Initial Sludge Concentration Research Articles

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The performance of EF (electroflotation) on the thickening of activated sludge were investigated using laboratory scale batch flotation reactor. In this paper, the effects of parameters such as electrode material, NaCl dosage, initial sludge concentration and electrode distance were examined. The results showed that the performance for sludge thickening of the five electrodes lay in: Pt/Ti > Ru/Ti > Ir/Ti > Ti mesh > Ti plate. The more NaCl dosage was high, the more sludge was thickened and the shorter thickening time was obtained. However, considering the final thickening time and sludge concentration, optimum NaCl dosage was 0.5 g/L. Thickening time and sludge concentration was not affected by electrode distance. In DAF (dissolved air flotation) system, optimum recycle ratio was 40% and thickening performance was lower than that of the EF.

Sludge concentration dynamic distribution and its impact on the performance of UNITANK

UNITANK is a biological wastewater treatment process that combines the advantages of traditional activated sludge process and sequencing batch reactor, which is divided into Tank A, B and C. In this study, the sludge distribution and its impact on performance of UNITANK were carried out in Liede Wastewater Plant (WWTP) of Guangzhou, China. Results showed that there was a strong affiliation between Tank A and B of the system in sludge concentration distribution. The initial sludge concentration in Tank A could present the sludge distribution of the whole system. The sludge distribution was mainly influenced by hydraulic condition. Unsteady sludge distribution had an impact on variations of substrates in reactors, especially in decisive reactor, and this could lead to failure of system. Settler could partially remove substrates such as COD and NO 3-N, but there was adventure of sludge deterioration. The rational initial sludge concentration in Tank A should be 4000–6000 mg/L MLSS.

Isotherms, kinetics and thermodynamics of dye biosorption by anaerobic sludge

Experiments were conducted to investigate the adsorption characteristics of dyes by anaerobic sludge in this study. Influence of dye type, sorption time, initial dye concentration, sludge concentration and temperature on dye biosorption was evaluated. Furthermore, the isotherms, kinetics and thermodynamic of biosorption were also explored. Experimental results show that anaerobic sludge had a much higher equilibrium adsorption density on Rhodamine B than on Eosin Y. The adsorption density of Rhodamine B onto sludge decreased with enhancing sludge concentration. At a lower Rhodamine B concentration, adsorption could reach saturation in a lower sludge concentration. Results also indicate that both Langmuir and Freundlich adsorption models were able to adequately describe the biosorption equilibrium of Rhodamine B onto anaerobic sludge. The biosorption followed the pseudo second-order adsorption kinetics.

Laboratory study on the bioremediation of petrochemical sludge-contaminated soil

This study evaluated by biological and chemical analyses the effectiveness of bioremediation of sludge from the petrochemical industry in systems containing artificially contaminated soil. The sludge–soil systems were prepared with three different initial concentrations of sludge, and during bioremediation 86–95% of the hydrocarbons was eliminated. Simultaneously, soil bacterial populations and inhibition of seed germination by aqueous extracts increased in all sludge–soil systems during the first 180 days of treatment. After 1 year of bioremediation, a loss in the catabolic capacity of the Gram-negative bacterial population was observed, but was not dependent on the initial sludge concentration. Furthermore, residual levels of hydrocarbons and seed germination inhibitory effect decreased sharply, but some level of toxicity remained in the systems containing the highest initial sludge concentration. Independent of the initial sludge concentration, the contaminated soils did not re-establish their original features even when residual hydrocarbon concentrations suggested the end of the process.

Effect of petrochemical sludge concentrations on changes in mutagenic activity during soil bioremediation process

AbstractThe present study was performed to assess the effect of the petrochemical sludge application rate on the mutagenic activity (Ames test) of soil and the persistence of mutagenic activity during laboratory soil bioremediation process. Sludge‐soil systems were prepared at four different sludge application rates (1.25, 2.5, 5, and 10% w/w). Unamended soil was used as a control. Immediately following sludge application, in the absence or presence of S9, a linear correlation between sludge application rates and mutagenicity was found but differed significantly (p < 0.05) from the control system only at higher application rates (5 and 10% w/w). The direct mutagenicity of all systems decreases during the bioremediation process, and after a year of treatment only the 10% system induced a mutagenic response that was significantly different from the control system. On the other hand, an initial increase of the indirect mutagenicity was observed at all application rates. The time required for observing this increase was inversely proportional to the initial sludge concentration. After a year of treatment, the indirect mutagenicity of all sludge‐amended soils was not significantly different but was significantly different from the unamended soils. The persistence of the direct mutagenic activity of the sludge‐amended soils was related to the sludge concentration, whereas the indirect mutagenic persistence was related to the relationship between easily degradable hydrocarbons and polynuclear aromatic hydrocarbons concentration and independent from the initial application rate.

A biological phosphorus removal potential test for wastewaters.

A simple test was proposed to assess whether phosphorus in a wastewater can be removed using a biological phosphorus removal (BPR) process. The test includes the measurement of phosphorus release during 2 hours of the anaerobic stage in a batch reactor containing phosphorus-accumulating organisms (PAOs) and estimation of the effluent phosphorus concentration using biochemical relationships. The BPR potential test developed allowed for the successful evaluation of BPR feasibility for five wastewater samples. The BPR potential test was validated by comparing the test results with the effluent phosphorus concentrations measured in a sequencing batch reactor (SBR). An effluent phosphorus concentration of 1.9 mg P/L predicted for the BPR potential test performed was close to the effluent phosphorus concentration of 1.8 mg P/L obtained from an SBR on the same day. During the anaerobic stage, phosphorus release was significantly affected by the sludge concentration initially, but became insignificant after 2 hours. The initial sludge concentration affected the phosphorus release rate; thus, it is recommended that the BPR potential test be conducted at a target mixed liquor volatile suspended solids concentration. It is also recommended that the BPR potential test be conducted at the site where the PAO-containing sludge is available and the wastewater sample can be delivered at 4 degrees C in less than 24 hours. The PAOs in different sludges had almost identical phosphorus release after 2 hours; however, the characteristics of facultative bacteria in sludges affected the phosphorus release. If the wastewater is prefermented for at least 3 days before the BPR potential test, the amount of phosphorus released by various PAO-containing sludges is expected to be identical.

EFFECT OF PETROCHEMICAL SLUDGE CONCENTRATIONS ON CHANGES IN MUTAGENIC ACTIVITY DURING SOIL BIOREMEDIATION PROCESS

The present study was performed to assess the effect of the petrochemical sludge application rate on the mutagenic activity (Ames test) of soil and the persistence of mutagenic activity during laboratory soil bioremediation process. Sludge-soil systems were prepared at four different sludge application rates (1.25, 2.5, 5, and 10% w/w). Unamended soil was used as a control. Immediately following sludge application, in the absence or presence of S9, a linear correlation between sludge application rates and mutagenicity was found but differed significantly (p < 0.05) from the control system only at higher application rates (5 and 10% w/w). The direct mutagenicity of all systems decreases during the bioremediation process, and after a year of treatment only the 10% system induced a mutagenic response that was significantly different from the control system. On the other hand, an initial increase of the indirect mutagenicity was observed at all application rates. The time required for observing this increase was inversely proportional to the initial sludge concentration. After a year of treatment, the indirect mutagenicity of all sludge-amended soils was not significantly different but was significantly different from the unamended soils. The persistence of the direct mutagenic activity of the sludge-amended soils was related to the sludge concentration, whereas the indirect mutagenic persistence was related to the relationship between easily degradable hydrocarbons and polynuclear aromatic hydrocarbons concentration and independent from the initial application rate.

Formaldehyde toxicity in anaerobic systems

Formaldehyde toxicity during acetoclastic methanogenesis exerted a dual character: It was in part reversible and in part irreversible. Toxicity was only reversible at very low formaldehyde concentration. The degree of irreversible toxicity was proportionally related to the initial sludge concentration, but was independent of the initial specific acetoclastic activity. Formaldehyde conversion seemed to be dependent on the concentration of the various trophic groups present in the anaerobic granular sludge used. Hence biomass diversity may play an important role in the outcome of toxicity studies and may furthermore contribute to the explanation of the controversies with respect to toxicity values reported in literature.

Development of refined clarifier operating diagrams using an updated settling characteristics database

An analysis of five sludge‐settling characteristics data sets is presented, representing data from 51 separate suspended growth biological wastewater treatment processes and including 214 separate runs and over 1 500 individual data points. The results indicate that the data can be characterized using a single relationship between the initial sludge settling velocity (Vi), the initial sludge concentration (Ci), and the sludge volume index (SVI). The predictive capability of this relationship is independently verified. These results suggest that this single relationship can be used to accurately characterize the settling characteristics of an activated sludge based only on the measured SVI. A comparison of alternate sludge‐settling indexes indicates that the predictive capability of the relationship can be further improved by use of the stirred SVI3.5 analysis rather than the SVI. More data are required to refine relationships developed based on the SSVI3.5 and the diluted SVI. Secondary clarifier‐operating diagrams based on the developed relationships are presented.

Disappearance and crop uptake of PCBs from sludge‐amended farmland

ABSTRACT: The Madison Metropolitan Sewerage District (MMSD) has conducted a five‐year (1985‐1990) field experiment to obtain data that provide a scientific basis for regulating land disposal of sludge contaminated with polychlorinated biphenyls (PCBs). Over 1 400 samples of soil and crop tissue were analyzed. This paper presents all the field data and interpretation. The experimental design included eight different sludge treatments and controls, making it possible to study the effects of sludge concentration, sludge loading rate, and sludge application pattern on the fate of PCBs in the soil system. Each treatment was replicated three times, giving thirty test plots in all (24 sludge applications and 6 control plots). Seventy‐nine PCB congeners were detected during the study and the concentration of each PCB congener was measured in the surface soil, corn stover, and corn grain. Surface runoff runoff studies were conducted in 1988 and 1990 and congener‐specific PCB analyses were made on these as well. A first‐order disappearance model, C = C0 exp(− Kt), was appropriate to evaluate the disappearance of PCBs from the surface soil layer. AT is the rate constant for PCB disappearance. Results indicate that the rate constant for disappearance of each individual PCB congener in the soil was independent of the initial PCB sludge concentration, the sludge loading rate, and sludge application pattern. Most of the 2‐, 3‐, and 4‐chlorinated PCB congeners showed significant decreases in their soil concentration with half‐lives in the range of 4 to 58 months. The more highly chlorinated PCBs were more persistent in the sludge amended farmland, but many of them did disappear. The concentration of PCBs in the runoff samples was correlated with surface soil concentration. The PCBs were associated with the runoff sediments and there was no measurable PCB in the liquid portion of the runoff. It was concluded that there is no PCB translocation into either corn grain or corn stover samples. The bioconcentration factor for PCBs in the crop tissues is zero.

Aerobic digestion of thickened activated sludge: Reaction rate constant determination and process performance

The aims of this work were to select which parameter—total suspended solids (TSS), volatile suspended solids (VSS) or degradable volatile suspended solids (DVSS)—best expressed the kinetics of aerobic digestion of waste secondary activated sludge: to define the relationship between the reaction rate constant and the initial concentration of sludges; to evaluate the effect of aerobic digestion on the filterability of the treated sludge as measured by the capillary suction time (C.S.T.). Batch experiments of aerobic digestion were performed in our laboratory on samples of sludges at a constant temperature of 20 C. The initial concentration of sludges ranged from 2600 to 22,000 mg l −1. TSS was found to be the parameter which most closely fits the kinetic model of aerobic digestion. The reaction rate constant was a linear, inverse function of the initial sludge concentration with TSS and with VSS as a parameter. Sludge filterability is affected by the process of aerobic digestion; a prolonged aeration time results in poorer dewatering; and the more concentrated the sample, the poorer the dewatering.