Characterization of particles and their relation with residual aluminum in water treated with pulsating floc blanket clarifiers and conventional clariflocculators using PACl

A pulsating floc blanket clarifier (PFBC) employing cyclic contractions and rarefactions to a bed of densely concentrated suspension of flocculated particles in fluidized state, was compared with conventional clariflocculator (CC) at pilot scale (8,000 L/day) in continuous mode of operation. For influent turbidity varied from 2 to 20 NTU, coagulation-flocculation behavior exhibited under the two fundamentally different treatment processes with PACl influenced inter-related performance parameters. The residual turbidity was found lower by 74%, flocs and fine colloids in suspension larger by 73 and 75% respectively, and the total and dissolved residual aluminum lower by 50 and 49% respectively on average for PFBC compared to CC. Particulate form comprised major fraction (≈72%) of total residual aluminum for both. PFBC abetted formation of a more consolidated floc structure which rendered the shape, size and morphology such that the settling velocity was 50% to 410% higher than that of the CC flocs. Reaction-limited aggregation (RLA) process and inter-particle bridging were dominant and the resulting floc structure and its formation mechanism have been presented.

Characterization of activated sludge flocs by confocal laser scanning microscopy and image analysis

The purpose of this study was to characterize microbial floc structure and properties under phosphorus (P) limiting and non-limiting regimes. The P-limitation applied to the biomass did not significantly impact on reactor performance in terms of COD removal and MLSS. The composition of EPS was affected by the P-limitation with significantly increased accumulation of carbohydrates, uronic acids and proteins. CLSM and glycoconjugate mapping revealed that the relative abundance of α and β- N -acetylgalactosaminyl/galactopyranosyl and N -acetylglucosaminyl residues was affected by P-limitation, suggesting changes in microbial populations within the floc structure, which in turn could cause the compositional changes of EPS. The image analysis performed on CLSM images indicated that under non-limiting conditions the cell clumps within the floc were significantly smaller as compared to P-limiting conditions. The fractal dimension and porosity under limiting conditions were either significantly higher or lower than under P-rich conditions.

Characterization of activated sludge flocs by confocal laser scanning microscopy and image analysis

The purpose of this study was to characterize microbial floc structure and properties under phosphorus (P) limiting and non-limiting regimes. The P-limitation applied to the biomass did not significantly impact on reactor performance in terms of COD removal and MLSS. The composition of EPS was affected by the P-limitation with significantly increased accumulation of carbohydrates, uronic acids and proteins. CLSM and glycoconjugate mapping revealed that the relative abundance of α and β- N -acetylgalactosaminyl/galactopyranosyl and N -acetylglucosaminyl residues was affected by P-limitation, suggesting changes in microbial populations within the floc structure, which in turn could cause the compositional changes of EPS. The image analysis performed on CLSM images indicated that under non-limiting conditions the cell clumps within the floc were significantly smaller as compared to P-limiting conditions. The fractal dimension and porosity under limiting conditions were either significantly higher or lower than under P-rich conditions.

Freeze–thaw combined with activated carbon improves electrochemical dewaterability of sludge: Analysis of sludge floc structure and dewatering mechanism

Freeze–thaw (F/T) and electrochemistry are environment-friendly and efficient sludge treatment technologies. In this study, F/T and electrochemistry were combined in the pretreatment of sludge dewatering in the laboratory, and activated carbon (AC) was added to improve the electrochemical dewatering performance of sludge. During the experiment, the effect of F/T on the floc structure was analyzed by a laser particle analyzer and scanning electron microscope. F/T treatment not only improved the dewatering performance of sludge, but also promoted the aggregation of sludge flocs into larger particles. The median diameter (D50) increased from 45.27 µm to 128.94 µm. Then, the intracellular polymer of large-particle sludge was analyzed by three-dimensional excitation–emission matrix (3D-EEM). The tightly bound extracellular polymeric substances (TB-EPS) still contained a large amount of protein substances, which hindered the improvement of sludge dewatering performance. AC was added to the thawed sludge solution before electrochemical treatment (EP). The conductivity of AC enhanced the effect of EP, thereby cracking the sludge flocs. Thus, the light intensity of TB-EPS in the 3D-EEM fluorescence spectroscopy was decreased, and the D50 was also reduced to 105.3 µm. The final specific resistance of filtration and water content were reduced by 96.39% and 32.17%, respectively. Element analysis of the sludge cake after dehydration showed that the addition of AC significantly improved the combustion efficiency of the sludge cake. Moreover, preliminary economic analysis showed that the cost of this research was low, which indicated the potential application value of combined treatment.

Influence of road salt thawing peaks on the inflow composition and activated sludge properties in municipal wastewater treatment

Operational data over 2 years from three large Austrian wastewater treatment plants (WWTPs) with design capacities of 4 million, 950,000 and 110,000 population equivalent (PE) were examined. Salt peaks, due to thawing road salt were detected and quantified by electrical conductivity, temperature and chloride measurement in the inflow of the WWTPs. Daily NaCl inflow loads up to 1,147 t/d and PE-specific loads of 0.26–0.5 kg NaCl/(PE · y) were found. To mimic the plants' behaviour in a controlled environment, NaCl was dosed into the inflow of a laboratory-scale activated sludge plant. The influence of salt peaks on important activated sludge parameters such as sludge volume index, settling velocity and floc size were investigated. Influent and effluent were sampled extensively to calculate removal rates. Respiration measurements were performed to quantify activated sludge activity. Particle size distributions of the activated sludge floc sizes were measured using laser diffraction particle sizing and showed a decrease of the floc size by approximately two-thirds. The floc structure was examined and documented using light microscopy. At salt concentrations below 1 g/L, increased respiration was found for autotrophic biomass, and between 1 and 3 g NaCl/L respiration was inhibited by up to 30%.

Analysis of the Mechanical Properties and Mechanism of Zinc Ion-Contaminated Red Clay

To study the effects of different concentrations of zinc ions on the mechanical strength, material composition, and microstructure of red clay, a triaxial test, an x-ray diffraction test, an x-ray fluorescence spectrometry test, a scanning electron microscopy test, and a mercury intrusion test were carried out on contaminated soil to investigate the mechanisms of zinc ion-contaminated red clay. The results show that the higher the concentration of zinc ions, the smaller the shear strength and cohesion of the red clay. The internal friction angle is increased first and then decreased. From material composition, zinc ion makes montmorillonite and hemite disappear in red clay. With the increase of zinc ion concentration, quartz semiquantitative increase and kaolinite semiquantitative decrease and the content of SiO2, Fe2O3, and Na2O reduces. Microscopically, the structure of red clay changes from floc structure to granular and aggregate structure after the zinc ions are added, while the contact of the particles is converted to point contact. With the increase of the concentration of zinc ions, the porosity and the fractal dimension of the red clay gradually increase, and the stability of the granular structure is weakened.