Water Science & Technology

Published by IWA Publishing
Online ISSN: 0273-1223
Publications
Article
The introduction of a national standard on odour measurement presents a new challenge for Australian olfactometry laboratories to meet tough new instrumental performance and panellist performance criteria. It also raises issues for end users of olfactometry results. For examples regulatory authorities may need to review the current status of odour regulations and guidelines. The paper reviews major issues pertaining to four components in odour impact assessment: measurement of odour, sampling techniques, air dispersion modelling, and the development of assessment criteria. The paper identifies and discusses the resolution of issues that could have a significant effect on the outcomes of odour impact assessment. It is hoped that the paper will provide a useful guide for industry and environmental protection authorities in the further development of an odour impact assessment procedure.
 
Article
Large amounts of produced water are generated during oil and gas production. Produced water, as it is known in the oil industry, is briny fluid trapped in the rock of oil reservoirs. The objective of this study was to test produced waters from a Montana USA oilfield using a mobile station to design a plant to cost efficiently treat the produced water for agricultural irrigation. We used combined physical and chemical treatment of produced water in order to comply with reuse and discharge limits. This mobile station consists of three stages: pretreatments, membrane filtration and post treatment. Two spiral-wound membrane units were employed and the rejections of various constituents were examined. The performance of two membranes, 20 kDa weight cut-off (MWCO) ultrafiltration and a polyamide-composite reverse osmosis membrane was investigated. The mobile station effectively decreased conductivity by 98%, COD by 100% and the SAR by 2.15 mgeqv(0.5) in the produced water tested in this study. Cost analysis showed that the treatment cost of produced water is less expensive than to dispose of it by injection and this treated water may be of great value in water-poor regions. We can conclude that the mobile station provided a viable and cost-effective result to beneficial use of produced water.
 
Article
Worldwide the water management sector is about to review the design standards for water systems, as expected climate changes may possibly increase the frequency of flood events. This paper reviews new flood standards for surface water systems in The Netherlands, also presenting a cost-benefit analysis. Flood standards were formulated after several serious incidents in 1998 and 2001 to inform residents about the level of protection that they may expect to receive. At this moment all water boards are about to evaluate their water systems using these standards. The cost-benefit approach has been applied to determine whether the necessary measures to comply with such standards were cost-effective. We found that the standards make too much a simplification of the variety of water systems, and lead to costly measures without being beneficial while many small-scale floods in The Netherlands do not cause any significant damage. A better starting point to anticipate on climate change is to prevent damage, instead of the prevention of flooding.
 
Article
The Arlington County Wastewater Pollution Control Plant (ACWPCP) is located in the southern part of Arlington County, Virginia, USA and discharges to the Potomac River via the Four Mile Run. The ACWPCP was originally constructed in 1937. In 2001, Arlington County, Virginia (USA) committed to expanding their 113,500 m³/d, (300,000 pe) secondary treatment plant to a 151,400 m³/d (400,000 pe) to achieve effluent total nitrogen (TN) to <3 mg/l and total phosphorus (TP) < 0.18 mg/l. Key to this conversion was the implementation of deep bed denitrification filters to simultaneously achieve both low effluent TN and TP concentrations. A challenge with implementing this technology is maintaining a health denitrifying biomass within the denitrification filters while reducing an essential nutrient, phosphorus, to very low concentrations. This paper will review the steps from concept to the first year of operation, including pilot and full-scale operating data and the capital cost for the denitrification filters.
 
Article
The treatment of high-saline wastewater from some salt-end markets including agro-food industry is a serious problem yet to be solved in some coastal cities. The conventional physical-chemical techniques are energy-consuming and their startup and running costs are still high. Biological methods using salt-tolerant bacterial strains for the treatment of hypersaline wastewater provide one possible solution. In this study, one salt-tolerant mutant named YWL-01 was screened out by sewage treatment and proved to be a genetically stable salt-tolerant strain for saline wastewater treatment. First, combined mutagenesis was done on an isolated sewage treatment strain Bacillus Y for the screening of salt tolerance, and 11 mutants were obtained after subculture for many times. Then, a secondary screening test was performed for COD (chemical oxygen demand) and TOC (total organic carbon) removal efficiency analyses. At last, the best mutant YWL-01 with increased capacity to treat saline wastewater was chosen for use. RAPD (Random Amplified Polymorphic DNA) analysis of genetic stability on the mutant YWL-01 showed that it is a hereditary mutant for the treatment of high-saline wastewater.
 
Article
Over a period of 6 months, pilot plant investigations were carried out with the purpose of bulking sludge control with different aerobic selectors. The wastewater was dominated by industrial dischargers, containing volatile fatty acids up to 450 mg/l. With complete-mix-selectors it was not possible to achieve a stable SVI below 150 ml/g. The bulking sludge could only be controlled with a sectionalized selector (HRT 5-8 minutes per section). The SVI decreased to values below 100 ml/g. Shock-loads and increased VFA-concentrations (by dosing NaC2H3OO) did not cause filamentous growth.
 
Article
The presence of industrial effluent in the wastewater incoming to municipal activated sludge treatment plants sometimes causes bulking events. In order to control one of these events a strategy of bacterial selection was applied with an anoxic selector before the main oxidation basin utilising the screw pumps basin. The result of this work confirms what is reported in the literature about the possibility to utilize a metabolic control of some filamentous forms (particularly Type 021 N) with high organic load. The remedial action could be realized using already existing facilities, without any additional costs.
 
Article
Chlorinated aliphatic hydrocarbons are widely used as solvents and as intermediates in chemical synthesis, so they can be found in industrial wastewaters and released to the environment where they became a serious health risk due to their toxic properties and high chemical stability. Most of these compounds are xenobiotic and recalcitrant to biodegradation. In this article we report the effect of different co-substrates in the 1,1,1,2-tetrachloroethane (1,1,1,2-TeCA) degradation by anaerobic granular sludge, and its degradative pathway. Our results show that this compound is easy and rapidly biodegradable under methanogenic conditions, even in the absence of external electron donors. 1,1,1,2-TeCA is equimolecularly degraded to 1,1-dichloroethene (1,1-DCE) by reductive dichloroelimination. 1,1-DCE is only completely biodegraded in the presence of lactic acid as co-substrate. Although 1,1,1,2-TeCA can be apparently removed by autoclaved granular sludge, the compound is not transformed but retained inside the granules. The primary biodegradation of 1,1,1,2-TeCE to 1,1-DCE is a biotic process mediated by anaerobic bacteria.
 
Article
The aim was to investigate the inhibitory effect of the xenobiotic 1,2-DCA on nitrification during the cometabolic degradation in a packed bed nitrifying biofilm reactor. This xenobiotic inhibited primarily the conversion of NH4-N to hydroxylamine by binding to the AMO enzyme. It had no inhibitory effect on the conversion of nitrite to nitrate. At high NH4-N loadings, the presence of 1,2-DCA inhibited NH4-N utilisation more severely than at low loadings. The suppressing effect of 1,2-DCA on NH4-N utilisation was found to be reversible due to the ability of cells to recover from inhibition. These results could fill a gap in the literature about the potential use of nitrifying biofilm systems for cometabolic treatment of 1,2-DCA and could be useful in the design of engineered 1,2-DCA remediation/treatment in biofilm reactors.
 
Article
Co-metabolic biodegradation of cis-dichloroethylene (cis-DCE) was investigated in a bench-scale fixed-film bioreactor inoculated with a mixed culture of methane oxidising bacteria. The aim of this work was to identify factors that affect the cis-DCE biodegradation. It was observed that the presence of methane was necessary to enhance the biodegradation of cis-DCE, but an excess of methane inhibited the cis-DCE removal. cis-DCE did not inhibit the methane biodegradation at concentrations up to 300 microg/L. Maximum cis-DCE removal was observed with a methane bulk concentration ranging from 0.2 to 0.7 mg/L. It was found that the activity of the biofilm was located in the upper 100 microm of the biofilm. On the basis of this study it is concluded that careful control of the oxygen and methane concentrations as well as of the biofilm thickness is necessary in order to optimise the biodegradation of cis-DCE in fixed film bioreactors.
 
1,2-DCA removal performance of UASB reactor inoculated with methanogenic sludge 
Article
Granular methanogenic sludge was able to dechlorinate 1,2-dichloroethane (1,2-DCA) to ethene in UASB reactors. Ethanol served as the sole carbon and energy source. The average dechlorination rate measured on the basis of ethene production varied between 1.7 and 2.1 micromol 1,2-DCA/(h.gVSS) (46.7 and 57.4 mg/L.d). In order to elucidate the microbial origin of this bioconversion, enrichment cultures of the methanogenic sludge were prepared with different carbon and electron sources: pyruvate, lactate, H2/CO2, ethanol and formate. Dithiothreitol (DTT) was the strong reductant in order to increase the negative redox potential in the media. A homo-acetogenic gram-positive strain could be isolated in the presence of formate. 16S rRNA of the isolated strain showed that the bacterium was closely related (99.7%) to Acetobacterium wieringae. The strain also grew on pyruvate, lactate, H2/CO2 and ethanol, although dechlorination rates of 1,2-DCA were at least 5 times higher when formate was the (only) electron source. Average conversion rates reached 3 micromol/(h.g(dry cells)) and appeared t relate to cometabolic biocatalysis on the corrinoid centers of the homo-acetogenic strain. Some perspectives of anaerobic in situ bioremediation of groundwater polluted with chloroethanes are presented.
 
Article
This work aims at obtaining experimental data on ozonation of 1,2-dihydroxybenzene (DHB) in the presence of activated carbon, with a view to assessing possible changes in its surface chemical structure and adsorption capacity. Experiments were conducted in a 0.5 L reactor, loaded with 2 g Filtrasorb 400 granular activated carbon, and 1-5 mM DHB aqueous solution at pH 2-8. Ozone gas was generated with an Ozocav generator, and fed into the reactor for a given exposure time, in the range 0.5-240 min, at 25 degrees C and 1 atm. After each run, liquid and activated carbon samples were taken for chemical assays. Soluble organic groups present on the active carbon surface were desorbed and analysed by GC-MS and HPLC. Activated carbon chemical surface properties were analysed using TPD, FT-IR, and XPS techniques. Reactions between ozone and adsorbed DHB were shown to be fast, leading to formation of C-6, C-4 and C-2 by-products. Oxygenated surface groups, particularly, COOH and C = O, increased as a result of ozonation.
 
Article
The presence of toxic aromatic organic compounds in industrial wastewater affects the efficiency of conventional biological treatment. The oxidizing power of ozone represents an interesting pretreatment to reduce toxicity and increase biodegradability. At low pH, ozone is known to attack electron-rich structures by direct electrophilic reactions which open aromatic rings, and generate smaller oxidized compounds. This paper reports experimental results on kinetic and toxicity aspects of ozone direct reactions with 1,2-dihydrobenzene. This toxic compound is frequently found in cellulose bleaching effluents. Although the reaction pathway is rather complex, 4-carbon compounds, such as maleic acid, are readily formed during the first stage of ozonation. These 4-carbon compounds are further oxidized to form smaller molecules (mostly 2-carbon, such as oxalic acid). The apparent kinetics of 1,2-dihydrobenzene follows a second order law, with a rate constant around 0.36 (dm3 mmol-1s-1), at pH 2 and 20 degrees C. Results show that the BOD:COD ratio increase five-fold as ozonation progresses. Furthermore, the mutagenicity of 1,2-dihydrobenzene totally disappears as the aromatic compound is destroyed by ozonation.
 
Formation and transformation of c-DCE epoxide during transformation of c-DCE by resting cell suspensions of the butane utilizers (4.3-mg TSS used) 
Article
Aerobic cometabolism of cis-1,2-dichloroethylene (c-DCE) by a butane-grown mixed culture was evaluated in batch kinetic tests. The transformation of c-DCE resulted in the coincident generation of c-DCE epoxide. Chloride release studies showed approximately 75% oxidative dechlorination of c-DCE. Mass spectrometry confirmed the presence of a compound with mass-to-charge-fragment ratios of 112, 83, 48, and 35. These values are in agreement with the spectra of chemically synthesized c-DCE epoxide. The transformation of c-DCE required O2, was inhibited by butane and was inactivated by acetylene (a known monooxygenase inactivator), indicating that a butane monooxygenase enzyme was likely involved in the transformation of c-DCE. This study showed c-DCE epoxide was biologically transformed, likely by a butane monooxygenase enzyme. c-DCE epoxide transformation was inhibited by both acetylene and c-DCE indicating a monooxygenase enzyme was involved. The epoxide transformation was also stopped when mercuric chloride (HgCl2) was added as a biological inhibitor, further support a biological transformation. To our knowledge this is the first report of the biological transform c-DCE epoxide by a butane-grown culture.
 
Effect of various substrate mixtures on biodegradation of VC during the first 76 days of microcosm operation. Results are shown for one serum bottle within each treatment; duplicate bottles behaved very similarly 
Article
Intrinsic biodegradation of trichloroethene and 1,1,1-trichloroethane in groundwater at a Superfund site in California has been observed. An anaerobic zone exists in the area closest to the source location, yielding the expected complement of reductive dechlorination daughter products, including cis-1,2-dichloroethene (cis-DCE) and vinyl chloride (VC). Significant levels of methane and ethene were also generated in the anaerobic zone. The groundwater returns to aerobic conditions downgradient of the source, with methane, ethene, VC, and several other compounds still present. Attenuation of VC in the aerobic zone suggests that it is being biodegraded. In this study microcosms were used to evaluate the role of methane and ethene as primary substrates for aerobic biodegradation of VC. Biodegradation of VC was fastest in the bottles containing ethene, with 40 mumol of VC consumed over a 150 day period, compared to approximately 15-20 mumol with methane or a mixture of methane and ethene. VC did not noticeably inhibit ethene biodegradation but did slow the rate of methane use. Methane inhibited ethene metabolism, which apparently caused a reduction in VC biodegradation when methane was present with ethene. These results suggest that ethene plays an important role during in situ natural attenuation of VC under aerobic conditions. Microcosms were also set up with VC alone. Following a 75 day lag period. VC consumption began and subsequent additions were consumed without a lag, suggesting the presence of organisms capable of using VC as a growth substrate. After providing VC alone for nearly 400 days, aliquots of the enrichment culture were used to evaluate its ability to biodegrade cis- and trans-DCE. Both compounds were readily consumed, although addition of VC as the primary substrate was needed to sustain biodegradation of repeated additions. This result suggests that organisms capable of using VC as a sole substrate may play an active role in aerobic natural attenuation of DCEs.
 
Article
Electrochemical degradation of 2,5-dichloro-1,4-phenylenediamine (DP) in aqueous solution by anodic oxidation was investigated. Linear sweep voltammograms and cyclic voltammograms were studied. The influence of operating parameters on electrochemical oxidation of DP was studied as a function of the current density, initial pH, and initial concentration of DP. The degradation kinetics analysis indicated that the electrochemical degradation of DP followed a first-order reaction. The degradation intermediates during electrochemical oxidation were analyzed by UV-vis spectrophotometer, ionic chromatograph (IC), and gas chromatography/mass spectrometry (GC/MS). The combustion efficiency of DP at the anode was also estimated. The electrochemical oxidation of DP resulted in the release of NH4(+) and Cl(-). Based on these results, a degradation mechanism for electrochemical degradation of DP by anodic oxidation was proposed.
 
Article
1,4-Dioxane is a probable human carcinogenic and refractory substance that is widely detected in aquatic environments. Traditional wastewater treatment processes, including activated sludge, cannot remove 1,4-dioxane. Removing 1,4-dioxane with a reaction kinetic constant of 0.32 L/(mol·s) by using ozone, a strong oxidant, is difficult. However, under alkaline environment, ozone generates a hydroxyl radical (•OH) that exhibits strong oxidative potential. Thus, the ozonation of 1,4-dioxane in water under different pH conditions was investigated in this study. In neutral solution, with an inlet ozone feed rate of 0.19 mmol/(L·min), the removal efficiency of 1,4-dioxane was 7.6% at 0.5 h, whereas that in alkaline solution was higher (16.3-94.5%) within a pH range of 9-12. However, the removal efficiency of dissolved organic carbon was considerably lower than that of 1,4-dioxane. This result indicates that several persistent intermediates were generated during 1,4-dioxane ozonation. The pseudo first-order reaction further depicted the reaction of 1,4-dioxane. The obvious kinetic constants (kobs) at pH 9, 10, 11 and 12 were 0.94, 2.41, 24.88 and 2610 L/(mol·s), respectively. Scavenger experiments on radical species indicated that •OH played a key role in removing 1,4-dioxane during ozonation under alkaline condition.
 
Article
The solvent stabilizer 1,4-dioxane could have harmful effects on an ecosystem. The discharge limit of 1,4-dioxane in a body of water will be regulated at 5 mg/L in Republic of Korea. Thus, the currently operating activated sludge used in the manufacture of polyester should be properly treated to meet the regulations. Accordingly, the removal rate of 1,4-dioxane and its microbial properties was assessed at K, H and T corporations. The highest removal efficiencies were recorded at H. However, the concentration of 1,4-dioxane in the effluent of T exceeded the criterion. In addition, a microbial degradation test was conducted on 100 mg/L of 1,4-dioxane inoculated with the activated sludge from each of the three corporations. After 7 days, the 1,4-dioxane was completely removed with the H sludge and efficiencies were 67% in the T sludge and 52% in the K sludge. These results confirm that the biodegradability of 1,4-dioxane may vary in relation to the microbial properties. The microbial diversity of activated sludge of each company was therefore investigated by 16S rDNA cloning methods. In conclusion, the activated sludge of H is the most effective for the biodegradation of 1,4-dioxane. This fact is of significant concern for the industrial sector.
 
Article
This paper describes the ozone oxidation kinetics of 1-naphthalene (1 NS), 1,5-naphthalene (1,5NDS), and 3-nitrobenzene (3NBS) sulphonic acid. The presence of hydroxyl radicals and their effect on the overall rate of reaction was studied. Second order kinetic constants of direct reactions were estimated at around 252 M(-1) s(-1), 41 M(-1) s(-1) and 22 M(-1) s(-1), for 1NS, 1,5NDS, and 3NBS sulphonic acids, respectively. At pH 3, the indirect reaction accounted for 2%, 15% and 4% of total primary oxidation of 1 NS, 1,5NBS, and 3NBS sulphonic acids, respectively. At pH 9, indirect reaction contribution increased to 73%, 84% and 48%, respectively. C4 compounds (maleic and fumaric acids), C2 (oxalic), C1 (formic) and sulphate were identified as oxidation by-products in all cases. TOC slowly decreased throughout ozonation, reaching around 40-60% and 60-70% reduction over 90 minutes at pH 7 and 3, respectively.
 
Article
The paper describes the method that led to the design of the 1,500 Ml/day dissolved air flotation (DAF) water treatment plant for Boston's water supply. In particular, the topics of flocculation techniques, floated solids removal and DAF recycle as they relate to very large capacity plant design are covered in detail. The use of mathematical models, including computational fluid dynamics (CFD) software, to refine the design is described.
 
Article
During a six-year period the Austrian Benchmarking System was developed. The main objectives of this benchmarking system are the development of process indicators, identification of best performance and determination of cost reduction potentials. Since 2004 this system is operated via an internet platform and automated to a large extent. Every year twenty to thirty treatment plants use the web-based access to this benchmarking platform. The benchmarking procedure comprises data acquisition, data evaluation including reporting and organised exchange of experience for the treatment plant managers. The process benchmarking method links the real costs with four defined main processes and two support processes. For wastewater treatment plants with a design capacity >100,000 PE these processes are further split up into sub-processes. For each (sub-) process the operating costs are attributed to six cost elements. The specific total yearly costs and the yearly operating costs of all (sub-)processes are related to the measured mean yearly pollution load of the plant expressed in population equivalents (PE(110): 110 gCOD/d corresponding to 60 g BOD(5)/d)). The specific capital costs are related to the design capacity (PE). The paper shows the benchmarking results of 6 Austrian plants with a design capacity >100,000 PE representing approximately 30% of the Austrian municipal wastewater treatment plant capacity.
 
Pilot reactor utilized for 4CP degradation 
Article
The evolution of degradsation capacity and in the viability of Pseudomonas aeruginosa ATCC 10145 acclimated to 25 mg4CP/L degradation and, later, exposed to starvation periods of 24, 48, 72, 96, 132 and 156 hours was studied. Degradation rate heterotrophic plate count and cell cytometry were used to evaluate the starvation influence. Results demonstrated that the exposition of P. aeruginosa to starvation produces a decrease in the viability and activity for the degradation of 4-chlorophenol.
 
Article
We developed a rapid and simple method for rRNA-based quantitative detection of a specific group of microorganisms in complex ecosystems. The method relies on the sequence-specific scission of 16S rRNA with ribonuclease H (RNase H) and oligonucleotides that specifically hybridize with targeted rRNA molecules. RNAs from a complex community were first mixed with an oligonucleotide and were subsequently digested with RNase H to achieve sequence-dependent rRNA cleavage at the hybridization site. For the quantitative detection of targeted rRNAs, the resulting RNA fragment patterns were analyzed by gel-electrophoresis, which separated and quantified cleaved and intact rRNA fragments. This method enabled the quantitative detection of microbes in a complex microbial community by a relatively simple and fast experimental procedure. We then applied the cleavage method to actual anaerobic microbial communities such as digested sewage sludge and UASB sludges. The results demonstrated that the present method was fully applicable to anaerobic digestor ecosystems containing complex anaerobic microorganisms.
 
Article
As part of the EU project "Bacteriophages in Bathing Waters" (January 1996-June 1999) research was carried out to optimise the method for detection and enumeration of somatic coliphages in water as described in ISO/CD 10705-2 of August 1995. It was concluded that this draft ISO standard needed to be amended in certain aspects. For determining the viable count of the host culture WG5 Escherichia coli, a membrane filtration technique should be used instead of spread plate technique as the latter gives lower and less reproducible results. A freshly prepared inoculum culture of host strain WG5 should be used instead of a frozen inoculum culture as freezing of the inoculum culture is found to negatively influence the phage counts. The double agar layer method (DAL) is preferred to the single agar layer method (SAL) for performing the phage analysis as the DAL method gives higher phage counts than the SAL method.
 
| Effect of different Cu(II) concentrations on (A) specific growth rate and (B) specific glucose consumption in relation to the biomass expressed as g glucose g biomass 2 1 . (- - - -) controlled aeration (— ) without aeration. 
| Intracellular copper concentration of R. mucilaginosa RCL-11 cultures with controlled (- - - -) and without (——) aeration. Specific bioaccumulation, q (mg Cu g biomass 2 1 ), at different initial Cu(II) concentrations: (A) 0.1; (B) 0.2; (C) 0.5 mM and (D) 1 mM Cu(II). ( ) controlled and ( ) without aeration. 
| (A) Total SOD activity in cell free extracts of R. mucilaginosa RCL-11 with ( ) and without ( ) controlled aeration. (B) Activity staining for SOD in cell free extracts (fermentor grown cell) in 10% native PAGE. Cell extracts were incubated in the presence of Cu(II) and SOD standards. lane 1, control cells; lane 2, cells incubated with 0.1 mM Cu(II); lane 3, cells incubated with 0.2 mM Cu(II); lane 4, cells incubated with 0.5 mM Cu(II); lane 5, cells incubated with 1 mM Cu(II); lane 6, bovine CuZnSOD and lane 7, E. coli MnSOD. (C) CAT activity in cell free extracts of R. mucilaginosa RCL-11 with ( ) and without ( ) controlled aeration. 
Article
The present study explored the ability of the yeast Rhodotorula mucilaginosa RCL-11 to adapt to increasing Cu(II) concentrations, measuring oxidative stress through superoxide dismutase and catalase activity in two parallel sequential batch assays. One assay was performed in Erlenmeyer flasks without aeration and a second in a fermentor in which the dissolved oxygen was maintained at 30% saturation. Both assays were carried out by increasing Cu(II) concentrations in five sequential steps: 0; 0.1; 0.2; 0.5 and 1 mM. Each assay was incubated at 30 degrees C, 250 rpm and pH 5.5. While growth parameters of R. mucilaginosa RCL-11 decreased 90-95% with increasing Cu(II) concentration in the culture medium, the oxidative stress level increased from 30 to 55% in both assays. Cells grown under controlled oxygen conditions showed 30% more copper bioaccumulation and 10% glucose consumption when compared with cells grown without aeration. SOD activity was higher under controlled than without aeration, whereas CAT activity was similar under both test conditions. Cu(II) bioaccumulation by R. mucilaginosa RCL-11 and a possible increase in this capacity by adaptation of the strain under controlled aeration represent a potential valuable tool for treatment of effluents or water bioremediation with high copper contents.
 
Article
There is a recognised need for methods that permit rapid estimation of the sanitary quality of water e.g. during raw water monitoring and emergencies involving water treatment failure or main breaks in a distribution network. In this study, two models for predicting the level of faecal contamination of water were studied. The first format, based on measurement of beta-galactosidase activity by the automated Colifast analyser, detected faecal contamination of high levels, corresponding to > 15 thermotolerant coliforms (FC)/5 mL, in 1-3 h, in a format that allowed for semi-quantification of results. By setting up a cut-off level, the system could be used as an operational tool identifying random increases in faecal contamination during routine raw water monitoring. A second Presence-Absence format was dependent upon the growth of low levels of FC with subsequent detection in the Colifast analyser. 95% of water samples containing 1-15 FC/sample volume showed positive detection after 11 h.
 
Article
This research was carried out on a full-scale pure oxygen thermophilic plant, operated and monitored throughout a period of 11 years. The plant treats 60,000 t y(-1) (year 2013) of high-strength industrial wastewaters deriving mainly from pharmaceuticals and detergents production and landfill leachate. Three different plant configurations were consecutively adopted: (1) biological reactor + final clarifier and sludge recirculation (2002-2005); (2) biological reactor + ultrafiltration: membrane biological reactor (MBR) (2006); and (3) MBR + nanofiltration (since 2007). Progressive plant upgrading yielded a performance improvement chemical oxygen demand (COD) removal efficiency was enhanced by 17% and 12% after the first and second plant modification, respectively. Moreover, COD abatement efficiency exhibited a greater stability, notwithstanding high variability of the influent load. In addition, the following relevant outcomes appeared from the plant monitoring (present configuration): up to 96% removal of nitrate and nitrite, due to denitrification; low-specific biomass production (0.092 kgVSS kgCODremoved(-1)), and biological treatability of residual COD under mesophilic conditions (BOD5/COD ratio = 0.25-0.50), thus showing the complementarity of the two biological processes.
 
Article
Five orange pigmented filamentous strains of Eikelboom's type 1851 were isolated from bulking activated sludge, and were examined for their phylogenetic lineage, morphology, and physiology. The analysis of 16S rDNA sequence revealed that the isolates belong to Chloroflexus subdivision in green non sulfur bacteria. They shared most common features with type 1851, but the result of gram stain was negative. Furthermore, they showed polymorphic nature and gliding motility, which could not be seen in activated sludge samples. General physiological tests were conducted under aerobic conditions although they could also grow by fermentation. Good growth was generally seen on sugars. The extremely slow growth rate (0.48-0.93 day(-1)) suggests the stimulation of this type exclusively in long SRT systems fed with sugars.
 
| Schematic representation of the OLAND SBR cycle. 
| Performance of the OLAND SBR. DO setpoints (SP) and remarks on the DO control mechanism are indicated per operational period. In period III, probe drifting resulted in a lower DO concentration compared to period II. In period VII, eight minutes without aeration were introduced at the end of the reaction phase. (A) Ammonium concentration in influent and effluent, and nitrite concentration in effluent. (B) Nitrogen removal rate and nitrate production expressed as a percentage of the ammonium removal. 
| Morphological differences in the OLAND SBR biomass. (A) Floccular biomass ( B ) Granular biomass. Scale bar 1⁄4 1.0 mm. 
| Specific aerobic and anoxic ammonium-oxidizing activity of the SBR inoculum, flocs and granules on day 65 (n ¼ 1). Note the break in the ordinate.
| FISH on OLAND SBR biomass. AOB (probe Nso1225 labelled with FITC) appear green, and anammox bacteria (probe Amx820 labelled with Cy3) appear red. (A) Floccular biomass (B) Granular biomass. Scale bar ¼ 20 mm. Subscribers to the online version of Water Science and Technology can access the colour version of this figure from http://www.iwaponline.com/wst.
Article
A novel and efficient way of removing nitrogen from wastewater poor in biodegradable organic carbon, is the combination of partial nitritation and anoxic ammonium oxidation (anammox), as in the one-stage oxygen-limited autotrophic nitrification/denitrification (OLAND) process. Since anoxic ammonium-oxidizing bacteria grow very slowly, maximum biomass retention in the reactor is required. In this study, a lab-scale sequencing batch reactor (SBR) was used to develop granular, rapidly settling biomass. With SBR cycles of one hour and a minimum biomass settling velocity of 0.7 m/h, OLAND granules were formed in 1.5 months and the nitrogen removal rate increased from 50 to 450 mg NL(-1) d(-1) in 2 months. The granules had a mean diameter of 1.8 mm and their aerobic and anoxic ammonium-oxidizing activities were well equilibrated to perform the OLAND reaction. Fluorescent in-situ hybridization (FISH) demonstrated the presence of both beta-proteobacterial aerobic ammonium oxidizers and planctomycetes (among which anoxic ammonium oxidizers) in the granules. The presented results show the applicability of rapidly settling granular biomass for one-stage partial nitritation and anammox.
 
Article
This paper reports on lab-scale investigations in relation to pre-selection of flocculants for sludge dewatering with decanter centrifuges. Results obtained were compared with CST-measurements and discussed in relation to findings under field conditions. Experiments were carried out with sewage sludges of different origin and characteristics and a number of commercial flocculants. Kinetics of sedimentation and clarification were measured as well as the compression behaviour and shear sensitivity of sludge sediments. To measure flocculant performance stability against intensive shearing, total solids in the sludge cake obtained and dewaterability of the sludge cake during the first 20-50 s of centrifugation were compared. A screening test procedure was developed. Efficient flocculants should produce high residual total solids and good initial compressibility. Lab-scale investigations deliver more reliable results if the dynamic behaviour of the sludge under centrifugal acceleration is also investigated. The separation analyser LUMiFuge 114 can provide results about the compression behaviour of sludges in the range between 10 and 100 s. So far no other method or device is known which can deliver such results.
 
| Effect of cell biomass concentrations on the nickel ions biosorption (dead biomass). Each point is the average of three determinations.
| Biosorption of nikel as affected by living biomass concentrations. Each point is the average of three determinations.
| Effect of metabolic inhibitors on the biosorption of nickel ions by bacterial species. Each point is the average of three determinations.
| Effects of chemical treatment on the functional groups involved in biosorption of nickel ions by bacterial species. Each point is the average of three determinations.
Article
Biosorption of nickel by two bacterial species: Bacillus subtilis 117S and Pseudomonas cepacia 120S was studied. The maximum uptake of nickel was achieved at 234.4 microg Ni2+ ml(-1) by P. cepacia 120S (living and dead biomass) and at 117.2 and 351.6 microg Ni2+ ml(-1) by living and dead biomass of B. subtilis 117S. The increase in biomass concentration has shown an increase in the nickel uptake. The nickel removal increased significantly during contact time from 1 to 8 h then remained constant until 24 h where the equilibrium occurred. Biosorption efficiency of nickel increased with increasing pH from 2 to 7 for living and dead biomass of P. cepacia 120S and B. subtilis 117S. Temperature had an important role in nickel biosorption by both species. The nickel removal by living biomass was significantly disturbed after pretreatment of bacterial biomass with sodium azide, mercuric chloride and formaldehyde. Esterification of carboxyl groups, methylation of amino groups and extraction of lipid fraction of biomass by acetone and benzene significantly reduced the biosorption capacity of nickel. Repeated biosorption and desorption operations exhibited that the biosorption capacity of bacterial biomass regenerated with HNO3 and NaOH as desorbing medium increased significantly in cycle 4 for P. cepacia 120S and B. subtilis 117S. In case of regeneration with HNO3 and distilled water the biosorption capacity increased significantly in cycle 4 for B. subtilis 117S and did not differ significantly from cycle 1 to cycle 4 for P. cepacia 120S. The biosorption capacity of living and dead biomass of B. subtilis 117S and dead biomass of P cepacia 120S (155.5 as compared to 175.6 and 169.8 mg Ni2+ g(-1)) was higher than that of sludge, tea and saw dust (148.4, 52.7 and 44.6 mg Ni2+ g(-1)).
 
Article
This study aims to compare the performance of two waterworks sludge samples, ferric chloride sludge (FCS) and polyaluminium chloride sludge (PACS), as coagulants to remove Acid Red 119 (AR119) dye from aqueous solution. A series of batch experiments were performed to investigate the effect of initial pH, coagulant dosage and initial dye concentration on coagulation/flocculation process efficiency. Results showed that the dye removal was strongly pH-dependent and followed the same trend for both coagulants, increasing steadily with decreasing initial pH in the range of 3-12. With the increase of coagulant dosage, the dye removal efficiency increased and no re-stabilization phenomenon was observed. However, the coagulant dosage needed for the maximum dye removal efficiency was much lower for FCS (150 mg dried sludge/L) in compare with PACS (5.5 g dried sludge/L). It seems that both charge neutralization and sweep flocculation mechanisms were involved in removal of AR119 using FCS and PACS. With the increase of initial dye concentration, Q (the amount of the removed dye per unit mass of coagulant) steadily increased and reached to a maximum value of 0.96 mg dye/mg sludge and 0.029 mg dye/mg sludge for FCS and PACS, respectively. FCS was more effective than PACS for AR119 dye removal due to the higher amount of dye removed per unit mass of sludge.
 
Article
Eleven years have now passed since the Stockholm Water Company took the initiative to establish the Stockholm Water Symposium. Since then our water conference has taken place each August here in Stockholm and, step by step, has increased its role to serve as the meeting point for leading actors in the water field. The Symposium has also become a core activity in the series of water events we call the World Water Week in Stockholm.
 
Article
Water security for the 21st century – building bridges through dialogue It is an honour and a great pleasure for me to address you at the opening of the 11th Stockholm Water Symposium. I am here in the place of the Swedish ministers most concerned: Kjell Larsson, the minister for environment and Maj-Inger Klingvall, the minister for development cooperation, who are involved in the annual Swedish cabinet recess to agree the priorities in next year's budget. Let me extend their and add my own congratulations to Professor Takashi Asano for his well deserved award of the 2001 Stockholm Water Prize. We all appreciate your important contribution to our common goal: to achieve a good and efficient use and reuse of water. Also I wish to commend the Stockholm International Water Institute, SIWI, and the other contributors for making this week in Stockholm not only a prominent event itself, but most importantly helping to put water in its proper place on the international development and environment agendas.
 
Article
Foaming incidents in activated sludge treatment plants are a worldwide problem and occur on a regular basis in both municipal and industrial activated sludge treatment plants. Foaming is most often caused by excessive growth of filamentous bacteria, especially the gram-positive ones affiliated within the Actinobacteria, e.g. the branched Mycolata or Candidatus Microthrix parvicella. Previous studies have shown that populations of Microthrix can be controlled by addition of certain polyaluminium compounds, but until now no effective chemicals have been identified to control other important foam formers such as the Mycolata. A new chemical (FilamentEx, FEX-120) was tested in full-scale in a Swedish wastewater treatment plant (WWTP) with immense foaming problems. In total, three different dosing events were carried out for more than 1 year. After only 8-17 weeks in each period, all foam had disappeared, and dosing of FEX-120 was stopped. Another 11 full-scale WWTPs in different countries were treated with FEX-120 because of severe Mycolata foaming on process tanks. In nine out of 11 plants, where the causative organisms were Gordonia or Skermania, a significant reduction of foam up to 100% was observed after treatment for approx. 10 weeks. In two WWTPs with unknown Mycolata organisms, no reduction was observed.
 
Article
To ensure that domestic wastewater treatment plants run in an efficient and reliable way, certifications already exist while others will be implemented soon. To date, we have listed eight standards: four from European countries (Germany, Great Britain, The Netherlands and Norway), one project from the European Union, two from North America (USA and Quebec) and one from Australia and New Zealand together. The European procedure includes verification of structure stability, water tightness and treatment capacity at test centre (38 weeks). The American Standard sets minimal standards for materials, dimensioning, building and performances of the plants. It also highlights the information and minimum service that should be provided by the manufacturer and distributors. The review process relating to treatment performances shares major similarities with the EU project since both documents were elaborated almost simultaneously. Australia and New Zealand have adopted a series entitled On-site Domestic Wastewater Treatment Units made up of three parts. The third one integrates construction requirements and describes quite an interesting procedure to efficiently test the small plant: after approximately 13 weeks of testing (half the total duration), the aeration chamber (provided it exists) is filled with sludge from septic tanks to simulate its operation after several years. Overview of the treatment efficiency test procedures of the three main standards is given.
 
Article
We have a huge and inspiring task ahead of us. By the year 2015, together we shall have contributed to halving the number of people on earth who do not have access to safe drinking water. Also by then we shall have halved the number of people living in poverty. Those are two of the Millennium Declaration Goals set by the UN General Assembly. These goals do not just show the tremendous responsibility we bear. The goals also point out how central water is for a decent life and a life in dignity.
 
| Flocs diameter of D (4,3) versus coagulation time at two constant dosage (raw water pH 7.5, raw water turbidity 70 NTU).
The Al species distribution of coagulants
Article
Flocculation of kaolin suspension with aluminium fractal polycations was investigated as a function of aluminium concentration and pH. Aluminium flocculants included Al(13) and Al(13) aggregates with OH/Al ratio of 2.6 and 2.8, respectively. The flocculation kinetics and floc size distribution were monitored by light scattering. The characterization of flocculants showed that the tridecatmer Al(13) and bridged [Al(13)](n) with out-sphere structure were the dominant species for all flocculants in a wide pH range. The coagulation results indicated that the pre and in situ-formed [Al(13)](n) play a key role in removing particles. With the increasing concentration of [Al(13)](n), coagulation mechanisms were transformed from charge-neutralization, electro-patch coagulation to bridge-aggregation. Moreover, sweep-flocculation was involved at higher dosage besides other three mechanisms when amorphous aluminium oxides formed. Hence, chemical interaction between particles and flocculants evolved from surface adsorption to surface precipitation for aluminium polycations by virtue of species transformation.
 
Article
Similar evolution was obtained for the stable carbon isotope signatures delta (13)CH(4) and the model-predicted relative rate of aceticlastic methanogenesis during mesophilic methanization of municipal solid wastes. In batch incubations, the importance of aceticlastic and hydrogenotrophic methanogenesis changes in time. Initially, hydrogenotrophic methanogenesis dominated, but increasing population of Methanosarcina sp. enhances aceticlastic methanogenesis. Later, hydrogenotrophic methanogenesis intensified again. A mathematical model was developed to evaluate the relative contribution of hydrogenotrophic and aceticlastic pathways of methane generation during mesophilic batch anaerobic biodegradation of the French and the Chinese Municipal Solid Wastes (FMSW and CMSW). Taking into account molecular biology analysis reported earlier three groups of methanogens including strictly hydrogenotrophic methanogens, strictly aceticlastic methanogens (Methanosaeta sp.) and Methanosarcina sp., consuming both acetate and H(2)/H(2)CO(3) were considered in the model. The total organic and inorganic carbon concentrations, methane production volume, methane and carbon dioxide partial pressures values were used for the model calibration and validation. Methane isotopic composition (delta (13)CH(4)) evolution during the incubations was used to independently validate the model results. The model demonstrated that only the putrescible solid waste was totally converted to methane.
 
Article
Natural isotopic composition in substrate may be used to reveal the metabolic pathways of substrate transformation by microbial community. In this paper, a change in δ(13)CH(4) during methanization of reconstituted municipal solid waste was described using a mathematical model based on stoichiometric chemical reactions, equation for the (13)C isotope accumulation in products at the low natural C(13)/C(12) ratio and microbial ecology. A set of experimental data used in the model was taken from Qu et al. (2009a). According to the model, during mesophilic municipal solid waste methanization initially hydrogenotrophic and further aceticlastic methanogenesis dominated. At the final stage hydrogenotrophic methanogenesis followed by acetate oxidation dominated again. In spite of rather high measured values of δ(13)C for CO(2) above -21‰, a sharp decrease in δ(13)CH(4) from -20‰ to -60‰ at the final stage was explained by a larger fractionation against (13)C during methanogenesis from H(2)/H(2)CO(3) due to a kinetic isotope effect when hydrogenotrophic methanogens preferentially take down light (12)C. The model also confirmed that in thermophilic conditions a comparatively stable value of δ(13)CH(4) about -60‰ measured earlier (Qu et al. 2009b) was due to a dominance of hydrogenotrophic methanogenesis during all methanization process of cardboard waste.
 
| Water courses in the Stockholm region, drinking water works, WWTPs and sampling points. The waters west of Stockholm City belong to Lake Mälaren. East of this point is the Baltic Sea. 
| Concentrations of APIs in receiving waters in a gradient from the central city through the Stockholm archipelago in the Baltic Sea. 
| Input from medicines and the Lake Mälaren (¼ 100%) and calculated percent fractions in the watercourse through Stockholm and in WWTP sludge
| The mass fl ow model represented by diclofenac. 
Article
Mass flows of 13 pharmaceutical active ingredients (APIS) found in drinking water were studied in the water cycle of Stockholm. Data were collected by analyzing samples of surface water, raw water and drinking water as well as influents, effluents and sludges from waste water treatment plants (WWTPs) in Stockholm area. A mass balance was performed, based on sold amounts of pharmaceuticals and the measured concentrations in water and sludge. The selected APls were all present in WWTP effluents and the removal rates for many of them were poor. Mass balance calculations showed that the three studied WWTPs in Stockholm release considerable amounts of the selected APIs into the Baltic Sea while the portions ending up in WWTP sludge were significantly lower. The levels of APIs found in drinking water are low at present, but may increase in the future unless the releases from WWTPs in the catchment of Lake Mälären are mitigated.
 
Article
Peroxidases can be used in the decolorization process. There is a growing interest for new sources of this enzyme and for obtaining economically viable processes. In this work, a low-cost vegetable peroxidase extraction process is proposed; the resulting enzyme is characterized to determine its optimum pH, temperature, and stability conditions, and it is then applied in the decolorization of reactive dye Remazol Turquoise G 133%. The turnip peroxidase (TP) was utilized as an enzymatic source. This enzyme exhibited maximum activity at pH 7.0, and it was active in the temperature range of 30 to 50 °C, which favors its use in industrial processes. Acetone was the most efficient solvent to induce precipitation. The removal of Remazol Turquoise G 133% was 56.0% complete after 50 min, while 41.0% of the same dye was removed with the commercial horseradish peroxidase enzyme in 50 min. TP presents potential as a viable alternative in the decolorization of textile wastewaters.
 
Article
Sludge bacterial extracellular (BEP) polymers exhibit a strong affinity with metals in addition to their role in the bioflocculation of activated sludge. It is of utmost importance in elucidating the chemical characterization of sludge BEP prior to a better understanding of its environmental behavior. Sludge BEP extracted from activated sludge was characterized by FT-IR, 1H-NMR, and 13C-NMR and fractionated into 6 fractions (hydrophilic acid, base, and neutral; and hydrophobic acid, base, and neutral). The results indicated that sludge BEP contained more polysaccharides but fewer amino acids or proteinaceous materials compared to dissolved organic matter (DOM) derived from sludge. No aromatic substance was found in sludge BEP as indicated by NMR. Sludge BEP was dominated by hydrophilic fractions, accounting for 65% of total DOC of sludge BEP and hydrophilic neutral constituted about 58% of the hydrophilic fraction. The chemical fraction and characterization indicated that sludge BEP might exhibit a higher capability in enhancing the transport of the associated contaminants through porous media than that of sludge DOM.
 
Article
The World Water Week in Stockholm is the only annual water meeting with such broad participation from different sectors of society, water professionals, technicians, scientists, policy makers, private sector actors, NGOs and many other stakeholders. This is what makes our week unique, your participation, and that is why we can offer such an interesting programme and such excellent opportunities for constructive dialogue. Building bridges through dialogue between different interest groups is a key goal that we increasingly feel that we are achieving.
 
Article
This study aimed at enhancing knowledge on the fate of diclofenac (DF), together with its main human metabolite 4'-hydroxydiclofenac (4'OHDF), during wastewater treatment by using a laboratory-scale membrane bioreactor (MBR). The reactor was fed continuously with non-radiolabelled diclofenac for a one month period prior to a single pulse of a 14C-radiolabelled solution of DF and 4'OHDF. The solution spike contained approximately 25% 4'OHDF and 65% DF, which corresponds to the ratio observed in municipal sewage, as well as traces of two other metabolites. The radioactivity was monitored for a total of twelve days in the various output streams. The calculation of the complete mass balance in the system demonstrated that the major part of the radioactivity left the reactor with the permeate (88.7%), while 2.1% was recovered in the excess sludge. Negligible amounts were recovered in the off-gas traps and on the membranes. Chromatographic analyses of effluent samples, by means of HPLC-MS coupled in parallel to a radiodetector, displayed a different pattern than the one of the spiked solution. It showed the occurrence of three additional metabolites.
 
Article
The aim of this study was to investigate the impact of a broad range of sulphate concentrations (0-10g SO4(-2) L(-1)) on the reduction of an azo dye (reactive orange 14 (RO14)) by an anaerobic sludge. An increase in the sulphate concentration generally stimulated the reduction of RO14 by sludge incubations supplemented with glucose, acetate or propionate as electron donor. Sulphate and azo dye reductions took place simultaneously in all incubations. However, there was a decrease on the rate of decolorization when sulphate was supplied at 10g SO4(-2) L(-1). Abiotic incubations at different sulphide concentrations (0-2.5 g sulphide L(-1)) promoted very poor reduction of RO14. However, addition of riboflavin (20 microM), as a redox mediator, accelerated the reduction of RO14 up to 44-fold compared to a control lacking the catalyst. Our results indicate that sulphate-reduction may significantly contribute to the reduction of azo dyes both by biological mechanisms and by abiotic reductions implicating sulphide as an electron donor. The contribution of abiotic decolorization by sulphide, however, was only significant when a proper redox mediator was included. Our results also revealed that sulphate-reduction can out-compete with azo reduction at high sulphate concentrations leading to a poor decolorising performance when no sufficient reducing capacity is available.
 
Article
A total of 14 types of sludge from household sewage, mixture of domestic and industrial wastewater, and industrial and oil wastewater treatment plants were selected to evaluate the effectiveness and adaptability of thermal hydrolysis pre-treatment. Organic solubilization, dewatering improvement, volume reduction, high-strength filtrate biodegradation, and dewatered sludge incineration were investigated using bench and pilot thermal hydrolysis experiments (170 °C/60 min). Results showed that sludge types significantly affected the treatment effects. Organic content has a primary influence on thermal effects. The relationship between suspended solid (SS) solubilization and raw sludge organic content was linear with an R(2) of 0.73. The relationship between raw sludge organic content and treated sludge dewatering was linear with an R(2) of 0.86 and 0.65 for pilot and bench pre-treatments, respectively. Household and oil sludge possessed incineration possibilities with high heat value. Industrial and oil sludge filtrate was unsuitable for digestion to recover bioenergy.
 
Article
Textile wastewater normally has a visible color although it has low concentration. This may affect the aquatic ecosystem. Two dyestuffs, Reactive Red 141 (RR141) and Basic Red14 (BR14) were used as compound models. RR 141 is an anionic dye which has a big molecule whereas BR 14 is a cationic dye and has a small molecule. The target organisms for toxicity test were green algae (Chlorella sp.) and waterfleas (Moina macrocopa). The effect of humic acid on the toxicity of dyestuffs to test organisms was also investigated. From the observation of cell counts, Chlorophyll a and dry weight of algae in the dye solutions for 4 days, it was found that all parameters increased as times increased. This revealed that algae could utilize dyestuffs as a carbon source. However, BR14 gave higher absorbance than RR141 at the wavelength of 430 nm which competed to the Chlorophyll a for algal photosynthesis. This resulted in the 96-h EC50 of BR14 and RR141 to Chlorella sp. were 10.88 and 95.55 mg/L, respectively. As for dye toxicity to waterfleas, the 48-h LC50 of BR14 and RR141 to waterfleas were 4.91 and 18.26 mg/L, respectively. The high toxicity of BR14 to waterfleas related to the small molecule of dye could pass into the cell and was absorbed by organelles of waterfleas. Toxicity of BR14 in humic acid solution to Chlorella sp. showed less toxic than RR141 in humic acid solution. This dues to the negative charge of humic acid could bound with a positive charge of BR14, resulted in low amount of BR14 remaining in the bulk solution. The toxicity of BR14 and RR141 in humic acid solution to waterfleas was increased as humic acid increased. Hence, the proper treatment of textile wastewater to yield low concentration of dyes in the effluent before discharging to the natural water is needed.
 
Article
The amount of wastewater treatment plants (WWTP) dealing with solid separation problems has significantly increased since the new requirements of the EU Directive 271/91 on nutrient removal. In Flanders a number of the nutrient removal WWTP are affected by solid separation problems mostly attributed to Microthrix parvicella being the most common dominant species. The effect of dosing polyaluminium chloride (PAX-14) on activated sludge is illustrated for WWTP solids separation problems, in particular because of Microthrix parvicella. The effects of the addition of PAX-14 on the microbiology and the morphology of Microthrix parvicella were studied in 9 full-scale WWTP. PAX-14 succeeded in reducing high SVI-values and controlled foaming problems whenever caused by Microthrix parvicella. Laboratory trials have shown that the dosage of PAX-14 should be less than 150 microL/L or 7 g Al3+/kg MLSS. At a dosage higher than 250 microL/L, an increase of free bacteria and a decrease of the protozoa activity are observed. In full-scale, PAX-14 is dosed at a concentration of 1.5 to 4.5 g Al3+/kg MLSS. Before addition, the mixed liquor scum layer--if present--should be removed. In our experience, the dosing should last for at least 3 weeks. During the first week, no drastic changes occur. At the end of the first week, an increase of SS and SVI is possible. The SVI and scum start to decrease after 10 to 15 days. The amount of filaments is reduced after 3 to 3 1/2 weeks. The morphological properties of Microthrix parvicella change, while other filaments such as Nostocoida limicola and Nocardia spp. are not affected. This study proves that PAX-14 is effective in controlling bulking and foaming problems at WWTPs when they are due to Microthrix parvicella. Prediction of when the SVI will decrease and when addition should be stopped is possible.
 
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Mark van Loosdrecht
  • Delft University of Technology
Peter A Vanrolleghem
  • Laval University
Gatze Lettinga
  • Wageningen University & Research
Irini Angelidaki
  • Technical University of Denmark
Mogens Henze
  • Technical University of Denmark