Long term effects of salt on activity, population structure and floc characteristics in enriched bacterial cultures of nitrifiers

The effect of salinity on the activity, the composition of nitrifiers and floc characteristics of nitrifying sludge was studied. Non-adapted and adapted (to 10 g NaCl-Cl⁻/L for one year) enriched cultures of nitrifiers were tested in three sequencing batch reactors. Salt was increased gradually with 5 up to 40 g Cl⁻/L.No difference in steady state activity was observed between the adapted and non-adapted sludge. The activities of ammonia and nitrite oxidizers dropped 36% and 11%, respectively, at salt concentrations of 10 g Cl⁻/L. At 40 g Cl⁻/L inhibition reached 95% of salt free activity for ammonia and nitrite oxidizers in both adapted and non-adapted reactors. Nitrosomonas europaea and Nitrobacter sp. (fluorescent in situ hybridization) were the only nitrifiers present at high salt levels. Increased salt concentrations resulted in better settling characteristics of the nitrifying sludge. After 118 days the sludge was brought back to the initial conditions (0 g Cl⁻/L for non-adapted and 10 g Cl⁻/L for adapted). Despite the change in population composition similar kinetics as before the salt stress were observed.     

Penalty free biphase linecoding for pattern independent FSKcoherent transmission systems

Biphase coding is used to eliminate the unwanted influence of nonuniform laser characteristics in frequency-shift-keying (FSK) transmission systems. Compared to other (ternary) linecoding schemes, biphase has the advantage that it does not give a 3-dB sensitivity penalty when properly decoded in the receiver. This has been demonstrated in a 140-Mb/s 280-Mbaud transmission experiment. The receiver features a new type of reliable unambiguous clock extraction. Due to the compact IF spectrum, as compared with ternary linecoding schemes, biphase equipped FSK systems are especially suited for efficiently spaced coherent multichannel (CMC) systems. FSK heterodyne transmission experiments show a sensitivity ηP of -56.7 dBm for 2¹⁰-1 pseudorandom patterns, only 4.8 dB from the shot-noise limit     

Biphase linecoding in optical FSK heterodyne transmission experiment, without sensitivity degradation compared to NRZ

A biphase linecoding scheme was used in a 140 Mbit/s optical FSK transmission experiment. Owing to the analogue decoding, only 0.3 dB sensitivity penalty was observed, compared to NRZ. A sensitivity of -54 dBm was achieved.<>     

工艺多样性是高效RF解决方案的关键

未来消费电子产品的RF应用将向更高的载波频率方向发展.这种趋势已经初现端倪,新提议的IEEE-802.11a数字网络标准在5GHz频率工作,超宽带(UWB)的带宽要求则介于3GHz和10GHz之间.汽车防撞雷达的工作频率是25GHz,而多种IEEE 802.16WirelessMAN(无线城域网)标准、本地多点分布式服务(LMDS)网络和卫星返回通道所需的带宽位于25GHz到 35GHz之间(参见图1).     

Why FSK and CPFSK have identical linewidth requirements

CPFSK is the most widely used modulation scheme in coherent optical transmission. Theoretical analyses so far predicted a much more stringent linewidth requirement compared to ASK and FSK systems with noncoherent IF-detection. In this paper we present a unified linewidth analysis of ASK, FSK, CPFSK, and DPSK receivers, with leads to the conclusion that the linewidth performance of these different schemes is to a large extent identical. The inclusion of post-detection filtering in the analysis is critical for obtaining these results, which are supported by practical system measurements on a 1 Gbit/s phase diversity CPFSK receiver     

Factors affecting the microbial populations at full-scale enhanced biological phosphorus removal (EBPR) wastewater treatment plants in The Netherlands

The influence of operating and environmental conditions on the microbial populations of the enhanced biological phosphorus removal (EBPR) process at seven full-scale municipal activated sludge wastewater treatment plants (WWTPs) in The Netherlands was studied. Data from the selected WWTPs concerning process configuration, operating and environmental conditions were compiled. The EBPR activity from each plant was determined by execution of anaerobic-anoxic-aerobic batch tests using fresh activated sludge. Fractions of Accumulibacter as potential phosphorus accumulating organisms (PAO), and Competibacter, Defluviicoccus-related microorganisms and Sphingomonas as potential glycogen accumulating organisms (GAO) were quantified using fluorescence in situ hybridization (FISH). The relationships among plant process configurations, operating parameters, environmental conditions, EBPR activity and microbial populations fractions were evaluated using a statistical approach. A well-defined and operated denitrification stage and a higher mixed liquor pH value in the anaerobic stage were positively correlated with the occurrence of Accumulibacter. A well-defined denitrification stage also stimulated the development of denitrifying PAO (DPAO). A positive correlation was observed between Competibacter fractions and organic matter concentrations in the influent. Nevertheless, Competibacter did not cause a major effect on the EBPR performance. The observed Competibacter fractions were not in the range that would have led to EBPR deterioration. Likely, the low average sewerage temperature (12+/-2 degrees C) limited their proliferation. Defluviicoccus-related microorganisms were seen only in negligible fractions in a few plants (<0.1% as EUB), whereas Sphingomonas were not observed.     

Model-based evaluation of nitrogen removal in a tannery wastewater treatment plant.

Computer modelling has been used in the last 15 years as a powerful tool for understanding the behaviour of activated sludge wastewater treatment systems. However, computer models are mainly applied for domestic wastewater treatment plants (WWTPs). Application of these types of models to industrial wastewater treatment plants requires a different model structure and an accurate estimation of the kinetics and stoichiometry of the model parameters, which may be different from the ones used for domestic wastewater. Most of these parameters are strongly dependent on the wastewater composition. In this study a modified version of the activated sludge model No. 1 (ASM 1) was used to describe a tannery WWTP. Several biological tests and complementary physical-chemical analyses were performed to characterise the wastewater and sludge composition in the context of activated sludge modelling. The proposed model was calibrated under steady-state conditions and validated under dynamic flow conditions. The model was successfully used to obtain insight into the existing plant performance, possible extension and options for process optimisation. The model illustrated the potential capacity of the plant to achieve full denitrification and to handle a higher hydraulic load. Moreover, the use of a mathematical model as an effective tool in decision making was demonstrated.     

Nitrification in bulk water and biofilms of algae wastewater stabilization ponds.

Nitrogen removal in wastewater stabilization ponds is poorly understood and effluent monitoring data show a wide range of differences in ammonium. For effluent discharge into the environment, low levels of nitrogen are recommended. Nitrification is limiting in facultative wastewater stabilization ponds. The reason why nitrification is considered to be limiting is attributed to low growth rate and wash out of the nitrifiers. Therefore to maintain a population, attached growth is required. The aim of this research is to study the relative contribution of bulk water and biofilms with respect to nitrification. The hypothesis is that nitrification can be enhanced in stabilization ponds by increasing the surface area for nitrifier attachment. In order to achieve this, transparent pond reactors representing water columns in algae WSP have been used. To discriminate between bulk and biofilm activity, 5-day batch activity tests were carried out with bulk water and biofilm sampled. The observed value for Rnitrbulk was 2.7 x 10(-1) mg-N L(-1) d(-1) and for Rbiofilm was 1,495 mg-N m(-2) d(-1). During the 5 days of experiment with the biofilm, ammonia reduction was rapid on the first day. Therefore, a short-term biofilm activity test was performed to confirm this rapid decrease. Results revealed a nitrification rate, Rbiofilm, of 2,125 mg-N m(-2) d(-1) for the first 5 hours of the test, which is higher than the 1,495 mg-N m(-2) d(-1), observed on the first day of the 7-day biofilm activity test. Rbiofilm and Rnitrbulk values obtained in the batch activity tests were used as parameters in a mass balance model equation. The model was calibrated by adjusting the fraction of the pond volume and biofilm area that is active (i.e. aerobic). When assuming a depth of 0.08 m active upper layer, the model could describe well the measured effluent values for the pond reactors. The calibrated model was validated by predicting effluent Kjeldahl nitrogen of algae ponds in Palestine and Colombia. The model equation predicted well the effluent concentrations of ponds in Palestine.     

140 Mbit/s and 560 Mbit/s FSK heterodyne polarisation diversity receiver using nearly perfect square law demodulators

A new frequency discriminator concept with nearly perfect square law demodulation characteristics is described. The performance of the device is verified in a 140 Mbit/s and 560 Mbit/s FSK heterodyne polarisation diversity transmission experiment.<>     

Temperature effects on glycogen accumulating organisms

Glycogen accumulating organisms (GAO) compete for substrate with polyphosphate-accumulating organisms (PAO), which are the microorganisms responsible for the enhanced biological phosphorus removal (EBPR) in activated sludge wastewater treatment systems. This can lead to the deterioration of the EBPR process. In this paper, the long-term temperature effects on the anaerobic and aerobic stoichiometry and conversion rates on adapted enriched cultures of Competibacter (a known GAO) were evaluated from 10 to 40 °C. The anaerobic stoichiometry of Competibacter was constant from 15 to 35 °C, whereas the aerobic stoichiometry was insensitive to temperature changes from 10 to 30 °C. At 10 °C, likely due to the inhibition of the anaerobic conversions of Competibacter, a switch in the dominant bacterial population to an enriched Accumulibacter culture (a known PAO) was observed. At higher temperatures (35 and 40 °C), the aerobic processes limited the growth of Competibacter. Due to the inhibition or different steady-state (equilibrium) conditions reached at long-term by the metabolic conversions, the short- and long-term temperature dependencies of the anaerobic acetate uptake rate of Competibacter differed considerably between each other. Temperature coefficients for the various metabolic processes are derived, which can be used in activated sludge modeling. Like for PAO cultures: (i) the GAO metabolism appears oriented at restoring storage pools rather than fast microbial growth, and (ii) the aerobic growth rate of GAO seems to be a result of the difference between PHA consumption and PHA utilization for glycogen synthesis and maintenance. It appears that the proliferation of Competibacter in EBPR systems could be suppressed by adjusting the aerobic solids retention time while, aiming at obtaining highly enriched PAO cultures, EBPR lab-scale reactors could be operated at low temperature (e.g. 10 °C).