Addition of activated carbon to batch activated sludge reactors in the treatment of landfill leachate and domestic wastewater

Leachate from a municipal landfill was combined with domestic wastewater and was treated in batch activated sludge systems. The effectiveness and applicability of the addition of Powdered Activated Carbon (PAC) to activated sludge reactors was investigated. Isotherm tests were carried out with PAC in order to estimate the extent of adsorption of organic matter onto PAC. Then, in activated sludge reactors COD (Chemical Oxygen Demand) removal and nitrification were studied both in the absence and presence of PAC for comparison purposes. In both cases, Oxygen Uptake Rates (OUR) were measured with respect to time in order to investigate substrate removal and change in microbial activity. Addition of PAC to activated sludge increased COD removal by removing mainly the non‐biodegradable fraction in leachate. The COD decreases in batch reactors were best expressed by a first‐order kinetic model that incorporated this non‐biodegradable leachate fraction. With added PAC, nitrification was also enhanced. But in all of the batch runs a significant accumulation of NO₂ ‐N took place, indicating that the second step of nitrification was still inhibited. © 2001 Society of Chemical Industry     

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     

污泥活性炭的制备及其脱色性能

以污水污泥为原料,采用物理活化法制得污泥活性炭,并用该活性炭处理染料废水,研究了pH值、污泥活性炭的投加量、温度、吸附时间等因素对染料废水的脱色率和COD去除率的影响。结果表明:用污泥制备的活性炭,其碘值和亚甲基兰吸附值分别为254.36 mg/g和20.26 mg/g,而且BET比表面积值为25.1995 m2/g,总孔容积为0.0399 m3/g,具有较好的吸附性能;将污泥活性炭用来吸附氨基黑染料,并与商品活性炭处理氨基黑染料的效果进行对比,自制污泥活性炭的脱色效果达到了商品活性炭的水平;污泥活性炭对氨基黑染料的吸附过程符合Langmuir吸附等温线。     

Effect of sludge retention time in sludge holding tank on excess sludge production in the oxic‐settling‐anoxic (OSA) activated sludge process

The activated sludge process is a core technology in wastewater treatment plants. Excess sludge produced in the process must be treated and disposed of properly and may account for up to 60% of total plant operating cost. Therefore, it is necessary to develop new biological concepts to minimize excess sludge production. The oxic‐settling‐anoxic process (OSA process), a modified activated sludge process, may produce less excess sludge than the conventional activated sludge process. The effect of sludge retention time in the sludge holding tank of the OSA process on excess sludge yield has been studied. Four pilot‐scale activated sludge systems were employed, one of which was a conventional activated sludge process, and was used as the control system. The other three were OSA systems operated with different sludge retention times (5.5 h, 7.6 h, and 11.5 h) in the sludge holding tank. All systems were operated with synthetic wastewater for 7 months. Results showed that the three OSA processes with 5.5 h, 7.6 h, and 11.5 h sludge retention time reduced the excess sludge by 33%, 23% and 14%, respectively. Compared to the control process, chemical oxygen demand (COD) removal efficiency and effluent NH₃–N concentration were not significantly influenced, but total nitrogen (TN) removal efficiency decreased by 0–9%. Total phosphorus (TP) removal efficiency of OSA processes with 7.6 h and 11.5 h sludge retention time increased by 19%. Sludge settleability was excellent in the three OSA processes. No distinct shift in the diversity of the predominant species was found in microbial populations. We conclude that the OSA system could reduce excess sludge production. Results suggest 6–7 h sludge retention time would be optimal. Copyright © 2007 Society of Chemical Industry     

Production of activated carbon from agricultural by‐products

The production of activated carbon from agricultural by‐products is a research field of increasing interest as it deals with the problem of the disposal of agro‐residues, at the same time producing an added‐value product that can be used in a number of environmental applications. The paper presents an overview of the latest developments in processes for the production of activated carbon from agricultural by‐products, with emphasis on the methodology applied, the effect of critical process parameters such as retention time, temperature, chemical to material ratio, as well as the adsorbing capacity of the activated carbons produced in removing select compounds from synthetic and real wastewaters. Agricultural by‐products can be a source for activated carbon production with high surface areas and high adsorption capacity. Copyright © 2008 Society of Chemical Industry     

针铁矿促进剩余污泥厌氧消化中的脱氮除碳

剩余污泥厌氧消化因其较低的能源转化率使其发展有所受限,且污泥中高浓度有机质也会影响脱氮效果。理论上,在含铁(Ⅲ)（氢）氧化物的厌氧消化系统中,微生物能通过异化铁还原去除有机物和氨氮（Feammox）,但两者同步去除还有待验证。因此本研究通过向污泥厌氧消化系统中添加针铁矿,探究铁(Ⅲ)（氢）氧化物对同步脱氮除碳的影响。结果显示,随着针铁矿添加量的增加,反应器中有机物浓度逐渐减少。当添加50mmol/L针铁矿时,甲烷累积产量达到695.1mL,相较于没有添加针铁矿的厌氧系统提升了30.3%;TS/VS去除率也提升了21.1%/33.8%,说明针铁矿可有效促进污泥减量化。添加针铁矿的反应器中总氮去除率也有一定提升,当针铁矿添加50mmol/L时,去除率达到21.0%。以上结果表明,添加针铁矿可以在污泥厌氧消化中起到同时脱氮除碳的效果。     

Comparison of the filtration characteristics between biological powdered activated carbon sludge and activated sludge in submerged membrane bioreactors

The filtration performances of submerged membrane bioreactors (SMBR) with and without the addition of powdered activated carbon (PAC) were investigated respectively under the same feed and operation conditions. A series of experiments were conducted to analyze near-critical flux, effect of air-scouring rate and time of stable filtration operation of both systems. The experimental results demonstrated that pronounced flux enhancement was achieved by adding 1.2 g/L PAC. The near-critical flux for the biological powdered activated carbon (BPAC) system was about 32% higher than that for the activated sludge (AS) system. Increasing the air-scouring rate led to a more significant flux improvement for the BPAC system compared to the AS system. Long-term operation indicated that, at constant flux, the TMP increasing rate of the BPAC system could be lagged and thus cause the extension of operating intervals about 1.8 times compared to the AS system. Quantitative calculations showed the total hydraulic resistance of the BPAC system was about 44% lower than that of the AS system, and this decrease was mainly caused by the reduction in cake resistance. Analyses were then made from various aspects such as floc size distribution and apparent viscosity of the mixed liquor to elucidate the major factors giving rise to different filtration characteristics.     

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     

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     

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     

The use of 3,3′,4′,5‐tetrachlorosalicylanilide as a chemical uncoupler to reduce activated sludge yield

To determine whether chemical additions can be used to reduce sludge production in biological wastewater treatment, 3,3′,4′,5‐tetrachlorosalicylanilide (TCS) was added to activated sludge cultures as a metabolic uncoupler. Batch tests confirmed that TCS is an effective chemical uncoupler in reducing the sludge yield at concentrations greater than 1.0 mg dm^?3; a TCS concentration of 1.0 mg dm^?3 reduced sludge yield by approximately 50%. Substrate removal capability and effluent nitrogen concentration were not affected adversely by the presence of TCS when dosed every other day in a range of 2.0–3.6 mg dm^?3 during the 40‐day operation of activated sludge batch cultures. Such sludge growth reduction was associated with the enhancement of microbial activities in terms of the specific oxygen uptake rate and dehydrogenase activity. Sludge settleability of the treated and control samples was qualitatively comparable and not significantly different. Filamentous bacteria continued to grow in sludge flocs only in the control reactor at the end of the 40‐day trial. These results suggest that TCS treatment of activated sludge systems may reduce excess sludge yield. Copyright © 2003 Society of Chemical Industry     

Effects of organic matter and initial carbon–nitrogen ratio on the bioconversion of volatile fatty acids from sewage sludge

BACKGROUND: The biodegradable organic matter and the initial carbon–nitrogen ratio can be substantially different in different batches of sewage sludge, which results in a difference in the acidification efficiency of sludge. Using sewage sludge from three different sources, batch tests were performed to analyze the relationship between volatile fatty acids (VFAs) and consumed organic matter, and to investigate the effects of initial carbon–nitrogen (C/N) ratio on the acidification efficiency of sludge. RESULTS: Maximum yields of 152.1 ± 3.5 mg total VFAs‐COD per gram volatile solid (VS) added and 22.4 ± 1.2 mg butyric acid‐COD g⁻¹ VS added were obtained from the sludge with the highest initial C/N ratio. Statistical analysis indicated that protein was the major substrate for the produced VFAs. The sludge with the least initial C/N ratio (5.01) had the least yield, and only acetic acid, which was also mainly related to protein, was detected. CONCLUSION: The initial carbon–nitrogen ratio was one of the most important factors influencing the distribution patterns of VFAs and the yield of total VFAs produced from sewage sludge. A high C/N ratio could not only improve the yield of total VFAs but also enhance the yield of butyric acid. Copyright © 2008 Society of Chemical Industry     

Dual solute adsorption of 2,4,6‐trichlorophenol and N‐[2‐(2,4,6‐trichlorophenoxy)propyl]amine on to activated carbon

The capacities of four activated carbon types to adsorb both 2,4,6‐trichlorophenol (TCP) and N‐[2‐(2,4,6‐trichlorophenoxy)propyl]amine (BTS40348), as single‐ and dual‐solutes, at pH 4, 7 and 9, were evaluated by use of the Freundlich isotherm model. Coal‐based activated carbon type F400 was found to most strongly adsorb both compounds, with adsorption optima at pH 4 and 9 for TCP and BTS40348, respectively. In dual‐solute isotherms, the adsorptive capacity for each solute was reduced with pH, dictating which solute was most strongly adsorbed. Compared with these batch isotherms, F400 adsorptive capacity was reduced in flow‐through column studies. Activated carbon bioregeneration was studied but the adsorptive capacity of the flow‐through column did not increase, indicating that biologically‐mediated desorption of solute did not occur. © 2001 Society of Chemical Industry