Powdered activated carbon‐assisted biotreatment of a chemical synthesis wastewater

The effect of powdered activated carbon (PAC) on the biotreatment of an industrial wastewater taken from a chemical plant synthesising drugs for the pharmaceutical sector was studied. Industrial and domestic wastewaters were combined at laboratory scale and the effect of PAC addition was tested in aerobic reactors. The aim of this addition was to decrease inhibitory and non‐biodegradable organics. Two different procedures were applied in testing the effectiveness of PAC. First, PAC was directly added to activated sludge mixed liquor. In the second case, industrial wastewater was first contacted with PAC and then treated biologically. In the evaluation of performance, COD measurements, oxygen uptake rate (OUR) measurements and measurements in the ultraviolet‐visible (UV‐Vis) spectra were taken into consideration. Both direct PAC addition and PAC pretreatment led finally to similar results. In both cases, the concentration of non‐biodegradable matter could be lowered. In particular, the colour of the wastewater was significantly reduced. Direct PAC addition appeared to be more practical and plausible. In any case, PAC addition to activated sludge increased the OUR of the sludge, indicating that inhibition could be decreased. The study also pointed out that in the assessment of PAC performance, the combined evaluation of OUR, spectral parameters and COD would be much more informative than the COD parameter alone. © 2001 Society of Chemical Industry     

Investigation of municipal and olive mill wastewater co‐treatment in activated sludge–powdered activated carbon (AS‐PAC) systems

BACKGROUND: The purpose of this study was to investigate the co‐treatment of olive‐mill wastewater (OMW) and municipal wastewater in activated sludge systems operating in the absence and presence of different adsorbent materials and to study the role of sorption and biodegradation in total phenols removal. RESULTS: Batch experiments were initially conducted to investigate total phenols' adsorption capacity on activated sludge (AS), olive pomace (OP) and powdered activated carbon (PAC). According to the results, PAC presented the best adsorption capacity. Three sequencing batch reactors (SBRs) were also operated, treating municipal wastewater and different amounts of OMW. The first SBR contained AS (AS‐System), the second AS and OP (AS‐OP System) and the third AS and PAC (AS‐PAC System). All SBRs operated sufficiently in the presence of 1% v/v OMW, achieving mean COD and total phenols removal efficiency higher than 86% and 85%, respectively, and satisfactory settling capacity. Increase of OMW concentration to 5% v/v affected the performance of SBRs, resulting in mean COD removal efficiencies that ranged between 61% (AS‐OP System) and 80% (AS‐PAC System). CONCLUSION: Among the SBRs used, the AS‐PAC System operated with highest performance in the presence of 1 and 2.5% v/v OMW, and showed better stability in the presence of 5% v/v OMW. Calculation of total phenols mass flux revealed that biodegradation was the principal mechanism of their removal. The highest values of mean biotransformation rates were calculated for the AS‐PAC System and ranged between 2.0 and 40.6 d^?1 for different experimental phases. Copyright © 2012 Society of Chemical Industry     

Optimum Process Parameters for the Treatment of Landfill Leachate Using Powdered Activated Carbon Augmented Sequencing Batch Reactor (SBR) Technology

The sequencing batch reactor (SBR) process was used for the treatment of raw landfill leachate. Optimum preliminary parameters of leachate/activated sludge ratio, powdered activated carbon (PAC) dosage, and settling time were studied. Optimum obtained parameters (mixing ratio of 10%, PAC dosage of 10 g/L, and settling time of 1.5 h) were applied on two types of SBRs, namely, non-powdered and powdered activated carbon (NPAC and PAC, respectively). Consequently, the effect of factors, the aeration rate and contact time, on both NPAC and PAC reactors were studied. Response surface methodology was used for the design, analysis, and optimization of the experiments. Removal efficiencies of ammonia (NH₃-N), color, chemical oxygen demand (COD), total dissolved salts (TDS), and sludge volume index (SVI) were measured for 13 experiments. Based on the obtained results, the optimum aeration rate and contact time for both NPAC and PAC reactors were 2 and 1 L/min and 5.56 and 5.5 h, respectively. Better performance (in terms of NH₃-N, color, COD, and TDS removal efficiencies and SVI values) was exhibited by PAC reactors rather than NPAC.     

Characterization and modelling of denim‐processing wastewaters for activated sludge

The study involved characterization of denim‐processing wastewaters, mainly to generate the necessary experimental data for the modelling and evaluation of the activated sludge process. The striking feature of the wastewater quality was the excessive suspended solids content requiring effective removal before biological treatment. COD fractionation was, however, typical for a textile effluent in general, with a biodegradable fraction of 90%, a readily biodegradable COD ratio of 20%, a predominantly soluble slowly biodegradable fraction of 55–60% and negligible particulate inert COD. Hydrolysis was identified as the significant step in the biodegradation kinetics with rate coefficients quite specific to plant operation. Evaluation of the hydrolysis kinetics showed that the magnitude of the slowly biodegradable COD could be reduced with a higher hydraulic detention time, effectively improving the quality of the soluble effluent. © 2001 Society of Chemical Industry     

Anaerobic degradation: the effect of the combined treatment of substrates on the refractory fraction

The anaerobic digestion of landfill leachates mixed with domestic sewage was studied using a batch reactor at laboratory scale. Batch assays were carried out with different proportions of leachate in the feed: 100, 70, 50 and 30% by volume, with and without adjustment of pH, in order to determine the percentage of acidification and methanization, COD removal, anaerobic biodegradability and biomass growth yield. The main effect of the mixing with sewage was a synergistic improvement of the anaerobic treatment of leachates, but in different ways; the greatest improvement in COD removal was obtained when the proportion of leachate in the feed was 70%, but the highest degree of anaerobic biodegradability was obtained with 30% of leachate in the feed. The kinetics of these assays was studied and the experimental data were fitted to a modification of the equation of Chen and Hashimoto. A new concept of ‘non‐biodegradable fraction’ is proposed. © 2002 Society of Chemical Industry     

Modelling a sequencing batch reactor to treat the supernatant from anaerobic digestion of the organic fraction of municipal solid waste

In this study, a lab‐scale sequencing batch reactor (SBR) has been tested to remove chemical oxygen demand (COD) and NH₄⁺‐N from the supernatant of anaerobic digestion of the organic fraction of municipal solid waste. This supernatant was characterized by a high ammonium concentration (1.1 g NH₄⁺‐N L^?1) and an important content of slowly biodegradable and/or recalcitrant COD (4.8 g total COD L^?1). Optimum SBR operating sequence was reached when working with 3 cycles per day, 30 °C, SRT 12 days and HRT 3 days. During the time sequence, two aerobic/anoxic steps were performed to avoid alkalinity restrictions. Oxygen supply and working pH range were controlled to promote the nitrification over nitrite. Under steady state conditions, COD and nitrogen removal efficiencies of more than 65% and 98%, respectively, were achieved. A closed intermittent‐flow respirometer was used to characterize and model the SBR performance. The activated sludge model ASM1 was modified to describe the biological nitrogen removal over nitrite, including the inhibition of nitrification by unionized ammonia and nitrous acid concentrations, the pH dependency of both autotrophic and heterotrophic biomass, pH calculation and the oxygen supply and stripping of CO₂ and NH₃. Once calibrated by respirometry, the proposed model showed very good agreement between experimental and simulated data. Copyright © 2007 Society of Chemical Industry     

Assessing chemical oxygen demand and nitrogen conversions in a multi‐stage activated sludge plant with alternating aeration

This paper provides a detailed investigation of the mass transfers involved in chemical oxygen demand (COD) and N removal in an intermittent aeration activated sludge plant, as described by the widely used ASM1 model. The model was calibrated and validated on a data set obtained during three intensive sampling campaigns. The mass transfers of COD and nitrogen were calculated with the calibrated model for every biodegradable variable of the model in each tank of the biological treatment. Only by making this balance can evaluation of the contribution of each reactor (anaerobic, anoxic and intermittently aerated) to carbon and nitrogen removal be done. It was pointed out that in such a plant (activated sludge under very low organic mass loading (F/M) ratios, sludge retention time of 30 days) operating at 20 °C, the contribution of the anoxic tank in the denitrification process is very low (only 17%). The oxygen transfer in this tank was also estimated and found partly responsible for the low denitrification efficiency. Copyright © 2007 Society of Chemical Industry     

PAC+FBR处理垃圾渗滤液的研究

由于垃圾渗滤液COD、NH4-N浓度高,并且含有重金属等有毒污染物,通常,单纯的生物处理方式效果并不理想.高COD浓度的垃圾渗滤液经混凝沉淀后,调节pH=12,进行氨吹脱,经此预处理后的垃圾渗滤液,进行Fed-Batch Reactor(FBR)好氧生物处理,比较投加粉末活性碳(PAC)和不投加两种情况下对COD和NH4-N去除效果.当PAC投加量为2 g/L时,COD去除率达86 %,NH4-N去除率达26 %.     

Particle size distribution based evaluation of biodegradation and treatability for leachate from organic waste

BACKGROUND: The study evaluated the relationship between particle size distribution (PSD) of chemical oxygen demand (COD) and treatability of leachate generated by organic waste. PSD determinations were performed together with physico‐chemical and biological treatability studies. Leachate biodegradation was also evaluated by means of oxygen uptake rate (OUR) profiles and experimental results were used for calibration of the adopted mathematical model. RESULTS: The leachate was characterized by a COD content of 80 000 mg L^?1 in summer. PSD analysis showed a bimodal distribution with around 60% of the COD below 2 nm and 25% above 1600 nm. Chemical treatment by lime and alum provided limited COD removal (30‐35%). The extent of COD removal was higher than the particulate COD fraction above 1600 nm, it also occurred in the soluble range below 2 nm through adsorption. A modeling study indicated three major COD fractions that could be correlated with PSD analysis: readily biodegradable COD and slowly biodegradable COD in the soluble range and hydrolyzable COD fraction in the particulate range. CONCLUSION: PSD‐based COD fractionation adequately explained limitations of chemical treatment efficiency; it was also a reliable complement to the currently used respirometric tests for biodegradation, providing insight to the fate of different COD fractions included in the soluble range (<2 nm) and yielding concrete supporting information on the generation of soluble residual microbial products. Copyright © 2011 Society of Chemical Industry     

Effect of activation type on bioregeneration of various activated carbons loaded with phenol

Thermally and chemically activated powdered carbons (PAC), and their granular countertypes (GAC) with similar physical characteristics were used to investigate the extent of bioregeneration in laboratory‐scale activated sludge reactors. Bioregeneration of activated carbon was determined by measurement of bulk phenol concentrations and loadings remaining on activated carbon. It was also followed by oxygen uptake rate measurements. For the carbons used in this study, bioregeneration of chemically activated carbons was found to be higher than thermally activated ones. This was in accordance with their higher reversibility of adsorption and showed that bioregeneration was controlled by the reversibility of adsorption. Oxidative polymerization of phenol was a plausible explanation for low bioregeneration of thermally activated carbons. However, bioregeneration efficiencies of thermally activated carbons were much higher than their total desorbabilities. This unexpectedly high bioregeneration indicated that some exoenzymatic reactions had occurred. These results suggest that carbon activation type is of crucial importance for bioregeneration. PAC and GAC countertypes showed comparable bioregeneration efficiencies indicating that carbon size was not an effective factor. The environmental scanning electron microscopy (ESEM) studies showed that microorganisms were attached both on the external surface and interval cavities of activated carbon particles. Copyright © 2006 Society of Chemical Industry     

Effect of sonolysis on waste activated sludge solubilisation and anaerobic biodegradability

Activated sludge processes are key technologies in wastewater treatment. These biological processes produce huge amounts of waste activated sludge (WAS) or otherwise biosolids. Mechanical, thermal, and/or chemical WAS conditioning techniques have been proposed to reduce the sludge burden. Among the WAS treatments, the pre-treatment with ultrasound (US) is one of the most innovative processes. In many anaerobic digestion processes for the treatment of the sludge produced in wastewater treatment plants, the hydrolysis of the organic matter has been identified as the rate limiting step.This study is focused on the effect of US pre-treatment of WAS to the anaerobic digestion. Particle size reduction, Chemical Oxygen Demand (COD) solubilization and biodegradability by anaerobic digestion were monitored in order to find the optimal dose in US pre-treatment.The results show the better sonolysis conditions (US density, sonication time, specific energy) which can significantly improve the COD solubilisation and the anaerobic biodegradability.     

Granulation of sludge under different loads of a glycerol fraction from biodiesel production

The aim of the research was to evaluate the possibility of using the crude glycerol fraction from biodiesel manufacturing processes for granular sludge production. The experiment was carried out simultaneously in four sequencing batch reactors (SBRs) at different carbon loads: 0.2 ± 0.08, 0.6 ± 0.16, 1.1 ± 0.27, and 1.3 ± 0.35 g COD/g TSS per cycle (COD – chemical oxygen demand, TSS – total suspended solids). Granulation did not occur in the reactor with the lowest organic carbon load. In the remaining reactors small granules began to appear after 25 cycles of reactor operation. In all reactors the efficiency of carbon removal remained at ca. 80%. The highest granular sludge production per cycle was 0.31 ± 0.28 g TSS/L; it was obtained at an organic load of 1.1 ± 0.27 g COD/g TSS per cycle. Most of the introduced COD was removed in the reactors during the first 5 h of aeration; the COD removal rate was correlated with the organic load and varied from 123.12 to 472.76 mg COD per litre and hour. Practical applications: With the increasing production of biodiesel fuel a problem arises with the utilization of glycerol that is a by‐product of the process. By‐product glycerol fraction from small agricultural installations is usually contaminated. Its composition varies depending on parameters of the transesterification process and it is unprofitable to purify it. In the present research we investigated one possible way of dealing with the by‐product. The glycerol fraction was successfully used as a carbon source for the production of aerobic granular sludge. The granules obtained can be used as a seed sludge in granule‐based reactors, or can be cofired with coal or directly combusted. Since aerobic granular sludge is one of the most promising technologies investigated during the last few years it appears to possess high utility.     

Physico‐Chemical Processes for Landfill Leachate Treatment: Experiments and Mathematical Models

Abstract

In this study, the adsorption of synthetic landfill leachate onto four kinds of activated carbon has been investigated. From the equilibrium and kinetics experiments, it was observed that coal based PAC presented the highest organic pollutants removal efficiency (54%), followed by coal based GAC (50%), wood based GAC (33%) and wood based PAC (14%). The adsorption equilibrium of PAC and GAC was successfully predicted by Henry‐Freundlich adsorption model whilst LDFA+Dual isotherm Kinetics model could describe well the batch adsorption kinetics. The flocculation and flocculation–adsorption experiments were also conducted. The results indicated that flocculation did not perform well on organics removal because of the dominance of low molecular weight organic compounds in synthetic landfill leachate. Consequently, flocculation as pretreatment to adsorption and a combination of flocculation–adsorption could not improve much the organic removal efficiency for the single adsorption process.     

Integration of continuous biological and chemical (ozone) treatment of domestic wastewater: 1. Biodegradation and post‐ozonation

The continuous treatment of domestic wastewater by an activated sludge process and by an integrated biological–chemical (ozone) oxidation process were studied in this work. Chemical oxygen demand (COD), biochemical oxygen demand (BOD), absorbance at 254 nm (UV₂₅₄) and nitrogenous compound content were the parameters followed in order to evaluate the performance of the two processes. Experimental data showed that both UV₂₅₄ and COD reductions are improved in the combined biological–chemical oxidation procedure. Thus, reductions of 59.1% and 37.2% corresponding to COD and UV₂₅₄, respectively were observed after the biological process (hydraulic retention time = 5 h; mixed liquor volatile suspended solids concentration = 3142 g m⁻³) compared with 71.0% and 78.4% obtained when a post‐ozonation step ( D _O3 = 41.7 g m⁻³) was included. During conventional activated sludge treatment, appropriate nitrification levels are only achieved with high hydraulic retention time and/or biomass concentration. Ozonation after the secondary treatment, however, allows improved nitrogen content reduction with total nitrite elimination. Post‐ozonation also leads to a higher biodegradability of the treated wastewater. Thus, the ultimate BOD/COD ratio goes from 0.16 after biological oxidation to 0.34 after post‐ozonation with 41.7 g O₃ m⁻³. © 1999 Society of Chemical Industry     

Effects of Fe(III) on floc characteristics of activated sludge

The effects of Fe(III) on floc characteristics of activated sludge were investigated in nine parallel sequencing batch reactors (SBRs). The results showed that Fe(III) improved the quality of organic matters in the effluent of reactors. Concentrations of Fe(III) up to 23.8 mg dm^?3 decreased suspended solids and turbidity in effluent but overdosage resulted in deterioration of these parameters. Activated sludge floc size measurements indicated that Fe(III) led to a shift in the size distribution from large to small flocs. Concentrations of Fe(III) less than 23.8mg dm^?3 did not significantly change the proportion of larger flocs, but overdosage of Fe(III) markedly decreased the fraction of larger flocs and produced a large number of smaller flocs, which may be responsible for the deterioration of effluent suspended solids and turbidity. Scanning electronic microscopic (SEM) observation suggested high Fe(III) concentrations lead to significant changes in floc morphology and reduction of filamentous microorganisms available for the formation of large aggregates. Copyright © 2005 Society of Chemical Industry     

Ozonation as a Means to Optimize Biological Nitrogen Removal from Landfill Leachate

In this study, we investigate factors that can affect nitrification and denitrification in a moving bed biofilm system, treating partly stabilized landfill leachate. The optimization of biological treatment by means of controlled ozonation is additionally evaluated. Results obtained with a laboratory-scale, continuous-flow biofilm system suggest that nitrogen removal can be limited by the low influent biodegradable substrate concentrations, and that autotrophic nitrification can be adversely impacted by the high alkalinity buffer and ammonium/ammonia concentration. Our results suggest an optimum ozone dosage as high as 0.5 g/L O₃ can be required to effectively decrease the effluent soluble COD concentration and pH profile in the aerobic reactors, improve the biodegradable COD production from inert compounds, and induce chemical nitrification in the system. The specific cost of ozonation evaluated is 0.36–0.73 euro/m³ with 911 mg/L average effluent soluble COD measured in the biofilm system.     

Thermal,chemical and thermo‐chemical pre‐treatment of waste activated sludge for anaerobic digestion

The influence of different pre‐treatments was studied in order to observe the effects of temperature, pH and treatment time on Waste Activated Sludge (WAS) solubilization, and anaerobic digestion of pre‐treated sludge. Results showed that thermo‐chemical pre‐treatments were the most efficient on Chemical Oxygen Demand (COD) solubilization, which could reach 83% at 170 °C with pH = 12. Yet, increase in COD solubilization in thermo‐chemical pre‐treatment was not linked to an increase in soluble Volatile Solids (VS) as optimal conditions were 170 °C, and 130 °C with pH = 10, for this criterion. So, temperature was found to be the most influential parameter on COD and VS solubilization. Biodegradability batch anaerobic tests confirmed results obtained on WAS solubilization, that is to say that 170 °C and 130 °C with pH = 10 were optimal conditions, with respectively 45% and 21% of anaerobic digestion enhancement. Thus these two conditions were chosen for sludge treatment before continuous anaerobic digestion. Results, after stabilization have shown a better efficiency of 170 °C compared with 130 °C with pH = 10 pre‐treatment, since after anaerobic digestion it led to 71% of COD degradation and 59% of Total Solids (TS) degradation, with an improvement of 54% in biogas production. The main differences between those two pre‐treatments could be due to the pre‐treatments themselves more than to an effect on anaerobic digestion, because the first one led to a partial loss of WAS COD (near 17% of initial COD) and the second one to an increase in TS due to addition of base. Copyright © 2004 Society of Chemical Industry     

Influence of an aerobic selector on copper and hexavalent chromium biosorption by activated sludge

The influence of an aerobic selector on biosorption of Cu and Cr(VI) by activated sludge was studied. In‐vitro batch adsorption tests were performed using sludge harvested from bench‐scale activated sludge systems. Metal biosorption by activated sludge was rapid with equilibrium usually reached within an hour. Adsorption behaviour closely followed a Freundlich isotherm model. Experimental data suggested that an aerobic selector increased the biosorption of the metal ions by activated sludge, confirming observations by others in a similar study but with different heavy metals. Freundlich isotherms indicated that the biosorption capacity of activated sludge was increased by 15% for Cu and 30% for Cr(VI). Activated sludge from both systems had a greater biosorption capacity for Cu than for Cr(VI). The effects of pH and sludge concentration were also investigated. The results indicate that these parameters may influence the biosorption characteristics of activated sludge. © 2002 Society of Chemical Industry     

Anaerobic Treatment of Leachates in a Pilot-Scale UASB: Strategy of Start-up

The anaerobic digestion of leachates from a solid urban wastes landfill was studied using an upflow anaerobic sludge blanket reactor in pilot scale. The strategy of start-up and acclimation was based on gradual substitution of easily biodegradable feed with landfill leachate. All modifications were based on the attainment of 70% COD removal. Having completed the start-up, the kinetics of leachate biodegradation were studied and the values of kinetic parameters were obtained by fitting experimental data to the equation of Chen and Hashimoto. The biodegradability assays indicated that 40–50% of COD in leachate was biodegradable. The highest COD removal was 90–100% if only the biodegradable matter was considered.     

The effect of substrate on the composition of polyhydroxyalkanoates in enhanced biological phosphorus removal

This paper primarily evaluates the effect of external substrate type on the composition of polyhydroxyalkanoates in enhanced biological phosphorus removal (EBPR). Two sets of sequencing batch reactors (SBRs) are operated for this purpose, one with acetate and the other with propionate as the sole carbon source at different influent COD/phosphate ratios in the range 6.7–20 mgCOD mg^?1P. Results indicate that propionate is a more efficient substrate for EBPR, enabling total phosphate removal regardless of the change in COD/phosphate ratio. Total polyhydroxyalkanoates formation of 267–291 mgCOD L^?1 with a slight increase at higher influent phosphorus levels is observed for acetate experiments, and a slightly lower level of 250–280 mgCOD L^?1, with a similar trend for propionate experiments. The volatile fatty acid type and composition in the influent induces a significant difference in the polyhydroxyalkanoates composition of the two sets of activated sludge sustained in corresponding SBR systems. Propionate is mostly stored as 3‐hydroxy‐2‐methylvalerate and polyhydroxyvalerate, while acetate is stored as polyhydroxybutyrate. The P uptake rate in SBRs fed with propionate is considerably higher than that in the acetate reactors. Parallel batch experiments yield different results, especially for systems fed with acetate, indicating that the enzymatic system to metabolize propionate is not rapidly established, always yielding a dominant polyhydroxybutyrate fraction in the generated polyhydroxyalkanoates regardless of the level of propionate in the feed. Copyright © 2007 Society of Chemical Industry