Sorption of quaternary ammonium compounds to municipal sludge

The sorptive behavior of four quaternary ammonium compounds (QACs) - hexadecyl trimethyl ammonium chloride (C₁₆TMA), dodecyl trimethyl ammonium chloride (C₁₂TMA), hexadecyl benzyl dimethyl ammonium chloride (C₁₆BDMA), and dodecyl benzyl dimethyl ammonium chloride (C₁₂BDMA) - to municipal primary, waste activated, mesophilic digested, and thermophilic digested sludges was assessed at 22 °C. Batch adsorption of all four separately tested QACs to primary sludge reached equilibrium within 4 h. At a nominal, initial QAC concentration of 300 mg/L and a sludge volatile solids concentration of 1 g/L, the extent of adsorption was 13, 88, 67, and 89% for the C₁₂TMA, C₁₆TMA, C₁₂BDMA, and C₁₆BDMA, respectively, and correlated positively to the QAC hydrophobicity and negatively to their critical micelle concentration. Equilibrium partitioning data were described by the Freundlich isotherm model. The adsorption capacity of the four sludges was very similar. In binary QAC mixtures, QACs with relatively high adsorption affinity and at relatively high aqueous concentrations decreased the adsorption of QACs with a low adsorption affinity. At pH 7, about 40% of the sludge-C₁₂TMA desorbed, whereas less than 5% of the sludge-C₁₆BDMA desorbed in 10 days. The effect of pH was negligible on the desorption extent of C₁₂TMA at a pH range 4-10 over 10 days, whereas increasing the solution pH to 10 resulted in more than 50% desorption of C₁₆BDMA. Given the fact that approximately 50% of the municipal biosolids are land-applied in the US, the data of this study would help in the assessment of the fate of QACs and their potential effect on human and environmental health.     

Rheological characterisation of municipal sludge: A review

Sustainable sludge management is becoming a major issue for wastewater treatment plants due to increasing urban populations and tightening environmental regulations for conventional sludge disposal methods. To address this problem, a good understanding of sludge behaviour is vital to improve and optimize the current state of wastewater treatment operations. This paper provides a review of the recent experimental works in order for researchers to be able to develop a reliable characterization technique for measuring the important properties of sludge such as viscosity, yield stress, thixotropy, and viscoelasticity and to better understand the impact of solids concentrations, temperature, and water content on these properties. In this context, choosing the appropriate rheological model and rheometer is also important.     

Heterotroph anoxic yield in anoxic aerobic activated sludge systems treating municipal wastewater

As input to the steady state design and kinetic simulation models for the activated sludge system, the correct value for the heterotroph anoxic yield is essential to provide reliable estimates for the system denitrification potential. This paper examines activated sludge anoxic yield values in the literature, and presents experimental data quantifying the value. In the literature, in terms of the structure of ASM1 and similar models, theoretically it has been shown that the anoxic yield should be reduced to approximately 0.79 the value of the aerobic yield. This theoretical value is validated with data from corresponding aerobic OUR and anoxic nitrate time profiles in a batch fed laboratory scale long sludge age activated sludge system treating municipal wastewater. The value also is in close agreement with values in the literature measured with both artificial substrates and municipal wastewater. Thus, it is concluded that, in ASM1 and similar models, for an aerobic yield of 0.67mg COD/mg COD, the anoxic yield should be about 0.53 mg COD/mg COD. Including such a lower anoxic yield in ASM1 and similar models will result in a significant increase in denitrification potential, due to increased denitrification with wastewater RBCOD as substrate. In terms of the structure of ASM3, for the proposed substrate storage yields and the aerobic yield of 0.63 mg COD/mg COD, experimental data indicate that the corresponding anoxic yield should be about 0.42 mg COD/mg COD. This is significantly lower than the proposed value of 0.54 mg COD/mg COD, and requires further investigation.     

Performance comparison of a pilot-scale UASB and DHS system and activated sludge process for the treatment of municipal wastewater

This study compares the performance of a pilot-scale combination of UASB and DHS system to that of activated sludge process (ASP) for the treatment of municipal sewage. Both systems were operated in parallel with the same sewage as influent. The study was conducted for more than 300 days, which revealed that organic removal efficiency of UASB+DHS system was comparable to that of ASP. Unfiltered BOD removal by both systems was more than 90%. However, UASB+DHS system outperformed ASP for pathogen removal. In addition, volume of excess sludge production from UASB+DHS was 15 times smaller than that from ASP. Moreover, unlike ASP, there is no requirement of aeration for the operation of UASB+DHS system, which makes it an economical treatment system. Considering the above observations, it was concluded that UASB+DHS system can be a cost-effective and viable option for the treatment of municipal sewage over ASP, especially for low-income countries.     

壳聚糖与硅藻土调理市政污泥

以污泥比阻为评价指标,综合考虑脱水率、泥饼含水率及过滤时间因素,研究使用壳聚糖与硅藻土对污泥单独调理的最佳条件及联合调理改善污泥脱水性能的效果,并与聚丙烯酰胺调理污泥的效果进行了对比。结果表明,先投加0.5g/g硅藻土调理污泥,再投加5 mg/g壳聚糖以30r/min搅拌反应150s,污泥比阻下降了95.43%,脱水率上升至91.02%,泥饼含水率降至83.13%,过滤时间降至29.5s。壳聚糖与硅藻土联合调理的效果明显优于壳聚糖或硅藻土单独调理的效果,且其联合调理改善污泥脱水综合性能的效果优于聚丙烯酰胺调理污泥的效果。     

Toxicity assessment of common xenobiotic compounds on municipal activated sludge: comparison between respirometry and Microtox

The toxicity of four xenobiotic compounds 3,5-dichlorophenol, formaldehyde, 4-nitrophenol and dichloromethane, representative of industrial wastewater contaminants was evaluated by a simple respirometric procedure set up on the basis of OECD Method 209 and by the Microtox bioassay. Very good reproducibility was observed for both methods, the variation coefficients being in the range of 2-10% for the respirometric procedure and 6-15% for Microtox, values that can be considered very good for a biological method. Comparison of EC(50) data obtained with the two methods shows that in both cases 3,5-dichlorophenol is more toxic than other compounds investigated and dichloromethane has a very low toxicity value. Intermediate EC(50) values were found for the two other chemicals, formaldehyde and 4-nitrophenol. Moreover, the Microtox EC(50) values are generally lower (except for dichloromethane) than the respirometric ones: these differences could be explained by the fact that the Microtox method uses a pure culture of marine species and, therefore, should not necessarily be expected to behave like a community of activated sludge bacteria. In conclusion, both methods can be usefully applied for toxicity detection in wastewater treatment plants but it is advisable to take into account that Microtox is more sensitive than respirometry in estimating the acute toxicity effect on the biomass operating in the plant.     

Detection of enteric viruses in municipal sewage sludge by a combination of the enzymatic virus elution method and RT-PCR

Pathogenic enteric viruses can be retained in municipal sewage sludge as has been reported by many researchers. Although the RT-PCR technique has been extensively employed for the virus detection from various environmental samples, the application of RT-PCR to the detection of viruses in sewage sludge has the difficulty because of inhibitory substances to the gene amplification. However, a combination of the enzymatic virus elution (EVE) method with RT-PCR made it possible to effectively detect viruses in sewage sludge. The enzymatic breakdown of sludge flocs in the EVE method enhanced the virus elution from poliovirus 1 (PV1)-inoculated sewage sludge, and the detection of PV1 was performed by RT-PCR without any inhibitions. On the contrary, the application of RT-PCR to the viral assay in the US EPA method using the 10% beef extract solution was not practical because of inhibitions to the viral gene amplification. The combination of the EVE method using lysozyme (polysaccharide-degrading enzyme), papain (protease), and chymotrypsin (protease) with RT-PCR resulted in a virus recovery efficiency of 31%, but a synergistic effect of these enzymes on the virus recovery efficiency was not observed. The EVE method using lysozyme or papain could be a promising procedure for the virus elution from sewage sludge in detecting these viruses with RT-PCR.     

Simulation and optimization of chemically enhanced primary/activated sludge treatment for small communities

Over the last two decades, the use of coagulation and flocculation has been emphasized for the enhancement of primary sedimentation in municipal wastewater treatment plants. This work is concerned with the development of an approach for the simulation and optimization of a chemically enhanced primary treatment (CEPT)/activated sludge scheme for municipal wastewater treatment using ferric chloride as a coagulant. A mathematical model has been developed which comprises empirical relations for the CEPT stage based on reported experimental data. The activated sludge model has been based on reported rules of thumb.

Optimization has been undertaken using the BOX Complex Routine to minimize a cost objective function with controlling parameters. The effect of varying operating cost components on the cost function has been also assessed via sensitivity analysis.

Results indicate that, for small communities, the addition of a CEPT stage is recommended based on technical and economic consideration for current and prospective costs and prices.     

城市污泥对固废陶粒的强度影响研究

以城市污泥、建筑弃土等固废烧制陶粒,利用XRD、MIP孔结构和SEM等测试手段研究城市污泥对陶粒强度影响。结果表明:通过正交试验获得较优的烧结制度,烧制出污泥掺量为20%的轻质高强陶粒;污泥掺量及对应陶粒氧化物含量(SiO₂及Al₂O₃)均影响陶粒强度;陶粒内部结构随着污泥掺量的增加而变得疏松,污泥掺量为20%的陶粒较掺量为5%的陶粒孔隙率大3.9%以上,陶粒孔径也随着污泥掺量的增加而增大,进而影响陶粒强度;对于氧化物,Al₂O₃含量是影响陶粒强度的主要因素,当其含量超过20.5%以后,陶粒主晶相由石英相逐渐转变为蓝晶石,对陶粒强度提升明显。     

Thermophilic anaerobic digestion of pulp and paper mill primary sludge and co-digestion of primary and secondary sludge

Anaerobic digestion of pulp and paper mill primary sludge and co-digestion of primary and secondary sludge were studied for the first time in semi-continuously fed continuously stirred tank reactors (CSTR) in thermophilic conditions. Additionally, in batch experiments, methane potentials of 210 and 230 m³CH₄/t volatile solids (VS)_added were obtained for primary, and 50 and 100 m³CH₄/tVS_added for secondary sludge at 35 °C and 55 °C, respectively. Anaerobic digestion of primary sludge was shown to be feasible with organic loading rates (OLR) of 1-1.4 kgVS/m³d and hydraulic retention times (HRT) of 16-32 d resulting in methane yields of 190-240 m³CH₄/tVS_fed. Also the highest tested OLR of 2 kgVS/m³d and the shortest HRT of 14-16 d could be feasible, if pH stability is confirmed. Co-digestion of primary and secondary sludge with an OLR of 1 kgVS/m³d and HRTs of 25-31 d resulted in methane yields of 150-170 m³CH₄/tVS_fed. In the digestion processes, cellulose and hemicellulose degraded while lignin did not. pH adjustment and nitrogen deficiency needs to be considered when planning anaerobic digestion of pulp and paper mill wastewater sludges.     

Recovery of nitrogen and phosphorus from alkaline fermentation liquid of waste activated sludge and application of the fermentation liquid to promote biological municipal wastewater treatment

In previous publications we reported that by controlling the pH at 10.0 the accumulation of short-chain fatty acids (SCFA) during waste activated sludge (WAS) fermentation was remarkably improved [Yuan, H., Chen, Y., Zhang, H., Jiang, S., Zhou, Q., Gu, G., 2006. Improved bioproduction of short-chain fatty acids (SCFAs) from excess sludge under alkaline conditions. Environ. Sci. Technol. 40, 2025-2029], but significant ammonium nitrogen (NH₄-N) and soluble ortho-phosphorus (SOP) were released [Chen, Y., Jiang, S., Yuan, H., Zhou, Q., Gu, G., 2007. Hydrolysis and acidification of waste activated sludge at different pHs. Water Res. 41, 683-689]. This paper investigated the simultaneous recovery of NH₄-N and SOP from WAS alkaline fermentation liquid and the application of the fermentation liquid as an additional carbon source for municipal wastewater biological nitrogen and phosphorus removal. The central composite design (CCD) of the response surface methodology (RSM) was employed to optimize and model the simultaneous NH₄-N and SOP recovery from WAS alkaline fermentation liquid. Under the optimum conditions, the predicted and experimental recovery efficiency was respectively 73.4 and 75.7% with NH₄-N, and 82.0 and 83.2% with SOP, which suggested that the developed models described the experiments well. After NH₄-N and SOP recovery, the alkaline fermentation liquid was added to municipal wastewater, and the influence of volume ratio of fermentation liquid to municipal wastewater (FL/MW) on biological nitrogen and phosphorus removal was investigated. The addition of fermentation liquid didn't significantly affect nitrification. Both SOP and total nitrogen (TN) removal were increased with fermentation liquid, but there was no significant increase at FL/MW greater than 1/35. Compared to the blank test, the removal efficiency of SOP and TN at FL/MW = 1/35 was improved from 44.0 to 92.9%, and 63.3 to 83.2%, respectively. The enhancement of phosphorus and nitrogen removal was mainly attributed to the increase of influent SCFA, or rather, the increase of intracellular polyhydroxyalkanoates (PHA) which served as the carbon and energy sources for denitrification and phosphorus uptake. The addition of alkaline fermentation liquid to municipal wastewater, however, increased the effluent COD, which was caused mainly by the increase of influent humic acid, not protein or carbohydrate.     

提高污泥浓度对市政污水处理的影响研究

综合分析了MLVSS的变化与MLSS之间的关系,以及COD,SS,氨氮的去除与MLSS的关系,并以某县城的污水处理厂为例,探讨了污泥浓度的变化情况,同时对浓度提高的污泥进行试验,结果表明:当MLSS不超过6 000 mg/L时,坚持正常的排泥较为合适。     

Compression dewatering of municipal activated sludge: effects of salt and pH

Even after mechanical dewatering, activated sludge contains a large amount of water. Due to its composition and biological nature this material is usually highly compressible and known to be difficult to dewater. In the present work, two treatments (salt addition and pH modification) are proposed to highlight some aspects which could explain the poor dewaterability of activated sludge. Dewatering tests are carried out in a pressure-driven device in order to well examine both, filtration and compression stages. Physico-chemical parameters, such as surface charge, hydrophobicity, extracellular polymeric substances (EPS) content and filtrate turbidity are measured on the tested sludge, for a better analysis of dewatering results.The dewatering ability of the sludge is widely linked to the cohesion of the flocculated matrix and the presence of fine particles. Both treatments alter the flocculated matrix and release fine particles. The release of fine particles tends to clog both, the filter cake and the filter medium. Consequently, the filtration rate decreases due to higher resistances to the flow. On another hand, the polymeric matrix breakdown enables to release some water trapped within the floc to the bulk liquid phase and thus facilitates its removal, which tends to decrease the moisture content of the filter-cake. It also impacts the compression dewatering step. The more destroyed structures lead to less elastic cakes and thus a slower primary consolidation stage. At the opposite, the mobility of the broken aggregates within the filter-cake does not seem to be improved by size reduction (the kinetics of the secondary consolidation stage are not significantly modified).     

Zero net growth in a membrane bioreactor with complete sludge retention

A bench-scale membrane bioreactor was operated with complete sludge retention in order to evaluate biological processes and biomass characteristics over the long term. The investigation was carried out by feeding a bench-scale plant with real sewage under constant volumetric loading rate (VLR=1.2 gCOD L_react⁻¹ h⁻¹). Biological processes were monitored by measuring substrate removal efficiencies and biomass-related parameters. The latter included bacterial activity as determined through respirometric tests specifically aimed at investigating long term heterotrophic and nitrifying activity. After about 180 days under the imposed operating conditions, the system reached equilibrium conditions with constant VSS concentration of 16–18 g L⁻¹, organic loading rate (OLR) below 0.1 gCOD gVSS⁻¹ d⁻¹ and specific respiration rates of 2–3 mgO₂ gVSS⁻¹ h⁻¹. These conditions were maintained for more than 150 days, confirming that an equilibrium had been achieved between biomass growth, endogenous metabolism, and solubilization of inorganic materials.     

Biological degradation of pharmaceuticals in municipal wastewater treatment: proposing a classification scheme

A simple classification scheme is suggested to characterize the biological degradation of micropollutants such as pharmaceuticals, musk fragrances and estrogens during wastewater treatment. The scheme should be a basis for the discussion about potential removal efficiencies. Hence, the biological degradation of 25 pharmaceuticals, hormones and fragrances was studied in batch experiments at typical concentration levels using activated sewage sludge originating from nutrient-eliminating municipal wastewater treatment plants. Since pseudo first-order degradation kinetics was observed for all compounds down to ng L(-1) levels, the removal rates can be predicted for various reactor configurations. Therefore dilution of wastewater (e.g. by extraneous water) is expected to reduce the degree of biological removal. Wastewater segregation and treatment at the source are therefore to be favoured for elimination of persistent micropollutants over centralized end-of-pipe treatment. For reactor configurations typical for nutrient removal in municipal wastewater, the derived formula for predicting removal allows the identification of three groups of micropollutants according to their degradation constant k(biol): compounds with k(biol)<0.1 L g(SS)(-1)d(-1) are not removed to a significant extent (<20%), compounds with k(biol)>10 L g(SS)(-1)d(-1) transformed by >90% and in-between moderate removal is expected. Based on the degradation of a heterogeneous group of 35 compounds (including literature data), state of the art biological treatment schemes for municipal wastewater are not efficient in degrading pharmaceuticals: only 4 out of 35 compounds are degraded by more than 90% while 17 compounds are removed by less than 50%.     

Behaviour of chlorophenoxy herbicides during the activated sludge treatment of municipal waste water

The potential of the activated sludge treatment process for the removal of chlorophenoxy herbicides (CPH) from domestic waste water has been investigated. A series of laboratory jar tests and pilot plant experiments were performed using real settled sewage fortified with 10 μl⁻¹ of each of six CPH. The experiments were designed with the objective of assigning any CPH removal which might occur to a particular removal mechanism. In particular, the effect of varying the sludge age between each pilot plant experiment was studied, in view of the importance of sludge age in determining the biodegradative potential of activated sludge.Generally, activated sludge treatment proved ineffective in removing CPH contaminants from settled sewage. Statistical treatment of the data suggested that neither adsorption nor catabolic biodegradation were responsible for those significant CPH removals that did occur. Indeed, there was no evidence of acclimatization of the mixed liquor to the presence of CPH contaminants. Furthermore, there was no obvious effect of sludge age on the efficiency of CPH removal from settled sewage. However, the extent and pattern of substitution of CPH appeared to be important in determining the efficiency of CPH removal, which implies that a biological mechanism was involved. The likelihood that co-metabolism was responsible for CPH removal has been considered.The possible implications of poor CPH removal by activated sludge treatment have been discussed, with reference to the relevant EEC legislation.     

搅拌对给水厂污泥浓缩的影响

通过试验研究了搅拌对给水厂污泥浓缩的影响,并分别探讨了快速搅拌和慢速搅拌对沉降效果的影响,结果表明:适当的慢速搅拌可以在一定程度上提高浓缩效果,建议最佳搅拌的速度梯度为1.4 s-1。     

利用城市污泥和电厂灰渣制备生态透水烧结砖的研究

以城市污泥和电厂灰渣为主要原料,少量助熔成孔剂为辅助料,制备力学性能和透水性能良好的生态透水烧结砖。通过对不同配比制品的性能研究,确定了原料的最佳配比及合理的工艺方法。试验结果表明,城市污泥30%左右,电厂灰渣53%～54%,助熔成孔剂(C)16%～17%,在1050～1080℃焙烧,可制得抗压强度大于30 MPa、透水系数大于0.01 cm/s的生态透水烧结砖,可广泛用于人行道、广场、停车场、公园、住宅区等。     

关于小城镇污水处理厂污泥处理处置的探讨

针对我国小城镇污水处理厂污泥的特点,阐述了几种适于小城镇污泥处置的方法的优缺点,建议根据当地的资金和技术水平,因地制宜的选择污水处理厂污泥处理处置的方法。     

Acidogenic fermentation of proteinaceous sewage sludge: Effect of pH

Proteinaceous sewage sludge represents the sludge in which the protein content exceeds the carbohydrate content, accounts for a considerable part of sewage sludge. In this study, volatile fatty acids (VFA) production and synthesis pathway as well as bacterial community in acidogenic fermentation of proteinaceous sewage sludge under different pH conditions were investigated. The results indicated that the alkaline pH improved the solubilization and biodegradation of proteins in the sludge. The soluble protein concentration at pH 11.0 was 67.88% higher than that at pH 3.0. Its biodegradation efficiencies were reduced with a decrease in pH. The pH influenced not only the total VFA production yield, but also the percentage of individual VFA. The total VFA yield at pH 9.0 was 10.70 times of that at pH 3.0. The metabolic conversion pathway of proteins to VFA in acidogenic fermentation systems was investigated using a stoichiometry approach. The Stickland reaction was found to be the main pathway for the VFA accumulation from the decomposition of proteins. pH also significantly influenced the biodiversity and bacterial community in the system. The abundance of microorganisms under alkaline or acidic pH conditions was less than that under neutral pH condition, suggesting that most anaerobic fermentative microorganisms could not tolerate the hostile environment. The terminal restriction fragment length polymorphism analysis showed that, when the pH was reduced from 12.0 to 7.0 and finally to 3.0, the dominant bacterial genuses and percentage of the total microorganisms were Granulicatella genus (65%), Clostridium genus (28%) and Bacillus genus (71%), respectively.