Oxygen Uptake Rate Of Sludge Research Articles

Controlling sludge retention time to alleviate inhibition of nitrosation and nitration by accumulated aluminum in an A/O-MBR

Severe membrane fouling and limited effect of biological phosphorus removal are the major drawbacks for anoxic-oxic membrane bioreactor (A/O-MBR). The dosing of poly-aluminum chloride in A/O-MBR can reduce membrane fouling and improve phosphorus removal certainly, but it may bring potential impacts on the specific oxygen uptake rate of sludge and the activity of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria with accumulated aluminum. Controlling sludge retention time (SRT) was firstly investigated to evaluate the effect on alleviating inhibition caused by accumulated aluminum in A/O-MBR. As compared to the performance without dosing of poly-aluminum chloride, the effluent ammonia concentration in the SRT-15d reactor was increased by 91.80% lower than that of SRT-30d reactor (111.84%). Due to higher sludge yield rate in the SRT-15d reactor, the amount of accumulated aluminum was 39.33 mg Al g−1 VSS less than that of the SRT-30d reactor. Besides, the decline of the activity of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria in the SRT-15d reactor was 4.4% and 18.3%, respectively lower than that of the SRT-30d reactor. Therefore, controlling shorter SRT can be used as an effective tool to alleviate inhibition of nitration and nitrosation by accumulated aluminum in A/O-MBR.

Influence of aluminium accumulation on biological nitrification and phosphorus removal in an anoxic-oxic membrane bioreactor.

Poly-aluminium chloride (PAC) is often used to enhance phosphorus removal and control membrane fouling in membrane bioreactors (MBRs). However, the influence of aluminium accumulation on the biological nitrification and phosphorus removal of MBRs has not been well assessed. In the present study, the effects of accumulated aluminium on sludge activity and morphology were investigated in a lab-scale anoxic-oxic membrane bioreactor. The reasonably high removal efficiencies of NH4+-N, TN, and COD, i.e. 94.9%, 84.8%, and 92.8%, respectively, were achieved in the reactor when the percentage of atomic aluminium on sludge surface increased to 14.2%. However, the decreases in the ammonia oxidation rate, nitrite oxidation rate, and specific oxygen uptake rate of sludge by 82.1%, 79.8%, and 46.4%, respectively, were observed. Meanwhile, the activity of phosphate-accumulating organisms was completely inhibited. Furthermore, the protein content in the extracellular polymeric substances of sludge decreased substantially, and the sludge became more dispersed due to the alum accumulation, compared with that of the initial phase. Therefore, long-term dosing of PAC in the MBR should be managed to avoid excessive aluminium accumulation in the sludge.

A concept development of an early warning system for toxic sewage detection

The article presents a concept of an EWS (early warning system) for toxic sewage detection upstream from Wroclaw Wastewater Treatment Plant. It includes design and construction of three toxicity warning stations, situated in municipal sewage system. Early detection of toxic contaminants provides time for corrective actions. Wastewater toxicity level is based on activated sludge OUR (Oxygen Uptake Rate) measurement. The database of normal level of activated sludge OUR is collected during the measurement initial phase. Hence, if toxic event occurs, device will measure decreased OUR value and WWTP operators will be alarmed. Additionally, flow measurement is carried out. It allows to estimate the volume of a toxic stream. Development of the early warning system requires solving minimum six different scientific and technical issues and is a subject for a complex research project.

Performance of membrane bioreactor in presence of flocculants

This study focused on evaluating the effects of flocculant addition on the performance of membrane bioreactor (MBR). Two different flocculants, aluminum sulfate (alum) and polyaluminum chloride (PACl), were tested and the performance of MBR system in terms of COD removal, membrane fouling, and sludge properties was investigated. Addition of both flocculants resulted in significant reduction of membrane fouling rate and polyaluminum chloride was found more effective than alum. The sustainable filtration time at optimum dosage of alum and PACl was, respectively, 2.5 and 4.2 times more than that in control MBR which had no flocculant. Additionally, sludge oxygen uptake rate (OUR) improved in the presence of both flocculants and average OUR values obtained from flocculant-added membrane bioreactors was about 1.5 times more than that in control MBR. The results also revealed that there were no significant difference in COD removal of flocculant-added MBRs and control MBR and the treatment in all the three MBRs led to high COD removal efficiencies.

Effect of EDTA and Fe-EDTA complex concentration on TCF Kraft mill effluent degradability. Batch and continuous treatments

The effect of ethylenediaminetetracetic acid (EDTA) and Fe-EDTA complex on synthetic totally chlorine-free (TCF) effluent degradability in batch and continuously operating reactors was evaluated. Under batch treatment, the addition of EDTA and Fe-EDTA complex was studied in the range of 80 to 320 mg l −1. Under continuously operated reactors, the Fe-EDTA complex concentration varied from 20 to 80 mg l −1, and the hydraulic retention time (HRT) varied from 48 to 24 h. Sludge oxygen uptake rate (OUR) and chemical oxygen demand (COD) removal decreased when EDTA concentration increased in the influent under batch treatment; however, this inhibitory effect was reduced by the addition of Fe-EDTA complex. Without the addition of EDTA, COD removal decreased from 71% to 8%. The most efficient EDTA removal treatment (almost 10%) was the treatment of 80 mg l −1 Fe-EDTA. Under continuously operated reactors, COD removal was greater than 57% in the synthetic TCF effluent with a Fe-EDTA concentration that varied from 20 to 80 mg l −1; however, EDTA removal was lower than 25% in all cases. Synthetic TCF effluent with a Fe -EDTA concentration higher than 80 mg l −1 could not be treated by the activated sludge treatment due to EDTA's inhibitory effect on the sludge.

The Effect of Sludge Age on Decomposition of Sludge in Batch Aerobic Degestion of Activated Sludge Acclimated to Glucose and Peptone.

Experiments on batch aerobic digestion in continuous aeration were carried out by using activated sludges acclimated to synthetic wastewater of glucose and peptone at various sludge ages. As sludge age decreased, VSS decreased quickly with the progress of digestion and the ratio of maximum VSS reduction to initial VSS increased, but VSS/SS was kept constant. The decomposition rate of sludge was proportional to the biodegradable VSS, and its proportional constant (rate constant of decomposition) increased as sludge age decreased. The oxygen uptake rate of sludge was related to the decomposition rate of sludge by using a reaction model where the composition of activated sludge cell was C5H7NO2. Moreover, the SVI of sludge increased with the progress of digestion, but the final SVI was within the range of good settleability.

Evaluation of Activated Sludge Oxygen Uptake Rate Test Procedures

A series of bench- and pilot-scale experiments was conducted to evaluate the ability of biochemical oxygen demand (BOD) bottle-based oxygen uptake rate (OUR) analyses to represent accurately in situ OUR in complete mix-activated sludge systems. Aeration basin off-gas analyses indicated that, depending on system operating conditions, BOD bottle-based analyses could either underestimate in situ OUR rates by as much as 58% or overestimate in situ rates by up to 285%. The use of a continuous flow respirometer system was used to verify the off-gas analysis observations and assess better the rate of change in OUR after mixed liquor samples were suddenly isolated from their normally continuous source of feed. OUR rates for sludge samples maintained in the completely mixed bench-scale respirometer decreased by as much as 42% in less than two minutes after feeding was stopped. Based on these results, BOD bottle-based OUR results should not be used in any complete mix-activated sludge process operational control strategy, process mass balance, or system evaluation procedure requiring absolute accuracy of OUR values.