, recovers nutrients from the hydrolysed liquor and removes nutrients from leftovers effectively. [ABSTRACT FROM PUBLISHER]