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ABSTRACTThe formation of stable surface foams, which is associated with characteristic filamentous microorganisms, is a worldwide phenomenon on activated‐sludge plants. In excess, it can create operating difficulties and may cause a violation of effluent consent conditions due to high concentrations of suspended solids and solids‐related biochemical oxygen demand. Despite its universal occurrence, the reasons for foaming are not clearly understood, and control measures tend to be non‐specific, hit‐or‐miss strategies.This paper presents an operator's perspective on (a) the current knowledge of foam‐forming microorganisms, and (b) methods to control them.

AbstractDuring the last thirty years, attempts have been made to increase the rate of treatment of wastewater in compact activated‐sludge systems whilst ensuring (a) an adequate supply of dissolved oxygen, (b) good settleability of activated sludge, and (c) consistently high‐quality effluents.This paper describes two successful systems, i.e. oxygenated activated sludge and the deep‐shaft process, which are used to intensify the rate of treatment in relatively compact aeration tanks. Data are presented of full‐scale oxygen activated‐sludge systems, including Vitox and Unox, together with information on the operation and performance of the deep‐shaft process.

ABSTRACTActivated SLUDGE SEWAGE treatment processes are often inadequate to comply with effluent criteria as promulgated in anti‐pollution legislation. Ozonation was studied as a means of improving nutrient removal activated sludge processes without the salinity and other disadvantages of the often used polyvalent metal salt addition. Direct ozonation into the aeration basin of a 150 I/d Phoredox (modified Bardenpho) system led to improved removal of organic substances. Nitrification was improved while phosphate removal was not adversely affected. Beneficial biological activity in the activated sludge was enhanced. The trihalomethane formation potential was reduced. Pollutional loads could be lessened, while an effluent with increased reuse potential was produced.

ABSTRACTThe predominant filamentous bacteria which are found in bulking activated sludge in the UK have been assessed from a microscopic analysis of samples taken over a three‐year period. There were major differences in the floc biology of samples received from plants treating predominantly domestic wastewaters and those of industrial origin. Most samples (84%) of domestic origin were dominated by two filament types: Microthrix parvicella was the dominant filament in 63% of the samples and Type 021N dominated in 21% of the samples. Nostocoida limicola and Sphaerotilus natans dominated in the remaining 16% of samples. The samples of industrial origin showed much greater filament diversity, with eight filament types routinely observed in high numbers. Type 021N was the most prevalent and M. parvicella was not observed in the industrial samples. Many domestic samples from sequencing batch reactors were dominated by M. parvicella. Based upon knowledge of the predominant filament type from microscopic examination. it was possible to identify the likely causes for their proliferation and suggest long‐term solutions to achieve their eradication.

Kinetics of iron reduction, formation of vivianite and the microbial community in activated sludge from two sewage treatment plants (STPs) with low (STP Leeuwarden, applying enhanced biological phosphate removal, EBPR) and high (STP Cologne, applying chemical phosphate removal, CPR) iron dosing were studied in anaerobic batch experiments. The iron reduction rate in CPR sludge (2.99 mg-Fe g VS-1 h-1) was 3-times higher compared to EBPR sludge (1.02 mg-Fe g VS-1 h-1) which is probably caused by its 3-times higher iron content. Accordingly, first order rate constants in both sludges are comparable (0.06 ± 0.001 h-1 in EBPR vs 0.05 ± 0.007 h-1 in CPR sludge), thus potential rates in both sludges are comparable. The measured Fe(III) reduction rates suggest that all iron in STP Leeuwarden and STP Cologne can be turned over within 15 h and 44 h respectively. Mössbauer spectroscopy and X-ray diffraction (XRD) indicated vivianite formation within 24 h in both sludges. After 24 h, 53% and 34% of all iron were bound in vivianite in the EBPR and CPR sludge respectively. Next generation sequencing (NGS) showed that the microbial community in the CPR sludge comprised more genera with iron-oxidizing and iron-reducing bacteria. Iron reduction and vivianite formation commence once activated sludge is exposed to oxygen free conditions. Our study reveals that the biogeochemistry of iron in STPs is very dynamic. By understanding the interactions between iron and phosphate crucial processes in modern sewage treatment, such as chemical phosphate removal or phosphate recovery from sewage sludge, can be optimized. ; This work was performed in the TTIW-cooperation framework of Wetsus, European Centre Of Excellence For Sustainable Water Technology (www.wetsus.nl). Wetsus is funded by the Dutch Ministry of Economic Affairs, the European Union Regional Development Fund, the Province of Fryslân, the City of Leeuwarden and the EZ/Kompas program of the "SamenwerkingsverbandNoord-Nederland". We thank the participants of the research theme "Phosphate Recovery" for their financial support and helpful discussions.