This study investigates the sludge and effluent characteristics of a new process of coupling an aerobic granular sludge bioreactor with a membrane filtration. The effluent and mixed liquor of sequencing batch airlift reactor (SBAR) were analyzed at various aeration shear stresses when fed with high nitrate containing wastewater. The presence of nitrate nitrogen and aerobic/anoxic condition was able to improve the sludge characteristics in terms of biomass retention, density and settling ability in SBAR. MLSS and SVI could reach 9 g/L and 44 mL/g respectively at the aeration rate of 0.6 cm/s. The presence of nitrate and the denitrification process could minimize the fouling potential. The membrane fouling can be better correlated to SBAR sludge characteristics than biomass concentration. The high aeration rate in the reactor increased the fouling resistance due to production of large MW soluble microbial products (30-50 kDa). The soluble fraction of SBAR effluent contained mainly hydrophilic substances when nitrate is present in the wastewater. 相似文献
The external nitrification (EN) biological nutrient removal (BNR) activated sludge (ENBNRAS) system shows considerable promise for full-scale implementation. As an aid for this implementation, a mathematical simulation model would be an invaluable tool. To develop such a model, a study was conducted to select the most suitable simulation model to serve as a starting point for further development. For this, the existing available simulation models for BNRAS systems are compared with one another and evaluated against experimental observations in the literature and on ENBNRAS systems. One process immediately apparent to be crucially important is the anoxic growth of phosphorus accumulating organisms (PAOs), with associated PAO denitrification and anoxic P uptake for polyP formation. These linked processes are lacking in the earlier kinetic simulation models for BNRAS systems, which were based on aerobic PAO growth and P uptake only, but have been incorporated into the more recent kinetic models. This provides a substantive body of information on modelling this aspect. Other processes of significance identified to require consideration are anaerobic slowly biodegradable COD (SBCOD) hydrolysis to readily biodegradable COD (RBCOD), and COD loss. Both processes have significant impact on the predicted BEPR performance. Due to the uncertainties associated with the mechanisms and quantification of these two processes, it is concluded that the most extensively validated kinetic simulation model should be selected for development, and that the omissions in this model should be addressed progressively, using the relevant information drawn from the existing models, the literature and observations on ENBNRAS systems. 相似文献
Emission of NO and N2O from a full-scale two-reactor nitritation-anammox process was determined during a measurement campaign at the Dokhaven-Sluisjesdijk municipal WWTP (Rotterdam, NL). The NO and N2O levels in the off-gas responded to the aeration cycles and the aeration rate of the nitritation reactor, and to the nitrite and dissolved oxygen concentration. Due to the strong fluctuations in the NO and N2O levels in both the nitritation and the anammox reactor, only time-dependent measurements could yield a reliable estimate of the overall NO and N2O emissions. The NO emission from the nitritation reactor was 0.2% of the nitrogen load and the N2O emission was 1.7%. The NO emission from the anammox reactor was determined to be 0.003% of the nitrogen load and the N2O emission was 0.6%. Emission of NO2 could not be detected from the nitritation-anammox system. Denitrification by ammonia-oxidizing bacteria was considered to be the most probable cause of NO and N2O emission from the nitritation reactor. Since anammox bacteria have not been shown to produce N2O under physiological conditions, it is also suspected that ammonia-oxidizing bacteria contribute most to N2O production in the anammox reactor. The source of NO production in the anammox reactor can be either anammox bacteria or denitrification by heterotrophs or ammonia-oxidizing bacteria. Based on the results and previous work, it seems that a low dissolved oxygen or a high nitrite concentration are the most likely cause of elevated NO and N2O emission by ammonia-oxidizing bacteria. The emission was compared with measurements at other reject water technologies and with the main line of the Dokhaven-Sluisjesdijk WWTP. The N2O emission levels in the reject water treatment seem to be in the same range as for the main stream of activated sludge processes. Preliminary measurements of the N2O emission from a one-reactor nitritation-anammox system indicate that the emission is lower than in two-reactor systems. 相似文献
A novel route of anoxic ammonia removal in the presence of organic carbon was identified recently from ecosystems contaminated with ammonia. Sequencing batch reactor (SBR) studies were carried out in anoxic condition at oxidation–reduction potential varied from −185 to −275 mV for anoxic ammonia oxidation with adapted biomass (mixed culture). SBR studies were carried out in absence and in the presence of externally added organic carbon and/or in the presence of inorganic electron acceptors like NO2−, NO3− and SO42−. The results showed anoxic ammonia oxidation to nitrate (in contrast to reported anammox process) in the presence of organic carbon available through endogenous respiration whereas anoxic ammonia oxidation was effective in the presence of externally added organic compound for nitrogen removal. The presence of externally added inorganic electron acceptors like NO2−, NO3− and SO42− was effective in anoxic ammonia oxidation, but failed to follow the reported anammox reaction's stoichiometry in nitrogen removal in the presence of organic carbon. However, the presence of NO2− affected best in total nitrogen removal compared to other electron acceptors and maximum ammonia removal rate was 100 mg NH4+/g MLVSS/d. Based on the results, it is possible to suggest that rate of anoxic ammonia oxidation depends up on the respiration activities of mixed culture involving organic carbon, NO2−, NO3− and SO42−. The process shows possibilities of new pathways of ammonia oxidation in organic contaminated sediments and/or wastewater in anoxic conditions. 相似文献
In this study, the removal of perchlorate (0.016 mM ) using Fe0-only (325 mesh, 10 g L−1) and Fe0 (10 g L−1) with UV (254 nm) reactions were investigated under oxic and anoxic conditions (nitrogen purging). Under anoxic conditions, only 2% and 5.6% of perchlorate was removed in Fe0-only and Fe0/UV reactions, respectively, in a 12 h period. However, under oxic conditions, perchlorate was removed completely in the Fe0-only reaction, and reduced by 40% in the Fe0/UV reaction, within 9 h. The pseudo-first-order rate constant (k1) was 1.63 × 10−3 h−1 in Fe0-only and 4.94 × 10−3 h−1 in Fe0/UV reaction under anoxic conditions. Under oxic conditions, k1 was 776.9 × 10−3 h−1 in Fe0-only reaction and 35.1 × 10−3 h−1 in the Fe0/UV reaction, respectively. The chlorine in perchlorate was recovered as chloride ion in Fe0-only and Fe0/UV reactions, but lower recovery of chloride under oxic conditions might due to the adsorption/co-precipitation of chloride ion with the iron oxides. The removal of perchlorate in Fe0/UV reaction under oxic conditions increased in the presence of methanol (73%, 9 h), a radical scavenger, indicating that OH radical can inhibit the removal of perchlorate. The removal of perchlorate by Fe0-only reaction under oxic condition was highest at neutral pH. Application of the Langmuir-Hinshelwood model indicated that removal of perchlorate was accelerated by adsorption/co-precipitation reactions onto iron oxides and subsequent removal of perchlorate during further oxidation of Fe0. The results imply that oxic conditions are essential for more efficient removal of perchlorate in Fe0/H2O system. 相似文献
Amending anoxic soils with stoichiometric amounts of sodium acetate led to the complete transformation of trifluralin within the 45 day treatment period. Under these conditions, a maximum trifluralin transformation rate of 4.9 mg kg−1 of soil per day was estimated, which corresponded to a chemical half life of 11.9 days. Regression analyses indicated that the zero order rate model provided the best fit to the experimental data, suggesting that the trifluralin transformation rate is independent of concentration during acetate addition. Using radiolabeled trifluralin, it was determined that the principal contaminant transformation mechanisms were degradation and bound residue formation (i.e., irreversible adsorption). Volatilization and mineralization of trifluralin were found to be negligible over the 45 day treatment period. Using poisoned controls, it was determined that trifluralin transformation under acetate-amended conditions was biologically mediated.
Amending trifluralin contaminated soils with stoichiometric amounts of iron sulfide resulted in complete trifluralin transformation within 24 hours of treatment. A maximum trifluralin transformation rate of 380 mg kg−1 of soil per day was estimated for this system, which corresponded to a chemical half life of 4.4 h. The rates of trifluralin transformation followed the first-order kinetic model during iron sulfide addition. Using radiolabeled trifluralin, it was found that chemical degradation was the principal removal mechanism. Neither volatilization nor mineralization was found to be a significant contaminant removal mechanism during iron sulfide treatment. Poisoned controls indicated that trifluralin transformation was mediated primarily by an abiotic chemical reaction mechanism. Additional study is required to clarify the rate limiting steps so that full scale soil treatment systems may be properly designed. 相似文献
In large and shallow lakes, the role of the redox-related release of phosphorus (P) from sediments has remained in the shadow of sediment resuspension. In the current study, we concentrated on this knowledge gap regarding factors controlling lake water quality. We combined long-term monitoring data with the studies on sediment P mobility in August 2018 by measuring redox potential, pore water concentrations of soluble reactive phosphorus (SRP), dissolved iron (Fe), sediment P fractions, and by calculating diffusive P flux. Using lake water total P (TP) concentrations for 21 years (1997–2018), we quantified internal P load based on water column summer increase of TP (ILin situ). Significant positive correlations were found between the diffusive P flux and the Fe-bound P concentration in the sediment for conditions of well-oxidized sediment surfaces. The analysis of long-term data showed that P mobilized in sediments is likely to be released via sediment disturbances. Sediment resuspension is favoured by decreased water level during late summer-early autumn. Additionally, the release of P from anoxic sediment surfaces is also possible, as was indicated by significant positive correlations of ILin situ with the anoxic factor (a measure of extent of anoxia) and August water temperature. The potential P release from anoxic sediment surfaces contributed about 80% to ILin situ in the northern basin, and about 280% in the more productive southern basin. Hence, the redox-related P release seems to sustain the high productivity of these large and shallow lake basins and is supported by sediment resuspension as a transport mechanism. 相似文献
This paper studied the effect of oxidation-reduction potential (ORP) in the anoxic sludge zone on the excess sludge production in the oxic-settling-anoxic process (OSA process), a modified activated sludge process. Two pilot-scale activated sludge systems were employed in this study: (1) an OSA process that was modified from a conventional activated sludge process by inserting a sludge holding tank or namely the "anoxic" tank in the sludge return line; and (2) a conventional process used as the reference system. Each was composed of a membrane bioreactor to serve the aeration tank and solid/liquid separator. Both systems were operated with synthetic wastewater for 9 months. During the operation, the OSA system was operated with different ORP levels (+100 to -250 mV) in its anoxic tank. It has been confirmed that the OSA system produced much less excess sludge than the reference system. A lower ORP level than +100 mV in the anoxic tank is in favor of the excess sludge reduction. When the ORP level decreased from +100 to -250 mV the sludge reduction efficiency was increased from 23% to 58%. It has also been found that the OSA system performed better than the reference system with respect to the chemical oxygen demand removal efficiency and sludge settleability. The OSA process may present a potential low-cost solution to the excess sludge problem in an activated sludge process because addition of a sludge holding tank is only needed. 相似文献